Amblyopia: Lazy Eye
Amblyopia is defined as decreased vision in one or both eyes caused by abnormal interaction between the eyes and brain. Basically what this means is that the brain is not getting the proper information from the eyes to develop normal vision, hence, visual learning impaired. Prevalence is estimated to be 1-4 %.
This condition is commonly known as lazy eye.
One simple way to understand this condition is to imagine that the eyes are like two cameras that are capturing light with its lenses ( the cornea and the lens) and transforming it to impulses in the retina that go to the brain (Monitor) via de optic nerve and there, those impulses are interpreted as images.
The brain knows that we have two eyes and ideally it wants to use both eyes together. If both images are the same a process called fusion happens within the brain where both images are joined to form one sole image.
But what happens if one eye is giving out different information compared to the other eye? Than the brain is not capable of fusion, it actually becomes confused and decides to block the image that is not as good as the other one. That is called suppression. It is just another word for ignoring. The eye with worse information gets ignored by the brain. Visual learning in the brain is a process that takes place during the first 8 years of age
There are different kinds of amblyopia:
- Strabismic amblyopia: Is the most common type. Strabismus is an alteration in eye alignment and when it is persistent ad non alternating it can lead to amblyopia. If the eyes are misaligned than the brain cannot use them together and there for is forced to suppress one of the images to avoid diplopia( double vision) leading to amblyopia. One of the mechanisms that brain uses to avoid amblyopia is alternating strabismus, that means the brain uses one eye at a time so it can develop equal vision in both eyes
- Refractive or anisometropic amblyopia: this type occurs when there is an important difference in the refractive error between both eyes. Basically what this means is that one eye is focusing properly giving good visual information to the brain while the other one is unfocused and giving blurry and bad quality information, hence the brain is forced to ignore it. Because the child has one good seeing eye this condition is not usually encountered until the child has a proper ophthalmological examination.
- Deprivation amblyopia : this type of amblyopia develops when the eye is not capable of receiving light stimulus or transforming light in to neural signal to the brain. For example a child that is born with congenital cataracts or develops one in early life is deprived from light entering the eye. Another example of the same type of deprivation are corneal opacities. Retinal or macular problems like congenital macular scars are also a type of deprivation amblyopia.
Amblyopia should be treated in early life. The younger the better! That is why I recommend eye exams at a very young age regardless if there are any symptoms or sign that may indicate visual problems. A routine exam during the first year of life can help us detect problems early and start treatment right away. Another great time for an eye exam is just before the child starts kindergarten and before the first grade. I would recommend an exam once a year as a routine.
Treatment options for lazy will depend on the type of amblyopia that we are dealing with but there are some basics that should be covered. Finding out if a child needs glasses is of paramount importance because this is directly related to strabismus and refractive amblyopia and this is the first step towards a successful treatment.
How does an ophthalmologist know if a child needs glasses?
Ophtahlmologists can know if a child of any age needs glasses or not by an exam called cycloplegic refraction which is done using drops.
Once that is sorted out patching is in order. Patching of the sound eye is necessary to force the brain to use the lazy eye and try to develop vision. Current literature says that three hours of patching a day is enough. The time that the child will have to do this depends on the advances seen by the ophthalmologist during follow ups. These follow ups are terribly important because the ophthalmologist has to monitor the progression of the treatment and the prevention of reversed amblyopia (amblyopia that occurs in the sound eye secondary to the patching) . if there is no adaptation of the child to the patching then penalization with cycloplegic -dilating drops is a good choice but close monitoring is necessary. During patching or penalization the child must engaged in visual demanding activities like watching television, play video games , play with coloring books or puzzles.
Some cases of strabismic amblyopia may require surgery after some vision has been recovered or alternation of the strabismus has been achieved.
Deprivation amblyopia usually associated with cataracts may require surgery in most cases with glasses and patching therapy later on.
Prognosis is reserved and is related to the type of amblyopia and the age of patient at the beginning of the treatment. The closer to eight years of age, the poorer the prognosis.
Family history of lazy eye is very important and children with relatives with amblyopia must be examined at an early age.
I hope this brief explanation of amblyopia has been useful and I will like to finish with this advice:
Routine eye exams for your children are necessary if even if there is no suspicion of visual problems because some ophthalmological problems can only be detected by a thorough eye exam by an expert.
Dr. Ricardo Toro
Pediatric Ophthalmology and Strabismus UBC
International Member of the American Association for Pediatric Ophthalmology and Strabismus AAPOS