Normal subjects when examined with the Friedmann Mark II Analyser often miss stimuli in the extreme (greater than 20 degrees) superior field and in the arcuate regions. The majority of misses in the superior field are believed to result from the subjects' eyelashes acting as partial occluders. The misses in the arcuate region are believed to be the result of the retinal blood vessels. Isolated missed points at 0.8 or more log unit above threshold were found in 9% of the subjects, which means that it is 13 times more likely that an isolated missed point comes from a normal subject than a glaucomatous one (the incidence of glaucoma is taken as 0.7% of the total population). Clusters of two missed stimuli in the arcuate region at 0.4 and 0.6 log unit above threshold were found in 8% and 0% of the population. Clusters of three missed stimuli in the arcuate region were found in 0.7% of the population. It is suggested that isolated missed stimuli should be retested with the eccentric fixation point.
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