Refractive Error of Students (15- to 18-year-olds) in Northwest Mexico.

SIGNIFICANCE: We assessed the prevalence of refractive error in a sample of children of Northern Mexico using the Refractive Error Study in Children protocol of the World Health Organization, which allows for the comparison with other global studies. PURPOSE: Uncorrected refractive error is the main cause of visual impairment in children. The purpose of this study was to assess the refractive error and visual dysfunctions of students (15 to 18 years old) in the upper-middle school system of Sinaloa, Mexico. METHODS: A total of 3468 students in Sinaloa's high school system participated in the study from 2017 to 2019. Optometrists and student clinicians from the Optometry Program of the Autonomous University of Sinaloa conducted the testing. Tests included visual acuities and static retinoscopy. We did not use a cycloplegic agent. RESULTS: The results showed a high prevalence of uncorrected refractive errors. Myopia, defined as a refractive error ≤-0.50 D, had a prevalence of 36.11% (95% confidence interval, 33.47 to 38.83%); hyperopia, defined as a refractive error ≥+2.00 D, had a prevalence of 1.49% (95% confidence interval, 0.09 to 2.33%); and astigmatism, defined as a refractive error with a cylinder ≥0.75 D, had a prevalence of 29.17% (95% confidence interval, 26.60 to 31.76%). We found a significant effect of sex on visual acuity. CONCLUSIONS: Our results are consistent with a high prevalence of myopia reported in adolescents worldwide and in Mexico's northern regions. The results suggest that students attending high school and entering universities should be required to have an optometric eye examination. Additional studies are needed to investigate the prevalence of refractive errors in children in Mexico.

The Effect of Zoom Magnification and Large Display on Video Comprehension in Individuals With Central Vision Loss.

Purpose: A larger display at the same viewing distance provides relative-size magnification for individuals with central vision loss (CVL). However, the resulting large visible area of the display is expected to result in more head rotation, which may cause discomfort. We created a zoom magnification technique that placed the center of interest (COI) in the center of the display to reduce the need for head rotation. Methods: In a 2 × 2 within-subject study design, 23 participants with CVL viewed video clips from 1.5 m (4.9 feet) shown with or without zoom magnification, and with a large (208 cm/82" diagonal, 69°) or a typical (84 cm/33", 31°) screen. Head position was tracked and a custom questionnaire was used to measure discomfort. Results: Video comprehension was better with the large screen (P < 0.001) and slightly worse with zoom magnification (P = 0.03). Oddly, head movements did not vary with screen size (P = 0.63), yet were greater with zoom magnification (P = 0.001). This finding was unexpected, because the COI remains in the center with zoom magnification, but moves widely with a large screen and no magnification. Conclusions: This initial attempt to implement the zoom magnification method had flaws that may have decreased its effectiveness. In the future, we propose alternative implementations for zoom magnification, such as variable magnification. Translational Relevance: We present the first explicit demonstration that relative-size magnification improves the video comprehension of people with CVL when viewing video.

Saccade Landing Point Prediction Based on Fine-Grained Learning Method.

The landing point of a saccade defines the new fixation region, the new region of interest. We asked whether it was possible to predict the saccade landing point early in this very fast eye movement. This work proposes a new algorithm based on LSTM networks and a fine-grained loss function for saccade landing point prediction in real-world scenarios. Predicting the landing point is a critical milestone toward reducing the problems caused by display-update latency in gaze-contingent systems that make real-time changes in the display based on eye tracking. Saccadic eye movements are some of the fastest human neuro-motor activities with angular velocities of up to 1,000°/s. We present a comprehensive analysis of the performance of our method using a database with almost 220,000 saccades from 75 participants captured during natural viewing of videos. We include a comparison with state-of-the-art saccade landing point prediction algorithms. The results obtained using our proposed method outperformed existing approaches with improvements of up to 50% error reduction. Finally, we analyzed some factors that affected prediction errors including duration, length, age, and user intrinsic characteristics.

An implementation of Bubble Magnification did not improve the video comprehension of individuals with central vision loss.

