COMMUNITY EYE CARE
Year : 2000 | Volume
: 48 | Issue : 1 | Page : 59--64
Unilateral visual impairment in an urban population in Southern India
L Dandona, R Dandona, M Srinivas, P Mandal, CA McCarty, GN Rao
Public Health Ophthalmology Service and International Centre for Advancement of Rural Eye Care, L.V. Prasad Eye Institute, Banjara Hills, Hyderabad-500034, India
Public Health Ophthalmology Service and International Centre for Advancement of Rural Eye Care, L.V. Prasad Eye Institute, Banjara Hills, Hyderabad-500034
This study assessed the prevalence and causes of unilateral visual impairment in the urban population of Hyderabad city as part of the Andhra Pradesh Eye Disease Study.
Stratified, random, cluster, systematic sampling was used to select 2,954 subjects from 24 clusters representative of the population of Hyderabad. Eligible subjects underwent detailed eye examination including logMAR visual acuity, refraction, slitlamp biomicroscopy, applanation tonometry, gonioscopy, dilatation, cataract grading, and stereoscopic evaluation of fundus. Automated threshold visual fields and slitlamp and fundus photography were done when indicated by standardised criteria. Unilateral visual impairment was defined as presenting distance visual acuity <6/18 in the worse eye and ≥6/12 in the better eye, which was further divided into unilateral blindness (visual acuity <6/60 in the worse eye) and unilateral moderate visual impairment (visual acuity <6/18-6/60 in the worse eye).
A total of 2,522 subjects (85.4% of eligible), including 1,399 ≥30 years old, participated in the study. In addition to the 1% blindness and 7.2% moderate visual impairment (based on bilateral visual impairment criteria) reported earlier in this sample, 139 subjects had unilateral visual impairment, an age-gender-adjusted prevalence of 3.8% (95% confidence interval 2.7-4.9%). The major causes of this visual impairment 39.9% were refractive error (42.9%), cataract (14.4%), corneal disease (11.5%), and retinal disease (11.2%). Of this unilateral visual impairment was blindness. The major causes of unilateral blindness were corneal disease (23.2%), cataract (22.5%), retinal disease (18%), and optic atrophy (12.9%). On the other hand, the predominant cause of unilateral moderate visual impairment was refractive error (67%) followed by cataract (9%). Of the total unilateral visual impairment, 34.3% was present in those <30 years old and 36.2% in those 30-49 years old.
Unilateral visual impairment afflicts approximately 1 in 25 persons in this urban population. A large proportion of this unilateral visual impairment is present in younger age groups. The causes of unilateral visual impairment, like those of bilateral visual impairment in this population, are varied, suggesting therefore, that in addition to the current focus of eye care in India predominantly on cataract, other causes of visual impairment need to be addressed as well.
|How to cite this article:|
Dandona L, Dandona R, Srinivas M, Mandal P, McCarty C A, Rao G N. Unilateral visual impairment in an urban population in Southern India.Indian J Ophthalmol 2000;48:59-64
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Dandona L, Dandona R, Srinivas M, Mandal P, McCarty C A, Rao G N. Unilateral visual impairment in an urban population in Southern India. Indian J Ophthalmol [serial online] 2000 [cited 2021 Sep 23 ];48:59-64
Available from: https://www.ijo.in/text.asp?2000/48/1/59/14848
Population-based assessment of unilateral visual impairment, in addition to bilateral visual impairment, would give a complete picture of visual impairment in a population. As part of a population-based epidemiologic study, the Andhra Pradesh Eye Disease Study (APEDS), we have recently reported data on bilateral blindness and bilateral moderate visual impairment in the urban population of Hyderabad in southern India. In this communication we report the prevalence and causes of unilateral visual impairment, and its demographic associations, in this urban population of Hyderabad.
Materials and Methods
The design of APEDS has been described in detail previously.[1,3] This study has been approved by the Ethics Committee of the L.V. Prasad Eye Institute. A brief description of the methods used in this study that are relevant to this communication follows.
The total sample for APEDS is 10,000 of which 2,500, is urban from Hyderabad, a city of about 3.5 million population. A total of 2,954 subjects were sampled from 24 blocks (clusters) representative of the Hyderabad population using a stratified, random, cluster, systematic sampling strategy.[1,3] Aiming for a recruitment rate of at least 85% this sample was expected to yield 2,500 participants needed for the urban segment of APEDS. The subjects participating in the study were interviewed in detail; the information also elicited details of income. Socioeconomic strata were classified based on per capita monthly income: extreme lower (Rs≤200 [US$ 5.1]), lower (Rs 201-500), middle (Rs 501-2000), and upper (Rs >2000).
