Nearwork and Familial Resemblances in Ocular Refraction: A Population Study in Newfoundland

Abstract

There is evidence that nearwork influences population variation in ocular refraction, and evidence of familial resemblances for this trait. The potential for nearwork, as an aspect of common familial environment, to inflate correlations for ocular refraction among nuclear family members was therefore investigated in a sample of 957 persons aged five years and over (approximately 80% of the population above that age) in three communities on the west coast of Newfoundland.

Refraction was evaluated using standard optometric methods, nearwork measured as h/day as reported by the subject, education measured as last completed grade in years.

It was reasoned that the education and nearwork measures combined, rather than that of nearwork alone, best indicated lifetime nearwork levels. The effect of nearwork on refraction resemblances was therefore evaluated by calculating correlations or regressions among relatives before and after removing the effects of nearwork and education on refraction by linear regression. Reductions in sib-sib correlations and offspring-parent regressions were achieved, but patterns of resemblances among relatives after adjustment suggest nearwork effects on refraction resemblances were not completely removed.

Appropriate evaluation of the nearwork-refraction relationship, and its effects on familial resemblances, will require population-based longitudinal data. It is reasonable to suspect that the extent to which effects of common familial environment are confounded with genetically determined variation in ocular refraction differs from population to population, and over time within populations.