Hypoxic, hypercapnic, and hyperoxic responses of the optic nerve head and subfoveal choroid blood flow in healthy humans

Purpose: To investigate the impact of different gas mixtures (hyperoxia, hypoxia, and hypercapnia) on the optic nerve head (ONH) and choroidal (Ch) hemodynamics. Methods: Twenty-three healthy subjects (28 ± 6 years) took part in the study. Variations in inspired oxygen and carbon dioxide fraction were produced by a gas mixing device. Arterial oxygen saturation (SpO2) was measured continuously using a transcutaneous sensor and end-tidal carbon dioxide partial pressure by capnography. The experiment comprised three successive periods: 3-minute baseline (room air breathing), 15-minute gas mixture inhalation (normocapnic hypoxia, hypercapnia, or hyperoxia), and 15-minute recovery (room air breathing). Laser Doppler flowmeter parameters—velocity (VEL), volume (VOL), and flow (BF) of red blood cells—were measured. Two-way ANOVAs were performed for statistical analysis. Results: In response to hyperoxia, ONHBF significantly decreased by −18% ± 6% (P = 0.04) from baseline, due to significant changes in VEL (−12% ± 3% P = 0.0002). During hypoxia at 85% SpO2, ONH VEL increased by +12% ± 3% (P = 0.0009), whereas VOL and BF did not change significantly. ChBF significantly increased by +7% ± 2% (P = 0.004) in response to hypoxia, due to significant changes in VEL +5% ± 2% (P = 0.03). Both Ch and ONHBFs did not vary significantly in response to hypercapnia. Conclusions: The magnitude of the blood flow response is the most significant during hyperoxia for ONH and hypoxia for ChBF. For ONHBF, a 37% difference between hyperoxia and hypoxia can be useful when vasoreactivity to O2 will be tested in patients

Enhancing visual scene categorization in people with age-related macular degeneration through perceptual learning

International audienceAge-related macular degeneration (AMD) is characterized by a central vision loss causedby the destruction of macular photoreceptors. Some studies have investigated the visualabilities of AMD patients in their residual vision. Contrast sensitivity measured using sinusoidal gratings has been shown to decrease for high and low spatial frequencies both at fovea and parafovea suggesting that deficits are not confined to central vision. Other studies confirmed a deficit in processing high spatial frequencies in large photographs of scenes in comparison to normally-sighted participants. The processing of low spatial frequencies was relatively well preserved, allowing effective perception of scenes in parafoveal vision. However, the processing of spatial frequencies is impaired by low-level luminance contrast. A promising readaptation strategy for patients is to train their residual vision through perceptual learning in order to diminish their visual deficits. In this study, we investigated whether perceptual learning could improve patients’ performance in processing spatial frequencies in visual scenes. Four AMD patients participated in an intensive training (12 one-hour sessions spread over 4 weeks). They had to categorize large filtered scenes (covering the residual visualfield) as indoor or outdoor scenes. Scenes were filtered in low spatial frequencies (LSF)or in high spatial frequencies (HSF) and luminance contrast was equalized between LSF and HSF stimuli. Perceptual learning improvements were assessed by comparing performances in sessions before and after the training, using the same categorization task of LSF and HSF filtered scenes, but different stimuli. For each patient, we compared correct responses between the pre- and post-training sessions by calculating an improvement rate. This allowed us to reduce disparities among patients using the formula: ((post-training results - pretraining results)/pre-training results) * 100. Patients showed an average rate improvement of 14.74% (standard error: 6.59%) in processing HSF filtered scenes and of 8.21% (standard error: 4.22%) in processing LSF filtered scenes. Although these findings are preliminary and have to be confirmed with more patients, they suggest that perceptual learning could be an efficient tool to improve AMD patients’ scene perception in their residual vision

Interaction between central and peripheral vision: Influence of distance and spatial frequencies

International audienceVisual scene perception is based on reciprocalinteractions between central and peripheralinformation. Such interactions are commonlyinvestigated through the semantic congruence effect,which usually reveals a congruence effect of centralvision on peripheral vision as strong as the reverse. Theaim of the present study was to further investigate themechanisms underlying central-peripheral visualinteractions using a central-peripheral congruenceparadigm through three behavioral experiments. Wepresented simultaneously a central and a peripheralstimulus, that could be either semantically congruent orincongruent. To assess the congruence effect of centralvision on peripheral vision, participants had tocategorize the peripheral target stimulus while ignoringthe central distractor stimulus. To assess the congruenceeffect of the peripheral vision on central vision, they hadto categorize the central target stimulus while ignoringthe peripheral distractor stimulus. Experiment 1revealed that the physical distance between central andperipheral stimuli influences central-peripheral visualinteractions: Congruence effect of central vision isstronger when the distance between the target and thedistractor is the shortest. Experiments 2 and 3 revealedthat the spatial frequency content of distractors alsoinfluence central-peripheral interactions: Congruenceeffect of central vision is observed only when thedistractor contained high spatial frequencies whilecongruence effect of peripheral vision is observed onlywhen the distractor contained low spatial frequencies.These results raise the question of how these influencesare exerted (bottom-up vs. top-down) and are discussedbased on the retinocortical properties of the visualsystem and the predictive brain hypothesis

