Prospective Pilot Study Looking at the Size and Variation of the Blind Spot Scotoma in Adults Measured on the Octopus 900 Field Analyser

Aims: Literature regarding the size of the blind spot is old and recorded on instruments no longer in production. This pilot study looks to provide normative data for the size of the visual blind spot scotoma in adults measured by the Octopus 900 kinetic perimeter.

Study Design: A prospective repeated measures study involving nineteen participants.

Place and Duration of Study: Ophthalmology department, Royal Hallamshire Hospital, Sheffield, between April 2012 and July 2012.

Methodology: The blind spot scotoma area was measured in degrees2 using three kinetic targets. Two trials were conducted to assess variability across the targets.

Results: The mean blind spot scotoma area decreased as target luminosity increased. The mean blind spot scotoma area was; 197.6±152.8 deg2 with the I1e, 63.6±21.7 deg2 with the I2e and 33.9±6.8 deg2 with the I4e.

Agreement between the first trial and second trial for the three different forms of target luminance was examined using Bland-Altman analysis. The target I4e has the closest mean difference to zero and the I4e also has the highest precision as shown by the SD; I1e bias -1.764±3.852SD, I2e bias -0.368±0.938SD and I4e bias -0.151±0.477SD.

Conclusion: This study found the mean size of the blind spot scotoma to be influenced by the luminosity of the target stimulus, with mean area (deg2) decreasing as target luminosity increases. This can be attributed to the blind spot’s amblyopic zone or light scattering across the refractive media of the eye. The target I4e shows the least variation between subsequent measures and would be the most reliable of the targets used for monitoring change in blind spot scotoma area over time.