Eyes are organ of sight which is able to perceive the radiant energy of visible light and can convert it into nerve impulse.
Eyeball is formed of following parts:
a. Fibrous tunic
- Outermost thick layer of eyeball
Formed of following parts
i. Sclera
- Non pigmented outermost covering
- Maintains shape of eyeball
- Form 5/6 part of eyeball
- Small portion is visible from outside called ‘white of eye’
ii. Cornea
- Form 1/6th part of fibrous tunic
- Transparent and avascular
- Converges the light to focus on retina.
iii. Conjunctiva
- Visible part of eye and cornea
- Meant for protection of cornea
b. Pigmented coat
It is middle and incomplete layer. Formed of following parts:
i. Choroid
- Darkly pigmented vascular layer present just beneath the sclerotic.
- Absorbs the light and prevent it from being refracted.
ii. Cilliary body
- Pigmented part present at junction of sclerotic and cornea
- Gave rise to suspensory ligament which holds the lens
- Contains cilliary muscle which contraction can change thickness of lens
- Lens plays important role to focus the image on retina.
iii. Iris
- Pigmented, provide color to eye
- Centrally perforated through which light enters into eyeball called Pupil.
- Determines amount of light entering into eyeball.
c. Retina
- Innermost, pigmented, most sensitive and incomplete layer.
- Formed of four cells. They are: Pigmented layer, Photosensitive layer, Bipolar layer and Ganglionic layer.
- Contains rods and cones cells
- Rods cells are numerous and sensitive to dim light
- Cones cells are less in number and sensitive to bright light.