Osmotic pressure of the interstitial fluid obtained from neonatal chick eyes and its variation under light and dark adaptation.

In experiments by Yoneyama et al. (1985) a hypertonic perfusing solution was used to record the c-wave from the isolated chick retina. We investigated whether the chick retina was surrounded by such hypertonic liquids. The following results were found: the osmolarity of the subchoroidal humor was markedly higher than that of fluids from other areas of the eye; the relative difference in osmolarity between both sides of the retina was 110-170 mOsmol in the light-adapted condition, whereas it was about 270 mOsmol in the dark-adapted condition; and in the dark-adapted state the volume of the subchoroidal humor decreased about 40% but increased in osmolarity about 30-40%, whereas osmolarity of the subvitreous humor decreased about 15-20 mOsmol. Results suggest the presence of an inward-directed pump mechanism for water-soluble components in the retina in addition to the proposed outward-directed pump mechanism of the pigment epithelium. The inward-directed pump may be more active in the dark-adapted state.