Heritability of the depth of the opening of the ciliary cleft in Samoyeds.

Ocular examination, including gonioscopy and ultrasonographic biometry (biological measurement), was performed in healthy, purebred Samoyeds. When the dogs were subclassified according to the degree of kinship with cases of primary angle-closure glaucoma, it was found that the opening of the ciliary cleft was wider in dogs less related to dogs with primary angle-closure glaucoma than in more closely related dogs. Furthermore, multivariate analysis of the material indicated that parentage of a dog has a substantial effect on the intraocular distances studied in this investigation (relative depth of the opening of the ciliary cleft, relative corneal thickness, relative anterior chamber depth, relative lens thickness, and relative length of the vitreous body). Finally, heritability of the relative depth of the opening of the ciliary cleft was estimated at 56% and that of the common environmental factor at 19%. The results are indicative of a hereditary component in primary angle-closure glaucoma in the Samoyed breed.

Age-related changes in ocular distances in normal eyes of Samoyeds.

Ocular biometry, using A-scan ultrasonography and ultrasonographic pachymetry, was performed in 52 Samoyeds, 2 months to 13 years old, without intraocular or systemic diseases. Furthermore, the relative depth of the opening of the ciliary cleft was estimated from goniophotographs. The values were analyzed, and statistical models of changes in ocular distances with increasing age were identified. It was found that the changes in corneal thickness, axial anterior chamber depth, lens thickness, relative lens position, length of the vitreous body, and axial length could best be described by 1 of the 2 nonlinear models f(x) = alpha + beta/x + gamma x + epsilon and f(x) = alpha + beta/x + gamma log x + epsilon. The course began with a period of rapid increase, after which the ocular distance either increased at a progressively slower rate toward infinity (corneal and lens thickness) or to a finite limit (relative lens position and axial length), or ceased to grow and finally started to decrease toward minus infinity (axial anterior chamber depth and length of the vitreous body). However, suitable model for determining relative depth of the opening of the ciliary cleft could not be established. Results indicated that age-related changes, mainly in lens thickness, cause a shallow anterior chamber, and it was suggested that this may be of importance for development of a relative pupillary block and, thus, primary angle-closure glaucoma, at least in preconditioned eyes of Samoyeds.