Ocular Anatomy, Physiology and Optics
Core anatomy to master
Know the layers of the cornea (epithelium, Bowman's, stroma, Descemet's, endothelium), the refractive index of each ocular medium (air 1.00, cornea ~1.376, aqueous ~1.336, crystalline lens ~1.42, vitreous ~1.336), and the reduced eye model (power ~60 D, nodal point ~7 mm behind cornea, principal planes). Understand the blood–aqueous barrier, the ciliary body's dual role (secretion and accommodation), and the drainage pathway (trabecular meshwork → Schlemm's canal → collector channels → episcleral veins). Know retinal layer order and the foveal avascular zone, plus the physiology of phototransduction and the Purkinje tree.
Traps
Questions often swap corneal endothelium and epithelium when asking which layer pumps fluid, or confuse the two sources of aqueous production (active secretion vs ultrafiltration). Watch for the anterior chamber depth (~3.0–3.5 mm) versus axial length (~24 mm), and for the optic nerve head's lack of photoreceptors. Total power of the eye is ~60 D; cornea contributes ~43 D.
Worked rule of thumb
Use the thin-lens formula P = 1/f. If a reduced eye has P = 60 D, then f = 1/60 m = 16.7 mm. If an object is at 25 cm, vergence = 1/0.25 = +4 D; the eye must add +4 D of accommodation to focus at infinity-equivalent.