Which term correctly names the boundary between the retina and the optic nerve at the nerve head?

• A. Intermediary tissue of Kuhnt
• B. Internal limiting membrane
• C. Lamina cribrosa
• D. Pia mater

Answer: (B)

The inner limiting membrane is the boundary between the retina and the optic nerve at the nerve head. It is the innermost retinal boundary, formed by the basement membrane of Müller cells, and it marks where retinal tissue ends and the nerve fibers begin to form the optic nerve behind the disc. The lamina cribrosa lies deeper in the scleral canal as a sieve through which the axons pass, so it isn’t the immediate border at the nerve head. The other terms describe structures not defining this border: the intermediary tissue of Kuhnt is a peripheral-retina feature, and pia mater lines the optic nerve sheath rather than the retina–nerve boundary.