Stereoacuity Research Articles

Visual and binocular status of Down syndrome children in Malaysia

Background: Down syndrome is a common chromosomal anomaly. Few reported studies make reference to the ocular status in Asian children with Down syndrome. The purpose of this study was to determine the visual and binocular status of a sample of Down syndrome children in Malaysia.Methods: A total of 73 Malaysian children with Down syndrome (38 boys and 35 girls) in the Kuala Lumpur area aged one to 12 years were examined. Cycloplegic refraction was performed on each eye and binocular visual acuity was assessed using the Cardiff acuity card or the LogMAR chart. Binocular functions were assessed using the cover test and Lang's stereo acuity test.Results: The mean age of the subjects was 6.01 ± 3.41 years. Refraction of the right eye showed that 10 per cent of the subjects were myopic, 20 per cent were hyperopic and 70 per cent had no significant refractive error. The mean spherical equivalent was +0.92 ± 2.32 DS for the right eye and +0.99 ± 2.21 DS for the left. The mean of binocular LogMAR VA was 0.36 ± 0.22 (6/12). Cover test revealed that 21 subjects had strabismus (of those, 33 per cent had unilateral esotropia, 52 per cent had alternating esotropia, nine per cent had unilateral exotropia and five per cent had alternating exotropia). Only 22 subjects gave clear positive response to the stereotest. Other ocular findings included ptosis (one per cent), abnormal head posture (seven per cent) and nystagmus (six per cent).Conclusion: Malaysian children with Down syndrome have a high incidence of refractive error and strabismus. Regular visual examination is important so that corrective lenses can be prescribed to improve vision and to enhance the quality of life of these children in Malaysia.

Stereoscopic acuity and observation distance

The amount of depth perceived from a fixed pattern of horizontal disparities varies with viewing distance. We investigated whether thresholds for discriminating stereoscopic corrugations at a range of spatial frequencies were also affected by viewing distance or whether they were determined solely by the angular disparity in the stimulus prior to scaling. Although thresholds were found to be determined primarily by disparity over a broad range of viewing distances, they were on average a factor of two higher at the shortest viewing distance (28.5 cm) than at larger viewing distances (57 to 450 cm). We found the same pattern of results when subjects' accommodation was arranged to be the same at all viewing distances. The change in thresholds at close distances is in the direction expected if subjects' performance is limited by a minimum perceived depth.

Spatial Localization in Visual Impairment

To investigate self-reported difficulties experienced by visually impaired subjects in real-world tasks requiring judgment of space and distance and to determine whether laboratory measures of spatial localization predict self-reported difficulty with spatial tasks better than traditional measures of visual function, such as visual acuity and contrast sensitivity. Forty-two subjects with visual impairment participated. The Spatial Localization Questionnaire (SLQ) was developed to investigate self-reported spatial localization difficulties, and subjects answered the questionnaire as part of the study. Subjects also completed a variety of clinical vision tests (visual acuity, contrast sensitivity, stereo acuity, and reading speed) and laboratory vision tests (vernier acuity, bisection acuity, and visual direction). The SLQ was found to have good validity. Several significant correlations were found between the Rasch analysis ability scores for the questionnaire and the clinical and laboratory vision tests. Using stepwise regression analysis, we found that vernier acuity and contrast sensitivity accounted for 42% of the variance in the Rasch scores (P < 0.001). The findings indicate that certain subjects with visual impairment have difficulty with real-world spatial tasks, as indicated by the SLQ. Of note, these difficulties were better predicted by vernier acuity (a resolution test) and contrast sensitivity, rather than vernier or bisection bias, which measure localization.

