Who should decide on yoked prisms?

With reference to the recent letter from Nicholas Whittingham, I would like to shed some light on the subject of the use of yoked prisms in learning difficulties. I have been using yoked prisms (prisms with the bases in the same direction) for over three years and have found them highly successful in a large number of cases to improve reading performance. Yoked prisms have been used for many years by behavioural optometrists in the US and Australia by practitioners such as Dr John Streff, formerly of the Gessell Institute of Child Development, and Professor Ed Howell from Melbourne University to improve educational, postural, and reading performance. These prism lenses, as do low plus, seem to work by expanding peripheral awareness and enlarging the 'field' for detailed visual processing. This can be easily demonstrated with the MacDonald Form Field Chart. It is not possible to give a definite explanation in this particular case as many of the tests I consider normal, such as pursuit and saccadic tracking, posture, accommodative facility and flexibility, ACA ratios, stereo acuity, binocularity, etc, are not included. I have submitted articles to optician on reduced functional fields in children and the use of low plus and yoked prisms to expand these fields, which expand on this in more detail. With reference to the comment relating to an explanation for the health authority, I do not consider that they have any right to an explanation for the lenses we prescribe. The optometrist is the refraction expert, not a civil servant form filler. Otherwise we would be spending all our time explaining why our patients, and in particular, children, 'need' bifocals for example - surely just readers are adequate. Geoff Shayler Wareham, Dorset