Improvement In Stereoacuity Research Articles

Recovering stereo vision by squashing virtual bugs in a virtual reality environment.

Stereopsis is the rich impression of three-dimensionality, based on binocular disparity-the differences between the two retinal images of the same world. However, a substantial proportion of the population is stereo-deficient, and relies mostly on monocular cues to judge the relative depth or distance of objects in the environment. Here we trained adults who were stereo blind or stereo-deficient owing to strabismus and/or amblyopia in a natural visuomotor task-a 'bug squashing' game-in a virtual reality environment. The subjects' task was to squash a virtual dichoptic bug on a slanted surface, by hitting it with a physical cylinder they held in their hand. The perceived surface slant was determined by monocular texture and stereoscopic cues, with these cues being either consistent or in conflict, allowing us to track the relative weighting of monocular versus stereoscopic cues as training in the task progressed. Following training most participants showed greater reliance on stereoscopic cues, reduced suppression and improved stereoacuity. Importantly, the training-induced changes in relative stereo weights were significant predictors of the improvements in stereoacuity. We conclude that some adults deprived of normal binocular vision and insensitive to the disparity information can, with appropriate experience, recover access to more reliable stereoscopic information.This article is part of the themed issue 'Vision in our three-dimensional world'.

Changes in stereopsis after photorefractive keratectomy

To evaluate the effects of photorefractive keratectomy (PRK) on the stereopsis of myopic and hyperopic patients. Farabi Eye Hospital, Tehran, Iran. Prospective case series. This study included patients having PRK to achieve emmetropia. The patients were divided into the following 3 groups: low myopia (<-6.0 diopters [D]), high myopia (>-6.0 D), and hyperopia (<+4.0 D). Near stereoacuity was measured using the Randot test under photopic conditions (with corrective glasses) at 40cm preoperatively (with corrective glasses) and 1, 3, and 12months postoperatively. Repeated-measure analysis of variance was used to assess changes in stereopsis over time in the 3 groups. Each group comprised 60 patients. The mean preoperative stereoacuity was 121.16seconds of arc (arcsec)±149.92 (SD), improving to 83.66±75.84 arcsec 1month postoperatively and 80.66±64.31 arcsec at 3months (both P<.001). It remained unchanged (83.33±75.01 arcsec) at 12months (P=.610). Patients with high myopia had the greatest improvement in stereopsis after PRK compared with low myopic and hyperopic patients (P<.001). The improvement in stereoacuity was significantly higher in the severe anisometropic group; the lowest improvement was in the group without anisometropia. Photorefractive keratectomy could result in an improvement in stereopsis. Patients with high myopia benefitted most from PRK in terms of improvement in stereopsis. None of the authors has a financial or proprietary interest in any material or method mentioned.

Effects of higher-order aberration correction on stereopsis at different viewing durations.

To better understand how the eye's optics affects stereopsis, we measured stereoacuity before and after higher-order aberration (HOA) correction with a binocular adaptive optics visual simulator. The HOAs were corrected either binocularly or monocularly in the better eye (the eye with better contrast sensitivity). A two-line stereo pattern served as the visual stimulus. Stereo thresholds at different viewing durations were obtained with the psychophysical method of constant stimuli. Binocular HOA correction led to significant improvement in stereoacuity. However, better eye HOA correction could bring either a bad degradation or a slight improvement in stereoacuity. As viewing duration increased, the stereo benefit approached the level of 1.0 for both binocular and better eye correction, suggesting that long viewing durations might weaken the effects of the eye's optical quality on stereopsis.