PURPOSE: People with central vision loss (CVL) watch television, videos and movies, but often report difficulty and have reduced video comprehension. An approach to assist viewing videos is electronic magnification of the video itself, such as Bubble Magnification. METHODS: We created a Bubble Magnification technique that displayed a magnified segment around the centre of interest (COI) as determined by the gaze of participants with normal vision. The 15 participants with CVL viewed video clips shown with 2× and 3× Bubble Magnification, and unedited. We measured video comprehension and gaze coherence. RESULTS: Video comprehension was significantly worse with both 2× (p = 0.01) and 3× Bubble Magnification (p < 0.001) than the unedited video. There was no difference in gaze coherence across conditions (p ≥ 0.58). This was unexpected because we expected a benefit in both video comprehension and gaze coherence. This initial attempt to implement the Bubble Magnification method had flaws that probably reduced its effectiveness. CONCLUSIONS: In the future, we propose alternative implementations of Bubble Magnification, such as variable magnification and bubble size. This study is a first step in the development of an intelligent-magnification approach to providing a vision rehabilitation aid to assist people with CVL.

The Impact of Field of View on Understanding of a Movie Is Reduced by Magnifying Around the Center of Interest.

Purpose: Magnification is commonly used to reduce the impact of impaired central vision. However, magnification limits the field of view (FoV) which may make it difficult to follow the story. Most people with normal vision look in about the same place at about the same time, the center of interest (COI), when watching "Hollywood" movies. We hypothesized that if the FoV was centered at the COI, then this view would provide more useful information than either the original image center or an unrelated view location (the COI locations from a different video clip) as the FoV reduced. Methods: The FoV was varied between 100% (original) and 3%. To measure video comprehension as the FoV reduced, subjects described 30-second video clips in response to two open-ended questions. A computational, natural-language approach was used to provide an information acquisition (IA) score. Results: The IA scores reduced as the FoV decreased. When the FoV was around the COI, subjects were better able to understand the content of the video clips (higher IA scores) as the FoV decreased than the other conditions. Thus, magnification around the COI may serve as a better video enhancement approach than simple magnification of the image center. Conclusions: These results have implications for future image processing and scene viewing, which may help people with central vision loss view directed dynamic visual content ("Hollywood" movies). Translational Relevance: Our results are promising for the use of magnification around the COI as a vision rehabilitation aid for people with central vision loss.

Validation of a vision-related activity scale for patients with retinitis pigmentosa.

PURPOSE: There have been few systematic reports of vision-related activity limitations of people with retinitis pigmentosa (RP). We report a merging of data from the National Eye Institute Visual Function Questionnaire (NEI-VFQ) obtained in five previous studies. We asked whether the Vision Function Scale (VFS; Pesudovs et al., 2010) which was developed for cataract patients would apply in this new population (condition). METHODS: Five hundred ninety-four individuals completed a total of 1753 questionnaires, with 209 participants providing responses over at least 4 years. Rasch analysis showed that the 15-item VFS was poorly targeted. A new instrument created by adding four driving-related items to the VFS had better targeting. As an indirect validation, VFS-plus person scores were compared to visual field area measured using a Goldmann perimeter, to the summed score for the combined 30-2 and 30/60-1 Humphrey Field Analyzer programs (HFA), to 30-Hz full-field cone electroretinogram (ERG) amplitude, and to ETDRS visual acuity. Changes in VFS-plus person scores with age and between four common heredity groups were also examined. RESULTS: The Rasch model of responses to the 19 VFS-plus items had person and item separation of 2.66 and 24.43 respectively. The VFS-plus person scores were related to each vision measure (p < 0.001). Over a five-year period, there was a reduction in person scores of 0.5 logits (p < 0.001). Person scores fell by an average of 0.34 logits per decade (p < 0.0001). Participants with an X-linked hereditary pattern had, on average, lower person scores (p < 0.001). CONCLUSIONS: The VFS-plus instrument quantified a highly-significant annual reduction in perceived vision-related ability over a five-year period. The outcome was consistent with clinical measures of vision, and detected lower perceived vision-related ability in participants with X-linked disease. It may be of use in future studies, but this needs to be tested in a representative population sample.

Narrative video scene description task discriminates between levels of cognitive impairment in Alzheimer's disease.

