DOI: 10.5301/ejo.5000409
Eur J Ophthalmol 2014; 24 ( 4 ): 599-607
ORIGINAL ARTICLE
Infantile nystagmus and visual deprivation: foveal instability and refractive development in a low vision register series Hans C. Fledelius1, Hanne Jensen2 1 2
Copenhagen University Eye Department, Rigshospitalet Copenhagen and Glostrup Hospital - Denmark Copenhagen University Eye Department, National Eye Clinic, Kennedy Centre, Glostrup - Denmark
Purpose: To evaluate whether effects of early foveal motor instability due to infantile nystagmus might compare to those of experimental visual deprivation on refraction in a childhood series. Methods: This was a retrospective analysis of data from the Danish Register for Blind and Weaksighted Children with infantile nystagmus recorded as prime diagnosis. We perused 90 records of children now aged 10-17 years, some of whom eventually exceeded the register borderline of 0.3 as best-corrected visual acuity. Spherical equivalent refraction was the primary outcome parameter, but visual acuity, astigmatism, and age were further considered. The series comprised 48 children with nystagmus as single diagnosis, whereas 42 had clinical colabels (Down syndrome [13], dysmaturity [9], and mental retardation, encephalopathy [20]). Results: Median binocular visual acuity was 0.3 in the full series, and median refraction was emmetropia in all subgroups. Compared with Danish control data, myopia was over-represented, and generally of juvenile onset. The Down syndrome subgroup was separated from the remainder by an even higher myopia prevalence. Astigmatism above 1 D cylinder value was recorded in 52% of all cases. Conclusions: The prevalence of myopia and astigmatism was higher among children with nystagmus than in controls. Myopia was mainly juvenile, and not related to the period of infancy when the motor foveal smear is considered most disturbing and possibly influencing visual development. Keywords: Deprivation myopia mechanisms, Foveal instability, Infantile nystagmus syndrome, Refractive distribution, Visual development Accepted: November 21, 2013
INTRODUCTION A clear retinal image is considered a precondition for human infants’ foveal maturation and the development of central vision. By visual feedback mechanisms, the imaging is part of the emmetropization, as usually is already apparent in Western populations at preschool age, and is manifested in a refractive distribution showing leptokurtosis (1-5). Skewness is added by the growing tail of juvenile
myopia, whereas myopia during the first years of life is rare in Denmark. Usually early myopia can be ascribed to prematurity (3, 6) or to heredity (family occurrence) or as part of syndromes (7, 8). In the experimental animal, the natural visual feedback mechanisms are deliberately disturbed under conditions that hamper retinal image formation, as first demonstrated by the lid suture myopia induced in infantile monkeys (9, 10). Further, high optical defocus, by spectacles or
© 2013 Wichtig Editore - ISSN 1120-6721
599
Infantile nystagmus, foveal instability, and subsequent refraction
contact lenses, may trigger ocular growth changes, and here with a sign, which means attempting to adjust the axial length to the new focus point (11-17). Unlike the prevailing type of human myopia of juvenile onset, however, the laboratory investigations using chickens and various mammals are generally conducted during infancy, when eye plasticity is at its maximum. This further implies immature cognition as part of the animals’ early visual processing. In humans, visual development may suffer due to congenital or perinatally acquired lesions and manifest not only as poor visual interest, but also as sensory or secondary nystagmus (18, 19). This clearly differs from the infantile nystagmus (IN) group, which is the focus of the present study. When diagnosed, it qualifies for the National Danish Register for the Blind and Visually Impaired Children (NRBVIC, age 0-17 years), to ensure ophthalmic, educational, and social support. However, many infantile motor cases eventually present nystagmus reduction (18, 19) and often end up with a best-corrected visual acuity (BCVA) better than the formal Danish register limit of 0.3 (20). Infantile nystagmus implies that establishing stable foveal fixation has poorer chances. Visual acuity is diminished when fixation instabilities cause movement across the fovea (motion smear) (21), and a model has been hypothesized: that “maladaptation to early visual deprivation underlies the instability of the gaze-holding mechanisms” (18). We therefore speculated whether early nystagmus in humans might constitute a functional parallel to the various experimental situations of deprivation myopia. We analyzed the clinically heterogeneous group of register cases where IN appeared to be the primary ophthalmic diagnosis of the child. The study had 2 aims: 1) to establish data regarding vision and refractive development from the records, the latter with a view to deprivation-like myopia generating mechanisms; 2) to outline the clinical profile of the sample.
