Fixation Disparity Research Articles

The preferred retinal loci when the eyes converge.

The preferred retinal locus (PRL) is the position on the retina to which humans direct stimuli during fixation. In healthy normal eyes, it has been shown to be very stable across time and between different tasks. Previous measurements of the PRL have been made under monocular viewing conditions. The current study examines where the PRLs in the two eyes' retinas are when subjects fixate binocularly and whether they shift when the demand for the eyes to converge is changed. Our apparatus allows us to see exactly where binocular stimuli fell on the two retinas during binocular fixation. Thus, our technique bypasses some of the issues involved in measuring binocular alignment with subjective techniques and previous objective techniques that use conventional eye trackers. These results show that PRLs shift slightly but systematically as the demand for convergence increases. The shifts cause under-convergence (also called exo fixation disparity) for near targets. They are not large enough to cause a break in binocular fusion. The fixation disparity we observed with increasing vergence demand is similar to fixation disparity observed in previous reports.

Fixation Disparity: A Possible Index of Visuospatial Cognition during Authentic Learning Tasks

AbstractThis article describes a novel method for quantifying fixation disparity and evaluates its role in visuospatial cognition during an authentic learning task, specifically, the determination of molecule chirality in organic chemistry involving mental rotation and pattern comparison. The first study examined the influence of molecular model dimensionality (2D vs. 3D) on chirality determination performance and visual attention of 55 participants. The second study explored how the sustained playing of the tile‐matching game Mahjong, a pattern comparison game, can affect visual attention and visuospatial performance during the chirality determination task of 59 participants. Fixation disparity was one of the eye tracking variables explored. Both studies revealed that (1) individuals with higher fixation disparity underperformed on the chirality task, which involves mental rotation and pattern comparison, and (2) fixation disparity improved over time in participants who played Mahjong. This work provides important implications for using fixation disparity as a possible biomarker of visuospatial performance.

Consistency of the PRL Across Vergence Demand as a Measure of Objective Fixation Disparity

Consistency of the PRL Across Vergence Demand as a Measure of Objective Fixation Disparity

Topical Review: Methodological Variables in Clinical and Laboratory Measurements of Fixation Disparity.

Fixation disparity is a small vergence error that does not disrupt fusion. Fixation disparity measures correlate with binocular symptoms. This article covers methodological differences between clinical fixation disparity measurement devices, findings when objective and subjective fixation disparities are compared, and the potential impact of binocular capture on fixation disparity measurements. Fixation disparity is a small vergence error that occurs in nonstrabismic individuals and does not disrupt fusion. This article reviews clinical fixation disparity variables and their clinical diagnostic value. Clinical devices that are used to measure these variables are described, as are studies in which the output from these devices has been compared. Methodological differences between the devices such as the location of the fusional stimulus, the rate at which judgments of dichoptic alignment are made, and the strength of the accommodative stimulus are all considered. In addition, the article covers theories of the neural origins of fixation disparity and control system models incorporating fixation disparity. Studies in which objective fixation disparities (oculomotor portion of fixation disparity assessed with an eye tracker) and subjective fixation disparities (sensory portion of fixation disparity assessed psychophysically with dichoptic Nonius lines) have been compared are also examined, and consideration is given to why some investigators find differences in these measures, whereas other investigators do not. The conclusion thus far is that there are likely complex interactions between vergence adaptation, accommodation, and the location of the fusional stimulus that lead to differences in objective and subjective fixation disparity measures. Finally, capture of the visual direction of monocular stimuli by adjacent fusional stimuli and the implications for fixation disparity measures are considered.

Analysis of Exophoria and Fixation Disparity before and after Vision Training according to Gender

Analysis of Exophoria and Fixation Disparity before and after Vision Training according to Gender

Fixation disparity and refractive error among first-year optometry students.

