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• Vision Restoration Therapy: a reply
  Lies Bouwmeester
  Published on: 5 December 2007
• Vision Restoration Therapy
  Philip L Clatworthy
  Published on: 8 May 2007

• Published on: 5 December 2007

  Vision Restoration Therapy: a reply

  • Lies Bouwmeester
  • Other Contributors:
    • Joost Heutink, Cees Lucas

  Dear Editor,

  We write in response to the eLetter by Philip L Clatworthy on our systematic review ‘the effect of visual training for patients with visual field defects due to brain damage’ (1).

  The focus of the study was to contribute to the development of appropriate methods for patients with visual field defects. During the literature search we were amazed that there were only few methodological sound tr...

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  Dear Editor,

  We write in response to the eLetter by Philip L Clatworthy on our systematic review ‘the effect of visual training for patients with visual field defects due to brain damage’ (1).

  The focus of the study was to contribute to the development of appropriate methods for patients with visual field defects. During the literature search we were amazed that there were only few methodological sound treatments. It became obvious that an important factor appeared to be the difficulty to create sufficient large groups due to the heterogeneity of the patients. Therefore, the RMD studies formed the majority of the selection and the only RCT study of Kasten (2) was part of the overall criticism to the effect of VRT and poor fixation control in the discussion section.

  However, after careful consideration we agree that our judgement of the methodological quality of the RCT of Kasten's study (2) might have been suboptimal on blinding and comparability of groups. Therefore, we thank our colleagues for their precise comments on the methodological quality of the of Kasten’s RCT (2).

  Yours sincerely,

  Lies Bouwmeester, Joost Heutink and Cees Lucas

  References

  1.Lies Bouwmeester MSc, Joost Heutink MSc, Cees Lucas PhD. The effect of visual training for patients with visual field defects due to brain damage. J Neurol Neurosurg Psychiatry 2007 Jun;78(6):555-64. Epub 2006 Nov 29.

  2. Kasten E, Wust S, Behrens-Baumann W, Sabel BA. Computer-based training for the treatment of partial blindness. Nat Med 1998;4(9):1083-1087.

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  Conflict of Interest:
  None declared.

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• Published on: 8 May 2007

  Vision Restoration Therapy

  • Philip L Clatworthy, Neurology Research Fellow
  • Other Contributors:
    • Jean-Claude Baron, Nicholas J Sarkies

  Dear Editor,

  We write in response to a recent review by Lies Bouwmeester(1) et al on the effectiveness of visual training for patients with brain damage. We do not agree with their comments on the study of Kasten et al (2). This remains (with its follow-up study) the only randomised placebo-controlled trial of Vision Restoration Therapy (VRT), and is the foundation of claims of effectiveness for this rehabilita...

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  Dear Editor,

  We write in response to a recent review by Lies Bouwmeester(1) et al on the effectiveness of visual training for patients with brain damage. We do not agree with their comments on the study of Kasten et al (2). This remains (with its follow-up study) the only randomised placebo-controlled trial of Vision Restoration Therapy (VRT), and is the foundation of claims of effectiveness for this rehabilitation technique.

  Bouwmeester's review includes only the retrochiasmal damage section of Kasten's study. It reports this trial to be of good quality. Specifically it states that it earned “a good methodological score on randomisation, blinding and comparability of the groups. We disagree that blinding or comparability was good.

  In relation to blinding, allocation of patients to treatment or placebo groups was double-blind but there is no mention of blinding of visual field measurement. These measurements were largely automated but fixation monitoring required direct visualisation by the examiner. Doubt has been cast on the effectiveness of the additional automatic fixation monitoring procedure. The examiner therefore played an important role in visual field measurement and field testing was thus a potential source of bias. One should be mindful that the strongest criticism of this study has related to the adequacy of fixation control(3,4). In addition there is no comment in the paper regarding concealment; the researchers were probably aware of which group each patient was in from an early point in the study.

  Regarding comparability of groups, Kasten’s Table 1 outlines the baseline characteristics of the two “post-chiasmatic injury groups. We stress that randomisation, particularly in small trials, does not guarantee that groups are comparable. We feel that in this study the groups differ in two important ways.

  First, both groups were heterogeneous with regard to the mechanism of injury. Most notably there were no patients with traumatic brain injury at all in the control group. Also, only 22% (2 of 9) of patients in the treatment group had stroke, compared with 80% (8 of 10) in the placebo group. There is little reason to believe that the pathologies grouped here behave identically, as we are reminded by Robert McFazdean in his recent review of Vision Restoration Therapy(5). Group differences could (at least in part) result from differences in group constitution rather than treatment effects. Certainly one should treat with caution the authors statement that the study illustrates that patients who suffer from partial blindness due to trauma or stroke can benefit from VRT.

  Second, the groups are not equivalent in lesion age. Spontaneous recovery is uncommon more than six months after brain injury, therefore for groups to be comparable the proportion of injuries less than six months old should be equivalent. Lesions in the treatment group were aged 6.8 +/- 11.4 months, compared with 7.2 +/- 6.3 months for the placebo group. A difference of 0.4 months between group means is not worrying but the spread of the groups is important. Assuming that the numbers quoted are mean +/- standard deviation (this information is not in the paper) the variance of the treatment group is over three times that of the placebo group. Since the treatment groups spread is larger than its mean and the lesion age cannot be negative, the distribution must be positively skew with a majority of values below the mean; a substantial proportion of lesions in this group must be well below the mean age (and below 6 months old). This is not true of the placebo group which has a lower spread and higher mean, and therefore contains more lesions more than 6 months old. Thus there is more inequality in the number of lesions less than 6 months old than is apparent from the means of the groups, there being more of the younger, potentially recoverable deficits in the treatment group.

  Taken together these factors indicate a risk of significant bias, in both cases likely to favour a positive finding of the study. Taken with other criticisms of the study they cast further doubt on the validity of its findings. This is a difficult and controversial area but we consider that such methodological shortcomings may account for apparently irreconcilable differences between studies and should be brought to light. Detailed criticism of published papers along with further meticulously designed research will hopefully lay this matter to rest in the not too distant future.

  Philip L Clatworthy

  References

  1. Bouwmeester L, Heutink J, Lucas C. The effect of visual training for patients with visual field defects due to brain damage. A systematic review. J Neurol Neurosurg Psychiatry 2006.

  2. Kasten E, Wust S, Behrens-Baumann W, Sabel BA. Computer-based training for the treatment of partial blindness. Nat Med 1998;4(9):1083-1087.

  3. Horton JC. Disappointing results from Nova Vision's visual restoration therapy. Br J Ophthalmol 2005;89(1):1-2.

  4. Horton JC. Vision restoration therapy: confounded by eye movements. Br J Ophthalmol 2005;89(7):792-794.

  5. McFadzean RM. NovaVision: vision restoration therapy. Curr Opin Ophthalmol 2006;17(6):498-503.

  Competing interests: none

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  Conflict of Interest:
  None declared.

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