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We performed focal electroretinography (FERG) in 10 patients with reduced vision of unknown cause. No patient gave a family history of uncorrectably reduced vision, and none had taken any drug known to damage the retina. Visual acuity claims ranged from 20/40 to finger counting. Color discrimination was reduced in all but one patient. Visual field sensitivity was reduced nonspecifically in five of the six patients who could perform perimetry reliably. Ophthalmoscopy showed no pertinent abnormality in four of 10 patients, mildly reduced foveal reflex in two of 10, arteriolar narrowing in two of 10, foveal pigment disturbance in one of 10, and preretinal gliosis in one of 10. Flash visual evoked potential (VEP) testing showed no abnormality in seven of 7 patients. The pattern VEP was reduced or delayed in five of 5 patients, only one of whom showed the expected amplitude loss with decreasing check size. Five patients completed full-field electroretinography, six patients completed fluorescein angiography, and none showed pertinent abnormality on either test. FERG was performed in both eyes of seven patients and in one eye of three others. Signals were non-recordable from four eyes, abnormal in nine, equivocal in three, and normal in one. The severity of FERG abnormality did not correlate with the severity of acuity loss. FERG abnormalities were found in fourteen of 17 eyes of 10 patients with vision loss out of proportion to clinical findings. In these patients only one of 5 pattern VEP tests, none of 5 full-field ERGs, and none of 7 fluorescein angiograms suggested correspondingly severe maculopathy. The FERG results in these cases mitigated suspicions of nonorganic vision loss and permitted speedier referral to retinal disease and low vision specialists.

Steady-state visual evoked potentials were recorded in response to contrast Reprint requests: Dr. Elmar T. Schmeisser, Division of Ocular Hazards, Letterman Army complex (sum of two spatial frequencies) suprathreshold sinusoidal gratings of two and six cycles/degree in a 5 degrees field. Sine mode counterphasing enhances the second temporal harmonic component of the evoked waveform; square mode counterphasing generates a response with essentially all the power at the fundamental temporal frequency. Digital sums of observed responses to simple gratings presented alone had significantly greater amplitudes than any observed response to presented complex gratings. Response amplitudes ranked significantly by condition: binocular greater than dichoptic greater than monoptic. It is concluded that (a) sinusoidal counterphasing stimuli lead to two stimulus events per shift (an observed grating onset and offset), and (b) spatial frequency channels that are harmonically related in 1:3 ratio do not destructively interfere with each other in either monoptic or dichoptic presentation.