Changes in stereopsis after photorefractive keratectomy

Stereopsis after corneal refractive surgeries: a systematic review and meta-analysis

PURPOSE

To systematically review the published manuscripts on stereopsis after corneal refractive surgery.

METHODS

The Web of Science, PubMed, Scopus, ProQuest, Clinical Key, Embase, and Cochrane Library were searched for relevant articles published until August 2020. The fixed- or random-effects models were used to estimate the Weighted mean difference (WMD) or Relative risk (RR) and 95% Confidence interval (CI) for postoperative stereopsis changes and incidence when applicable. Meta-regression was conducted for adjusting the effects of potential confounders.

RESULTS

Seven studies (1266 eyes) in adults and ten studies in pediatrics (259 eyes) were included. In adults, stereopsis improved significantly compared to the preoperative state (WMD = - 27.4, 95% CI = - 40.0, - 14.7; I² = 97.8%; P < 0.001). In pediatrics, proportion of patients with stereoacuity postoperatively was 2.18 times compared to preoperative evaluation. (RR = 2.18, 95% CI = 1.2, 3.9; I² = 68.6%, P < 0.001).

CONCLUSIONS

Stereopsis improves after corneal refractive surgery in adults and pediatrics.

Screening for Stereopsis Using an Eye-Tracking Glasses-Free Display in Adults: A Pilot Study

Purpose:

To explore the feasibility and repeatability of a novel glasses-free display combined with random-dot stimulus and eye-tracking technology for screening stereopsis in adults.

Methods:

A total of 74 patients aged 18–44 years were recruited in this study (male: female, 32:42), including 33 patients with high myopia [≤ -6.0 diopters (D)] and 41 patients with moderate-to-low myopia (>-6.0 D). Stereopsis was measured using glasses-free, polarized, and Titmus stereotests. All patients completed a visual fatigue questionnaire after the polarized stereotest and glasses-free test. Kendall's W and Cohen's Kappa tests were used to evaluate repeatability and consistency of the glasses-free stereotest.

Results:

The stereotest results using the glasses-free monitor showed strong repeatability in the three consecutive tests (W = 0.968, P < 0.01) and good consistency with the polarized stereotest and Titmus test results (vs. polarization: Kappa = 0.910, P < 0.001; vs. Titmus: Kappa = 0.493, P < 0.001). Stereopsis levels of the high myopia group were significantly poorer than those of the moderate-to-low myopia group in three stereotest monitors (all P < 0.05). There was no significant difference in visual fatigue level between the polarized and the glasses-free display test (P = 0.72). Compared with the polarized test, 56.76% of patients preferred the glasses-free display and found it more comfortable, 20.27% reported both tests to be acceptable.

Conclusions:

In our adult patients, the new eye-tracking glasses-free display system feasibly screened stereopsis with good repeatability, consistency, and patient acceptance.

Impact on binocular visual function of small-incision lenticule extraction for high myopia

PURPOSE

To assess whether small-incision lenticule extraction (SMILE) for high myopia reduces the binocular visual function assessed by stereoacuity, binocular visual acuity, binocular contrast sensitivity, and binocular summation.

SETTING

University hospital.

DESIGN

Prospective case series.

METHODS

Patients with a myopic spherical equivalent of at least 6.00 diopters (D) scheduled for SMILE aimed at emmetropia were included. Psychophysical testing was performed with correction preoperatively but no correction postoperatively. Stereoacuity was assessed with the Randot Circles test and the near Frisby test, visual acuity (monocular and binocular) was assessed with high-contrast Early Treatment Diabetic Retinopathy Study charts, and contrast sensitivity (monocular and binocular) was assessed with the Pelli-Robson chart and the Freiburg Acuity and Contrast Test. Binocular summation was calculated by comparing the binocular score against the best monocular score.

