Changes In Visual Performance Research Articles

Differential Functional Changes in Visual Performance during Acute Exposure to Microgravity Analogue and Their Potential Links with Spaceflight-Associated Neuro-Ocular Syndrome.

Spaceflight-Associated Neuro-Ocular Syndrome (SANS) is a complex pathology threatening the health of astronauts, with incompletely understood causes and no current specific functional diagnostic or screening test. We investigated the use of the differential performance of the visual system (central vs. perimacular visual function) as a candidate marker of SANS-related pathology in a ground-based microgravity analogue. We used a simple reaction time (SRT) task to visual stimuli, presented in the central and perimacular field of view, as a measure of the overall performance of the visual function, during acute settings (first 10 min) of vertical, bed rest (BR), -6°, and -15° head-down tilt (HDT) presentations in healthy participants (n = 8). We built dose-response models linking the gravitational component to SRT distribution parameters in the central vs. perimacular areas. Acute exposure to microgravity induces detectable changes between SRT distributions in the perimacular vs. central retina (increased mean, standard deviation, and tau component of the ex-Gaussian function) in HDT compared with vertical presentation. Functional testing of the perimacular retina might be beneficial for the earlier detection of SANS-related ailments in addition to regular testing of the central vision. Future diagnostic tests should consider the investigation of the extra-macular areas, particularly towards the optic disc.

Changes in visual performance after implantation of different intraocular lenses.

To evaluate the trending visual performance of different intraocular lenses (IOLs) over time after implantation. Ninety-one patients received cataract surgery with implantations of monofocal (Mon) IOLs, segmental refractive (SegRef) IOLs, diffractive (Dif) IOLs, and extended-depth-of-focus (EDoF) IOLs were included. The aberrations and optical quality collected with iTrace and OQAS within postoperative 6mo were followed and compared. Most of the visual parameters improved over the postoperative 6mo. The postoperative visual acuity (POVA) of the Mon IOL, SegRef IOL, and EDoF IOL groups achieved relative stability in earlier states compared with the Dif IOL group. Nevertheless, the overall visual performance of the 3 IOLs continued to upturn in small extents within the postoperative 6mo. The optical quality initially improved in the EDoF IOL group, then in the Mon IOL, SegRef IOL, and Dif IOL groups. POVA and objective visual performance of the Mon IOL and EDoF IOL groups, as well as POVA and visual quality of the Dif IOL group, improved in the postoperative 1mo and stabilized. Within the postoperative 6mo, gradual improvements were observed in the visual acuity and objective visual performance of the SegRef IOL group, as well as in the postoperative optical quality of the Dif IOL group. The visual performance is different among eyes implanted with different IOLs. The findings of the current study provide a potential reference for ophthalmologists to choose suitable IOLs for cataract patients in a personalized solution.

Measurement of visual function in infantile nystagmus: a systematic review

Background/aimsRecent work has called into question the ability of visual acuity (VA) to accurately represent changes in visual function in infantile nystagmus (IN). This systematic review investigated factors affecting visual...

Absolute prediction of relative changes in contrast sensitivity with aberrations using a single metric of retinal image quality.

Metrics of retinal image quality predict optimal refractive corrections and correlate with visual performance. To date, they do not predict absolutely the relative change in visual performance when aberrations change and therefore need to be a-posteriori rescaled to match relative measurements. Here we demonstrate that a recently proposed metric can be used to predict, in an absolute manner, changes in contrast sensitivity measurements with Sloan letters when aberrations change. Typical aberrations of young and healthy eyes (for a 6 mm pupil diameter) were numerically introduced, and we measured the resulting loss in contrast sensitivity of subjects looking through a 2 mm diameter pupil. Our results suggest that the metric can be used to corroborate measurements of visual performance in clinical practice, thereby potentially improving patient follow-ups.

Improvement of neural contrast sensitivity after long-term adaptation in pseudophakic eyes.

An adaptive optics (AO) system was used to investigate the effect of long-term neural adaptation to the habitual optical profile on neural contrast sensitivity in pseudophakic eyes after the correction of all aberrations, defocus, and astigmatism. Pseudophakic eyes were assessed at 4 and 8 months postoperatively for changes in visual performance. Visual benefit was observed in all eyes at all spatial frequencies after AO correction. The average visual benefit across spatial frequencies was higher in the pseudophakic group (3.31) at 4 months postoperatively compared to the normal group (2.41). The average contrast sensitivity after AO correction in the pseudophakic group improved by a factor of 1.73 between 4 and 8 months postoperatively. Contrast sensitivity in pseudophakic eyes was poorer, which could be attributed to long-term adaptation to the habitual optical profiles before the cataract surgery, in conjunction with age-related vision loss. Improved visual performance in pseudophakic eyes suggests that the aged neural system can be re-adapted for altered ocular optics.

