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Community outreach

An indicator for assessment of prevalence of amblyopia

Magdalene, Damaris; Bhattacharjee, Harsha; Choudhury, Mitalee; Multani, Prabhjot Kaur; Singh, Anshul; Deshmukh, Saurabh; Gupta, Krati

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Indian Journal of Ophthalmology: July 2018 - Volume 66 - Issue 7 - p 940-944
doi: 10.4103/ijo.IJO_1335_17
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Abstract

Amblyopia has been defined as the diminution of vision, unilateral or bilateral, caused by the deprivation of pattern vision or abnormal binocular interaction, for which no cause can be detected.[1] Amblyopia is the most common cause of uniocular visual impairment among the children, young and middle-aged adults and has a prevalence rate of about 1%–4%.[234] Anisometropia, high refractive errors, squint, media opacities, or their combinations are the various causes of amblyopia commonly encountered in outpatient departments. The prognosis of amblyopic patients depends on multiple factors, which include the age of the patient at detection, its cause, severity, the presence of co-morbidities, the interval between the onset and initiation of treatment, and the patient compliance.[5] Parent education and awareness of the disease also play an important role. Treatment regimens include optical correction, patching, atropinization, and vision therapy. In case of deprivation amblyopia, it is necessary to treat the cause. Amblyopia can lead to permanent loss of vision if timely corrective measures are not taken. The ominous documented consequence of amblyopia is the risk of blindness if unaffected eye becomes diseased or damaged later in life, resulting in significant health and social consequences.[678] Early detection of amblyogenic risk factors such as strabismus, refractive errors, and media opacities along with disease awareness among the parents is essential to identify the disease early in its course and initiate treatment to reduce the burden of the disease. This will reduce the overall prevalence and severity of visual loss in children. Refractive error correction can significantly improve visual acuity (VA) to the level that further amblyopia treatment may not be required.[910]

However, there have been limited studies elucidating the prevalence, cause, and magnitude of amblyopia; and less emphasis is given to amblyopia in the tertiary eye hospitals, with more attention toward cataracts and other ocular morbidities. This study aims to determine the prevalence, causes, and magnitude of amblyopia and its subtypes in Kamrup district of Guwahati, Assam, India.

Methods

Patient selection and examination

This was a prospective, observational study conducted from January 2015 to December 2016. The first step in the implementation of this project was to train the workers of the nongovernmental organization (NGO) “Seven Look” to check vision correctly and brief them about the project and the survey to be done. A brochure stating the basics of the project (both in English and Assamese) and referral forms were distributed by the workers in each home. About 39,651 children between the age of 6 months and 16 years were first screened by trained workers who went door to door in Kamrup district and brought at-risk patients to the camps arranged at sixty places in the district. Institutional academic and research committee as well as ethics committee approval was obtained. Prior informed written consent was obtained from all the patients involved in the study. Age, sex, and other relevant clinical parameters were noted. The assessment involved obtaining a detailed ocular history relevant to the age at which the first eye examination was performed and history of any prior treatment (use of glasses, occlusion therapy, or surgery).

Difficulties were encountered in examining the children below 5 years of age, so the parents were given a referral paper and were asked to report to the institute by themselves with the referral paper. In some areas, we visited the pediatric units and assessed the children below 5 years. This assessment was done by experienced personnel. Hence, the children below 5 years were directly referred to the tertiary eye care institute, Sri Sankaradeva Nethralaya, where a detailed examination was done.

Ocular examination included the assessment of unaided and best-corrected visual acuity (VA) with the help of appropriate vision charts such as Kay picture charts, E charts, Landolt C chart, and Lea symbols depending on the age and cooperation level of the child. In a child familiar with alphabets, ETDRS chart with letters was used. Children who were too young to perform VA testing, in them vision assessment was done by central-steady-maintained with 10 prism diopter (PD) vertical prism and preferential looking method with Cardiff VA tests.

For the children above 6 years of age after the door-to-door survey, camps were conducted in the nearby schools for children who failed to read the 6/9 line of the Snellen chart. Sixty camps were conducted, in each camp, about 150 patients were examined. The children who did not pass the criteria were referred to the institute. Detailed photographic documentation of the camp work was done. Indirect ophthalmoscopy was also performed to assess the posterior segment and rule out any other cause of diminution of vision. In cases with very high refractive errors, axial length and corneal topography were also performed to determine the accuracy of the refractive errors.

