Naturally occurring vitreous chamber-based myopia in the Labrador retriever

PURPOSE. To investigate whether myopia is present in a breed of domestic do g, the Labrador retriever, and how the ocular components are related to ref ractive error in this breed. METHODS. Cycloplegic refractive error was measured in 75 Labrador retriever s by retinoscopy. Corneal and crystalline lens radii of curvature were meas ured in the right eyes of 57 of these dogs using a video-based keratophakom eter, with axial ocular dimensions measured using A-scan ultra-sonography. RESULTS. Of the 75 dogs tested, 11 (14.7%) were myopic by at least -0.50 D in one eye, and 6 (8.0%) were myopic in both eyes (full range of refractive errors, +3.50 D to -5.00 D). Of the 57 dogs with ocular component measurem ents, seven (12.3%) were myopic by at least -0.50 D in the right eye. There was a significant negative correlation between refractive error and vitreo us chamber depth (Spearman r = -0.42; P < 0.001). Myopic eyes had an elonga ted vitreous chamber depth (10.87 +/- 0.34 mm for myopic dogs, 10.02 +/- 0. 40 mm for nonmyopic dogs; P < 0.0001, Kruskal-Wallis test). There was also a significant quadratic association between lens thickness and vitreous cha mber depth (P < 0.005, R-2 = 0.11), indicating that thinner lenses occurred at both shorter and longer vitreous chamber depths. CONCLUSIONS. Myopia in the Labrador retriever is analogous to human myopia in that it is caused by an elongated vitreous chamber. Thinner crystalline lenses found at longer vitreous chamber depths may be analogous to lens thi nning documented in human ocular development. The Labrador retriever warran ts investigation as a potential model of myopia that is naturally occurring rather than experimentally induced.