Characteristic features of blind spot size and location, when evaluated with automated perimetry: Values obtained in normal subjects

Abstract

Characteristic features of the size and location of the blind spot were analyzed by computerized perimetry. A new strategy devised for relatively fast and precise measurement of the blind spot was used, with an Octopus 2000R perimeter.In a first series of 30 normal subjects, height and width, average of height and width, square root of the product of height and width, and horizontal and vertical coordinates of the center were computed. In a second series consisting of 49 normal subjects, repeatability of the measures was evaluated. The influence of the stimulus intensity was evaluated.Height of the blind spot exceeded its width. However, the correlation between width and height values was weak. This suggested that, even in normal subjects, assessing the width of the blind spot did not provide a substantial indication of its height. Decreasing stimulus intensity was associated with increase in width and height. In addition, a temporal shift of the mean horizontal coordinates of the center was demonstrated when weaker stimuli were used, indicating that the nasal sensitivity slope was steeper than the temporal one. The asymmetry in slopes is probably related to the fact that the exit of the optic nerve is often tilted nasally, and the ending of the retinal tissues at the margin of the disc is asymmetric.Repeatability of measurements was found excellent for clinical purpose. Along the vertical axis, poorer reproducibility was found with weak stimuli, probably due to the presence of angioscotomata.To our knowledge, this is the first systematic study of blind spot characteristics conducted in a large series of subjects using high-resolution automated perimetry.