Long-term outcome following bilateral lateral rectus recession for intermittent exotropia

Abstract Background: Bilateral lateral rectus recession is the most common surgical treatment of intermittent exotropia in children. Success rates in previous studies differ because longer follow-up periods may change success rate as the eyes drift out with time. Initial overcorrection was thought to be appropriate management, but the preferred initial postoperative deviation has not been well quantified. Objective: To study long-term outcomes (≥3 years) of bilateral lateral rectus recession for intermittent exotropia and to evaluate factors influencing long-term success. Methods: This retrospective descriptive study reviews patients with intermittent exotropia who underwent bilateral lateral rectus recession with a minimum follow up of 3 years. Long-term motor outcome was classified as good (within 8 prism diopters (PD) of esodeviation and 10 PD of exodeviation), acceptable (exodeviation 11-20 PD), and poor (esotropia &gt;8 PD or exotropia &gt;20 PD). Stereoacuity testing pre- and postoperatively was used to evaluate sensory outcome. Correlation between long-term outcome and various pre- and postoperative factors were analyzed. Results: A total of 59 patients met the selective inclusion criteria. The mean age at time of surgery was 7.1 years with a mean follow-up time of 4.5 years. At the time of the last visit, 69% (41 patients) had good outcomes, 24% (14 patients) had acceptable outcomes, and 7% (4 patients) had poor outcomes. Initial postoperative ocular deviation significantly correlated with long-term outcome (P &lt; 0.05). Mean initial postoperative ocular deviation of patients with good outcome was esodeviation 12.7 PD (range ortho to esodeviation 25 PD). In 45 patients whose stereoacuity could be assessed, 58% (26 patients) had stereoacuity improvement. Conclusion: Good long-term motor outcome can be achieved in 69% of patients following bilateral lateral rectus recession for intermittent exotropia. Initial postoperative ocular deviation correlated with long-term motor success.

Presbyopia: a pilot investigation of the barriers and benefits of near visual acuity correction among a rural Filipino population

BackgroundPresbyopia is the age-related decline in accommodation that diminishes the ability of the eye to focus on near objects. Presbyopia is common and easy to correct; however, many communities lack access to basic eye care. The purpose of this project was to assess the burden of uncorrected presbyopia in a rural Filipino population and to pilot an intervention aimed at increasing access to reading glasses in the community.MethodsIndividuals above the age of 40 who presented to a health outreach in the Philippines were invited to undergo a near vision exam to detect the presence of functional presbyopia and be fitted with ready-made, single-vision glasses. The change in stereoacuity was used as a surrogate measure of functional improvement after near vision correction. A questionnaire was administered to assess this population’s perceived barriers and benefits to correcting near vision.ResultsThe average age of the participants was 57 ± 11 years, with 87.6% of participants having an uncorrected near visual acuity of <20/50. Reading glasses improved near vision to 20/40 or better in 77.7% of participants having near-vision impairment (uncorrected near visual acuity of <20/40). Over 75% of participants also showed improvement in stereoacuity. Cost, rather than availability, was perceived to be the greater barrier to the procurement of glasses, and 84% of participants reported that the glasses dispensed would greatly improve their ability to earn a living.ConclusionsDispensing ready-made, single-vision glasses is a simple and cost-effective intervention to improve near vision and enhance depth perception. A greater understanding of the barriers and benefits to correcting near vision will inform the design and execution of a sustainable program to correct presbyopia in developing countries.

Evaluation of FD2 (Frisby Davis distance) stereotest in surgical management of intermittent exotropia

AimTo evaluate Frisby Davis distance (FD2) stereotest for determining the timing of surgical intervention in intermittent exotropia (X(T)).MethodsA prospective case–control study was conducted including 30 patients with X(T) and 30...

Transcranial direct current stimulation enhances recovery of stereopsis in adults with amblyopia.

Amblyopia is a neurodevelopmental disorder of vision caused by abnormal visual experience during early childhood that is often considered to be untreatable in adulthood. Recently, it has been shown that a novel dichoptic videogame-based treatment for amblyopia can improve visual function in adult patients, at least in part, by reducing inhibition of inputs from the amblyopic eye to the visual cortex. Non-invasive anodal transcranial direct current stimulation has been shown to reduce the activity of inhibitory cortical interneurons when applied to the primary motor or visual cortex. In this double-blind, sham-controlled cross-over study we tested the hypothesis that anodal transcranial direct current stimulation of the visual cortex would enhance the therapeutic effects of dichoptic videogame-based treatment. A homogeneous group of 16 young adults (mean age 22.1 ± 1.1years) with amblyopia were studied to compare the effect of dichoptic treatment alone and dichoptic treatment combined with visual cortex direct current stimulation on measures of binocular (stereopsis) and monocular (visual acuity) visual function. The combined treatment led to greater improvements in stereoacuity than dichoptic treatment alone, indicating that direct current stimulation of the visual cortex boosts the efficacy of dichoptic videogame-based treatment. This intervention warrants further evaluation as a novel therapeutic approach for adults with amblyopia.

