The effect of uncorrected ametropia on ocular torsion induced by changes in fixation

Background and Objective Ocular torsion, the eye movements to rotating around the line of sight, has not been well investigated regarding the influence of refractive errors. The purpose of this study was to investigate the effect of uncorrected ametropia on ocular torsion induced by fixation distances. Methods Seventy-two subjects were classified according to the type of their refractive error, and ocular torsion of the uncorrected eye was compared based on changes induced by different fixation distances. Ocular torsion was measured using a slit-lamp biomicroscope equipped with an ophthalmic camera and a half-silvered mirror. Results In all groups, excyclotorsion values increased as the fixation distance decreased, but the myopia and astigmatism groups had larger amounts of ocular torsion than the emmetropia group. In addition, as the amount of uncorrected myopia and astigmatism increased, the amount of ocular torsion increased. Conclusion Since the amount of ocular torsion caused by a change to a shorter fixation distance was larger when the refractive error was uncorrected, we suggest that ametropia should be fully corrected in patients frequently exposed to ocular torsion due to changes in fixation distance.

Does Vergence Affect Perceived Size?

Since Kepler (1604) and Descartes (1637), it has been suggested that ‘vergence’ (the angular rotation of the eyes) plays a key role in size constancy. However, this has never been tested divorced from confounding cues such as changes in the retinal image. In our experiment, participants viewed a target which grew or shrank in size over 5 s. At the same time, the fixation distance specified by vergence was reduced from 50 to 25 cm. The question was whether this change in vergence affected the participants’ judgements of whether the target grew or shrank in size? We found no evidence of any effect, and therefore no evidence that eye movements affect perceived size. If this is correct, then our finding has three implications. First, perceived size is much more reliant on cognitive influences than previously thought. This is consistent with the argument that visual scale is purely cognitive in nature (Linton, 2017; 2018). Second, it leads us to question whether the vergence modulation of V1 contributes to size constancy. Third, given the interaction between vergence, proprioception, and the retinal image in the Taylor illusion, it leads us to ask whether this cognitive approach could also be applied to multisensory integration.

Drivers’ Gaze Behaviors are Influenced by Vehicle Position

Drivers’ gaze behaviors in naturalistic and simulated driving tasks have been investigated for decades. Many studies focus on driving environment to explain a driver’s gaze. However, if there is a great need to use compensatory steering for lane-keeping, drivers could preferentially acquire information directly required for the task. Therefore, we assumed that a driver’s gaze behavior was influenced not only by the environment but also the vehicle position, especially the lateral position. To verify our hypothesis, we carried out a long-time driving simulator experiment, and the gaze behaviors of two participating drivers were analyzed. Results showed that gaze behavior—the fixation distance and the lateral deviation of the fixation—was influenced by the lateral deviation of the vehicle. Consequently, we discussed processes that determined drivers’ gaze behaviors.

Can Clinical Measures of Postoperative Binocular Function Predict the Long-Term Stability of Postoperative Alignment in Intermittent Exotropia?

Purpose. To evaluate whether clinical measures of postoperative binocular functions could predict the long-term stability of postoperative ocular alignment in children with intermittent exotropia. Methods. A retrospective study was performed in thirty-nine children (median: 7 years) who have been surgically treated from intermittent exotropia without overcorrection (less than 10 prism diopters [pd] of exodeviation at 1 month postoperatively). Angles of deviation and binocular functions were measured preoperatively and at 1 month, 6 months, and the final follow-up visit (≥24 months) postoperatively. We examined the relationships between postoperative drift (change of ocular alignment) and binocular functions (sensory fusion, fusional convergence amplitude, and stereoacuity). Results. The surgical success rate (esophoria/tropia ≤5 pd to exophoria/tropia ≤10 pd) dropped to 76.9% at 6 months after surgery and to 53.8% at individuals’ last visit (mean: 37 months). The mean exodrift was 7.7 ± 9.2 pd from the postoperative month 1 to the final visit (p<0.001) on distance fixation. Distance stereoacuity, central fusion, and fusional convergence amplitude significantly improved following surgery (p<0.05). However, no significant correlation was found between their binocular functions measured at the beginning of each follow-up period and the postoperative drift (all p>0.13). Conclusion. Our findings suggest that the clinical measures of sensory fusion, fusional convergence amplitude, and stereoacuity cannot serve as a robust predictor for the long-term stability of postoperative ocular alignment in patients who underwent successful surgery without overcorrection at 1 month postoperatively.

