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It is important to distinguish the anecdotal from the proven. It is tempting to assume what seems to be a good idea to be the truth. Our media are full of such suggestions and this can filter through to clinical practice.

Beliefs ranging from the wearing of prisms to improve reading performance and undertaking certain eye tracking exercises to improve hand-eye coordination are all based on some good solid science but have yet, in varying degrees, to be completely validated by double-blind randomised controlled trials. The danger is that certain clinical techniques may then be undertaken (and charged for) on the basis of less than completely scientific foundation. This may ultimately be to the detriment of the profession. A counter argument might be that, by introducing new techniques, their success or otherwise may be better determined by their effects. The great danger, however, with any technique that claims to influence visual performance or has any subjective element to it is that the placebo effect may be strong. If there is a perceived difficulty with, for example, reading, the simple act of paying some apparently professional attention to it may influence that process in future. Furthermore, individual successes may be interpreted as proof of success as a whole.

In 2000 Dr Adrian Jennings published a review of all the studies into behavioural techniques (Jennings A (2000), Optometry in Practice, 1: 67-78) and concluded that there was a lack of controlled clinical trials to support the use of behavioural strategies. A new study (yet to be published) by Dr Brendan Barrett of Bradford University examined whether the situation has now changed.

It builds on the work by Jennings and looks at published evidence of the effectiveness or otherwise of behavioural techniques, mainly in refereed and behavioural specialist journals since 2000's report. Interestingly, tinted lenses and overlays for specific reading difficulties are not included as there have been randomised controlled trials in this area and the technique is increasingly being viewed as part of normal everyday practice.

Vision therapy for accommodation and vergence appears to have some benefits, but there are criticisms of study design, such as results suggesting improvement occurring after intense therapy without proper control that may in fact result from the extra attention addressed to the problem. The review concludes that 'further large-scale controlled trials are needed.' It then looks at specific conditions linked with childhood underachievement. There is 'very little concrete evidenceto support the role of vision therapy in the management of' dyspraxia. Despite an association between attention deficit disorders and visual symptoms, it is not certain whether one causes the other and, as such, there is no evidence for the beneficial role of vision therapy as yet. With regard to dyslexia, the report concludes that 'vision therapy cannot currently be considered as an evidence-based treatment for reading or learning disorders'. Interestingly, the Cochrane Collaboration in 2004 commissioned a literature search in this area, soon to be published, that may shed further light on the potential for behavioural intervention in reading disorders.

The use of yoked prisms (bilateral equivalent prisms with the same base direction) is widespread in the US, less so in the UK, in managing postural problems and some near vision binocular instability states. Their use would appear 'controversial' and their ability to alter posture in neurologically normal patients 'highly questionable' and 'experimental'.

The use of low-plus prescriptions for the 'alleviation of near point stress' remains unproven, though the study mentions how their use in pre-presbyopic patients in conventional optometric practice is a point of controversy and widely undertaken in some quarters. Barrett suggests that further research into Rx adjustments would be of benefit to the optometric profession as a whole. There is some proven benefit, albeit limited, in the use of low-plus reading lenses to slow myopic progression. Whether this is a behavioural or conventional intervention is 'a moot point' as the slowing down is minimal. Therapy to slow down myopic progression is widely undertaken in the US and there may be something in this beyond merely a patient adaptation to blur. Yet again, much more research is needed.

There have been no published reports of behavioural approaches to strabismus since 2000, but there are many studies suggesting benefits of amblyopia therapy although 'the benefits of vision therapy in amblyopia treatment over those which accrue from passive modes of therapy are as yet unproven'.

The use of syntonics, practised by a handful of UK behavioural optometrists is 'highly contested'. Perhaps even more significantly, in this Olympic year with sports vision therapy garnering increasing levels of popularity in the UK, 'there is a paucity of evidence to show that therapy produces any beneficial effect'. Only one controlled trial has been published and this showed no benefit after vision therapy.

Finally, the use of yoked prisms in the rehabilitation of neurological conditions (autism, chronic pain, stroke etc), though perhaps more the remit of the occupational therapist, is increasingly being looked at, but again there is a need for more research before any claims about improvement can be justified.

With too little evidence from well designed trials, the report concludes that 'the continued absence of rigorous scientific evidence to support behavioural management approaches, and the paucity of controlled trials in particular, represents a major challenge to the credibility of the theory and practice of behavioural optometry'. While some practitioners may be convinced from their own experience as to the effectiveness of behavioural optometry, the lack of any good sound evidence-based research supporting this stance will always leave it open to the criticism that all it does is pay attention to a perceived problem, thereby influencing its expression. It might also seem less than ethical therefore to charge for such interventions under a cloak of clinical practice until good evidence for the techniques exists.

● The views expressed are those of the clinical editor.

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