Amblyopia, also known as “lazy eye,” occurs in 2% to 3% of babies and, in the US, in 75,000 3-year-olds per year. In this condition, poor vision in one or both eyes may result in the eyes not pointing in the same direction (misalignment) or in the eyes becoming crossed (strabismus). Amblyopia may be inherited or caused by uncorrected refractive error (nearsightedness, farsightedness, or astigmatism; see Refractive Errors, below). Amblyopia results when there is a difference in the quality of the images recorded by each eye and sent to the brain. The brain picks the better of the two images sent to it and disregards the blurry or cloudy image. When the brain disregards this image, the visual system develops more slowly for the eye that sent the discarded image than for the eye that sent the good image.
Parents usually cannot recognize a lazy eye merely by looking at it, because the problem is in the brain as well as the eye. The brain blocks vision from the lazy eye because the brain is unable to use both eyes together. An infant with normal vision learns to use both eyes together (binocular vision), and the pictures from the left and right eye are then combined (fused) into one picture by the brain. Because binocular vision permits us to tell how far away an object is in relation to other objects (depth perception), children with amblyopia have poor depth perception.
Signs of Amblyopia
Most babies with amblyopia show no obvious signs of the condition, which must be diagnosed by an eye doctor. In some infants, however:
- The weak eye turns (see the diagrams under “Strabismus”).
- The weak eye tends to close.
- The child squints.
- The child constantly rubs one eye.
If you notice any of these signs in your child, let your eye doctor know right away.
Treatments for Amblyopia
- Patch therapy: A patch is worn over the good eye so the weak eye will be used and will develop. In this situation, the BabyEyesT DVD can help to stimulate and strengthen vision in the weak eye.
- Glasses, which help correct poor vision in one or both eyes.
- Eye surgery may be required in rare cases in which the child is born with a clouded crystalline lens (a congenital cataract), or if amblyopia is combined with strabismus.
- If amblyopia is not treated before 4 years of age, it can become permanent and untreatable. This is one reason why a visit to the eye doctor before 14 months of age is so important!
Strabismus is the medical term for “crossed” or “turned” eye. This condition occurs in 2% to 4% of children. There are three common types of strabismus, as illustrated in the diagrams below:
- Crossed eye (esotropia)
- Wall eye (exotropia)
- One eye pointing upward or downward (vertical deviation)
Signs of Strabismus
Strabismus can be indicated by all of the signs of amblyopia plus a constant or occasional turning of the eyes or tilting of the head.
Treatments for Strabismus
When vision is normal, the images sent by each eye to the brain are fused together so the brain receives one combined image. Strabismus is treated by training both eyes to work together to send one fused image to the brain for interpretation. Treatments include:
- Surgery to correct weakness or imbalance in the eye muscles.
At birth, the upper part of the nose (the bridge, the space between the eyes) is flat. Some babies have prominent folds of skin between the bridge of the nose and the inner corners of the eyes. These skin folds (epicanthal folds) may make the baby seem cross-eyed, when actually the baby’s eyes are normal. This “false” cross-eyed appearance (pseudostrabismus) gradually vanishes as the baby’s nose bridge grows out and separates the eyes. There is no need to worry about this condition, as it is not really an eye disorder at all but only seems like one. Of course, whenever you become concerned about your baby’s vision for any reason, you should contact an eye doctor (see “Warning Signs at Any Age,” below)
Blocked tear duct
Babies often develop a blocked tear duct (nasolacrimal duct obstruction). In this condition, the delicate drainage tube that leads from the eye to the nose is clogged, or the membrane that covers this tube’s entryway does not open (as it normally would after birth).
Signs of blocked tear duct
- Too much tearing (tears may even run down the cheeks).
- Watery or cloudy liquid draining from the eyes.
- Crusty eyelashes upon awakening.
- Constant rubbing of the eyes.
Treatments for blocked tear duct
- Mild pressure is applied to the area between the eye and the nose and this area is gently massaged.
- Antibiotic drops or ointments are applied.
- Corrective surgery is done if the above options do not work over time.
Refractive errors are problems in the way the crystalline lens and the cornea focus light on the retina. In order for the eye to send a clear, sharp image to the brain, light rays need to be brought to a point (focused) directly on the retina, and particularly on the center of the retina (the fovea centralis; see the diagram above under “How Do We See?”). In some common disorders, glasses or contact lenses are needed to focus the light.
