Distance Fixation Research Articles

Spasm of Near Reflex in a Patient with Autism Spectrum Disorder: A Case Report

Spasm of near reflex (SNR) involves intermittent spasm of one or more of the three near reflex components. Psychiatric disorders are one cause of SNR. We describe a patient with SNR diagnosed with autism spectrum disorder (ASD). A 36-year-old male with esotropia since childhood was referred due to headache and dizziness. The alternate prism cover test showed 30 prism diopters at both near and distant fixation. Four months after his first visit, he was diagnosed with ASD. Twenty-nine months after his first visit, he underwent strabismus surgery to treat concomitant esotropia. Postoperatively, the angle of strabismus improved but remained variable. Because the angle of strabismus varied, we suspected SNR; the diagnosis was performed after evaluating the patient’s microfluctuations in accommodation with Speedy-K. However, it was difficult to distinguish convergence spasm from concomitant esotropia in this patient because he has had a history of esotropia since childhood. In a patient with concomitant esotropia, if the symptoms are not exclusively due to strabismus, SNR should be suspected. Although the relationship between SNR and the pathology of ASD is unknown, it is possible that patients with ASD are more likely to develop SNR.

Comparing Eye-tracking System Effectiveness in Field and Driving Simulator Studies

Background: Several studies have been conducted by combining the benefits of eye-tracking systems with driving simulators to simultaneously investigate driving behavior and the potential source of distraction. However, little effort has been made in terms of eye-tracking validation in the driving simulator environment. Objective: The overall aim of this study is to validate an eye-tracking system within the context of a driving simulation environment by considering a specific urban context application. Methods: A field survey and a driving simulation experiment were conducted for a case study in Rome, Italy. The selected real road sections and events were reproduced on the driving simulator system. An eye-tracking system was used to record eye movements both on a real vehicle and the simulator. The eye movements of 14 participants in the field survey and 18 participants in the driving simulation tests, as well as their driving performances, were collected while approaching an urban intersection in relation to two specific road events: i) the presence of a speed limit sign and ii) the presence of a crossing pedestrian. Results: Eye tracker parameters and driving performances were compared between the real driving tests and driving simulator experiments in order to validate the eye-tracking system. It was validated for both events in terms of duration and distance of the eye fixation. Conclusion: The results demonstrated that an eye-tracking system is an effective tool for studies and applications in a virtual reality environment.

Results of Unilateral Lateral Rectus Recession Surgery in 15 - 30 PD Intermittent Exotropia.

To evaluate the surgical outcomes of unilateral lateral rectus muscle recession (ULR) with low surgical dosage in patients with intermittent exotropia (IXT) of 15 - 30 prism dioptres (PD). We retrospectively analysed 92 eyes of 92 patients who underwent ULR surgery with the diagnosis of IXT of 15 - 30 PD at distance fixation between January 2017 and June 2019. ULR surgery of 6.5 mm was performed for exotropia of 15 - 20 PD, 7.5 mm for that of 20 - 25 PD, and 8.5 mm for that of 25 - 30 PD and postoperative results were evaluated at the 1st week, 1st month, 6th month, and the 2nd year. Orthophoria or IXT less than 10 PD was accepted as successful. The mean preoperative deviation angle at distance was 22.3 ± 4.4 PD. Mean postoperative deviation angles at distance were 2.5 ± 1.7, 3.9 ± 2.4, 6.5 ± 3.0, and 8.7 ± 3.1 at 1 week, 1 month, 6 months, and 2 years, respectively. The surgical success rate of ULR was 100, 96.7, 84.7, and 77.1% at the 1st week, 1st month, 6th month, and the 2nd year, respectively. In the long-term results, there were no complications such as lateral gaze incomitance, overcorrection, or deterioration in stereopsis. Using the ULR technique, we were able to obtain effective surgical results in IXT with less surgical dosage and without any serious complications. ULR surgery can be used as an effective method in patients with IXT of 15 - 30 PD.

Differences in visual stimulation between reading and walking and implications for myopia development.