RESULTS

A total of 138 eyes of 69 patients were included. The mean spherical equivalent changed from -7.46 D ± 1.06 (SD) to -0.23 D ± 0.40 postoperatively. Stereoacuity did not change significantly postoperatively; median change (interquartile range) was -0.32 (-6.21 to 1.55) seconds of arc with the Frisby test and 0.00 (-7.5 to 5.0) seconds of arc with the Randot test (P ≥ .06). Binocular postoperative uncorrected distance visual acuity was not different from the preoperative corrected distance visual acuity (P = .40). Contrast sensitivity declined slightly monocularly with both tests of contrast sensitivity but was unaltered binocularly (P ≥ .08). Binocular summation for visual acuity and contrast sensitivity was unaltered following surgery (P ≥ .09).

CONCLUSIONS

SMILE for high myopia did not reduce the binocular function assessed by stereoacuity, binocular visual acuity, binocular contrast sensitivity, and binocular summation.

Threshold Values of Myopic Anisometropia Causing Loss of Stereopsis

Purpose

The aim of the study was to determine the threshold values of myopic anisometropia that lead to the loss of stereoacuity in most of patients.

Materials and Methods

Forty healthy subjects were included in the study. The inclusion criteria were as follows: lack of any functional or morphological ophthalmological disorders, or detectable damage to the visual system, anisometropia equal or less than 0.25 D in a spherical equivalent, and full stereoscopic vision for near and for distance. Myopic anisometropia was evoked by placing different focusing lenses in front of the right eye of the subject in the trial frame. Stereoscopic vision was assessed with the use of the Titmus test (dots) (Stereo Fly Test Stereo Optical Co. Inc.) for near and the Randot test for distance (Distance Randot Stereotest Stereo Optical Co. Inc.).

Results

The threshold values for different types of myopic anisometropia for the loss of stereopsis in more than 50% of patients were determined. For near, this value was 3 D for sphere and “against the rule astigmatism” and 4 D for “with the rule astigmatism”. For distance, the values were 2 D for sphere and “against the rule astigmatism” and 3 D for “with the rule astigmatism.” Conclusions. Myopic anisometropia of more than 2 D can cause a significant impairment of binocular vision. Stereoacuity at distance is more sensitive to myopic anisometropia than stereoacuity at near. Myopic anisometropia involving “against the rule” astigmatism potentially affects binocularity more than anisometropia with regular astigmatism. A prompt correction of anisometropia of more than 2 D is needed in children to prevent the development of amblyopia.

Stereoacuity after Wavefront-guided Photorefractive Keratectomy in Anisometropia

PURPOSE

To determine changes in stereoacuity in anisometropic myopic eyes after photorefractive keratectomy (PRK).

METHODS

Myopic patients with at least 1 diopter (D) of anisometropia in sphere, astigmatism, or spherical equivalent who were referred to our hospital for excimer refractive surgery were enrolled as a prospective sequential interventional case series. All patients underwent wavefront-guided photorefractive keratectomy (WFG-PRK) using the Technolas Perfect Vision (217z) Excimer laser machine. Changes in binocular stereoacuity were evaluated using the TNO and Butterfly stereoacuity tests before and at 2 weeks, 1 month, and 3 months after the operation.

RESULTS

Between January and November 2015, a total of 98 eyes of 49 patients (71.4% men) with a mean age of 28 ± 5.5 years, mean myopia of -3.32 ± 1.74 D, and mean astigmatism of 1.3 ± 1.3 D were enrolled in this study. Preoperative mean stereoacuity values were 102 ± 103.44 and 56.8 ± 41 seconds of arc (s/arc)as measured by the TNO and Butterfly stereoacuity tests. Mean stereoacuity improved to 90 ± 110.52 s/arc (P = 0.009) and 56.5 ± 41.3 s/arc (P = 0.80), respectively, 6 months after WFG-PRK. Overall improvement in stereoacuity was 10.2% and 6.12% according to the TNO and Butterfly stereoacuity tests, respectively.

CONCLUSION

Stereoacuity improves after WFG-PRK for treatment of anisometropic myopia. This improvement is more accurately detectable by the TNO than the Butterfly stereoacuity test.