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.
Treatment of neglected long-standing bilateral congenital cataract offers a rare opportunity to study the natural history of treatable diseases. It also provides insight on the pathophysiology of developmental disease; a unique example is Aphakic or Pseudo-phakic Glaucoma. Glaucoma is the most common optic neuropathy and characterized by increased intra ocular pressure (IOP) that leads to a pronounced loss of ganglion cells in the retina and their fibers along the optic nerve. This results in tunnel vision, (i.e. narrowing of the visual field) and eventually blindness.
Aphakic or Pseudo-phakic Glaucoma (also known as Glaucoma following cataract surgery) is a secondary glaucoma that develops in around 20% of babies born with congenital cataract which are operated during early infancy. The current common hypothesis is that this secondary Glaucoma develops after the cataract surgery as a result of outflow blockage due to an inflammatory post-surgical process. In other words, the cataract surgery during infancy is to be blamed for the secondary Glaucoma. However, an alternative hypothesis that could not be ruled out is that the same genetic aberration which resulted in the formation of congenital cataract is responsible for the later development of glaucoma. Our study, taking advantage of "nature's experiment" offered a unique opportunity to discriminate between the above two alternatives. In a recently published paper we found that pediatric cataract surgery at a relatively late age (mean =11 yr) actually reduced IOP (from mean of 18.4mm hg preop to 14.5 mm hg postop). Moreover, of the 15 eyes (24%) which had increased IOP ([ 21 mmHg) preoperatively, only 3 remained at that level after surgery. Positive correlations were found between IOP, axial length and cup-to-disc ratio. None of the patients required pressure-lowering procedures.
Our conclusion is that Bilateral congenital cataracts is likely to be associated with ocular hypertension, with possible progression to glaucoma if left untreated, rather than a direct outcome of surgery in itself.
Our study might therefore prove to be a pivotal study on the subject of Glaucoma following cataract surgery, as it gives another, totally novel, direction of research. We are still in the process of collecting data to substantiate our initial findings. We also found, in the same cohort of patients, a statically significant improvement in visual outcome, when measured either by LogMar or by ambulatory vision (defined as following objects or better). Patients were significantly more likely to have ambulatory VA after the operation. This is supported by previous findings of our group as well as others, describing pediatric cataract extractions at a later age in developing countries. We conclude that even in a setting of late treatment and limited resources, cataract surgery has mostly beneficial visual outcomes.
Finally, a personal note: Before their surgical treatment, almost all children suffer from near-total loss of vision, which severely limits their capabilities for full development of their potential skills. The most rewarding aspect in this project, is to see their first emotional smile after surgery, their acquisition of visual skills, and in some cases seeing them leave the blind school to start an independent life.