Basic Ocular Anatomy and Physiology
Core concepts
Master the layered structure of the eye: the fibrous tunic (cornea and sclera), vascular tunic (iris, ciliary body, choroid), and neural tunic (retina). Know the flow of aqueous humor from the ciliary body through the posterior chamber, pupil, and anterior chamber to the trabecular meshwork and canal of Schlemm. Understand the corneal layers (epithelium, Bowman's, stroma, Descemet's, endothelium) and that the endothelium does not regenerate, so its pump function is critical for corneal clarity. Learn retinal anatomy-photoreceptors, the avascular fovea, the optic disc as the blind spot-and the physiology of phototransduction and the visual cycle involving rhodopsin and vitamin A.
Traps
Questions frequently test the direction of aqueous flow (posterior to anterior chamber) and the site of resistance (trabecular meshwork). Another trap is the blood supply of the fovea, which is supplied by the choroid rather than retinal vessels. Watch for confusion between rods (dim light, peripheral) and cones (color, central, high acuity). Also remember that the optic nerve head lacks photoreceptors, creating a physiologic scotoma.
Worked example / rule of thumb
Rule of thumb: "Endothelium pumps, epithelium regenerates." If a stem describes corneal edema after surgery, think endothelial pump failure. If it describes a rapid surface healing after a scratch, think epithelial regeneration.
Study focus
Review the ciliary body's dual roles (aqueous production and accommodation via the zonules) and the iris sphincter/dilator muscles and their innervation, since these recur in pharmacology questions.