Disease of the neuromuscular system of the eye (squints, amblyopia, and diplopia)

If a patient's eyes do not look in the same direction, he has a squint. Squints are common in the developing world, and are usually accepted with resignation. Although treating a squint needs relatively simple technology, it is time-consuming and needs skill, so squints will probably be low in your list of priorities.

If his eyes do not look in the same direction, he will see two images. This causes confusion, and to avoid it he tends to suppress the sight in one of them. If this suppression continues for long enough, he may lose vision in that eye. This is called amblyopia, which is a reduction in vision, due to lack of use of an apparently normal eye. If amblyopia is not corrected by the age of 7, it becomes permanent. So try to diagnose and refer squints before this age.

SQUINTS AND AMBLYOPIA SQUINTS DIAGNOSIS. The corneal light reflex and the cover test will demonstrate a manifest squint.

The corneal light reflex. Shine a pen torch directly in front of you, and ask the patient to look at it. If each of his eyes is properly fixing the torch, its reflection from his corneal mirrors will be the same, and more or less central on each cornea. Are the reflections from your torch equally centred on his pupils?

The cover test. Ask him to look straight ahead at some target in the distance. Cover his left eye with a piece of paper. If his right eye moves, in or out, to fix on the distant target, it was previously squinting. If it does not move, it was looking straight at the target.

Now put the paper in front of his right eye. If his left eye moves as you remove the paper, it was previously squinting in or out. If it does not move, he does not have a manifest squint, and both eyes look straight.

MANAGEMENT is limited.

If an adult has a squint and no double vision it may be the cause of reduced vision in the squinting eye (amblyopia). There is no treatment at this age.

If an adult has a squint and double vision, this suggests a serious recent disease of his extraocular muscles or their nerves, such as diabetic neuropathy, myasthenia gravis, or raised intracranial pressure. He needs a full medical and neurological examination.

If a child under the age of 7 years presents with a squint:

(1) Dilate both his pupils, and use an ophthalmoscope to make sure that his squint is not due to a retinoblastoma in one of his eyes (an uncomon cause of squint, 32.7). Look for a yellowish mass on his retina.

(2) If his retinae are normal, try to assess his visual acuity in both eyes. This may be possible if he is [mt]3 years, but rarely if he is younger.

If he has reduced vision in either eye, or a definite squint, and he is under 7, refer him. He may need glasses, occlusion therapy to treat amblyopia, and perhaps surgery on his extraocular muscles.

CAUTION ! Never occlude the eye of a child under 7 years for several days, because this may cause amblyopia.

If you cannot refer him, correct any refractive error and occlude the eye that he normally uses. Occlude it for 1/2 to 2 hours a day while he is doing close work, reading, or drawing. The duration of treatment depends on the duration of his ambylopia. If treatment is prompt, a 6[nd]8 weeks of occlusion may be enough. If it is delayed he may need it for a year, or it may fail.