To determine the fixation disparity and refractive error of first-year optometry students to ascertain any relationship between them and also identify any association between fixation disparity and visual symptoms at near. It was an analytical cross-sectional study involving 85 participants aged 17 to 27 years (18.60±1.37), 41% of whom were males. Subjective refraction was done at 3m and fixation disparity was measured with and without spectacle correction using the Wesson Fixation Disparity Card. All analysis was set within a 95% confidence interval with a p-value≤0.05 considered statistically significant. Refractive error ranged from 0.25 SEQ (spherical equivalent) to 5.50 SEQ. Mean fixation disparity ranged from 2.9±2.6 to 3.9±2.8min arc. There was no statistically significant correlation between refractive error and fixation disparity without correction (r=-0.180, p=0.098) and with correction (r=0.155, p=0.157). For fixation disparity in the ortho and exo direction, mean fixation disparity with correction of participants who experienced headaches during or after reading (5.1±2.6min arc) was significantly higher (p=0.032) than participants who did not (2.0±2.6min arc). Myopia is common among first-year optometry students. Refractive error has no significant effect on fixation disparity. Headache is significantly associated with exo fixation disparity at near.

The effects of breaks on digital eye strain, dry eye and binocular vision: Testing the 20-20-20 rule.

To evaluate the benefits on the eyes of taking breaks based on the 20-20-20 rule. Bespoke computer software using the laptop webcam to assess user breaks, eye gaze and blinking, and emitting personalized reminders of breaks based on the 20-20-20 rule, was downloaded onto the laptops of 29 symptomatic computer users. Digital eye strain (DES), binocular vision and dry eye were assessed before and after two weeks of using the reminders and one week after the discontinuation of the strategy. Binocular measurements included visual acuity, accommodative posture, stereopsis, fixation disparity, ocular alignment, accommodative facility, positive/negative vergences and near point of convergence. Symptoms were evaluated using the computer vision syndrome questionnaire, ocular surface disease index (OSDI), and symptom assessment in dry eye questionnaire (SANDE) versions one and two. Dry eye signs were assessed by measuring tear meniscus height, conjunctival redness, blink rate and incomplete blinking, lipid layer thickness, non-invasive keratograph break-up time, corneal and conjunctival staining and lid wiper epitheliopathy. A decrease in the duration of computer work and the duration of breaks, along with an increase in the number of breaks taken per day was observed as a result of the 20-20-20 rule reminders (p≤0.015). No changes on any binocular parameter were observed after the management period (p≥0.051), except for an increase in accommodative facility (p=0.010). Dry eye symptoms and DES decreased with the rule reminders (p≤0.045), although this improvement was not maintained one week after discontinuation (p>0.05). No changes on any ocular surface and tear film parameter were observed with the rule reminders (p≥0.089). The 20-20-20 rule is an effective strategy for reducing DES and dry eye symptoms, although 2weeks was not enough to considerably improve binocular vision or dry eye signs.

Comparison of Visual Skills between Federated and Non-Federated Athletes.

To perform motor tasks, athletes must gather a considerable amount of visual information quickly. Evidence shows that visual skills vary between athletes and non-athletes, and impact athletic performance. However, there is no scientific evidence suggesting that there are any differences between the visual skills of federated and non-federated athletes. As such, the objective of this paper was to compare how visual skills influence the sports performance of federated and non-federated athletes, respectively. A visual examination has been conducted on a total of 52 athletes between 18 and 37 years of age. The COI-Sport Vision system screen (International Optometry Center, Madrid, Spain) was used to examine static visual acuity, dynamic visual acuity, contrast sensitivity, stereopsis, fixation disparity, visual memory, identification, anticipation time, peripheral awareness, and hand-eye coordination. On average, federated athletes train more hours per day than non-federated athletes (1.4 ± 0.8) (p = 0.046). A significant correlation was observed between the average time of visual memory (β = -0.0683, p < 0.001), the average time of anticipation (β = 0.006, p = 0.009), the average time of peripheral awareness (β = 0.026, p = 0.002), hand-eye coordination (β = 0.028, p = 0.004), dynamic visual acuity (β = 0.055, p < 0.001), and the number of training hours. Results suggest that federated athletes are more concerned about their ocular health. Nonetheless, no differences were found in the oculomotor skills of both groups. Further investigation is required to consider each sport discipline individually.

Binocular Vision Function and Migraine: A Review

Migraine is a multifactorial disease characterized by recurrent headaches and has complex neuronal and vascular mechanisms, including a wide range of clinical symptoms and other ocular findings. During migraine attacks in migraine sufferers, the accommodative response increases significantly. Migraine sufferers are predisposed to have a subtle deficit in binocular vision coordination, reduced stereopsis, reduced fixation disparity, slightly higher prevalence of heterophoria, and reduced stereopsis. Convergence insufficiency can be associated with migraine and may be the persistent cause of reduced visual functioning. Binocular vision coordination difficulties are the most common findings among migraine sufferers.

