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Refractive errors happen if light rays are not focused on the retina (light sensitive tissue at the back of the eye) that converts light to nerve impulses enabling our brains to see clearly.
The types of refractive errors are myopia (near sightedness), hyperopia (far sightedness) and astigmatism (blurred vision from an irregular curvature of the cornea). Myopia is the most common refractive error in Costello syndrome, where objects in the distance appear blurry but can be seen more clearly close up. Hyperopia causes near and distant objects to appear blurry - although if mild, objects in the distance can be clear. Astigmatism causes blurring of both near and distant vision. Refractive errors are easily correctable by glasses.
Strabismus (crossed eyes, wandering eyes) is a condition when there is misalignment of one or both eyes - the eyes are not straight when looking at an object. One or both eyes may turn in, out, up or down. "Constant strabismus" is when the eye turn occurs all of the time and "intermittent strabismus" is when the eye turn occurs only some of the time. If the eyes turn inward it is called esotropia and if they turn outward it is called exotropia. Depending on the type of strabismus, correction can be done with glasses or surgery or both.
Amblyopia (lazy eye) is a decrease in the child?s vision that can happen when one or both eyes send a blurry image to the brain, which could be from an uncorrected refractive error or strabismus, for example. The brain "turns off" the eye with the blurry image, causing amblyopia. If untreated, amblyopia can cause permanent decrease in vision. Treatment is involves correcting the underlying cause, and by patching or drops.
Nystagmus describes an involuntary shaking, ?to and fro? movement of the eyes. It can be idiopathic (cause unknown) or an underlying disorder of the eye such as optic nerve hypoplasia.
The optic nerve functions like a cable, transmitting visual signals from the eye to the brain. Optic nerve hypoplasia (ONH) is a condition in which the optic nerve is underdeveloped (described as small, grey or anomalous). ONH can vary from mild to severe and may affect one or both eyes. Vision impairment varies from mild to severe. It is usually stable and non-progressive, vision does not deteriorate with time. In some instances of delayed visual maturation (the processing of the images in the brain develops later than usually expected), vision improves with time.
Optic nerve swelling or optic atrophy (degeneration) can sometimes develop as a complication of central nervous system problems such as hydrocephalus (also called ?water on the brain?) if left untreated. An MRI is recommended if any optic nerve problem is seen.
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