Faculty Bibliography

Flicker sensitivity increases in the peripheral retina when relatively large targets are used. This enhancement of cone system-mediated temporal sensitivity persists even when corrections are made for cortical magnification factors. It has been suggested that the differences in temporal frequency response characteristics across the retina are based on differences in receptor morphology between the peripheral and central cones. We have examined a possible retinal origin of this phenomenon by obtaining psychophysical and electroretinographic data at a variety of locations on the temporal retina. Psychophysical results show an increased sensitivity for high temporal frequency stimuli (above 30 Hz) with retinal eccentricity whether or not the stimulus size was scaled. Focal electroretinograms recorded with a constant size stimulus did not show an increase in amplitude with eccentricity. However, when an equal number of receptors were stimulated by scaling the target size, focal amplitudes were larger in the periphery. The electrophysiological findings are consistent with a possible retinal origin for this flicker enhancement phenomenon

Visual evoked potential contrast adaptation was measured in normal subjects using a real-time-retrieval swept contrast analysis. Results demonstrated orientation specific adaptation suggesting a cortical locus. Conditions which disturb cortical inhibition (i.e., epilepsy and dopaminergic agents) altered this adaptation effect.

We studied the effects of intra-arterial chemotherapy on the visual system of 29 consecutive patients with gliomas. As expected, infra-ophthalmic carotid infusion of cisplatin or carmustine (BCNU) was associated with clinically apparent anterior visual pathway lesions. Electroretinography revealed retinal dysfunction in patients without clinical abnormalities. Supra-ophthalmic carotid infusion of cisplatin or BCNU caused no retinal or optic nerve lesions. Electroretinography was abnormal in only one of these patients. Our results indicated that BCNU and cisplatin cause ischemic damage and are toxic to both retinal and neural tissue in patients with gliomas

Psychophysical, reflectometric, and electrophysiologic studies were done on four members of a dominant pedigree with progressive cone dystrophy. The two youngest individuals were asymptomatic at the initial examination, and none of the subjects complained of problems associated with night vision. Nevertheless, absent or grossly reduced cone-mediated electroretinographic (ERG) responses showed the widespread loss of cone function, and moderate elevations (less than 1 log unit) in absolute threshold together with reductions in rhodopsin levels in the mid-peripheral retina provided evidence of impairment of the rod system. The progressive nature of the disease was apparent from the case histories and the changes in visual performance that occurred on re-test after a 5-year interval. Moreover, the results of increment threshold measurements at several retinal loci suggested that peripheral cones may be affected earlier and more severely than those in the central retina

Loss in foveal sensitivity in retinitis pigmentosa (RP) has been attributed to a decrease in quantal catching ability. Using a psychophysical technique (the probe-flash paradigm), we previously found that the results obtained for six RP patients under light adapted conditions were not consistent with a quantal catch hypothesis. To test further this hypothesis twelve RP patients were examined in dark adapted conditions. Probe thresholds were normal for five patients and increased for seven patients. The decreased quantal catching hypothesis was rejected for six of the seven patients

A patient with congenital stationary night blindness (CSNB) (Schubert-Bornschein type) transmitted as an autosomal recessive trait was studied with several tests of electrical function as well as a variety of psychophysical procedures. Comparison of the patient's present findings with those obtained 23 years earlier showed that while rod thresholds have remained the same, cone sensitivity has decreased. Subjective flicker thresholds obtained following a bleach were unchanged during the course of dark adaptation. The absence of rod-cone interaction, together with an absent scotopic b-wave, implies that the defect is in the mid-retinal layers. Further, the absence of oscillatory potentials in the photopic electroretinogram (ERG) suggests that the interplexiform cell may be implicated in some manner. The focal ERG of the CSNB patient showed normal amplitude and normal phase delays, supporting the idea that the focal ERG samples primarily cone photoreceptor activity

Seven related patients had a progressive pigmentary retinal degeneration, characterized by nyctalopia, visual field restriction, and cystic macular degeneration in younger patients and a macula of nonspecific atrophic appearance in older patients. In addition, each patient had high hyperopia (+9.50 to +16.00) and nanophthalmos (axial lengths, less than 20 mm), with diffuse choroidal thickening on ultrasound. Younger patients had slitlike anterior chamber angles; older patients developed progressive synechial angle closure and eventual glaucoma. Chromosomes were normal. On electroretinographic testing, younger patients had absent rod signals, with normal cone wave form and near-normal b-wave amplitudes but markedly delayed cone b-wave implicit times; older patients had severely diminished or extinguished electroretinograms. This family appears to represent a newly recognized autosomal-recessive syndrome

Psychophysical, reflectometric, and electrophysiological studies were performed on four members of a dominant pedigree with progressive cone dystrophy. The two youngest individuals were asymptomatic at the initial examination, and none of the subjects complained of problems associated with night vision. Absent or grossly reduced cone-mediated ERG responses revealed the widespread loss of cone function. Moderate elevations (1 log unit) in absolute threshold together with reductions in rhodopsin levels in the midperipheral retina provided evidence of a mild impairment of the rod system also, although not to the degree seen in a cone-rod dystrophy. The progressive nature of the disease was apparent from the case histories and the changes in visual performance that occurred on re-test after a 5-year interval. Likewise, the results of incremental threshold measurements at several retinal loci suggested that peripheral cones may be affected earlier and more severely than those in the central retina