Effects of low stereo acuity on performance, presence and sickness within a virtual environment

To examine the effect of stereo vision on performance, presence and oculomotor disturbances within a virtual environment (VE), two groups of 23 participants (good stereo acuity/low stereo acuity) were evaluated. Groups were matched in terms of gender, age and VE design factors (the latter were accounted for to ensure a similar VE experience between groups). Participants were immersed in a VE maze for up to 1 h during which time they interacted with the environment while performing a number of stationary and movement-based tasks. Individuals with low stereo acuity traveled further to complete two tasks in the VE, yet performance time on these tasks was comparable to participants with good stereo acuity. Although participants with impaired stereo vision likely did not fully benefit from a stereoscopic view of the scene, they may have received sufficient depth information from movement-based cues to efficiently accomplish these tasks in a comparable amount of time. Overall performance, based on both the number of tasks completed and the total translational distance moved (based on input device movement) within the VE was not hindered for those with low stereo acuity. In addition, the expected increase in oculomotor disturbances for this group was not evident in this study, and both groups reported comparable amounts of presence from VE exposure. These results suggest that when head tracking is included as part of the VE experience (i.e., motion parallax cues exist), participants with low stereo acuity can be expected to perform comparable to normal sighted individuals, experience a comparable sense of presence, and report no increase in adverse effects when viewing scenes via stereoscopic displays. Thus, motion parallax cues may adequately provide a sense of depth within a VE, and alleviate theorized performance decrements for individuals with low stereo acuity. The results of this study have implications for those designing entertainment simulations or other such applications open to the general public, where people with low stereo acuity may routinely participate.

Stereoacuity before and after surgery in patients with acquired excyclotorsion

To investigate the stereoacuity before and after superior oblique sagittal transposition in patients with acquired excyclotorsion. 14 cases of acquired excyclotorsion who had complaints of forward and downward torsional diplopia were treated with superior oblique sagittal transposition. All patients were examined with Titmus test prior and after surgery. Surgical treatment greatly improved torsional diplopia. The stereoacuity improved gradually from 800 to 60 seconds of arc, peripheral to macular stereoacuity, and even foveal stereoacuity. The superior oblique sagittal transposition is an effective method for primary and down gaze acquired excyclotorsion. The operation not only alleviated diplopia in the practical fixation field, but also improved stereoacuity.

1359: Validation of Novel and Objective Measures of Microsurgical Skill: Hand-Motion Analysis and Stereoscopic Visual Acuity

1359: Validation of Novel and Objective Measures of Microsurgical Skill: Hand-Motion Analysis and Stereoscopic Visual Acuity

Essential fatty acids, DHA and human brain

Essential fatty acids cannot be synthesized in the body but they are required for maintenance of optimal health. There are two classes of polyunsaturated fatty acids (PUFAs)--omega-6 and omega-3. The parent omega-6 fatty acid, linoleic acid (LA) is desaturated in the body to form arachidonic acid while parent omega-3 fatty acid alpha-linolenic acid (ALA) is desaturated by microsomal enzyme system through a series of metabolic steps to form eicosapentaenoic acid (EPA) and decosahexaenoic acid (DHA). But there is a limited metabolic capability during early life to metabolize PUFAs to more active long-chain fatty acids. There is a critical role of EFAs and their metabolic products for maintenance of structural and functional integrity of central nervous system and retina. Most of the brain growth is completed by 5-6 years of age. At birth brain weight is 70% of an adult, 15% brain growth occurs during infancy and remaining brain growth is completed during preschool years. DHA is the predominant structural fatty acid in the central nervous system and retina and its availability is crucial for brain development. It is recommended that the pregnant and nursing woman should take at least 2.6 g of omega-3 fatty acids and 100-300 mg of DHA daily to look after the needs of her fetus and suckling infant. The follow-up studies have shown that infants of mothers supplemented with EFAs and DHA had higher mental processing scores, psychomotor development, eye-hand coordination and stereo acuity at 4 years of age. Intake of EFAs and DHA during preschool years may also have a beneficial role in the prevention of attention deficit hyperactivity disorder (ADHD) and enhancing learning capability and academic performance.

Development of Stereoscopic Acuity: Longitudinal Study Using a Computer-based Random-dot Stereo Test

To investigate the development of stereoscopic acuity (stereoacuity) in children longitudinally. Seven full-term normal infants whose age at the beginning of the study was between 12 and 23 weeks were studied. A computer-based random-dot test of stereoscopic vision (TV-Random Dot Stereo Test) was used to measure stereoacuity. The test was repeated at 2- to 3-month intervals until the children reached 2 years of age, and then every 6 to 12 months until they reached 5 years of age. All of the infants were found to have a stereoacuity of 2480 seconds of arc (2480'') with this test by 26 weeks of age. The first reliable measurement of stereoacuity was obtained from a 16-week-old infant. Stereoacuity did not improve significantly between 6 and 12 months, but it improved rapidly after 12 months. All children had a stereoacuity of 100'' with the Titmus Stereo Tests at 5 years of age, but the best stereoacuity with the TV-Random Dot Stereo Test was 229'' at 28.9 months. The development of stereoacuity studied longitudinally was similar to that obtained by cross-sectional studies. The TV-Random Dot Stereo Test is a useful program for measuring stereopsis in preverbal children.

