Just Because You See Well Does Not Mean Your Child Does!
We often take it for granted that our children see as well as we do. This may not be the case if your child has a lazy eye or is cross eyed. Normal vision develops early in life when the brain learns to fuse the images from both the left and right eye forming a single image. This is referred to as binocularity. Lazy eye (amblyopia) on the other hand is a reduction in vision that results from abnormal visual development in infancy and early childhood. Amblyopia is the leading cause of decreased vision among children, affecting 2-3% of the population.
Amblyopia develops when the nerve pathways between the brain and eye are not properly stimulated. As a result, the brain favors the eye with the clearer image and turns off or blocks the image from the eye with poor vision. Turning off an eye is called suppression. As the brain suppresses the lazy eye early in life, clear vision does not have a chance to develop and both eyes are not used together, effectively resulting in reduced binocularity. Most cases of amblyopia affect only one eye, but some cases are bilateral.
Lazy eye is hereditary and commonly seen among children born prematurely or with a low birth weight, or in those who have a family history, childhood cataracts or a serious eye disease.
What Causes Amblyopia? (Lazy Eye)
Strabismus – The most common cause of lazy eye is strabismus (eye turn or wandering eye), an imbalance in the muscles responsible for aligning the eyes, resulting in one eye pointing in or out, up or down. When the eyes are not aligned, two different images are being sent to the brain resulting in double vision. The brain is then forced to turn off the image coming from the misaligned eye to create a single image. The child only uses his straight eye to see, and vision in the turned eye does not have a chance to develop.
Deprivation – The most severe type of amblyopia in terms of vision loss resulting from an obstruction that “deprives” the child of clear vision in the eye is deprivation. Examples include a cloudy area in the lens (cataract), droopy eyelid, or opacity.
Refractive – The result of a significant difference between the vision in each eye, due to nearsightedness, farsightedness or an imperfection on the surface of the eye (astigmatism) that makes it difficult for the eyes to focus together is refractive. An infant has no way of telling his parents that one of his eyes does not see as clear as the other. Since it is difficult for the visual system to fuse a clear image with a blurred image, the brain learns to suppress the blurred eye causing vision to stop developing in that eye.
Lazy Eye Symptoms & Signs
Signs and symptoms of lazy eye include:
- An eye that wanders in or out, up or down
- Eyes that may not appear to work together
- Poor depth perception (3D vision)
- Early eye examination is key to detection and diagnosis
We begin to see children as early as 6 months of age to screen for lazy eye and eye turns. As part of the examination, a thorough medical, ocular and family history is taken, visual acuity is assessed for each eye looking for differences in vision between the eyes or reduced in vision, and tests are done to check focusing, binocularity, eye teaming and eye tracking. The need for correction such as glasses and/or contact lenses and an ocular health assessment is also performed.
Lazy Eye Treatment
If a child is diagnosed with amblyopia, depending on the cause and the degree to which the vision is affected, treatment options can include:
- Corrective eyewear, such as glasses and/or contact lenses, to help equalize the vision in both eyes
- Eye patches to stimulate the weaker eye
- Eye drops to temporarily blur vision in the stronger eye in order to encourage the use of the weaker eye
- Vision therapy or eye exercises to help establish binocularity, focusing and eye tracking
- Surgery to align the eyes or correct the droopy eyelid or remove the cataract
Ideally, the earlier the treatment is initiated the better the outcome, as the connections between the eye and brain are forming. If a lazy eye is left untreated, permanent vision loss can occur.
Background & Indication For Eye Muscle Surgery
Eye muscle surgery or “strabismus surgery” is an outpatient procedure. The goal of surgery is to surgically align your child’s eyes to better achieve binocular fusion (the eyes working together to give maximal depth perception) and to improve or normalize the field of vision (the total visual area, including “side vision”). Surgery is intended to align or straighten the eyes without much effort on the part of the child. Eye muscle surgery involves either tightening or weakening one or more of the six muscles on the surface of the eye. Nothing is done inside of the eye to change the vision. The eyes are never taken out during surgery.
When strabismus surgery is recommended, we feel that the risk of not doing surgery is higher than the risk of surgery. Each child heals differently. We carefully measure the amount of misalignment using prisms prior to surgery, so the correct amount of surgery can be accomplished.