What does the conjunctiva do?

The conjunctiva is indeed a thin mucous membrane that lines both the inner surfaces of the eyelids and the outer surface of the eye itself, covering the sclera. This membrane serves several important functions, including protecting the eye from dust, debris, and microorganisms while also providing lubrication to keep the eye moist. Its structure and placement help facilitate the movement of the eye within the socket, allowing for a wide range of motion. This functional aspect is critical for visual acuity and comfort.

Other functions mentioned in the other options relate to specific components of the eye. For instance, protecting the lens pertains to structures like the iris and cornea, while nerve impulse transmission is a function of the optic nerve and cells in the retina. Additionally, adjusting pupil size involves muscles in the iris. Each of these elements plays a unique role, but the specific definition of the conjunctiva accurately reflects its unique anatomical and functional significance.