Faculty Bibliography

Seven patients with longstanding monocular optic atrophy had normal flash electroretinograms when compared to the results from control observers or when compared to the results from their own unaffected eye, or the eyes of control observers. These findings are contrasted with prior investigations that report either depression or augmentation of ERG amplitudes. We found that optic nerve damage does not cause trans-synaptic changes in the retina, or loss of efferent inhibition that can be measured by electroretinography

1. Strabismic and anisometropic amblyopes typically have elevated contrast thresholds. Despite these threshold losses, previous research has shown that some amblyopic observers demonstrate normal suprathreshold contrast matching. 2. One explanation for these contrasting results is a differential impairment of independent contrast mechanisms. 3. We used a swept visual evoked potential threshold technique to electrophysiologically isolate and compare absolute and suprathreshold contrast mechanisms in a group of strabismic and anisometropic amblyopes. 4. For both groups of amblyopes, the sensitivities of the absolute and the suprathreshold mechanisms were equally elevated. 5. These results indicate that, in these amblyopes, both threshold and suprathreshold mechanisms of the VEP are impaired

1. At stimulation frequencies near 10 Hz, the focal electroretinogram (FERG) is non-linear, containing significant second harmonic amplitude. 2. We performed a series of experiments directed at identifying the origin of this nonlinearity. Three hypotheses were tested: (a) The frequency doubling reflects the summed contribution of responses to stimulus onset and offset. (b) The frequency doubling reflects interactions between the responses of different cone systems. (c) The frequency doubling is due to temporally separated contributions from the rod and cone systems. 3. The results of the present experiments did not support either the first (off response) or the second hypothesis (cone difference signal). The third hypothesis received the most support

Temporal sensitivity was assessed in patients with primary open-angle glaucoma (POAG) and ocular hypertension (OHT). Three measures of flicker sensitivity were obtained: psychophysical modulation thresholds, visual-evoked potentials (VEPs), and focal electroretinograms (FERGs). We found elevated psychophysical thresholds at higher temporal frequencies (30-50 Hz) in patients with POAG, relative to thresholds for age-matched controls. The OHT patients had elevated psychophysical thresholds only at 50 Hz. On the other hand, VEP amplitudes in POAG patients were reduced at all temporal frequencies, with the magnitude of the loss increasing with temporal frequency. The OHT patients, however, showed no reductions in VEP amplitude at any temporal frequency. Finally, POAG patients' FERG amplitudes were reduced at 30-50 Hz; whereas FERG amplitudes in the OHT patients were normal at all temporal frequencies. These results indicate that OHT patients can exhibit psychophysical threshold losses at high temporal frequencies which are not observed in the suprathreshold electrophysiological amplitude measures. On the other hand, patients with POAG show both psychophysical and VEP losses across a range of temporal frequencies. In addition, the decreases in FERG amplitudes in POAG patients suggest changes in the functioning of the outer retina in this disease