Visual input plays an important role in the development of myopia (nearsightedness), a visual disorder that blurs vision at far distances. The risk of myopia progression increases with the time spent reading and decreases with outdoor activity for reasons that remain poorly understood. To investigate the stimulus parameters driving this disorder, we compared the visual input to the retina of humans performing two tasks associated with different risks of myopia progression, reading and walking. Human subjects performed the two tasks while wearing glasses with cameras and sensors that recorded visual scenes and visuomotor activity. When compared with walking, reading black text in white background reduced spatiotemporal contrast in central vision and increased it in peripheral vision, leading to a pronounced reduction in the ratio of central/peripheral strength of visual stimulation. It also made the luminance distribution heavily skewed toward negative dark contrast in central vision and positive light contrast in peripheral vision, decreasing the central/peripheral stimulation ratio of ON visual pathways. It also decreased fixation distance, blink rate, pupil size, and head-eye coordination reflexes dominated by ON pathways. Taken together with previous work, these results support the hypothesis that reading drives myopia progression by understimulating ON visual pathways.

Early post-operative angle as a predictor of surgical success in adult patients with intermittent exotropia

ABSTRACT Purpose: Intermittent exotropia is a condition where divergent strabismus is present at certain times or fixation distances and is surgically treated with bilateral lateral rectus recession or unilateral lateral rectus recession with medial rectus resection. The main purpose of our study is to assess the relationship between the initial post-operative deviation and surgical outcomes in adult exotropes undergoing recess-resect surgery. Methods: A retrospective chart review was performed on adult patients who underwent unilateral recess-resect surgery for intermittent exotropia between March 2010 and February 2022 at a single institution with at least 3 months of follow-up. Based on their motor alignment at 2 weeks following surgery, they were categorized as having exodeviation, esodeviation within 10 PD and esodeviation exceeding 10 PD. Surgical success was defined as motor alignment within 10 PD of exotropia and 5 PD of esotropia at distance and near at final follow-up. Results: 93 patients were included, 55% female and average age was 37 years. At postoperative week 2, 26 patients demonstrated residual exodeviation (Group A), 53 patients demonstrated an esodeviation of within 10 PD (Group B) and 14 patients demonstrated an esodeviation greater than 10 PD (Group C). There were no significant differences in pre-operative and demographic factors between the group. At the final follow-up, surgical success was observed in 57 patients: 12 in Group A, 41 in Group B and 4 in Group C (P < .01). Conclusion: Overcorrection of within 10 PD at 2 weeks following surgery showed a more favorable surgical outcome compared to exodeviation or esodeviation exceeding 10 PD.

Possibility of Neurological Diseases Associated with Acute Acquired Comitant Esotropia.

This study investigated the possibility of neurological etiologies causing acute acquired comitant esotropia (AACE) and to evaluate the differences in clinical features between younger children, older children, and adults. In this retrospective analysis, patients who had been diagnosed with AACE between July 2017 and June 2021 were included. Data on clinical findings, medical history, brain or orbital imaging, and ophthalmological and orthoptic examinations were retrieved from medical records and analyzed. Patients were divided into three groups based on their age: younger children (<10 years), older children (10-18 years), and adults (>18 years). Overall, 41 patients with AACE (15 females and 26 males) were examined. Most patients were children. Mild hyperopia was observed in children, while adults had moderate to high myopia. The mean angle of esotropia at a distance fixation was 43.57 ± 9.77, 51.54 ± 8.75, and 30.14 ± 12.39 prism diopters (PD) in younger children, older children, and adult groups, respectively. The mean angle of esotropia at a near fixation was 43.57 ± 9.37, 51.15 ± 9.39, and 31.43 ± 12.15 PD in younger children, older children, and adult groups, respectively. Significant differences were found in the mean angles of esotropia in patients with AACE at both near and far distances according to their age (all p < 0.001). Among 36 patients with previous neuroimaging data, none had AACE secondary to intracranial lesions. Over 2 years, five patients who were under continuous observation did not develop any neurological abnormalities. AACE was more common in children than in adults. The angle of deviation was larger in children than in adults. Coexisting or underlying neurological diseases were not present in patients with isolated AACE, which eliminated the need for neuroimaging. Continuous follow-up evaluations are warranted when signs of intracranial disease are observed in patients who have not undergone an imaging investigation.

