A twin study was undertaken to reevaluate a widely held monogenic hypothesis relating to the ocular hypertensive steroid response. In the present (part II) analysis, intrapair differences for steroid response among the monozygotic (MZ) and dizygotic (DZ) samples were compared. Responsiveness was treated as both a qualitative and quantitative trait. For the parameter change in pressure, significant differences were never observed between the MZ and DZ samples and heritability index was consistently low. For final pressure, differences between the twin classes showed a mixed pattern of significance; the heritability index was low- to mid-range. Such observations do not support a predominant role of inheritance. It seems evident that a theory of simple monogenic determination can be questioned on the basis of these new findings.
Schwartz JT, Reuling FH, Feinleib M, Garrison RJ, Collie DJ. Twin Study on Ocular Pressure Following Topically Applied DexamethasoneII. Inheritance of Variation in Pressure Response. Arch Ophthalmol. 1973;90(4):281-286. doi:10.1001/archopht.1973.01000050283006