AN41.1-3 | Eyeball — Glossary

Opaque white fibrous coat forming the posterior 5/6 of the eyeball; provides structural support and attachment for extraocular muscles

Transparent avascular anterior 1/6 of the eyeball providing approximately 2/3 of total refractive power (~43 dioptres)

Junction between the cornea and sclera; contains corneal stem cells for epithelial renewal and the trabecular meshwork for aqueous drainage

Posterior 2/3 of the uvea; highly vascular pigmented layer nourishing the outer retinal layers via the choriocapillaris

Annular structure containing the ciliary muscle (accommodation) and ciliary processes (aqueous humour production); connected to the lens by zonular fibres

Pigmented muscular diaphragm with the pupil at centre; contains sphincter pupillae (parasympathetic, miosis) and dilator pupillae (sympathetic, mydriasis)

Inner neural coat with photoreceptors (rods for dim light, cones for colour); outer RPE attached to choroid; inner neural layer detaches in retinal detachment

Region lateral to the optic disc with highest cone density; responsible for central detailed vision; fovea centralis at its centre has highest visual acuity

Central depression of the macula with pure cones and no overlying cell layers; highest visual acuity point of the retina

Site where optic nerve fibres exit the retina; no photoreceptors (physiological blind spot); supported by the lamina cribrosa of the sclera

Sieve-like area of the sclera where optic nerve fibres exit; the weakest point of the sclera; site of glaucomatous cupping from raised IOP

Clear fluid produced by ciliary processes filling the anterior and posterior chambers; maintains IOP and nourishes the avascular cornea and lens

Circular venous sinus at the limbus draining aqueous humour from the trabecular meshwork into the episcleral veins

Raised intraocular pressure causing progressive optic nerve damage; open-angle (commonest, painless) or closed-angle (acute emergency)

Opacity of the crystalline lens causing progressive painless visual loss; accounts for 66% of blindness in India; treated by phacoemulsification

End artery from the ophthalmic artery supplying the inner retinal layers; occlusion causes sudden painless monocular blindness with cherry-red spot

Fundoscopic sign in CRAO where the thin fovea allows the choroidal red to show through against the pale oedematous surrounding infarcted retina

Process of changing lens shape for near vision via ciliary muscle contraction relaxing zonular fibres allowing the elastic lens to become more convex

Reflex constriction of the pupil in response to light; afferent CN II, efferent CN III; bilateral response via pretectal nucleus connections

Relative afferent pupillary defect (Marcus Gunn pupil); detected by the swinging flashlight test; indicates optic nerve or severe retinal disease

Ultrasonic fragmentation and aspiration of the cataractous lens followed by intraocular lens implant; the standard cataract surgery technique