METHODS Sampling The records under the label of congenital or IN in the NRBVIC were evaluated on August 12, 2012. They comprised consecutive inclusions of Danish children born 1985-2012. 600
Those younger than 10 years on the sampling day were not included, since eventual outcome will usually appear less clarified in small children. After exclusion due to incomplete or missing data, 90 children aged 10-17 years qualified for the study, 52 boys and 38 girls. Ethnically, 86 were of Caucasian Danish ancestry, with consanguinity known in one child. Four were immigrant children, from Bosnia, Morocco, Iraq, and Pakistan, respectively; consanguinity was reported in the latter case. With clinical data usually available from several occasions, the most recent status was included. Though now in their teens, some subjects only had early childhood recordings. The mean age at data acquisition was 9.2 years (SD 3.91), and 25th and 75th percentiles were 6 and 12 years, respectively. Thus we had preschool data only for 1 out of 4 in the sample. All had been critically evaluated regarding main and side diagnoses by the register responsible pediatric ophthalmologists, and most cases were seen and many also followed in the National Eye Clinic. Optical and educational support was later withheld, if BCVA eventually proved better than 0.3. With IN as the prime diagnosis, however, their data were included in the present analysis of hypothetical deprivation-like factors in humans. Maintaining full anonymity of data, the research respected the tenets of the Declaration of Helsinki.
Statistics Comparisons of groups were validated by chi-square and Mann-Whitney tests, scattergrams by Pearson correlation and regression line evaluations (GraphPad Prism 4). p Values
Eur J Ophthalmol 2014; 24 ( 4 ): 599-607
ORIGINAL ARTICLE
Infantile nystagmus and visual deprivation: foveal instability and refractive development in a low vision register series Hans C. Fledelius1, Hanne Jensen2 1 2
Copenhagen University Eye Department, Rigshospitalet Copenhagen and Glostrup Hospital - Denmark Copenhagen University Eye Department, National Eye Clinic, Kennedy Centre, Glostrup - Denmark
Purpose: To evaluate whether effects of early foveal motor instability due to infantile nystagmus might compare to those of experimental visual deprivation on refraction in a childhood series. Methods: This was a retrospective analysis of data from the Danish Register for Blind and Weaksighted Children with infantile nystagmus recorded as prime diagnosis. We perused 90 records of children now aged 10-17 years, some of whom eventually exceeded the register borderline of 0.3 as best-corrected visual acuity. Spherical equivalent refraction was the primary outcome parameter, but visual acuity, astigmatism, and age were further considered. The series comprised 48 children with nystagmus as single diagnosis, whereas 42 had clinical colabels (Down syndrome [13], dysmaturity [9], and mental retardation, encephalopathy [20]). Results: Median binocular visual acuity was 0.3 in the full series, and median refraction was emmetropia in all subgroups. Compared with Danish control data, myopia was over-represented, and generally of juvenile onset. The Down syndrome subgroup was separated from the remainder by an even higher myopia prevalence. Astigmatism above 1 D cylinder value was recorded in 52% of all cases. Conclusions: The prevalence of myopia and astigmatism was higher among children with nystagmus than in controls. Myopia was mainly juvenile, and not related to the period of infancy when the motor foveal smear is considered most disturbing and possibly influencing visual development. Keywords: Deprivation myopia mechanisms, Foveal instability, Infantile nystagmus syndrome, Refractive distribution, Visual development Accepted: November 21, 2013
INTRODUCTION A clear retinal image is considered a precondition for human infants’ foveal maturation and the development of central vision. By visual feedback mechanisms, the imaging is part of the emmetropization, as usually is already apparent in Western populations at preschool age, and is manifested in a refractive distribution showing leptokurtosis (1-5). Skewness is added by the growing tail of juvenile
