Strabismus

Strabismus
refers to the nonalignment of the
eyes such that an object in space is not visualized
simultaneously by the fovea of each
eye. Phoria refers to the potential for an eye
to turn. Once it turns it is called a tropia.

Causes of strabismus

1 Paralytic strabismus is due to cranial nerve
(III, IV, or VI) disease or eye-muscle weakness
from thyroid disease, traumatic contusions,
myasthenia gravis, or orbital floor fractures.
2 Nonparalytic strabismus is due to a malfunction
of a center in the brain. It is often
inherited and begins in childhood.

Complications of strabismus:

1. Amblyopia
Also called lazy eye, amblyopia is decreased
vision due to improper use of an eye in childhood.
The two common causes are an eye turn
(strabismic  amblyopia) or a refractive error
(refractive amblyopia), uncorrected before age 8. In strabismus, children unconsciously
suppress the deviated eye to avoid diplopia.
Strabismic amblyopia is treated by patching
the good eye , thereby forcing the
child to use his amblyopic eye. The better eye
is patched full time—one week for each year
of age. It is repeated until there is no
improvement on two consecutive visits.
Refractive amblyopia is treated by correcting
the refractive error with glasses and patching
the better eye. Both types must be treated in
early childhood because after age 5, it is difficult
to improve vision. After age 8, improvement
is almost impossible, but should be
tried.

2. Poor cosmetic appearance
Tropias that cannot be corrected with spectacles
may be cosmetically unacceptable and
the patient may desire surgery.

3. Loss of fusion
Fusion occurs when the images from both
eyes are perceived as one object, with resulting
stereopsis (three-dimensional vision).
Many patients with tropias never gain the
ability to fuse. Finer grades of fusion are
assessed by using the Wirt stereopsis test.