By L. E. Leguire Ph.D., MBA
Vision Recovery in the Amblyopic Eye Following Loss of Vision in the Good Eye
In older children as well an in adults with permanent amblyopia, it is strongly recommended that the amblyopic patient wear glasses to protect the remaining good eye because amblyopic patients are at an increased risk of injury to that eye. For example, Tierney (1989) notes that amblyopic patients have a probability of injury to the remaining good eye of between 0.1 and 0.2 percent (about 1-2 per 1,000 patients). Therefore, if your child has completed therapy and still has significant amblyopia, protective glasses are in order. In addition, the glasses should be made with polycarbonate lenses – a very high impact plastic (i.e., glasses have less of a chance of shattering when hit by a high velocity object).
The implicit assumption of requiring amblyopic patients to wear glasses to protect the remaining good eye is that if the patient lost vision in their good eye that they would have to rely on the poor vision in the amblyopic eye to live. Many patients with permanent amblyopia are legally blind in their amblyopic eye, so if they lost vision in their good eye they would be, to say the least, worse off. However, as with most things, there are exceptions to the rule and this applies to amblyopia.
Over the past 20 years or so, there have been numerous “case reports” of an amblyopic patient losing vision in their good eye through disease or accident and, surprisingly, vision in the amblyopic eye actually improved! While this is an exception to the general rule, the phenomenon has occurred enough times to warrant study; and perhaps, knowledge gained from these unusual cases might provide avenues for future research.
Hoffmann and Lippert (1982) performed animal studies in which the animals were made amblyopic (by blocking vision to one eye during early life and thus creating amblyopia) and then the good eye was either closed (eyelids closed) or the good eye was surgically removed. They found that vision in the amblyopic eye was about 33 percent better when the good eye was removed compared to when the eyelids were just closed. As a follow-up to this study, Rabin (1984) first reported about an amblyopic patient who lost central vision in the good eye and there was subsequent improved vision in the amblyopic eye.
Tierney (1989) reported a case study of a 65-year-old man who had a hemorrhage in his good eye and vision recovered in his amblyopic eye. Lengyel and Valmaggia (2006) also reported a patient who lost vision in the good eye via a stroke. Following the loss of vision in the good eye due to the stroke (retinal arterial occlusion), the patient went from about 20/200 visual acuity (legal blindness) to 20/63 (good enough to drive a car during the day) over a three-month period.
The million-dollar question is why? Why is vision in the amblyopic eye able to recover following loss of vision in the good eye? No one really knows. Animal studies of amblyopia show that structural changes take place in the brain due to amblyopia, like smaller cells and less number of cells responsible for vision in the amblyopic eye. The old adage “Use it or lose it,” comes to mind. However, there are also strong interactions, at the cellular level, between the good eye and amblyopic eye, even in adults.
The good eye is known to suppress or “turn-off” some of the vision in the amblyopic eye. Such a suppression process helps to create single vision, particularly when the eyes are not pointing in the same direction, such as in the case of amblyopic patients with an eye misalignment (i.e., strabismus). In addition, many cells in the visual parts of the brain are binocular; that is, the cells respond to visual information coming from either eye, with the good eye providing more or better input than the amblyopic eye. It is possible that when a patient loses vision in the good eye, the amblyopic eye is released from suppression and thus “sees better.” On the other hand, perhaps the binocular cells of the brain are able to respond better to input from the amblyopic eye once visual input from the good eye is of a poor quality or, in the worse case, no longer available (as in the case of the good eye being removed).
Whatever the reason for vision recovery in the amblyopic eye following loss of vision in the good eye, it is hoped that no one will ever have to face such a situation—better to protect the remaining good eye from injury in the first place.
Tierney, DW. Vision recovery in amblyopia after contralateral subretinal hemorrhage. J. American Optometric Assoc. 1989; 60 (4), p281 – 283.
Hoffmann, KP and Lippert, P. Recovery of vision with the deprived eye after loss of the non-deprived eye in cats. Hum Neurobiology. 1982; 1 (1), p45 – 48.
Rabin, J. Visual improvement in amblyopia after visual loss in the dominant eye. Am. J. Optometry and Physiological Optics. 1984, 61 (5), p334 – 337.
Lengyel, D and Valmaggia, C. Visual improvement of an amblyopic eye in an adult patient after vision loss in the non-amblyopic eye (German) Klin Monatsbl Augrnheilkd. 2006, 223 (5), p462 – 464.