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

Purpose: To determine whether "isolation" of short wavelength sensitive mec hanisms (i.e., exclusive detection of a threshold stimulus by a short wavel ength sensitive mechanism) is maintained in areas of glaucomatous Visual fi eld damage as measured with short-wavelength automated perimetry (SWAP). Methods: Data from conventional automated perimetry and SWAP were analyzed for both eyes of 60 normal control subjects, 38 patients with ocular hypert ension, and 22 patients with early to moderate glaucomatous field damage (m ean defect better than -12 dB). Comparisons of results of SWAP and conventi onal perimetry were performed by determining the deviation from the mean no rmal sensitivity for the two procedures. Locations with sensitivity <3 dB f or either procedure were rejected, as 3 dB is near the maximum stimulus lum inance and may have introduced a bias by underestimating defects. The inter val between deviation from normal (the isolation interval) on conventional perimetry and SWAP was examined to determine the likelihood of short wavele ngth mechanism isolation loss for different levels of glaucomatous visual f ield damage. Results: Using normal isolation estimates of 13 dB and 10 dB as bases for d etermining the likelihood that isolation of short wavelength sensitive mech anisms may have been lost, it was found that this was an infrequent possibi lity, as low as 0.39 to 1.63% for normal control subjects and 2.53 to 10.44 % for patients with glaucoma. Conclusion: Analyses indicate that isolation of short wavelength sensitive mechanisms is mostly maintained for SWAP, even in areas of moderate glaucom atous field damage. One limitation of SWAP for evaluating extensive glaucom atous damage is its dynamic range. This could be overcome by using a more i ntense stimulus light source.