Vertical section of the eye:
Sclera: Tough outer white layer of the wall of the eye.
Cornea: Transparent ‘window’ of the eye, focusing of light on the retina.
Iris: The colored sheet of muscle controls the pupil size so controls entry of light.
Pupil: A hole in the iris letting light into the back of the eye.
Ciliary Body: A ring of muscle controlling the shape of the lens.
Suspensory Ligaments: Transfer the pull of the ciliary body to the lens.
Lens: Accommodation — The fine adjustment to the focusing of light onto the retina.
Retina: Light sensitive layer of rods and cones converting light into nerve impulses.
Fovea or Yellow Spot: A tiny area of densely packed cones for detailed and coloured vision.
Choroid: A black-pigmented layer preventing internal reflection of light.
Blind Spot: Exit point of the optic nerve cutting through the retina so no rods or cones here.
Optic Nerve: Carries the impulses from the rods and cones to the visual centre of the brain.
Aqueous Humour: A clear liquid in front of the lens maintaining the shape of the cornea.
Vitreous Humour: A clear jelly offering support and shape to the back of the eye.
Eye Defects and Correction:
a. Short Sight (Myopia):
Condition: Can view close objects clearly but distant objects are out of focus. Light rays are focussed short of the retina.
Cause: Eyeball is too long or the focusing elements of the eye are too strong.
Correction: Use a concave (divergent) lens to widen the angle over which the light rays have to be refracted.
b. Long Sight (hypermetrpia):
Condition: Can view distant objects clearly but close objects are out of focus. The focal point is long of the retina i.e. is behind retina.
Cause: Eyeball is too short or the focusing elements of the eye are too weak.
Correction: Use a convex (convergent) lens to reduce the angle over which the light rays have to be refracted.