Binocular Summation Is Intact in Intermittent Exotropia After Surgery

Purpose: To determine binocular summation of surgically treated intermittent exotropia (IXT) patients by measuring the contrast threshold.Methods: We recruited 38 surgically treated IXT patients aged 8–24 years and 20 age-matched healthy controls. All participants had normal or corrected-to-normal visual acuity (Snellen ≥ 20/20) in both eyes. The IXT patients had undergone the surgery at least a year prior to the study. Twenty-one of them obtained good alignment and 17 experienced a recurrence of exotropia. We measured the observers' monocular and binocular contrast sensitivities (CS) at six spatial frequencies (1.5, 3, 6, 12, 18, 24 cycles/degree) as an index of visual information processing at the threshold level. Binocular summation was evaluated against a baseline model of simple probability summation based on the CS at each spatial frequency and the area under the log contrast sensitivity function (AULCSF).Results: The exo-deviation of IXTs with good alignment was −6.38 ± 3.61 prism diopters (pd) at 33 cm and −5.14 ± 4.07 pd at 5 m. For the patients with recurrence, it was −23.47 ± 5.53 pd and −21.12 ± 4.28 pd, respectively. There was no significant difference in the binocular summation ratio (BSR) between the surgically treated IXT patients, including those with good alignment and recurrence, and normal controls at each spatial frequency [F(2,55) = 0.416, P = 0.662] and AULCSF [F(2,55) = 0.469, P = 0.628]. In addition, the BSR was not associated with stereopsis (r = −0.151, P = 0.365).Conclusion: Our findings of normal contrast sensitivity binocular summation ratio in IXT after surgical treatment suggest that the ability of the visual cortex in processing binocular information is intact at the contrast threshold level.

Lower Internal Additive Noise and Better Perceptual Template Characterize Binocular Contrast Sensitivity Summation

Binocular summation is generally defined as the superiority of binocular over monocular performance. Here, we investigated how external noise modulates the effect of binocular summation on the contrast sensitivity function (CSF) and clarified the corresponding mechanisms with a perceptual template model (PTM). The contrast sensitivity (CS) over 10 spatial frequencies and three external noise levels was assessed under one binocular and two monocular viewing conditions. The binocular summation ratio (BSR) was calculated by dividing the area under the log CSF (AULCSF), or the CS of using both eyes, by that of only using the “good eye” (BSRG) or the “bad eye” (BSRB), respectively. We found that: (1) based on the AULCSF, the BSRB was higher than the BSRG; (2) based on the AULCSF, the BSR was more pronounced under zero-noise than under low-noise conditions, but the BSR was not higher than 1 under high-noise conditions due to a large individual difference; (3) based on the CS, with increasing spatial frequencies, the BSRB steadily increased; (4) both decreased internal additive noise and an improved perceptual template accounted for the gain in binocular summation. These results help us better understand the features of binocular CS and shed light on the clinical studies on populations with monocular CS loss.

Improvement of binocular summation in intermittent exotropia following successful postoperative alignment

To investigate the improvement of binocular summation (BiS) at high contrast (100%) and different low contrasts (10, 5 and 2.5%) in patients with intermittent exotropia (IXT) after successfully postoperative alignment. A total of 76 patients (aged 9–40 years) with IXT and poor control at distance before surgery were enrolled in this study. The postoperative deviations ranged between 4 PD esophoria to 10 PD exotropia in the primary position (at near and at distance) in all the enrolled patients. The follow-up visits were 2–3 months after the surgery. We analyzed preoperative and postoperative BiS and the proportions of patients with different BiS for the high contrast and the low contrasts. Binocular summation (BiS) was classified into three situations: binocular summation, equal and inbibition. The results of the distant random dots stereograph (RDS) were grouped into A, unable to recognize; B, moderate, 200″ ≤ RDS ≤ 400″ and C, good, RDS < 200″. Following the successful postoperative alignment, the proportion of patients with BiS were increased from 9.2 to 40.8%, 17.1 to 53.9%, 21.1 to 76.1% and 21.1 to 72.4% at 100%, 10%, 5% and 2.5% contrasts respectively. At 2.5% contrast, (1) more patients presented binocular summation in the groups B and C; (2) postoperative improvements of binocular visual acuity (BVA) in groups B (1.5 ± 1.03 lines) and C (1.57 ± 1.26 lines) were significantly different from the BVA in the group A (0.74 ± 1.00 line); and (3) in the group with central fusion, more patients presented BiS after surgery and the postoperative BVA improved by 1.43 ± 1.16 lines. Binocular summation for high contrast and different low contrasts can be improved in patients with IXT after successful surgical treatment. The improvement of BiS was associated with obtaining central fusion, recovering distant stereopsis and good alignment after the surgeries. The most significant improvement was shown at 2.5% contrast and was associated with good stereopsis and central fusion. The improvement of BiS, particularly at low contrast, has benefits for the daily activities in the real environment. BiS improvement could be used as a supplementary assessment of binocular function in patients with IXT before and after treatment.