The process of interpreting and acting upon the visual environment requires both intact cognitive and visual systems. The narrative description (ND) task, initially developed to detect changes in ecologically relevant visual function in people with impaired vision, is an objective measure of the ability to perceive, understand, and describe a visual scene in a movie clip. OBJECTIVE: Because the ND task draws heavily on semantic and working memory ability in addition to basic visual perception, we aimed to assess the discriminative performance of this task across levels of cognitive impairment. METHOD: We recruited 56 participants with cognitive status ranging from normal cognition to mild dementia (median age 82, range 66 to 99 years) to watch 20 30-s video clips and describe the visual content without time constraints. These verbal responses were transcribed and processed to generate ND shared word scores using a "wisdom of the crowd," natural-language processing approach. We compared ND scores across diagnostic groups, and used linear mixed models to examine decrements in task performance. RESULTS: There was a stepwise decline of ND scores with increasing levels of cognitive impairment. Additional analyses showed that ND performance was highly related to performance on the Montreal Cognitive Assessment (MoCA) and domain-specific neuropsychological tests for semantic fluency and set shifting. Other models demonstrated differences in ND performance related video content between cognitively normal and impaired participants. CONCLUSION: The ND test was able to detect decrements in task performance between levels of cognitive impairment and was related to other global neuropsychological measures. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Orientation of the preferred retinal locus (PRL) is maintained following changes in simulated scotoma size.

Although macular lesions often enlarge, we know little about what happens when the preferred retinal locus (PRL) is enveloped by the lesion. We present a prospective study of subjects with normal vision who were trained to develop a PRL using simulated scotomas with a gaze-contingent visual display. We hypothesized that, when subjects had developed a robust PRL and the scotoma size was increased, the PRL would move to remain outside the scotoma and in a direction that maintained the orientation (theta) of the PRL relative to the fovea. Nine subjects with normal vision were trained to develop a PRL and were then exposed to scotoma sizes that ranged from 4° to 24° in diameter. Subjects tracked a stimulus using saccades or smooth pursuits. Fixation stability was measured by calculating the bivariate contour ellipse area (BCEA). To measure the reassignment of the oculomotor reference (OMR) to the PRL, we analyzed the spread (BCEA) of saccade first landing points. All subjects developed a robust PRL that did not vary more than 0.8° on average between blocks of trials of a scotoma size, and they maintained the orientation of the PRL as the simulated scotoma size varied (±9° median standard deviation in theta, defined as orientation angle). Fixation stability and OMR to the PRL worsened (larger BCEA) with increasing scotoma size. This, and related studies, could guide development of a PRL training method to help people with central vision loss.

A free database of eye movements watching "Hollywood" videoclips.

The provided database of tracked eye movements was collected using an infra-red, video-camera Eyelink 1000 system, from 95 participants as they viewed 'Hollywood' video clips. There are 206 clips of 30-s and eleven clips of 30-min for a total viewing time of about 60 hours. The database also provides the raw 30-s video clip files, a short preview of the 30-min clips, and subjective ratings of the content of the videos for each in categories: (1) genre; (2) importance of human faces; (3) importance of human figures; (4) importance of man-made objects; (5) importance of nature; (6) auditory information; (7) lighting; and (8) environment type. Precise timing of the scene cuts within the clips and the democratic gaze scanpath position (center of interest) per frame are provided. At this time, this eye-movement dataset has the widest age range (22-85 years) and is the third largest (in recorded video viewing time) of those that have been made available to the research community. The data-acquisition procedures are described, along with participant demographics, summaries of some common eye-movement statistics, and highlights of research topics in which the database was used. The dataset is freely available in the Open Science Framework repository (link in the manuscript) and can be used without restriction for educational and research purposes, providing that this paper is cited in any published work.

People With Central Vision Loss Have Difficulty Watching Videos.

Purpose: People with central vision loss (CVL) often report difficulties watching video. We objectively evaluated the ability to follow the story (using the information acquisition method). Methods: Subjects with CVL (n = 23) or normal vision (NV, n = 60) described the content of 30-second video clips from movies and documentaries. We derived an objective information acquisition (IA) score for each response using natural-language processing. To test whether the impact of CVL was simply due to reduced resolution, another group of NV subjects (n = 15) described video clips with defocus blur that reduced visual acuity to 20/50 to 20/800. Mixed models included random effects correcting for differences between subjects and between the clips, with age, gender, cognitive status, and education as covariates. Results: Compared to both NV groups, IA scores were worse for the CVL group (P < 0.001). IA reduced with worsening visual acuity (P < 0.001), and the reduction with worsening visual acuity was greater for the CVL group than the NV-defocus group (P = 0.01), which was seen as a greater discrepancy at worse levels of visual acuity. Conclusions: The IA method was able to detect difficulties in following the story experienced by people with CVL. Defocus blur failed to recreate the CVL experience. IA is likely to be useful for evaluations of the effects of vision rehabilitation.

