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Abstract #6678 Published in IGR 4-1
Description of ciliary body anatomy and identification of sites for transscleral cyclophotocoagulation in the equine eye
Miller TL; Willis AM; Wilkie DA; Hoshaw Woodard S; Stanley JRVeterinary Ophthalmology 2001; 4: 183-190
OBJECTIVE: To determine the most appropriate anatomical location for diode laser probe placement to accurately photoablate the equine ciliary body using a contact, transscleral approach. DESIGN: Original research. PROCEDURES: Forty-two freshly enucleated adult equine eyes were evaluated. The horizontal, medial vertical, central vertical, and lateral vertical lengths of the cornea were measured from limbus to limbus. Needles were inserted perpendicular to the sclera at specific distances posterior to the external limbus at the one, two, four, five, six, seven, eight, ten, 11 and 12 o'clock positions. The per cent frequency that needles penetrated internal anatomical regions (lens, lens zonules, pars plicata, anterior, middle, and posterior pars plana, ora ciliaris retinae, or retina), when inserted at 2, 4, 6, and 8 mm posterior to the limbus, were calculated for all eyes combined, for right versus left, for males versus females, and for three age groups. The internal distance from the limbus to the anterior pars plana, and from the anterior pars plana to the ora ciliaris retinae were also measured in six of the horses (12 eyes). Mean distances and standard deviations were computed for all parameters. RESULTS: Average corneal sizes and standard deviations were: 30.24 mm ± 1.53 (horizontal); 24.69 mm ± 1.52 (central vertical); 22.79 mm ± 1.49 (medial vertical); and 19.79 mm ± 1.55 (lateral vertical). Internal distances of the pars plicatas ranged from 5.33 mm ± 0.49 to 10.67 mm ± 1.15. Internal distances of the pars planas ranged from 0.33 mm ± 0.49 to 3.17 mm ± 0.39. High probabilities of penetrating the pars plicata correspond to positions 4 mm posterior to the external limbus dorsotemporal ten, 11 o'clock (OD), and one, two o'clock (OS), dorsonasal one o'clock (OD) and 11 o'clock (OS), and ventrotemporal five to seven o'clock (OU). Low probabilities of penetrating the pars plicata correspond to positions ventronasal four o'clock (OD), eight o'clock (OS) and dorsonasal two o'clock (OD), ten o'clock (OS) at 4 and 6 mm posterior to the external limbus as well as ventrotemporal four o'clock (OS), eight o'clock (OD) at 6 mm posterior to the external limbus. CONCLUSIONS: Transscleral cyclophotocoagulation may be a viable alternative to medical therapy for control of intraocular pressure in horses with glaucoma. Overall, the most accurate anatomical position on the sclera for cyclophotocoagulation of the equine eye is 4-6 mm posterior to the limbus, avoiding the nasal quadrants. Accurate transscleral cyclophotocoagulation should optimize the therapeutic outcome and minimize potential side-effects such as retinal detachment and cataract formation.
Dr. T.L. Miller, Department of Veterinary Clinical Sciences, The Ohio State University, Columbus, OH, USA. Tammy_Miller@ncsu.edu
Classification:
5 Experimental glaucoma; animal models
12.10 Cyclodestruction (Part of: 12 Surgical treatment)