2. Abnormality of the eye muscles or in their nerve supply as in:
- Myasthenia gravis.
- Sixth Cranial Nerve Palsy (in children, this occurs frequently post a viral infection and may cause sudden onset of esotropia).
- Trauma to the eye.
- Duane’s Syndrome.
- Strabismus Fixus.
- In adults Usually an untreated childhood squint.
- Following previous Squint surgery.
- Decompensating squint, previously under control but now getting worse.
- Paralytic squint – sudden onset in patients with underlying hypertension or diabetes.
- Thyroid Eye Disease, due to inflammation/swelling caused by scarring of the eye muscle. Once the inflammation has subsided, surgery is advised if symptoms of double vision are present.
- Trauma to eye muscles e.g., as a complication of sinus surgery.
- Early Diagnosis: If the proper visual impulses are not transmitted to the brain in the first few months after birth, which is the critical period of visual development, amblyopia will develop and there will be loss of 3D (binocular) vision.
Non Surgical Treatment:
Prisms: These are specialised glasses used to treat double vision of sudden onset. They can be used as a temporary measure and are later incorporated into the usual spectacles. They can also improve the appearance of a squint in some patients where surgery is not an option.
Botox: In adults and occasionally in children, Botulinium toxin may be the first line of treatment. The toxin is injected into the muscle at the surface of the eye. It temporarily paralyses the muscle in the direction of the squint and balances the forces producing the misalignment. It causes an overcorrection initially and the eye may move in the direction opposite to the squint in the first few weeks. The eye will gradually straighten and then return to its original position. Repeat injections are usually required to maintain the corrected position of the eye.
To achieve surgical correction, the eye muscles in one or both eyes (depending on the degree and direction of the squint), are tightened or loosened. The muscles are shortened and reattached to the eye to tighten or moved further back which has the effect of loosening. If the eye is turning in (convergent squint), the muscle which pulls the eye in (the medial rectus) is moved back and the outer muscle (the lateral rectus) is tightened to straighten the eye. The amount of surgery is based on normograms that are tables which have been developed based on results of muscle surgery in thousands of patients