Out of water in the dark: Plasticity in visual structures and function in an amphibious fish

Many fishes encounter periods of prolonged darkness within their lifetime, yet the consequences for the visual system are poorly understood. We used an amphibious fish (Kryptolebias marmoratus) that occupies dark terrestrial environments during seasonal droughts to test whether exposure to prolonged darkness diminishes visual performance owing to reduced optic tectum (OT) size and/or neurogenesis. We performed a 3-week acclimation with a 2 2 factorial design, in which fish were either acclimated to a 12 h:12 h or 0 h:24 h light:dark photoperiod in water or in air. We found that water-exposed fish had poorer visual acuity when acclimated to the dark, while air-acclimated fish had poorer visual acuity regardless of photoperiod. The ability of K. marmoratus to capture aerial prey from water followed a similar trend, suggesting that good vision is important for hunting effectively. Changes in visual acuity did not result from changes in OT size, but air-acclimated fish had 37% fewer proliferating cells in the OT than water-acclimated fish. AsK. marmoratus are unable to eat on land, reducing cell proliferation in the OT may serve as a mechanism to reduce maintenance costs associated with the visual system. Overall, we suggest that prolonged darkness and air exposure can impair vision in K. marmoratus, and that changes in visual performance may be mediated, in part, by OT neurogenesis. More broadly, we show that plastic changes to the visual system of fishes can have potential consequences for organismal performance and fitness.

Efficacy and Safety of Different Add Power Soft Contact Lenses on Myopia Progression in Children: A Systematic Review and Meta-Analysis

Background: In children, myopia has become a widespread and serious global public health problem. Soft multifocal contact lenses (SMCLs) have been widely studied to control myopia progression in children. However, their efficacy in myopia control in children and its adverse effects and which added power SMCLs are more effective and safer remains to be explored. Objectives: Evaluate the efficacy and safety of various add power SMCLs to slow myopia progression in children. Method: Eligible randomized controlled trials were retrieved from PubMed, MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials databases. The present meta-analysis analyzed the mean differences (MD) in myopic progression, axial length, and odds ratios for adverse effects and dropout rates between SMCLs with different added powers and control groups. Changes in visual performance were also systematically evaluated. Results: Seven independent studies involving 805 children were included in the present meta-analysis. At 1-year, the weighted MD (WMD) in myopia progression between SMCL and control groups was −0.22 diopters (D) (95% confidence interval [CI]: −0.56 to 0.12 D) for low add power SMCLs, 0.09 D (95% CI: 0–0.19 D) for medium add power SMCLs, and 0.2 D (95% CI: 0.13, 0.27 D) for high add power SMCLs. At 2-years, the WMD for medium add power was 0.12 D (95% CI: −0.03 to 0.27 D), and for high add power was 0.25 D (95% CI: 0.14–0.35 D). No differences were detected for adverse effects (p = 0.2) and acceptability (p = 0.74) between different added powers. Additionally, differences in visual performance changes, produced by different added powers, were not detected. Conclusions: The present meta-analysis showed that high add power SMCLs are more effective and stable to control myopia progression. Besides, the adverse effects and acceptability were not related to the added power.

Changes in Visual Performance under the Effects of Moderate-High Alcohol Consumption: The Influence of Biological Sex.

The purpose of this study was to analyze the changes in visual functions under the effects of moderate–high breath alcohol concentrations (BrACs), and the influence of biological sex on visual deterioration, considering different factors. A total of 37 healthy habitual alcohol users were enrolled in the experiment. The participants underwent a baseline session and a second session after an intake of 450 mL of red wine, so that all of them reached a BrAC above 0.25 mg/L. Visual performance was assessed by measuring the contrast sensitivity function, the halo perception, the stereopsis, and finally the retinal image quality. A Visual Deterioration Score (VDS) was calculated using the deterioration of these visual variables. All visual functions analyzed were significantly impaired following alcohol consumption (p < 0.05). The VDS was associated with the BrAC (ρ = −0.476). The VDS was also significantly higher in females, with the BrAC having a significant effect on the variability of the VDS in males and females (p < 0.05). However, the body mass index showed no significant effect (p > 0.05). Visual functions were significantly impaired under the influence of alcohol, and this deterioration was greater in females. The deterioration depends on the BrAC reached, being the primary thing responsible for the differences observed between males and females.