How reading speed is affected by prism correction in exophoric patients

Reading is a very crucial part of life. Good reading ability is necessary for daily tasks. People who have difficulty in reading (for any reason) can find it very frustrating throughout the day and can suffer from symptoms such as headaches, eye strain, etc. Reading speed is a factor that can indicate reading ability. Among many different factors that affect reading speed, one of the factors is the condition of exophoria. This is when the eyes tend to diverge and usually presents with difficulty to converge. When reading at a near distance the eyes must converge, making reading more difficult for people with exophoria. Measuring the eyes' deviation can be performed in different ways, giving different amounts of prisms needed to correct the exophoria and give more comfort. In this study, two methods are used (Fixation Disparity and Maddox Rod) to determine how many prisms would be necessary to prescribe and then test reading speed with each number of prisms. The results showed no significant difference in reading speed using each method to test for prisms, although subjectively it appears that there is a trend toward faster reading with prisms measured according to Fixation Disparity.

Update zur Fixationsdisparität

Purpose. The aim of the paper is to summarise and discuss the current state of knowledge on the overall topic of fixation disparity (FD). Material and Methods. A systematised PubMed literature search based on the term “fixation disparity” was conducted; in addition, the publication relies on the reference book on “Perceiving in Depth” written by I. P. Howard. Results. Until the 1990s, the understanding regarding subjective FD was quite uniform. Studies with high-resolution, objective examination methods and simultaneous measurement of subjective and objective FD have since shown that the vergence error (= objective FD) is usually not very well correlated with the vernier error (= subjective FD). It can therefore be assumed that the two types of FD are two different phenomena. The objective vergence error can indicate how large the shift of the image position on the retina is within the central panum area. Subjective FD, on the other hand, must be seen as the result of multiple processing events in the brain. Conclusion. There is a difference between subjective and objective FD. This finding does not contradict the clinical rel- evance of subjective FD. Aligning prisms to correct subjective FD are effective in reducing visual complaints in certain cases. It is possible that aligning prisms reduce a relevant proportion of heterophoria. Keywords binocular vision, fixation disparity, vergence error, vernier error

Why testing vergence is so complicated – The subjective and the objective fixation disparity

Purpose. This review article describes recent findings of eye movement research of ocular vergence and provides an in- terpretation regarding those aspects of binocular vision that are assessed by clinical nonius tests. Material and Methods. In the clinical practice of binocular testing, different types of nonius tests are traditionally used for the vergence position of the eyes: near to a fusion stim- ulus, the test includes monocularly presented nonius lines; the perceived nonius offset is understood as a measure of “subjective fixation disparity”. However, in basic research precise eye movement recording systems are applied since the 1980s for measuring the “objective fixation disparity”. Results. The correlation between subjective and objective measures of fixation disparity tends to be low. Subjective measures are typically much smaller than objective measures. Conclusion. A precise terminology for the results of these measurements allows one to describe the physiological dif- ferences between the two aspects of fixation disparity. Recent research findings may be the basis for reconsidering the mechanisms of motor and sensory fusion and interpreting the clinical findings accordingly. With the help of video eye track- ers, it is now possible to conduct clinically-oriented optom- etric research of subjective and objective fixation disparity. Keywords Binocular vision, fixation disparity, vergence, fusion

Verändern MKH-Prismen den binokularen Vorteil beim Lesen?

Purpose. Reading with both eyes comes with a binocular advantage (shorter total reading times and fixation durations in binocular compared to monocular reading), which results from binocular fusional processes. Binocular advantages in reading typically vary with the amount of individual, horizontal heterophoria and thus, we investigated whether prismatic lenses (measured with the MCH method and worn to com- pensate any heterophoria) have a short- or long-term effect on binocular advantages when reading. Material and Methods. We measured the binocular eye movements (Eyelink II) of 54 participants with individual horizontal heterophoria when reading a total of 120 Ger- man-language sentences (1) monocularly, (2) binocularly, (3) binocularly with disparity (corresponding to an MCH prism), and (4) binocularly with disparity after 6 months. In the 6-month interval between measurements (3) and (4), 29 participants wore glasses with prismatic corrections, while 25 participants were considered the control group. Results. Our data showed a clear, significant advantage for binocular reading on all participants. A short-term, individual disparity (analogous to an MCH prism) did not alter this result. An additional tendency towards a greater binocular advan- tage in the “prism group” compared to the “control group” was only observed after using a prismatic lens for 6 months. Additionally, saccade disconjugacy increased slightly and the objective fixation disparity decreased significantly. Conclusion. Individual prismatic corrections (MCH) had an effect on some aspects of the binocular coordination during reading and increased the binocular advantage in our het- erophoric participants after 6 months of wearing prismatic corrections. This delayed effect on fusion during reading is new and calls for further research. Keywords binocular advantage, horizontal heterophoria, binocular vision, reading, binocular coordination