A cross-sectional study of ophthalmologic examination findings in 5385 Koreans presenting with intermittent exotropia

The Korean Intermittent Exotropia Multicenter Study (KIEMS) was a retrospective, cross-sectional and multicenter study for the investigation of intermittent exotropia involved 65 strabismus specialists from 53 institutions in Korea. Purpose of this study was to present ophthalmologic findings of intermittent exotropia from the KIEMS. Consecutive patients with intermittent exotropia of ≥ 8 prism diopters (PD) at distance or near fixation were included. Best-corrected visual acuity, cycloplegic refraction data, angles of deviation at several cardinal positions, ocular dominance, fusion control, oblique muscle function, and binocular sensory outcomes were collected. A total of 5385 participants (2793 females; age 8.2 years) were included. Non-dominant eye was more myopic than the dominant eye (− 0.60 vs. − 0.47 diopters, P < 0.001). Mean exodeviation angles were 23.5 PD at distance and 25.0 PD at near fixation. Basic type (86.2%) was the most, followed by convergence insufficiency (9.4%) and divergence excess (4.4%) types. Alternating ocular dominance and good fusion control were more common at near than at distance fixation. Good stereopsis at 40 cm was observed in 49.3% in Titmus stereo test (≤ 60 arcsec) and in 71.0% in Randot stereo test (≤ 63 arcsec). Intermittent exotropia was mostly diagnosed in childhood and patients with the condition showed relatively good binocular functions. This study may provide objective findings of intermittent exotropia in a most reliable way, given that the study included a large study population and investigated comprehensive ophthalmology examinations.

The Statistics of Eye Movements and Binocular Disparities during VR Gaming: Implications for Headset Design.

The human visual system evolved in environments with statistical regularities. Binocular vision is adapted to these such that depth perception and eye movements are more precise, faster, and performed comfortably in environments consistent with the regularities. We measured the statistics of eye movements and binocular disparities in virtual-reality (VR) - gaming environments and found that they are quite different from those in the natural environment. Fixation distance and direction are more restricted in VR, and fixation distance is farther. The pattern of disparity across the visual field is less regular in VR and does not conform to a prominent property of naturally occurring disparities. From this we predict that double vision is more likely in VR than in the natural environment. We also determined the optimal screen distance to minimize discomfort due to the vergence-accommodation conflict, and the optimal nasal-temporal positioning of head-mounted display (HMD) screens to maximize binocular field of view. Finally, in a user study we investigated how VR content affects comfort and performance. Content that is more consistent with the statistics of the natural world yields less discomfort than content that is not. Furthermore, consistent content yields slightly better performance than inconsistent content.

COI gene analyses of the Daghestan pine vole (Microtus daghestanicus Shidlovsky, 1919) population from northeastern Turkey

Daghestan pine vole (Microtus daghestanicus Shidlovsky, 1919) is spread in Caucasia, Turkey and Northwestern Iran and distribution of this species is limited to Northeastern Anatolia in Turkey. Few molecular studies on M. daghestanicus have been performed so far, and it was analysed in this study with the mitochondrial cytochrome oxidase subunit I (COI) region and compared with other Terricola species (Microtus subterraneus and Microtus majori) and other Microtus species found in its distribution area (Microtus arvalis and Microtus mystacinus). For this purpose, mean genetic distance values and fixation index values were calculated. Also, Bayesian Inference tree and Median-joining network were constructed. The acquired results showed that M. daghestanicus was clearly separated in the Pleistocene Period and was closer to M subterraneus than M. majori in the subgenus Terricola.

