Assessment of the outcome of surgical treatment in children suffering from amblyopia due to early-onset cataract
Dr Itay Ben Zion
Amblyopia, or the lazy eye syndrome, is a vision development disorder in which one fails to achieve normal visual acuity, even with prescription eyeglasses or contact lenses. It typically begins during infancy and early childhood. Amblyopia can result from any condition that prevents the eye from focusing clearly. Occasionally, amblyopia is caused by a clouding of the lenses, a condition called cataract. Usually, amblyopia affects one eye, whose input to the brain is suppressed by the dominant eye, but in some cases it can affect both eyes. One of these cases is deprivational amblyopia caused by lack of a clear visual image to both eyes, as in the case of congenital bilateral cataract. A significant number of children remain blind in sub-Saharan Africa due to untreated cataract which causes very poor image quality on the retina, and eventually, deprivational amblyopia.
Untreated bilateral congenital cataract is so devastating, because the brain is deprived of essential visual input during the critical period of visual development in early infancy. It is currently unclear, if and to what extent can a cataract removal surgery turn the wheel back, offering the newly sighted children full sight recovery.
In 2007 Dr. Ben Zion has spent a year in Ethiopia setting up a pediatric ophthalmology service in Hawassa referral hospital. During this period, seventy three children who suffered from early onset cataract were operated by him. The mean age at diagnosis was 7.1 years (range, 0.5-15 years). Fifty-five patients had unilateral cataract and 18 had bilateral cataract. Before surgery, visual acuity ranged from 6/60 to light perception, with 13 eyes (14%) having ambulatory vision (better than hand motion). The mean postoperative visual acuity was significantly improved, ranging from light perception to 6/9. Seventy-five eyes (82%) achieved ambulatory vision.
The figure below depicts the main results of that study. It suggested that cataract surgery may be beneficial even if done at an age which is beyond the classical critical period (7-9 years), although it was clearly limited in its study of functional vision following surgical treatment. It categorized the patients' vision according to standard ophthalmology ranking from mere Light perception (LP), to hand motion (HM), to finger counting (FC) from various distances, and finally to visual acuity measures (6/120 and above).
Project eye-opener has opened the possibility for a rigorous study of these aspects, and the possibilities for better rehabilitation strategies.
Visual acuity measure of the treated eyes (N=91) of 73 congenital cataract patients, before (A) and after (B) surgery. Note the clear shift to the left in B indicating improvement of the patients' condition.