Ocular Anatomy, Physiology, and Pathology
Organization of the Eye
The globe is divided into anterior (cornea, anterior chamber, iris, lens, posterior chamber) and posterior (vitreous, retina, choroid, sclera, optic nerve) segments. The cornea has five layers - epithelium, Bowman layer, stroma, Descemet membrane, and endothelium - memorized as EBSDE. The endothelium is a non-regenerating pump that keeps the stroma deturgesced; endothelial loss causes corneal edema and haze. Aqueous is produced by the ciliary epithelium of the pars plicata and flows posterior chamber → pupil → anterior chamber → trabecular meshwork → Schlemm canal → episcleral veins. Obstruction at the meshwork raises intraocular pressure.
The uveal tract comprises iris, ciliary body, and choroid. The retina's photoreceptors lie outermost, so light passes through several layers before transduction; ganglion cell axons form the optic nerve, whose head sits nasal to the fovea. Rods dominate the periphery and dim-light vision; cones cluster at the foveola for acuity and color.
Muscles and Nerves
The six extraocular muscles are supplied by CN III except the superior oblique (CN IV) and lateral rectus (CN VI). All arise from the annulus of Zinn except the inferior oblique.
Traps: questions love the non-regenerating endothelium, the posterior-to-anterior direction of aqueous flow, and the fact that the fovea is temporal to the disc. Do not confuse the cornea's avascular stroma with the vascularized limbus.
Rule of thumb: if a question mentions corneal clarity after injury, think endothelial pump; if it mentions a defect that stains with fluorescein, think epithelium.
Worked example: a patient with a scratch shows a bright green area under cobalt blue light after fluorescein - an epithelial defect, since fluorescein is taken up where epithelium is absent, not by intact endothelium.