Partially Accommodative Esotropia Manifesting as Cyclic Esotropia: A Case Study

Purpose: Cyclic esotropia is a rare disease with alternating cycles of recurrent esotropia that has been reported after strabismus surgery, head trauma, and psychological stress. We report a patient who presented with accommodative esotropia that deteriorated to cyclic esotropia and was managed successfully.Case Summary: A 2-year-old girl with no previous ophthalmological or neurological illnesses presented with esotropia. The alternate prism cover test showed 16 prism diopters (PD) of esotropia during distance and near fixation, and cycloplegic refraction showed +2.00 diopters (D) right eye and +1.50 D left eye. Under the impression of accommodative esotropia, she was prescribed glasses to fully correct her cycloplegic refraction. Nine months later, her esotropia was 14 PD with hyperopic correction. Her parents also complained that she had ‘non-squinting’ and ‘squinting’ days. The history and clinical findings suggested cyclic esotropia and she was asked to start a daily diary documenting the presence or absence of her squint. This revealed that the esotropia alternated on a 24-hour cycle. With a diagnosis of cyclic esotropia, she underwent right medial rectus recession. Postoperatively, her angle of esodeviation improved to orthotropia (near and distance) and stereoacuity was restored; this was maintained at the 1-year follow-up.Conclusions: A daily diary documenting the presence or absence of squint in patients who complain of alternating esotropia, even after hyperopic correction, is important. Cyclic esotropia often responds well to surgical management.

High-dose medialis recession in latent nystagmus

Large muscle recessions reduce anomalous head turn (AHT) in infantile nystagmus syndrome (INS). Their quantitative effect to reduce AHT in fusion maldevelopment nystagmus syndrome (FMNS) is unknown. To evaluate the reduction of AHT by large medial rectus muscle recession in patients with FMNS. We analyzed data of 12patients with pure FMNS who received large medial rectus muscle recessions on the sound eye or only eye between 2014 and 2019. Medians and ranges (min-max) were: age at surgery 14years (3-43 years); decimal BCVA sound eye/fellow eye 0.56 (0.4-1.0)/0.01 (0-0.4); AHT at 5 m/0.3 m fixation distance 35° (15-45°)/20° (0-45°); amount of recession 13 mm (11.5-15 mm); follow-up13 (4-39) months. At the final visit, AHT at 5 m/0.3 m was 10° (0-20°/0-15°). The individual reduction of AHT at 5 m amounted to 25° (8-35°) without any overcorrection. The available visual field of functionally monocular patients increased correspondingly. Slight overcorrection at 0.3 m occurred in 2cases. Adduction of the sound eye was limited to 25e-40°). BCVA and anomalous head posture in vertical and frontal planes did not improve. Large medial rectus muscle recession on the sound eye improves AHT in FMNS by asimilar amount compared to INS and the available visual field of functionally monocular patients.

Effect of bimedial recession on near-distance disparity in esotropia.

Esotropia may be associated with a difference in the deviation at near and distance fixation termed near-distance disparity (NDD). Convention suggests patients with NDD may benefit more from bilateral medial rectus recessions (BMR) as opposed to a unilateral recession/resection (RR). The aim of this study is to establish the effect of BMR for the treatment of esotropia on both the near and distance deviation and NDD. Retrospective patient records search from 2011 to 2021. comitant esotropia, first surgery, equal and normal vision with free alternation. incomitant, neurological or restrictive strabismus, previous surgery, clinically significant amblyopia. 49 patients met the inclusion criteria. 19 patients were female; the average age was 17 years. Following surgery, the average near deviation reduced from 39PD base out (BO) to 11PD BO. The average distance deviation reduced from 33PD to 9PD. Average preoperative NDD was 12 PD. NDD resolved in 15 out of 18 patients with NDD (83%). The average PD gain per mm of recession was 2.7 for near and 2.2 for distance. BMR is an effective surgical treatment for esotropia and has a greater effect on near deviation than distance. It is also an effective and simple technique for lesser degrees of NDD. BMR has several advantages over RR: no tissue loss, readily reversible, the scars are easier to hide and it avoids potential motility limitations due to leash effects following resection.

