Are early losses of visual function in glaucoma selective or non-selective?

Purpose. The purpose of this study was to test the hypotheses that early glaucoma losses (1) occur selectively for magnocellular or parvocellular mechanisms, (2) occur selectively for large diameter fibers, or (3) occur on a non-selective basis, but are more noticeable for mechanisms with sparse representation (reduced redundancy). We examined these hypotheses by evaluating a variety of visual functions throughout the central visual field of patients with evidence of very early glaucomatous damage and comparing test results performed in the same individuals. Methods. Ten eyes of 8 patients with evidence of very early glaucomatous visual field loss were tested with conventional automated perimetry (Humphrey 30-2), Short Wavelength Automated Perimetry (SWAP), red-green opponent process perimetry, displacement threshold perimetry, low frequency (2 Hz) flicker perimetry, high frequency (16 Hz) flicker perimetry and frequency doubling perimetry. To directly compare results of different tests, all results were compared to age-matched normative values. The extent of visual field that demonstrated sensitivity below the 5% and 1% normal confidence limits was determined for each procedure. Results. Overall, the greatest amount of loss was obtained for SWAP. In 7 out of 10 eyes, SWAP deficits were more extensive than those observed for all other test procedures. The other test procedures generally showed similar amounts of loss across all subjects. Although some functions were more greatly affected than others in individual eyes, there were no consistent trends observed, except for SWAP. Conclusions. At the present time, SWAP appears to have the best performance of any of the visual function tests for detection of early glaucomatous damage. Our findings do not support the concept that early glaucomatous losses are predominantly to magnocellular mechanisms or those pathways with the largest fiber diameters. Further studies are needed to determine whether the basis of early glaucomatous loss is selective to short-wavelength-sensitive mechanisms or to reduced redundancy.