Composition of the Inner Nuclear Layer in Human Retina

PURPOSE. The purpose of this study was to measure the composition of the inner nuclear layer (INL) in the central and peripheral human retina as foundation data for interpreting INL function and dysfunction. METHODS. Six postmortem human donor retinas (male and female, aged 31-56 years) were sectioned along the temporal horizontal meridian. Sections were processed with immunofluorescent markers and imaged using high-resolution, multichannel fluorescence microscopy. The density of horizontal, bipolar, amacrine, and Muller cells was quantified between 1 and 12 mm eccentricity with appropriate adjustments for postreceptoral spatial displacements near the fovea. RESULTS. Cone bipolar cells dominate the INL a with density near 50,000 cells/mm(2) at 1 mm eccentricity and integrated total similar to 10 million cells up to 10 mm eccentricity. Outside central retina the spatial density of all cell populations falls but the neuronal makeup of the INL remains relatively constant: a decrease in the proportion of cone bipolar cells (from 52% at 1 mm to 37% at 10 mm) is balanced by an increasing proportion of rod bipolar cells (from 9% to 15%). The proportion of Muller cells near the fovea (17%) is lower than in the peripheral retina (27%). CONCLUSIONS. Despite large changes in the absolute density of INL cell populations across the retina, their proportions remain relatively constant. These data may have relevance for interpreting diagnostic signals such as the electroretinogram and optical coherence tomogram.