Refractive amblyopia is the most common type of lazy eye. It occurs most commonly when a child is born with a high refractive error (diminished acuity or blurriness) in one eye, despite having perfectly aligned eyes. For example, one eye may have significant nearsightedness or farsightedness, while the other eye does not. Or one eye may have significant astigmatism and the other eye does not. This develops because of abnormal visual experience early in life that changes the nerve pathways between a thin layer of tissue (retina) at the back of the eye and the brain. The weaker eye receives fewer visual signals. Eventually, the eyes' ability to work together decreases, and the brain suppresses or ignores input from the weaker eye.
Amblyopia generally develops from birth up to age 7 years. It is the leading cause of decreased vision among children. Rarely, lazy eye affects both eyes.
So what is refractive amblyopia? Because one eye has good vision and the other does not, the vision of the child does not develop normally. A difference in sharpness of vision between the eyes (refractive amblyopia). A significant difference between the prescriptions in each eye — often due to farsightedness but sometimes to nearsightedness or an uneven surface curve of the eye (astigmatism) — can result in lazy eye or refractive amblyopia. In such cases, the brain relies on the eye that has less uncorrected refractive error (better acuity) and "tunes out" the blurred vision (this is called suppression) from the other eye, causing amblyopia in that eye from disuse. The brain uses images from the two eyes to determine things like, spatial awareness and movement. When the brain does not get equal signals from both eyes, it must choose the signal that is the clearest and strongest.
It is important to note that a young child with amblyopia rarely expresses any symptoms or knows that what they are experiencing isn't normal. Refractive amblyopia cannot be seen -- it is not the same as strabismic amblyopia which often times can be seen due to a misalignment of the eyes. Amblyopia must be diagnosed by an eye care professional and early intervention is important. It is the most common eye problem among children and left untreated it can cause significant problems and lead to vision loss.
People with refractive amblyopia will have poor binocular vision skills to varying degrees. This can cause difficulty with things like driving and parking a car, difficulty with reading and learning, and more. They may seem clumsy or uncoordinated. Patients have reported trouble with things like riding a bike, navigating a room full of people, seeing in 3D, participating in sports, etc.
There are some patients, however, that are able to build work arounds for the refractive amblyopia. In these cases, patients don't often report double vision, or other more common symptoms of refractive amblyopia. In fact, they may even be self reported reading fanatics. These patients may also benefit from vision therapy and/or Vivid Vision. They may have deep imbedded work arounds but ultimately can benefit from vision therapy and/or Vivid Vision.
Improvements are possible at any age, but early detection and treatment offer the best outcome. Even if no signs or symptoms are noticed, it is important that children are taken to an optometrist for a comprehensive visual assessment during the first year of life to help catch problems like refractive amblyopia at an early stage.
Treatment of refractive amblyopia can include vision therapy, eye patching, eye drops, refractive surgery, or a combination of those options. Vision therapy may include the use of virtual reality technology in treatment of lazy eye. It is also common for patients with refractive amblyopia to wear prescription lenses or contact lenses as a form of or as part of their treatment.
Why is it important, as a primary care optometrist, to know how to diagnose and treat amblyopia? First, it is not an uncommon condition; the prevalence has been reported to be between 1% and 5% of the population, and it is the most common cause of vision impairment in children and young adults. Second, it is critical not only to the ocular health but also to the overall well-being of our patients that we correctly diagnose and treat this condition.
It is often difficult to convince patients and parents to invest time and money into treating an amblyopic eye if the patient has good vision in the fellow eye. It is important to educate all parties about what happens if the child loses vision from injury or ocular disease in the non-amblyopic eye. Patients with amblyopia have almost twice the incidence of bilateral visual impairment as those without amblyopia, and their lifetime risk of serious vision loss in both eyes is estimated to be between 1.2% and 3.3%. A bilateral loss of visual acuity can impact a patient’s ability to drive, maintain employment and function in the world. It is our job, therefore, to not only diagnose and manage this condition, but to also educate our patients on the importance of treating amblyopia.
Eye patching is a time-tested treatment for amblyopia. It is low-risk and relatively low-cost. Kids often dread wearing it, and parents can have trouble forcing and monitoring their children to keep the patch on; however, it has improved the vision of millions of patients with lazy eye for the last thousand years.
Eye patching should typically be tried before or alongside other treatments like vision therapy and Vivid Vision. Eye patching doesn't work for everyone, particularly adults, and the amblyopia often regresses. Binocular visual experience is necessary in successful treatment of amblyopia and strabismus, and this experience is not provided during eye patching. Most cases require something more targeted and comprehensive such as vision therapy and/or Vivid Vision. Vision therapy is a comprehensive approach to the use of both eyes together that should be considered for all patients with refractive amblyopia. Vision therapy engages the patient as well as the eyes and brain in a new and novel way. This aids in the treatment of refractive amblyopia and should be considered for treatment with patients with refractive amblyopia.
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