By L. E. Leguire Ph.D., MBA
“What do you mean she has lazy eye in both eyes!” exclaimed Judy’s mother. Shocked, she sat in disbelief as the eye doctor explained the results of Judy’s comprehensive eye exam. “Isn’t lazy eye a problem with one eye and not two?” Judy’s mother asked.
Judy has high hyperopia in both eyes, the eye doctor explained; she is a +5 in both eyes. In other words, Judy is very farsighted and will need rather thick glasses in order to see clearly, particularly near objects like books. Right now, Judy can see the 20/40 line on the visual acuity chart with each eye. Given her age of six years, she should see at least the 20/25 line on the eye chart and ideally the 20/20 line. “What can we do to fix her eye problem?” her mother asked. “We’ll place her in the glasses she needs and often glasses alone can fix the problem,” the eye doctor said. “The glasses will also help prevent her eyes from becoming misaligned, a condition called strabismus, which is a common problem in children with high hyperopia like Judy.”
Judy selected the glasses she wanted from the eye doctor’s office and her mother scheduled her for a follow-up appointment in four weeks. Judy liked her glasses and became more interested in looking at books. Also, Judy’s teacher sent a note home saying that that Judy seemed much more interested in reading and seemed more outgoing in school.
One month later, Judy and her mother returned to the eye doctor’s office and Judy’s mother was relieved to learn that Judy’s vision was improving. “Good news!” the eye doctor told Judy’s mother, “Judy’s visual acuity has improved to the 20/30 line and her eyes are straight. Let’s see her back again in one month to chart her progress.”
Another month went by and Judy’s vision continued to improve. At the next eye doctor appointment, Judy’s visual acuity was 20/25 in each eye, which is normal for her age. Both Judy’s mother and the eye doctor were pleased with Judy’s progress and that her “lazy eyes” were normal. Judy continued to do well and at seven years of age her visual acuity was 20/20 in each eye and her eyes remained straight thanks to her glasses.
Amblyopia in both eyes is called “isoametropic amblyopia,” “bilateral amblyopia,” or sometimes “refractive amblyopia.” Refractive amblyopia refers to the fact that the amblyopia is caused by a refractive error (i.e., need for glasses), but may refer to amblyopia in one or both eyes. Usually, bilateral amblyopia is due to high hyperopia—the child is very farsighted and usually has greater than about +4.5 diopters of refractive error in both eyes (Klimek et al, JAAPOS, 2004, p310-313). In children with such high hyperopia, there is about a nine percent chance that they may have bilateral amblyopia (Klimek et al, 2004).
Long-term studies have shown that children with bilateral amblyopia usually have a good outcome once they receive glasses (full hyperopic correction) and wear them for one year; there is a good chance that their vision will return to normal. Fern (1989, Optom Vis Sci, p649-658) found that 57 percent of children with bilateral amblyopia had 20/20 vision after one year of wearing glasses and that no child had worse than 20/40 visual acuity, which is good enough for driving a car, for example. It appears that the degree of hyperopic correction relates to whether or not there was a good outcome—the higher the refractive error, the worse the outcome. In some of the children studied, vision continued to improve after one year of wearing the glasses. Further, there is often a real need to wear glasses for high hyperopia to keep the eyes from turning in, a condition called “accommodative esotropia.”
Sometimes, amblyopia may occur in both eyes during the course of occlusion therapy (patching) for amblyopia in younger children and infants. In the very young, if the infant has typical amblyopia, the standard treatment is occlusion of the good eye. Sometimes, occlusion of the good eye can lead to amblyopia in the occluded eye and a return of normal vision in the previous amblyopic eye—the amblyopia seems to have moved from one eye to the other eye. In these rare cases, the eye doctor may balance occlusion between the eyes—a therapy called “alternating occlusion.” For example, the eye doctor may prescribe occlusion of one eye on one day and to alternate the occlusion between the eyes on different days. Therefore, in this latter case, the patient may have had amblyopia in both eyes, but at different times.