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Cornea plana congenita is believed to occur in a mild autosomal dominant (CNA1) and a more severe autosomal recessive (CNA2) form. We recently assigned a CNA2 locus to a region on chromosome 12 by linkage analysis. In this study we compared these traits clinically and genetically. Using the horizontal corneal refraction value in diopters (D) as a parameter, a control population (n = 473) had a mean value of 43 center dot 4 (SD 1 center dot 5 D) for men and 43 center dot 7 (SD 1 center dot 6 D) for women, whereas in 51 subjects affected with CNA2 the mean value was 29 center dot 9 (SD 5 center dot 2 D) and in five subjects affected with CNA1 the mean value was 37 center dot 8 (SD 1 center dot 6 D). By linkage analysis in two CNA1 families the CNA2 locus could be conclusively excluded. These data suggest that at least two forms of hereditary cornea plana exist which are both clinically and genetically distinct.

As a part of a longitudinal birth cohort study, refraction was measured at the age of 20 years in 236 persons known to have had myopia at the age of 14 years and 266 controls (2982 refractions). The earlier the myopia had started, the more myopic the eyes were at the age of 20 years. The greatest mean refraction values, -4.94 D for males and -6.62 D for females were found when the change to myopia had started before the age of 10. The mean progression of myopia (the mean progression curves were achieved by calculating the mean refraction values at different ages) seems to continue at least to the age of 20. A female child with a myopic mother is more likely to develop myopia than a female child with a non-myopic mother and the same relation holds good between a male child and his father. The myopic refractive error seems to be greater in the children than in their parents.