Effect of Bilateral Age-Related Cataract on Stereoacuity

Aim of the study: The objective of this study is to determine the effect of bilateral age-related cataract on stereoacuity. The outcome of cataract surgery is usually measured against the gold standard of visual acuity but stereoacuity necessary for fine motor tasks is often ignored.Methodology: Stereoacuity threshold was measured in 142 participants with bilateral age-related cataracts using Frisby stereo test prior to any cataract surgery and 6 weeks after cataract surgery in the second eye with bilateral monofocal PMMA PC-IOL implantation.Outcome: Significant improvement in postoperative stereoacuity was found after extraction of bilateral age-related cataracts and PMMA PC-IOL implantation (p < 0.0001). Reduced stereoacuity was associated with increased age. There was no significant correlation of postoperative stereoacuity with duration of symptoms (p = 0.883).

Can improving prism fusion range with training also improve stereo-acuity?

Aim: We tested whether prism fusion range (PFR) could be improved by training and whether any improvement in PFR also led to improvement in stereo-acuity. Methods: The PFR and stereo-acuity thresholds of 15 participants with normal or corrected-to-normal vision were tested intially then at 1 week and 5 weeks. Eight of the participants, the experimental group, were instructed in training their base-in and base-out near prism fusion at home for 10 minutes twice each day for 1 week. Seven participants, the control group, were simply tested on three occasions without training. Results: For the experimental group after 1 week both near and distant PFR had significantly improved, by over 10 ∆ compared with the control group. Stereo-acuity had improved significantly but modestly by about 3 sec arc. However, 4 weeks later, during which no further training occurred, both PFR and stereo-acuity were no longer significantly different between the groups. Conclusions: Although in visually normal participants training of near PFR can lead to improvement in near and distant PFR and stereo-acuity, in the longer term no differences were found between the trained group and a control group who were untrained. These results emphasise the importance of including for comparison a non-treatment group in such studies.

Improvement in Stereoacuity through Training with Correlated Cues

Improvement in Stereoacuity through Training with Correlated Cues

Evaluation of factors influencing distance stereoacuity on Frisby–Davis Distance Test (FD2) in intermittent exotropia

AimTo evaluate the factors affecting the restoration of stereoacuity after surgery in cases of intermittent exotropia.MethodsThirty consecutive patients of intermittent exotropia X (T) scheduled for surgical intervention underwent preoperative evaluation,...

Phakic anterior chamber intraocular lens (Verisyse&amp;trade;) implantation in children for treatment of severe ansiometropia myopia and amblyopia: Six-month pilot clincial trial and review of literature

