Bienvenido V. Castillo, Jr., M.D.

It comes as a surprise to many parents when they receive notice from their child’s school of a failed vision screening.  A common remark I hear in the Clinic is, "Johnny can see a small airplane in the sky. How can he have an eye problem?"  The answer to that question is that he sees perfectly with his good eye, but the other eye is "lazy," or has amblyopia.

Amblyopia is a condition wherein the visual part of the brain does not develop properly due to poor image received from the eye.  Just as the quality of the picture we see on a television screen relies on the signal received from a satellite dish, the image processed by the brain is dependent on the image received and transmitted by our eyes.  The critical period for visual development in children is from birth to seven years of age.  Interruption of vision at an earlier age causes greater loss in brain visual development.  The nerve wiring between the eye and brain becomes more permanent after seven years of age, making it difficult to correct amblyopia after this age. 

The most common reason for amblyopia is that the image is out of focus due to significant astigmatism, far-sightedness (hyperopia), or near-sightedness (myopia).  Astigmatism refers to the shape of the cornea, which is the clear part of the eye.  Instead of being perfectly round like a basketball, an astigmatic cornea is misshapen like a football.  A hyperopic (far-sighted) eye is a small eye, while a myopic (near-sighted) eye is a long eye.  Amblyopia occurs when there is a significant difference between the two eyes.  The eye which has more astigmatism or hyperopia is at greater risk of developing amblyopia because it cannot compete with the better eye.  These children appear and behave normally, so it is difficult to tell that they have amblyopia unless the vision is tested in each eye.

Another cause for amblyopia is strabismus, which is more commonly known as a wandering eye. The eyes may appear crossed (esotropia) or splayed out (exotropia). Occasionally, one eye may drift up or down.  It may occur during the first six months of infancy, or at two years of age.  The cause during infancy is congenital, whereas in toddlers it is usually due to significant hyperopia.  When the eyes are not aligned straight, the result is double vision.  To prevent double vision, a child’s brain suppresses or ignores the image from one eye.  Chronic suppression of one eye may then lead to amblyopia.  This type of amblyopia is usually caught early because the eye crossing is apparent.

Less common causes for amblyopia are eye conditions which prevent light from entering the eye such as corneal scarring (due to infection, trauma, or chronic inflammation), bleeding inside the eye, and cataracts.  Other congenital eye problems associated with amblyopia are congenital glaucoma, optic nerve hypoplasia, and optic nerve coloboma.

A pediatric ophthalmologist is a specially trained medical doctor who can evaluate and treat amblyopia in infants and toddlers. A complete dilated eye examination is performed to look for structural abnormalities in the eye.  During an exam, the eyes are also checked to determine if there is significant astigmatism, far-sightedness, or near-sightedness, which may cause amblyopia.

The treatment for amblyopia depends on the cause of the problem.  Glasses are given to correct astigmatism, far-sightedness, and near-sightedness.  Patching of the good eye may be needed in addition to glasses to strengthen the “lazy” eye.  If there is eye crossing and it does not improve with glasses, then eye muscle surgery is performed after amblyopia has been corrected.

The key to successful amblyopia treatment is early detection. This starts at the nursery before the baby goes home.  The doctor checks the “red reflex” (red eye in photographs) to make sure that there is no clouding of the cornea, cataract, or bleeding inside the eye that may block light entering the child’s eye. At three months of age, babies should be able to track or follow faces and objects, and the eyes should be straight.  An unequal red reflex is a common sign of a lazy eye.  At three to four years of age, vision in each eye should be checked in the pediatrician’s or family doctor’s office.  Vision testing at school should be the last step in the vision screening process to catch any children who may have fallen through the cracks.