Dear Editor

Dr Newsham's effort to inform parents of children with amblyopia about occlusion therapy is laudable but incomplete. Ethical considerations of informed consent require full disclosure of all aspect of the proposed treatment. In the current instance this compels inclusion of the following points:

1. Occlusion therapy has never been scientifically validated with a randomized, controlled study.

2. The dose / response relationship has never been defined. Flynn et al. stated that 'Success was not related to the duration of occlusion therapy, type of occlusion used'. [1] The variety of treatment protocols accentuate another dilemma 'owing to our paucity of knowledge on the dose-effect relation - a situation one finds hard to imagine for any comparably established therapy outside ophthalmology. In other words we have no understanding of the dose-effect relation of occlusion in amblyopia therapy'. [2]

3.The application of 'greater levels of occlusion being prescribed for more severe amblyopia is compromised by the observation 'that success was related to the depth of visual loss before treatment'.[4]

4. The benefits of treatment are likely to deteriorate following cessation of patching. [5]

5. Visual acuity normally improves as children become more mature, literate, and familiar with vision testing protocols. [6] This is also true for amblyopic eyes. In amblyopic children between 3 and 7 years old without treatment visual acuity was shown to consistently improve in each older age group. [7]

6. Both the occluded and the amblyopic eyes improve at the same rate during treatment. [8]

7. Success in amblyopia treatment is usually defined as improvement by a minimum of three lines. [9]Many of the successfully treated patients, by that criterion, will still not have normal vision at the end of presumably successful treatment. One quarter of treated patients with initial acuity better than 20/100 do not even achieve these limited goals. The comments about achieving normal vision may raise expectations that will not be achieved.

Moreover, it is not clear that performance on reading an eyechart is a complete indicator of visual function. Acuity improvement with occlusion may not be accompanied by improved performance on the other tests - such as vernier acuity or contrast sensitivity. [10]

8. Occlusion therapy does have potential adverse effects beyond disruption of family and social life [11] and interference with education. [12]

9.Despite decades of occlusion therapy the prevalence of amblyopia in the adult population is similar to that of the school-age population. [13] Moreover, 'the prevalence of unilateral amblyopia was not found to be statistically different by age group'. [14] This suggests that long term benefits of conventional therapy are not demonstrated in demographic studies.

Patients and their families should be provided with comprehensive information concerning proposed treatments in order to make appropriate judgements. Physicians are obliged to make this information accurate and inclusive.

References

(1) Flynn JT, Schiffman J, Feuer W, Corona A The therapy of amblyopia: an analysis of the results of amblyopia therapy utilizing the pooled data of published studies. Trans Am Ophthalmol Soc 1998;96:431-50; discussion 450-3.

(2) Simonsz HJ, Polling JR, Voorn R, van Leeuwen J, Meester H, Romij C, Dijkstra BG. Electronic monitoring of treatment compliance in patching for amblyopia. Strabismus 1999 Jun;7(2):113-23.

(3) Newsham D. A randomised controlled trial of written information: the effect on parental non-concordance with occlusion therapy. Br J Ophthalmol 2002;86:787-91.

(4) Beardsell R, Clarke S, Hill M. Outcome of occlusion treatment for amblyopia. J Pediatr Ophthalmol Strabismus 1999 Jan-Feb;36(1):19-24.

(5) von Noorden GK, Attiah F Alternating penalization in the prevention of amblyopia recurrence. Am J Ophthalmol 1986 Oct 15;102(4):473-5.

(6) Robinson BE, Oladeji MM, Bobier WR. Visual acuity assessment in preschool children in Oxford County. ARVO 2000 Abstract # 4955.

(7) The Pediatric Eye Disease Investigator Group. The clinical profile of moderate amblyopia in children younger than 7 years. Arch Ophthalmol 2002;120:281-7. (Table 3 Baseline characteristics according to age at enrollment).

(8) Dorey SE, Adams GG, Lee JP, Sloper JJ. Intensive occlusion therapy for amblyopia. Br J Ophthalmol 2001 Mar;85(3):310-3.

(9) The Pediatric Eye Disease Investigator Group. A randomized trial of atropine vs patching for treatment of moderate amblyopia in children. Arch Ophthalmol 2002;120:268-78.

(10) Levi DM, Polat U, Hu YS. Improvement in Vernier acuity in adults with amblyopia. Practice makes better. Invest Ophthalmol Vis Sci 1997 Jul;38(8):1493-510.

(11) Snowdon SL, Stewart-Brown SL. Amblyopia and Disability: A Qualitative Study. Health Services Research Unit: University of Oxford.

(12) Yang LL, Lambert SR. Reappraisal of occlusion therapy for severe structural abnormalities of the optic disc and macula. J Pediatr Ophthalmol Strabismus 1995 ;32(1):37-41.

(13) Buch H, Vinding T, La Cour M, Nielsen NV. The prevalence and causes of bilateral and unilateral blindness in an elderly urban Danish population. The Copenhagen City Eye Study. Acta Ophthalmol Scand 2001 Oct;79(5):441-9.

(14) Brown SA, Weih LM, Fu CL, Dimitrov P, Taylor HR, McCarty CA. Prevalence of amblyopia and associated refractive errors in an adult population in Victoria. Australia Ophthalmic Epidemiol 2000 Dec;7(4):249-58.