Function of eye = conversion of light energy to electrical energy and carried to brain by CN2 optic nerve. Eye is 3 layered wall which holds fluid and lens.
The eye has 3 chambers = A. aqueous chamber (aqueous humor fluid), split into anterior chamber (btw iris and cornea) and posterior (btw lens and iris). B. vitreous chamber – posterior to lens, filled with vitreous humor. C. Outer fibrous layer includes sclera and cornea.
1. The cornea – transparent area of eye, where light enters eye. Collagen fibers are very regularly arranged within bundles to give direct transmission of light and no reflection. Light passed to retina unaltered. Water balance essential and strictly monitored by epithelium and if damaged becomes opaque.
2. Sclera – posterior portion of eyeball made of dense white fibrous CT. collagen fibers are irregularly arranged into bundles, scatters light so appears white. Function = protect inner layers, point of insertion of inter ocular muscles. Sclera and cornea meet at limbus (junction).
Cornea – Does not contain blood vessels. Nutrients for its cells permeate the substantia propria (bulk thickness of cornea) from vessels in the limbus or are carried to its surface in the lacrimal fluid and aqueous humor (from ciliary body).
Lacrimal apparatus brings about production of tears and protection of cornea.
2 glands, 1. Lacrimal (dorsolateral wall of orbit). 2. 3rd eyelid gland (at base). Drains via puncta lacrimalia (adjacent to caruncle) and feed into lacrimal sac. Nasolacrimal duct drains into nasal cavity.
Tear film nourishes outer cornea. Middle layer is aqueous layer and 2/3 of this is from lacrimal gland.
Aqueous humor: clear and watery. maintains shape of eyeball – ocular pressure and distention of anterior chamber. drainage = production to maintain constant intraocular pressure.
The aqueous humor is secreted into the posterior chamber by the cillary body, (non pigmented epithelium). It flows through the narrow cleft between front of the lens and the back of the iris to escape through the pupil into the anterior chamber and then drain out of the eye via the trabecular meshwork (iridocorneal = drainage angle or filtration angle) = goes to venous sinuses in sclera.
(From here, it drains into Schlemm’s canal by one of two ways: directly, via aqueous vein to the episcleral vein, or indirectly, via collector channels to the episcleral vein by intrascleral plexus and eventually into the veins of the orbit.)
The aquous humor is continually produced by cillary processes and rate of the production must equal rate of aqueous humour drainage.
Dorso corneal angle: where the base of the iris attaches to the peripheral cornea and sclera; the site of aqueous drainage from the anterior chamber. Iridocorneal meshwork.