Software for digitization and three-dimensional volumetric measurement of Kinetic Perimetry

Abstract

Purpose : To create and validate software to digitize the seeing and non-seeing areas as well as calculate total volume, in three dimensions, for Semi-Automated Kinetic Perimetry (SKP) performed on the Octopus 900.

Methods : The Casey Reading Center developed custom software to interrogate the data file from the Octopus 900 to display the response points on the SKP image to allow accurate digitization. Solid angle steradian (sr) values are calculated from the digitized image for each target intensity according to (Table 1)¹. Adjustments were made to use the Pythagorean theorem so values of x=0 for response x had a value of 90 degrees for Theta (deg), and including the last point digitized as a reference to first point digitized. Steradian values are summed together to obtain the total solid angle value for seeing and non-seeing areas (isopters). Solid angles in steradians were converted to Goldmanns for the “heights” (in log 10³ (cd/m²)⁻¹), where cd=candela and m=meter, for each isopter using Table 2, equation Figure 2. For total volume, individual isopters were converted into mesas, with flat tops and vertical sides and calculate the volume of the mesa to create stacked mesas. The mesa sides are determined by the isopter boundary and the mesa height is determined by the stimulus size (target size and intensity). Isopters from less-luminant stimuli are given more “height” to indicate the greater visual sensitivity needed to detect them. Mesas are stacked to form 3-dimensional stepped-slope models of the hill of vision. Total volume is calculated by summing the contributions from all mesas (isopters), Figure 1. Volume does not combine different stimulus sizes, as is done in static perimetry.
The Hill of Vision volumes are in units of Goldmanns = sr log 10³ (cd/m²) ⁻¹ as modified from the Christoforidis paper (Table 2).
If a brighter stimulus mesa overhangs a lower level the software will not modify the total volume calculation in any way.
A validation strategy (Figure 3) confirmed that the software is calculating the correct steradian and Goldmann values for solid angle and total volume.

Results : We developed custom software that accurately digitizes SKP fields and calculates a three-dimensional volumetric measurement for all existing target intensities for the Octopus 900.

Conclusions : Digitization and volumetric analysis can be performed with semi-automated kinetic perimetry performed on the Octopus 900

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.