This blog post was inspired by a presentation by Dr. Matthew Walsh. Dr. Walsh is a Resident in Vision Therapy at SUNY Optometry. All the residents are required to present a 1 hr. continuing education lecture on a topic of their choice. Dr. Walsh’s presentation was entitled: Visual Pathway Pathology Masquerading as Amblyopia in Children.
What is amblyopia? What is not amblyopia? Let’s consider the definition of amblyopia from the American Optometric Association and its clinical application.
Amblyopia is a unilateral or infrequently bilateral condition in which the best corrected visual acuity is poorer than 20/20 in the absence of any obvious structural anomalies or ocular disease.
In other words, amblyopia can only be diagnosed when ocular disease has been ruled out. The optometrist must perform a comprehensive examination including a full evaluation of ocular health. This is likely to include the use of dilating drops in order to examine the retina. The doctor will also perform additional procedures to rule out specific causes of vision loss.
Functional amblyopia occurs before the age of 6-8 years and is attributable to deprivation, strabismus or anisometropic, although it may persist for life once established.
When other causes of the vision loss are ruled out, amblyopia must be ruled IN, by the presence of an identified amblyogenic condition: strabismus, anisometropia/isometropia, or deprivation. Strabismus is an eye turn, and amblyopia is more likely to develop if the eye turn is constant and unilateral. Anisometropia is a a large difference in refractive error between the two eyes; isometropia is very high refractive error in both eyes. Several physical conditions may cause deprivation of visual stimulation to one eye, such as a congenital cataract or a ptosis (droopy eyelid). These amblyogenic factors must be present during the “critical period” of visual development, which is considered the first 8 years of life. The visual system is far less susceptible to disruption after this time period. Although the condition MAY persist for life once established, the visual system is amenable to treatment at almost any age. The critical period applies only to the development of amblyopia, and not to its treatment and resolution.
Amblyopia represents a syndrome of compromising deficits, rather than simply reduced visual acuity, including:
- Increased sensitivity to contour interaction effects
- Abnormal spatial distortions and uncertainty
- Poor eye tracking ability
- Reduced contrast sensitivity
- Inaccurate accommodative responses
Amblyopia is not an eye problem, it is a brain problem. The brain has great difficulty not only recognizing small letters, but also processing and responding to all types of visual information: words printed on a page, faces in a crowd, cars moving down the road, reflections in a mirror, moguls on the ski slope, etc. That’s why treatment of amblyopia involves more than just patching. The brain learns how to process visual information in much the same way humans learn most skills… by starting with a relatively easy task, practicing, and then making the task more difficult as competency increases. Amblyopic brains have to learn many new skills and this is best accomplished in a structured learning environment. A vision therapy program will also emphasize the integration of vision with other sensory inputs and the ability to use vision to guide motor outputs.
One more point to be considered: amblyopia is ruled in when ocular disease is ruled out, except in rare instances when amblyopia AND ocular disease coexist. In addition to performing a comprehensive examination, the optometrist will consider the degree of vision loss and monitor progress during treatment. Only when all the causes of vision loss are considered can the prognosis be determined and the best treatment plan be put into action.