Faculty Bibliography

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

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

Retinitis pigmentosa (RP) frequently leads to a decrease in cone system sensitivity. A number of alternative explanations have been proposed for this decrease. Based on the results of a psychophysical technique, the probe-flash paradigm, the authors suggest that a decrease in responsiveness of retinal elements can account for much of this loss. In this paper the decreased responsiveness hypothesis is tested by obtaining data at two levels of steady adaptation. The results of the study indicate that sensitivity loss is greater for the dark adapted than the light adapted state. The data rule out the decreased responsiveness hypothesis coupled with a simple model of adaptation. More complicated adaptation models cannot be excluded. The importance of considering models of adaptation when testing models of disease-related sensitivity loss is underscored

Various noninvasive test procedures were used to evaluate retinal function in a patient who had become night blind following vincristine chemotherapy. The results obtained were strikingly similar to those reported previously in subjects with recessively inherited stationary night blindness; the dark-adaptation curve was monophasic (ie, no evidence of a scotopic branch), rhodopsin kinetics were entirely normal, and spectral threshold data revealed the presence of residual rod-mediated vision. Also like the heritable condition, the b-wave of the ERG was depressed grossly despite normal a-wave potentials. These findings, and the fact that vincristine is known to disrupt the structural integrity of neuronal microtubules, suggest that the drug-induced defect involves the process of synaptic transmission between the photoreceptors and their second-order neurons

Retinal disease preferentially affects the sensitivity of the 'blue'-cone pathways. This vulnerability to disease may be due, in part, to a more limited response range. A psychophysical technique, the probe-flash paradigm, was used to test this hypothesis. The data suggest that the S-cone pathways have a more limited response range than the L-cone pathways. Explanations for blue-cone vulnerability are discessed in the context of this finding

A psychophysical procedure, the probe-flash paradigm, was used to test explanations of early foveal sensitivity loss in retinitis pigmentosa. The findings suggest that this loss may be due to a decreased responsiveness of retinal elements and not to a decrease in quantum catching ability of functioning photoreceptors