Farsightedness Nearsightedness Astigmatism Focusing an image sharply on the retina (the light-sensitive layer at the back of the eye) depends mainly on the lens, the size of the eyeball, and the cornea. Muscles around the lens contract or relax to change the shape of the lens (and therefore its focusing power) in order to adjust focus between near and far objects.
In farsightedness (hyperopia), the eyeball is too short relative to the focusing power of the lens, making distant objects clear but nearby ones blurred. In nearsightedness (myopia), the eyeball is too long relative to the focusing power of the lens, so distant objects appear blurred but nearby objects can be seen clearly. In astigmatism, the shape of the lens or cornea is irregular.
As a result, all of the light rays entering the eye cannot be focused on the retina, causing vision to be distorted or blurred.
All three of these conditions can be corrected by glasses, by contact lenses, or by laser surgery to reshape the cornea

Othere related diseases

GLAUCOMA
Normally, fluid is continually secreted into the front of the eye by a structure called the ciliary body to nourish the tissues and maintain the shape of the ey...

LABYRINTHITIS
Labyrinthitis is inflammation of the labyrinth of the inner ear, which contains the organs of hearing and balance. It is usually caused by a bacterial or viral ...

MACULAR DEGENERATION
Macular degeneration (also known as age-related macular degeneration, or AMD) is a deterioration of the macula, the central area of the retina responsible for s...

MENIERES DISEASE
Ménière’s disease is an inner ear disorder characterized by recurrent attacks of vertigo, tinnitus (ringing in the ear), and hearing loss. It is due to a bu...

OTITIS EXTERNA
In otitis externa, the outer ear canal becomes inflamed, usually due to a bacterial, viral, or fungal infection. It is sometimes called “swimmer’s ear,” b...

OTITIS MEDIA
Glue ear Otitis media is inflammation of the middle ear, usually due to a bacterial or viral infection. It is more common in children, because their Eustachian ...

OTOSCLEROSIS
In otosclerosis, there is abnormal growth of bone around the stapes, one of the three tiny bones in the middle ear that transmit sounds to the inner ear.
T...

PRESBYCUSIS
A form of sensorineural deafness, presbycusis is progressive loss of hearing that occurs with age. It is due to the natural degeneration and death of sensory ne...