Individual changes in visual performance in non-demented Parkinson's disease patients: a 1-year follow-up study.

Cognitive deficits in Parkinson's disease (PD) are heterogeneous entities, and the cognitive status fluctuates over time. However, individual changes in longitudinal cognitive performance in PD are not fully understood. We evaluated three visual indices (visuoperception, visuoconstruction, and visuospatial ability) and four cognitive domains (attention/working memory, executive function, memory, and language) at baseline (Time1) and at 1-year follow-up (Time2) in 36 patients with PD and 32 healthy controls (HCs). To explore the magnitude and frequency of cognitive changes, we analyzed data using the simple difference method and the standardized regression-based method. We also explored the correlations between changes in test scores and several clinical predictors, using logistic regression analysis. At 1 year, patients with PD showed higher rates of change in scores on several cognitive tests, especially the Incomplete Letters test of visuoperception, compared to HCs. After adjusting for demographic variables, the visuoperceptual change was 61.1% overall, with the largest effect size. The changes in scores of visuoperception correlated with those of memory (r = 0.672, p < 0.001), language (r = 0.389, p < 0.05), and visuospatial ability (r = 0.379, p < 0.05). The severity of olfactory disturbance, the MDS-UPDRS Part I score, and younger PD onset predicted the significant changes observed in the Incomplete Letters test scores. Visuoperception changed more in non-demented PD patients than in HCs at 1-year follow-up. The changes in visuoperception could relate to involvement of the ventral occipitotemporal pathway, the more widespread temporal lobe, and brain reserve in PD.

Reliable sideline ocular-motor assessment following exercise in healthy student athletes

ObjectivesTo assess the reliability and effect of exercise on sideline dynamic visual performance measures of ocular-motor function using a portable visual assessment system (EYE-SYNC®). DesignProspective cohort study. MethodsHealthy student athletes, ages 18–25 years, performed eye-tracking six times—three times consecutively prior to and after practice—using EYE-SYNC® goggles. Ocular-motor performance was assessed by calculating five gaze error outcomes between target position and actual gaze position to inform dynamic visual synchronization. We assessed reliability by calculating the intraclass correlation coefficient (ICC) for each outcome (we defined the standard deviation of tangential error (SDTE) as our primary outcome) and calculated differences in mean pre- and post-practice scores. ResultsICCs for the SDTE score were 0.86 (95% confidence interval, CI: 0.82–0.9) and 0.88 (0.84–0.91) at pre- and post-practice, respectively. 133 (89%) and 135 (90%) of 150 athletes had at least one measurement at pre- and post-practice, respectively. 117 (78%) and 122 (81%) athletes had more than one SDTE score at pre- and post-practice, respectively. The absolute mean (SD) differences between pre- and post-practice mean scores ranged from 0.02 (0.05) for horizontal gain to 0.1 (0.5) for SDTE. ConclusionsWe observed high ICC scores indicating excellent reliability of visual synchronization measurements, suggesting that one measurement would be sufficient. Most athletes had similar scores before and after practice, indicating little change in visual performance following exercise. EYE-SYNC® goggles have the potential for use in obtaining objective visual performance measures of ocular-motor function for sideline assessment of concussion and return to play decisions.

Visual training in hemianopia alters neural activity in the absence of behavioural improvement: a pilot study.

BackgroundDamage to the primary visual cortex (V1) due to stroke often results in permanent loss of sight affecting one side of the visual field (homonymous hemianopia). Some rehabilitation approaches have shown improvement in visual performance in the blind region, but require a significant time investment.MethodsSeven patients with cortical damage performed 400 trials of a motion direction discrimination task daily for 5 days. Three patients received anodal transcranial direct current stimulation (tDCS) during training, three received sham stimulation and one had no stimulation. Each patient had an assessment of visual performance and a functional magnetic resonance imaging (fMRI) scan before and after training to measure changes in visual performance and cortical activity.ResultsNo patients showed improvement in visual function due to the training protocol, and application of tDCS had no effect on visual performance. However, following training, the neural response in motion area hMT+ to a moving stimulus was altered. When the stimulus was presented to the sighted hemifield, activity decreased in hMT+ of the damaged hemisphere. There was no change in hMT+ response when the stimulus was presented to the impaired hemifield. There was a decrease in activity in the inferior precuneus after training when the stimulus was presented to either the impaired or sighted hemifield. Preliminary analysis of tDCS data suggested that anodal tDCS interacted with the delivered training, modulating the neural response in hMT+ in the healthy side of the brain.ConclusionTraining can affect the neural responses in hMT+ even in the absence of change in visual performance.

