the middle (pupil). Iris consist of muscles
that change pupil size by constricting and
relaxing. IT is a part of the eye choroid. Iris
is responsible for the colour of the eyes (if
it is blue this means it contains few pigment
cell, if brown – a lot). Its function is same as
of aperture in a camera – to adjust light flow.
Pupil is an aperture in iris. Its size usually
depends on the illumination level. The more
light the smaller the pupil.
Crystalline lens:
It is the eye “natural lens’. It is transparent,
elastic – can change its shape, focusing in
almost instantly, therefore one can see well
both near and far. It is located in a capsule and
is withheld by ciliary zonule. The crystalline
lens like cornea is a part of the eye optic.
Vitreous body:
It is a gel-like transparent substance located
in the posterior part of the eye. The vitreous
body supports the sphere of the eyeball and is
part of the intraocular metabolism. It is a part
of the optic system.
Retina:
It consists of photoreceptors (light sensing)
and nerve (ganglion) cells. There are two types
of receptor (transducer) cells in retina: cones
and rods. These cells producing rhodopsin
enzyme transform light energy (photons)
into electric energy of neural tissue, i.e.,
photochemical reaction takes place.
Rods have high light sensitivity and allow
seeing in poor light, they are also responsible
for periphery vision. Cones adversely need
plenty of light for functioning but allow to
distinguish small details (responsible for
direct vision) and ensure colour appreciation.
Most cones are located in macula which is
responsible for the sharpest vision. Retina
adjoins choroid but not too snug in some areas.
It is here that it may detach under various
retina diseases.
Sclera:
It is the non-transparent outer coat of the eye
bulb and in the frontal part of the eye it verges
into the transparent cornea. 6 eye moving
muscles are attached to it. It contains a few
nerve terminals and vessels.
Choroid:
It inlays the back part of sclera, it adjoins
retina and is closely linked to it. Choroid is
responsible for blood supply of intraocular
structures. And with retina disorders it is
usually involved in the pathology process.
Choroid has no nerve terminals therefore when
there is a trouble there, there is no pain which
usually alarms about a problem.
Optic nerve:
It transfers signals from nerve terminals to
the brain.
The orbit is the bony cavity that contains the
eyeball, muscles, nerves, and blood vessels, as
well as the structures that produce and drain
tears. Each orbit is a pear-shaped structure that
is formed by several bones.
The outer covering of the eyeball consists of a
relatively tough, white layer called the sclera
(or white of the eye). Near the front of the eye,
in the area protected by the eyelids, the sclera
is covered by a thin, transparent membrane
(conjunctiva), which runs to the edge of the
cornea.
The conjunctiva also covers the moist back
surface of the eyelids and eyeballs.
Light enters the eye through the cornea, the
clear, curved layer in front of the iris and pupil.
The cornea serves as a protective covering
for the front of the eye and also helps focus
light on the retina at the back of the eye.
After passing through the cornea, light travels
through the pupil (the black dot in the middle
of the eye).
The iris—the circular, colour area of the eye
that surrounds the pupil—controls the amount
of light that enters the eye. The pupil dilates
(enlarges) and constricts (shrinks) like the
aperture of a camera lens as the amount of light
in the immediate surroundings changes. The
iris allows amount of light into the eye when
the environment is dark and allows less light