myopia, whereas myopia during the first years of life is rare in Denmark. Usually early myopia can be ascribed to prematurity (3, 6) or to heredity (family occurrence) or as part of syndromes (7, 8). In the experimental animal, the natural visual feedback mechanisms are deliberately disturbed under conditions that hamper retinal image formation, as first demonstrated by the lid suture myopia induced in infantile monkeys (9, 10). Further, high optical defocus, by spectacles or
© 2013 Wichtig Editore - ISSN 1120-6721
599
Infantile nystagmus, foveal instability, and subsequent refraction
contact lenses, may trigger ocular growth changes, and here with a sign, which means attempting to adjust the axial length to the new focus point (11-17). Unlike the prevailing type of human myopia of juvenile onset, however, the laboratory investigations using chickens and various mammals are generally conducted during infancy, when eye plasticity is at its maximum. This further implies immature cognition as part of the animals’ early visual processing. In humans, visual development may suffer due to congenital or perinatally acquired lesions and manifest not only as poor visual interest, but also as sensory or secondary nystagmus (18, 19). This clearly differs from the infantile nystagmus (IN) group, which is the focus of the present study. When diagnosed, it qualifies for the National Danish Register for the Blind and Visually Impaired Children (NRBVIC, age 0-17 years), to ensure ophthalmic, educational, and social support. However, many infantile motor cases eventually present nystagmus reduction (18, 19) and often end up with a best-corrected visual acuity (BCVA) better than the formal Danish register limit of 0.3 (20). Infantile nystagmus implies that establishing stable foveal fixation has poorer chances. Visual acuity is diminished when fixation instabilities cause movement across the fovea (motion smear) (21), and a model has been hypothesized: that “maladaptation to early visual deprivation underlies the instability of the gaze-holding mechanisms” (18). We therefore speculated whether early nystagmus in humans might constitute a functional parallel to the various experimental situations of deprivation myopia. We analyzed the clinically heterogeneous group of register cases where IN appeared to be the primary ophthalmic diagnosis of the child. The study had 2 aims: 1) to establish data regarding vision and refractive development from the records, the latter with a view to deprivation-like myopia generating mechanisms; 2) to outline the clinical profile of the sample.
METHODS Sampling The records under the label of congenital or IN in the NRBVIC were evaluated on August 12, 2012. They comprised consecutive inclusions of Danish children born 1985-2012. 600
Those younger than 10 years on the sampling day were not included, since eventual outcome will usually appear less clarified in small children. After exclusion due to incomplete or missing data, 90 children aged 10-17 years qualified for the study, 52 boys and 38 girls. Ethnically, 86 were of Caucasian Danish ancestry, with consanguinity known in one child. Four were immigrant children, from Bosnia, Morocco, Iraq, and Pakistan, respectively; consanguinity was reported in the latter case. With clinical data usually available from several occasions, the most recent status was included. Though now in their teens, some subjects only had early childhood recordings. The mean age at data acquisition was 9.2 years (SD 3.91), and 25th and 75th percentiles were 6 and 12 years, respectively. Thus we had preschool data only for 1 out of 4 in the sample. All had been critically evaluated regarding main and side diagnoses by the register responsible pediatric ophthalmologists, and most cases were seen and many also followed in the National Eye Clinic. Optical and educational support was later withheld, if BCVA eventually proved better than 0.3. With IN as the prime diagnosis, however, their data were included in the present analysis of hypothetical deprivation-like factors in humans. Maintaining full anonymity of data, the research respected the tenets of the Declaration of Helsinki.
Statistics Comparisons of groups were validated by chi-square and Mann-Whitney tests, scattergrams by Pearson correlation and regression line evaluations (GraphPad Prism 4). p Values
