Ocular Anatomy, Physiology, and Pathology
Domain focus
Anatomy and pathology questions link structure to function: which layer produces aqueous, which pathway carries visual signals, and which lesion explains a pupil finding or visual field defect.
Anterior segment
The cornea has five layers: epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. The endothelium pumps fluid out; endothelial loss causes corneal edema. The tear film is lipid (meibomian glands), aqueous (lacrimal glands), and mucin (goblet cells). Aqueous is secreted by the ciliary epithelium, flows from the posterior chamber through the pupil into the anterior chamber, then through the trabecular meshwork into Schlemm's canal and episcleral veins. Outflow obstruction raises IOP. The lens has cortex and nucleus; the uvea comprises iris, ciliary body, and choroid.
Posterior segment and pathways
The retina has photoreceptors, bipolar cells, and ganglion cells; the fovea has the highest cone density and is avascular, relying on the choroid. Optic nerve axons travel to the chiasm, where nasal fibers cross, then to the optic tract, lateral geniculate nucleus, optic radiations, and occipital cortex. The pupil afferent runs with the optic nerve; the efferent runs with CN III and the ciliary ganglion. Extraocular muscles: CN III supplies medial rectus, inferior rectus, inferior oblique, and superior rectus; CN IV supplies superior oblique; CN VI supplies lateral rectus.
Pathology
Diabetic retinopathy produces microaneurysms, dot-blot hemorrhages, exudates, and neovascularization. AMD shows drusen, geographic atrophy, or choroidal neovascular membranes. Glaucoma is an optic neuropathy with retinal nerve fiber layer loss and characteristic field defects. Keratoconus causes corneal thinning and ectasia. Retinal detachment presents with flashes, floaters, and a curtain; uveitis shows cells and flare.
Worked example
A right relative afferent pupillary defect means light in the right eye drives a weaker response. When the light swings to the left eye, both pupils constrict because the left afferent pathway is intact. The lesion is in the right optic nerve or severe right retina, not in the iris or CN III.
Traps
Do not confuse aqueous production (ciliary epithelium) with drainage (trabecular meshwork); do not attribute an RAPD to cataract; do not call drusen hemorrhages; do not forget that the fovea is avascular.