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JH Salmon, KA Roberge, BC Gilger; Ocular Parameters Related To Trans-Scleral Drug Transport In The Canine and Equine Eye . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2309.
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Purpose:To measure the thickness and surface area of canine and equine sclera as well as aqueous and vitreous humor volumes to determine whether trans-scleral diffusion of drugs is feasible for the treatment of posterior segment ocular disease in these models. Methods:Normal canine and equine eyes were enucleated immediately after euthanasia and fixed in formalin for 24 hours. Surface area was measured by fluid displacement, and corneal and optic nerve diameters were measured. Globes were hemi-sected, anterior to posterior, and aqueous and vitreous humor was collected and volume measured. Scleral thickness measurements were made directly, starting at the limbus and extending posteriorly to the optic nerve, using a digital caliper, and indirectly by measuring tracings from projected photographs of the images as previously described (Olsen TW, Aaberg SY, Geroski DH et al, Am J Ophthalmol 1998;125:237-241) Results:Mean scleral surface area was 12.9 ± 2.2 cm2 and 57.2 ± 5.6 cm2 in the dog and horse, respectively. Mean aqueous humor volume in the dog was 0.8 ± 0.2 ml and 3.0 ± 1.3 ml in the horse. Mean vitreous volume was 1.7 ± 0.9 ml and 26.2 ± 4.9 ml in the dog and horse, respectively. No significant difference was found between measurement techniques of scleral thickness. The mean canine scleral thickness was 0.68 ± 0.03 mm at the limbus, 0.24 ± 0.03 mm at the equator, and 0.45 ± 0.08 mm near the optic nerve. The mean equine scleral thickness was 0.80 ± 0.08 mm at the limbus, 0.31 ± 0.06 mm at the equator, and 1.05 ± 0.29 mm near the optic nerve. Conclusion:Although aqueous and vitreous humor volumes and scleral surface area in the equine eye are much greater than that found in the human eye, scleral thickness at the equator is similar. In the dog, the aqueous humor volume is greater and the vitreal humor volume is less than the human eye, but scleral thickness is similar. Therefore, the canine and equine eye may be valuable in vitro or in vivo models of transcleral drug transport.
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