1040-5488/15/9205-0623/0 VOL. 92, NO. 5, PP. 623Y631 OPTOMETRY AND VISION SCIENCE Copyright * 2015 American Academy of Optometry
ORIGINAL ARTICLE
Relationship between Vision and Visual Perception in Hong Kong Preschoolers Wing-Cheung Ho*, Minny Mei-Miu Tang†, Ching-Wah Fu‡, Ka-Yan Leung§, Peter Chi-Kong Pang||, and Allen Ming-Yan Cheong*
ABSTRACT Purpose. Although superior performance in visual motor and visual perceptual skills of preschool children has been documented in the Chinese population, a normative database is only available for the US population. This study aimed to determine the normative values for these visuomotor and visual perceptual tests for preschool children in the Hong Kong Chinese population and to investigate the effect of fundamental visual functions on visuomotor and visual perceptual skills. Methods. One hundred seventy-four children from six different kindergartens in Hong Kong were recruited. Distance visual acuity, near visual acuity, and stereopsis were tested, along with two measures of visual perception (VP): Visual-Motor Integration (VMI) and Test of Visual-Perceptual Skills (TVPS). Raw VMI and TVPS scores were converted into standard/ scaled scores. The impact of basic visual functions on VP (VMI and TVPS) was examined using multiple regression. Results. Visual functions were generally good: only 9.2 and 4.6% of subjects had unilateral and bilateral reduced habitual vision, respectively (distance visual acuity in the better eye 90.3 logMAR [logarithm of the minimum angle of resolution]). Performance in the VMI and in the visual memory and spatial relationships subtests of the TVPS exceeded that reported for age-matched children from the United States. Multiple regression analysis provided evidence that age had the strongest predictive value for the VMI and VP skills. In addition, near visual acuity was weakly associated with performance in the VMI and the visual discrimination and spatial relationships subtests of the TVPS, accounting for a limited proportion of the intersubject variability (R2 G 3%; p G 0.001). Conclusions. Hong Kong preschoolers outperformed their US peers in the VMI and visual memory/spatial relationships of TVPS subtests, perhaps attributed to greater exposure to such material during their preschool home education. This study provided normality data for VMI and four subtests of the TVPS for Hong Kong Chinese preschool children as a reference for future studies. (Optom Vis Sci 2015;92:623Y631) Key Words: preschool children, visual function, visual perception, visual motor, Hong Kong Chinese
V
ision plays an important role in early childhood development. Children with visual disorders face significant barriers in their learning and daily activities. Early detection and treatment of visual deficits in young children can improve the prognosis for normal eye development, prevent further vision loss, and reduce the impact of learning problems, poor school performance, developmental delays, and behavior concerns.1
*BSc(Hons), PhD † PDip(OT) MA ‡ MA § BSc(Hons) || MPhil, PDP (Optom) School of Optometry, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China (W-CH, K-YL, PC-KP, AM-YC); and Ebenezer School & Home for the Visually Impaired, Hong Kong Island, Hong Kong, China (MM-MT, C-WF).
The eyes collect visual information from the environment and transmit it to the brain for further processing and interpretation. An eye examination includes measuring a series of sensory functions (such as visual acuity and binocular visual performance) and assessing ocular health. However, the measurement of these basic visual functions alone may not be sufficient to identify all children with visual processing disorders: some children with good vision may have difficulty in interpreting what is seen. Visual perception (VP) is the ability of the brain to understand and interpret what the eyes see,2 whereas visual-motor integration (VMI) is the ability to coordinate body movements with VP, which involves interactions between visual, visual-perceptual, and motor skills.3,4 Visual perception is important for reading, writing, and driving,5 whereas VMI is important for writing.6Y8 Hence, both VP and VMI are important skills for processing visual information and play integral roles in childhood development. Children with deficits in VP or
Optometry and Vision Science, Vol. 92, No. 5, May 2015
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624 Vision and Visual Perception in PreschoolersVHo et al.
VMI show inferior academic performance,9,10 including mathematics achievement,11 reading achievement,12,13 and handwriting.6,14 Numerous studies have investigated the causes of vision disorders in school-aged students15Y21 (aged 5 to 15 years) and preschool children (aged 2.5 to 6 years)22Y30 and found that refractive error is the most common cause (Table 1 summarizes the prevalence rates of abnormal visual acuity in preschool children from various populations). By contrast, very few studies have explored the relationship between basic visual functions and VP and their interactive impacts on children’s development. In those studies that have addressed this issue, the VMI and VP of children born prematurely,31Y35 with low birth weight,31 with brain disorders,36,37 or with congenital abnormalities38 have been examined. Recently, a handful of studies have compared VP abilities in Chinese-speaking and English-speaking preschool children of the same age in different countries.39Y41 The findings suggest that VP skills among Chinese-speaking children exceed those of age-matched English-speaking children, probably because of the differences in language as well as the education system.39Y41 Similar findings are seen for the VMI skills, with Chinese children outperforming US
children over the 5 to 9 years age range.41 In addition, perceptual and motor skills are found to depend on culture,42,43 language,39 region,44 academic level,10,11 race, and socioeconomics.45 Because of these diverse demographic and cultural differences, each population needs to establish its own normative database, rather than applying the US-based normative database to identify children with deficits in the VMI or VP skills. Hong Kong has a distinctive education system, which is different from both Western countries and mainland China. For instance, children’s education in Hong Kong includes infant education (i.e., babies’ early education) and training to preschool age covering topics such as physical fitness, language, mathematics, and arts.46 It is possible that this type of early childhood education further facilitates the development of VP and VMI skills. Hence, applying the US normative database to examine Hong Kong children’s VP and VMI performances might not be appropriate, stressing the importance to develop a Hong KongYbased normative database. On the other hand, although VP and VMI skills are known to be affected by developmental problems,31Y38 these cognitive skills might also be affected if blur or poor image quality is
TABLE 1.
Prevalence of abnormal visual acuities in preschool children reported in previous studies Study
Country (year)
Age, mo
N
BPEDS
United States (2008)
30Y71
1504
MEPEDS30
United States (2013)
30Y72
1840
MEPEDS26
United States (2009)
30Y72
3207
SPEDS28
Australia (2011)
30Y72
1188
Chia et al.23
Singapore (2010)
30Y72
1682
Taiwan (2007)
36Y72
4907
Hong Kong (2011)
36Y72
823
Korea (2004) Malaysia (2013)
36Y71 48Y72
35,226 400
25
Chang et al.22
Fan et al.24
Lim et al.27 Premsenthil et al.29
Definition of ‘‘abnormal’’ visual acuity, mo Presenting visual acuity 90.40 logMAR (30Y47 mo) 90.30 logMAR (48Y72 mo)
Q0.18 logMAR (did not mention whether habitual glasses were allowed) 1. Uncorrected visual acuity 2. Q0.30 logMAR (36Y47 mo) Q0.22 logMAR (48Y59 mo) Q0.15 logMAR (60Y71 mo) Q0.10 logMAR (72Y83 mo) 1. Best-corrected visual acuity 2. Q0.30 logMAR (36Y48 mo) 92-line difference in best-corrected visual acuity between 2 eyes 90.30 logMAR 90.30 logMAR in one or both eyes (did not mention whether habitual glasses were allowed)
Prevalence, % Both eyes White: 1.2% Black: 1.8% Worse eye Asian: 3.4% Non-Hispanic white: 2.6% Better eye Asian: 0.8% Non-Hispanic white: 0.8% Worse eye African: 8.6% Hispanic: 10.5% Better eye African: 3.9% Hispanic: 3.5% 6.4% (worse eye) 2.7% (better eye) Either eye: 2.8%
10.3%
2.7% (17% with some abnormalities)
Right eye only: 5.6% One or both eyes: 5% (screening)
BPEDS, Baltimore Pediatric Eye Disease Study; MEPEDS, Multi-Ethnic Pediatric Eye Disease Study; SPEDS, Sydney Paediatric Eye Disease Study. Optometry and Vision Science, Vol. 92, No. 5, May 2015
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Vision and Visual Perception in PreschoolersVHo et al.
perceived by children with visual deficits. However, no study has examined the effect of basic sensory functions on these higher cognitive skills. In this study, we examined a sample of Hong Kong preschoolers with no history of birth-related problems or congenital diseases, with the aims of (1) investigating the performance of VP and VMI skills, (2) examining the relationship between basic visual functions and VP performance, and (3) establishing preliminary normative values for the VMI and VP tests for preschool children in Hong Kong.
METHODS Subjects Six kindergartens from 6 different districts (out of 18 districts) in Hong Kong were chosen using incidental sampling. Invitations to take part in the study were made to parents or legal guardians of preschoolers aged 4 to 7 years in the selected kindergartens. Subjects who fulfilled the following criteria were recruited: (1) informed consent given by parents or legal guardians (response rate, 90.9%); (2) no history of cardiovascular or nervous system diseases; (3) no reported specific learning difficulties,47 autism spectrum disorder,48 and attention-deficit/hyperactivity disorder as indicated by parents/legal guardians,49 or observable physical and intellectual disabilities as indicated by an experienced occupational therapist50; (4) a gestation period of at least 37 weeks32; and (5) capable of following instructions during the assessments. The study followed the tenets of the Declaration of Helsinki and was approved by the Human Ethics Committee of the School of Optometry, The Hong Kong Polytechnic University. Demographic information (age, sex, parents-perceived general and ocular health, and history of last eye examination) was collected through a structured questionnaire (Table 2). Parents were asked to rate the health status of their children using a five-point Likert scale.
