We introduced a novel approach to topographic function assessment in visual impairment that requires neither fixation nor reading.
The test measures the time it takes for patients to find and identify 32 targets on a screen. The task discourages steady fixation and the subjects can make eye movements as needed to solve the task. Target size is always double the size threshold, and no manual action is required.
We have used this test on many low vision patients with varying diagnoses. Measurements yielded a wide variety of performance levels, with a factor of 14-16 between best and worst performers. The highest correlation existed between median response latency in the search task and best attainable reading speed. Only a weak correlation was found between performance and visual acuity, and no significant correlations were found with age or diagnosis..
What have we learned? The “search-and-identify” paradigm and continuous text reading share an important mechanism that determines performance in both tasks. We think that the factor enabling patients to perform well in both paradigms is oculomotor skill and/or eye movement strategy. We showed that the Macular Search Test is a useful tool for the easy assessment of impaired vision independent of language, level of literacy and reading habits.
Reference
MacKebenM & Fletcher DC. (2011) Target search and identification performance in low vision patients. Invest Ophthalmol Vis Sci. 2011, Sep 29;52(10): 7603-9
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