Binocular summation is affected by crowding and tagging

In perceptual crowding, a letter easily recognized on its own, becomes unrecognizable if it is surrounded by other letters, an effect that confers a limit on the visual processing. Models assume that crowding is a hallmark of the periphery but that it is almost absent in the fovea. However, recently it was shown that crowding occurs in the fovea of people with an abnormal development of functional vision (amblyopia), when the stimulus is presented for a very short time. When targets and flankers are dissimilar, the crowding is reduced (tagging). Since a combination of binocular inputs increases the processing load, we investigated whether color tagging the target reduces crowding in the fovea of subjects with normal vision and determined how crowding is combined with binocular vision. The crowding effect at the fovea was significantly reduced by tagging with a color target. Interestingly, whereas binocular summation for a single letter was expected to be about 40%, it was significantly reduced and almost absent under crowding conditions. Our results are consistent with the notion that the crowding effect produces a high processing load on visual processing, which interferes with other processes such as binocular summation. We assume that the tagging effect in our experiment improved the subject's abilities (sensitivity and RT) by creating a "segmentation", i.e., a visual simulated separation between the target letter and the background. Interestingly, tagging the target with a distinct color can eliminate or reduce the crowding effect and consequently, binocular summation recovers.

Efficacy of Vision Therapy Software (CureSee) in Amblyopia

A developmental disorder of spatial vision, Amblyopia is defined clinically as a decrease in visual acuity (VA) in one, or more often in both eyes, in the absence of a clear disorder or ocular disease Amblyopia is the most common cause of monocular vision loss in children [1]. Affected individuals exhibit stereo acuity impairment and abnormal binocular summation [2]. Binocular therapies designed to improve amblyopia by binocular stimulation are highly differentiated into perceptual learning and differential training. Objective • To determine the efficacy of Vision Therapy software (CureSee) in Amblyopia. • To compare Stereopsis findings before and after VT • To compare Visual Acuity before and after VT • To compare Vergence amplitude before and after VT. Methodology: 68 Amblyopic Subjects who are visiting Ahooja Eye & Dental Institute, Gurugram for eye examination and Amblyopia management were taken. Patients diagnosed with Amblyopia were included as well as Patients with Ocular surgery done within 2 months and Patients with any Ocular pathology were excluded. Verbal Consent was taken and selected patients were enrolled into CureSee Vision Therapy Software management for Amblyopia. Data is collected prior and post the use of CureSee Vision Therapy Software by patients and the collected data were decoded and tabulated using the Ms. Excel 2010 computer program and IBM Statistical Package for Social Sciences (SPSS) statistics version 23.0 was used for the analysis of data. Result and Conclusion: Visual Acuity improved significantly by 0.14 LogMar to the Median Values of Right Eye and by 0.60 LogMar to the Median Values of Left Eye. Stereopsis improved from 800 ± 520 sec of arc to 60 ± 60 sec of arc with P≤0.001. PFV and NFV also improved significantly after the use of Vision Therapy Software. Results conclude that Vision Therapy software is effective in improving Stereopsis, Visual Acuity and Vergence values in Amblyopic patients.

Improvement of Binocular Summation in Intermittent Exotropia Following Successful Postoperative Alignment

Purpose: To investigate the improvement of binocular summation (BiS) for the high (100%) contrast and different low contrasts (10%, 5%, 2.5%) and the relationship of BiS with stereopsis and central fusion in patients with intermittent exotropia (IXT) after strabismic surgeries.Design: Prospective studyParticipants: Seventy-six patients with IXT aging 9 to 40 years with poor control at distance before strabismus surgeries. Methods: To analyze preoperative and postoperative BiS records and the proportions of patients with different BiS for the high (100%) contrast and the low contrasts (10%, 5%, 2.5%). The score of visual acuity (log Mar) was recorded when patient recognizing the full line with full refraction correction. BiS was classified into three situations depending on whether binocular visual acuity (BVA) was better, worse or equal to that of the better-seeing eye . The results of distant random dots stereograph(RDS) were grouped into A, unable to recognize; B, moderate, 200”≤RDS≤400” and C, good, RDS<200”.Results: The patients with binocular summation were increased from 9.2% to 40.8% for 100%contrast, from 17.1% to 53.9% for 10% contrast, from 21.1% to 76.1% for 5% contrast, from 21.1% to 72.4% for 2.5% contrast after surgeries, respectively. Tested using 2.5% contrast, (1) more patients presented binocular summation in the groups B and C ; (2) postoperative improvements of BVA in group B(1.5±1.03 lines) and group C (1.57±1.26 lines) differed significantly with that in the group A (0.74±1.00 line); (3)more patients presented binocular summation and the improvement of BVA was 1.43±1.16 lines in the group with central fusion after surgeries.Conclusions: BiS for high contrast and different low contrasts can be improved in IXT after successful surgical treatment. It may be associated with obtaining central fusion, recovering stereopsis at distance and good alignment after the surgeries. BiS for 2.5% contrast was improved significantly and sensitive to the good stereopsis and central fusion. Improvement of BiS, particularly for low contrast, has benefit for the daily activities in the real environment. BiS could be as supplementary assessment of binocular function for the patients with IXT before and after treatment.