Multifocal electroretinography and spectral-domain optical coherence tomography in macula-off rhegmatogenous retinal detachment: A prospective cohort study

International audiencePurpose: To analyze the temporal trends in structural changes using spectral-domain optical coherence tomography and functional changes using multifocal electroretinogram after rhegmatogenous retinal detachment surgery. Methods: This prospective cohort study enrolled 69 patients with macula-off rhegmatogenous retinal detachment who underwent successful surgery. Early Treatment Diabetic Retinopathy Study visual acuity, multifocal electroretinogram evaluation of the central 5 degrees, and spectral-domain optical coherence tomography were recorded at 1, 3, 6, and 12 months (M) after surgery. The fellow eye served as the control group for multifocal electroretinogram parameters. Results: Between M1 and M12, visual acuity improved from 64 to 75 letters (P = 0.001) and implicit time of N1 decreased from 27.8 to 25.2 milliseconds (P = 0.001), whereas the other parameters did not vary significantly. Amplitude and implicit time values did not reach normal values at M12. Alterations of the ellipsoid zone and the external limiting membrane decreased over time (P = 0.001). P1 implicit time correlated independently with the alteration of the external limiting membrane (P = 0.007). Conclusion: Foveal wave amplitudes remain lower than normal values after successful surgery of rhegmatogenous retinal detachment, whereas anatomical improvement was found for outer retinal abnormalities and subretinal edema fluid. Retinal recovery improves N1 implicit time over time. Disruption of external limiting membrane seems to be predictive of increased P1 implicit time

Effect of eplerenone on choroidal blood flow changes during isometric exercise in patients with chronic central serous chorioretinopathy

To investigate choroidal blood flow changes after isometric exercise in patients with chronic central serous chorioretinopathy nontreated or treated with mineralocorticoid receptor antagonists (MRA). Foveolar choroidal laser Doppler flowmetry parameters – velocity (ChVel), volume (ChVol) and blood flow (ChBF) – of 22 eyes of 22 treated patients, 16 eyes of 16 untreated patients and 19 healthy controls were measured during a squatting test. Treatment consisted in MRA administration (eplerenone 50 mg/day or spironolactone 50 mg/day). The experiment comprised three successive periods: 30 seconds of rest, 2 min of continuous squatting exercise, and 150 seconds of recovery. Significance levels were calculated using a generalized estimating equation. During the squatting period, nontreated CSCR eyes had a similar change in ChVel (p = 0.8), ChVol (p = 0.8), ChBF (p = 0.5) and resistance to healthy eyes. Treated CSCR eyes exhibited significantly smaller changes in ChVel (−0.1 ± 11%, p = 0.04) than healthy eyes (6 ± 8%). No significant difference was found for ChVol and ChBF between the groups. The increase in ChVol from baseline in the nontreated CSCR group (4.4 ± 9%) was lower than that of treated group (6.7%±11%; p = 0.01). Finally, ChBF and ChVel changes in the CSCR groups were not significantly different. No abnormalities were detected in the changes in ChBF parameters during increased ocular perfusion pressure in nontreated CSCR patients compared with controls. MRA treatment in CSCR patients induced a significant reduction in ChBVel and an increase in ChBVol in response to isometric exercise, suggesting that MRA exerts effects on choroidal vascular changes

MULTIFOCAL ELECTRORETINOGRAM IN BIRDSHOT CHORIORETINOPATHY

International audiencePURPOSE:To characterize multifocal electroretinogram parameters in patients with birdshot chorioretinopathy.METHODS:Twenty-eight patients with birdshot chorioretinopathy consecutively included from 2006 to 2011 were matched to 27 healthy subjects for age, axial length, and lens status. Multifocal electroretinogram was prospectively evaluated using the Vision Monitor system.RESULTS:Birdshot chorioretinopathy eyes differed significantly from healthy eyes by a decrease in mean root mean square values (-24.7%), P1 (-17.3%) and N2 (-27.5%) amplitude, and the P1/N1 ratio (-26.3%) as well as an increase in N1 (8.7%) and P1 (5.4%) implicit time (IT). An effect of the degree of eccentricity (5 zones) was found for root mean square (P < 0.001), P1 (P < 0.001) and N2 (P < 0.001) amplitude, and P1 IT (P < 0.001). Root mean square, the P1/N1 ratio, P1 and N2 amplitudes, P1 and N1 ITs were significantly correlated with visual acuity, mean defect of visual field, foveal threshold, and color vision score. The fluorescein angiographic score was significantly correlated to N1 and N2 amplitudes and N1 IT.CONCLUSION:Amplitudes and ITs of the multifocal electroretinogram parameters are impaired in patients with birdshot chorioretinopathy and are well correlated with other anatomical and functional tests. Periodic testing could guide the immunosuppressive treatment