| Summary: | 碩士 === 國立中興大學 === 獸醫學系暨研究所 === 104 === Ametropia, including myopia (near-sightedness) and hyperopia (far-sightedness), due to refractive error is the most common ocular disorders among humans. Now, it had been found occurring naturally not only in human but also in various animal species. The prevalence of ametropia in dogs is breed dependent. Similarly, domestic shorthair (DSH) cats were significantly more likely to be myopic than were domestic mediumhair or domestic longhair cats. Some studies had been done to investigate the probable cause of the ametropia in some breeds of dogs. In the present study, axial length(AL), corneal radius of curvature(CR), and the refractive error of both eyes were determined by use of A-scan ultrasonography and auto kerato-refractometer in maltese dogs and DSH cats. The refractive power of the crystalline lens of each eye was calculated by using the Bennett’s formula1, and A and B-constants were calculated based on the schematic eye models of dog and cat proposed by O’Keefe and Coile. The average spherical equivalent refractive errors(SE) for maltese dogs, juvenile DSH cats and adult DSH cats were +3.07 ± 0.35 D (hyperopia), -1.24 ± 1.12 D (myopia) and -0.15 ± 1.45 D (Emmetropia). The juvenile cats were more myopic than adult cats. Mean corneal curvature of maltese dogs, juvenile cats and adult cats were 43.51 ± 2.52 D, 38.72 ± 1.25 D and 37.83 ± 1.12 D, respectively. There was a high prevalence of against-the-rule astigmatism in both species. In the analysis of refractive errors, there was a significant negative correlation between SE and vitreous chamber depth in maltese dogs and DSH cats. Otherwise, there was also a significant positive correlation between SE and either corneal power or AL/CR ratio in maltese dogs while there was a significant negative correlation between SE and AL/CR in DSH cats. In conclusion, the cause of the myopia in DSH cats appeared to be from vitreous chamber elongation while the cause of the hyperopia in maltese dogs might be associated with shorter vitreous chamber. Maltese dogs and DSH cats may be promising models for the study of ametropia in humans.
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