First-finder-related Clinical Features of Intermittent Exotropia

Purpose: To determine whether the clinical features of intermittent exotropia (IXT) needing muscle surgery were different in the ophthalmologist-detected and non-specialist-detected groups (including parents).Methods: Medical records of 218 children (mean age: 5.9 ± 1.4 years) with IXT of ≥ 20 prism diopters (PD) were reviewed retrospectively. The angles of deviation were measured using the prism and alternate cover test and assessed by two ophthalmologists using photographs with a translucent occluder (photographic angle). The IXT subtype, fusional control, stereopsis, suppression, and spherical equivalent (SE) were compared between the ophthalmologist-detected and non-specialist-detected groups.Results: Mean 25.8 ± 6.8 PD of distant angle of IXT was first detected by the ophthalmologist in 41 patients (18.8%) and the non-specialists in 177 patients (81.2%). The deviated eye was more myopic in the ophthalmologist-detected than non-specialist- detected group (-0.77 ± 1.59 diopters [D] vs. -0.19 ± 1.48 D, &lt;i&gt;p&lt;/i&gt; = 0.03). There were no other differences between the two groups. A comparison of 39 age- and non-dominant eye SE-matched pairs demonstrated that the measured angles for distant and near fixation were smaller in the ophthalmologist-detected than non-specialist-detected group (24.0 ± 6.8 PD vs. 28.5 ± 6.4 PD and 26.9 ± 6.6 PD vs. 31.0 ± 6.4 PD, respectively, &lt;i&gt;p&lt;/i&gt; &lt; 0.01), while the remaining characteristics, including the photographic angle, were similar.Conclusions: In cases with small angles of deviation or myopia, IXT with angles requiring surgical correction were commonly first detected by ophthalmologists during examinations.

Perceptual Guidelines for Optimizing Field of View in Stereoscopic Augmented Reality Displays

Near-eye display systems for augmented reality (AR) aim to seamlessly merge virtual content with the user’s view of the real-world. A substantial limitation of current systems is that they only present virtual content over a limited portion of the user’s natural field of view (FOV). This limitation reduces the immersion and utility of these systems. Thus, it is essential to quantify FOV coverage in AR systems and understand how to maximize it. It is straightforward to determine the FOV coverage for monocular AR systems based on the system architecture. However, stereoscopic AR systems that present 3D virtual content create a more complicated scenario because the two eyes’ views do not always completely overlap. The introduction of partial binocular overlap in stereoscopic systems can potentially expand the perceived horizontal FOV coverage, but it can also introduce perceptual nonuniformity artifacts. In this arrticle, we first review the principles of binocular FOV overlap for natural vision and for stereoscopic display systems. We report the results of a set of perceptual studies that examine how different amounts and types of horizontal binocular overlap in stereoscopic AR systems influence the perception of nonuniformity across the FOV. We then describe how to quantify the horizontal FOV in stereoscopic AR when taking 3D content into account. We show that all stereoscopic AR systems result in a variable horizontal FOV coverage and variable amounts of binocular overlap depending on fixation distance. Taken together, these results provide a framework for optimizing perceived FOV coverage and minimizing perceptual artifacts in stereoscopic AR systems for different use cases.

Postoperative diplopia test—repeatability and prediction of surgical outcomes

The postoperative diplopia test (PODT) is used to assess the risk of postoperative diplopia in older children and adults prior to strabismus surgery for nonfunctional reasons. The purpose of this study was to evaluate the test-retest and interobserver reliability of the PODT and its predictive value in assessing diplopia risk. In the first phase of this study, the repeatability of the PODT method was prospectively assessed with two groups of patients (group 1, test-retest; group 2, interobserver). In the second phase, notes were reviewed retrospectively to evaluate the predictive value of the PODT. For phase 1, 39 participants were recruited. In group 1, 12 participants showed agreement in the area of suppression for both near and distance fixation; 8 showed variability. In group 2, 10 showed agreement for near, and 9 showed variability; 9 showed agreement for distance, and 10 showed variability. Group 1 differences ranged from 0 to 9 points (median, 0.5; IQR, 0-3); group 2, from 0 to 36 points (median, 1; IQR, 0-4.5). In phase 2, outcomes of 39 strabismus surgeries were reviewed: none of the patients without diplopia on PODT and 2 of 14 patients with diplopia on PODT had persistent diplopia 3 months after surgery. Many patients develop diplopia postoperatively, but this generally resolves spontaneously. Current testing procedures have excessive test-retest and interobserver variability and insufficient predictive value to be useful in predicting postoperative diplopia.

