Objective Assessment of Visual Functions

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The objective assessment of visual function, namely visual acuity, is becoming increasingly important, often for medico-legal reasons. In an earlier project we developed an appropriate technique yielding an acuity estimate with an associated confidence interval. This is in routine use and has been licensed by industry. Experience has shown that we need to make two major improvements:The first is to solve an emergent methodological problem: previous visual display units employed the cathode-ray principle. They are no longer being produced, as LCDs have taken their place. While useful for most applications, LCDs have marked luminance artifacts, which render them quite unsuitable for estimating visual function. We hope to solve this problem with new stimulation regimes that disambiguate artifactual luminance responses from pattern responses in the Fourier domain.The other problem is a physiological one: the so-called notch, a marked amplitude loss in an intermediate spatial frequency region; this occurs in about 50% of all subjects. Its physiological basis is not understood. We hypothesize this to be due to the destructive superposition either of local dipole responses from an extent of cortical sources, or the temporal overlap of response components with opposite polarity. Using multichannel recordings (never applied to this question before) and higher-order Laplace derivations in combination with a wide range of visual field extents and temporal presentation rate, we are aiming at two goals: (1) to improve our understanding of the physiological basis of the notch, and (2) to arrive at an optimized stimulation and recording paradigm applicable to routine estimations of visual function in all patients.