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Table of Contents
ORIGINAL ARTICLE
Year : 2022  |  Volume : 4  |  Issue : 1  |  Page : 27

An observational study of exotropia with the application of the Classification of Eye Movement Abnormalities and Strabismus


Department of Ophthalmology, MGM Medical College, Aurangabad, Maharashtra, India

Date of Submission11-Mar-2022
Date of Decision09-May-2022
Date of Acceptance20-Apr-2022
Date of Web Publication23-Jun-2022

Correspondence Address:
Snehal R Thakre
Department of Ophthalmology, MGM Medical College and Hospital, N-6 CIDCO, Aurangabad - 431 006, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/pajo.pajo_17_22

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  Abstract 


Exotropia is a cosmetically distressing strabismus with lasting negative psychosocial impact on the patient.
Aim: The purpose of our study was to apply the Classification of Eye Movement Abnormalities and Strabismus (CEMAS) to the patients of exotropia (XT) in our study, identify the common types and causes of this cosmetically and psychosocially distressing strabismus, and to determine if any of these causes are preventable.
Materials and Methods: A prospective, cross-sectional study was carried out in patients aged 6 months and more with exotropia attending the ophthalmology outpatient department of a tertiary care hospital from December 2016 to July 2018. Complete strabismus evaluation of the patients was done, the exotropia seen in the patients was categorized in types according to the CEMAS classification and possible causes of exotropia were studied.
Results: Of the total 120 patients, 110 had comitant XT, whereas 10 had incomitant. Of the 110 comitant cases, intermittent XT was maximum – 54 (45%). A significant number of patients had XT due to sensory or neurological causes 46 (38.8%). The etiology of XT due to sensory or neurological causes included amblyopia due to uncorrected refractive errors, trauma, media opacities in cornea and lens, and posterior segment diseases. Other causes included developmental delay, congenital fibrosis of the extraocular muscles, isolated 3rd N palsy, and basic XT.
Conclusions: Our study shows that although majority of the patients had intermittent exotropia, a significant number of patients had exotropia due to visual or neurological causes, which may be preventable in many cases. Diagnosis of the cause of XT at the appropriate time may prevent unnecessary visual loss and reduce the negative psychosocial impact of squint.

Keywords: Causes, Classification of Eye Movement Abnormalities and Strabismus, exotropia, types


How to cite this article:
Thakre SR, Malgi VS, Deshmukh PA. An observational study of exotropia with the application of the Classification of Eye Movement Abnormalities and Strabismus. Pan Am J Ophthalmol 2022;4:27

How to cite this URL:
Thakre SR, Malgi VS, Deshmukh PA. An observational study of exotropia with the application of the Classification of Eye Movement Abnormalities and Strabismus. Pan Am J Ophthalmol [serial online] 2022 [cited 2022 Dec 3];4:27. Available from: https://www.thepajo.org/text.asp?2022/4/1/27/348000




  Introduction Top


Exodeviations or outward deviations of the eye are more prevalent among the Asian population,[1],[2],[3] including Indians.[3],[4],[5] However, Saxena et al. have reported that esotropia and exotropia have been seen in equal frequency in India.[6]

The presence of strabismus affects not only the quality of vision of the patient but also on the psyche of the patient. Although most studies show that amblyopia is more common with esotropes as compared to exotropes,[7] Saxena et al. have shown that amblyopia is equally distributed among them.[6] Furthermore, although patients with intermittent exotropia have good vision and maintain stereopsis, patients with sensory exotropia have poor vision in the affected eye and will also not have stereopsis.

Cosmetically, exodeviations are obvious and distressing. Psychosocial and emotional distress is seen in all types of strabismus patients (55%) as well as their parents (70%).[8] A significant improvement in the Appearance Scale 20 (AS20) health-related quality of life questionnaire for adults with strabismus (AS20) was noted following strabismus surgery. It compared preoperative and postoperative changes in patient's quality of life after strabismus surgery with changes in angle in deviation.[9]

Considering these lifelong impacts of strabismus including exodeviations, the query arises whether exodeviations are preventable or avoidable. To answer this, one must classify the exodeviation appropriately and know the etiology of the exotropia. The many classifications of exodeviations (which mainly apply to intermittent exotropia) described in the literature are confusing and do not include all types of exodeviations [Table 1]. To simplify this matter and going with the current trend toward outcome-based research and multicenter therapeutic trials, the National Eye Institute (US) in 1999–2001 sponsored a workshop toward a uniform classification of strabismus, nystagmus, and involuntary eye movements.[10] This is the Classification of Eye Movement Abnormalities and Strabismus (CEMAS). The purpose of the CEMAS workshop and the resulting document was to provide a foundation of systematic classification of primary eye movement abnormalities and strabismus conditions that can be utilized for clinical research.
Table 1: Classifications of exotropia

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The classification is extensive, providing first a general outline and then a brief description box of each entity that outlines the major criteria for diagnosis, common associated findings, possible etiology, and some general comments.

