What forms the inner limiting membrane in regions of the retina outside the optic disc?

• A. Footplates of Müller cells
• B. Astrocyte endfeet
• C. Ganglion cell layer
• D. RPE

Answer: (A)

The inner limiting membrane is the boundary between the retina and the vitreous on the inner surface of the retina. It is formed by the footplates of Müller glial cells, which extend to the vitreous face and create a thin basement membrane that the vitreous adheres to. Outside the optic disc, these Müller cell endfeet are the primary source of the ILM. Near the optic disc, astrocyte endfeet contribute to the membrane, but across the rest of the retina the Müller cell-derived endfeet dominate. The other structures listed don’t form the ILM: the ganglion cell layer is a retinal layer, RPE relates to the outer retina, and while astrocyte endfeet participate at the optic nerve head, they are not the main formers of the ILM throughout the retina outside the disc.