Isolation of short-wavelength sensitive mechanisms in normal and glaucomatous visual field regions

To determine whether "isolation" of short wavelength sensitive mechanisms (i.e., exclusive detection of a threshold stimulus by a short wavelength sensitive mechanism) is maintained in areas of glaucomatous visual field damage as measured with short-wavelength automated perimetry (SWAP).

Data from conventional automated perimetry and SWAP were analyzed for both eyes of 60 normal control subjects, 38 patients with ocular hypertension, and 22 patients with early to moderate glaucomatous field damage (mean defect better than -12 dB). Comparisons of results of SWAP and conventional perimetry were performed by determining the deviation from the mean normal sensitivity for the two procedures. Locations with sensitivity <3 dB for either procedure were rejected, as 3 dB is near the maximum stimulus luminance and may have introduced a bias by underestimating defects. The interval between deviation from normal (the isolation interval) on conventional perimetry and SWAP was examined to determine the likelihood of short wavelength mechanism isolation loss for different levels of glaucomatous visual field damage.

Using normal isolation estimates of 13 dB and 10 dB as bases for determining the likelihood that isolation of short wavelength sensitive mechanisms may have been lost, it was found that this was an infrequent possibility, as low as 0.39 to 1.63% for normal control subjects and 2.53 to 10.44% for patients with glaucoma.

Analyses indicate that isolation of short wavelength sensitive mechanisms is mostly maintained for SWAP, even in areas of moderate glaucomatous field damage. One limitation of SWAP for evaluating extensive glaucomatous damage is its dynamic range. This could be overcome by using a more intense stimulus light source.