The purpose of our study was to apply the CEMAS to the patients of exotropia in our study, identify the common types and causes of this cosmetically and psychosocially distressing strabismus, and to determine if any of these causes are preventable.


  Materials and Methods Top


A prospective, cross-sectional study was carried out in patients aged 6 months and more with exotropia attending the ophthalmology outpatient department of a tertiary care hospital from December 2016 to July 2018. Complete strabismus evaluation of the patients was done, the exotropia seen in the patients was categorized in types according to the CEMAS classification and possible causes of exotropia were studied.

Patients with exophoria were excluded from the study.


  Results Top


One hundred and twenty patients with exotropia were included in the study, of whom 58 (48.33%) were male and 62 (51.66%) were female. [Table 2] shows the age of presentation of the patients with the complaint of exotropia to the hospital as well as the age of onset of the exotropia. It is seen that although most of the study population –103 (85.83%) out of 120– noticed the presence of exotropia in the first decade of life, only 48 (40%) presented to the hospital for it during the same time period of their life.
Table 2: Age of patients no when they presented to the hospital with the exotropia and the age of onset of the exotropia

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Of the 120 patients, 110 (91.67%) had a comitant deviation, with only 10 (8.33%) having an incomitant type [Table 3] and [Table 4].
Table 3: Types of comitant exotropia

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Table 4: Types of incomitant exotropia

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In comitant type, intermittent exotropia (59.4%) and exotropia due to visual and neurologic cause (sensory exotropia) (51.7%) were the frequently encountered types, whereas in the incomitant type, exotropia due to third nerve palsy and congenital fibrosis of the extraocular muscles was seen.

Intermittent exotropia with normal accommodation-induced convergence (previously referred to as exotropia with normal AC/A ratio) was the most common subtype seen [Table 5]. In the sensory exotropia (now referred to as exotropia due to visual or neurologic cause), refractive amblyopia and sequalae of ocular trauma were the prevalent causes [Table 6].
Table 5: Subclassification of intermittent exotropia

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Table 6: Causes of exotropia d/t visual and neurologic disease

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  Discussion Top


In our study of 120 patients, although most gave a history of onset of exotropia in the first decade of life, only 40% of these sought medical attention for it in the first decade of life. This delayed presentation of our patients to the physician could be due to the intermittency of deviation or simply ignorance on the part of their parents or caretakers. Some studies showed similar age of presentation[2],[5] whereas others showed an younger age at presentation.[11],[12],[13]

We applied the CEMAS to classify the exotropia for the sake of providing uniformity and ease of comparison for any future studies on exotropia specifically and strabismus as a whole. This classification was formulated with this purpose.[10] We could find no data in the literature which classifies exotropia based on this classification. Although this classification is inclusive of all types of exotropia, the drawback of this classification is the confusing terminology.

We saw that maximum of our patients had a comitant exotropia (110/120). Intermittent exotropia (IXT) was by far the most common type of comitant exotropia seen clinically. This was comparable to other studies which also showed that intermittent exotropia was the most common type of exotropia seen.[2],[11],[12],[14],[15],[16] Contrarily, Attada et al. found more of sensory exotropia in their study population as compared to intermittent exotropia,[5] possibly due to the initial intermittency of the strabismus and rural, illiterate population in the study who also held the belief that strabismus is a harbinger of good luck.

It was seen that in our study, of the subtypes, intermittent exotropia, the one with normal accommodation-induced convergence (old – normal AC/A ratio/basic), was the most common type. Of the other subtypes of intermittent exotropia, there were four cases of simulated divergence excess (pseudo-divergence excess). There were no cases belonging to the other subtypes namely, true divergence,increased accommodation - induced convergence (old high AC/A ratio), or of decreased accommodation - induced convergence (old low AC/A ratio). Pan et al. in a study of the epidemiology of intermittent exotropia also had the highest number of cases of basic type of exotropia, which is similar to exotropia with normal accommodation-induced convergence (old – normal AC/A ratio) in our study.[13] The difference between the two studies was that they included the patients with pseudo-divergence (simulated divergence) in the basic exotropia group after performing an occlusion test.

