| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH |
|
|
|
|||||||
|
|||||||||
Electronic Letters to:
|
|
Electronic letters published:
![[Read eLetter]](/icons/misc/sectionDOWN.gif){kind=icon}
Treatment Dose-Response in Amblyopia Therapy: MOTAS
Author Response: Treatment Dose-Response in Amblyopia Therapy: MOTAS
|
|
|||
|
Philip Lempert
Send letter to journal:
eyechartplus{at}aol.com Philip Lempert
|
The article by Stewart et al.1 accentuates persistent questions2,3 concerning the methodology and hypotheses of clinical amblyopia studies. The authors point out that even after 250 years, occlusion therapy has not been standardized, there is no proven dose-response relationship, and its effectiveness has not been established. The report then raises additional caveats. Control groups4 are central to the validity of clinical trials. Acuity improvements attributed to treatment in these trials must be differentiated from the effects of correction of significant refractive error, maturation (Robinson BE, et al. IOVS 2000;41:ARVO Abstract 4955), improved literacy, improved performance with repetition,5 and the Hawthorn effect.6 A prospective, randomized, controlled study is the best vehicle for addressing these confounding factors.4 As a minimum, treated and control subjects should have the same frequency of visits to the eye clinic, the same level of parental attention, and a reward similar in magnitude to discontinuance of the patch. This has not been done by Dr. Stewart's group nor by any other amblyopia investigators. The authors noted that visual acuity improved in both the occluded and non-occluded eye. This was also observed by Dorey et al.7 No explanation was offered for this bilateral improvement. The factors improving the acuity of the patched eye were also operative for the unpatched eye, and this bilateral progress undermines the theoretical basis for occlusion therapy. Selection bias is a potential problem for all clinical studies.8 It is illustrated, in this instance, by the exclusion of children with "learning difficulties."1 This criterion is undefined and could exclude children who are apt to be less compliant and/or attentive.9 Likewise, the authors' inclusion of subjects with 20/25 visual acuity enhances the impression of a favorable treatment outcome. The authors are aware of the lack of quantitative data in previous clinical amblyopia studies. Nonetheless, this report also has a paucity of quantitative diagnostic information. No data is offered on the type or degree of refractive errors, strabismus, or other systemic factors, such as low birth weight,10,11 that could be related to impaired vision. Moreover, the authors assert that their subjects "had a full ophthalmic assessment,"1 but they apparently relied on subjective funduscopy to screen for optic nerve disorders. The glaucoma literature contains many examples of the limitations of subjective disc evaluation. For this reason, fundus photography is accepted as being superior, and a variety of new devices and techniques for evaluating optic disc anatomy have come into general use. Failure to apply these clinically available methods risks misdiagnosing patients with optic nerve hypoplasia12,13,14 and/or dysplasia.15 The 1997 York Report found that there were "no studies of natural history of amblyopia, no studies sufficient to draw any firm conclusions about the impact of amblyopia on quality of life, no randomised controlled trials of treatment vs. no treatment."16 In response, studies have been carried out in an effort to provide more justification for occlusion therapy. The objectivity of these researchers may have been compromised by ingrained beliefs and traditional interests since, as the authors of this study point out, "approximately 90% of children's eye services work is amblyopia related"1 and "[t]he mainstay of treatment for more than 250 years has been occlusion of the better eye by an opaque patch."1 In addition, advocacy of a particular therapeutic regimen or involvement with a proprietary device, such as the Occlusion Dose Monitor,17 can potentially skew scientific objectivity. The need for accurate and impartial information in medicine is well recognized.18 Editors of leading international medical journals have noted the risks of selective reporting and recommend "full transparency with respect to performance and reporting of clinical trials."8 Hopefully, these concepts will encourage improvements in the clinical research of amblyopia. Philip Lempert Cayuga Medical Center, Ithaca, New York References 1. Stewart CE, Moseley MJ, Stephens DA, Fielder AR.
Treatment dose-response in amblyopia therapy: The Monitored
Occlusion Treatment of Amblyopia Study (MOTAS). Invest Ophthalmol Vis Sci. 2004;45:3048-3054. |
|||
|
|
|||
|
Catherine Stewart
Send letter to journal:
c.stewart{at}imperial.ac.uk Catherine Stewart
|
Dr. Lempert offers a wide-ranging critique of the MOTAS study recently reported in this journal and elsewhere.1,2 His concerns encompass not only the philosophy of our approach but specific aspects of our findings and methodology. The focus of much of Dr Lempert's criticisms stems from our decision not to have employed a control group, which he cites as being "central to the validity of clinical trials." However, even a cursory reading of our paper reveals that we did not attempt to conduct a clinical trial, a fact which renders much of Dr. Lempert's reproach misplaced. What we did undertake was a determination of the dose-response relationship of occlusion therapy, knowledge of which we stated "would greatly inform the design of future RCTs" (emphasis added).1 We had previously noted that those occlusion regimens chosen for evaluation within RCTs have been chosen on an ad hoc basis, a position from which we sought to advance. Dr. Lempert notes that we report an improvement in fellow eye acuity, the significance of which we fail to elaborate upon. These small, on average around 0.1 log unit gains, seen over the course of our therapy protocol can be attributed to adaptation to spectacle wear ('refractive adaptation') and to the likelihood that, given the age of the children and the duration of the study, some maturation of visual function is likely to have occurred. These are unremarkable observations and, contrary to Dr. Lempert, we do not believe that they "[undermine] the theoretical basis for occlusion therapy." Our exclusion criteria drew further comment. Children were only excluded from MOTAS if their learning difficulties resulted from a previously diagnosed chromosomal abnormality (e.g., Trisomy 21) that would, in all likelihood, render the demands of the study protocol overwhelming either for the parent, the child, or both. We are further criticized for "a paucity of quantitative diagnostic information" but would point out that papers published in Investigative Ophthalmology & Visual Science are subject to a strict word limit, and therefore we chose to present those findings we considered to be of principal interest to readers of a journal with a combined focus on clinical and basic science. We are happy to inform Dr. Lempert that much of the information that he considers lacking in our original report is to be published in a companion paper.3 Finally, we are at a loss to surmise how our "objectivity . . . may have been compromised by ingrained beliefs and traditional interests" solely on the basis of our observation that "overall, approximately 90% of children's eye services work is amblyopia related" and that "[t]he mainstay treatment for more than 250 years has been occlusion of the better eye."1 We would suggest that most informed readers would find these statements to be uncontroversial. We are further criticized for our "involvement with a proprietary device . . . the Occlusion Dose Monitor." Even had we employed the specific device whose US patent Dr. Lempert cites — which we did not — we know of no other generic means of quantitatively recording episodes of patching in children undergoing occlusion therapy that we could have incorporated into the design of MOTAS. Catherine E. Stewart Department of Visual Neuroscience, Imperial College London, UK References 1. Stewart CE, Moseley MJ, Stephens DA, Fielder AR on behalf of the MOTAS cooperative. Treatment-dose response in amblyopia therapy: The Monitored Occlusion Treatment of Amblyopia Study (MOTAS). Invest Ophthalmol Vis Sci. 2004;45:3048-3054. |
|||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH |
eLetters: