Xiao-Ying Yao

Retinal Adhesiveness In Surgically Enucleated Human Eyes

Purpose: Retinal adhesion in rabbits and monkeys has been shown to involve the interphotoreceptor matrix and depend on environmental factors, such as temperature, pH, and calcium concentration. This study was designed to see whether these same factors modulate retinal adhesiveness in humans. Methods: Four surgically enucleated human eyes were studied. Strips of eyecup were placed in experimental baths shortly after enucleation to evaluate environmental conditions. Retinal adhesive strength was quantified by the amount of retinal pigment epithelial pigment adherent to retina peeled from strips of eyecup. Cone and rod sheaths of the interphotoreceptor matrix were studied by microscopic examination of samples stained with the lectins peanut and wheat germ agglutinin. Results: Retinal adhesiveness fell to 0 approximately 40 minutes after enucleation. Adhesive strength was maintained by cold temperature and was weakened by low pH or low calcium in the bath. Cone and rod matrix sheaths became stretched (indicating a bond) as outer segments and retinal pigment epithelium were peeled apart. Conclusion: Retinal adhesion in humans appears to involve similar mechanisms as in rabbits and monkeys.

Cytochalasin D reversibly weakens retinal adhesiveness

This study asks whether retinal adhesiveness is affected by cytochalasin D, a drug that is known to alter the apical morphology of the retinal pigment epithelium (RPE). Cytochalasin D was injected intravitreally in Dutch rabbits and retinal adhesiveness measured 0.5 to 72 h later by two methods: in vitro peeling of the retina from retinal pigment epithelium to observe the amount of adherent pigment, and in vivo measurement of the pressure needed to achieve retinal separation. Electroretinograms were recorded, and RPE apical morphology was examined by scanning electron microscopy. The injection of 60 microM cytochalasin D caused in vitro retinal adhesiveness to fall within 3 h to 10% of normal although the electroretinogram (a, b, and c-waves) remained normal. Smaller doses of cytochalasin D had a lesser effect. The RPE apical surface at 3 h showed large bullet-like microvilli, swollen cone sheaths, and an absence of filamentous microvilli. The severity of these changes was dose-related. At 72 h after cytochalasin D, retinal adhesiveness had largely recovered, and RPE apical morphology appeared normal again. Thus, cytochalasin D weakens retinal adhesiveness acutely but reversibly, and both the initial effect and recovery correlate with changes in RPE microvillar morphology. This suggests that actin microfilaments may be involved in mechanisms of retinal adhesion.