Analysis of Anterior Ocular Segment Using Ultrasound Biomicroscopy in Normal Pigeons and Topical Anti-Glaucoma Drug Treated Dogs

Abstract

The purpose of the present study was to analyze anterior ocular segments of pigeons and dogs using ultrasound biomicroscopy (UBM). <br/> In Chapter I, the feasibility of UBM was evaluated in pigeons and normal biometric dimensions of anterior ocular segment of pigeons were established. UBM was performed in 10 pigeons (Columba livia var. domestica). On each obtained image, the ciliary cleft (CC) length, CC width, CC area, and iridocorneal angle (ICA) were measured. The UBM scanning procedure was well tolerated in all pigeons. Mean ± standard deviation values of CC length, CC width, CC area, and ICA were 1.55 ± 0.17 mm, 0.36 ± 0.05 mm, 0.39 ± 0.04 mm2, and 15.17 ± 1.06°, respectively.<br/> In Chapter II, to demonstrate the mechanism of action of topical latanoprost in dogs, the effects of topical latanoprost on the anterior segment and ciliary body were evaluated. UBM scans were performed before and 2 hours after topical latanoprost instillation. From the next day on, latanoprost was topically applied twice daily for 7 days. After 1 week of instillation, the UBM scans were repeated. The ciliary body thicknesses (CBT) as well as the anterior segment parameters, including the ICA, CC entry width, CC length, and mid-CC width were measured. The topical latanoprost decreased the ICA and CC entry width and increased the mid-CC width without any significant alterations in CC length. There were time-dependent alterations in CBT: a reduction in CBT after 2 hours of instillation and rebound thickening after 1 week of instillation. This might be a reflection of the mechanism of the uveoscleral outflow enhancement induced by the topical latanoprost.<br/> In Chapter III, to assess the role of miosis in reducing intraocular pressure (IOP), different classes of topical miotics were selected including latanoprost which induces ciliary muscle relaxation and prostaglandin-mediated miosis and pilocarpine which induces ciliary muscle contraction and cholinergic-mediated miosis. The CC morphology was compared between prostaglandin-mediated miosis and cholinergic-mediated miosis using UBM. Despite the similar degree of miosis, the posterior width of CC (CCW) was varied according to the contractility status of ciliary muscle and cholinergic mediated miosis caused significantly wider CCW than prostaglandin-mediated miosis. When both miotics were used in combination, the order of administration affected ciliary muscle contractility such that the first drug determined the ciliary muscle contractility and associated cleft morphology. <br/> In conclusion, UBM was demonstrated to be clinically feasible in evaluating anterior ocular segments in small avian species and dogs. Using UBM, uveoscleral outflow enhancement by topical latanoprost was indirectly demonstrated in dogs. In addition, prostaglandin-mediated miosis by topical latanoprost and cholinergic-mediated miosis by topical pilocarpine resulted in different CC configurations in dogs. Since aqueous outflow resistance could be influenced by the width of CC, the findings of the present study should be considered in medical managements of canine glaucoma. <br/>