Laser in situ keratomileusis for treated anisometropic amblyopia in awake, autofixating pediatric and adolescent patients

To establish the safety and efficacy of laser in situ keratomileusis (LASIK) in pediatric and adolescent patients with anisometropic amblyopia who completed amblyopia therapy and had a visual acuity of 20/30 or better bilaterally. Department of Ophthalmology and Visual Science, University of Texas-Houston Medical School, Houston, Texas, USA. From August 2000 to March 2002, LASIK was performed in 21 eyes of 19 consecutive patients meeting eligibility requirements. The procedure was performed with the Summit Autonomous LADARVision 4000 excimer laser (Alcon Laboratories, Inc.) in the amblyopic eye for the correction of anisometropia or in both eyes. All patients were awake and autofixating during the procedure. The mean patient age was 13.14 years (range 8 to 19 years). Seventeen patients were treated in the amblyopic eye only to correct anisometropia; treatment was performed in both eyes of 2 patients who were older than 18 years. Patients were followed for a mean of 18.0 months (range 8.6 to 26.5 months). Anisometropia was greater than 2.00 diopters (D) in all cases (mean 4.43 D, range 13.25 to 2.25 D). The percentage deviation from the attempted correction in the myopic group was 4.0% +/- 4.0% (SD) (range 2.0% to 10.0%) and 38.0% +/- 13.0% (range 5.0% to 58.0%) in the hyperopic group. Anisometropia decreased uniformly to less than 2.00 D in all patients (mean 1.52 D). The percentage of patients with stereo acuity increased from 63.0% preoperatively to 84.0% postoperatively. Laser in situ keratomileusis safely and effectively reduced anisometropia in these patients. If stereo acuity is not possible preoperatively, it may be obtained postoperatively.

Binocularity following surgical correction of strabismus in adults

This is a retrospective study to determine the pre- and postoperative binocular status of adults who have undergone surgical correction of strabismus. A list of all consecutive adult patients who underwent surgery for strabismus between June 1990 and December 2001 (surgery by MBM) was compiled and their medical charts were reviewed. Patients who had at least 6 weeks postoperative follow-up were included if their charts were available for review and if information on binocularity was recorded. Binocularity was measured by the Titmus stereo test (Stereo Optical Co., Inc., Chicago), and/or the Worth 4-Dot test for distance (Scioto Medical Products, Powell, OH [discontinued]), and/or the Worth 4-Dot near test (Gulden Ophthalmics, Inc., Elkin Park, PA). Improvements or decreases in stereo acuity were noted 6 weeks postoperatively and at the final office visit. Prism management was incorporated pre- and/or postoperatively in some of our patients. A total of 112 patients underwent surgery for strabismus. Of these, 72 patients, aged 16 to 80 years, were included; 24 were excluded as their charts did not contain any information on stereo acuity 6 weeks postoperatively or were lost to follow-up after surgery, and 16 were excluded because their charts were unavailable from storage. The mean follow-up for the study patients was 16.5 months (range 6 weeks to 79 months). Overall, 30 of the 72 patients improved in binocular function (42%), 38 remained the same (53%), and 4 decreased (5%). If you exclude those patients with 40 sec of stereo acuity preoperatively whose stereopsis, by definition, could not improve further, and look only at the 59 surgical patients who could improve, then 51% improved. A variety of surgical procedures was performed, the most common being a bilateral medial rectus recession. Eleven patients required a second surgical procedure and two required a third surgical procedure. The benefits of surgical correction of strabismus in adults include improvement in binocular function as seen in 51% of the patients in the study.