Interocular Phase Disparity Tuning of Binocular Contrast Summation Depends on Carrier Spatial Frequency and Orientation.

Binocular summation is a sensitive metric of binocular integration. As such, characterization of the mechanisms underlying binocular summation is a key step in translating and applying this knowledge to abnormal binocular systems afflicted with strabismus and amblyopia. Computational models of binocular summation have advocated the operation of mechanisms sensitive to the interocular phase disparity of first-order carrier gratings. This study investigated if such generalization depended on carrier spatial frequency and orientation. Monocular and binocular contrast detection thresholds were measured in nine observers with normal binocular vision. Stimuli comprised Gabor targets presented with one of three spatial frequencies (1, 3, and 9 cycles per degree [cpd]), two orientations (horizontal and vertical), and five interocular phase disparities (0, ± π /2, ± π radians). Horizontal and vertical fixation disparities were measured for each binocular threshold condition. Binocular summation ratios were computed by dividing the mean monocular detection threshold by the respective binocular detection threshold. Binocular summation ratio varied significantly with interocular phase disparity for the 1- and 3-cpd horizontal and vertical gratings. Phase dependency was reduced with the 9-cpd horizontal grating and absent for the 9-cpd vertical grating, even though binocular summation ratio exceeded predictions of probability summation. Computational modeling that incorporated the variability of fixation disparity into a vector summation model predicted a reduction in peak binocular summation ratio with increasing carrier spatial frequency but did not account for the reduction of phase sensitivity noted with the 9-cpd stimulus. Binocular summation magnitude is less dependent on interocular phase disparities for carrier spatial frequencies that exceed 3 cpd, especially with vertical gratings. Although vergence variability due to fixation disparities contributes to the overall reduction in binocular summation magnitude with increasing carrier spatial frequency, it does not provide a complete account for the lack of interocular phase disparity tuning noted with high grating spatial frequencies.

Comparison of Static and Dynamic Stereopsis before and after Distance Subjective Fixation Disparity Correction

Comparison of Static and Dynamic Stereopsis before and after Distance Subjective Fixation Disparity Correction

Comparison of Prescription Values for Fixation Disparity Alignment Prism and Phoria Prism

Comparison of Prescription Values for Fixation Disparity Alignment Prism and Phoria Prism

Differences in Visuospatial Expertise between Skeet Shooting Athletes and Non-Athletes.

Background: Sports vision is a specialisation of optometry whose objective is to improve and preserve visual function to increase sports performance. The main objective of the present study was to compare the visual expertise of non-athletes to skeet shooting athletes. Methods: Participants underwent an optometric assessment in which all those with severe deviations from normal vision, after compensating for visual abnormalities, were eliminated. After that, the following six visuospatial components were measured: hand–eye coordination, peripheral awareness, fixation disparity, saccadic eye movements, speed of recognition and visual memory. To measure the aforementioned components, the following tests were used: directional arrows, similar and different characters, the dichromatic disparity test, character marking, a tachistoscopic test and tic-tac-toe using COI-vision software. Results: Skeet shooting athletes performed significatively better (p ≤ 0.05) in two out of the six tests: hand–eye coordination and visual memory. Conclusions: Although this study does not support the theory that athletes—in this case, skeet shooting athletes—perform significantly better in most components of the visuospatial tests, visual memory and hand–eye coordination are exceptions. To be more accurate in distinguishing between athletes and non-athletes, specific testing methods that can be used by a wide variety of disciplines should be developed. Training the weakest aspects of athletes can improve their sports performance.

