This section explains in simple terms the various components of the eye that contribute to human vision.
Cornea:
It is the transparent dome-shaped outer structure of the eye. The cornea covers the eye and provides most of its optical power. Together with the lens, the cornea refracts light and this helps the eye focus.
Lens:
The natural lens of the eye works like that of a camera and focuses the light rays on the retina. The lens changes its shape, allowing the eye to change its focal point and focus from distant to near.
Iris:
This is the part that gives the eye its colour (i. e. brown, black, blue, green)
Pupil:
This is the opening in the middle of the iris. It functions like the diaphragm of a camera, controlling the amount of light that enters the eye. The pupil becomes small in bright light and enlarges in dim light.
Aqueous humor:
It is the watery fluid that is continuously produced in the eye. The fluid supplies nutrition to the inner parts of the eye. An increase in the fluid pressure of the eye can result in a condition called ‘Glaucoma’.
Vitreous humor:
It is a jelly-like liquid that fills the space behind the lens thereby giving firmness to the eyeball.
Retina:
It is the innermost layer of the eye, sensitive to light and similar to a film in a camera. It has specialized cells called ‘rods’ and ‘cones’ that convert the light rays into electric signals. These signals travel through the optic nerve to the brain, forming images of objects in front of the eye.
Fovea:
This is the centre of the retina and is most sensitive to light. Cone cells are densely packed in this area and are responsible for clarity of vision.
Optic nerve:
This is the nerve that runs from the eyeball to the brain. It carries information from the retina to the brain for interpretation of images.
Emmetropic Eye (Normal eye) :
In a normal or Emmetropic eye, parallel rays from an object enter, converge and focus on the retina forming a clear image.
Ammetropic eye:
When the parallel rays of light remain unfocused upon the retina, the eye is known as an ammetropic eye. This kind of an eye has refractive error.
Refractive errors cause imperfect vision:
Refractive errors are the most commonly found type of vision defects.
Refractive errors are of three types:
