Hyperosmolarity response of ocular standing potential as a clinical test for retinal pigment epithelium activity chorioretinal dystrophies

Pigmented paravenous retinochoroidal atrophy (Review)

Pigmented paravenous retinochoroidal atrophy (PPRCA) is an uncommon disease characterized by perivenous aggregations of pigment clumps associated with peripapillary and radial zones of retinochoroidal atrophy that are distributed along the retinal veins. Patients are usually asymptomatic and the disease process is non-progressive or slow and subtly progressive. It is commonly bilateral and symmetric. The cause of the condition may be unknown or idiopathic, although a dysgenetic, degenerative, hereditary etiology or even an inflammatory cause has been hypothesized. A non-inflammatory cause is referred to as primary, while inflammation-associated PPRCA is referred to as secondary or pseudo PPRCA. The present study reviewed and summarized the features of PPRCA.

Corneal D.C. recordings of slow ocular potential changes such as the ERG c-wave and the light peak in clinical work. Equipment and examples of results

A set-up for D.C. recordings of slow ocular potentials such as the c-wave of the electroretinogram (ERG) as well as the fast oscillation (FO), the light peak (LP) and the dark trough (DT) in both clinical and experimental work is described. It includes matched calomel half-cells connected by saline-agar bridges to a corneal contact lens on the eye and a reference chamber on the forehead, a low-drift differential-input D.C. amplifier, an A/D converter, a computer, a thermoprinter, a flexible disc memory, a plotter, and a device for light stimulation controlled by the computer. Examples of the usefulness of the set-up in clinical work are shown in the form of D.C. c-wave ERGs of normal subjects as well as of patients with vitelliform macular degeneration, choriocapillaris atrophy, and retinitis pigmentosa. The direct corneal recording of the FO and LP is demonstrated as well. The different origins of the standing potential (SP) of the eye, the ERG c-wave, the FO and the LP are reviewed briefly.

Hyperosmolarity-induced hyperpolarization of the membrane potential of the retinal pigment epithelium

The hyperosmolarity-induced changes of the apical (Vap) and basal (Vba) membrane potentials of the retinal pigment epithelium (RPE) were studied in an in-vitro RPE-choroid preparation of the frog. Both Vap and Vba were simultaneously hyperpolarized by hyperosmolarity at either the apical or basal side of the RPE. Hyperosmolarity at the apical side hyperpolarized Vap greater than Vba, and increased the trans-epithelial potential (TEP) across the RPE. Hyperosmolarity at the basal side hyperpolarized Vba, simultaneously hyperpolarized Vap by a smaller amount, and reduced the TEP. The hyperosmolarity response (a decrease of the ocular standing potential induced by an intravenous hypertonicity) is due mainly to a hyperpolarization of Vba.