Neurophysiological indicators of internal attention: An fMRI–eye-tracking coregistration study

Many goal-directed, as well as spontaneous everyday activities (e.g., planning, mind-wandering), rely on an internal focus of attention. This fMRI–eye-tracking coregistration study investigated brain mechanisms and eye behavior related to internally versus externally directed cognition. Building on an established paradigm, we manipulated internal attention demands within tasks utilizing conditional stimulus masking. Internally directed cognition involved bilateral activation of the lingual gyrus and inferior parietal lobe areas as well as wide-spread deactivation of visual networks. Moreover, internally directed cognition was related to greater pupil diameter, pupil diameter variance, blink duration, fixation disparity variance, and smaller amounts of microsaccades. FMRI–eye-tracking covariation analyses further revealed that larger pupil diameter was related to increased activation of basal ganglia and lingual gyrus. It can be concluded that internally and externally directed cognition are characterized by distinct neurophysiological signatures. The observed neurophysiological differences indicate that internally directed cognition is associated with reduced processing of task-irrelevant information and increased mental load. These findings shed further light on the interplay between neural and perceptual mechanisms contributing to an internal focus of attention.

Effects of aiming lines and visual function on the golf putting alignment

Background: In golf, a player hits a ball with a club, aiming to transfer the ball successively into a series of hole cups in a course consisting of 18 (or fewer) holes. This study aimed to compare the impact of visual function and the presence and number of aiming lines on golf putting alignment between beginner and expert golfers.
 Methods: In this prospective comparative study, 43 participants with a mean ± standard deviation (SD) of corrected distance binocular visual acuity of –0.07 ± 0.74 logarithm of the minimum angle of resolution, who knew their average golf scores, were divided into beginner and expert golfers. Six visual function tests were conducted to assess heterotropia, dominant eye, verification of current spectacles, static visual acuity, stereopsis, and fixation disparity. At the putting distances of 1.5 m and 3 m, alignment errors were measured five times each, using golf balls with 1 and 3 aiming line(s) and putters with 1 and 3 aiming line(s).
 Results: The mean ± SD of age was 48.33 ± 10.07 years for study participants overall. The accuracy of ball alignment was not affected by the career or number of aiming lines, but the putter alignment was higher for the 3-lines putter than for the 1-line putter (P < 0.05). When the number and shape of the aiming line were the same for both the ball and putter, the aiming accuracy was found to be higher. In both stereopsis and fixation disparity, the combination of putting distance and a 3-lines ball showed negative values; all other combinations showed positive values, but no statistically significant correlation was detected (all P > 0.05). 
 Conclusions: The accuracy of golf ball alignment did not depend on the number of aiming lines and the golfer’s career. However, the predicted putting success rate and subjective satisfaction were increased when three-line golf balls and putters were used, as compared to when one-line golf balls and putters were used.
 
 How to cite this article: Kim YJ, Jin YG, Koo BY, Jang JU, Mah KC. Effects of aiming lines and visual function on the golf putting alignment. Med Hypothesis Discov Innov Optom.2021 Spring; 2(1): 41-49. DOI: https://doi.org/10.51329/mehdioptometry124

Agreement of Fixation Disparity Curve between Two Different Instruments.

Fixation disparity tests with various characteristics of fusional stimulus are very important for assessment of decompensated heterophoria. The results suggest that there was no reasonable agreement between the fixation disparity curve's parameters of the modified near Mallett unit and the Sheedy disparometer. The purpose of this study was to determine the agreement of the fixation disparity curve parameters between the modified near Mallett unit and the Sheedy disparometer in patients with decompensated near heterophoria. A total of 147 young adults (mean age, 22.7 ± 4.8 years) participated in this cross-sectional study. After applying the exclusion criteria, the statistical analysis was done on the data of 134 individuals. All participants underwent preliminary optometric examinations including the measurement of uncorrected and best-corrected visual acuity, objective and subjective refraction, and unilateral and alternating cover tests. The fixation disparity was evaluated using the modified near Mallett unit and the Sheedy disparometer at 40 cm, and forced-vergence fixation disparity curves were generated. There were statistically significant differences in the fixation disparity curve parameters (except the center of symmetry) between the two devices. The median fixation disparity measured by the Sheedy disparometer was more positive compared with the modified near Mallett unit (toward more esodisparity or less exodisparity). The median associated phoria measured by the Sheedy disparometer was more positive compared with the Mallett unit. Also, the slope of the curve obtained by the Mallett unit was steeper. The wide limits of agreement indicated the poor agreement of all fixation disparity curve parameters between the two instruments.