AC TA 0 P H T H A L M 0 L O G I CA

69 (1991) 788-790

Astigmatism and school myopia Olavi Parssinen Department of Ophthalmology,Central Hospital of Central Finland,Jyvaskyla, Finland

Abstract. Changes in astigmatism were followed for

a

3-year period among 238 myopic children as part of a clinical trial of myopia treatment. Children with mild myopia and no previous myopic spectacle correction and astigmatism 5 2D were included in the study. The prevalence of astigmatism of at least 0.25D was 55% at the beginning of the follow-up at a mean age of 10.9 years, increasing to 76% during the 3-year period. At the same time the mean astigmatism increased from -0.26D to -0.45D. Most of the astigmatism was against the rule; with the rule astigmatism represented 18%of the astigmatism at the beginning and 24%at the end of the study. There was a weak correlation between the spherical equivalent and astigmatism at the beginning of the follow-up (r = 0.122, n = 240, P= 0.029) but not at the end of the follow-up. Myopic progression controlled for the spherical equivalent, was not related to degree of astigmatism at the beginning of the study. Key words: myopia - school myopia - astigmatism - myopic progression.

The prevalence and amount of astigmatism has been shown to decrease during the first years of life (Abrahamsson et al. 1988; Hirsh 1964), with the rate of change greatest during the first 2 years. The axis of astigmatism has also been shown to change in childhood. In the study by Dobson et al. (1984) astigmatism against the rule among children younger than 3.5 years was 2.5 times as common as astigmatism with the rule. In children older than 5.5 years the same study showed the prevalence of astigmatism with the rule to be 3 times as much as against the rule. A connection between myopia and astigmatism has also been demonstrated (Fulton et al. 1982; Alward et al. 1985). Fulton et al. (1982)supposed that astigmatism could be one rea786

son for myopic development. On the other hand a connection between astigmatism and hyperopia has also been observed (PPssinen 1986). The purpose of this study was to investigate the changes in astigmatism in school myopia and the relations between astigmatism and the progression of myopia as a part of a clinical trial for the treatment of myopia (Parssinen et al. 1989).

Materialsand Methods Myopic children from the 3rd and 5th grades of primary school were selected for a follow-up study of myopia treatment (Hemminki & Parssinen 1987). Children who did not wear spectacles for myopia and whose spherical equivalent was 2-3.OD or ~ - 0 . 2 5 D in the worse eye were considered for inclusion in the study. Cases of astigmatism over 2D or of ocular pathology or general disease were excluded from the study. 119 boys and 121girls participated in the study. The mean age of the children at the commencement of the study was 10.9 years. The children were examined annually over 3 successive years. The complete 3-year follow-up proved possible for 238 children. The selection of the material and exclusions have been described in more detail in an earlier paper (Hemminki & Parssinen 1987). The children were randomly allocated to one of three different treatment groups: 1)fully corrected spectacles to be used continuously, 2) to be used for distant vision only, 3) bifocals with + 1.75D near add. Refraction was measured about 45-60 min after

administering one drop of Oftan-Syklo"(l% cyclopentolate-hydrochloride)twice within about 5 min. The smallest correction giving the best subjective vision at 5 m distance, controlled using the duochrome test so that red was better or equal to green, was regarded as the refraction value. The finalastigmatism was tested with f0.25 D cross-cylinder. The minus cylinder axis was regarded as the axis of astigmatism. All the refractions were done by the author. The astigmatism was regarded as with the rule astigmatism if the axis of the minus cylinder formed an angle 30" or less with the horizontal plane and against the rule if it made the same angle with the vertical plane. For this report the values obtained for the right eye were used, but when presenting the distribution of the axes of astigmatism the values for both right and left eyes were used. The correlations between the means of refraction and its changes and astigmatism were calculated by means of Pearson's product moment correlation coefficients. The partial correlation technique for controlling the effect of the spherical equivalent was used when calculating the correlations between astigmatism at the beginning' of the follow-up and myopic progression. Analysis of variance was used when comparing the spherical equivalent and astigmatism between the three myopia treatment groups. The two-tailed t-test was used to compare myopic progression in with the Table 1. The distribution of refracive astigmatism of the right eye at the beginning and at the end of the study. I

I

Astigmatism (D)

N = 238 (Yo)

2.50 2.25 2.00 1.75 1.50 1.25 1.oo 0.75 0.50 0.25 0.00

0 ( 0.0) 0 ( 0.0) 0 ( 0.0) 0 ( 0.0) 0 ( 0.0) 5 ( 2.1) 4 ( 1.7) 18 ( 7.6) 47 (19.7) 57 (23.9) 107 (45.0)

50*

N = 238 (%) 1 ( 0.4) 0 ( 0.0)

2 ( 0.8) 1 ( 0.4) 4 ( 1.7) 8 ( 3.4) 18 ( 7.6) 27 (11.3) 54 (22.7) 67 (28.2) 56 (23.5)

rule and against the rule cases of astigmatism, as well as astigmatism between the right and left eye and between boys and girls. The difference between the final and the initial spherical equivalents were regarded as myopic progression. There were no statistically significant differences between the three treatment groups in either eye in the spherical equivalent at the beginning of the follow-up (Hemminki & Pkssinen 1987).The myopic progression of the left eye was somewhat faster in the distant use group than in the continuous use group (two-tailed t-test: P< 0.01).The final myopia of the left eye was also somewhat faster in the distant use group than in the continuous use group (two-tailed t-test: P

Astigmatism and school myopia.

Changes in astigmatism were followed for a 3-year period among 238 myopic children as part of a clinical trial of myopia treatment. Children with mild...
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