Procedures Basic Visual Functions and Ocular Health Assessment Visual acuity, color vision, stereopsis, binocular alignment, and ocular health were examined. Monocular distance and near visual acuities were measured at 3 m and 40 cm, respectively, using the crowded LEA Symbols 15-Line Distance Chart and a near vision card without confusion bars (Good-Lite Co, Elgin, IL) in logMAR [logarithm of the minimum angle of resolution] notation under room lighting of about 200 lux. Subjects were required to wear glasses for visual acuity measurement if they had them. Credit was given for each correctly recognized symbol. Color vision was tested with the Color Vision Made Easy test (Precision Vision, La Salle, IL). Stereoacuity was assessed using the Randot Stereotest (Stereo Optical Company, Inc, Chicago, IL) at 40 cm. Subjects were graded as passing the stereopsis test if their stereoacuity was less than 70 minutes of arc.51,52 Ocular alignment was assessed using both the cover test and Hirschberg test. Types of tropia, characteristics (intermittent or constant), and the degree of deviation (prism diopters) were recorded. Two drops of 0.5% tropicamide and 0.5% phenylephrine (Mydrin-P; Santen Pharmaceutical Co, Ltd) were instilled, 10 minutes apart, for each subject to relax accommodation. Cycloplegic autorefraction using an open-field autorefractor
625
TABLE 2.
Structured questionnaire for the parents/legal guardians of participating children 1. Prenatal infection g Yes 2. Preterm baby (G37 wk) g Yes 3. Personal general health a. Cerebral palsy g Yes b. Meningitis g Yes c. Strabismus g Yes d. Amblyopia g Yes 4. Family ocular health a. Color weakness/color blindness g Yes b. Strabismus g Yes c. Amblyopia g Yes d. Congenital/hereditary g Yes (if yes, please eye diseases state: ______) Please rate the general health of your child g Excellent g Very good g Good g Satisfactory g Poor Please rate the ocular health of your child g Excellent g Very good g Good g Satisfactory g Poor
g No g No g g g g
No No No No
g g g g
No No No No
Remarks: Please put a ‘‘( ’’ for each question.
(Model: NVision-K 5001, Shin-Nippon, Rexxam Co Ltd, Tokyo, Japan) was conducted 30 minutes after drug instillation. A fixation target placed at 6 m was used to control the fixation and accommodation during the measurement. All vision and perceptual tests were completed before pupil dilation. The ocular health examination included slit-lamp biomicroscopy and indirect ophthalmoscopy to evaluate the anterior and posterior eye, respectively. Subjects were graded as passing the ocular health assessment if no signs of ocular infection, media opacity, hereditary retinal degeneration, or retinal disease were identified.
VMI Skills Visual-motor integration skills were tested with the BeeryBuktenica Developmental Test of Visual-Motor Integration (Berry VMI, 6th edition),4 administered in standard classrooms under normal room illumination, following the instructions in the test manual.4 The subjects were arranged in groups of six for each test administrator. They were required to wear their habitual glasses to attend the tests if they had them. The VMI test contains 15 geometric forms ranging from the simplest to the most difficult. Subjects were asked to copy the forms on the test booklet in the given order, and the test was ended when three consecutive shapes could not be copied or were copied incorrectly. All subjects were given as much time as needed to complete the test. The administrator examined each drawing according to the VMI manual, and each correctly drawn form was scored as one point. The raw score is the sum of the number of correctly drawn forms. According to the subject’s age, each individual raw score was converted to a ‘‘standard score,’’ based on the VMI tabular norms for 12,500 US school-aged children.4
VP Skills Visual perception skills were tested with the Test of VisualPerceptual Skills (nonmotor), Third Edition (TVPS-3),50
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626 Vision and Visual Perception in PreschoolersVHo et al.
administered following the instructions in the TVPS-3 manual, on a one-to-one basis. The full TVPS contains seven subtests for measuring different interrelated VP parameters. In this study, only the four subtests (visual discrimination, visual memory, spatial relationships, and form constancy) that form the basic visual processes composite were administered. Each subject’s VP performance was examined by one administrator. Children were again required to wear their habitual glasses if they had them. In the visual discrimination subtest (i.e., form analysis), subjects had to point to the design matching that shown in a figure. In the visual memory subtest (i.e., form analysis with a memory component), subjects had 5 seconds to view a design on one page of the test book and then select the same design from among the choices on the following page. In the spatial relationships subtest (i.e., form and spatial/orientation discrimination), subjects had to select the design that differed from among a series of designs. In the form constancy subtest (i.e., dominant feature discrimination), subjects had to match a design that differed in size or orientation from among a set of designs on the same page. Each correct answer was scored as one point, and each subtest was ended when three consecutive questions were answered incorrectly. The raw score was computed as the total number of correct responses and converted to a ‘‘scaled score’’ with reference to the TVPS-3 tabular
norms from 2008 US school-aged children or adults. The sum of the scaled scores for the four subtests was then converted to a standard score with reference to the look-up table in the manual.
Statistical Analysis Data were analyzed using IBM SPSS version 18 (Statistical Package for the Social Sciences). Stepwise multiple regression analyses were used to determine whether the predictors, age, near visual acuity (in the better eye), and stereopsis could predict visual perceptual skills (VP or VMI).10 Descriptive data for the VMI and VP subtests including percentiles for six age groups from 4 to 7 years were calculated. An independent samples t test was used to test for any significant difference in VMI and each VP test of our subjects against the US normative value (i.e., 100 for both VMI and basic process of VP, 10 for all VP subtests). A p value of 0.05 was considered statistically significant.
RESULTS One hundred seventy-four subjects (male, 101; female, 73) met the inclusion criteria and completed all of the assessments. The mean (TSD) age of the subjects was 5.1 (T0.7) years. Of the 170
TABLE 3.
Distribution of visual functions and visual disorders for each age group Age groups 6.0Y6.11*
All
0.50 (j0.75, 2.13) 0.63 (j0.25, 2.21) 0.63 (j0.75, 2.12) 0.56 (j0.22, 2.28)
0.75 (j0.60, 2.60) 0.69 (j0.62, 2.60)
0.63 (j0.59, 2.25) 0.63 (j0.70, 2.32)
0.14 (j0.04, 0.46) 0.11 (j0.06, 0.38)
0.04 (j0.08, 0.34)
0.12 (j0.06, 0.43)
0.14 (j0.03, 0.41) 0.12 (j0.08, 0.28)
0.08 (j0.10, 0.41)
0.12 (j0.06, 0.36)
4.0Y4.11* Autorefraction, in spherical equivalent, D Right eye, median (5th, 95th percentile) Left eye, median (5th, 95th percentile) Visual function measures Distance visual Right eye, median acuity, logMAR (5th, 95th percentile) Left eye, median (5th, 95th percentile) Unilateral reduced habitual visual acuity (logMAR 9 0.30), n (%) Bilateral reduced habitual visual acuity, n (%) Near visual acuity, Right eye, median logMAR (5th, 95th percentile) Left eye, median (5th , 95th percentile) Stereoacuity Stereoacuity, median (5th, 95th percentile), minute of arc Fail stereoacuity (970 minutes of arc), n (%) Color vision defects Fail color vision (G8 corrected plates), n (%) Ocular abnormalities Strabismus, n (%) Ocular health abnormalities,† n (%)
5.0Y5.11*
9 (10.8)
5 (7.4)
2 (8.7)
16 (9.2)
3 (3.6)
3 (4.4)
2 (8.7)
8 (4.6)
0.12 (j0.08, 0.30) 0.07 (j0.08, 0.23)
0.00 (j0.10, j0.19) 0.10 (j0.08, 0.25)
0.10 (0.06, 0.29)
0.00 (j0.10, 0.23)
40 (40, 100)
0.04 (j0.08, 0.23) 40 (40, 100)
7 (8.4)
10 (14.7)
8 (9.6) 2 (2.4) 0 (0.0)
40 (40, 100)
0.08 (j0.08, 0.24) 40 (40, 100)
3 (13.0)
20 (11.5)
4 (5.9)
2 (8.7)
14 (8.0)
1 (1.5) 1 (1.5)
1 (4.3) 0 (0.0)
4 (2.3) 1 (0.6)
*The number before the decimal point indicates the number of years and the number after the decimal point denotes the number of months. †In ocular health examination, we examined any signs of ocular infection, media opacity, hereditary retinal degeneration, or retinal diseases. Optometry and Vision Science, Vol. 92, No. 5, May 2015
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Vision and Visual Perception in PreschoolersVHo et al. TABLE 4.
