Effect of binasal occlusion in children with esotropia

Introduction

Esotropia is a common pediatric ophthalmologic disorder that, if left untreated, can have a significant impact on the binocular visual function and appearance of the child. In clinical practice, the best treatment for esotropia is surgical correction during the sensitive period of visual development after cyclorefraction by atropine and full correction to restore binocular vision. However, when surgical correction is not possible for the time being because of different reasons such as the child is too young to cooperate with the examination, the systemic condition does not allow general anesthesia, or the parents refuse the surgery, it is necessary to take non-surgical measures to alleviate the impact of esotropia on the child.

Binasal occlusion (BNO) refers to the placement of angled translucent clear tape, thick layers of clear nail polish, or opaque electrical tape on the inner third of the spectacle to provide an unobstructed field of vision at the distance as well as proximally. The concept of this technique originated from the ancient Egyptian “mask of strabismus” (1,2), which was used to prevent children from using the nasolateral field of vision. The BNO has been used for more than 100 years, and Louis Jacques, an American optometrist, started to use this technique mainly for the treatment of esotropia (3,4). Later, there were also some case reports of BNO improving dizziness and balance problems caused by abnormal visual stimuli, as well as eye pain caused by eye movements in patients with mild traumatic brain injury (mTBI) (5-7).

There is no consistent theoretical basis for BNO and its therapeutic efficacy has been controversial. The therapy is still used in optometric medicine (5), but the corresponding clinical reports remain scarce. These studies either have a small sample size, only study the treatment effect of BNO on a certain type of esotropia, or include adult patients. In this study, we hope to clarify the effects of BNO on the angle of strabismus, visual function, and diplopia in children with various types of esotropia, providing a certain research basis for the treatment of esotropia with BNO. Therefore, the results of using BNO to treat multiple types of esotropia in children between October 2022 and September 2023 in our hospital are reported below. We present this article in accordance with the STROBE reporting checklist (available at https://tp.amegroups.com/article/view/10.21037/tp-24-340/rc).

Methods

This study was conducted in accordance with the Declaration of Helsinki (revised in 2013). This study has been approved by the Ethics Committee of the Affiliated Hospital of Yunnan University (No. 2024064), and patients’ legal guardian signed an informed consent form.

Object

Inclusion criteria included: (I) patients with esotropia after atropine ophthalmic ointment dilated correction of refractive error by prescription lenses, and the parents refused to perform surgery, insisted on continuing conservative treatment, or the patient’s condition was not suitable for surgical treatment, and the parents signed the informed consent for BNO; (II) multiple types of esotropia (e.g., acute acquired concomitant esotropia, partially accommodative esotropia; etc.); (III) a follow-up period of at least 3 months.

Exclusion criteria included: (I) esotropia with amblyopia; (II) esotropia with vertical strabismus; (III) periodic esotropia; (IV) esotropia with nystagmus; (V) esotropia with neurological abnormalities.

This observational study summarized a total of 41 patients who attended the pediatric ophthalmology department of the Affiliated Hospital of Yunnan University Hospital from October 2022 to September 2023 and met the above criteria.

Study methods

Conduct a detailed inquiry into the patient’s medical history and perform neurological and ophthalmological assessments to rule out any pathology. All children underwent bilateral dilated with atropine sulfate ophthalmic ointment at the first visit, and were given a fully corrected prescription, followed by BNO. Best corrected visual acuity (BCVA), dominant eye, eye position, prism and alternate cover test (sin corrección and con corrección) and binocular visual function were examined before BNO. The above indices were reviewed at 3 months of BNO and the position of the depressor membrane was adjusted according to the strabismus at the time of review. All prism and alternate cover tests examinations were performed by the same person.

Occlusion method: after wearing the lenses, the child gazed at the 33 cm visual field in the natural state, the main deviation eye was completely covered, and the pupil was centered in the pupil of the fixating eye with a suppression film (Bangerter Occlusion Foil, Switzerland), so that the pupil was divided equally by the edges of the film and did not obscure the spot of the reflector. The fixation eye was then completely covered, and frosted plastic tape was placed over the center of the pupil of the dominant deviation eye so that the pupil was divided equally by the edge of the suppression film and did not obscure the reflecting spot. The edge of the suppression film is tilted inward and downward by 10° to 15° for near viewing (Figure 1).

Figure 1 Method and glass of binasal occlusion.

