Ophthalmoscopic attachment for the diagnosis of eccentric fixation.

THERE iS much need for earlier and more careful examination of patients, particularly children, who present with amblyopia in a squinting eye, with a view to the detection of eccentric fixation. It is true that in many cases considerable improvement of visual acuity may occur as a result of occlusion of the non-squinting eye, but there are others, mainly those with eccentric fixation, in which vision remains unaffected. Indeed, occlusion of the non-squinting eye only serves to condition the eccentric fixation reflex, when this is present, as well as to increase the macular suppression. Thus treatment of the amblyopia, when it is eventually undertaken on modern lines (Mayweg and Massie, 1958), becomes a more lengthy and uneconomical procedure. Only gross degrees of eccentric ixation can be detected by means of the cover test. Lesser degrees of eccentric fixation, especially when the fixation is perior para-macular, cannot be diagnosed without some special instrument such as the Visuscope, although eccentricity may be strongly suspected to be present in cases in which vision has not improved beyond 6/60, or even 6/24, after several months of total occlusion. The ready availability of a simple instrument for the examination of fixation in these cases of amblyopia is desirable. It is more satisfactory for all concerned if the ophthalmologist can decide about the position of the fixation for himself before treatment is started. For this purpose a palegreen filter (No. 21 pea-green), in which there is a central uncoloured hole of 3/1,000 in., may easily be fitted to most of the ophthalmoscopes in common use. This pale-green filter with the clear centre does not present too great a contrast when viewing the fundus, such as occurs when the green in the filter is too dark. On the Keeler ophthalmoscope this filter can now be supplied as an extra attachment, and it is fitted onto the rotating dome holding the different-sized apertures. A filter can easily be fitted on the A.I.M. ophthalmoscope, and it fits as a cap over the condensing lens on the Lister Morton ophthalmoscope. The white circle of light is clearly projected onto the fundus, and because of the simultaneous contrast, is easily visible