Effects of Myopic Orthokeratology on Visual Performance and Optical Quality.

To analyze the changes in visual performance and optical quality after orthokeratology (ortho-k) treatment and its correlation with the magnitude of lens decentration and the diameter of treatment zone (TxZ). A prospective study was conducted in 27 eyes of 27 patients wearing ortho-k contact lens. Area under log contrast sensitivity function (AULCSF), modulation transfer function cutoff values (MTFcutoff), Strehl ratio (SR), and objective scattering index (OSI) were measured and compared before and 1 month after ortho-k lens treatment. Refractive sphere, astigmatism, and diameter and decentration of TxZ were tested against the change in AULCSF, MTFcutoff, SR, and OSI after ortho-k treatment in stepwise multiple linear regression models. Objective scattering index significantly increased and AULCSF, MTFcutoff, and SR significantly decreased after ortho-k lens wear (all P<0.001). The mean TxZ diameter was 3.61±0.26 mm, and the mean magnitude of TxZ decentration was 0.60±0.16 mm. The amount of lens decentration significantly correlated with the change in AULCSF and MTFcutoff (P=0.027 and P=0.005, respectively). The diameter of TxZ significantly correlated with the change in MTFcutoff and SR (P=0.005 and P=0.024, respectively). Visual and optical quality decreases after ortho-k treatment, which can be alleviated by a larger TxZ diameter and a smaller lens decentration.

Mechanisms Underlying Early-Stage Changes in Visual Performance and Retina Function After Experimental Induction of Sustained Dyslipidemia.

Visual and retinal function was measured in a mouse model of chemically induced, sustained dyslipidemia to determine the contribution of dyslipidemia to the pathogenesis of retinopathy in the context of metabolic syndrome. Fifteen male C57BL/6Crl mice were divided into three groups. Poloxamer 407 (P-407), 14.5% w/w was delivered at a rate of 6µl/day by implanted osmotic mini-pumps either subcutaneously (P-407 SQ) or intraperitoneally (P-407 IP) to P-407-treated mice, whereas saline was administered at the same rate to control mice using only the subcutaneous route of administration. Total cholesterol (TC) and true triglyceride (TG) levels were quantified from plasma. Optomotor responses to stimuli of varying spatial frequency or contrast were used to measure visual acuity and contrast sensitivity. Retinal function was determined using Ganzfeld flash electroretinography (ERG). At 32 days, TC for the P-407 IP group was significantly elevated compared to saline controls (169.4 ± 16.5mg/dl, 0.001 < P < 0.01). TG levels for both the P-407 SQ (59.3 ± 22.4mg/dl, 0.01 < P < 0.05) and P-407 IP groups (67.7 ± 18.0mg/dl, 0.001 < P < 0.01) were significantly elevated relative to controls. Electroretinography demonstrated a very significant decline in the b/a ratio (1.80 ± 0.11, P < 0.01) for the P-407 IP group. The b/a ratio exhibited a moderate, significant correlation with TC levels (r = - 0.4425, P = 0.0392) and a strong, very significant correlation with TG levels (r = - 0.6190, P = 0.0021). Delivery of P-407 via osmotic mini-pump resulted in the sustained, significant elevation of plasma TC and TG levels. This elevation in plasma lipid levels was correlated with a decline in inner retinal function.

Normative best-corrected values of the visual image quality metric VSX as a function of age and pupil size.

The visual image quality metric the visual Strehl ratio (VSX) combines a comprehensive description of the optics of an eye (wavefront error) with an estimate of the photopic neural processing of the visual system, and has been shown to be predictive of subjective best focus and well correlated with change in visual performance. Best-corrected visual image quality was determined for 146 eyes, and the quantitative relation of VSX, age, and pupil size is presented, including 95% confidence interval norms for age groups between 20 and 80 years and pupil diameters from 3 to 7mm. These norms were validated using an independently collected population of wavefront error measurements. The best visual image quality was found in young eyes at smaller pupil sizes. Increasing pupil size caused a more rapid decrease in VSX than increasing age. These objectively determined benchmarks represent the best theoretical levels of visual image quality achievable with a sphere, cylinder, and axis correction in normal eyes and can be used to evaluate both traditional and wavefront-guided optical corrections provided by refractive surgery, contact lenses, and spectacles.

