CAMBRIDGE STIMULATOR TREATMENT FOR AMBLYOPIA An evaluation

Eighty consecutive patients with amblyopia ex anopsia were treated with the Cambridge Stimulator (Cam.). Each patient received an average of six, 15 minute treatment sessions at a frequency of 7-2 per week. Treatment was terminated after two consecutive treatments indicated no change in visual acuity. Sixty-nine patients were given mmimal occlusion simultaneously with Cam. treatment. Eleven patients were given full-time conventional occlusion simultaneously with Cam. treatment. Of the first group, 47% achieved 6/ 12 or better visual acuity, although if the 14 eccentric fixators were excluded, 60% achieved 6/ 12 or better visual acuity. Of the second group, 91 % improved to 6/ 12 or better vision. This means the patients treated with full-time occlusion and Cam. showed an improvement of visual acuity of near/y twice the extent of those patients treated with minimal occlusion and Cam. over the same period of time. INTRODUCTION In the treatment of amblyopia ex anopsia patching of the good eye is routinely acceptable for a period of 3-6 months in patients with less than 6/18 vision. There are several disadvantages with this form of treatment. One problem is the prolonged time factor and, consequent on this, the educational and psychological handicap placed on the child. This results in a 30?k failure rate in tolerating the patch.’ There is also a risk factor, in that patching the good eye disrupts all the binocular visual reflexes and so tends to cause ocular deviation.2 The dissociative effect of a patch may increase a cosmetically acceptable strabismus to uncosmetic dimensions creating a need for cosmetic surgery. In many cases occlusion has to be reapplied, as amblyopia can recur until a child is eight to nine years of age. In certain cases, where all horizontal recti have already been operated and amblyopia recurs yet again, it is difficult to decide which is best for the patient to improve the amblyopia at the risk of oiving the patient an uncorrectable, uncosmetic squint with 9 medico-legal implications or to leave him with an aniblyopic eye for the duration of his life. Another problem with full-time conventional occlusion therapy is that in some cases, the good eye can become amblyopic suddenly, creating either a situation of bilateral amblyopia or amblyopia of the originally good eye. From the author’s experience, Atropine occlusion is an effective therapy only if the patient’s amblyopic eye has an acuity of 61 12 or better. The treatment of amblyopia has been considered to be unsatisfactory for all the previously mentioned reasons. Ingram, in a survey as recent as 1979, reported that in a series of over 200 patients with a three year follow-up, there was no measurable improvement in amblyopia despite treatment involving a large number of outpatient attendances3 The first clinical results of Cam. treatment were reported by Campbell in 1978.4 Cam. treatment for amblyopia consists of rotating high-contrast square-wave gratings in front of the amblyopic eye while the child is performing some task requiring (‘AMI3RIIX;L: STIMULATOR I R E A T M E S T F O K A M B L Y O P I A 12 1 visual concentration. Campbell's paper claimed that in a course of three 7 minute treatments, 73'; of patients achieved 6/12 or better vision. While this method of treatment was considered to be a highly significant advance in the treatment of strabismic and aniso-metropic amblyopia there was concern as to possible dangers involved with its use. Because of the effectiveness of the treatment, it was thought that intractable diplopia could be induced with all its disastrous and possible medico-legal consequences. The Cam. method of treatment as an alternative to conventional occlusion attracted great interest as it reduced the patching of the good eye to terms of minutes rather than months and thus eliminated the educational and psychological handicap to the child. It also reduced the risk of dissociation of binocular reflexes and therefore eliminated the essential problems associated with conventional full-time occlusion therapy. Mrrrericrls and Methods This series of 80 patients was drawn from one orthoptic private practice. Treatment was standardised and carried out by one person. Patients were assessed for treatment in the manner described by Banks et a1 in 197g5. All patients were fully assessed orthoptically and ophthalmologically and wore their glasses where relevant. Visual acuity was tested for near and distance with linear charts and Sheridan Gardiner single optotypes. Where the age of the child permitted, all four visual acuity tests were performed pre and post Cam. treatment sessions. As it is sometimes felt that amblyopia is due to subtle macular changes not detectable by ordinary ophthalmoscopy, two additional tests were undertaken to try to better assess macular function. These were the checking of fixation with a visuscope and the Arden contrast sensitivity test.6 Treatment consisted of viewing an apparatus of which any one of a range of high contrast. sharp-edged gratings were rotated at one revolution per minute behind a transparent plate on which the child was encouraged to play drawing games to ensure his concentration. If two children of approximately the same age were seated in front of the same viewing apparatus with 122 the non-amblyopic eye occluded, co-operation and concentration tended to be better than giving individual treatment sessions. Contrast thresholds were assessed for the normal and the amblyopic eye both pre and post Cam. treatment using circular square-wave. test plates of , varying contrasts. These plates contained high. medium and lo\v spatial frcquencies and were presented to the child. besinning :it the highest contrast. The child \{.as asked to identify the correct orientation. This procedure determined the grating size to he used for treatment and also assessed visual performance. A grating coarser than the tinest one perceived b! the child was placed on the turntable as a starting point and at intervals. relative to the total treatment time. this was progressively changed to ;I tiner ?rating. The Arden grating contrast sensitivit! plates were dso used. where the age of the child permitted. to assess visual function. The methods ot' treating the patient were similar to those reported previously but with two main modifications. In t1ii.j beries. each treatment session lasted for 15 minutes (rather than 7 minutes). All patients were encouraged t o occlude their good eye either on a full-time basis or for a minimal, daily period of fifteen minutes at home. during which time they were required to perform some difficult visual task (for euniple. filling in the 0's in the newspaper) in conjunction with their Cam. treatment. Patient.; in the previous reports were not given additional occlusion. The patients in this series were treated 1-2 times weekly. receiving an average of 6 treatment sessions. Treatment was ceased when visual acuity remained unchanged at two consecutive treatment sessions. Resicks Age of' oiiset. Of the 80 patients treated. 20 were anisometropic aniblyopes and 60 were strabismic amblyopes. The mean age of this series was 7-8 years (Figure la). 40'; of these patients were referred to their respective ophthalmologists by the School Medical Service and 5 7 were referred by the Lions Save-Sight Foundation amblyopia screenings. The mean age of onset was 4.4 years (Figure lh) and the mean age of formal ophthalmological diagnohih i t a s 4.7 years (Figure Ic). 4tiSTK.4I.I.A\ l O l R \ 41. 0 1 OPH-I HAI .MOI.O<;Y OlSTRlBUTlON OF A6E OF .. AMBLYOPES TREATEO WITH CAM