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Reduction in the threshold value of the primary points resulting in depressed points on the pattern deviation plot of Humphrey visual fields was observed in a series of four perimetrically naive subjects. The defect disappeared on repeated testing. This primary point defect could be attributed to the patient's poor understanding of the test, response bias or poor instruction by the perimetrist.
Dr. R. George, Glaucoma Department, Medical and Vision Research Foundation, Sankara Nethralaya, 18 College Road, Chennai 600 006, India. chennaigs@rediffmail.com