P. M. Leuenberger

Experimental Retinal Branch Vein Occlusion in Miniature Pigs Induces Local Tissue Hypoxia and Vasoproliferative Microangiopathy

In miniature pigs, retinal veins were experimentally occluded using argon laser coagulation. Microvascular modifications leading to retinal hemorrhages and retinal edema were observed some hours after the occlusion. These lesions resolved progressively within 3 weeks after the occlusion, but in most cases ischemic retinal territories persisted. Preretinal partial pressure of oxygen (PO2) measurements, using double barrelled O2-sensitive microelectrodes, showed that all the ischemic areas were indeed hypoxic. In half of the experiments, preretinal and intravitreal new vessels grew on the ischemic territories. Tissue hypoxia appears to be a key step in triggering neovascularization. However, the critical level of hypoxia was not determined.

Scatter Photocoagulation Restores Tissue Hypoxia in Experimental Vasoproliferative Microangiopathy in Miniature Pigs

Experimental retinal branch vein occlusion using argon laser photocoagulation in miniature pigs induced the development of ischemic retinal territories associated with preretinal neovascularization. Preretinal partial pressure of oxygen (PO2) measurements on the ischemic territories, using O2-sensitive microelectrodes, established that the ischemic retinal areas were hypoxic. Scatter photocoagulation of these ischemic hypoxic territories restores the local PO2 to the normal values within 2 weeks. Hence, the reported inhibitory effect of photocoagulation on the development of retinal neovascularization could be due to a reversal effect on tissue hypoxia.

Chalcosis: A Study of Natural History

Ten patients harboring a small, intra-vitreal, copper foreign body in one eye for 4 months to 29 years have been studied clinically and electrophysiologically. Nine of the ten affected eyes had a visual acuity of 20/60 or better. Some asymmetry existed in the electrophysiologic responses of seven affected eyes as compared to the controls, but all of these responses were within the normal range. The electroretinogram was reduced in one eye but was consistent with vitreous opacification. Vitreous opacification and copper deposition in the macula were potentially serious sequelae observed in four eyes. Small, intraocular copper foreign bodies can be tolerated for long periods of time without retinal toxicity, but vitreous changes of maculopathy may necessitate intervention.

Senile Retinal Deficiencies in Astrocytes and Blood Vessels

Vessels in the mammalian retina are surrounded by astrocytes and Muller cells forming the glial limitans. The spatial correlation between astrocytes and blood vessel in the inner retina has been largely recognized and the functional implication of astrocytes in vessel permeability has been suggested.