Normative data of performances in the VMI and each subtest of TVPS (raw score) for each age group Age range 10th 25th 50th 75th 90th VMI
4.0Y4.5 4.6Y4.11 5.0Y5.5 5.6Y5.11 6.0Y6.5 6.6Y6.11 TVPS Visual 4.0Y4.5 discrimination 4.6Y4.11 5.0Y5.5 5.6Y5.11 6.0Y6.5 6.6Y6.11 Visual memory 4.0Y4.5 4.6Y4.11 5.0Y5.5 5.6Y5.11 6.0Y6.5 6.6Y6.11 Spatial 4.0Y4.5 relationships 4.6Y4.11 5.0Y5.5 5.6Y5.11 6.0Y6.5 6.6Y6.11 Form constancy 4.0Y4.5 4.6Y4.11 5.0Y5.5 5.6Y5.11 6.0Y6.5 6.6Y6.11
11.0 14.0 14.3 14.5 15.0 16.0 2.0 2.0 2.0 3.5 3.0 4.0 2.0 2.8 1.3 3.0 5.0 6.0 1.0 2.0 3.3 4.5 5.0 5.0 0.0 1.0 1.0 0.0 2.0 1.5
12.3 15.0 16.0 16.0 16.0 17.0 2.0 2.0 3.0 4.8 5.0 5.0 3.0 4.0 3.0 6.0 6.0 6.0 3.0 4.0 5.0 6.0 5.0 11.0 1.8 2.0 3.0 3.0 3.8 3.0
14.0 17.0 17.0 18.0 18.0 20.0 4.0 4.0 6.0 7.0 6.0 7.0 4.5 6.0 6.0 7.5 9.0 8.0 5.0 7.0 9.5 8.5 12.0 13.0 4.0 4.0 4.0 5.0 4.5 4.0
16.0 18.0 18.0 19.0 19.0 21.0 5.0 7.0 7.0 9.0 9.0 10.0 7.0 8.0 8.0 9.0 11.0 9.0 8.0 9.0 12.0 11.0 14.0 13.0 5.0 5.8 5.0 7.0 6.0 5.0
17.5 19.0 19.0 20.0 21.0 21.0 6.0 8.0 9.0 10.0 12.0 10.0 8.0 9.0 10.4 11.0 13.0 9.0 10.0 12.2 13.0 12.5 15.0 13.0 7.0 8.9 8.5 9.0 8.0 9.0
Values under the column ‘‘Age range’’ are presented as follows: The number before the decimal point indicates the number of years and the number after the decimal point denotes the number of months.
respondents, 71 subjects (41.8%) had never had an eye examination, whereas 86 subjects (50.6%) had had at least one eye examination in the past.
627
Characteristics of Visual Functions and Prevalence of Visual Disorders Table 3 summarizes the distribution of visual functions and visual disorders by age group. Because visual acuity and stereopsis were not normally distributed, medians with 5th and 95th percentile (in parentheses) are presented. The median spherical equivalent refractive error for all subjects was +0.63 diopters (D) (j0.59, 2.25 D) and +0.61 D (j0.70, 2.32 D) for right and left eyes, respectively. Presenting distance visual acuity was 0.12 (j0.06, 0.43) and 0.12 (j0.06, 0.36) logMAR for right and left eyes, respectively, whereas presenting near visual acuity was 0.10 (j0.08, 0.25) and 0.08 (j0.08, 0.24) logMAR. Following Wong et al.,53 unilateral and bilateral reduced habitual visual acuity were defined as distance acuity worse than 0.30 logMAR (equivalent to Snellen 6/12) in any eye or both eyes, respectively. In our sampled population, 9.2 and 4.6% subjects had unilateral and bilateral reduced visual acuity, respectively, in which all cases were not attributed to pathological changes. Subjects had relatively good stereoacuity (median, 40 minutes of arc), with 11.5% failing the stereotest (970 minutes of arc).51,54 Fourteen (8%) subjects failed the color vision test. Only 1 (0.6%) subject failed the ocular health assessment, because of a red eye.
Characteristics of Visual Motor and Visual Perceptual Skills Normative data of performances in the VMI and each subtest of TVPS (raw score), including percentiles for six age groups from 4 years to 6 years 11 months are presented in Table 4. Mean and SD of the derived standard/scaled scores for each age group for the VMI and TVPS (four subtests) are shown in Table 5. The average standard score of VMI was 112.8 (T9.2), which exceeded the standardized score of 100, suggesting that the overall performance of our Chinese kindergarten subjects was better than that of agematched US children (t173 = 19.3, p G 0.001). Similar results were found for the visual memory and spatial relationships of the TVPS. The scaled scores of visual memory and spatial relationships were 11.2 (T3.7) (t173 = 3.6, p G 0.01) and 13.1 (T3.8) (t173 = 10.1, p G 0.001), respectively, compared with the age norm of 10 for US children. The mean scores for visual discrimination and
TABLE 5.
Mean T SD of the standard/scaled scores for VMI and TVPS for each age group TVPS Age 4.0Y4.5 4.6Y4.11 5.0Y5.5 5.6Y5.11 6.0Y6.5 6.6Y6.11 Overall
n
VMI*
38 45 38 30 16 7 174
116.2 T 10.2 117.7 T 7.5 112.2 T 7.2 109.2 T 7.6 104.0 T 7.3 102.7 T 6.2 112.8 T 9.2
Visual discrimination† Visual memory† Spatial relationships† Form constancy† Basic processes* 9.7 T 1.6 10.1 T 3.3 10.1 T 3.3 11.1 T 3.1 10.8 T 3.5 10.9 T 2.7 10.3 T 3.0
11.2 T 3.1 12.0 T 3.5 10.1 T 4.5 11.3 T 3.6 12.0 T 3.8 10.4 T 2.1 11.2 T 3.7
12.6 T 3.2 12.9 T 3.7 13.3 T 4.3 12.9 T 3.3 14.3 T 4.8 15.4 T 3.7 13.1 T 3.8
11.7 T 3.0 10.6 T 4.7 9.8 T 3.3 8.4 T 4.1 8.8 T 2.8 8.1 T 2.3 10.0 T 3.9
107.1 T 9.6 107.3 T 12.2 104.2 T 13.1 104.1 T 11.6 107.6 T 11.7 106.4 T 9.3 106.0 T 11.6
Values under the column ‘‘Age’’ are presented as follows: The number before the decimal point indicates the number of years and the number after the decimal point denotes the number of months. *Standard score. †Scaled score. Optometry and Vision Science, Vol. 92, No. 5, May 2015
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628 Vision and Visual Perception in PreschoolersVHo et al.
form constancy were 10.3 (T3.0) and 10.0 (T3.9), respectively, which were similar to the performance in US children (t173 = 1.4, p = 0.16; t173 = j1.1, p = 0.26). The mean standard score for the basic processes, an index representing performance in the four subtests, was 106.0 (T11.8), suggesting that visual perceptual skills for Hong Kong children were slightly but significantly better than those for US children (t173 = 6.7, p G 0.001). There is no consensus on criteria for classifying subjects with VMI or TVPS deficits. For example, a performance score at the 30th percentile and the 16th percentile55 has been used as the cutoff point for failing the VMI, whereas scores at the 16th and 10th percentiles have been used to define persons with a TVPS deficit.56 In this study, we adopted the 10th percentile as the cutoff point to classify subjects having a deficit in either VMI or TVPS. According to our study’s definition, no subject had VMI deficiency. In contrast, the prevalence of an overall TVPS deficit in basic visual processing was 3.4%, although the prevalence in each subtest varied from 2.2% for spatial relationship to 10.6% for form constancy.
Relationships among Basic Visual Functions, Visual Motors, and VP Given the significant differences in VMI and VP components between children in our study and in the United States, raw scores of VMI and each subtest of TVPS instead of derived scores (standard scores or scaled scores) were used to investigate the impact of basic visual functions (near visual acuity and stereopsis) on visual motor and VP performance. Multiple regression analysis suggested that age was the best predictor of VMI and TVPS raw scores (except form constancy). Near visual acuity had a significant, although subtle contribution to the variances in VMI and in the visual discrimination and spatial relationships of TVPS (accounting for 1 to 3% of the intersubject variation, p G 0.05, Table 6).
In contrast, near visual acuity and near stereoacuity were not predictive of subjects’ performance in visual memory and form constancy of TVPS (Table 6).
DISCUSSION A low prevalence (4.6%) of deficits in basic visual functions was found in Hong Kong Chinese preschoolers, comparable to that reported in other epidemiology studies (Table 1). Poor habitual vision was not attributed to pathological changes but rather to uncorrected or undercorrected refractive error, which was preventable and/or amenable to treatment. In accordance with earlier reports in Chinese preschoolers,39Y41,44,57 Hong Kong Chinese preschoolers’ VP performance in our study was good for both VMI and TVPS. In VMI, Hong Kong children performed substantially better than US children (average raw and standard score of 16.7 and 112.8, respectively) but only slightly better than children from mainland China (average raw and standard scores of 13.0 and 109.9, respectively).41 It has been argued that the former effect is related to the difference in the school curriculum between the two countries: US children are mainly taught cognitive and psychosocial skills during the preprimary stage,58 whereas Chinese children are taught academic knowledge (including reading and writing) and physical activities.46 Indeed, Hong Kong children are generally required to learn and copy simple and complex pictures and/or characters from an early age (e.g., age 2 for prenursery and age 3 for kindergartens). Writing starts in the second year at kindergartens (age 4). Previous studies have demonstrated the importance of VMI skills in the writing process6,9,10,49 because writing requires the brain to send signals to control body posture and the movement of the limbs. On the other hand, physical activity helps children develop better control of their body and limbs.
