Binocular summation in comitant exotropia: Change after surgery

Purpose: To assess the change in binocular summation (BiS) in comitant exotropia (XT) after strabismus surgery. Methods: This is a prospective study on 20 patients who underwent surgery for comitant XT over a one year period. Patients with sensory exotropia and nystagmus were excluded. Best?corrected visual acuity (VA) and contrast sensitivity (CS) of both eyes separately and together (binocularly) were recorded. BiS score was calculated as binocular score minus better eye score. BiS score at the end of 3 months was compared with the preoperative data. Results: The mean ± SD of BiS score increased from 2.95 ± 0.88 to 4.55 ± 0.68 (P?value < 0.0001) for VA (on ETDRS letters) and from 2.75 ± 0.44 to 4.5 ± 0.76 (P?value < 0.001 for CS (on Pelli–Robson chart) after surgery. Conclusion: There is significant improvement in BiS in XT after strabismus surgery. Authors recommend its inclusion in evaluation of functional outcome of XT surgery

Subnormal Binocular Contrast Sensitivity Summation in Patients with Intermittent Exotropia

BACKGROUND: To evaluate binocular summation ratio using contrast sensitivity (CS) testing and correlation between binocular summation and stereoacuity, and control scale in intermittent exotropia (IXT). METHODS: We conducted a prospective case-control study. Thirty-seven IXT and 41 controls were evaluated with both monocular and binocular CS testing. We compared the binocular summation ratio of IXT to that of controls. Near and distance stereoacuity was assessed and office-based control scale was evaluated. We investigated correlation between binocular CS summation ratio and stereoacuity, and control scale in IXT, respectively. RESULTS: IXT had lower binocular CS summation ratio than controls at 1.5 and 3.0 cycles/degree (1.01 ± 1.02 vs. 1.62 ± 1.88 and 1.17 ± 0.96 vs. 1.86 ± 1.75, Both P < 0.05). We found significant correlation between binocular CS summation ratio at 3.0 cycles/degree and both near and distance stereoacuity (r = −0.411, P = 0.012 and r = −0.624, P = 0.005), and ratio at 1.5 cycles/degree also correlated significantly with distance stereoacuity (r = −0.397, P = 0.034) in the IXT. Binocular CS summation ratio was correlated to control scale at 1.5 and 3.0 cycles/degree (r = −0.327, P = 0.041 and r = −0.418, P = 0.028), and the ratio significantly differed in control scale groupings analysis at the same frequencies (Both P < 0.05). CONCLUSION: Our findings of subnormal binocular CS summation ratio in IXT had correlation with stereoacuity and control scale suggest that binocular CS testing may be a useful method in assessing binocular visual function in IXT.

Effects of Monocular Blur on Clinical Measurements of Stereopsis and Binocular Contrast Sensitivity / Jurnal Sains Kesihatan Malaysia

Visual conditions such as anisometropia, monovision and monocular undercorrection affect the combination of visual input from both eyes. This study investigated the effects of monocular blur, in binocularly normal participants, on stereoacuity and binocular contrast sensitivity. Fifteen young adults (age range between 19 and 23 years old) with normal visual acuity and binocular vision participated in this study. Stereopsis was measured using the TNO test with a series of positive spherical lenses placed before the dominant eye. The procedure was repeated using the Titmus Stereotest on five participants as a control experiment. Monocular and binocular contrast sensitivities were also measured using the Pelli-Robson Contrast Sensitivity Chart. Blur was induced monocularly with a series of positive spherical lenses placed before the dominant eye and binocular contrast sensitivity was re-measured. Stereopsis scores decreased significantly when monocular blur was imposed. Across blur levels, absolute stereopsis scores measured with TNO test were worse than those measured with Titmus stereotest (all p < 0.05). However, the ratio of scores obtained without blur and under monocular blur appeared to be similar for both tests. Stereopsis without blur was between 6.82× to 8× better than that obtained with the highest level of imposed monocular blur. Binocular contrast sensitivity score decreased significantly with increasing level of monocular blur (p < 0.01). Binocular contrast sensitivity score without blur was 1.62× better than that obtained under binocular viewing with highest level of imposed blur. Stereopsis tests are more sensitive than measurements of binocular contrast sensitivity as an indicator of interocular acuity discrepancies which could occur in anisometropic or monovision patients. However, the choice of stereopsis test is crucial, as the TNO test appears to be more sensitive to monocular blur than the Titmus stereostest.