Laser in situ keratomileusis for high hyperopia in awake, autofixating pediatric and adolescent patients with fully or partially accommodative esotropia

Purpose: To establish the safety and efficacy of laser in situ keratomileusis (LASIK) in pediatric and adolescent patients with bilateral visual acuity of 20/30 or better and accommodative or partially accommodative esotropia. Setting: Department of Ophthalmology and Visual Science, University of Texas-Houston Medical School, Houston, Texas, USA. Methods: The study comprised 30 eyes of 15 consecutive patients with accommodative or partially accommodative esotropia who met eligibility requirements and had bilateral LASIK using the Alcon Summit Autonomous LADARVision® excimer laser to correct a refractive error after January 2001. All patients were awake and autofixating during the procedure. Results: The mean age of the patients was 13.9 years (range 9.1 to 18.8 years) and the mean refractive error, +5.35 diopters (D) (range +3.75 to +8.50 D) with anisometropia of 2.0 D or less. The mean follow-up was 15.7 months (range 9.5 to 22.5 months). No intraoperative complications were encountered. The percentage of undercorrection {100% − [(treatment achieved/treatment attempted) × 100%]} [mean 34% ± 17% (SD), coefficient of variation (SD/mean) 0.50, range 5% to 58%] was higher than expected. Seven patients (47%) required enhancement due to undercorrection of hyperopia with diplopia (6 patients) or astigmatism with decreased visual acuity (1 patient). In this small series, no patient lost best corrected visual acuity or stereo acuity. Conclusion: Laser in situ keratomileusis can safely and effectively reduce refractive error in this group of patients; however, patient selection is extremely critical and enhancement was required in almost half the patients.

Treatment outcomes in refractive accommodative esotropia

Purpose To document and compare the clinical features and functional outcomes in patients with accommodative esotropia. To assess the efficacy of conventional management of accommodative esotropia, to determine functional outcomes of amblyopia and binocular vision, and to analyze possible risk factors involving the development of amblyopia. Methods We retrospectively reviewed the charts of 147 patients whose esotropia was corrected to within 10 prism diopters of orthotropia at both distance and near with use of full cycloplegic hyperopic correction. Multiple parameters were reviewed, including initial and final cycloplegic refraction, distance, and near deviation with and without glasses, stereoacuity, age of onset, and initiation of treatment, presence of anisometropia, and change in hyperopia. Results At presentation, 87 (59.2%) of the 147 patients were amblyopic, and anisometropia was found to be the only statistically significant risk factor for this ( P = .001). Only 24.2% of these patients have stereo acuity between 40 and 100 sec/arc, 20.96% of patients have 200 to 800 sec/arc, and 22.58% of patients have 1980 to 3000 sec/arc; the remaining 32.26% had no stereo acuity. Fusion was achieved in 73.5% of the patients and later presentation (> 24 months) of esodeviation significantly determined their fusional ability ( P = .031). Consecutive exotropia developed in 5.4 % of the patients an average of 5.5 years after institution of full optical correction. For clinical and functional outcomes we did not find any statistically significant difference between early onset (before 1 year old) and typical onset (2 to 3 years) age groups. The trend towards decreasing hyperopia was apparent, averaging −0.16 ± 0.20 diopters annually in 80.5% of the patients with at least 5 years follow-up, although 23% of patients still had 20/40 or worse visual acuity in the amblyopic eye. Conclusions Amblyopia is a commonly associated finding at presentation for patients with accommodative esotropia. Most of the patients developed good fusion but poor stereopsis at the end of treatment.

Disparity increment thresholds for gratings.

The classic increment disparity threshold function rises steeply, usually exponentially, with disparity pedestal. Thus a smaller difference in stereoscopic depth can be resolved the nearer it is to the fixation plane. This result has been obtained with relatively broad-bandwidth stimuli. We show here that the increment threshold function for narrow-bandwidth stimuli differs subtly from the classic function: Thresholds vary only modestly over a +/- quarter-cycle pedestal range, by a factor of about 2, and frequently show a dip, yielding best stereo acuity not at the fixation plane but at moderate disparities (20 degrees-30 degrees in phase) on either side of it. Though the dip has not been noted previously, it is consistent with models of disparity processing in which filter sensitivity or selectivity is greatest at a disparity of zero. Moreover, the relatively flat increment threshold function observed at any one scale is compatible with a steeply rising function for broad-bandwidth stimuli.

