Dr Ben Wild
Overview |
Eye movements are controlled by 6 extra-ocular muscles. The superior rectus pulls the eye upwards, the inferior rectus pulls the eye downwards, the lateral rectus pulls the eye outwards and the medial rectus pulls the eye inwards. The superior oblique muscle connects to the eye after passing through a pulley called the trochlea and is mainly responsible for rotating the eye inwards and pushing the eye downwards. The inferior oblique follows a similar path as the superior oblique, except underneath the eye and does not travel through a pulley system.
A frontal image of a right eye with the extra-ocular muscles. If any of these muscles are too tight, too loose, too strong or too weak, there is the potential for an eye turn (strabismus).
Strabismus can occur when one of these muscles is either working too hard or not hard enough and an eye turn is noticed. Exotropia is a wandering eye, esotropia is a crossed eye, hypotropia is one eye is looking downwards and hypertropia is one eye is looking upwards.
Normally, the eye muscles are able to focus the eyes very closely to a single target. When the images from each eye are similar, a fusion reflex kicks in so that the person can see a single target with depth (3 dimensions instead of 2). When the muscles are unable to align both eyes towards a single target, the fusion reflex is unable to activate, and the patient either has double vision or the patient’s brain suppresses (ignores) the image from one eye to avoid double vision. Other ways to avoid double vision is adopting a head tilt or turn, raising the chin or lowering the chin.
Pseudo-strabismus occurs when one eye looks like it is not pointing in the same direction as the other but it actually is. This is common in babies. Babies have an extra fold of skin called the epicanthal fold that can sometimes make an eye look crossed. Also, if the distance between the eyes is either very narrow or very wide, the eyes can look crossed or wandering.
A normal pair of eyes looking off into the distance.
An image showing the right eye is turned inwards. This is an esotropia style of strabismus.
Signs and Symptoms |
Signs
One eye looking in a different direction compared to the other eye. Head tilt, head turn, raised chin or lowered chin.
Symptoms
Possible double vision, lack of depth perception.
Causes and Risk Factors |
Causes
One or more muscles not working hard enough or working too hard.
Risk Factors
Difference in prescriptions between the two eyes (anisometropia), different image sizes between the two eyes (aniseikonia), decreased vision due to eye problem (cataract, corneal scar, retinal degeneration, etc.), congenital malformation.
Prevention and Treatment |
Prevention
1st eye exam around 1 year old followed by another at 3-4 years old to ensure proper development of the eyes and eye muscles. Early intervention if issues arise.
Treatments
· Treat any cause for decreased vision.
· Glasses or contacts after a cycloplegic refraction (prescription done after dilating drops).
· Treat lazy eye by patching good eye 2hrs/day to full time.
· Vision therapy (eye exercises to regain proper eye muscle control).
· Surgery by age of 1 or 2 if born with strabismus or upon 1st discovering a strabismus is constant (doesn’t come and go).
Prognosis |
If born with strabismus, surgery can align the eyes but the patient may need several re-alignment surgeries in their lifetime. There is also only a slim chance of gaining depth perception. If the strabismus develops after the age of 3-4, full glasses prescription and vision therapy can often correct the alignment issue, and if not, surgery can re-align the eyes. Regaining depth perception in this case is likely but not promised. For pseudo-strabismus, as babies grow and lose their epicanthal eyelid folds, their eyes will look aligned.
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