Central retinal artery occlusion.: Retinal survival time
Introduction
Central retinal artery occlusion (CRAO) produces sudden, catastrophic visual loss. It is a true ophthalmic emergency, in that every minute that elapses increases the chances of irreversible retinal damage. In 1980, based on experimental studies in rhesus monkeys, Hayreh and co-workers (Hayreh et al., 1980, Hayreh and Weingeist, 1980a, Hayreh and Weingeist, 1980b) reported that retinal damage following CRAO is reversible if CRAO lasts for 97–98 min, but the retina suffers irreversible damage after ischemia of 105 min. This contradicted the conventional thinking based on findings in the brain, that irreversible ischemic damage in the retina occurred much sooner. Critics felt that the retina survived as long as it did in that study because the monkeys were young, normal and healthy, and that typical CRAO patients, who are generally old, atherosclerotic and hypertensive, would probably have a much shorter retinal ischemic tolerance time. To investigate whether that was the case, we embarked upon the development of a cohort of rhesus monkeys which would mimic typical CRAO patients — by means of experimental atherosclerosis and chronic arterial hypertension, lasting for many years. By the time we undertook the present experimental study on CRAO, the monkeys were indeed old, atherosclerotic and hypertensive.
Section snippets
Material and methods
The study comprised 38 rhesus monkeys (Macaca mulatta) with a mean age of 19·5±2·8 years (mean±s.d.; median: 20 years; range, 13–24 years; human equivalent about 50–90 years). The study design complied with the National Institute of Health's as well as the University of Iowa's Institutional Guidelines for the Care and Use of Laboratory Animals. In these monkeys atherosclerosis was produced experimentally by feeding the animals a special atherogenic diet continuously for many years (Hayreh et
Follow-up duration from CRA unclamping onwards
All animals, except for one (with CRAO for 105 min that died on the day of CRAO), were followed serially by doing various studies mentioned above. The median (25–75th percentile) follow-up duration was: (i) 5·93 (2·00–8·86) weeks for 97 min CRAO, (ii) 8·00 (4·86–11·86) weeks for 105–120 min CRAO, (iii) 9·28 (7·36–10·78) weeks for 150–165 min CRAO, and (iv) 10·72 (7·00–15·86) weeks for ≥180 min CRAO. The duration of follow-up was not significantly different among the four CRAO duration groups (p
Discussion
The primary objective of the present study was to find out from an experimental study in rhesus monkeys how long it takes for CRAO to produce irreversible retinal damage, because of the paramount importance of that fact in the management of patients with CRAO. There is much confusion in the literature about this length of time, based on anecdotal clinical case reports and experimental studies (Hayreh and Weingeist, 1980b).
Acknowledgments
We are grateful to Mrs Donna McAllister and Ms Betty Follmer for their expert assistance with the experimental study, and to Ms Georgiane Perret and Ms Trish Duffel for help with bibliography. Supported in part by grants EY-1576 from the National Institutes of Health, Bethesda, MD, USA, and in part by unrestricted grant from Research to Prevent Blindness, Inc., New York, USA.
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Dr S.S. Hayreh is a Research to Prevent Blindness Senior Scientific Investigator.