What Is Amblyopia?
Amblyopia is the medical term that describes poor vision in one eye from lack of use. This is the same as having an arm in a cast: while the cast is on, the arm muscles are not being used, and when the cast is removed the muscles are shrunken and weak.
What Causes Amblyopia?
The brain decides not to use vision from one eye. Why would the brain do this?
- Crossed eye or wandering eye: the brain shuts off the picture from one eye in order to avoid double vision.
- Unequal focus: the brain shuts off information from the poorly focused eye to concentrate on the clear picture from the healthy eye. This unequal focus can be due to many reasons, including need for glasses, cataract, or injury to the eye.
When the brain always shuts off the picture from the same eye, that eye can develop amblyopia. Some children with crossed eyes will take turns using one eye and then the other eye. Because both eyes get used part of the time, amblyopia is less common. However, many children always have the same eye cross in, wander out, or turn up. In this case, it is always the same eye that is ignored by the brain. Even though the eye is not damaged, vision does not develop properly because the brain is not paying attention to signals from the eye that is sending the wrong picture.
Treatment of Amblyopia
The first step in amblyopia due to poor focus is to improve the focus. This usually means glasses. If there is something blocking the proper focus of light, such as a cataract, then surgery may be needed. In children with crossed or wandering eyes, glasses are frequently helpful as well. Sometimes the problem is due to poor focus and crossing at the same time. A small number of children improve with glasses alone. Most children require some treatment that forces the brain to use the eye with amblyopia instead of the strong eye.
Blocking light from entering the eye. The best way to force the brain to use the eye with amblyopia is to block light from entering the strong eye. There are several options:
- Adhesive skin patch. These are basically egg-shaped bandaids. They are available in our Optical Shop. You can also buy these patches at drugstores and in supermarkets. If the child has glasses, the patch is put on the skin and then the glasses are put on over the top. The advantage of skin patching is that it is very difficult for the child to peek (cheat) around the patch. The disadvantage is that in hot weather the patches tend to sweat off, and some children develop a rash to the adhesive. If a rash develops, it can usually be easily treated by rubbing over-the-counter hydrocortisone onto the skin at bedtime as needed. Some parents substitute the jumbo size “Knee bandaids” which will also work if they stay on.
- Patch-Works patch. This is a cloth patch that fits over the glasses. These are available in our Optical Shop. The advantage is that there are no problems with patch rash or the patch coming off the skin. The disadvantage is that it is slightly easier to peek around the cloth patch. If your child pulls his glasses down to avoid the patch, the treatment will not work.
Pirate patches are NOT recommended as it is too easy for children to peek around them.
- Opaque Contact Lens. In special circumstances the child can be fitted with a special soft contact lens which has been dyed black. This contact must be inserted and removed daily. For older children who are in school all day, the opaque contact lens can be an excellent treatment because it is just as effective as skin patching (blocks all light) but it is almost unnoticeable to others (especially in dark-eyed children). Unlike the other treatments listed, the opaque contact lens does place the good eye at very slight risk for injury from infection or corneal scratches.
Blurring light that enters the eye. This is another alternative in children with milder amblyopia. These are not “fast” treatments. They can be useful for maintenance treatment after maximum improvement in vision has occurred using stronger methods.
- Contact Paper. Clear contact paper can be put on the inside of the eyeglass lens in front of the strong eye, which significantly blurs the vision. Another person standing only a few feet away from the child might not notice the contact paper at all or might think the lens was slightly dirty. This is a good treatment for older children who are shy about wearing a patch in public. It is not a good treatment for younger children who will pull down their glasses or take them off to avoid the blurry contact paper.
A Good Tip from a Parent: the contact paper can be removed and stuck to the refrigerator, and then reused for several days.
- Atropine: Atropine is an eye drop or ointment that blurs vision in farsighted children. It is put into the strong eye once a day in the morning. In some kids, the glasses lens in front of the strong eye is changed to plain glass. Atropine can be easier than patching, but it doesn’t work in children with very bad amblyopia. Atropine is sometimes used in combination with patching for kids who cannot be closely watched all day. Atropine has rare side effects such as sleepiness, crankiness, flushing of the face, and stomach aches or change in potty habits. These typically occur only in younger children. If Dr. Brown prescribes atropine for your child and you think side effects are happening (it usually takes 2-3 days of eye drops before side effects start) please stop the atropine and call the office.
Copyright Sandra M. Brown MD, March 28, 2005