The current study aims to evaluate both safety and efficacy of Verisyse() (AMO, Irvine, CA) phakic anterior chamber intraocular lens (IOL) in the reduction of clinically significant (>-8 D) myopic anisometropia in children who are noncompliant to traditional medical treatment including spectacle correction or contact lenses. Retrospective interventional case series. Six anisometropic myopic pediatric patients in one practice were identified through chart-review. None of the patients were compliant with specatacle correction or contact lens wear and as a result had dense amblyopia of less than 20/400 by Snellen or Allen visual acuity (mean <20/400). All patients underwent Verisyse() phakic IOL implantation in the more myopic eye by one surgeon (AP). Pre- and post-operative visual acuity, anterior/posterior segment examination, stereoacuity, axial biometry measurements, cycloplegic refraction, and endothelial cell counts were performed in all patients whenever feasible. The age of patients ranged from 5-11 years. The mean post-operative follow-up time was six months from the time of IOL insertion. Improvement in visual acuity >6 lines was achieved in four patients (mean visual acuity of 20/70 at six months). Improvement in stereoacuity was noted in all six patients (from total mean zero seconds-arc to six-months post-operative mean of 500 seconds-arc by randot stereoacuity testing). Improvement of >2 lines of visual acuity lines was achieved in the other two patients. No patient lost any lines of visual acuity. Enhanced physical activity, coordination, and improved social interaction were noted in patients and were reported by the parents. No intra/post-operative complications were noted. Irreversible or intractable amblyopia secondary to severe anisometropic myopia is a serious medical concern in the pediatric population. Failure of compliance with contact lens therapy consistently leads to visual loss. Anterior chamber phakic IOLs may provide a safe alternative in treatment of noncompliant anisometropic myopic patients who do not accept spectacle wear or contact lens therapy. To reduce or eliminate highly significant anisometropic myopia in children who are noncompliant with traditional medical treatment, phakic anterior chamber IOL implantation may be considered as an alternative modality of treatment.

Improvement in distance stereoacuity following surgery for intermittent exotropia

To evaluate whether distance stereoacuity improves following surgery for intermittent exotropia using the Frisby Davis Distance (FD2) and Distance Randot stereotests. Eighteen patients (median age, 24 years; range, 5 to 68 years) with intermittent exotropia were prospectively enrolled. Stereoacuity was measured pre- and 6 weeks postoperatively using the FD2 and Frisby near tests (real depth tests) and Preschool Randot and Distance Randot tests (polaroid vectographs). Distance stereoacuity measured with the FD2 improved from a median preoperative value of 80 to 40 arcsec postoperatively (p = 0.04) and stereoacuity measured with the Distance Randot improved from a median of nil to 200 arcsec (p = 0.06). In those that had subnormal stereoacuity preoperatively, there was even more marked improvement in distance stereoacuity (FD2 median nil vs 40 arcsec, p = 0.002; Distance Randot median nil vs 200 arcsec, p = 0.004). Near stereoacuity measured with Frisby and Preschool Randot remained unchanged pre- to postoperatively (median, 60 and 80 arcsec, respectively). There was improvement in distance stereoacuity measured with both the FD2 and the Distance Randot stereotests in patients who underwent surgery for intermittent exotropia. The FD2 and Distance Randot may be useful outcome measures in future clinical trials of interventions for intermittent exotropia.

Randot ® Preschool Stereoacuity Test: Normative data and validity

The Randot Preschool Stereoacuity Test is a widely used three-book test for the assessment of binocular status. Using a prototype, we previously reported high testability in children as young as 3 years, validity data, and some normative data. Here we report extensive normative and validity data for the final version of the test. In addition, we report normative data for a new, fourth book that adds finer disparities. The Randot Preschool Stereoacuity Test was administered to 4355 normal children aged 3 to 18 years and 39 adults in multiple settings. In addition, the Randot Preschool Stereoacuity Test along with the new, fourth book that added 30 arcsec and 20 arcsec disparity levels was administered to 1402 normal children aged 3 to 18 years and 33 normal adults. Both the four-book Randot((R)) Preschool Stereoacuity Test and the Randot circles were administered to 242 patients with amblyogenic conditions aged 3 to 18 years. Mean normal stereoacuity improved from 100 arcsec at 3 years of age to 60 arcsec by 5 years and 40 arcsec by 7 years. The lower limit of normal was 400 arcsec at 3 years, 200 arcsec at 4 years, and 60 arcsec at 7 years. Using the new four-book version, further improvement in mean stereoacuity could be appreciated beyond 7 years of age to 30 arcsec in the 11- to 18-year-old and adult groups. Among the 242 patients, Randot Preschool Stereoacuity Test stereoacuity was strongly associated with Randot circle stereoacuity (chi(2) = 261.0, p < 0.001). Normative data for the Randot Preschool Stereoacuity Test show a monotonic improvement of stereoacuity from age 3 years through the teen years. Patient data support the validity of the Randot Preschool Stereoacuity Test.

