Refraction of young myopes and their parents--a reanalysis

Familial clustering and myopia progression in Singapore school children

BACKGROUND

Familial factors may be related to the progression of myopia in children. A cohort study was conducted to determine the relationship between familial factors and myopia progression in children.

METHODS

From a larger clinical trial (n = 311), 153 Singapore children aged 6--12 years were recruited to participate in a cohort study of the risk factors for myopia progression. An in-person interview was conducted whereby information on the history of myopia in first-degree relatives was obtained. Other information collected included housing type, parental education and income. Cycloplegic refractive error as measured by subjective refraction and autorefraction were ascertained every six months. The average length of follow-up was 28 months.

RESULTS

The adjusted mean rate of progression of myopia was -0.60 (95% confidence interval -0.66, -0.55) diopters per year. The average rate of progression of myopia for children with a parental history of myopia was -0.63 (95% confidence interval -0.69, -0.56) diopters per year compared to -0.42 (95% confidence interval -0.57, -0.27) diopters per year for children whose parents were not myopic. The different measures of family history of myopia were related to rate of change in refractive error and refractive error in the final visit. There was no association between close work and myopia progression.

CONCLUSIONS

A positive family history is related to the progression of myopia and final refractive error in Singapore children, thus supporting evidence that hereditary factors may play an important role in myopia progression.

Role of heredity in the genesis of myopia

Previous studies suggest that myopia in parents may influence the genesis of myopia in their offspring. In this study, we surveyed 2888 children of Chinese descent in China and Hong Kong to determine the relationship between the refractive state of parents and their children. The age range of the children was 7-17 years. Refraction was measured using a Canon R-22 objective infrared autorefractor and a survey on family history of ametropia was conducted using a questionnaire. We found that children with myopic parents are more likely to be myopic.

Degree of myopia in relation to intelligence and educational level

Intelligence test scores and educational levels were compared for 5943 myopic and 9891 non-myopic 18-year-old men being drafted for military service in Denmark. The former were grouped by degree of myopia, in the range -0.25 diopters (D) to -7.75 D, according to the power of correcting lenses required. Myopes of all degrees had significantly higher test scores and educational levels than non-myopes. However, the relation of these two variables to degree of myopia was not linear; for both variables there were no significant differences among myopia groups in the range -2.0 to -7.75 D. Whereas factors associated with intelligence and education seem to be important in triggering the onset of myopia, they seem to be much less important in determining the degree to which myopia progresses.

Selection against genetic defects in semen donors

Artificial insemination donor selection requires predicting which men are likely to beget the healthiest offspring. Methods are developed for calculating the "offspring excess recurrence risk", delta R, for an anomaly in the offspring of an afflicted father. Mainly from published family survey and population data delta R is computed for 38 disorders. From a small survey a value for the with-treatment "affliction burden", Bt, is assigned to each anomaly. For each disorder the "offspring excess burden expectation" is delta RBt. Defects such as cataract, hereditary Parkinson disease, psoriasis, seropositive rheumatoid arthritis, and schizophrenia have such a high delta RBt that they are individually sufficient cause for rejecting a donor candidate. A candidate may be rejected because of a combination of lesser defects with sigma delta RBt exceeding an acceptable limit. A limit should also be placed on Bt, because the affliction burden for Tay-Sachs disease or cystic fibrosis is intolerable, however infrequent. Most of the important hereditary defects are late onset, and for the older donor the opportunity to select more directly against late-onset disorders offsets the added risk of newly-arising gene mutations. The most careful donor selection cannot completely eliminate the risk of a child inheriting some disorder, but selection can reduce the average total burden by as much as 17%.