|Year : 1983 | Volume
| Issue : 4 | Page : 375-378
Treatment of amblyopia by cam vision stimulator study of 40 cases
Anil K Bavishi, Chhotubhai K Patel
Nagri Eye Hospital, Ellisbridge, Ahmedabad-6, India
Anil K Bavishi
Above Imperial Hotel, Near Relief Cinema, Relief Road, Ahmedabad-1
Source of Support: None, Conflict of Interest: None
|How to cite this article:
Bavishi AK, Patel CK. Treatment of amblyopia by cam vision stimulator study of 40 cases. Indian J Ophthalmol 1983;31:375-8
Banks and others found that visual acuity of an amblyopic eye may recover markedly after brief periods of inspection of high contrast grating stimuli. Their observations have led to a new treatment for amblyopia, based upon a device marketed by Clement Clarke as Cambridge vision stimulator popularly known as CAM Vision stimulator.
| Materials and methods
In order to test the efficacy of the instrument 40 cases of amblyopia were treated and examined, each having atleast 2 lines of amblyopia with a maximum of 6/12 in the amblyopic eye.
All children in this survey were refracted under atropine and a full correction was ordered. A fundus examination was also carried out and only those with normal fundi were included in this study. Any glasses that had been prescribed were worn for atleast 10 days before CAM treatment was started. Complete orthoptic examination was carried out in each patient before and after the study. At each CAM session visual acuity for Distance and near was tested before and after treatment using both linear optotype and single letters.
| Use of apparatus
Before starting the treatment, the contrast sensitivity is assessed.
Seven plates are provided with high spatial frequencies. This set contains spatial frequency grating at different contrast levels. The threshold can be measured by placing all the gratings of the set on a table in front of the child and asking the child to indicate the orientation of the grating by pointing the directions the lines are running. The amblyopic eye is occluded and the low spatial frequency (wide stripes) is tested first, ending with the highest spatial frequency (Narrow stripes) last.
The faintest (lowest contrast) grating for which the child can correctly identify its orientation is recorded as the threshold. The normal eye is then covered and the test repeated for the amblyopic eye.
Since the distance of the grating from the child determines its spatial frequency, this distance should be recorded and maintained constant before and after treatment. The spatial frequency of each grating is marked assuming a working distance of 28 cm. The actual spatial frequency can be calculated if distance other than 28 cms. are used by dividing the distance used in cms by 28 cm. and multiplying the result by the stipulated frequency of the grating. For example, if the viewing distance is 56 cm. instead of 28 cm. and the stipulated spatial frequency is 5 cycle/deg. Then the corrected spatial frequency is 66/28 x 5=10 cycles/deg.
The large sequence of square wave gratings which fit on the apparatus are now shown on the patient whose normal eye is covered. The widest stripes are presented first and treatment is commenced using the finest stripes that he can see. The disc is now placed on the central spindle of the apparatus and the plastic perspex cover is placed over it. The patient is seated in front of the apparatus and is asked to draw or play games on the perspex plates with the clinician or orthoptist whilst the disc rotates under the plate. If possible, two patients matched for age and intelligence should play together, as they tend to concentrate better under these circumstances.
The patient should be asked to hold his head as far away from the apparatus as he can. The suggested distance is 28 cm. This disc is rotated for two minutes and the next finer grating is placed on the spindle and game repeated. This is carried out till the finest grating is used. If patient can see clearly first three coarse grating and finding difficulty in fourth, then treatment can be started with third coarse grating instead of first and thus saving the time.
After the treatment is finished, the grating acuity using the test gratings is again assessed. This is followed by an assessment of the visual acuity for distance and near. The treatment are repeated at intervals which can be as short as daily or as long as weekly. It is usual to do the treatment frequently initially, and lengthen the interval between treatment as the visual acuity improves. No occlusion is necessary in between treatments.
Treatment is discontinued if no further improvement of visual acuity occurs on 5 successive attempts. Those who respond well to this treatment usually do so within the first two or three treatment. The orthoptic assessment is repeated at the end of complete treatment.
Forty patients have completed this treatment schedule. The age range of the children included in this study was from 4 years to 15 years. The lower age limit is determined by the ability to concentrate on the gratings.
Out of the 40 cases treated, 21 had some previous from of treatment i.e. occlusion and glasses, while 19 cases had been newly referred.
There were about thirteen children with eccentric fixation and 27 children with central fixation. Patients with Central fixation and those with eccentric fixation respond differently in the rate of improvement but the average numbers of sessions required to achieve the maximum improvement is the same, i.e. 5 sessions.
As can be seen from above table patients who had previous treatment and failed to improve need more CAM session than those without any previous treatment. Reason being that this group of patients comprised more of eccentric fixation, high hypermetropia, congenital esotropia or early onset convergent squint.
One case in No treatment group and two cases in previous treatment group showed no improvement after 5 session and hence dropped from the study. The near visual acuity improved considerably more than distance visual acuity in all but 3 cases which were dropped from the study.
Repeat treatment in 10 cases in whom vision dropped give improvement once again in 6 cases and no improvement is 4 cases.
For patients with eccentric fixation following procedure was adopted. The patient was given constant occlusion of the squinting eye except for the period of time spent for CAM session. As the visual acquity improved the occlusion was changed from the squinting eye to the fixing eye for increasing longer periods until the acquity was adequate enough to enable constant occlusion of the fixing eye.
Of the 40 patients who have been treated with this instrument distance visual acuity improved in 33 cases and Near Visual acuity improved in 37 cases. Out of the 40 patient 30 patient i.e. 75%, of cases improved 6,112 or better. Out of the 13 patient with eccentric fixation of 6 improved considerably 6/18 or better.
The number of patients who have completed treatment is small but results shows that this therapy is better than that achieved from conventional occlusion and that some improvement can be expected in those in whom the response to conventional occlusion has failed.
There were no cases in this series were there was reduction of vision or diplopia.
How and why this therapy works is still largely a matter of conjecture. By some animal and human experiments, it has been shown that cells in the visual areas of the brain respond best to gratings at a certain size (Spatial frequency) and to exercise the majority of visual cells, the stimulus should contain high contrast gratings at all orientation. With this idea in mind this device has been invented.
Benefits of this new treatment
(1) Patient who have previously failed to respond to conventional occlusion therapy have shown good response to CAM.
(2) Even patients with eccentric fixation improves.
(3) The course of treatment is very short 10 minutes per session and only 5 to 10 such sessions.
(4) The need for long periods of occlusion, with all its attendant social and educational disadvantages is avoided.
Banks R.V. Campbell F.W., Hess R.F. and Watson P.G. 1978 Brit. Orthop. J.
[Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5], [Table - 6]