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Lazy Eye in Children

Parenthood Magazine September'13 issue







LAZY EYE IN CHILDREN
BY DR HELEN TAN CHEN CHEN

WHAT IS LAZY EYE?
Lazy eye occurs in 2-3 of every 100 children. In order to understand about lazy eye, we have to know how our eyes and brain work together to produce vision. Both of our eyes act like a camera which capture the image and this information will be sent to the brain and the brain will interpret the image that we are seeing. This is a learning process which begins soon when a child was born, similar to motor and language skills. The visual development continues, slowly a child learns to perceive colour, shapes, depth and motion. Any insult to the eyes and brain during this period may result in lazy eye. 
Most parents mistaken squinting eye or unequal size of eye as lazy eye. Lazy eye or in medical term, amblyopia is defined as poor vision in one or both eyes even with the best glasses prescribed due to abnormal development of the eye. Our brain has the ability to fuse both objects seen by right and left eye into one image ( Figure 1 ). If one of the eyes is faulty due to any cause, the brain will favour the image from the good eye and suppress the faulty eye, leading to lazy eye. Lazy eye can also affect both eyes if both of the eyes have abnormality.

WHEN TO SUSPECT THAT YOUR CHILD HAS LAZY EYE?
•    If your child shows signs of poor vision such as squeezing eyes, turning or tilting head to one side, avoiding close work, holding reading material closer than usual and disinterest in the activities that other kids used to enjoy.
•    Misalignment or squinting of eyes. Squint can be a cause of the lazy eye or as a consequence of the untreated lazy eye.
•    Drooping of eyelids, which is the cause of the lazy eye.
•    Any apparent structural abnormality of the eye such as media opacity.
   
WHAT ARE THE COMMON CAUSES OF LAZY EYE?
Refractive error – when one eye’s refractive error, either short-sighted, long-sighted or astigmatism is  significantly higher than the fellow eye, the brain cannot fuse the image due to dissimilar clarity and tends to suppress the poor eye causing lazy eye. If both of the eyes have equally very high refractive error, both eyes can be lazy as well.
Squint- squint or strabismus happens when one eye is deviated from its normal alignment which can be outward, inward, upward or downward. In this condition two images from different directions are sent to the brain and the result is double vision (Figure 2). The brain is forced to turn off the misaligned image to avoid seeing double, so the misaligned eye will be ignored and become lazy eye.
Other rare causes of lazy eye are:-
Ptosis- drooping of eyelid causing mechanical blockage of vision.
Media opacity- including corneal opacity and cataract of any cause.
Retinal diseases.

WHAT ARE THE TREATMENT FOR LAZY EYE?
In all cases of lazy eye, thorough examination should be done in the first visit to detect any eye diseases and if present should be treated, before lazy eye treatment is initiated.
In the refractive type, glasses are prescribed first to equalize and improve the vision. In mild cases, lazy eyes can improve with the glasses and no further treatment is required except monitoring. In more severe and non-responsive cases, patching treatment must be combined with glasses. Patching treatment simply means to patch the poor eye for 1-3 hours per day, depending on the age and severity to improve the sharpness of the vision. This may take months to years to see the outcome. Vision therapy is often needed to establish the binocularity (the normal two-eyed vision) and develop the visual skills. In a very young child, the sequence may be different. Patching may be the first treatment to stimulate the vision as they do not tolerate glasses easily. Glasses and patching may also be prescribed at the same time depending on the case.  The critical age for treatment is still debatable. Conventionally lazy eye treatment is believed should be treated only before the age of 9 years old, but few research show that some children still show improvement even after the age of 9 years old especially if treatment is combined with glasses, patching and vision therapy.
In the strabismic type, surgery is required in certain types of crossed eye. Even though the eyes can be aligned to normal, often binocularity is difficult to achieve. On average only less than 20% of the child who had undergone surgery achieves a good visual outcome. 

WHAT IS THE OUTCOME OF TREATMENT OF LAZY EYE?
Timing is an important factor in the outcome of lazy eye treatment. Early diagnosis and early treatment carry a very favorable outcome.  Once the desired vision is achieved, the child  still need to continue the treatment for some time to maintain the vision. In many cases lazy eye treatment failed mainly because of the poor compliance to the treatment. Therefore parents play a very important role. Daily patching especially in a very young child with very poor vision can be frustrating to both the child and the parents. It is even more frustrating for the parents if the child’s vision did not improve over the expected period of time. In the face of these hardship, patching often fails because the child and the parents give up.   

HOW TO PREVENT LAZY EYE?
There is no way an infant or young toddler can tell the parents about their poor vision, unless there is an apparent abnormality that are visible to parents. Due to this reason, lazy eye problem usually present late. One simple way to prevent this is to bring your child for vision test and eye examination at least once before they enter the school, ideally at the age of 4 when they are able to co-operate and give response during the vision test. Clear vision and two-eyed binocular vision are extremely important for development of good hand-eye coordination and depth perception in children. Children with severe untreated lazy eye will have limited choice of career when they grow up to be adults. It is our responsibility as a parent to prevent lazy eye from happening.