Ophthalmic Basic Sciences
Core concepts
The basic sciences underpin every clinical question. For anatomy, know the layers of the cornea and the course of the optic nerve and chiasm, the blood supply of the retina (central retinal artery and the choroidal circulation), and the orbital apex relations. Physiology centres on aqueous dynamics (production by the ciliary epithelium, outflow through trabecular meshwork and uveoscleral routes), tear film layers, and photoreceptor transduction. Optics requires fluency with vergence, the reduced eye, spectacle and contact lens power relationships, and the principles of retinoscopy and keratometry. Pathology demands recognition of inflammation, ischaemia, neoplasia, and wound healing patterns. Pharmacology tests receptor targets (alpha and beta agonists, prostaglandin analogues, antimetabolites) and pharmacokinetics of topical drops. Genetics covers inheritance patterns and common mutations (e.g. RB1, rhodopsin).
Traps
Questions often exploit near-miss distinctions: corneal endothelium does not regenerate; the fovea is avascular; the chiasm fibres from nasal retina cross. In optics, confuse vertex distance changes with lens power. In pharmacology, remember preservative toxicity versus true allergy.
Worked example
A reduced eye has power 60 D. A +2 D spectacle lens sits 12 mm from the eye. The effective power at the eye is greater than 2 D because a plus lens moved closer becomes more effective; use F_effective = F/(1 - dF) with d in metres. Here 2/(1 - 0.012×2) ≈ 2.05 D. Rule of thumb: plus lenses gain power as they approach the eye; minus lenses lose it.