Unstable Depth Perception of Aerial Images in Crossed Mirror Array Can Be Controlled by Changing Fixation Distance

The unstable depth perception of aerial images in a crossed-mirror array (CMA) can be improved by changing the distance of fixation points. The perceived depths of aerial images in CMA suffer from large instability even when an aerial image is a geometrical optical real image. The perceived depth instability of aerial images is mainly influenced by their geometrical position from CMA. The perceived depths of aerial images shift toward the fixation points, and the stable depth perception of aerial images can be obtained if the fixation points are located near the aerial image distance. To stabilize the depth perception of aerial images, it is sufficient to appropriately control the observer's vergence even if the fixation point is not a real object. In addition, the luminance of aerial images affects the stability of their depth perception.

A new digitised screen test for strabismus measurement

PurposeOur study presents a digitised tangent screen test for ocular motility analysis according to the Harms and Hess tests (measurement of the squint angle in all fields of vision). This test uses an image beamer to display the tangent screen, a position sensor to measure the patient’s head orientation, and a distance sensor to measure the fixation distance. Digital measurement of head orientation allows for a test procedure that eliminates the conventional requirement for a light pointer in the patient’s hand. Thus, the digital screen test is presented, and the uncertainty of the measurement system is evaluated. MethodsA mathematical relationship was given between the measured squint angles, as well as the angle of diagnostic gaze direction, and the influence quantities on their measurement uncertainty. The individual uncertainties resulted from deviations in the measured values by the position and distance sensors, the calibration of the projection image of the beamer in length units, and the finite image resolution of the beamer. The individual standard uncertainties of the influence quantities were determined. The combined standard measurement uncertainties of the squint and gaze direction angles were given based on the model equation of the error propagation law at the tangent table according to Harms at a test distance of 2.5 m. The patient’s uncertainty contribution to the mobility analysis was not considered. ResultsThe combined standard uncertainty of the measurement system (coverage factor k = 2 for 95% confidence level) for the squint angle is ≤ 0.43° for the angle of diagnostic gaze direction ≤ 3.13° at the test distance of 2.5 m. The individual standard uncertainties of the influence quantities on the angles are (k = 1): 1.55°/1.01° (horizontal/vertical angle of the position sensor), 0.19° (distance sensor), 0.06° (calibration of the projection image of the beamer), and 0.02° (image resolution of the beamer). The maximum valid test distance of the digital screen test is 3.8 m. ConclusionThe digital screen test is compact and can be used at different locations. Compared to the traditional test, the time required for examination via the digitised test is less; additionally, its documentation is simplified. The measurement uncertainty of the diagnostic gaze direction angle is dominated by the sensor drift of the position sensor in the horizontal direction (yaw angle) and is due to the sensor technology. However, this drift error does not affect the squint angle measurement result nor its measurement uncertainty because the measurement principle used here is based on the congruence between the position cross and the fixation object and the confusion principle and compensates for the drift error. The measurement uncertainties of the determined measurement system are the lower limits of the uncertainties in the clinical use of the digital screen test if there are no effects due to significant patient deviations.

Long-term strabismus outcomes after unilateral infantile cataract surgery in the Infant Aphakia Treatment Study

