Sensitivity losses in a long wavelength sensitive mechanism of patients with retinitis pigmentosa

Tactile Cues for Improving Target Localization in Subjects with Tunnel Vision

The loss of peripheral vision is experienced by millions of people with glaucoma or retinitis pigmentosa, and has a major impact in everyday life, specifically to locate visual targets in the environment. In this study, we designed a wearable interface to render the location of specific targets with private and non-intrusive tactile cues. Three experimental studies were completed to design and evaluate the tactile code and the device. In the first study, four different tactile codes (single stimuli or trains of pulses rendered either in a Cartesian or a Polar coordinate system) were evaluated with a head pointing task. In the following studies, the most efficient code, trains of pulses with Cartesian coordinates, was used on a bracelet located on the wrist, and evaluated during a visual search task in a complex virtual environment. The second study included ten subjects with a simulated restrictive field of view (10°). The last study consisted of proof of a concept with one visually impaired subject with restricted peripheral vision due to glaucoma. The results show that the device significantly improved the visual search efficiency with a factor of three. Including object recognition algorithm to smart glass, the device could help to detect targets of interest either on demand or suggested by the device itself (e.g., potential obstacles), facilitating visual search, and more generally spatial awareness of the environment.

Assessment of foveal cone photoreceptors in Stargardt's macular dystrophy using a small dot detection task

We measured frequency-of-seeing curves for tiny (1.125 and 3.375 min arc) stimuli flashed briefly at absolute threshold to estimate the density of foveal cones in normals and in subjects with Stargardt's macular dystrophy. Foveal absolute thresholds for Stargardt's were elevated 1.5 log units over normal. Analysis using Poisson counting statistics indicated that the quantal absorption to stimulate individual cones was normal for Stargardt's but that effective optical density of individual cones was reduced by > 1 log. Numerical density of foveal cones was reduced 1 log unit for Stargardt's patients with acuities of 20/30-20/100.

Losses of temporal modulation sensitivity in retinal degenerations

Sensitivity losses in patients with retinitis pigmentosa (RP) have been attributed to a decrease in photopigment density, to a reduction in the number of photoreceptors, and also to a change in temporal response properties of the receptors. The sensitivity losses in patients with macular degeneration have also been attributed to a loss of photoreceptors. To test these explanations for sensitivity loss we obtained electrophysiological and psychophysical temporal modulation transfer functions (MTFs) on normal subjects in response to varying stimulus luminances and retinal loci. These stimulus manipulations did not duplicate the changes observed in the temporal MTFs of patients. The temporal response properties of the receptors were tested electrophysiologically by manipulating stimulus presentation interval. The results provided evidence for sensitivity losses in RP patients being due to alterations in the temporal response properties of the receptors.

Foveal sensitivity changes in retinitis pigmentosa

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.

Dependence of cone b-wave implicit time on rod amplitude in retinitis pigmentosa

Computer-averaged full-field rod and cone electroretinograms (ERGs) were evaluated in 63 patients with retinitis pigmentosa and 116 normal subjects. Cone b-wave implicit times to 30 Hz white flicker and to 1.0 Hz white flashes on a white background were both inversely proportional to the log amplitude of the dark-adapted rod b-wave, even when controlling for the log amplitude of the dark-adapted cone b-wave. Cone ERGs were also obtained from a subset of 12 patients with retinitis pigmentosa in the presence of photopically-matched red and blue backgrounds that allowed direct assessment of the effect of rod function on cone b-wave implicit time in the patients. The effectiveness of the blue background in reducing cone b-wave implicit time relative to that obtained with the red background varied with the amplitude of the rod ERG. The results of both experiments suggest that delays in cone b-wave implicit time obtained with 30 Hz white flicker or with background adaptation in patients with retinitis pigmentosa are due, at least in part, to rod disease.