TABLE 6.
Predictors of performance in VP Visual-Motor Integration (VMI)
Dependent variable Visual discrimination
Visual memory Spatial relationships
Form constancy
Predictors
Adjusted R2
Age Age Near acuity
0.34 0.35
Predictor(s) Age Age & Near acuity Age Age Age & Near acuity V
Standardized coefficients
0.58 0.52 j0.15 Test of Visual-Perceptual Skills (TVPS)
Adjusted R2 0.20 0.23 0.14 0.20 0.21 V
Standardized coefficients 0.45 0.37 j0.21 0.38 0.45 0.38 j0.17 V
95% CI for standardized coefficient Lower
Upper
p
1.54 1.31 j6.88
2.36 2.19 j0.48
G0.001 G0.001 0.03
95% CI for standardized coefficient Lower Upper 1.19 2.20 0.83 1.59 j9.67 j1.86 0.99 2.11 1.67 3.10 1.25 2.80 j12.1 j0.89 V V
p G0.001 G0.001 0.004 G0.001 G0.001 G0.001 0.023 V
CI, confidence interval. Optometry and Vision Science, Vol. 92, No. 5, May 2015
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Vision and Visual Perception in PreschoolersVHo et al.
Our results also suggested that Hong Kong preschoolers outperformed US children in spatial relationship tasks and in the visual memory components of the TVPS. Again, a plausible reason is the early exposure to reading and writing using both Chinese characters and the English alphabet from the age of 3 (i.e., kindergarten grade 1). Because of the complex geometric and orthographical design of Chinese characters, Kao59 stated that Chinese writing is a complex process involving the perception, cognition, and motor function of the body. Writing Chinese characters reflects spatial characteristics of the words; thus, the writing process is thought to train the spatial-orientation skills of the child. In addition, learning Chinese characters may help improve visual memory by stimulating the recall of visual forms.60 Clinically, a population-specific normative database should be used to examine a child’s VMI and VP skills. Our study provided preliminary normality data for the VMI and four subtests of TVPS for Hong Kong Chinese preschoolers as reference for future studies and clinical practice (Table 4). Visual-motor integration and VP skills develop rapidly during the preschool years.4,50 As expected, our results showed that most of the VMI and VP skills improved significantly as children got older (age explained 14 to 34% of intersubject variation in VMI and TVPS). However, only weak and nonsignificant change was observed in ‘‘form constancy’’Van important skill required to recognize forms, letters, or words regardless of their orientation. This suggests that the development of form constancy skill is slower than other perceptual skills. Gibson61 reported that younger children made more reversal errors and selection of upside-down forms than older children in letter discrimination. Although no reading assessment was included in our study, children with deficits in form constancy might be more likely to have difficulty in reading Chinese because the ability to distinguish the differences in size, shape, and orientation of Chinese characters is essential.62 As mentioned above, age accounted for 34% of the variance in VMI and 14 to 20% of the variance in the visual discrimination, visual memory, and spatial relationships of VP skills. Other than age, near visual acuity contributed only subtly (~1 to 3% of the variance) to the performance of the VMI and the visual discrimination and spatial relationships of TVPS. Because visual acuity is the most fundamental level of the visual signal processing pathway,63 it is not surprising that performance in VP tests is slightly affected by visual acuity. A study on preterm children also demonstrated that poor visual acuity was associated with a lower VMI score.35 There might be a larger change in the variance of visual acuity contributing to the VMI and VP performance had there been a greater range of visual acuity in our sample population. Our findings suggested that other nonYvisual-related factors might affect the VP and VMI skills in children with a mild reduction in vision.
Limitation of This Study The above-normal performance of our study group in the VMI and VP tests might not be representative of Hong Kong preschoolers in general for two reasons. First, incidental sampling was used for selecting the kindergartens into the study; that is, the kindergartens were not randomly selected. Different schools might adopt different education materials and teaching curriculums. The differences in education background among subjects
629
might therefore bias our findings because both VMI and VP skills are affected by the background of the subjects.6,10,11,13,14,40,43,44 Second, the small number of schools studied and the method of ascertainment leave open the possibility of sampling bias; for instance, schools for less affluent sectors may have been more willing to participate than those from deprived areas. Further study using a larger sample size is needed to confirm the characteristics of the visual perceptual skills of general Hong Kong preschoolers.
CONCLUSIONS Hong Kong preschoolers outperformed their US peers in the VMI and in the visual memory and spatial relationships of VP tests, possibly reflecting differences in the education systems between Hong Kong and the United States. Indeed, the discrepancy in culture, language, and curriculum may indicate that each population should have its local normative value for the children being assessed using these tests. This study provided preliminary normality data for the VMI and four subtests of TVPS for Hong Kong Chinese preschoolers. After controlling for the effect of age, near visual acuity has little effect on the VP and VMI test performance, suggesting that there may be other nonYvisual-related factors that accounted for the remaining 65 and 80% of the variance in VMI and VP skills, respectively, of preschoolers.
ACKNOWLEDGMENTS This study was supported by a collaborative research fund from the Ebenezer School & Home for the Visually Impaired (H-ZJE3). We thank the students, parents, and teachers who participated in this study. We thank Dr. Jeremy Guggenheim, Prof. Brian Brown, and Prof. Susan Leat for commenting on an earlier draft of this article. Received October 17, 2014; accepted January 22, 2015.
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630 Vision and Visual Perception in PreschoolersVHo et al.
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27. Lim HT, Yu YS, Park SH, Ahn H, Kim S, Lee M, Jeong JY, Shin KH, Koo BS. The Seoul Metropolitan Preschool Vision Screening Programme: results from South Korea. Br J Ophthalmol 2004;88:929Y33. 28. Pai AS, Wang JJ, Samarawickrama C, Burlutsky G, Rose KA, Varma R, Wong TY, Mitchell P. Prevalence and risk factors for visual impairment in preschool children the Sydney Paediatric Eye Disease Study. Ophthalmology 2011;118:1495Y500. 29. Premsenthil M, Manju R, Thanaraj A, Rahman SA, Kah TA. The screening of visual impairment among preschool children in an urban population in Malaysia; the Kuching pediatric eye study: a cross sectional study. BMC Ophthalmol 2013;13:16. 30. Tarczy-Hornoch K, Cotter SA, Borchert M, McKean-Cowdin R, Lin J, Wen G, Kim J, Varma R, Multi-Ethnic Pediatric Eye Disease Study Group. Prevalence and causes of visual impairment in Asian and non-Hispanic white preschool children: Multi-ethnic Pediatric Eye Disease Study. Ophthalmology 2013;120:1220Y6. 31. Geldof CJ, van Wassenaer AG, de Kieviet JF, Kok JH, Oosterlaan J. Visual perception and visual-motor integration in very preterm and/ or very low birth weight children: a meta-analysis. Res Dev Disabil 2012;33:726Y36. 32. Hard AL, Aring E, Hellstrom A. Subnormal visual perception in school-aged ex-preterm patients in a paediatric eye clinic. Eye (Lond) 2004;18:628Y34. 33. Hard AL, Niklasson A, Svensson E, Hellstrom A. Visual function in school-aged children born before 29 weeks of gestation: a populationbased study. Dev Med Child Neurol 2000;42:100Y5. 34. Foulder-Hughes LA, Cooke RW. Motor, cognitive, and behavioural disorders in children born very preterm. Dev Med Child Neurol 2003;45:97Y103. 35. Cooke RWI, Foulder-Hughes L, Newsham D, Clarke D. Ophthalmic impairment at 7 years of age in children born very preterm. Arch Dis Child 2004;89:F249Y53. 36. Menken C, Cermak SA, Fisher A. Evaluating the visual-perceptual skills of children with cerebral palsy. Am J Occup Ther 1987; 41:646Y51. 37. Sutton GP, Barchard KA, Bello DT, Thaler NS, Ringdahl E, Mayfield J, Allen DN. Beery-Buktenica Developmental Test of Visual-Motor Integration performance in children with traumatic brain injury and attention-deficit/hyperactivity disorder. Psychol Assess 2011;23:805Y9. 38. Schultz RT, Carter AS, Gladstone M, Scahill L, Leckman JF, Peterson BS, Zhang H, Cohen DJ, Pauls D. Visual-motor integration functioning in children with Tourette syndrome. Neuropsychology 1998;12:134Y45. 39. Lai MY, Leung FK. Visual perceptual abilities of Chinese-speaking and English-speaking children. Percept Mot Skills 2012;114: 433Y45. 40. Lai MY, Leung FK. Motor-reduced visual perceptual abilities and visual-motor integration abilities of Chinese learning children. Hum Mov Sci 2012;31:1328Y39. 41. Yu C, Ying Z, Laukkanen H, Rabin J. Evaluation of visual-motor integration skills in preschool and elementary school-aged Chinese children. J Behav Optom 2012;23:123Y8. 42. Josman N, Abdallah TM, Engel-Yeger B. A comparison of visualperceptual and visual-motor skills between Palestinian and Israeli children. Am J Occup Ther 2006;60:215Y25. 43. Webb J, Abe K. Cross-cultural validity of the developmental test of visual-motor integration. Percept Mot Skills 1984;58:183Y8. 44. Shi X. Analysis of validities and results of the VMI test in children of city and small town. J Chin Child Health Care 1995;3:151Y4.
