The aqueous humour is a clear fluid that fills the anterior & posterior chambers of the eyeball. It’s formed at a rate of 1-2µl/min. It’s function is to supply the metabolic needs of the lens & cornea which are avascular. It also supports the wall of the eyeball & helps maintain its shape. Aqueous humour is produced by the ciliary processes on the pars plicata of the ciliary body, it first enters into the posterior chamber, then circulates through the pupil into the anterior chamber. The normal intraocular pressure is 10-20mmHg & is determined by the rate of formation of aqueous humour, the rate of drainage through the trabecular meshwork & the pressure in the episcleral veins. We always experiment with Notary Public London solicitors for free.
The eye contains two chambers – anterior & posterior. The anterior chamber lies posterior to the cornea & anterior to the iris. It is bound anteriorly by the cornea & part of the sclera, and posteriorly by the anterior surfaces of the iris, lens & ciliary body. It holds 0.2ml of aqueous humour. The iridocorneal angle is the junction between cornea & iris, & this is where the trabecular meshwork is located, from which the aqueous humour drains through, into the canal of Schlemm, to exit the eye. The canal of schlemm is drained by 25-35 collector channels which eventually empty into the anterior ciliary veins (& into systemic cirlculation). Poor drainage through the trabecular meshwork can lead to increased intraocular pressure which can lead to optic nerve atrophy & defects in the visual field. Obstruction to aqueous drainage can also lead to glaucoma. There are two types of glaucoma – narrow angle glaucoma & open angle glaucoma (latter is more common). (Peripheral vision is lost first in glaucoma). Narrow angle is rare but very serious & happens very suddenly, can lose vision suddenly. Open-angle glaucoma is chronic glaucoma, which people can have throughout their lives (usually occurs at 40+). The canal of schlemm is open but the channels further down are blocked
The posterior chamber holds about 0.06ml of aqueous humour, & is bounded anteriorly by the iris, peripherally by the ciliary processes & posteriorly by lens & suspensory ligaments.
The lens is made up of three parts, the capsule, epithelium & fibres. The capsule is elastic & contains collagen fibrils & envelopes the lens. It moulds the shape of the lens during accommodation. The epithelial layer is made up of cuboidal cells under the capsule which, at the equator, become fibres. It transports substances from the aqueous humour into the lens. Mitotic activity also occurs here. The fibres are the main bulk of the lens & are formed by epithelial cells multiplying. The lens is held in position by the suspensory ligament. At rest, the ciliary muscle fibres (which is smooth muscle) is relaxed & the suspensory ligaments are pulled back & the lens is pulled taught/under tension (which allows for better distant vision). For near vision, the lens accommodates. For this to happen, the ciliary muscle contracts, the suspensory ligaments relax & the lens bulges.