Diagnostic criteria

(I) Strabismus: at the 3-month review, the children’s strabismus was observed by using a prism in the uncovered state: a reduction of ≥15 prism diopters (PD) of 33 cm or an orthoptic position of the eye was considered as markedly corrected, a reduction of 10 to <15 PD was considered as effectively corrected, and a reduction of <10 PD was considered as invalid; (II) visual function: at the 3-month review, the children were examined for simultaneous vision, fusion function, and stereopsis using a synoptiscope; (III) diplopia: whether or not the diplopia has improved was judged mainly based on the child’s complaints.

Statistical analysis

SPSS 26.0 statistical software was used for analysis. Normally distributed measurements were expressed as mean ± standard deviation, visual acuity, refraction after pupil dilation and strabismus before and 3 months after occlusion were analyzed by Wilcoxon signed-rank test, and clinical count data were compared and analyzed by Fisher’s exact test. Differences were considered statistically significant at P<0.05.

Results

A total of 41 patients who visited our hospital from October 2022 to September 2023 and met the selection criteria were included in this study, including 18 cases of nonaccommodative esotropia, 5 cases of acute acquired concomitant esotropia, 8 cases of partially accommodative esotropia, and 10 cases of intermittent exotropia with postoperative overcorrection. There were 16 males and 25 females, aged 3 to 15 years (Table 1).

The BCVA of the children after 3 months of BNO was significantly improved, and the difference was statistically significant (P=0.01). The refractive error of both eyes decreased, and the difference was statistically significant [OculusDexter (OD): P=0.007; OculusSinister (OS): P=0.004] (Table 2).

Strabismus before and after BNO

The mean value of the near strabismus was 25.22±18.25 PD (range, 5 to 80 PD) and the mean value of distance strabismus was 23.65±17.45 PD (range, 5 to 60 PD) before BNO. After BNO for 3 months, the mean value of the near strabismus was 9.63±11.92 PD (range, −8 to 40 PD) and the mean value of distance strabismus was 9.27±12.47 PD (range, −5 to 40 PD). There was a significant reduction in strabismus, and the difference was statistically significant (P<0.001) (Table 2). Twenty-six cases were markedly corrected, 6 cases were effectively corrected, 9 cases were invalid. Among the 18 children with nonaccommodative esotropia, correction was markedly corrected in 14 cases (77.78%) and invalid in 4 cases (22.22%); among the 5 children with acute acquired concomitant esotropia, correction was markedly corrected in 2 cases (40.00%), effectively corrected in 1 case (20.00%), and invalid in 2 cases (40.00%); and among the 8 children with partially accommodative esotropia, correction was markedly corrected in 5 cases (62.50%), 2 (25.00%) were effectively corrected and 1 (12.50%) was invalid; among the 10 children with postoperative overcorrection of intermittent exotropia, correction was markedly corrected in 5 (50.00%), 3 (30.00%) were effectively corrected and 2 (20.00%) were invalid. There was no significant difference in the efficacy of BNO between the various types of esotropia (P=0.15) (Table 3). Examples of children wearing lenses for BNO are shown in Figure 2.

Figure 2 Appearance of child (female, 4 years and 9 months old) with partially accommodative esotropia before/after BNO. (A) Full correction with glasses, the angle of deviation (near) is +20 PD; (B) the first time to take BNO; (C) review after BNO for 3 months. This image is published with the consent of patient’s guardian. BNO, binasal occlusion; PD, prism diopter.

Vision function of children with esotropia before and after BNO

Binocular visual function tests require a certain level of understanding. The results of only 32 children were included in the analysis because 9 children could not yet understand the synoptic machine before BNO, and the results of 34 children were included in the analysis because 7 children could not yet understand the synoptic machine at 3 months of BNO. Only 3 cases improved from no simultaneous vision to binocular stereopsis before and after BNO (Table 4).

Diplopia before and after BNO

According to the patients’ complaints, 15 children had diplopia before BNO, 14 children reported that the diplopia disappeared after 3 months of BNO, and only 1 child reported that the diplopia was still present. The success rate was 93.33%.