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Vision and Visual Perception in PreschoolersVHo et al. 45. Dunn M, Loxton H, Naidoo A. Correlations of scores on the developmental test of visual-motor integration and copying test in a South African multi-ethnic preschool sample. Percept Mot Skills 2006;103:951Y8. 46. Hong Kong Curriculum Development Council. Guide to the Preprimary Curriculum. Hong Kong: The Education Bureau HKSAR; 2006. Available at: http://www.edb.gov.hk/attachment/en/edusystem/preprimary-kindergarten/overview/pre-primaryguide-net_en_928.pdf. Accessed February 19, 2015. 47. Hung SS, Fisher AG, Cermak SA. The performance of learningdisabled and normal young men on the test of visual-perceptual skills. Am J Occup Ther 1987;41:790Y7. 48. Fulkerson SC, Freeman WM. Perceptual-motor deficiency in autistic children. Percept Mot Skills 1980;50:331Y6. 49. Shen IH, Lee TY, Chen CL. Handwriting performance and underlying factors in children with Attention Deficit Hyperactivity Disorder. Res Dev Disabil 2012;33:1301Y9. 50. Martin NA. Test of Visual Perceptual Skills, 3rd ed. Novato, CA: Academic Therapy Publications; 2006. 51. Lam SR, LaRoche GR, De Becker I, Macpherson H. The range and variability of ophthalmological parameters in normal children aged 4 1/2 to 5 1/2 years. J Pediatr Ophthalmol Strabismus 1996;33:251Y6. 52. Almubrad T. Statistical stereo-acuity norms in Saudi children. Clin Exp Optom 2006;89:155Y9. 53. Wong HB, Machin D, Tan SB, Wong TY, Saw SM. Visual impairment and its impact on health-related quality of life in adolescents. Am J Ophthalmol 2009;147:505Y11. 54. Simons K. Stereoacuity norms in young children. Arch Ophthalmol 1981;99:439Y45. 55. Solan HA, Ficarra AP. A study of perceptual and verbal skills of disabled readers in grades 4, 5 and 6. J Am Optom Assoc 1990;61: 628Y34.
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Allen Ming-Yan Cheong School of Optometry The Hong Kong Polytechnic University Hung Hom, Hong Kong China e-mail: [email protected]
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ORIGINAL ARTICLE
Relationship between Vision and Visual Perception in Hong Kong Preschoolers Wing-Cheung Ho*, Minny Mei-Miu Tang†, Ching-Wah Fu‡, Ka-Yan Leung§, Peter Chi-Kong Pang||, and Allen Ming-Yan Cheong*
ABSTRACT Purpose. Although superior performance in visual motor and visual perceptual skills of preschool children has been documented in the Chinese population, a normative database is only available for the US population. This study aimed to determine the normative values for these visuomotor and visual perceptual tests for preschool children in the Hong Kong Chinese population and to investigate the effect of fundamental visual functions on visuomotor and visual perceptual skills. Methods. One hundred seventy-four children from six different kindergartens in Hong Kong were recruited. Distance visual acuity, near visual acuity, and stereopsis were tested, along with two measures of visual perception (VP): Visual-Motor Integration (VMI) and Test of Visual-Perceptual Skills (TVPS). Raw VMI and TVPS scores were converted into standard/ scaled scores. The impact of basic visual functions on VP (VMI and TVPS) was examined using multiple regression. Results. Visual functions were generally good: only 9.2 and 4.6% of subjects had unilateral and bilateral reduced habitual vision, respectively (distance visual acuity in the better eye 90.3 logMAR [logarithm of the minimum angle of resolution]). Performance in the VMI and in the visual memory and spatial relationships subtests of the TVPS exceeded that reported for age-matched children from the United States. Multiple regression analysis provided evidence that age had the strongest predictive value for the VMI and VP skills. In addition, near visual acuity was weakly associated with performance in the VMI and the visual discrimination and spatial relationships subtests of the TVPS, accounting for a limited proportion of the intersubject variability (R2 G 3%; p G 0.001). Conclusions. Hong Kong preschoolers outperformed their US peers in the VMI and visual memory/spatial relationships of TVPS subtests, perhaps attributed to greater exposure to such material during their preschool home education. This study provided normality data for VMI and four subtests of the TVPS for Hong Kong Chinese preschool children as a reference for future studies. (Optom Vis Sci 2015;92:623Y631) Key Words: preschool children, visual function, visual perception, visual motor, Hong Kong Chinese
V
ision plays an important role in early childhood development. Children with visual disorders face significant barriers in their learning and daily activities. Early detection and treatment of visual deficits in young children can improve the prognosis for normal eye development, prevent further vision loss, and reduce the impact of learning problems, poor school performance, developmental delays, and behavior concerns.1
*BSc(Hons), PhD † PDip(OT) MA ‡ MA § BSc(Hons) || MPhil, PDP (Optom) School of Optometry, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China (W-CH, K-YL, PC-KP, AM-YC); and Ebenezer School & Home for the Visually Impaired, Hong Kong Island, Hong Kong, China (MM-MT, C-WF).
The eyes collect visual information from the environment and transmit it to the brain for further processing and interpretation. An eye examination includes measuring a series of sensory functions (such as visual acuity and binocular visual performance) and assessing ocular health. However, the measurement of these basic visual functions alone may not be sufficient to identify all children with visual processing disorders: some children with good vision may have difficulty in interpreting what is seen. Visual perception (VP) is the ability of the brain to understand and interpret what the eyes see,2 whereas visual-motor integration (VMI) is the ability to coordinate body movements with VP, which involves interactions between visual, visual-perceptual, and motor skills.3,4 Visual perception is important for reading, writing, and driving,5 whereas VMI is important for writing.6Y8 Hence, both VP and VMI are important skills for processing visual information and play integral roles in childhood development. Children with deficits in VP or
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624 Vision and Visual Perception in PreschoolersVHo et al.
VMI show inferior academic performance,9,10 including mathematics achievement,11 reading achievement,12,13 and handwriting.6,14 Numerous studies have investigated the causes of vision disorders in school-aged students15Y21 (aged 5 to 15 years) and preschool children (aged 2.5 to 6 years)22Y30 and found that refractive error is the most common cause (Table 1 summarizes the prevalence rates of abnormal visual acuity in preschool children from various populations). By contrast, very few studies have explored the relationship between basic visual functions and VP and their interactive impacts on children’s development. In those studies that have addressed this issue, the VMI and VP of children born prematurely,31Y35 with low birth weight,31 with brain disorders,36,37 or with congenital abnormalities38 have been examined. Recently, a handful of studies have compared VP abilities in Chinese-speaking and English-speaking preschool children of the same age in different countries.39Y41 The findings suggest that VP skills among Chinese-speaking children exceed those of age-matched English-speaking children, probably because of the differences in language as well as the education system.39Y41 Similar findings are seen for the VMI skills, with Chinese children outperforming US
children over the 5 to 9 years age range.41 In addition, perceptual and motor skills are found to depend on culture,42,43 language,39 region,44 academic level,10,11 race, and socioeconomics.45 Because of these diverse demographic and cultural differences, each population needs to establish its own normative database, rather than applying the US-based normative database to identify children with deficits in the VMI or VP skills. Hong Kong has a distinctive education system, which is different from both Western countries and mainland China. For instance, children’s education in Hong Kong includes infant education (i.e., babies’ early education) and training to preschool age covering topics such as physical fitness, language, mathematics, and arts.46 It is possible that this type of early childhood education further facilitates the development of VP and VMI skills. Hence, applying the US normative database to examine Hong Kong children’s VP and VMI performances might not be appropriate, stressing the importance to develop a Hong KongYbased normative database. On the other hand, although VP and VMI skills are known to be affected by developmental problems,31Y38 these cognitive skills might also be affected if blur or poor image quality is
TABLE 1.