Pseudoamblyopia in Congenital Cyclotropia.

Purpose To study the effect of surgery on amblyopia and suppression associated with congenital cyclovertical strabismus. Methods The fixation pattern was investigated with microperimetry before and soon after surgery in ten consecutive children operated for congenital superior oblique palsy at the S. Martino Hospital, Belluno, Italy, between September 2014 and December 2015. Changes in visual performance in terms of best-corrected visual acuity (BCVA) and stereopsis between the day before and one week after surgery were also evaluated. No other amblyopia treatment has been administered during the time study. Results Surgical correction of the excyclodeviation in congenital SO palsy determined monocular and binocular sensory consequences: monocularly, in the cyclodeviated amblyopic eye, BCVA (0.46–0.03 LogMAR; p < 0.0001) and the fixation pattern improved, as demonstrated by microperimetry examination. Binocularly, stereopsis improved or emerged while suppression at the Worth four-dot test disappeared. Conclusions In the absence of further amblyopic factors such as coexisting constant vertical and/or horizontal deviation and anisometropia, the amblyopia encountered in congenital SO palsy may resolve soon after the surgical alignment. Therefore, it may be considered and defined “pseudoamblyopia.”

Exploring the Use of Sensorial LTP/LTD-Like Stimulation to Modulate Human Performance for Complex Visual Stimuli.

Is it possible to passively induce visual learning/unlearning in humans for complex stimuli such as faces? We addressed this question in a series of behavioral studies using passive visual stimulation (flickering of faces at specific temporal frequencies) inspired by well-known synaptic mechanisms of learning: long-term potentiation (LTP) vs long-term depression (LTD). We administered a face identity change detection task before and after a passive stimulation protocol to test for potential changes in visual performance. First, with bilateral stimulation, subjects undergoing high-frequency LTP-like stimulation outperformed those submitted to low-frequency LTD-like stimulation despite equivalent baseline performance (exp. 1). Second, unilateral stimulation replicated the differential modulation of performance, but in a hemifield-specific way (exp. 2). Third, for both stimulation groups, a sudden temporary drop in performance on the stimulated side immediately after the stimulation, followed by progressive recovering, can suggest either ‘visual fatigue’ or ‘face adaptation’ effects due to the stimulation. Fourth, we tested the life-time of these modulatory effects, revealing they vanish after one hour delay (exp. 3). Fifth, a control study (exp. 4) using low-level visual stimuli also failed to show longer-term effects of sensory stimulation, despite reports of strong effects in the literature. Future studies should determine the necessary and sufficient conditions enabling robust long-term modulation of visual performance using this technique. This step is required to consider further use in fundamental research (e.g., to study neural circuits involved in selective visual processing) and potential educational or clinical applications (e.g., inhibiting socially-irrelevant aspects of face processing in autism).

Hydrogel Inlay for Presbyopia: Objective and Subjective Visual Outcomes

To evaluate changes in visual performance and ocular optical quality after implantation of a corneal hydrogel inlay as a treatment for presbyopia. A Raindrop Near Vision Inlay (ReVision Optics, Lake Forest, CA) was implanted monocularly on the stromal bed of a femtosecond laser-assisted generated corneal flap of non-dominant eyes of 22 patients with emmetropic presbyopia (preoperative spherical equivalent range: -0.50 to 1.00 diopters). Efficacy was determined by measuring near and distance visual acuities and ocular aberrations, and satisfaction was assessed by a patient questionnaire. The preoperative monocular uncorrected near visual acuity of the inlay inserted eye was 20/129 ± 1 Snellen (range: 20/135 to 20/61 Snellen) and improved to 20/35 ± 2 Snellen (range: 20/61 to 20/20 Snellen) (P < .01) at 6 months postoperatively. The monocular uncorrected distance visual acuity of the eye receiving the inlay was 20/25 ± 2 Snellen (range: 20/50 to 20/20 Snellen) preoperatively and 20/25 ± 1 Snellen (range: 20/50 to 20/20 Snellen) at 6 months postoperatively (P =.257). According to the questionnaire responses, 82% of patients were satisfied. This was despite near glasses needs remaining in 13.6% of the cohort and the presence of glare and a decrease in night vision in approximately 40% of patients. The primary spherical aberration coefficient Z4(0) changed from positive to negative values in all patients (P < .01). However, the point spread function showed no significant change. Hydrogel corneal inlays improve uncorrected near visual acuity in patients with presbyopia with only moderate effect on visual quality. However, the satisfaction with this therapy was relatively lower in these Korean patients than that reported previously in Western patients.