The effect of Nd:YAG laser posterior capsulotomy on stereoacuity

To assess the effect of Nd:YAG laser posterior capsulotomy in the context of unilateral posterior capsular opacification (PCO) on spatial acuity, contrast sensitivity, and stereoacuity. This prospective study involved 60 consecutive subjects with unilateral PCO. The aforementioned parameters of visual function were assessed immediately prior and 3 weeks subsequent to unilateral posterior capsulotomy. In eyes that underwent laser posterior capsulotomy, the median spatial acuity (log minimum angle of resolution (MAR)) improved from 0.34 (20/44) to 0.16 (20/29) (P=<0.001, Wilcoxon test), while the median contrast sensitivity improved from 22.4 to 35.5 dB (P=<0.001, Wilcoxon test) after posterior capsulotomy. Fellow eyes exhibited negligible change in these visual parameters. The median stereoacuity improved from 240 to 60 s of arc (P=<0.001, Wilcoxon test). In the context of unilateral opacification of the posterior capsule, Nd:YAG laser posterior capsulotomy affords significant improvement in stereoacuity, apparently in excess of improvements in spatial acuity and contrast sensitivity. Routine measurement and documentation of these parameters of visual function is recommended especially when subjective visual disability appears disproportionate with impairment of spatial acuity.

Randot Preschool Stereoacuity test: Normative data and validity

Introduction: The Randot Preschool Stereoacuity test (RPST) is a widely used three-book test for the assessment of binocular status. Using a prototype, we reported high testability in children as young as 3 years, validity data, and some normative data. An artifact noted for 1 of the 800 seconds stimuli in the prototype led to a redesign. Here we report normative and validity data for the final three-book version of the RPST. In addition, we report normative data for a new fourth book that adds finer disparities. Methods: The RPST was administered to 4338 normal children ages 3 to 18 years and 39 adults in both clinical and screening settings. In addition, the RPST along with the new fourth book that added 30 and 20 seconds disparity levels was administered to 1402 normal children ages 3 to 18 years and 33 normal adults. Both the four-book RPST and the Randot circles were administered to 242 patients aged 3 to 18 years. Results: Mean normal stereoacuity improved from 100 seconds at 3 years of age to 60 seconds by 5 years and 40 seconds by 7 years. The lower limit of normal was 400 seconds at 3 years, 200 seconds at 4 years, and 60 seconds at 7 years. Using the new four-book version, further improvement in mean stereoacuity could be appreciated beyond 7 years of age to 30 seconds in the 11- to 18-year-old and adult groups. Among the 242 patients, RPST stereoacuity (four-book test) was strongly associated with Randot circle stereoacuity (c2 = 261.0, p < 0.001). Conclusions: Normative data for the RPST show a monotonic improvement of stereoacuity from age 3 years through teens. Patient data support the validity of the four-book version of the test.

Effects of Perceptual Learning on Local Stereopsis and Neuronal Responses of V1 and V2 in Prism-Reared Monkeys

Visual performance improves with practice (perceptual learning). In this study, we sought to determine whether or not adult monkeys reared with early abnormal visual experience improve their stereoacuity by extensive psychophysical training and testing, and if so, whether alterations of neuronal responses in the primary visual cortex (V1) and/or visual area 2 (V2) are involved in such improvement. Strabismus was optically simulated in five macaque monkeys using a prism-rearing procedure between 4 and 14 wk of age. Around 2 yr of age, three of the prism-reared monkeys ("trained" monkeys) were tested for their spatial contrast sensitivity and stereoacuity. Two other prism-reared monkeys received no training or testing ("untrained" monkeys). Microelectrode experiments were conducted around 4 yr of age. All three prism-reared trained monkeys showed improvement in stereoacuity by a factor of 7 or better. However, final stereothresholds were still approximately 10-20 times worse than those in normal monkeys. In V1, disparity sensitivity was drastically reduced in both the trained and untrained prism-reared monkeys and behavioral training had no obvious effect. In V2, the disparity sensitivity in the trained monkeys was better by a factor of approximately 2.0 compared with that in the untrained monkeys. These data suggest that the observed improvement in stereoacuity of the trained prism-reared monkeys may have resulted from better retention of disparity sensitivity in V2 and/or from "learning" by upstream neurons to more efficiently attend to residual local disparity information in V1 and V2.