Whether this type of exotropia can be prevented or controlled is difficult to predict as the management of intermittent exotropia is a conundrum. The aim of treatment is often to normalize or improve ocular alignment while maintaining or improving binocular functions and stereoacuity.[17] As majority of the children are asymptomatic, intervention is offered to those whose exotropia is manifest for at least 50% of their waking hours. This is based on the premise that extended periods of misalignment are associated with suppression and hence loss of binocular single vision. Intervention is also encouraged when the presence of exotropia causes social problems.[17] There is controversy regarding the best treatment option available for intermittetn exotropia – surgical/nonsurgical or a combination of both, about the appropriate timing of surgical intervention and also which surgery is the most appropriate choice. There is lack of data to positively declare that one form of treatment is definitely superior over the other. Surgical outcomes might be improved by coincident additional therapy such as orthoptic exercises/occlusion before surgery or binocular vision training therapy after surgery. While nonsurgical interventions seem to be less effective in terms of improving angle of deviation, they are rarely associated with adverse outcome.[18] A meta-analysis by Dong et al. showed that early surgery for IXT provides a better long-term follow-up outcome when patients are younger than 4 years old or choose the BLR surgical method.[19]

Kushner in a study spread over 31 years states that part-time alternate occlusion and overminus glasses with prisms can defer the need for surgery in a large percentage of patients,[20] while Mohney et al. in a 3-year observational study of children with IXT between the ages of 3 and 10 years noted that stereoacuity deterioration or progression to constant exotropia was uncommon with simple observation and no intervention.[21] The recent Cochrane review on intervention for IXT concludes that patching confers a clinical benefit in children aged 12 months to 10 years of age with basic-or distance-type X (T) compared with active observation, whereas there is insufficient evidence to conclude that which surgical procedure – bilateral lateral rectus recession or unilateral lateral rectus recession plus medial rectus resection – is better.[22]

Thus, it is difficult to predict whether IXT can be controlled or even treated successfully, but going with the current literature, a nonsurgical management option can be given to every child at diagnosis and an attempt made to control the amount and duration of deviation with the maintenance of stereoacuity.

Intermittent exotropia (59.4%) is followed closely by exotropia due to visual and neurological causes or sensory exotropia (51.7%). Our study reported a considerably higher number of these cases. Attada et al. also reported a higher number of cases of sensory exotropia (78% of their cases of sensory strabismus had exotropia) than intermittent exotropia in their study.[5] This proportion in Indian studies is comparatively higher than that seen by Mohney[14] – 10.2%, Govindan et al.[15] – 8.25%, and Chia et al.[16] (4%).

In our study, it was seen that the in causes of the exotropia due to visual and neurological causes (sensory exotropia), refractive amblyopia (uncorrected astigmatism was the most common cause) and that due to poor vision secondary to ocular trauma were most frequent. Other causes included media opacities due to congenital cataract or corneal opacities, posterior segment diseases such as macular coloboma, Stargardt's disease, and children with developmental delay. Havertape et al., in a study of 123 cases of sensory strabismus, concluded that those with acquired vision loss are significantly more likely to develop exotropia, P <.001; patients with congenital vision loss are significantly more likely to develop esotropia, P < 0.005.[23] Chia et al. analyzed the causes of secondary exotropia in 19 patients and found that 6 were due to dense amblyopia, 7 due to neurological or systemic impairment, 3 due to cerebral palsy, and 5 due to various affections of the posterior segment.[15] Although the overall number of sensory exotropia was less in the study by Chia et al., the proportion of the causes was similar to our study, i.e., the refractive amblyopia was a common factor. Early detection of refractive errors is a simple and effective way to prevent this cause of exotropia. Intensive implementation of early screening of children – neonates (term and preterm) in programs such as the It is government sponsored screening in India.[24] and similar in other countries – would go a long way in the detection of causes of visual deprivation amblyopia and consequent exotropia due to visual and neurological cause (sensory exotropia). A similar national program should be implemented in India to screen for refractive errors in preschool children. In our study, the second most common cause was exotropia as a sequela of ocular trauma. The report of the 58th round of the National Sample Survey Organisation of 2002 of physically disabled persons in India revealed that injury-related visual disability was seen in 51 persons/1000 population.[25] The incidence of pediatric ocular trauma in India has been found to be high at 12.8%[26]–18.9%.[27] Acquired vision loss predisposes to the development of exotropia.[23] This stresses on the importance of taking preventive measures by educating the stakeholders – general population, especially the children, teachers, the employers about the consequences of ocular trauma, creating response teams as well as improving standards of treatment provided to such patients.[26]

Our study of 120 patients included 6 (6.6%) cases of infantile exotropia in neurologically normal infants, which is rarely seen in the western population[11],[12],[15] and 2 in children with developmental delay.

Of the ten cases of incomitant exotropia seen, six (5%) were due to third nerve palsy and four were due to congenital fibrosis of the extraocular muscles (CFEOMs). Paralytic strabismus was similar to other studies.[12],[15] The number of cases seen due to CFEOMs was higher than normal as we had examined the entire family once we saw the proband. Although all subtypes of CFEOMs can present with exotropia, it is most common in Type 2.[28]


  Conclusions Top


Our study attempts not only to classify exotropia as per the CEMAS but also makes an effort to identify the common causes of exotropia in a part of the Indian population (Marathwada region of the western state of Maharashtra). It identifies the common causes of exotropia (intermittent and sensory) and suggests possible preventive strategies for sensory exotropia. A further large-scale study may help confirm whether the same causes are present pan India.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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