Prevalence of abnormal visual acuities in preschool children reported in previous studies Study
Country (year)
Age, mo
N
BPEDS
United States (2008)
30Y71
1504
MEPEDS30
United States (2013)
30Y72
1840
MEPEDS26
United States (2009)
30Y72
3207
SPEDS28
Australia (2011)
30Y72
1188
Chia et al.23
Singapore (2010)
30Y72
1682
Taiwan (2007)
36Y72
4907
Hong Kong (2011)
36Y72
823
Korea (2004) Malaysia (2013)
36Y71 48Y72
35,226 400
25
Chang et al.22
Fan et al.24
Lim et al.27 Premsenthil et al.29
Definition of ‘‘abnormal’’ visual acuity, mo Presenting visual acuity 90.40 logMAR (30Y47 mo) 90.30 logMAR (48Y72 mo)
Q0.18 logMAR (did not mention whether habitual glasses were allowed) 1. Uncorrected visual acuity 2. Q0.30 logMAR (36Y47 mo) Q0.22 logMAR (48Y59 mo) Q0.15 logMAR (60Y71 mo) Q0.10 logMAR (72Y83 mo) 1. Best-corrected visual acuity 2. Q0.30 logMAR (36Y48 mo) 92-line difference in best-corrected visual acuity between 2 eyes 90.30 logMAR 90.30 logMAR in one or both eyes (did not mention whether habitual glasses were allowed)
Prevalence, % Both eyes White: 1.2% Black: 1.8% Worse eye Asian: 3.4% Non-Hispanic white: 2.6% Better eye Asian: 0.8% Non-Hispanic white: 0.8% Worse eye African: 8.6% Hispanic: 10.5% Better eye African: 3.9% Hispanic: 3.5% 6.4% (worse eye) 2.7% (better eye) Either eye: 2.8%
10.3%
2.7% (17% with some abnormalities)
Right eye only: 5.6% One or both eyes: 5% (screening)
BPEDS, Baltimore Pediatric Eye Disease Study; MEPEDS, Multi-Ethnic Pediatric Eye Disease Study; SPEDS, Sydney Paediatric Eye Disease Study. Optometry and Vision Science, Vol. 92, No. 5, May 2015
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Vision and Visual Perception in PreschoolersVHo et al.
perceived by children with visual deficits. However, no study has examined the effect of basic sensory functions on these higher cognitive skills. In this study, we examined a sample of Hong Kong preschoolers with no history of birth-related problems or congenital diseases, with the aims of (1) investigating the performance of VP and VMI skills, (2) examining the relationship between basic visual functions and VP performance, and (3) establishing preliminary normative values for the VMI and VP tests for preschool children in Hong Kong.
METHODS Subjects Six kindergartens from 6 different districts (out of 18 districts) in Hong Kong were chosen using incidental sampling. Invitations to take part in the study were made to parents or legal guardians of preschoolers aged 4 to 7 years in the selected kindergartens. Subjects who fulfilled the following criteria were recruited: (1) informed consent given by parents or legal guardians (response rate, 90.9%); (2) no history of cardiovascular or nervous system diseases; (3) no reported specific learning difficulties,47 autism spectrum disorder,48 and attention-deficit/hyperactivity disorder as indicated by parents/legal guardians,49 or observable physical and intellectual disabilities as indicated by an experienced occupational therapist50; (4) a gestation period of at least 37 weeks32; and (5) capable of following instructions during the assessments. The study followed the tenets of the Declaration of Helsinki and was approved by the Human Ethics Committee of the School of Optometry, The Hong Kong Polytechnic University. Demographic information (age, sex, parents-perceived general and ocular health, and history of last eye examination) was collected through a structured questionnaire (Table 2). Parents were asked to rate the health status of their children using a five-point Likert scale.
Procedures Basic Visual Functions and Ocular Health Assessment Visual acuity, color vision, stereopsis, binocular alignment, and ocular health were examined. Monocular distance and near visual acuities were measured at 3 m and 40 cm, respectively, using the crowded LEA Symbols 15-Line Distance Chart and a near vision card without confusion bars (Good-Lite Co, Elgin, IL) in logMAR [logarithm of the minimum angle of resolution] notation under room lighting of about 200 lux. Subjects were required to wear glasses for visual acuity measurement if they had them. Credit was given for each correctly recognized symbol. Color vision was tested with the Color Vision Made Easy test (Precision Vision, La Salle, IL). Stereoacuity was assessed using the Randot Stereotest (Stereo Optical Company, Inc, Chicago, IL) at 40 cm. Subjects were graded as passing the stereopsis test if their stereoacuity was less than 70 minutes of arc.51,52 Ocular alignment was assessed using both the cover test and Hirschberg test. Types of tropia, characteristics (intermittent or constant), and the degree of deviation (prism diopters) were recorded. Two drops of 0.5% tropicamide and 0.5% phenylephrine (Mydrin-P; Santen Pharmaceutical Co, Ltd) were instilled, 10 minutes apart, for each subject to relax accommodation. Cycloplegic autorefraction using an open-field autorefractor
625
TABLE 2.
Structured questionnaire for the parents/legal guardians of participating children 1. Prenatal infection g Yes 2. Preterm baby (G37 wk) g Yes 3. Personal general health a. Cerebral palsy g Yes b. Meningitis g Yes c. Strabismus g Yes d. Amblyopia g Yes 4. Family ocular health a. Color weakness/color blindness g Yes b. Strabismus g Yes c. Amblyopia g Yes d. Congenital/hereditary g Yes (if yes, please eye diseases state: ______) Please rate the general health of your child g Excellent g Very good g Good g Satisfactory g Poor Please rate the ocular health of your child g Excellent g Very good g Good g Satisfactory g Poor
g No g No g g g g
No No No No
g g g g
No No No No
Remarks: Please put a ‘‘( ’’ for each question.
(Model: NVision-K 5001, Shin-Nippon, Rexxam Co Ltd, Tokyo, Japan) was conducted 30 minutes after drug instillation. A fixation target placed at 6 m was used to control the fixation and accommodation during the measurement. All vision and perceptual tests were completed before pupil dilation. The ocular health examination included slit-lamp biomicroscopy and indirect ophthalmoscopy to evaluate the anterior and posterior eye, respectively. Subjects were graded as passing the ocular health assessment if no signs of ocular infection, media opacity, hereditary retinal degeneration, or retinal disease were identified.
VMI Skills Visual-motor integration skills were tested with the BeeryBuktenica Developmental Test of Visual-Motor Integration (Berry VMI, 6th edition),4 administered in standard classrooms under normal room illumination, following the instructions in the test manual.4 The subjects were arranged in groups of six for each test administrator. They were required to wear their habitual glasses to attend the tests if they had them. The VMI test contains 15 geometric forms ranging from the simplest to the most difficult. Subjects were asked to copy the forms on the test booklet in the given order, and the test was ended when three consecutive shapes could not be copied or were copied incorrectly. All subjects were given as much time as needed to complete the test. The administrator examined each drawing according to the VMI manual, and each correctly drawn form was scored as one point. The raw score is the sum of the number of correctly drawn forms. According to the subject’s age, each individual raw score was converted to a ‘‘standard score,’’ based on the VMI tabular norms for 12,500 US school-aged children.4
VP Skills Visual perception skills were tested with the Test of VisualPerceptual Skills (nonmotor), Third Edition (TVPS-3),50
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626 Vision and Visual Perception in PreschoolersVHo et al.
administered following the instructions in the TVPS-3 manual, on a one-to-one basis. The full TVPS contains seven subtests for measuring different interrelated VP parameters. In this study, only the four subtests (visual discrimination, visual memory, spatial relationships, and form constancy) that form the basic visual processes composite were administered. Each subject’s VP performance was examined by one administrator. Children were again required to wear their habitual glasses if they had them. In the visual discrimination subtest (i.e., form analysis), subjects had to point to the design matching that shown in a figure. In the visual memory subtest (i.e., form analysis with a memory component), subjects had 5 seconds to view a design on one page of the test book and then select the same design from among the choices on the following page. In the spatial relationships subtest (i.e., form and spatial/orientation discrimination), subjects had to select the design that differed from among a series of designs. In the form constancy subtest (i.e., dominant feature discrimination), subjects had to match a design that differed in size or orientation from among a set of designs on the same page. Each correct answer was scored as one point, and each subtest was ended when three consecutive questions were answered incorrectly. The raw score was computed as the total number of correct responses and converted to a ‘‘scaled score’’ with reference to the TVPS-3 tabular
norms from 2008 US school-aged children or adults. The sum of the scaled scores for the four subtests was then converted to a standard score with reference to the look-up table in the manual.
Statistical Analysis Data were analyzed using IBM SPSS version 18 (Statistical Package for the Social Sciences). Stepwise multiple regression analyses were used to determine whether the predictors, age, near visual acuity (in the better eye), and stereopsis could predict visual perceptual skills (VP or VMI).10 Descriptive data for the VMI and VP subtests including percentiles for six age groups from 4 to 7 years were calculated. An independent samples t test was used to test for any significant difference in VMI and each VP test of our subjects against the US normative value (i.e., 100 for both VMI and basic process of VP, 10 for all VP subtests). A p value of 0.05 was considered statistically significant.
RESULTS One hundred seventy-four subjects (male, 101; female, 73) met the inclusion criteria and completed all of the assessments. The mean (TSD) age of the subjects was 5.1 (T0.7) years. Of the 170
TABLE 3.