Listening to classical music can (slightly) improve stereo-acuity in normal observers

Aims: To test for improvements in stereo-acuity, relative to pre-test measurements, after listening to pieces of classical music and whether any stereo-­acuity improvement tended to be found following enjoyable stimuli. Methods: In a double-masked repeated measures study 15 participants with normal vision had their stereo-acuity measured to threshold using the Frisby stereo-test on five occasions: prior to exposure to the test stimuli, and then on four subsequent occasions each time after listening to a particular stimulus for 10 minutes. Participants also rated their enjoyment of each stimulus. Results: After listening to each of the musical stimuli stereo-acuity was improved significantly when com­pared with the pre-test level, but listening to the control white noise stimulus produced no significant improvement in stereo-acuity. There was no signifi­cant difference between any of the musical pieces in cither their effect on stereo-acuity or enjoyment rating. The white noise stimulus was found to be significantly less enjoyable than any of the musical pieces. This suggested that the effect of the music was possibly due to a change in participants’ mood. Conclusion: Our findings for stereo-acuity are con­sistent with previous studies that have shown that listening to classical music can improve performance in spatial tasks.

Characterizing the mechanisms of improvement for position discrimination in adult amblyopia.

Adult amblyopes can improve positional acuity through practice; however, the neural mechanisms underlying this improvement are still not clear. In this study, seven adult amblyopes repeatedly practiced a position discrimination task in the presence of positional noise. We found that six of the seven showed systematic and significant improvements in position acuity that were both eye and orientation specific. Using a position-averaging model, we were able to parse the improvement in performance with practice into two factors: improvement in sampling efficiency and reduction of equivalent input noise. Three of the seven showed improved efficiency with no change in equivalent noise, two showed a significant reduction in equivalent noise with no change in efficiency, and one showed both improved efficiency and reduced equivalent noise. Interestingly, all observers showed substantial improvement in visual acuity, and one observer showed substantial improvement in stereoacuity. Three observers were also tested on a counting task, and all three improved after practicing positional discrimination. Our results reveal the mechanisms underlying perceptual learning in amblyopic vision, and may provide a basis for developing more effective and efficient strategies for the treatment of amblyopia.

Interactions between chromatic- and luminance-contrast-sensitive stereopsis mechanisms

It is well known that chromatic information can assist in solving the stereo correspondence problem. It has also been suggested that there are two independent first-order stereopsis mechanisms, one sensitive to chromatic contrast and the other sensitive to luminance contrast ( Vision Research 37 (1997) 1271). Could the effect of chromatic information on stereo correspondence be subserved by interactions between these mechanisms? To address this question, disparity thresholds (1/stereoacuity) were measured using 0.5 cpd Gabor patches. The stimuli possessed different relative amounts of chromatic and luminance contrast which could be correlated or anti-correlated between the eyes. Stereoscopic performance with these compound stimuli was compared to that with purely isoluminant and isochromatic stimuli at different contrasts. It was found that anti-correlated chromatic contrast severely disrupted stereopsis with achromatic stimuli and that anti-correlated luminance contrast severely disrupted stereopsis with chromatic stimuli. Less dramatic, but still significant, was the improvement in stereoacuity obtained using correlated colour and luminance contrast. These data are consistent with there being positive and negative interactions between chromatic and achromatic stereopsis mechanisms that take place after the initial encoding of disparity information, but before the extraction of stereoscopic depth. These interactions can be modelled satisfactorily assuming probability summation of depth sign information between independent mechanisms.