Resemblance between tonometer readings on relatives and spouses

The resemblance between tonometer readings on relatives and spouses was studied in a material derived from a population survey and consisting of 1042 unique individuals forming 365 nuclear families and 1333 pairs divided into groups with different sex-composition and type of connection. Persons in whom glaucoma was suspected were excluded. The general level of resemblance in the present study was similar to that in previous studies. Differences between groups with different sex-composition conformed to a pattern expected from environmental effects. The resemblance between husbands and their wives was highly significant and of the same order of magnitude as that in relatives sharing a common genetic background. We concluded that a common environment contributes materially to the resemblance between tometer readings on relatives. The possibility of a cumulative environmental effect was suggested by an increase in resemblance with age.