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D.M. Eifler, F.M. Montiani–Ferreria, F.F. Cardoso, C.A. Johnson, S.M. Petersen–Jones; Comparison of Corneal Thickness Between Dogs With Retinal Dystrophy Due to a Null Mutation in Cyclic GMP Phosphodiesterase Alpha (PDE6A) and Phenotypically Normal Heterozygous Carriers . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2180.
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Purpose: To compare the corneal thickness of dogs with a retinal dystrophy model of retinitis pigmentosa due to a null mutation in PDE6A with closely related phenotypically normal dogs heterozygous for the mutation. Methods: The central corneal thickness was measured by ultrasonic pachymetry in a colony of Cardigan Welsh Corgi dogs with a mutation in PDE6A that results in rod dysfunction and retinal degeneration. Measurements were performed in 28 dogs from 2 – 40 weeks of age (11 homozygous for the PDE6A mutation and 17 phenotypically normal dogs heterozygous for the mutation). In some dogs measurements were repeated at different ages. The average corneal thickness between the right and left eyes was not significantly different, therefore these measurements were averaged to obtain a mean corneal thickness for each animal at each age tested. Statistical analyses were performed on corneal thickness by repeated measures ANOVA as a preliminary analysis that determined the significance of disease status, eye, gender, and time effects. Segmented nonlinear least square regression was used to capture the two phases observed in the corneal development plotted against age. The first phase, corresponding to a decrease in thickness after neyelid opening, was modeled by a quadratic polynomial function on age, and the second phase corresponding to the corneal growth was modeled by a logistic growth curve. Results: Homozygous PDE6A mutant dogs had a mean corneal thickness of 0.565 +/– 0.010 mm, which was significantly greater than that of heterozygous carriers (0.533 +/– 0.009 mm). There was no significant difference between males and females and no interaction between gender and disease status. The corneal thickness of the maturing eye of homozygous mutant dogs fitted a different prediction equation model than that of the carriers, the difference appearing to be greater in the younger dogs. Conclusions: This study showed that dogs with a retinal dystrophy due to a null mutation in the PDE6A gene had a significantly greater corneal thickness than closely related heterozygous carriers of the mutation. This difference could result from effects on ocular growth due to the abnormal retinal function of mutant dogs or might be due to the effects of a gene linked to the PDE6A locus.
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