Visual Consequences of Molecular Changes in the Guanylate Cyclase-Activating Protein

We characterized and modeled changes in visual performance associated with a Tyr99Cys mutation in guanylate cyclase-activating protein-1 (GCAP1) in four family members aged between 39 and 55 years old. Guanylate cyclase and its activating protein are molecules in the visual transduction pathway that restore cyclic GMP (cGMP) following its light-activated hydrolysis. The mutation causes an excess of cGMP in the dark and results in progressive photoreceptor loss. L-cone temporal acuity was measured as a function of target irradiance, and L-cone temporal contrast sensitivity was measured as a function of temporal frequency. All four mutant GCAP1 family members showed sensitivity or acuity losses relative to normal observers. The data for the youngest family member are consistent with an abnormal speeding up of the visual response relative to that in normals, but those for the older members showed a progressively higher-frequency sensitivity loss consistent with a slowing down of their response. The speeding up of the visual response in the youngest observer is consistent with the Tyr99Cys mutation that results in the more rapid replacement of cGMP after light exposure and, thus, in a reduction of temporal integration and relative improvement in high-frequency sensitivity compared to normals. The high-frequency losses in the older observers are consistent with their vision being limited by the interposition of some sluggish process. This might result from some residual or malfunctioning molecular process limiting transduction within damaged photoreceptors or from an active or passive postreceptoral reorganization caused by the paucity of functioning photoreceptors.

Astigmatism Impact on Visual Performance

Astigmatic subjects are adapted to their astigmatism and perceptually recalibrate upon its correction. However, the extent to which prior adaptation to astigmatism affects visual performance, whether this effect is axis dependent, and the time scale of potential changes in visual performance after astigmatism correction are not known. Moreover, the effect of possible positive interactions of aberrations (astigmatism and coma) might be altered after recalibration to correction of astigmatism. Visual acuity (VA) was measured in 25 subjects (astigmats and non-astigmats, corrected and uncorrected) under induction of astigmatism and combinations of astigmatism and coma while controlling subject aberrations. Astigmatism (1.00 diopter) was induced at three different orientations, the natural axis, the perpendicular orientation, and 45 degrees for astigmats and at 0, 90, and 45 degrees for non-astigmats. Experiments were also performed, adding coma (0.41 μm at a relative angle of 45 degrees) to the same mentioned astigmatism. Fourteen different conditions were measured using an 8-Alternative Forced Choice procedure with Tumbling E letters and a QUEST algorithm. Longitudinal measurements were performed up to 6 months. Uncorrected astigmats were provided with proper astigmatic correction after the first session. In non-astigmats, inducing astigmatism at 90 degrees, produced a statistically lower reduction in VA than at 0 or 45 degrees, whereas in astigmats, the lower decrease in VA occurred for astigmatism induced at the natural axis. Six months of astigmatic correction did not reduce the insensitivity to astigmatic induction along the natural axis. Differences after orientation of astigmatism were also found when adding coma to astigmatism. The impact of astigmatism on VA is greatly dependent on the orientation of the induced astigmatism, even in non-astigmats. Previous experience to astigmatism plays a significant role on VA, with a strong bias toward the natural axis. In contrast to perceived isotropy, the correction of astigmatism does not shift the bias in VA from the natural axis of astigmatism.

Rapid Simultaneous Enhancement of Visual Sensitivity and Perceived Contrast during Saccade Preparation

Humans and other animals with foveate vision make saccadic eye movements to prioritize the visual analysis of behaviorally relevant information. Even before movement onset, visual processing is selectively enhanced at the target of a saccade, presumably gated by brain areas controlling eye movements. Here we assess concurrent changes in visual performance and perceived contrast before saccades, and show that saccade preparation enhances perception rapidly, altering early visual processing in a manner akin to increasing the physical contrast of the visual input. Observers compared orientation and contrast of a test stimulus, appearing briefly before a saccade, to a standard stimulus, presented previously during a fixation period. We found simultaneous progressive enhancement in both orientation discrimination performance and perceived contrast as time approached saccade onset. These effects were robust as early as 60 ms after the eye movement was cued, much faster than the voluntary deployment of covert attention (without eye movements), which takes ∼300 ms. Our results link the dynamics of saccade preparation, visual performance, and subjective experience and show that upcoming eye movements alter visual processing by increasing the signal strength.