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Parapapillary chorioretinal atrophy in chronic high-pressure experimental glaucoma in rhesus monkeys
S S Hayreh1, J B Jonas, M B Zimmerman
1Department of Ophthalmology and Visual Sciences, College of Medicine, University of Iowa, Iowa City, USA.
Purpose:
To evaluate in rhesus monkeys parapapillary chorioretinal atrophy in chronic high-pressure glaucoma and the effects of age, atherosclerosis, and chronic arterial hypertension in a prospective, planned study.
Methods:
Seventy-six eyes from 38 monkeys were studied. First, experimental atherosclerosis and chronic arterial hypertension were produced in 24 animals. Then experimental high-pressure glaucoma was produced by laser photocoagulation of the anterior chamber angle in 38 eyes from the 38 animals. Intraocular pressure measurements and fundus photography were serially performed. The photographs were morphometrically analyzed.
Results:
In the glaucomatous eyes, area and frequency of beta zone of parapapillary atrophy were significantly (P < 0.0001) larger at the end of the study than at baseline. Area of beta zone was significantly (P < 0.0001) and negatively correlated with neuroretinal rim area. In an intraindividual intereye comparison, beta zone was significantly (P < 0.0001) larger in the glaucomatous than in the contralateral nonglaucomatous eyes. Increase of beta zone and loss of neuroretinal rim were independent of presence and size of beta zone at start of the study. Beta zone was significantly (P = 0.036) greater in older than in younger monkeys; however, atherosclerosis-arterial hypertension had no significant influence on frequency and size of beta zone. Area and frequency of alpha zone showed no significant change between baseline values and those at the end of study.
Conclusions:
In experimental chronic high-pressure glaucoma in monkeys, beta zone of parapapillary atrophy was positively correlated with glaucomatous optic nerve damage. This confirms previous biomorphometric and histomorphometric studies on patients with glaucoma. In chronic experimental high-pressure glaucoma, neuroretinal rim loss and an increase of beta zone may be independent of preexisting parapapillary atrophy. Increase of beta zone may be independent of concomitant atherosclerosis-arterial hypertension.