Microsaccades reflect the dynamics of misdirected attention in magic.

The methods of magicians provide powerful tools for enhancing the ecological validity of laboratory studies of attention. The current research borrows a technique from magic to explore the relationship between microsaccades and covert attention under near-natural viewing conditions. We monitored participants' eye movements as they viewed a magic trick where a coin placed beneath a napkin vanishes and reappears beneath another napkin. Many participants fail to see the coin move from one location to the other the first time around, thanks to the magician's misdirection. However, previous research was unable to distinguish whether or not participants were fooled based on their eye movements. Here, we set out to determine if microsaccades may provide a window into the efficacy of the magician's misdirection. In a multi-trial setting, participants monitored the location of the coin (which changed positions in half of the trials), while engaging in a delayed match-to-sample task at a different spatial location. Microsaccades onset times varied with task difficulty, and microsaccade directions indexed the locus of covert attention. Our combined results indicate that microsaccades may be a useful metric of covert attentional processes in applied and ecologically valid settings.

Measuring the Difficulty Watching Video With Hemianopia and an Initial Test of a Rehabilitation Approach.

PURPOSE: If you cannot follow the story when watching a video, then the viewing experience is degraded. We measured the difficulty of following the story, defined as the ability to acquire visual information, which is experienced by people with homonymous hemianopia (HH). Further, we proposed and tested a novel rehabilitation aid. METHODS: Participants watched 30-second directed video clips. Following each video clip, subjects described the visual content of the clip. An objective score of information acquisition (IA) was derived by comparing each new response to a control database of descriptions of the same clip using natural language processing. Study 1 compared 60 participants with normal vision (NV) to 24 participants with HH to test the hypothesis that participants with HH would score lower than NV participants, consistent with reports from people with HH that describe difficulties in video watching. In the second study, 21 participants with HH viewed clips with or without a superimposed dynamic cue that we called a content guide. We hypothesized that IA scores would increase using this content guide. RESULTS: The HH group had a significantly lower IA score, with an average of 2.8, compared with 4.3 shared words of the NV group (mixed-effects regression, P < 0.001). Presence of the content guide significantly increased the IA score by 0.5 shared words (P = 0.03). CONCLUSIONS: Participants with HH had more difficulty acquiring information from a video, which was objectively demonstrated (reduced IA score). The content guide improved information acquisition, but not to the level of people with NV. TRANSLATIONAL RELEVANCE: The value as a possible rehabilitation aid of the content guide warrants further study that involves an extended period of content-guide use and a randomized controlled trial.

People with Hemianopia Report Difficulty with TV, Computer, Cinema Use, and Photography.

SIGNIFICANCE: Our survey found that participants with hemianopia report more difficulties watching video in various formats, including television (TV), on computers, and in a movie theater, compared with participants with normal vision (NV). These reported difficulties were not as marked as those reported by people with central vision loss. PURPOSE: The aim of this study was to survey the viewing experience (e.g., frequency, difficulty) of viewing video on TV, computers and portable visual display devices, and at the cinema of people with hemianopia and NV. This information may guide vision rehabilitation. METHODS: We administered a cross-sectional survey to investigate the viewing habits of people with hemianopia (n = 91) or NV (n = 192). The survey, consisting of 22 items, was administered either in person or in a telephone interview. Descriptive statistics are reported. RESULTS: There were five major differences between the hemianopia and NV groups. Many participants with hemianopia reported (1) at least "some" difficulty watching TV (39/82); (2) at least "some" difficulty watching video on a computer (16/62); (3) never attending the cinema (30/87); (4) at least some difficulty watching movies in the cinema (20/56), among those who did attend the cinema; and (5) never taking photographs (24/80). Some people with hemianopia reported methods that they used to help them watch video, including video playback and head turn. CONCLUSIONS: Although people with hemianopia report more difficulty with viewing video on TV and at the cinema, we are not aware of any rehabilitation methods specifically designed to assist people with hemianopia to watch video. The results of this survey may guide future vision rehabilitation.

