The effect of the neutral-grey filter indicated that both the Freiburg and the Haase Tests can be used to measure fractions of ocular prevalence, although the Freiburg Test carries a higher reproducibility. Spontaneous ocular prevalence occurs frequently in persons with equal vision of their two eyes. This suggests that ocular prevalence does not represent a condition that requires treatment. Rather, partial suppression of one eye, the correlate of ocular prevalence, may play a physiological role in that it helps to disregard double images at stereo-disparities close to the limits of Panum's area.

A sctoma centered on the fixation point with a sloping border is highly characteristic of ON, while an inferior altitudinal defect with a sharp border along the horizontal meridian, particularly in the nasal periphery, is highly characteristic of AION. To identify these diagnostic criteria, it can be necessary to examine full fields. With restriction of perimetry to 30 degrees a large central scotoma can be mistaken for a diffuse defect and the border in the nasal periphery can be missed.

PSYCHOMETRIC FUNCTION: According to the European standard EN ISO 8596 the Landolt-C in 8 different orientations has to be used to measure visual acuity. With decreasing size of the Landolt-C the hit rate declines from 100% to the chance level of 12.5%. This gradual transition is described by the "psychometric function". The steepest point of the psychometric function is in the middle between 100 and 12.5, i.e., at 56.25%. This point of the psychometric function (approximated by 5 of 8 Landolt-Cs) has been selected as the threshold for visual acuity, because it is there that the visual acuity is influenced least by (incidental) fluctuations. The subject has to answer by forced choice; a response like "I cannot detect anything" is not acceptable. "NORMAL" VISUAL ACUITY: Cannot be assigned to a certain value, like 1.0 or 6/6. With the standard test procedure, visually healthy, young subjects achieve a visual acuity of about 2.0 or 12/6, while in senior subjects 0.5 (3/6) may be "normal". AVERAGING VISUAL ACUITY: Logarithmic, not arithmetic, scaling of visual acuity approximates the perceptual metric. Consequently, visual acuity values may not be averaged arithmetically. Instead, three steps are required: all values have to be converted to logarithms, then averaged, and finally the average can be reconverted. Geometric averaging is equivalent. "MINIMUM ANGLE OF RESOLUTION" NOT NECESSARY: MAR is the reciprocal of visual acuity. In many studies, clinical outcome has been assessed using log(MAR). Though statistically correct, this term is unnecessary, as log(acuity) has identical statistical properties. Furthermore, log(MAR) is contra-intuitive as its value becomes smaller when vision improves. COMPUTER-ASSISTED INSTRUMENTATION: Facilitates complying with the EN ISO 8596. For instance, the Freiburg Visual Acuity Test relieves the examiner from observing whether 5 responses have been correct, and that not more than 8 tests are given per level.

No abstract

We report on the psychopathology and illness-related changes of life in patients with benign essential blepharospasm (BEB) or hemifacial spasm (HFS). Fifty-six patients with BEB and 40 patients with HFS completed the SCL 90R, a screening instrument for psychiatric symptomatology, and the Freiburg Questionnaire for Dystonia (FQD), a questionnaire about psychosocial changes in subjects with movement disorders. In both BEB and HFS patients, the mean scores on all but one subscale of the SCL 90R remained within the double standard deviation of normal. In comparing BEB to HFS patients in illness-related changes of life, BEB patients were more severely disabled in all areas of life examined. Psychological distress in BEB, but not in HFS, correlated with physical disability and in particular with impairment of vision.