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

Abstract

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.

Distinctive Mechanisms and Patterns of Exudative Versus Tractional Intraretinal Cystoid Spaces as Seen With Multimodal Imaging

“…Fluid normally flows in a vitreous to choroid direction due to osmotic gradient. 8,9,[15][16][17] In physiological conditions the retinal interstitial space is relatively dry, as the volume of interstitial fluid is strictly controlled by the retinal capillary plexus and the retinal glial cells, mainly the Müller cells, which can regulate fluid absorption via aquaporin channels. 2 This delicate equilibrium can be altered by RPE and vascular dysfunction, the action of mechanical forces, or any combination thereof.…”

“…The "hydration" theory, already proposed by Tornambe, is consistent with the early observation by Sato et al, who postulated the existence of an inward-oriented passive fluid flow generated by a Na+dependent inward current of viable photoreceptor outer segments. 17,29 In chronic macular hole with flat edges such inward fluid flow may be defective, as suggested by the described lower prevalence of macular edema in chronic versus "acute" lesions. 30 A recent report showing resolution of full thickness macular hole edema with laser photocoagulation seems to support this assumption.…”

“…According to Sato et al, an inward osmotic gradient may be present between the rod-cone layer and the internal limiting membrane favoring the flow of intersitial fluid through the retina. 17 Such an inward-directed gradient is physiologically compensated by the outward-directed pump of the retinal pigment RPE. When the neuroretina is detached, at the edge of the hole, the inward flow of fluid overcomes the outward-directed RPE pump, which is ineffective in removing all the fluid from the interstitium.…”

Gamma-aminobutyric acid- and picrotoxin-induced changes in c-wave and light peak of retinal potentials in the chick

“…The GABA released in the inner plexiform layer may be transported passively to the outer plexiform layer by the outward-directed osmotic gradient across the retina. (Sato et al, 1985b;Yoneyama et al, 1986).…”