When Watching Video, Many Saccades Are Curved and Deviate From a Velocity Profile Model.

Commonly, saccades are thought to be ballistic eye movements, not modified during flight, with a straight path and a well-described velocity profile. However, they do not always follow a straight path and studies of saccade curvature have been reported previously. In a prior study, we developed a real-time, saccade-trajectory prediction algorithm to improve the updating of gaze-contingent displays and found that saccades with a curved path or that deviated from the expected velocity profile were not well fit by our saccade-prediction algorithm (velocity-profile deviation), and thus had larger updating errors than saccades that had a straight path and had a velocity profile that was fit well by the model. Further, we noticed that the curved saccades and saccades with high velocity-profile deviations were more common than we had expected when participants performed a natural-viewing task. Since those saccades caused larger display updating errors, we sought a better understanding of them. Here we examine factors that could affect curvature and velocity profile of saccades using a pool of 218,744 saccades from 71 participants watching "Hollywood" video clips. Those factors included characteristics of the participants (e.g., age), of the videos (importance of faces for following the story, genre), of the saccade (e.g., magnitude, direction), time during the session (e.g., fatigue) and presence and timing of scene cuts. While viewing the video clips, saccades were most likely horizontal or vertical over oblique. Measured curvature and velocity-profile deviation had continuous, skewed frequency distributions. We used mixed-effects regression models that included cubic terms and found a complex relationship between curvature, velocity-profile deviation and saccade duration (or magnitude). Curvature and velocity-profile deviation were related to some video-dependent features such as lighting, face presence, or nature and human figure content. Time during the session was a predictor for velocity profile deviations. Further, we found a relationship for saccades that were in flight at the time of a scene cut to have higher velocity-profile deviations and lower curvature in univariable models. Saccades characteristics vary with a variety of factors, which suggests complex interactions between oculomotor control and scene content that could be explored further.

The Preferred Retinal Locus Used to Watch Videos.

Purpose: Eccentric viewing is a common strategy used by people with central vision loss (CVL) to direct the eye such that the image falls onto functioning peripheral retina, known as the preferred retinal locus (PRL). It has been long acknowledged that we do not know whether the PRL used in a fixation test is also used when performing tasks. We present an innovative method to determine whether the same PRL observed during a fixation task was used to watch videos and whether poor resolution affects gaze location. Methods: The gaze of a group of 60 normal vision (NV) observers was used to define a democratic center of interest (COI) of video clips from movies and television. For each CVL participant (N = 20), we computed the gaze offsets from the COI across the video clips. The distribution of gaze offsets of the NV participants was used to define the limits of NV behavior. If the gaze offset was within this 95% degree confidence interval, we presumed that the same PRL was used for fixation and video watching. Another 15 NV participants watched the video clips with various levels of defocus blur. Results: CVL participants had wider gaze-offset distributions than NV participants (P < 0.001). Gaze offsets of 18/20 CVL participants were outside the NV confidence interval. Further, none of the 15 NV participants watching the same videos with spherical defocus blur had a gaze offset that was decentered (outside the NV confidence interval), suggesting that resolution was not the problem. Conclusions: This indicates that many CVL participants were using a PRL to view videos that differed from that found with a fixation task and that it was not caused by poor resolution alone. The relationship between these locations needs further investigation.

Dynamic gaze-position prediction of saccadic eye movements using a Taylor series.

Gaze-contingent displays have been widely used in vision research and virtual reality applications. Due to data transmission, image processing, and display preparation, the time delay between the eye tracker and the monitor update may lead to a misalignment between the eye position and the image manipulation during eye movements. We propose a method to reduce the misalignment using a Taylor series to predict the saccadic eye movement. The proposed method was evaluated using two large datasets including 219,335 human saccades (collected with an EyeLink 1000 system, 95% range from 1° to 32°) and 21,844 monkey saccades (collected with a scleral search coil, 95% range from 1° to 9°). When assuming a 10-ms time delay, the prediction of saccade movements using the proposed method could reduce the misalignment greater than the state-of-the-art methods. The average error was about 0.93° for human saccades and 0.26° for monkey saccades. Our results suggest that this proposed saccade prediction method will create more accurate gaze-contingent displays.

Changes in visibility as a function of spatial frequency and microsaccade occurrence.

