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A comparison of various methods of treatment of amblyopia: A block study
CURRENT
OPHTHALMOLOGY
361
Photoreceptor recovery following retinal reattachment has been estimated by measurement of outer segment length. Unfortunately there are insufficient numbers of eyes examined at each time point, and no sampling numbers given, to conclude that outer segment lengths differed significantly with changes in detachment and/or reattachment times. The data presented suggests that longterm detachment, even after longterm reattachment, results in areas of shortened outer segments, atrophied inner segments, and a thinning of the outer nuclear lamina. This study demonstrates that the RPE-photoreceptor interface can regain an extensive amount of normal morphology after retinal reattachment, and that abnormalities are localized to small areas. These abnormalities appear to become more extensive with prolonged periods before reattachment. The paper is important for it provides a possible understanding of poor visual recovery following macula detachment. LOUISE WALKER, PH.D. 1.m CONSTABLE, M.D. NEDLANDS, WESTERN A~JSTRALIA
A Comparison of Various Methods of Treatment of Amblyopia: A Block Study, by P.G. Watson, A.S. Sanac, and M.S. Pickering. Truns Ophthalmol Sot UK 104:319-328, 1985 This study reports the results of conventional full-time occlusion compared to partial occlusion or minimal occlusion with the cam stimulator in the treatment of amblyopia. This study involved two disparate populations, one from Cambridge, England, the other Ankara, Turkey. Each of these methods of treatment was equally effective as an initial therapy. However, ifone form of therapy was ineffective or only partly successful, then further improvement could be obtained by using an alternative method in many patients. A quarter of the patients showed no improvement in vision at all despite vigorous and active treatment. It is suggested that minimal occlusion should be the first method of treatment, but if this fails, either or both conventional occlusion and cam treatment should be used, and therapy should not be abandoned until all these methods have been attempted. (Aurhor’s address: P.G. Watson, F.R.C.S., Addenbrooke’s Hospital, Cambridge, England)
Comment Dr. Watson and coworkers have performed a study comparing the effect on amblyopia of full-time and short-time occlusion. The latter method can be subdivided into “minimal occlusion” performed for 20-30 min per day and the CAM treatment, consisting of stimulation of the amblyopic eye with square wave gratings for 7-10 min once a week. The main finding is that all three methods are equally effective in relieving amblyopia and that treatment effects do not depend on the type ofamblyopia (i.e., strabismic and nonstrabismic), the age of the child at treatment or the length of the treatment period. To most clinical ophthalmologists these findings would seem quite surprising, since one would expect full-time occlusion to be superior to other treatment. My might work, but also why I find this study is comments will concern ideas on why “minimal occlusion” inconclusive in demonstrating it. At the outset it would be fair to state that the CAM treatment does not work in the fashion originally the specific spatial frequency channels that suffer from disuse in proposed, i.e., as a means of activating amblyopia. In my opinion, it has been demonstrated beyond doubt that the rotating striped pattern does not contribute to CAM effects but that CAM is basically a method of “minimal occlusion,” utilizing the visual stimulation of near work and eye-hand cooperation during a period of attention and alertness. It has been shown in animal experiments that the orientation specificity of striate neurons can be augmented during attention and reduced during drowsiness. It is possible that noradrenergic pathways are active in the alertness reactions of the visual cortex, as shown in animal experiments, and it is also possible that the locus coerulius or other alertness controlling areas in the brainstem are involved. If such mechanisms were also active in humans, this would provide a functional explanation for the effects of minimal occlusion on visual acuity in amblyopia, and possibly also for the beneficial effects of a change of treatment, as demonstrated by the authors. In the latter case, other psychological factors could play a part as well.
362
Surv Ophthalmol
3 l(5) March-April
1987
CURRENTOPHTHALMOLOGY
can improve visual acuity in amblyopia, It is suggested in this paper and others that “minimal occlusion” but it is not yet proven that it is as effective as full-time occlusion in this respect. In order to show this, a controlled study is needed, preferably a prospective one. The groups of amblyopic children tested should be matched with respect to age, onset and duration of amblyopia, type of amblyopia, previous treatment, and so on. The treatment schemes should be randomly assigned to children in each group, with no linkage to socioeconomic factors, which might influence the capabilities of the parents to assist in the treatment. To some extent this requirement was met in the present study. The kind ofstudy I suggest would be a tedious study to carry out, but, in my opinion, it is the only way many of the questions that arise from the present study could be answered. 1) Why were so many children (25-30%) treatment failures, and how is this correlated to the different amblyo-genetic factors and their occurrence during the so called critical period ofvisual development? 2) Why are treatment effects not related to age? Does this depend on previous treatment, and what was the effect of that treatment? 3) Why are treatment effects independent of type of amblyopia? Is there a difference between strabismic and nonstrabismic cases? (It has been shown in recent studies that visual functions in the central and peripheral parts of the fields differ in strabismic and nonstrabismic amblyopia, with m-ore extensive deficits in the nonstrabismic group.) 4) How does the measurement ofacuity in percent affect the outcome of the statistical analysis? Would it be better to refer all treatment effects to the acuity level before treatment? (In the present study a twofold increase in acuity from 10 to 20% will not have the same weight as an increase from 40 to 80% in the statistical analysis of the results.) Thus, I think that a controlled study should be undertaken to evaluate the efficiency of “minimal occlusion.” Some attempts have been made in this respect but not on the scale necessary to demonstrate conclusively whether minimal occlusion is a useful alternative to full-time occlusion. In view of the great psychological burdens that amblyopia treatment may impose on the child and its parents, such a study is worthwhile and badly needed. GUNNAR LENNERSTRAND STOCKHOLM. SWEDEN