The optical coherence tomography angiography manifestation of strabismus amblyopia with eccentric fixation

BackgroundTo explore the application value of optical coherence tomography angiography (OCTA) in patients with strabismus amblyopia accompanied by eccentric fixation.MethodsThe following data were collected from patients with strabismus amblyopia accompanied by eccentric fixation: best corrected visual acuity (BCVA); spherical equivalent (SE) and deviation angle; eccentric fixation distance using OCTA system software tools, with µm as the unit of measurement of the distance between the retinal fixed point and the macular fovea; macular fovea vessel length density (VLD); perfusion density (PD); foveal avascular zone (FAZ) area; and perimeter and circularity of the superficial retinal vascular plexus. The entry criteria were as follows: OCTA scanning quality and signal strength of 8 or above (range 0 to 10).ResultsData from a total of 34 patients were collected: 17 patients with strabismus amblyopia with eccentric fixation were included in the experimental group, and 17 patients without strabismus with central fixation were included in the control group. The average deviation angle of the experimental group was 26.71 ± 25.88 prism dioptres (PD), the amblyopic eye BCVA was 0.24 ± 0.22, the SE was 4.35 ± 2.98 D, the stereoscopic median was 800", the eccentric fixation distance was 632.18 ± 310.62 µm, the macular fovea retinal thickness was 207.82 ± 17.79 µm, the VLD of the superficial retinal vascular plexus was 7.31 ± 3.84 mm− 1, the PD was 0.16 ± 0.08, the FAZ area was 0.28 ± 0.17 mm2, the FAZ perimeter was 2.05 ± 0.56 mm, and the FAZ circularity was 0.67 ± 0.06. These results showed statistically significant differences in the SE and BCVA compared with the lateral eye and the control group, but there were no statistically significant differences in the macular fovea retinal thickness, VLD, PD, or FAZ. The eccentric fixation of amblyopic eyes was directly related to the deviation angle, and the regression formula was as follows: the eccentric fixation distance of amblyopic eyes = 8.319 × the deviation angle + 410.002 (F = 13.878, P = 0.002 < 0.01).ConclusionThe eccentric fixation distance of strabismus amblyopia with eccentric fixation is related to the deviation angle; the greater the deviation angle is, the greater the distance of eccentric fixation.Trial registrationChinese Clinical Trial Registry, ChiCTR1900022830. Registered 27 April 2019, http://www.chictr.org.cn/

Visuomotor feedback gains are modulated by gaze position

During goal-directed reaching, people typically direct their gaze to the target before the start of the hand movement and maintain fixation until the hand arrives. This gaze strategy improves reach accuracy in two ways. It enables the use of central vision at the end of movement, and it allows the use of extraretinal information in guiding the hand to the target. Here we tested whether fixating the reach target further facilitates reach accuracy by optimizing the use of peripheral vision in detecting, and rapidly responding to, reach errors during the ongoing movement. We examined automatic visuomotor corrections in response to displacements of the cursor representing the hand position as a function of gaze fixation location during unimanual goal-directed reaching. Eight fixation targets were positioned either in line with, or at different angles relative to, the straight-ahead movement direction (manipulation of fixation angle), and at different distances from the location of the visual perturbation (manipulation of fixation distance). We found that corrections were fastest and strongest when gaze was directed at the reach target compared with when gaze was directed to a different location in the workspace. We found that the gain of the visuomotor response was strongly affected by fixation angle, and to a smaller extent by fixation distance, with lower gains as the angle or distance increased. We submit that fixating the reach target improves reach accuracy by facilitating rapid visuomotor responses to reach errors viewed in peripheral vision. NEW & NOTEWORTHY It is well known that directing gaze to the reach target allows the use of foveal visual feedback and extraretinal information to improve the accuracy of reaching movements. Here we demonstrate that target fixation also optimizes rapid visuomotor corrections to reach errors viewed in peripheral vision, with the angle of gaze relative to the hand movement being a critical determinant in the gain of the visuomotor response.