Which structure separates photoreceptor cells from the outer nuclear layer?

• A. External limiting membrane
• B. Internal limiting membrane
• C. Bruch's membrane
• D. Inner plexiform layer

Answer: (A)

Understanding how the retina is organized helps here: photoreceptor cell bodies sit in the outer nuclear layer, while their inner segments extend toward the inner retina. The external limiting membrane is the boundary between these two parts, formed by adherens junctions between photoreceptor inner segments and Müller glial processes. This junction creates a barrier that separates the photoreceptor portions from the outer nuclear layer, keeping the lamination intact. The other structures listed do not form this boundary: the internal limiting membrane lines the vitreous-retina interface, Bruch’s membrane lies beneath the retina between the RPE and choroid, and the inner plexiform layer is a synaptic layer further inside the retina.