OPHTHALMOLOGY
361
Photoreceptor recovery following retinal reattachment has been estimated by measurement of outer segment length. Unfortunately there are insufficient numbers of eyes examined at each time point, and no sampling numbers given, to conclude that outer segment lengths differed significantly with changes in detachment and/or reattachment times. The data presented suggests that longterm detachment, even after longterm reattachment, results in areas of shortened outer segments, atrophied inner segments, and a thinning of the outer nuclear lamina. This study demonstrates that the RPE-photoreceptor interface can regain an extensive amount of normal morphology after retinal reattachment, and that abnormalities are localized to small areas. These abnormalities appear to become more extensive with prolonged periods before reattachment. The paper is important for it provides a possible understanding of poor visual recovery following macula detachment. LOUISE WALKER, PH.D. 1.m CONSTABLE, M.D. NEDLANDS, WESTERN A~JSTRALIA
A Comparison of Various Methods of Treatment of Amblyopia: A Block Study, by P.G. Watson, A.S. Sanac, and M.S. Pickering. Truns Ophthalmol Sot UK 104:319-328, 1985 This study reports the results of conventional full-time occlusion compared to partial occlusion or minimal occlusion with the cam stimulator in the treatment of amblyopia. This study involved two disparate populations, one from Cambridge, England, the other Ankara, Turkey. Each of these methods of treatment was equally effective as an initial therapy. However, ifone form of therapy was ineffective or only partly successful, then further improvement could be obtained by using an alternative method in many patients. A quarter of the patients showed no improvement in vision at all despite vigorous and active treatment. It is suggested that minimal occlusion should be the first method of treatment, but if this fails, either or both conventional occlusion and cam treatment should be used, and therapy should not be abandoned until all these methods have been attempted. (Aurhor’s address: P.G. Watson, F.R.C.S., Addenbrooke’s Hospital, Cambridge, England)
Comment Dr. Watson and coworkers have performed a study comparing the effect on amblyopia of full-time and short-time occlusion. The latter method can be subdivided into “minimal occlusion” performed for 20-30 min per day and the CAM treatment, consisting of stimulation of the amblyopic eye with square wave gratings for 7-10 min once a week. The main finding is that all three methods are equally effective in relieving amblyopia and that treatment effects do not depend on the type ofamblyopia (i.e., strabismic and nonstrabismic), the age of the child at treatment or the length of the treatment period. To most clinical ophthalmologists these findings would seem quite surprising, since one would expect full-time occlusion to be superior to other treatment. My might work, but also why I find this study is comments will concern ideas on why “minimal occlusion” inconclusive in demonstrating it. At the outset it would be fair to state that the CAM treatment does not work in the fashion originally the specific spatial frequency channels that suffer from disuse in proposed, i.e., as a means of activating amblyopia. In my opinion, it has been demonstrated beyond doubt that the rotating striped pattern does not contribute to CAM effects but that CAM is basically a method of “minimal occlusion,” utilizing the visual stimulation of near work and eye-hand cooperation during a period of attention and alertness. It has been shown in animal experiments that the orientation specificity of striate neurons can be augmented during attention and reduced during drowsiness. It is possible that noradrenergic pathways are active in the alertness reactions of the visual cortex, as shown in animal experiments, and it is also possible that the locus coerulius or other alertness controlling areas in the brainstem are involved. If such mechanisms were also active in humans, this would provide a functional explanation for the effects of minimal occlusion on visual acuity in amblyopia, and possibly also for the beneficial effects of a change of treatment, as demonstrated by the authors. In the latter case, other psychological factors could play a part as well.
362
Surv Ophthalmol
3 l(5) March-April
1987
CURRENTOPHTHALMOLOGY
can improve visual acuity in amblyopia, It is suggested in this paper and others that “minimal occlusion” but it is not yet proven that it is as effective as full-time occlusion in this respect. In order to show this, a controlled study is needed, preferably a prospective one. The groups of amblyopic children tested should be matched with respect to age, onset and duration of amblyopia, type of amblyopia, previous treatment, and so on. The treatment schemes should be randomly assigned to children in each group, with no linkage to socioeconomic factors, which might influence the capabilities of the parents to assist in the treatment. To some extent this requirement was met in the present study. The kind ofstudy I suggest would be a tedious study to carry out, but, in my opinion, it is the only way many of the questions that arise from the present study could be answered. 1) Why were so many children (25-30%) treatment failures, and how is this correlated to the different amblyo-genetic factors and their occurrence during the so called critical period ofvisual development? 2) Why are treatment effects not related to age? Does this depend on previous treatment, and what was the effect of that treatment? 3) Why are treatment effects independent of type of amblyopia? Is there a difference between strabismic and nonstrabismic cases? (It has been shown in recent studies that visual functions in the central and peripheral parts of the fields differ in strabismic and nonstrabismic amblyopia, with m-ore extensive deficits in the nonstrabismic group.) 4) How does the measurement ofacuity in percent affect the outcome of the statistical analysis? Would it be better to refer all treatment effects to the acuity level before treatment? (In the present study a twofold increase in acuity from 10 to 20% will not have the same weight as an increase from 40 to 80% in the statistical analysis of the results.) Thus, I think that a controlled study should be undertaken to evaluate the efficiency of “minimal occlusion.” Some attempts have been made in this respect but not on the scale necessary to demonstrate conclusively whether minimal occlusion is a useful alternative to full-time occlusion. In view of the great psychological burdens that amblyopia treatment may impose on the child and its parents, such a study is worthwhile and badly needed. GUNNAR LENNERSTRAND STOCKHOLM. SWEDEN