The eyeball is a roughly spherical organ about 24 mm across that sits in the front of the orbit, cushioned by fat and moved by six extraocular muscles. Its wall has three layers: a tough outer fibrous coat (sclera and cornea), a middle vascular coat (choroid, ciliary body and iris) and an inner neural coat (retina). Inside, the lens divides the eye into a fluid-filled front segment and a larger gel-filled back segment.
| Location | Anterior part of the bony orbit, protected in front by the eyelids |
|---|---|
| Parts | |
| Nerve Supply | Optic nerve (CN II, vision); Short and long ciliary nerves (sensory from the nasociliary nerve, plus autonomic fibres) |
| Blood Supply | Ophthalmic artery; Central retinal artery; Short and long posterior ciliary arteries; Anterior ciliary arteries |
Focuses light onto the retina and converts it into nerve signals that travel to the brain for vision. Its shape and clear media keep images sharp, and its pupil and lens adjust to light level and distance.
Most of the eye's focusing power comes from the cornea, while the lens fine-tunes focus for near work, so refractive errors reflect a mismatch between eye length and optical power. Intraocular pressure is normally about 10-21 mmHg and is kept stable by the balance between aqueous production and drainage. A sudden painful red eye with blurred vision, a fixed mid-dilated pupil or vision loss needs same-day ophthalmic assessment.
A full-thickness wound of the cornea or sclera from a sharp object or severe blunt trauma. It is an emergency: the eye should be shielded without pressure and repaired surgically.
Short-sightedness, usually because the eyeball is too long for its optical power, so distant images focus in front of the retina. High myopia raises the risk of retinal detachment and glaucoma.
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