Discussion

Esotropia is a very diverse disorder encountered in clinical practice. It may be congenital or acquired. Congenital esotropia is defined as a dominant esotropia that develops within the first 6 months of life, and acquired concomitant esotropia is characterized by acute or subacute episodes of esotropia, with a consistent angle of deviation of the optic axis detected in all directions of gaze. It may have a full or partial accommodation component, in which case it is usually associated with a hyperopic refractive error. Although full correction with lenses reduces esotropia, orthophoria is rarely achieved, and children may still have small-angle esotropia (<15 PD). Partial esotropia may be associated with a variety of neurological disorders, which requires clinicians to conduct comprehensive eye and neurological assessments to provide a basis for subsequent treatment. Although surgical correction is currently the best treatment for esotropia, there are still some cases in which the parents of the children refuse to have surgery because of the psychological burden of surgery, or the children are not suitable for surgery because of their general condition, or their esotropia does not meet the indications for surgery, or there is significant diplopia in the children. We need to adopt non-surgical methods to alleviate the effects of esotropia on children.

BNO is the symmetrical attachment of a low-transmittance film (e.g., a suppression film) to the nasal side of bilateral lenses. The temporal edge of the film is located on the nasal side of the pupil of the orthostatic eye, while the lower edge is tilted inward and downward by 10–15°, without affecting the near-sighted set. BNO is different from binasal visual field loss. The binasal field of view is only obscured when the eye is looking straight ahead, because the suppression film is fixed on the spectacles but the eye is free to move. In side vision, this effect is closer to monocular occlusion in the inward-focused eye, with a relatively fuller field in the outward-focused eye.

Degree of strabismus

Esotropia can easily cause abnormal retina correspondence. Usually, there is center-concave suppression in the strabismic eye in order to avoid diplopia and visual confusion, and the center-concave of the fixating eye at this stage usually abnormally corresponds to the nasal retinal area of the strabismic eye. In this study, the mean value of the near strabismus was 25.22±18.25 PD and the mean value of distance strabismus was 23.65±17.45 PD before BNO. After BNO for 3 months, the mean value of the near strabismus was 9.63±11.92 PD and the mean value of distance strabismus was 9.27±12.47 PD. It indicated that there was a significant improvement in strabismus after 3 months of BNO. We hypothesize that BNO reduces visual stress associated with diplopia and binocular rivalry and reduces abnormal retinal correspondence. Unlike masking the entire visual field of one eye, BNO permits some degree of binocular vision, which emphasizes the role of binocular function in peripheral vision: objects located on the right can only be fixated by the right eye, whereas objects located on the left can only be fixated by the left eye. The earliest clinical studies of BNO in the United States were reported in Louis Jacques’ Corrective and Preventive Optometry published in 1950 (3). BNO can help transform a patient’s unilateral strabismus into a patient’s alternating strabismus, eliminating visual suppression and allowing “the opportunity to establish the basic visual pattern of a normal person”.

Samiguet Badoche, a French optometrist, reported that 384 children with common esotropia who were effectively trained with BNO and parental supervision converted to orthophoria in 44% of patients after 1 year, 15% were essentially orthophoric in appearance, and the remaining 41% required extraocular muscle surgery (8). Our observations showed that after 3 months of BNO, the children’s horizontal strabismus was significantly reduced, with 26 cases of markedly corrected, 6 cases of effectively corrected, and 9 cases of invalid, and there was no significant difference in the efficacy of the BNO between each type of esotropia, confirming that BNO has a certain therapeutic effect on different types of esotropia. Surgery is still recommended for children aged ≥6 years, with an esotropia angle of ≥20 PD after 3 months of occlusion, especially for those who have failed to undergo correction. When the child is younger than 6 years old, the family may choose to continue BNO according to the family’s wishes. For example, in a case of acute acquired concomitant esotropia, 12 years and 8 months old, the effect was not obvious, and the strabismus was 40 PD before and after BNO. Considering the age of the child, the large angle of esotropia may affect the recovery of the visual function of both eyes. After communicating with the family, we changed to surgical treatment.

Vision and visual function

In this study, the children’s best-corrected visual acuity showed significant improvement after receiving BNO treatment. The reason for the improvement may be that patients reduced or eliminated binocular visual suppression after straightening the eye position, and the change in fixation nature promoted the formation and establishment of binocular vision, thus improving visual acuity. However, the fixation may be unstable and needs further confirmation. We also observed that the number of cases with simultaneous and fusion did not change before and after BNO, and only three children with no simultaneous vision improved to become stereoscopic. The possible reasons are: (I) the observation time of this study is 3 months, which is not enough for the children to improve stereopsis while improving eye position; (II) the children were young when the esotropia appeared, and the damage of visual function itself is very serious, even if the eye position is completely improved, restoring binocular visual function requires some training; (III) in the effective cases, although the improvement of the children’s strabismus is more than 15 PD, some of them have larger strabismus, which still affects binocular visual function; (IV) all three children with improved visual function had less than 30 PD of strabismus before BNO, and two of them were after surgery. The timely surgery in the early stage may have protected the visual function of the children and provided a good visual foundation for the subsequent treatment.