Fixational eye movements (FEMs), including microsaccades, drift, and tremor, shift our eye position during ocular fixation, producing retinal motion that is thought to help visibility by counteracting neural adaptation to unchanging stimulation. Yet, how each FEM type influences this process is still debated. Recent studies found little to no relationship between microsaccades and visual perception of spatial frequencies (SF). However, these conclusions were based on coarse analyses that make it hard to appreciate the actual effects of microsaccades on target visibility as a function of SF. Thus, how microsaccades contribute to the visibility of stimuli of different SFs remains unclear. Here, we asked how the visibility of targets of various SFs changed over time, in relationship with concurrent microsaccade production. Participants continuously reported on changes in target visibility, allowing us to time-lock ongoing changes in microsaccade parameters to perceptual transitions in visibility. Microsaccades restored/increased the visibility of low SF targets more efficiently than that of high SF targets. Yet, microsaccade rates rose before periods of increased visibility, and dropped before periods of diminished visibility, for all the SFs tested, suggesting that microsaccades boosted target visibility across a wide range of SFs. Our data also indicate that visual stimuli fade/become harder to see less often in the presence of microsaccades. In addition, larger microsaccades restored/increased target visibility more effectively than smaller microsaccades. These combined results support the proposal that microsaccades enhance visibility across a broad variety of SFs.

V1 neurons respond differently to object motion versus motion from eye movements.

How does the visual system differentiate self-generated motion from motion in the external world? Humans can discern object motion from identical retinal image displacements induced by eye movements, but the brain mechanisms underlying this ability are unknown. Here we exploit the frequent production of microsaccades during ocular fixation in the primate to compare primary visual cortical responses to self-generated motion (real microsaccades) versus motion in the external world (object motion mimicking microsaccades). Real and simulated microsaccades were randomly interleaved in the same viewing condition, thereby producing equivalent oculomotor and behavioural engagement. Our results show that real microsaccades generate biphasic neural responses, consisting of a rapid increase in the firing rate followed by a slow and smaller-amplitude suppression that drops below baseline. Simulated microsaccades generate solely excitatory responses. These findings indicate that V1 neurons can respond differently to internally and externally generated motion, and expand V1's potential role in information processing and visual stability during eye movements.

Characteristics of Spontaneous Square-Wave Jerks in the Healthy Macaque Monkey during Visual Fixation.

Saccadic intrusions (SIs), predominantly horizontal saccades that interrupt accurate fixation, include square-wave jerks (SWJs; the most common type of SI), which consist of an initial saccade away from the fixation target followed, after a short delay, by a return saccade that brings the eye back onto target. SWJs are present in most human subjects, but are prominent by their increased frequency and size in certain parkinsonian disorders and in recessive, hereditary spinocerebellar ataxias. SWJs have been also documented in monkeys with tectal and cerebellar etiologies, but no studies to date have investigated the occurrence of SWJs in healthy nonhuman primates. Here we set out to determine the characteristics of SWJs in healthy rhesus macaques (Macaca mulatta) during attempted fixation of a small visual target. Our results indicate that SWJs are common in healthy nonhuman primates. We moreover found primate SWJs to share many characteristics with human SWJs, including the relationship between the size of a saccade and its likelihood to be part of a SWJ. One main discrepancy between monkey and human SWJs was that monkey SWJs tended to be more vertical than horizontal, whereas human SWJs have a strong horizontal preference. Yet, our combined data indicate that primate and human SWJs play a similar role in fixation correction, suggesting that they share a comparable coupling mechanism at the oculomotor generation level. These findings constrain the potential brain areas and mechanisms underlying the generation of fixational saccades in human and nonhuman primates.

Fixational eye movement correction of blink-induced gaze position errors.

Our eyes move continuously. Even when we attempt to fix our gaze, we produce "fixational" eye movements including microsaccades, drift and tremor. The potential role of microsaccades versus drifts in the control of eye position has been debated for decades and remains in question today. Here we set out to determine the corrective functions of microsaccades and drifts on gaze-position errors due to blinks in non-human primates (Macaca mulatta) and humans. Our results show that blinks contribute to the instability of gaze during fixation, and that microsaccades, but not drifts, correct fixation errors introduced by blinks. These findings provide new insights about eye position control during fixation, and indicate a more general role of microsaccades in fixation correction than thought previously.