Purpose: Frequency-doubling technology (FDT) perimetry was developed as a screening test for glaucoma. Patients with damage to the neuro-ophthalmic sensory visual pathways have different patterns of visual loss than patients with glaucoma. The current study was designed to determine the sensitivity and specificity of FDT as a screening test, compared with conventional automated perimetry (CAP) in neuro-ophthalmic disorders and to test the extent to which it may isolate the M(y) cells.
Methods: FDT and CAP were performed in 97 patients with sensory neuro-ophthalmic disorders and 42 subjects from the general population. The total and pattern-deviation probability plots for test loci common to the two perimetric tests were compared. The gold standard was an unequivocal clinical diagnosis.
Results: The sensitivity of FDT was 81.3%, with a specificity of 76.2%. The difference in sensitivity and specificity of CAP, 87.5% and 81.0%, respectively, was not statistically significant (by chi(2) test). In subjects with optic neuropathies, the similarity of the defect shown on FDT and CAP was judged good or fair in 62 of 72 cases. The extent of the defect as seen with FDT and CAP was equal in 41 of 72 cases, more extensive with FDT in 12, and more extensive with CAP in 19. In the patients with hemianopia, scattered abnormal test locations with FDT testing masked the hemianopic nature of the defect in 15 of 25 patients. Also, test locations along the vertical midline in densely hemianopic areas were seen with FDT testing in some patients with hemianopia, probably due to light scatter across the vertical midline and into the uninvolved hemianopic field.
Conclusions: FDT has sensitivity and specificity similar to that of CAP for detecting visual field defects in patients with optic neuropathies. However, defects in patients with hemianopias may be missed because of the presence of scattered abnormal test locations and failure to detect test locations along the vertical meridian. The defects demonstrated by both tests in patients with optic neuropathies are similar in number, extent, and shape of the defects. This suggests FDT may not be isolating the magnocellular (M) cells with nonlinear responses to stimulus contrast (M(y) cells) in patients with visual loss.