To characterize long-term strabismus outcomes in children in the Infant Aphakia Treatment Study (IATS). This study was a secondary data analysis of long-term ocular alignment characteristics of children aged 10.5 years who had previously been enrolled in a randomized clinical trial evaluating aphakic management after unilateral cataract surgery between 1 and 6 months of age. In the IATS study, 96 of 109 children (88%) developed strabismus through age 10.5 years. Half of the 20 children who were orthophoric at distance through age 5 years maintained orthophoria at distance fixation at 10.5 years. Esotropia was the most common type of strabismus prior to age 5 years (56/109 [51%]), whereas exotropia (49/109 [45%]) was the most common type of strabismus at 10.5 years (esotropia, 21%; isolated hypertropia, 17%). Strabismus surgery had been performed on 52 children (48%), with 18 of these (35%) achieving microtropia <10Δ. Strabismus was equally prevalent in children randomized to contact lens care compared with those randomized to primary intraocular lens implantation (45/54 [83%] vs 45/55 [82%]; P = 0.8). Median visual acuity in the study eye was 0.56 logMAR (20/72) for children with orthotropia or microtropia <10Δ versus 1.30 logMAR (20/400) for strabismus ≥10Δ (P = 0.0003). Strabismus-in particular, exotropia-is common irrespective of aphakia management 10 years following infant monocular cataract surgery. The delayed emergence of exotropia with longer follow-up indicates a need for caution in managing early esotropia in these children. Children with better visual acuity at 10 years of age are more likely to have better ocular alignment.

Don't watch your step: gaze behavior adapts with practice of a target stepping task.

Vision plays a vital role in locomotor learning, providing feedback information to correct movement errors, and feedforward information to inform learned movement plans. Gaze behavior, or the distribution of fixation locations, can quantify how visual information is used during the motor learning process. How gaze behavior adapts during motor learning and in response to changing motor performance is poorly understood. This study examines if and how an individual's gaze behavior adapts during a sequence learning, target stepping task. We monitored the gaze behavior of 12 healthy young adults while they walked on a treadmill and attempted to precisely step on moving targets that were separated by variable distances (80%, 100%, and 120% of preferred step length). Participants completed a total of 11 trial blocks of 102 steps each. We hypothesized that both mean fixation distance would increase (participants would look farther ahead), and step error would decrease with experience. Following practice, participants significantly increased their fixation distance (P < 0.001) by 0.27 ± 0.18 steps and decreased their step error (P < 0.001) by 4.0 ± 1.7 cm, supporting our hypothesis. Our results suggest that early in the learning process, participants gaze behavior emphasized gathering visual information necessary for feedback motor control. As motor performance improved with experience, participants shifted their gaze fixation farther ahead placing greater emphasis on the visual information used for feedforward motor control. These findings provide important information about how gaze behavior changes in parallel with improvements in walking performance.NEW & NOTEWORTHY People consistently vary how they use visual information to inform walking. However, what drives this variation and how sampled visual information changes with locomotor learning is not well understood. Here, we find that gaze fixation locations moved farther ahead while step error decreases as participants practice a target stepping task. The results suggest that participants increasingly used a feedforward locomotor control strategy with practice.

Determining vertical fusion values from digital photographs of healthy eyes.

To determine the mean difference of vertical corneal light reflex (VCLR) among healthy eyes via digital photography. Retrospective study. The study enrolled 155, healthy eyes participants, 71 males and 84 females with a mean age of 14.7years (range 12-19years). The participants received complete eye examinations and 2 digital photographs were taken, with the flash on, while participants fixated their eyes on a near and a distant target. Two hundred and eighty qualified photographs were analyzed by Photo-Hirschberg testing using computer software. The vertical corneal light reflex ratio (VCLRR) was calculated as the distance of the corneal light reflex (CLR) to the inferior limbus or to the pupillary border divided by the horizontal corneal diameter, defined as VCLRR1 or VCLRR2. VCLRR was analyzed using Spearman's correlation. The mean ± SD of horizontal corneal diameter in near and distance photographs was 11.47 ± 0.62 and 11.37 ± 0.58mm, respectively. For correlation analysis, at 1m fixation and 6m fixation, the number of participants within an acceptable range of vertical fusion were 94.6% and 100% of participants. The 95th percentiles (estimated as the mean ± 1.64SD) in VCLRR1 between the two eyes at near and at distance fixation were 0.0316 and 0.0272, respectively; whereas the corresponding values for VCLRR2 were 0.0309 and 0.0240, respectively. The normal range of the vertical corneal light reflex ratio suggests that the Photo-Hirschberg test could be used for screening vertical strabismus cases depending on iris pigment.