Evidence for the effectiveness of interventions for congenital, infantile and childhood cataract
Certain groups are often excluded from trials of new interventions, typically pregnant women and children, but also people unable to give informed consent. Children are not included perhaps because of a distaste for ‘experimenting’ on little ones and a reluctance to admit to clinical uncertainty when faced with anxious parents.
Unfortunately such attitudes lead to continuing uncertainty about the effectiveness of key interventions in these population subgroups who are often, ironically, the subject of our special concern.
Cataract in children is an important cause of childhood blindness and treatment can make a difference if it can be delivered effectively and in time. But there are many questions about how this is best achieved – clinical questions which need good evidence for an answer. And before addressing these, there are others – about how best to detect cataracts in babies (there are no randomised trials as yet) and whether or not there is any potential for prevention. Immunisation for rubella is relevant, and, of course, understanding genetics.
Treatment of bilateral cases
There are numerous surgical procedures described for the treatment of cataract including peripheral iridectomy (for central opacities), needling and aspiration, lensectomy, optic captured posterior chamber intraocular lens after phaco-emulsification (termed ‘bag in the lens’ procedure by one group). So what is the best procedure in terms of visual outcome, short and long term complications and cost-effectiveness? A Cochrane Systematic review was published in 2001 asking the question “What is the effectiveness of surgical interventions for bilateral congenital cataract”. As in most Cochrane reviews, only the best evidence was included, i.e. randomised controlled trials. Only one trial was found comparing pars plana lensectomy to lens aspiration and primary capsulotomy. Though both groups did well in terms of visual outcome, there were more complications in the aspiration group but follow-up was not long enough to address the important concern about late glaucoma after lensectomy. The review is now in the process of being updated. Since it was published, clinical practice has been changing and lens implantation in the bag with or without primary posterior capsulotomy or with capture of the optic within anterior and posterior capsulorhexis is becoming more common. The age at which surgeons are happy to intervene is also falling.
The situation is made more complex by the fact that several different parameters are being modified simultaneously so that it is hard to determine which are the key components to improved outcome.
Since 2001, seven new trials have so far been identified including a large one from China comparing acrylic and polymethyl methacrylate lenses (though it is not clear if this was truly randomised) and four on various aspects of technique relating to optic capture. The other two are on the use of trypan blue for capsulorhexis and a comparison of two methods of hydrodissection.
Treatment of unilateral cases
The treatment of unilateral congenital cataract is another question and is the subject of much discussion though so far there are no trials. A study examining the feasibility of randomising children in USA to intraocular lens or contact lens correction of aphakia has been published in the Journal of American Association of Pediatric Ophthalmology and Strabismus (AAPOS). This article also describes the considerable amount of stress that such interventions place on both the child and parents when the results of preserving useful sight in the cataractous eye are not great.
The treatment of stimulus deprivation amblyopia in both unilateral and bilateral cases is also in need of good evidence of effectiveness and a title for a Cochrane review on this subject has been registered.
This remains an issue of intense importance in the control of childhood blindness and, as yet, the quality of evidence is relatively poor. But the signs are encouraging and there are indications that those involved in this work are increasingly aware of the need for it. It is of particular importance in countries with emerging economies where the volume of need is substantial and the opportunities for high quality research now exist.