Effects of quantum noise and binocular summation on dose requirements in stereoradiography

In the case of a quantum-noise limited detector, signal detection theory suggests that stereoradiographic images can be acquired with one half of the per-image dose needed for a standard radiographic projection, as information from the two stereo images can be combined. Previously, film-screen stereoradiography has been performed using the same per-image dose as in projection radiography, i.e., doubling the total dose. In this paper, the assumption of a possible decrease in dose for stereoradiography was tested by a series of contrast-detail experiments, using phantom images acquired over a range of exposures. The number of visible details, the effective reduction of the dose, and the effective decrease in the threshold signal-to-noise ratio were determined using human observers under several display and viewing conditions. These results were averaged over five observers and compared with multiple readings by a single observer and with the results of an additional observer with limited stereoscopic acuity. Experimental results show that the total dose needed to produce a stereoradiographic image pair is approximately 1.1 times the dose needed for a single projection in standard radiography, indicating that under these conditions the human visual system demonstrates almost ideal binocular summation.

Binocularity following surgical correction of strabismus in adults.

This is a retrospective study to determine the preoperative and postoperative binocular status of adults who have undergone surgical correction of strabismus. A list of all consecutive adult patients who underwent surgery for strabismus between June 1990 and December 2001 (surgery performed by M.B.M.) was compiled, and their medical charts were reviewed. Patients were included if their charts were available for review and if information on binocularity was recorded. Binocularity was measured by the Titmus stereo test, Worth 4-dot test, or synoptophore. Improvements or decreases in stereo acuity were noted 6 weeks postoperatively and at the final office visit. Prism management was incorporated preoperatively and/or postoperatively in some of our patients. A total of 112 patients underwent surgery for strabismus. Of these, 72 patients, aged 16 to 80, were included; 24 were excluded because their charts did not contain any information on stereo acuity at least 6 weeks postoperatively or they were lost to follow-up after surgery, and 16 were excluded because their charts were unavailable from storage. A variety of surgeries were performed, the most common being a bilateral medial rectus recession. Eleven patients required a second surgery, and two required a third surgery. Overall, 30 (42%) of the 72 patients improved in binocular function, 38 (53%) remained the same, and 4 (5%) had decreases in their stereo acuity. The benefits of surgical correction of strabismus in adults include improvement in binocular function, as seen in 42% of the patients in the study.

Validation of novel and objective measures of microsurgical skill: Hand‐motion analysis and stereoscopic visual acuity

Our purposes were: 1) to establish the predictive validity of stereoscopic visual acuity and microsurgical performance, and 2) to establish the construct and concurrent validity of hand-motion analysis as an objective and sensitive measure of microsurgical performance. Using a surgical microscope, 50 surgical residents completed a standardized microsurgical suturing task at baseline and following microsurgical training. Microsurgical performance was evaluated by blinded, expert microsurgeons using global rating scales. Measures of stereoscopic visual acuity and hand-motion analysis were correlated with expert global rating scores. Global rating scores correlated significantly with number of hand movements (r = -0.47, P = 0.001) and hand-travel distance (r = -0.37, P = 0.008). Economy of hand-motion improved significantly following microsurgical training (number of hand movements, P = 0.046; hand-travel distance, P = 0.04). Measures of stereoscopic visual acuity did not correlate significantly with global rating scores. Hand-motion analysis appears to be an objective and sensitive instrument for assessing microsurgical performance, with evidence of both concurrent and construct validity. The predictive validity of stereoscopic visual acuity and microsurgical performance remains unclear.

Influence of chromaticity on vernier and stereo acuity

Vernier offset thresholds for targets modulated in luminance or isoluminantly along the L-M axis were confirmed to be equal for targets whose contrasts were equal multiples of those required for detection. On the other hand, stereoscopic depth thresholds were elevated by a factor of 10 or more for isoluminantly modulated targets. Thresholds for vernier targets are 2 or 3 times larger with a gap of 20 arcmin than for a gap of 1 arcmin for both isoluminant and luminance targets. On the other hand, stereo thresholds decrease by a factor of 2 to 3 for both classes of target over the same range. We consider our results in the light of recent electrophysiological and psychophysical evidence and conclude that our results are consistent with the notion that stereo thresholds are mediated by a single class of mechanism for targets modulated in luminance or isoluminantly. We test and reject the hypothesis that stereopsis is subserved by independent chromatic and luminance mechanisms.

