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C.D. Brocard, A. Kawasaki, M. Monhart; The Influence of Vector Quality Assessment in Defining a Scotoma . Invest. Ophthalmol. Vis. Sci. 2006;47(13):795.
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© ARVO (1962-2015); The Authors (2016-present)
When mapping a scotoma using standard kinetic perimetry, the stimulus meridian is generally selected at an angle perpendicular to an imaginary line between two points of previous stimulus detection. Octopus semiautomated kinetic perimetry can record the speed and meridian of each stimulus (vector) used for mapping a scotoma so that the vector sequence in subsequent examinations is identical. We examined the influence of vector angle on the definition of a scotoma border and area over repeated examinations.
Eleven patients with a stable static visual field defect underwent scotoma mapping with semiautomated kinetic perimetry on six separate visits with two examinations per visit. The first two visits were used to establish the stimulus vectors for subsequent automated testing and to overcome any learning effect by the patient. The scotoma determined from the first examination of the third visit was used as a baseline to assess the angle at which each vector crossed the scotoma border. Vectors with an angle of 60 degrees or less were considered poor quality vectors. Thereafter, all the scotomas from visits 3 through 6 were mapped and evaluated before and after vector quality assessment, i.e. elimination of poor quality vectors.
A scotoma was defined by a minimum of 8 and maximum of 18 vector responses before quality assessment and a minimum of 6 and maximum of 10 responses after quality assessment. The test–retest variability was calculated as the percentage change in scotoma area (corrected for reaction time). After elimination of poor quality vectors, the test–retest variability decreased in 17 of 31 examinations with the majority of variability reduction (maximum difference of 37%) occurring in larger–sized scotomas (scotomas with area greater than 100 degrees2) , and the general shape of the scotoma became more uniform.
Assessment of vector quality is one factor which can improve the repeatability of scotoma definition. The percentage change in scotoma area may be a useful quantitative measure of variability in larger scotomas but appears to have limited utility in smaller scotomas. In such cases, individual analysis of the fluctuation for each vector may be necessary to identify regions of variability versus real change within any given scotoma.
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