Ocular Blood Flow in Early Glaucoma Patients Before and After Treatment With Dorzolamide

Overview

Impaired ocular blood flow is an important risk factor in the pathogenesis of primary open angle glaucoma (POAG). A few studies suggest that topical dorzolamide 2% may increase optic nerve perfusion. The objectives of this study are to learn the effects of dorzolamide on the retinal and optic nerve blood flow of glaucoma patients. The present study is a prospective, randomized, double-masked, crossover design study of newly diagnosed or already treated patients with early glaucoma. The investigators will check ocular blood flow parameters using the Canon Laser Blood Flowmeter (CLBF), used to evaluate retinal arteriole blood flow, and the Heidelberg retinal flowmeter (HRF), which measures blood flow through capillary beds in the retina and optic nerve head. Any demonstrated improvements to retinal and optic nerve blood flow with dorzolamide, will mean that the drug may protect against ischaemic nerve and retinal damage. Any documented improvement in flow could lead to a major change in the management of glaucoma patients as well as other retinal ischemic diseases such as diabetic retinopathy and central retinal vein occlusion.

High intraocular pressure (IOP) is the major risk factor for glaucoma. Lowering intraocular pressure is still the only accepted form of treatment for glaucoma. Over the past decade, epidemiological and experimental evidence suggested that impaired ocular blood flow is an important risk factor with an important role in the pathogenesis of primary open angle glaucoma (POAG). Several studies suggest that ischemia-promoting vascular factors may contribute to glaucomatous damage including vasospasm, impaired ocular perfusion pressure and general vascular disorders such as low blood pressure, especially dips in blood pressure at night. Different techniques are employed to assess vascular dysfunction in the eye. As the methodology of ocular blood flow assessment is complex and differs in various aspects (e.g. target tissue and physiological parameters), comparative studies are required in order to enhance the interpretation of these measurements. Our laboratory has state of the art equipment to assess ocular blood flow. One study done by us suggested that one drop of Dorzolamide 2% does not improve retinal blood flow in normal eyes. In the present study we plan to extend this study to 2 weeks of treatment in patients with POAG. Dorzolamide hydrochloride 2% is a topical carbonic anhydrase inhibitor which reduces intraocular pressure (IOP) by decreasing the production of aqueous humour. Pharmacological studies on volunteers and glaucoma patients, using Color Doppler Imaging (measuring the retrobulbar blood flow) and Scanning laser Ophthalmoscopy (measuring arteriovenous passage time), indicate that topically applied Dorzolamide may increase perfusion of the optic nerve and peripapillary retina.