Distribution of visual functions and visual disorders for each age group Age groups 6.0Y6.11*
All
0.50 (j0.75, 2.13) 0.63 (j0.25, 2.21) 0.63 (j0.75, 2.12) 0.56 (j0.22, 2.28)
0.75 (j0.60, 2.60) 0.69 (j0.62, 2.60)
0.63 (j0.59, 2.25) 0.63 (j0.70, 2.32)
0.14 (j0.04, 0.46) 0.11 (j0.06, 0.38)
0.04 (j0.08, 0.34)
0.12 (j0.06, 0.43)
0.14 (j0.03, 0.41) 0.12 (j0.08, 0.28)
0.08 (j0.10, 0.41)
0.12 (j0.06, 0.36)
4.0Y4.11* Autorefraction, in spherical equivalent, D Right eye, median (5th, 95th percentile) Left eye, median (5th, 95th percentile) Visual function measures Distance visual Right eye, median acuity, logMAR (5th, 95th percentile) Left eye, median (5th, 95th percentile) Unilateral reduced habitual visual acuity (logMAR 9 0.30), n (%) Bilateral reduced habitual visual acuity, n (%) Near visual acuity, Right eye, median logMAR (5th, 95th percentile) Left eye, median (5th , 95th percentile) Stereoacuity Stereoacuity, median (5th, 95th percentile), minute of arc Fail stereoacuity (970 minutes of arc), n (%) Color vision defects Fail color vision (G8 corrected plates), n (%) Ocular abnormalities Strabismus, n (%) Ocular health abnormalities,† n (%)
5.0Y5.11*
9 (10.8)
5 (7.4)
2 (8.7)
16 (9.2)
3 (3.6)
3 (4.4)
2 (8.7)
8 (4.6)
0.12 (j0.08, 0.30) 0.07 (j0.08, 0.23)
0.00 (j0.10, j0.19) 0.10 (j0.08, 0.25)
0.10 (0.06, 0.29)
0.00 (j0.10, 0.23)
40 (40, 100)
0.04 (j0.08, 0.23) 40 (40, 100)
7 (8.4)
10 (14.7)
8 (9.6) 2 (2.4) 0 (0.0)
40 (40, 100)
0.08 (j0.08, 0.24) 40 (40, 100)
3 (13.0)
20 (11.5)
4 (5.9)
2 (8.7)
14 (8.0)
1 (1.5) 1 (1.5)
1 (4.3) 0 (0.0)
4 (2.3) 1 (0.6)
*The number before the decimal point indicates the number of years and the number after the decimal point denotes the number of months. †In ocular health examination, we examined any signs of ocular infection, media opacity, hereditary retinal degeneration, or retinal diseases. Optometry and Vision Science, Vol. 92, No. 5, May 2015
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Vision and Visual Perception in PreschoolersVHo et al. TABLE 4.
Normative data of performances in the VMI and each subtest of TVPS (raw score) for each age group Age range 10th 25th 50th 75th 90th VMI
4.0Y4.5 4.6Y4.11 5.0Y5.5 5.6Y5.11 6.0Y6.5 6.6Y6.11 TVPS Visual 4.0Y4.5 discrimination 4.6Y4.11 5.0Y5.5 5.6Y5.11 6.0Y6.5 6.6Y6.11 Visual memory 4.0Y4.5 4.6Y4.11 5.0Y5.5 5.6Y5.11 6.0Y6.5 6.6Y6.11 Spatial 4.0Y4.5 relationships 4.6Y4.11 5.0Y5.5 5.6Y5.11 6.0Y6.5 6.6Y6.11 Form constancy 4.0Y4.5 4.6Y4.11 5.0Y5.5 5.6Y5.11 6.0Y6.5 6.6Y6.11
11.0 14.0 14.3 14.5 15.0 16.0 2.0 2.0 2.0 3.5 3.0 4.0 2.0 2.8 1.3 3.0 5.0 6.0 1.0 2.0 3.3 4.5 5.0 5.0 0.0 1.0 1.0 0.0 2.0 1.5
12.3 15.0 16.0 16.0 16.0 17.0 2.0 2.0 3.0 4.8 5.0 5.0 3.0 4.0 3.0 6.0 6.0 6.0 3.0 4.0 5.0 6.0 5.0 11.0 1.8 2.0 3.0 3.0 3.8 3.0
14.0 17.0 17.0 18.0 18.0 20.0 4.0 4.0 6.0 7.0 6.0 7.0 4.5 6.0 6.0 7.5 9.0 8.0 5.0 7.0 9.5 8.5 12.0 13.0 4.0 4.0 4.0 5.0 4.5 4.0
16.0 18.0 18.0 19.0 19.0 21.0 5.0 7.0 7.0 9.0 9.0 10.0 7.0 8.0 8.0 9.0 11.0 9.0 8.0 9.0 12.0 11.0 14.0 13.0 5.0 5.8 5.0 7.0 6.0 5.0
17.5 19.0 19.0 20.0 21.0 21.0 6.0 8.0 9.0 10.0 12.0 10.0 8.0 9.0 10.4 11.0 13.0 9.0 10.0 12.2 13.0 12.5 15.0 13.0 7.0 8.9 8.5 9.0 8.0 9.0
Values under the column ‘‘Age range’’ are presented as follows: The number before the decimal point indicates the number of years and the number after the decimal point denotes the number of months.
respondents, 71 subjects (41.8%) had never had an eye examination, whereas 86 subjects (50.6%) had had at least one eye examination in the past.
627
Characteristics of Visual Functions and Prevalence of Visual Disorders Table 3 summarizes the distribution of visual functions and visual disorders by age group. Because visual acuity and stereopsis were not normally distributed, medians with 5th and 95th percentile (in parentheses) are presented. The median spherical equivalent refractive error for all subjects was +0.63 diopters (D) (j0.59, 2.25 D) and +0.61 D (j0.70, 2.32 D) for right and left eyes, respectively. Presenting distance visual acuity was 0.12 (j0.06, 0.43) and 0.12 (j0.06, 0.36) logMAR for right and left eyes, respectively, whereas presenting near visual acuity was 0.10 (j0.08, 0.25) and 0.08 (j0.08, 0.24) logMAR. Following Wong et al.,53 unilateral and bilateral reduced habitual visual acuity were defined as distance acuity worse than 0.30 logMAR (equivalent to Snellen 6/12) in any eye or both eyes, respectively. In our sampled population, 9.2 and 4.6% subjects had unilateral and bilateral reduced visual acuity, respectively, in which all cases were not attributed to pathological changes. Subjects had relatively good stereoacuity (median, 40 minutes of arc), with 11.5% failing the stereotest (970 minutes of arc).51,54 Fourteen (8%) subjects failed the color vision test. Only 1 (0.6%) subject failed the ocular health assessment, because of a red eye.
Characteristics of Visual Motor and Visual Perceptual Skills Normative data of performances in the VMI and each subtest of TVPS (raw score), including percentiles for six age groups from 4 years to 6 years 11 months are presented in Table 4. Mean and SD of the derived standard/scaled scores for each age group for the VMI and TVPS (four subtests) are shown in Table 5. The average standard score of VMI was 112.8 (T9.2), which exceeded the standardized score of 100, suggesting that the overall performance of our Chinese kindergarten subjects was better than that of agematched US children (t173 = 19.3, p G 0.001). Similar results were found for the visual memory and spatial relationships of the TVPS. The scaled scores of visual memory and spatial relationships were 11.2 (T3.7) (t173 = 3.6, p G 0.01) and 13.1 (T3.8) (t173 = 10.1, p G 0.001), respectively, compared with the age norm of 10 for US children. The mean scores for visual discrimination and
TABLE 5.
Mean T SD of the standard/scaled scores for VMI and TVPS for each age group TVPS Age 4.0Y4.5 4.6Y4.11 5.0Y5.5 5.6Y5.11 6.0Y6.5 6.6Y6.11 Overall
n
VMI*
38 45 38 30 16 7 174
116.2 T 10.2 117.7 T 7.5 112.2 T 7.2 109.2 T 7.6 104.0 T 7.3 102.7 T 6.2 112.8 T 9.2
Visual discrimination† Visual memory† Spatial relationships† Form constancy† Basic processes* 9.7 T 1.6 10.1 T 3.3 10.1 T 3.3 11.1 T 3.1 10.8 T 3.5 10.9 T 2.7 10.3 T 3.0
11.2 T 3.1 12.0 T 3.5 10.1 T 4.5 11.3 T 3.6 12.0 T 3.8 10.4 T 2.1 11.2 T 3.7
12.6 T 3.2 12.9 T 3.7 13.3 T 4.3 12.9 T 3.3 14.3 T 4.8 15.4 T 3.7 13.1 T 3.8
11.7 T 3.0 10.6 T 4.7 9.8 T 3.3 8.4 T 4.1 8.8 T 2.8 8.1 T 2.3 10.0 T 3.9
107.1 T 9.6 107.3 T 12.2 104.2 T 13.1 104.1 T 11.6 107.6 T 11.7 106.4 T 9.3 106.0 T 11.6
Values under the column ‘‘Age’’ are presented as follows: The number before the decimal point indicates the number of years and the number after the decimal point denotes the number of months. *Standard score. †Scaled score. Optometry and Vision Science, Vol. 92, No. 5, May 2015
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628 Vision and Visual Perception in PreschoolersVHo et al.
form constancy were 10.3 (T3.0) and 10.0 (T3.9), respectively, which were similar to the performance in US children (t173 = 1.4, p = 0.16; t173 = j1.1, p = 0.26). The mean standard score for the basic processes, an index representing performance in the four subtests, was 106.0 (T11.8), suggesting that visual perceptual skills for Hong Kong children were slightly but significantly better than those for US children (t173 = 6.7, p G 0.001). There is no consensus on criteria for classifying subjects with VMI or TVPS deficits. For example, a performance score at the 30th percentile and the 16th percentile55 has been used as the cutoff point for failing the VMI, whereas scores at the 16th and 10th percentiles have been used to define persons with a TVPS deficit.56 In this study, we adopted the 10th percentile as the cutoff point to classify subjects having a deficit in either VMI or TVPS. According to our study’s definition, no subject had VMI deficiency. In contrast, the prevalence of an overall TVPS deficit in basic visual processing was 3.4%, although the prevalence in each subtest varied from 2.2% for spatial relationship to 10.6% for form constancy.
