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G.J. McLellan, D.M. Betts, K. Sigle, S. Grozdanic; Congenital Glaucoma in the Siamese Cat – A Novel Spontaneous Animal Model for Glaucoma Research . Invest. Ophthalmol. Vis. Sci. 2005;46(13):134.
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Purpose:We have identified a strain of purebred Siamese cats with congenital, open–angle glaucoma. The purpose of this study was to characterize the clinical features of this disease and to evaluate its potential suitability as a spontaneously occurring animal model for human glaucoma. Methods: A prospective study was initiated to evaluate cats closely related to the proband for clinical evidence of primary glaucoma. All cats included in the study were subjected to thorough ocular examination that included slit–lamp biomicroscopy, gonioscopy, applanation tonometry, indirect and direct ophthalmoscopy, and ultrasound biometry.Results: The 14 cats available for examination comprised the proband, its’ parents, and 11 of the 13 surviving full siblings from 4 separate litters. Six male and 8 female cats were examined. Age at first examination ranged from 3 weeks to 3 years. All cats were found to have bilateral mild to moderate buphthalmos and moderate elevation in intraocular pressure (IOP). Mean IOPs at initial presentation were 31.6 mmHg and 29.7 mmHg in affected cats, in the right and left eyes respectively. Normal reference range for IOP in cats is 19.7 +/– 5.6mmHg. Prominent, elongated ciliary processes were observed in all 10 cats older than 5 months of age at initial examination, but were not seen in kittens examined at 3 weeks of age. Haab’s striae were noted in 7 of 20 eyes and lens subluxation was evident in 10 of 20 eyes. Although a tendency to spherophakia was noted in affected eyes, lens size was not significantly different from that of age–matched, normal cats on ultrasound biometry. All eyes appeared visual at the time of initial examination and optic disc cupping was evident in only 2 eyes. Mild mydriasis and increase in latency of the pupillary light reflex were noted. Gonioscopy revealed open or slightly narrowed iridocorneal angles, with mild pectinate ligament dysplasia and sparse prominent iris processes (24/24 eyes). Conclusions: Clinical features identified in affected Siamese cats showed remarkable similarities to those seen in human primary congenital glaucoma. The early onset of clinical disease, combined with relatively modest elevation in intraocular pressure and slow progression of vision loss indicate that this inherited feline disease shows considerable promise as a spontaneously occurring "large eye" model of human glaucoma. A breeding colony has now been established in order to facilitate further clinical, pathological and genetic characterization of the disease.
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