Amblyopia occurs when the image coming from one eye is of much worse quality than the image coming from the other eye, and the brain responds by ignoring the image produced by the poorer eye. If left untreated, the brain can eventually lose its ability to process visual information from one eye. A patient's depth perception and a portion of their visual field can be permanently lost. Amblyopia occurs in approximately 4% of the population. Amblyopia is sometimes referred to as "lazy eye", but this is a non-medical term that is also used to describe strabismus (eye misalignment) and ptosis (lid drooping). Although amblyopia is often associated with strabismus, it can also occur in the absence of eye misalignment.
Amblyopia is a medical condition that requires intervention in order to have any possibility of visual rehabilitation. There are different types of amblyopia, including:
- Deprivation amblyopia
- Refractive amblyopia
- Strabismic amblyopia
Deprivation amblyopia occurs when the visual axis is blocked by some obstruction, preventing a clear image from forming on the retina. The blockage can come from a drooping eyelid, as in congenital ptosis, or from an opaque lens (cataract) or opaque cornea due to corneal disease. The disease process of deprivation amblyopia may be bilateral, for example in cases of bilateral congenital cataracts. If left untreated for too long, a child with deprivation amblyopia will be permanently unable to develop good vision.
Refractive amblyopia occurs when a child has either a very large refractive error or the left and right eyes have very different refractions. Generally, the brain receives a blurrier image from the eye that is more far-sighted or has a higher degree of astigmatism. Too often, refractive amblyopia can go undetected because no eye misalignment is present. The disease process of refractive amblyopia may be unilateral or bilateral.
Strabismic amblyopia occurs when the eyes are misaligned and the brain receives conflicting information from the deviated eye. To avoid double vision or visual confusion, the child's brain will stop using the turned eye and the vision will correspondingly decrease. The treatment of strabismic amblyopia may involve glasses, surgery, patching, or a combination of all three.
Treatment for amblyopia consists primarily of glasses combined with patching or atropine 1% eye drops. With patching, a patch is placed over the better eye in order to encourage the brain to develop better visual processing of the information coming from the weaker eye. A child's vision usually takes time to improve after initiating amblyopia treatment, as changes in the way the brain processes visual information develop gradually. Older children with amblyopia often require longer periods of treatment than younger children. Although many children will have some response to amblyopia treatment, not all children will obtain 20/20 vision. Atropine 1% eye drops are indicated if a child is unable to wear a patch and the weaker eye has vision equal to 20/100 or better. The use of atropine 1% drops has had similar response outcomes as patching treatment in amblyopia treatment studies.
A NIH study with the Pediatric Eye Disease Investigator Group found that amblyopia treatment may be initiated even for teenagers with some potential for improvement in the vision of the weaker eye. However, better success rates are achieved when younger children are treated.
Binocular treatments of amblyopia have also been studied using iPad devices. Children can play video games while wearing special glasses to improve their amblyopia. The response rates and outcomes thus far in PEDIG studies have been less than patching. Alternative treatments including optical penalization foils and combination treatments. Oral administration of levodopa has also been studied as a treatment option to stimulate the visual pathway neurons.
In cases of recalcitrant or unresponsive amblyopia, polycarbonate glasses are indicated to protect the better seeing eye.