Biology subjects

Domdei, N.

Publications and source records attributed to Domdei, N..

6 recordsLinked to original sources

bioRxiv2024

Neural contrast sensitivity is not affected by myopic blur

PurposeThe prevalence of myopia is increasing worldwide, accompanied by an increase of potentially under-corrected myopes. Because the neural pathways processing the retinal image are prone to adaptation in relation to the retinal image quality, we wondered to what extent neural contrast sensitivity (NCS) is altered in the presence of myopic blur. Additionally, the impact of retinal abnormalities like foveal hypoplasia with albinism on NCS was tested. MethodsNCS was psychophysically determined for 11 emmetropic, 23 myopic well-corrected and 15 myopic under-corrected otherwise healthy young (27 {+/-} 6 years) participants and 1 albinism patient. Aberration-free stimulation, independent of the eyes refractive state, was achieved by using a unique spatial light modulator-based interferometric system to bypass the eyes optics. ResultsNo significant differences in NCS were observed between the three groups (Median area-under-curve: 61.9, 62.1, and 62.9 for emmetropes, well-corrected, and under-corrected myopes, respectively; all p > 0.1) but were significantly equivalent between emmetropes and myopes (all p < 0.001). However, the NCS function of the albinism patient differed significantly from the here defined "normal" NCS function. ConclusionsNCS is unaffected by myopic blur and remains stable even for under-correction of up to 1.5 D. This means, that long-term under-corrected myopes still can achieve normal visual acuity as soon as their refractive errors are sufficiently corrected. Furthermore, NCS testing can relate visual deficits to an underlying neurological disorder.

neuroscience↗

bioRxiv2024

Action potential propagation speed compensates for traveling distance in the human retina

Neural information processing requires accurately timed action potentials arriving from presynaptic neurons at the postsynaptic neuron. However, axons of ganglion cells in the human retina feature low axonal conduction speeds and vastly different lengths, which poses a challenge to the brain for constructing a temporally coherent image over the visual field. Combining results from microelectrode array recordings, human behavioral measurements, transmission electron microscopy, and mathematical modelling of the retinal nerve fiber layer, we demonstrate that axonal propagation speeds compensate for variations in axonal length across the human retina including the fovea. The human brain synchronizes the arrival times of action potentials at the optic disc by increasing the diameters of longer axons, which increases their propagation speeds.

neuroscience↗

bioRxiv2024

Assessing visual performance during intense luminance changes in virtual reality

During indoor-outdoor transitions humans encounter luminance changes beyond the functional range of the photoreceptors, leaving the individual at risk of overlooking harmful low-contrast objects until adaptation processes re-enable optimal vision. To study human visual performance during intense luminance changes, we propose a virtual reality based testbed. After linearization of the headsets luminance output, detection times were recorded for ten participants. The small (FWHM = 0.6 degree) low-contrast stimuli appeared randomly in one of four corners ({+/-}10 degree) after luminance changes of three magnitudes within 1 or 3 seconds. Significantly decreased detection times were observed for the conditions with simulated self-tinting lenses compared to lenses with fixed transmission rates after luminance decreases. In cases of luminance increases all detection times were similar. In conclusion, the proposed virtual reality testbed allows for studying vision during or after steep luminance changes and helps to design technical aids like self-tinting lenses. HighlightsThe HTC Vive headset provides a practicable luminance range of 3 magnitudes, allowing the simulation of indoor-outdoor transitions. Visual performance after steep luminance decreases was significantly better with simulated self-tinting spectacles reducing the encountered luminance step. Different transmission rates of the simulated lenses did not affect the detection times for small low-contrast stimuli after luminance increases.

neuroscience↗

bioRxiv2021

Human gaze is precisely aligned with the foveolar cone topography of both eyes

The small physical depression of the human retina, the fovea, is the retinal locus of prime visual resolution, achieved by a peaking topography of the light sensitive cone photoreceptor outer segments 1-3 and a post-receptor wiring scheme preserving high-density sampling 4,5. Humans dynamically direct their gaze such that the retinal images of objects of interest fall onto the foveola, the central one-degree diameter of the fovea 6-8, but it is yet unclear if a relationship between the individual photoreceptor topography at this location and visual fixation behavior exists 9,10. By employing adaptive optics in vivo imaging and micro-stimulation 11-13, we created topographical maps of the complete foveolar cone mosaics in both eyes of 20 healthy participants while simultaneously recording the retinal location of a fixated visual object in a psychophysical experiment with cellular resolution. We found that the locus of fixation was systematically shifted away from the topographical centers towards a naso-superior quadrant on the retina, about 5 minutes of arc of visual angle on average, with a mirror symmetrical trend between fellow eyes. In cyclopean view, the topographical centers were superior to the fixated target, corresponding to areas in the visual field usually more distant 14,15 and thus containing higher spatial frequencies. Given the large variability in foveal topography between individuals, and the surprising precision with which fixation is repeatedly directed to just a small bouquet of cones in the foveola, these findings demonstrate a finely tuned, functionally relevant link between the development of the cellular mosaic of photoreceptors and visual behavior.

neuroscience↗

bioRxiv2021

Retinal factors of visual sensitivity in the human fovea

Humans direct their gaze towards visual objects of interest such that the retinal images of fixated objects fall onto the fovea, a small anatomically and physiologically specialized region of the retina displaying highest visual fidelity. One striking anatomical feature of the fovea is its non-uniform cellular topography, with a steep decline of cone photoreceptor density and outer segment length with increasing distance from its center. We here assessed in how far the specific cellular organization of the foveola is reflected in visual function. Increment sensitivity to small spot visual stimuli (1 x 1 arcmin, 543 nm light) was recorded psychophysically in 4 human participants at 17 locations placed concentric within a 0.2-degree diameter around the preferred retinal locus of fixation with adaptive optics scanning laser ophthalmoscopy based microstimulation. While cone density as well as maximum outer segment length differed significantly among the four tested participants, the range of observed threshold was similar, yielding an average increment threshold of 3.3 {+/-} 0.2 log10 photons at the cornea. Thresholds were correlated with retinal eccentricity, as well as cone density and outer segment length. Biophysical simulation allowed to develop a model of foveal sensitivity based on these parameters, explaining at least 37% of the observed threshold variability. Based on high reproducibility in replicate testing, the residual variability is assumed to be caused by individual cone and bipolar cell weighting at the specific target locations.

neuroscience↗

bioRxiv2019

Eye tracking-based estimation and compensation of chromatic offsets for multi-wavelength retinal microstimulation with foveal cone precision

Multi-wavelength ophthalmic imaging and stimulation of photoreceptor cells requires consideration of chromatic dispersion of the eye, manifesting in longitudinal and transverse chromatic aberrations. Current image-based techniques to measure and correct transverse chromatic aberration (TCA) and the resulting transverse chromatic offset (TCO) in an adaptive optics retinal imaging system are precise, but lack compensation of small but significant shifts in eye position occurring during in vivo testing. Here we present a method that requires only a single measurement of TCO during controlled movements of the eye to map retinal chromatic image shifts to the image space of a pupil camera. After such calibration, TCO can be compensated by continuously monitoring eye position during experimentation and by interpolating correction vectors from a linear fit to the calibration data. The average change rate of TCO per head shift and the correlation between Kappa and the individual foveal TCA are close to the expectations based on a chromatic eye model. Our solution enables continuous correction of TCO with high spatial precision and avoids high light intensities required for re-measuring TCO after eye position changes, which is necessary for foveal cone-targeted psychophysical experimentation.

biophysics↗