Relationships among Basic Visual Functions, Visual Motors, and VP Given the significant differences in VMI and VP components between children in our study and in the United States, raw scores of VMI and each subtest of TVPS instead of derived scores (standard scores or scaled scores) were used to investigate the impact of basic visual functions (near visual acuity and stereopsis) on visual motor and VP performance. Multiple regression analysis suggested that age was the best predictor of VMI and TVPS raw scores (except form constancy). Near visual acuity had a significant, although subtle contribution to the variances in VMI and in the visual discrimination and spatial relationships of TVPS (accounting for 1 to 3% of the intersubject variation, p G 0.05, Table 6).
In contrast, near visual acuity and near stereoacuity were not predictive of subjects’ performance in visual memory and form constancy of TVPS (Table 6).
DISCUSSION A low prevalence (4.6%) of deficits in basic visual functions was found in Hong Kong Chinese preschoolers, comparable to that reported in other epidemiology studies (Table 1). Poor habitual vision was not attributed to pathological changes but rather to uncorrected or undercorrected refractive error, which was preventable and/or amenable to treatment. In accordance with earlier reports in Chinese preschoolers,39Y41,44,57 Hong Kong Chinese preschoolers’ VP performance in our study was good for both VMI and TVPS. In VMI, Hong Kong children performed substantially better than US children (average raw and standard score of 16.7 and 112.8, respectively) but only slightly better than children from mainland China (average raw and standard scores of 13.0 and 109.9, respectively).41 It has been argued that the former effect is related to the difference in the school curriculum between the two countries: US children are mainly taught cognitive and psychosocial skills during the preprimary stage,58 whereas Chinese children are taught academic knowledge (including reading and writing) and physical activities.46 Indeed, Hong Kong children are generally required to learn and copy simple and complex pictures and/or characters from an early age (e.g., age 2 for prenursery and age 3 for kindergartens). Writing starts in the second year at kindergartens (age 4). Previous studies have demonstrated the importance of VMI skills in the writing process6,9,10,49 because writing requires the brain to send signals to control body posture and the movement of the limbs. On the other hand, physical activity helps children develop better control of their body and limbs.
TABLE 6.
Predictors of performance in VP Visual-Motor Integration (VMI)
Dependent variable Visual discrimination
Visual memory Spatial relationships
Form constancy
Predictors
Adjusted R2
Age Age Near acuity
0.34 0.35
Predictor(s) Age Age & Near acuity Age Age Age & Near acuity V
Standardized coefficients
0.58 0.52 j0.15 Test of Visual-Perceptual Skills (TVPS)
Adjusted R2 0.20 0.23 0.14 0.20 0.21 V
Standardized coefficients 0.45 0.37 j0.21 0.38 0.45 0.38 j0.17 V
95% CI for standardized coefficient Lower
Upper
p
1.54 1.31 j6.88
2.36 2.19 j0.48
G0.001 G0.001 0.03
95% CI for standardized coefficient Lower Upper 1.19 2.20 0.83 1.59 j9.67 j1.86 0.99 2.11 1.67 3.10 1.25 2.80 j12.1 j0.89 V V
p G0.001 G0.001 0.004 G0.001 G0.001 G0.001 0.023 V
CI, confidence interval. Optometry and Vision Science, Vol. 92, No. 5, May 2015
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Vision and Visual Perception in PreschoolersVHo et al.
Our results also suggested that Hong Kong preschoolers outperformed US children in spatial relationship tasks and in the visual memory components of the TVPS. Again, a plausible reason is the early exposure to reading and writing using both Chinese characters and the English alphabet from the age of 3 (i.e., kindergarten grade 1). Because of the complex geometric and orthographical design of Chinese characters, Kao59 stated that Chinese writing is a complex process involving the perception, cognition, and motor function of the body. Writing Chinese characters reflects spatial characteristics of the words; thus, the writing process is thought to train the spatial-orientation skills of the child. In addition, learning Chinese characters may help improve visual memory by stimulating the recall of visual forms.60 Clinically, a population-specific normative database should be used to examine a child’s VMI and VP skills. Our study provided preliminary normality data for the VMI and four subtests of TVPS for Hong Kong Chinese preschoolers as reference for future studies and clinical practice (Table 4). Visual-motor integration and VP skills develop rapidly during the preschool years.4,50 As expected, our results showed that most of the VMI and VP skills improved significantly as children got older (age explained 14 to 34% of intersubject variation in VMI and TVPS). However, only weak and nonsignificant change was observed in ‘‘form constancy’’Van important skill required to recognize forms, letters, or words regardless of their orientation. This suggests that the development of form constancy skill is slower than other perceptual skills. Gibson61 reported that younger children made more reversal errors and selection of upside-down forms than older children in letter discrimination. Although no reading assessment was included in our study, children with deficits in form constancy might be more likely to have difficulty in reading Chinese because the ability to distinguish the differences in size, shape, and orientation of Chinese characters is essential.62 As mentioned above, age accounted for 34% of the variance in VMI and 14 to 20% of the variance in the visual discrimination, visual memory, and spatial relationships of VP skills. Other than age, near visual acuity contributed only subtly (~1 to 3% of the variance) to the performance of the VMI and the visual discrimination and spatial relationships of TVPS. Because visual acuity is the most fundamental level of the visual signal processing pathway,63 it is not surprising that performance in VP tests is slightly affected by visual acuity. A study on preterm children also demonstrated that poor visual acuity was associated with a lower VMI score.35 There might be a larger change in the variance of visual acuity contributing to the VMI and VP performance had there been a greater range of visual acuity in our sample population. Our findings suggested that other nonYvisual-related factors might affect the VP and VMI skills in children with a mild reduction in vision.
Limitation of This Study The above-normal performance of our study group in the VMI and VP tests might not be representative of Hong Kong preschoolers in general for two reasons. First, incidental sampling was used for selecting the kindergartens into the study; that is, the kindergartens were not randomly selected. Different schools might adopt different education materials and teaching curriculums. The differences in education background among subjects
629
might therefore bias our findings because both VMI and VP skills are affected by the background of the subjects.6,10,11,13,14,40,43,44 Second, the small number of schools studied and the method of ascertainment leave open the possibility of sampling bias; for instance, schools for less affluent sectors may have been more willing to participate than those from deprived areas. Further study using a larger sample size is needed to confirm the characteristics of the visual perceptual skills of general Hong Kong preschoolers.
CONCLUSIONS Hong Kong preschoolers outperformed their US peers in the VMI and in the visual memory and spatial relationships of VP tests, possibly reflecting differences in the education systems between Hong Kong and the United States. Indeed, the discrepancy in culture, language, and curriculum may indicate that each population should have its local normative value for the children being assessed using these tests. This study provided preliminary normality data for the VMI and four subtests of TVPS for Hong Kong Chinese preschoolers. After controlling for the effect of age, near visual acuity has little effect on the VP and VMI test performance, suggesting that there may be other nonYvisual-related factors that accounted for the remaining 65 and 80% of the variance in VMI and VP skills, respectively, of preschoolers.
ACKNOWLEDGMENTS This study was supported by a collaborative research fund from the Ebenezer School & Home for the Visually Impaired (H-ZJE3). We thank the students, parents, and teachers who participated in this study. We thank Dr. Jeremy Guggenheim, Prof. Brian Brown, and Prof. Susan Leat for commenting on an earlier draft of this article. Received October 17, 2014; accepted January 22, 2015.
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630 Vision and Visual Perception in PreschoolersVHo et al.
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Allen Ming-Yan Cheong School of Optometry The Hong Kong Polytechnic University Hung Hom, Hong Kong China e-mail: [email protected]
Optometry and Vision Science, Vol. 92, No. 5, May 2015
Copyright © American Academy of Optometry. Unauthorized reproduction of this article is prohibited.
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