The Eye- Anatomy
Eye ball is about 2.5 cm in diameter. It has three layers,
- Outer fibrous coat
- Middle vascular coat
- Inner nervous coat
The fibrous coat
The anterior 1/6 th is the cornea and posterior 5/6 th is the sclera. Cornea has five layers and rich in nerve fibers to carry pain sensation. It transmits light. It has no blood supply.
Sclera is the white part and has a rich blood supply. The optic nerve and the muscles of eye rotation are attached to sclera. Anterior part of sclera is covered with a mucous membrane known as conjunctiva.
The vascular coat
It contains choroid plexus, iris and ciliary bodies. Lens is held by the ciliary bodies. It is a transparent biconcave structure and has a central nucleus. Iris is circular and has an opening called pupil. Aques humour is the fluid present in the anterior and posterior chambers of the eye ball. It is secreted by ciliary processes.
The nervous coat
It is called retina. It has rods and cones and 10 microscopic layers. It receives the light impulses and sends it to the brain.
Vitreous humour is a jelly like, hyaloid membrane which is situated deep to retina and lens. It gives shape to the lens.
Functions of the Eye
- Vision is the main function of the eye
- The light from objects enters the eye and reaches the retina.
- The image on the retina is passed through the optic nerve and reaches the geniculate body.
- Finally it reaches the visual area in the occipital lobe of the brain.
- Hence the image is felt
- Pupil regulates the amount of light entering the eye
- Ciliary muscles accommodate the lens for near or distant vision
Diseases of Eye
- Xerophthalmia – dryness of eyes
- Keratomalacia – due deficiency of vitamin A
- Nyctalopia or night blindness
- Cataract due to opaque lens
- Diplopia or double vision
- Colour blindness, an inherited disease
- Glaucoma or increased intraocular tension
- Myopia or short sight
- Hypermetropia or long sight’
- Presbyopia or loss of accommodative power of lens
- Conjunctivitis, an inflammation of conjunctiva
Tips for healthy vision
- Have diet rich in vitamin A which is essential for visual cycle
- Have more green leafy vegetables
- Don’t study under dim light
- Avoid reading, while in bus or train
- Never try to watch bright sun
- Use sunglass whenever needed
- Watching cool moon is good for vision
- Good sleep is essential for good vision
- Never use cheap cosmetics on eyes
- Never remove your eyebrows completely. They protect your eyes by channeling the sweat from your fore head
- If dust falls in your eyes don’t try to remove it with hands. Instead wash with cool water
- Wash your make-up before you get to bed
- Never sleep with make-up or face packs
- Avoid eyes during facials and bleach