- Near-sightedness (myopia) occurs in 4% of babies. A person is near-sighted when light rays are focused in front of the retina, rather than on the retina (specifically, light focuses toward the center of the eye rather than on the back of the eye). This can occur when the eye is too deep or the cornea or is too curved.
- Far-sightedness (hyperopia)occurs in 20% of babies. A person is far-sighted when the light rays are focused behind the retina, rather than on the retina (specifically, light focuses behind the back of the eye rather than on it). This can happen when the eye is too shallow or the cornea is not curved enough. Most children can correct for far-sightedness by flexing muscles inside their eyes. This constant flexing can cause headaches, eyestrain, and turning of the eye (strabismus).
- Astigmatism (distortion) occurs in 10% of babies. In this condition, the cornea is football-shaped rather than spherical, and so reflects light in a distorted way. Two perpendicular sets of light rays focus at different points on or near the retina, so the image perceived by the brain is warped. Astigmatism can occur by itself or together with other refractive errors.
Less common eye diseases in children
While the above eye disorders are common and easy to correct if detected and treated early, eye diseases can be much more serious. Some of them can be treated and cured; others are incurable. Fortunately, these diseases are rare. Examples of eye diseases are:
Retinopathy of prematurity (ROP): Babies born with a very low birth weight have an increased risk of developing abnormal peripheral retinal blood vessels that can cause the retina to come loose (detached retina), which can lead to blindness. Those babies who do not develop this problem in childhood still have an increased risk of retinal detachment later in life, and should be seen regularly by an eye doctor to check for retinal detachments.
Familial (congenital) blindness: If there is a history of blindness in the family of either the father or mother, parents may want to seek genetic counseling to help determine the risk of blindness in their children.
Retinitis pigmentosa: In this inherited disease, the retina in both eyes degenerates more and more over time (progressively). Children become unable to see at night (develop night blindness) and then lose their side (peripheral) vision. Tunnel vision (no side vision at all, as if in a tunnel) develops, followed by complete blindness.
Leber’s congenital amaurosis: Blindness or near-blindness occurs in children with this disease because they lose nerve function in the retina of both eyes. A jerky movement of the eyes (nystagmus) may occur, as well as hypersensitivity to light and sunken eyes.
Congenital glaucoma: In this disease, high pressure of the fluid within the eye, together with an enlarged cornea, can cause nerve damage in newborns and infants. A common cause is malformation of some parts of the eye. Too much tearing (excessive watering) can be a warning sign of congenital glaucoma, but may also indicate less serious conditions, such as a blocked tear duct.
Congenital cataract: The crystalline lens, usually crystal clear at birth, is cloudy (opaque), so not enough light from the outside object reaches the retina. Vision is unclear or blocked. This disease can be cured by eye surgery, which is often necessary. Cataracts are also common in the elderly, in whom they also can be cured by surgery.
Dermoid cysts: These are bumps usually found on the side of the head near the eyebrow. They are not cancer, but are actually capsules containing skin tissue, hair, fat, or other body tissue. Dermoid cysts should be removed before the child begins to walk, because they can break open during a fall and cause painful inflammation.
Make an appointment with an eye doctor-either an optometrist or an ophthalmologist – if you see any of the following signs in your child:
- Eyes flutter quickly from side to side (nystagmus).
- Eyes are watery all the time.
- Eyes are always sensitive to light.
- Eyes change in any way from their usual appearance.
- White or yellow material appears in the pupil-the dark circle at the center of iris (the colored area of the eye).
- Redness in either eye persists for several days.
- Puss or crust appears in either eye.
- Eyes looked crossed or “wall-eyed.”
- The child constantly rubs his or her eyes.
- The child often squints.
- The child’s head is always tilted.
- Eyelids tend to droop.
- One or both eyes seem to bulge.
- One pupil is larger or smaller than the other (asymmetric pupil size).
- Baby does not make eye contact by 3 months of age.
- Baby does not focus on and follow objects by 3 months of age.
- Baby does not reach for objects by 6 months of age.
- Baby covers or closes one eye.
- One eye constantly or sometimes (intermittently) turns in, out, up, or down.