Visual perception in strabismic amblyopia and the influence of occlusion therapy
Purpose: Besides all the other facets of strabismic amblyopia (reduced visual acuity and binocularity, eccentric fixation), defective spatial localisation is an important feature. Increased uncertainty and systematic errors of spatial judgements have been demonstrated in a variety of tasks, e.g. vertical alignment (Bedell and Flom 1981; Fronius and Sireteanu 1989; Haase 1989; Hess and Holliday 1992).
We investigated several aspects of spatial localisation both in adults and in children with strabismic amblyopia. In children we followed in a prospective study whether these errors (and thus monocular geometry) are influenced by occlusion therapy. Sixteen children between 4½ and 10 years of age were repeatedly tested during al least 6 months of treatment.
Method: The subjects task was to align a vertical test line (3,4 by 32 minarc) with the apices of two vertically aligned reference triangles separated by 5 deg (modified from Bedell and Flom, Invest Ophthalmol Vis Sci 20 263-268, 1981). After a binocular test run, right and left eyes were tested monocularly (15 trials in each condition). Usually, fixation had to be kept on the vertical test line. In a control experiment, subjects were allowed to scan the entire test stimulus, including the reference triangles.
Results: The experimental data yielded a complex feature of localisation errors, composed of the following
Vertical alignment of the amblyopic eyes depended on the spatial and temporal presentation of the test stimuli.
Eye movements, although known to be abnormal in strabismus, may improve spatial localisation.
Occlusion therapy may alter not only the clinical parameters, but also the outcome of the vertical alignment experiments.
Conclusion: Our data add to the knowledge about disturbances of spatial localisation in strabismic amblyopia. Further investigations have to clarify their substrate.
Max-Planck-Institut für Hirnforschung, Deutschordenstr. 46, D - 60528 Frankfurt/Main