It has been suggested that the nasal retina of patients with esotropia is usually in a state of habitual inhibition, and masking the temporal retina will enhance the sensitivity of the nasal retina (9). When the BNO enhances the nasal side retina sensitivity, the patient can perceive a wider temporal side visual field. The peripheral perception visual training can be carried out to enhance the effect of peripheral perception, and the dispersion of the eye position orthophoria can lead to the widening of the visual field. Therefore, in the future study, we can add the corresponding visual function training, which can enhance the success rate of BNO while trying our best to improve the children’s visual acuity and visual function. Although some of the children did not have significant improvement in strabismus after BNO and still needed surgical correction, we also tried to minimize the amount of trauma to the extraocular muscles during the surgery.

Diplopia and the mechanism of BNO

In this study, BNO was effective in eliminating diplopia in children. According to the patients’ complaints, 15 children had diplopia before occlusion, 14 children reported that the diplopia disappeared after 3 months of BNO, with an effective rate of 93.33%. Only 1 child reported that the diplopia still existed. This could be caused by the direct reduction of abnormal visual information input by BNO or reduction of strabismus after BNO.

There is no unified conclusion about the mechanism of BNO. In recent years, BNO has been more frequently used to improve symptoms related to visual deficits (e.g., inattention, diplopia, headache, fatigue, etc.) in patients with mTBI. Ciuffreda et al. (10) proposed two mechanisms in patients with mTBI and visual motion sensitivity (VMS) symptoms. The first is the concept of “diffusion of inhibition”, a well-documented cortical-based neurophysiological phenomenon present in normal (11,12) and abnormal (13) binocular vision. When the cortex inhibits a specific stimulus, it also spreads to neighboring regions. In individuals with mTBI and VMS, they will attempt to habitually suppress this visuomotor information in the retinal periphery in order to reduce their peripheral visuomotor overload. With the addition of BNO, suppression in the occluded bitemporal regions now becomes unnecessary. The second possible mechanism is based on the notion that TBI has a “faulty” filtering mechanism (14,15). Neural filtering of irrelevant peripheral visuomotor information by the brain is a normal visual processing phenomenon, and individuals with mTBI and VMS may not be able to filter/suppress this unwanted and troublesome peripheral visuomotor information from entering their visual processing stream. With the addition of BNO, however, less of the irrelevant visual information would be entering the visual system simply based on bitemporal occlusion of parts of the problematic regions of the visual field. A third mechanism may be related to visual attention (9). Assuming that the BNO reduces some of the irrelevant and distracting peripheral visuomotor information coming from the blocked bitemporal retinal regions, the attentional weights will shift back to the central visual field to some extent.

The present study has the following limitations. Firstly, this study did not include a control group, so it is not possible to clearly determine whether the improvement in patients was due to the treatment with BNO or the natural progression of the disease itself Secondly, our sample size was small, including only 41 children. The study had a short time span, observing the effects of occlusion therapy for only 3 months, and it is not possible to judge the long-term treatment effects. Further clinical observation is needed to determine whether the recurrence of strabismus will occur if the BNO is removed after 3 months, and the duration of BNO. Currently, there is a relative lack of research and literature on BNO. In the upcoming research, we need to set up a control group to clarify the therapeutic effect of BNO, while combining BNO with other treatments for esotropia to achieve better therapeutic outcomes.

Conclusions

BNO is an effective non-surgical treatment measure, which can effectively reduce the strabismus degree of many types of esotropia and improve the visual double-image situation, providing a good basis for the establishment of the subsequent visual function.

Acknowledgments

Funding: This work was funded by the “Double First Class” Construction Project of Yunnan University, Innovation Team for Prevention and Control of Children’s Low Vision (No. CY22634106), and the Leading the Charge of Yunnan Province Health System (No. L-2018018).

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://tp.amegroups.com/article/view/10.21037/tp-24-340/rc

Data Sharing Statement: Available at https://tp.amegroups.com/article/view/10.21037/tp-24-340/dss

Peer Review File: Available at https://tp.amegroups.com/article/view/10.21037/tp-24-340/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tp.amegroups.com/article/view/10.21037/tp-24-340/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki (revised in 2013). This study has been approved by the Ethics Committee of the Affiliated Hospital of Yunnan University (No. 2024064), and patients’ legal guardian signed an informed consent form.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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