The difference of distance stereoacuity measured with different separating methods

Binocular visual function improvement after pars plana vitrectomy for epiretinal membrane

PURPOSE

To report binocular visual function changes after pars plana vitrectomy for epiretinal membrane (ERM) and the related outcomes.

METHODS

Twenty-three eyes of 23 patients operated on for ERM were included in a retrospective study. Clinical data, best-corrected visual acuity (BCVA), contrast sensitivity and binocular visual function were assessed pre- and 1 and 3 months post-operatively. Binocular visual function assessment included the evaluation of fusional amplitudes (i.e., vergences) by the synoptophore, far distance stereopsis using polarized glasses and near stereopsis using Randot and TNO tests. Central macular thickness (CMT) was measured on Spectral Domain - Optical Coherence Tomography.

RESULTS

Mean age of the patients was 67 years. Mean BCVA and contrast sensitivity significantly improved post-operatively at one (p = 0.0006 and p = 0.0022, respectively) and 3 months (p < 0.0001 and p < 0.0001, respectively), while CMT significantly decreased after 1-3 months (p < 0.0001 and p < 0.0001, respectively). Fusional amplitudes improved after 3 months (p < 0.0001). Far distance and near stereopsis significantly improved after 3 months (p < 0.0001 and p = 0.0007 for Randot test, and p < 0.0001 for TNO test, respectively).

CONCLUSIONS

Pars plana vitrectomy for ERM surgery leads to an improvement of monocular and binocular visual functions (i.e., binocular fusion, near and far distance stereopsis), within 3 months post-operatively.

A novel clinical dynamic stereopsis assessment based on autostereoscopic display system

Background

Although it is recognized that dynamic stereopsis is vital in daily life, there is still room for improvement in assessment methods. A novel clinical dynamic stereopsis assessment method was created based on an autostereoscopic display system that did not require additional auxiliary glasses. This study evaluated the optical parameters and clinical performance of the autostereoscopic display system for clinical dynamic stereopsis assessment.

Methods

The autostereoscopic dynamic stereopsis assessment device was based on a directional backlight technology. Experiment 1 was performed under the same environmental conditions to compare luminance, crosstalk, and spectrum between the autostereoscopic dynamic stereopsis assessment device and the conventional dynamic random-dot stereopsis measuring instrument. Experiment 2 was an observational, analytic, cross-sectional study involving 135 healthy participants, each of whom was asked to complete measurements on both the autostereoscopic and conventional devices in random order. Stereo acuity, operating time, acceptance, and visual fatigue scores were recorded for clinical evaluation.

Results

The autostereoscopic device had brighter luminance (139 and 140 cd/m² for 2 eyes, respectively), lower crosstalk (4.50% for both eyes), and higher color restoration degree than those of the conventional instrument. Clinically, the novel dynamic stereopsis assessment was as accurate as the traditional method [170" (0.00") and 170" (0.00") respectively; P=0.317], and with more efficiency (166±58.9 and 298±116 s, respectively; P<0.001), higher acceptance (3.36±0.93 and 2.02±0.59 points, respectively; P<0.001), lesser fatigue (0.27±0.46 and 0.73±0.66 points, respectively; P<0.001). The autostereoscopic dynamic stereopsis assessment device with brighter luminance, lower crosstalk, and higher color restoration degree was more effective than the traditional instrument at displaying dynamic clues for clinical dynamic stereopsis assessment. Furthermore, its high-quality image and user-friendly interface provided accurate assessment results in all 3 dynamic stereopsis assessment task conditions, with a higher level of acceptance and lesser visual fatigue, than the traditional assessment method.

Conclusions

The autostereoscopic device has excellent functions in both optical parameters and clinical performance, and therefore has the potential to be applied and popularized in future assessments.

Evaluating the Mechanism by Which the TNO Stereo Test Overestimates Stereo Thresholds

Several studies have revealed that results of the TNO stereo test may overestimate the stereoacuity value (the less the better) compared with other testing measurements. The manner in which vision is divided among two eyes of a person wearing anaglyph glasses may play an important role. This study aimed to examine the effect of anaglyph glasses on stereopsis measurements. A stereopsis measurement system using a phoropter and two Sony smartphones was established. Four types of test patterns, including the original TNO stereo test pictures, isoluminant red-green pictures, grayscale pictures, and black and white dots pictures, were designed. A total of 32 participants were recruited for this study. A significant difference was found among the four groups (Friedman test, chi-square = 50.985, P < 0.001). The Wilcoxon signed-rank test was used to detect differences between the groups. The stereoacuity of the original TNO group was significantly worse than those of the isoluminant, grayscale, and black-white groups. However, no significant difference was found between the isoluminant and grayscale groups. The correlation coefficient between the original TNO and isoluminant groups was 0.952 (Spearman's rho, P < 0.001; 95% confidence interval (CI), 0.901–0.988), while that between the original and grayscale groups was 0.771 (Spearman's rho, P < 0.001; 95% CI, 0.550–0.916). Anaglyph glasses played an important role in determining the stereoacuity values with the TNO stereo test, and the results were overestimated when compared with that of the other testing methods. The imbalance of chroma and luminance between the two eyes caused by the anaglyph glasses was indicated as one of the reasons for the overestimation of stereo thresholds.

The effect of dot size in random-dot stereograms on the results of stereoacuity measurements

Background

This study aimed to evaluate the effect of the size of the dots in random-dot stereograms on the results of stereoacuity measurements.

Methods

A stereopsis measurement system was created using a phoropter and two 4 K smartphones. Three dot sizes, including 1 × 1 pixel, 6 × 6 pixels, and 10 × 10 pixels (equivalent to 0.17 min arc, 1 min arc, and 1.68 min arc, respectively), were used to form random-dot arrays, and each test pattern had one Lea symbol hidden within it. The resulting stereograms were tested on 30 subjects with normal acuity and stereoacuity.

Results

Stereoacuity measured with the 1-pixel dots was significantly worse than that measured with the 6-pixel dots (Wilcoxon signed-rank test, Z = -4.903, P < 0.001) and the 10-pixel dots (Z = -4.941, P < 0.001). No significant difference was found between 6-pixel dot and 10-pixel dot stereograms (Z = -1.000, P = 0.317).

Conclusion

The size of the dots in random-dot stereograms affects the test results significantly when the dots are too small for the eye to resolve.