Amblyopia was suspected in children who had the presence of amblyogenic factors such as congenital cataract, strabismus, and high refractive errors in the absence of any pathological cause. Cycloplegic refraction was performed on all the children examined. Assessment of ocular alignment, fixation pattern, and ocular motility was done. A detailed fundus evaluation was done in all amblyopic children to rule out any posterior segment pathology.

Study definition of amblyopia

Unilateral amblyopia was defined as the 2-line interocular difference in VA with a VA of at least 6/12 (fails to read 6/9 line) or worse in the worse eye (with unilateral amblyogenic factors). Bilateral amblyopia was defined as VA of 6/12 or less in both eyes (with bilateral amblyogenic factors).[11]

Classification of amblyopia

For each patient, amblyopia was classified as refractive, strabismic, and deprivation amblyopia.[12]

Strabismic amblyopia was defined as amblyopia in the presence of heterotropia at a distance and/or near or a history of strabismus surgery (or botulinum toxin injection) and in the absence of refractive error meeting the criteria for aniso-strabismic amblyopia. Accommodative esotropia is one of the most common types of strabismus in childhood. In accommodative esotropia, there is over-convergence associated with the accommodation to overcome a hyperopic refractive error, causing loss of binocular control and leading to the development of esotropia.

In our study, we defined aniso-strabismic amblyopia as amblyopia associated with either a heterotropia at a distance and/or near fixation or a history of strabismus surgery (or botulinum toxin injection), and anisometropia, 1.00 D or more in spherical equivalent for hypermetropia, 3.00 D or more for myopia, and 1.50 D or greater difference in astigmatism in any meridian.[13]

Deprivation amblyopia includes patients with known documented cases of sensory deprivation (cataract, ptosis, or other media opacities) with no primary heterotropias or refractive errors that could be causally related to amblyopia.

The diagnosis of refractive/anisometropic was made when hypermetropia was >4.00 D, myopia >6.00 D, and astigmatism >2.50 D with no related strabismus or ocular pathology.[13]

Results

Prevalence of amblyopia

Of the total population of 1,517,542 (Census 2011) in Kamrup district, there were 39,651 children who belonged to the age group 6 months to 16 years.[14] The door-to-door screening was done and 8388 children were advised to attend camps organized at different places and children below 5 years were referred to the tertiary eye care institute directly. Of these 8388 children, 1.75% (n = 692) were diagnosed to have amblyopic. Of the 692 children who were diagnosed to have amblyopia, 223 were diagnosed at the institute [Fig. 1a]. A total of 2107 children reported to the institution either after the door-to-door survey or from the camps during the 1½-year study period. 469 patients were diagnosed at the camps organized by Sri Sankaradeva Nethralaya at 21 different police stations in and around Guwahati. Out of total 692 amblyopic children, 47.50% (n = 329) were females and 52.50% (n = 363) were males.

Figure 1
Figure 1:
(a) Pie chart showing distribution of amblyopia patients diagnosed at the institute and camp level. (b) Pie chart showing the involvement of the eyes (right eye, left eye, and both eyes)

Geographic distribution of patients

Maximum patients were found in Sonapur, followed by Khetri and Bharalmukh [Fig. 2].

Figure 2
Figure 2:
Number of amblyopia patients diagnosed in different areas

Demographic profile of amblyopic children

The mean age of children was found to be 13.5 (±2) years. More than half of the amblyopic children (63.58% [n = 440]) were above 11 years of age. Males were affected more than the females, i.e., 246 males and 223 females among those screened at the camp level [Fig. 3a]. Based on laterality, both eyes were diagnosed to have amblyopia in 278 cases, right eye in 82 cases, and left eye in 109 cases [Fig. 1b].

Figure 3
Figure 3:
(a) Gender distribution of patients with amblyopia. (b) Age group-wise distribution of patients with amblyopia

Majority patients diagnosed at camp level belonged to the age group of 11–16 years, i.e., 343 patients out of 469, followed by 106 patients in the 6–10-year age group and 20 patients in the 6 months to 5 years age group [Fig. 3b]. Detailed age-wise distribution showed that the maximum number of patients was in the age group of 13–14-year age group, i.e., 128 out of 469 children [Fig. 4].

Figure 4
Figure 4:
Detailed age-wise distribution of patients

Distribution of amblyopia

Most of the patients were found to have refractive amblyopia (45.29% [n = 101]) followed by deprivation amblyopia (40.36% [n = 90]). Strabismic amblyopia was found to be the least of all, (14.35% [n = 32]) among the patients reported to the institute [Fig. 5].

