When someone tells us that they have a lazy eye, we often have to ask more questions to clarify what the individual means. Most commonly, individuals mean that they either have a strabismus (eye turn inward or outward) also known as a crossed eye or that even with their best glasses, one eye still sees significantly worse than the other eye (amblyopia) and that decrease in vision is not due to eye disease.
A “lazy eye” is not lazy at all. Amblyopia is a disorder of the brain’s ability to use both eyes together as a team. Amblyopia is an active process due to suppression, or the brain actively ignoring the information coming from one eye. In addition to poor visual acuity, people with amblyopia are more prone to have difficulties with depth perception, eye movements related to reading, and visual decision making while driving.
It is important to note that a child with amblyopia rarely has any symptoms. They are generally unaware there is a problem until their better seeing eye is covered.
Strabismus, also known as an “eye turn” or “cross-eye”, is a condition characterized by the improper alignment of the eyes. One of the eyes may look straight ahead, while the other eye turns inward, outward, upward, or downward. The eye turn may be permanent, or may only occur occasionally. At times, the straight and misaligned eye may even alternate positions.
The eye turn is usually noticed in the first few years of the child’s life, but It can also occur later in life, particularly as a result of a traumatic brain injury or a neurological incident.
The misalignment of the eyes in a strabismic patient means that the eyes may be unable to work together to provide the brain with accurate binocular visual information. This can result in blurry vision or double vision, overlapping images, and difficulty with depth perception.
Amblyopia, commonly known as lazy eye, is the eye condition noted by reduced vision not correctable by glasses or contact lenses and is not due to any eye disease. The brain, for some reason, does not fully acknowledge the images seen by the amblyopic eye. This almost always affects only one eye but may manifest with reduction of vision in both eyes. It is estimated that three percent of children under six have some form of amblyopia.
Anything that interferes with clear vision in either eye during the critical period (birth to 6 years of age) can cause amblyopia. The most common causes of amblyopia are constant strabismus (constant turn of one eye), anisometropia (different vision/prescriptions in each eye), and/or blockage of an eye due to cataract, trauma, lid droop, etc.
Amblyopia is a neurologically active process. In other words, the loss of vision takes place in the brain. If one eye sees clearly and the other sees a blur, the brain can inhibit (block, ignore, suppress) the eye with the blur. The brain can also suppress one eye to avoid double vision due to the binocular vision dysfunction. The inhibition process (suppression) can result in a permanent decrease in the vision in the blurry eye that cannot be corrected with glasses, lenses, or lasik surgery.
A lazy eye is likely to be just as strong as the other eye, but because of impaired binocular vision, the signals from the amblyopic eye to the brain have been turned off.
Treatment involves glasses, drops, vision therapy and/or patching. Recent medical research has proven that amblyopia is successfully treated up to the age of 17. Clinical experience of Developmental Optometrists that provide office based vision therapy have shown that the negative effects of amblyopia can be lessened even into adulthood. Treatment of amblyopia after the age of 17 is not dependent upon age but requires more effort including vision therapy. Although improvements are possible at any age with proper treatment, early detection and treatment still offer the best outcome.
To quote Dr. Leonard J. Press, FAAO, FCOVD: "It's been proven that a motivated adult with strabismus and/or amblyopia who works diligently at vision therapy can obtain meaningful improvement in visual function. As my patients are fond of saying: "I'm not looking for perfection; I'm looking for you to help me make it better". It's important that eye doctors don't make sweeping value judgments for patients. Rather than saying "nothing can be done", the proper advice would be: "You won't have as much improvement as you would have had at a younger age; but I'll refer you to a vision specialist who can help you if you're motivated."
Every amblyopic patient deserves an attempt at treatment.
The goal of vision therapy is to teach the brain and eyes to work together to correct the eye misalignment and thus achieve clear and comfortable vision. Vision therapy can also strengthen neuro-visual processing to further alleviate challenges caused by the eye turn.
Vision therapy strengthens the child’s visual skills, resulting in improved reading abilities, clearer focus, better balance, improved coordination, and more accurate depth perception.