Binocularity in Refractive Accommodative Esotropia

To investigate whether restoration of normal stereo acuity is possible in refractive accommodative esotropia. Twenty patients with refractive accommodative esotropia were included in the study. The cycloplegic refraction and the best corrected visual acuity of each patient were recorded. The patients were evaluated by the 4-prism-diopter test, Bagolini striated glasses, the Worth 4-dot test, the TNO stereo test, and the stereo fly plate of the Titmus test. Eight patients had orthotropia with normal retinal correspondence and 12 patients had a small deviation with abnormal retinal correspondence. Nine patients (8 patients with orthotropia and 1 patient with microtropia) demonstrated a gross level of stereo acuity, whereas the others demonstrated no stereopsis. In patients with refractive accommodative esotropia, the prognosis is not favorable for restoration of normal stereopsis, even if orthotropia is achieved.

Congenital ptosis: amblyogenic refractive errors, amblyopia, manifest strabismus and stereopsis related to the types of ptosis. Data on 77 patients and review of the literature

Former reports on amblyogenic refractive errors, amblyopia and binocular vision in congenital ptosis usually comprise all forms of ptosis without any differentiation. This study is an analysis of different kinds of ptosis. 154 eyes (98 ptotic eyes) of 77 patients with congenital ptosis aged > or = 1 year (56 unilateral ptoses: 45 simple, 1 with rectus superior paresis, 7 with Marcus Gunn's syndrome, 2 congenital oculomotor palsies, 1 unilateral fibrosis syndrome; 21 bilateral ptoses: 10 simple, 2 with bilateral double elevator paresis, 7 blepharophimosis syndromes and 2 bilateral fibrosis syndromes) were investigated concerning visual acuity, refractive error (94 % in cycloplegy), strabismus and stereo acuity. As amblyogenic refractive errors were defined: astigmatism > or = ldpt, anisometropia > or = 1 dpt (spherical equivalent) and hyperopia > or = 3 dpt; amblyopia was defined as visual acuity less than 1.0 or a difference between both eyes of at least 0.2. Altogether were found: Hyperopia > or = 3 dpt in 28.6 % (n = 28); astigmatism > or = 1 dpt in 63.3 % (n = 62), anisometropia in 27.3 % (n = 21), amblyopia in 65.3 % (n = 64), strabismus in 29.9 % (n = 23) and stereopsis in 76.6 % (n = 59). In unilateral simple ptosis, astigmatism of the fellow eye was found in 26.8 % (n = 14). In unilateral ptosis, esotropia was 21.4 % (n = 12), in bilateral ptosis, exotropia 19 % (n = 4), as well as astigmatism > or = 3 dpt 26.2 % (n = 11). As was to be expected, ptosis groups with motility disorders were associated with higher rates of strabismus and amblyopia. The blepharophimosis syndrome could be differentiated by the typical lid anomalies. The subgroups of congenital ptosis differ in frequency of amblyogenic factors. In unilateral ptosis these are also frequent in the fellow eye.

Apparent motion processing in strabismic observers with varying levels of stereo vision

Deficits of motion processing have been reported in individuals with infantile strabismus. Here we examined motion perception in early and late onset strabismic individuals with varying levels of stereo acuity using the Fine Grain Motion Illusion (FGMI). The FGMI is an illusion of motion, where under some conditions, observers report exaggerated motion. It has been speculated that this illusion is due to the spatial range of cortical cells stimulated. We used this illusion to compare this motion exaggeration in the central vision of both the deviating and non-deviating eye of strabismic observers with control eyes. While individuals with early onset strabismus showed some mild exaggeration of motion, those with low stereo acuity, regardless of age at onset, showed significantly larger exaggeration of this motion illusion in both the deviating and non-deviating eyes as compared with control observers. These results might indicate that this illusion and stereopsis involve common mechanisms.