Figure 5
Figure 5:
Frequency distribution of amblyopia patients presenting to the institute directly

93 children (19.83%) out of 469 at the campsite and 30 children (13.45%) out of 223 at the institution were already diagnosed to have amblyopia and were taking some form of treatment such as spectacle correction or patching.

Most of the cases of deprivation amblyopia were due to congenital cataract and had undergone cataract surgery in the past. Of the total cases of strabismic amblyopia, most of them had esotropia.

Among the 2107 patients who reported to the institute directly following the screening, 1512 children were above the age of 6 years and 595 belonged to the age group of 6 months to 5 years. Of these, 158 children in the age group of 6 years and above, and 65 in the age group of 6 months to 5 years were diagnosed to have amblyopia.

These patients (above 6 years, n = 158) were further categorized on the basis of the type of amblyopia, i.e., refractive, deprivation, and strabismic amblyopia. Most patients were found to have refractive amblyopia (45.29%), followed by deprivation amblyopia (40.36%) and strabismic amblyopia was found to be the least of all (14.35%).

In the age group of 6 months to 5 years (n = 65), deprivation and strabismic amblyopia had almost equal distribution, that is, 43.08% and 44.62%, respectively. Refractive amblyopia was relatively less common in this age group, that is, 12.30%.

Discussion

Amblyopia is a major health issue as it can lead to permanent visual impairment if not treated on time.[15] Review of literature showed that the prevalence of amblyopia ranges from 0.8% to 3% worldwide, depending on the population studied and the definition used.[1617181920] Prevalence of amblyopia in our study was found to be 1.75% in children between 6 months and 16 years of age. It was more prevalent in males as compared to females.

Identification of amblyopia was done by trained workers, optometrist and confirmed by an ophthalmologist at the field level. Due to limitation of time, manpower and large population to be examined, classification of amblyopia was not done at field level. Uncorrected refractive error was a major cause of amblyopia in children who reported to the institute. The majority of amblyopic children in our study, 45.29% had refractive amblyopia, 40.36% and 14.35% of children had deprivation and strabismic amblyopia, respectively. In contrast to our study, Menon V et al. found strabismic amblyopia to be the most prevalent type of amblyopia (37.88%).[16] This could be because children with apparent pathology, that is, exotropia, esotropia, etc., tend to attend hospitals more frequently than simple refractive errors.

A study conducted in Israel found the rate of amblyopia among the subjects with refractive error to be 14.6% among the immigrants as opposed to 8% among the native Israelis.[17] However, in our study, we considered children as amblyopic on the basis of VA immediately after correction, without considering that children may not be amblyopic after certain weeks of optical correction. This is one of the major limitations of our study that may have resulted in the overestimation of the percentage of children with refractive amblyopia.

Many studies have shown that appropriate refractive correction alone causes improvement in VA in patients with refractive amblyopia.[1819] Another important finding of the study was that a significant number (40.36%) of children had deprivation amblyopia. The deprivation was due to congenital cataract in most cases and they had undergone surgery at different tertiary eye care centers. All these children were wearing aphakic glasses, but none had undergone patching therapy.

In our study, the mean age of amblyopic children was 13.5 ± 2 years. Although many Pediatric Eye Disease Investigator Group (PEDIG) studies have shown that children respond to treatment at even an older age, treatment may be less effective than it would have been at a younger age.[920] Amblyopia remains undetected in a large number of children as seen in our study (n = 692), of this 17.77% (n = 123) were already diagnosed with refractive amblyopia at the time of presentation.

Many government and NGO-supported school screening programs are conducted every year; however, they are unable to cover all the areas of the Kamrup district. The lack of school vision screening programs and awareness among the parents, lead to late detection of the visual defects which ultimately leads to amblyopia.

Conclusion

Majority of the children in our study had amblyopia due to uncorrected refractive error, which could be simply avoided by detecting and correcting the refractive error on time. Lack of knowledge and awareness about amblyopia and its timely management leads to late presentation and significant visual impairment.

Clinical implications

The study shows that the true magnitude of disease is actually more than we see in our outpatient departments because only 32% children had reported to the institute in contrast to 68% children which were diagnosed at the camp level following door-to-door screening.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Acknowledgment

We would like to thank Sri Kanchi Sankara Health and Educational Foundation and SEVEN LOOK NGO, Guwahati, India.

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Keywords:

Amblyopia; community ophthalmology; pediatric ophthalmology; population-based study; screening program

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