• cornea allows the light to pass into the eye. Due to its
curvature, it helps in focusing a real inverted image of
the object on retina.
• The cornea also serves as a filter, screening out some
of the most damaging ultraviolet (UV) wavelength in
sunlight.
• at the junction of sclera and cornea, there is a circular
canal of Schlemm. The aqueous humour is drained
off into this canal and then into the blood.
(iii) conjunctiva
• It is a thin, transparent, membranous layer present
over the cornea, and is continuous with the corneal
epithelium.
• It is composed of a stratified epithelium and also
lines the eyelids.
• The conjunctiva is thin, mildly cornified and richly
supplied with free nerve endings. It is nourished by
tiny blood vessels that are nearly invisible to the naked
eyes.
• In the sore or “pink” eyes condition, the conjunctiva
gets inflammed, causing conjunctivitis.
• Conjunctiva protects the cornea and also secretes oil
and mucus that moisten and lubricate the eye.
B. Vascular coat
(i) choroid
• It is a pigmented layer present beneath the sclera. It
is composed of connective tissue and is of dark brown
colour.
• It is homologous to the pia-arachnoid of the brain.
• It contains numerous blood vessels which nourish the
retina. The pigmentation prevents reflection within the
eye.
(ii) ciliary body
• The ciliary body extends towards the inside of the eye
from the choroid coat.
• This part of the eye is less vascular, thick, less pigmented
and composed of ciliary muscles and ciliary
processes, attached to the lens capsule by suspensory
ligaments.
• The ciliary processes secrete aqueous humour in the
anterior chamber of the eye ball.
• Ciliary muscles are a complex set of smooth muscles
and are of two types: circular and meridional. These
are controlled by autonomic nervous system, and alter
the shape of lens.
• The contraction of ciliary muscles results in spherical
shape of the lens and the relaxation, in the flattened
shape (i.e. accommodation).
(iii) iris
• It is the anterior part of vascular coat which lies behind
the cornea. It is centrally perforated by pupil.
• Its pigment gives eye its colour (depending upon the
amount of pigment present) like black, blue or
green.
• In some cases there is no pigment at all, so the eye is
light. Albinos lack pigments in the skin, hair and iris.
Their pink colour of iris is due to reflection of light from
the blood vessels of iris.
• The movement of iris controls the size of pupil. The iris
contains two sets of smooth muscles : circular muscles
or sphincters and radial muscles or dilators, of
ectodermal origin. These muscles regulate the amount
of light entering the eye ball. The radial muscles contract
in dim light, and the circular muscles contract in bright
light.
• Pupil in woman is larger than that in man.c. nervous coat : retina
• The third and inner coat of the eyeball, the retina
(nervous tunic), lines the posterior three-quarters of the
eyeball and is the beginning of the visual pathway.
• The retina consists of a pigment epithelium (nonvisual
portion) and a neural portion (visual portion). The
pigment epithelium is a sheet of melanin-containing
epithelial cells that lies between the choroid and the
neural portion of the retina.
• melanin in the choroid and the pigment epithelium
absorb stray light rays, thereby preventing reflection
and scattering of light within the eyeball. This ensures
that the image on the retina is sharp and clear. The
pigmented layer is continuous over choroid, ciliary body
and iris while the nervous layer terminates just before
ciliary body. This point is called ora serrata.
• The neural portion is thick and composed of four layers