: large anterior one, between iris and cornea and a
small posterior region between the iris and the lens.• Both the parts of aqueous chamber are filled with a
clear, watery fluid, the aqueous humour, secreted by
the ciliary processes of the ciliary body.
• It contains most of the diffusible substances of the plasma
and is rich in vitamin c, glucose, amino acids and respiratory
gases.
• The aqueous humour nourishes the lens and cornea,
and is continuously secreted. It is drained into the
venous system via the canal of Schlemm.
(ii) Vitreous chamber
• The vitreous chamber (the largest chamber) is full of
a thick, transparent, jelly-like substance, the vitreous
humour, or vitreous body.
• The latter consists of water (99%), protein vitrein,
hyaluronic acid and collagen fibres. It is apparently
secreted by the retina during development of the eye.
• Vitreous humour is not replaced.
• In rabbits, vitreous chamber contains a lymphoid
hyaloid canal extending from centre of lens to blind
spot.
• however, it is absent in man, as it gets absorbed and
obliterated in the embryo.
Functions of the humours
- The humours maintain the form of the eyeball by
keeping it inflated with their hydrostatic pressures. - They support the lens and help in focusing the light
rays. - aqueous humour nourishes the cornea and lens,
both of which are avascular. - The humours also contribute to the intraocular
pressure, especially aqueous humour.
Extrinsic eye muscles and their nerve
supply
• The extrinsic eye muscles (smooth fibres), for the
movement of the eye ball, are 4 straight muscles–
median rectus, lateral rectus, superior rectus, inferior
rectus, and 2 oblique muscles– superior oblique and
inferior oblique, inserted into the sclera.
• The 3 rd cranial nerve (oculomotor) innervates the
median rectus, superior rectus, inferior rectus and
inferior oblique.
• The 4th cranial nerve (trochlear) supplies the superior
oblique. The 6th cranial nerve (abducens) innervates
the lateral rectus.Accessory structures of the eye
(i) Eye brows are supra-orbital arched eminences bearing
obliquely projecting hair. They can be brought down to
protect the eye ball from dust, sweat and other foreign
bodies.
(ii) Eyelids (Palpebrae) are a pair of movable skin folds
supported by stiff fibrous connective tissue plates lined
internally by conjunctiva (palpebral conjunctiva).
• Eyelids bear stiff hair or eye lashes at the edges. The
inner surface of eye lids is lined by mucous membrane
called palpebral conjunctiva. It is highly vascular and
papillate.
• Eyelashes and blinking are protective against dust
particles, flies, rain, germs, mechanical injury etc.
• a small reddish patch on the inner corner of eye is
called plica semilunaris (vestigial third eye lid or
nictitating membrane).Modified glands of eyelids- Glands of Moll are modified sweat glands
present at the edge of the eyelid, between the
eyelashes, and help in lubrication. - Glands of Zeis are modified sebaceous glands,
which open into follicles of eyelashes. Infection of
one of these glands causes sty or hordeolum. - Meibomian or tarsal glands are modified
sebaceous glands which open on the free margins
of eyelids, for lubricating them as well as covering
cornea with oil for frictionless blinking, holding tears
over cornea, catching dust particles and keeping
away rain drops.
(iii) Tear gland (lacrimal = lacrymal gland) is an
almond shaped racemose gland lying in the upper part
of orbit that secretes a watery fluid or tear having
antibacterial lysozyme + water + sugar + amino acids
- proteins + minerals + salt + urea.
• The lacrimal secretion or tear moistens and cleanses the
eyeball and eyelids, provides protection from microbes and
nourishes the cornea.
• Tear is drained out by two lacrimal canaliculi
(superior and inferior), each arising from inner angle of
eye through an opening called punctum.