The subjects participating in the study were brought for examination to a clinic specially set up for the study. Written informed consent was obtained, and the examination was performed by two ophthalmologists and two optometrists who had been trained specially in the procedures of the study. Presenting distance and near visual acuity was measured under standard conditions with the logarithm of the minimum angle of resolution (logMAR) charts. External examination of the eye and anterior segment examination was done with the slitlamp. Intraocular pressure (IOP) was measured with Goldmann applanation tonometer or with Perkins applanation tonometer in those children who could not sit at the slitlamp or in those debilitated subjects who were examined at home (described later). Gonioscopy was done with NMR-K two-mirror goniolens (Ocular Instruments Inc, Bellevue, WA, USA), and the angle was graded according to the classifications of Scheie and Shaffer. If the subject could not cooperate with gonioscopy, the angle was graded at the slitlamp using the van Herick technique. All subjects had their pupils dilated unless contraindicated due to risk of angle closure. The lens was examined with slitlamp after dilatation, and nuclear cataract graded using the Lens Opacity Classification System (LOCS) III, and the cortical and posterior subcapsular cataract graded using the Wilmer classification. Stereoscopic fundus examination was done at the slitlamp using the 78 D lens and with the indirect ophthalmoscope using the 20 D lens. Standard classifications were used to grade diabetic retinopathy and age-related macular degeneration.
Humphrey automated threshold central 24-2 visual fields were done in subjects with any suspicion of glaucoma or other optic nerve pathology, higher visual pathway lesion, or significant macular/retinal pathology (such as retinitis pigmentosa) according to uniform predefined criteria. If the visual field was abnormal or unreliable it was repeated on another day.
Documentation of anterior segment pathology was done with the Nikon photographic slitlamp, and pathology of optic disc and macula/retina with the Zeiss fundus camera.
Those subjects who were physically debilitated and unable to attend the clinic were examined at home with portable equipment. This examination was similar to the one at the clinic except that gonioscopy, 78 D examination, automated visual fields, and photography could not be done.
Definition of unilateral visual impairment
In our previous reports from APEDS, we have defined bilateral blindness as presenting distance visual acuity <6/60 or central visual field <20° in the better eye, and bilateral moderate visual impairment as presenting distance visual acuity <6/12-6/60 or equivalent visual field loss in the better eye. For this paper, unilateral visual impairment was defined as presenting distance visual acuity <6/18 in the worse eye and≥6/12 in the better eye in order to exclude all subjects previously included in any of the bilateral visual impairment categories. Unilateral visual impairment was further classified as blindness if acuity was <6/60 or moderate visual impairment if acuity was <6/18-6/60.
Cause of visual impairment
If both cataract and posterior segment lesion were present such that removal of cataract would not restore vision, the cause of visual impairment was considered to be posterior segment lesion. On the other hand, if index myopia due to cataract was present, and even if the vision improved with myopic correction, the cause of visual impairment was considered to be cataract.
The estimates of unilateral visual impairment were adjusted for the age and gender distribution of Hyderabad. The design effect of the sampling strategy was calculated and taken into account in determining the 95% confidence intervals of the estimates. After excluding subjects with bilateral blindness and bilateral moderate visual impairment, the association of unilateral visual impairment with age, gender, socioeconomic status, and religion was assessed using univariate analysis followed by multivariate multiple logistic regression analysis.
Of the 2,954 eligible subjects, 2,522 (85.4%) were interviewed and examined between October 1996 and June 1997. The age of these subjects ranged from 1 month to 102 years; 1,399 (55.5%) were ≥30 years of age, and 1,347 (53.4%) were female. Twenty three (0.9%) subjects were examined at home.
Forty nine of these subjects have been previously reported to have bilateral blindness, an age-gender-adjusted prevalence of 1%, and 303 to have bilateral moderate visual impairment, an age-gender-adjusted prevalence of 7.2%. In addition to these, there were 139 subjects with unilateral visual impairment, an age-gender-adjusted prevalence of 3.8% (95% confidence interval 2.7-4.9%). Of these 139 subjects, 57 (age-gender-adjusted proportion 39.9%) had unilateral blindness, and 82 (age-gender-adjusted proportion 60.1%) had unilateral moderate visual impairment. Of those with unilateral blindness, 83.5% had presenting distance visual acuity <3/60 in the worse eye and the remaining 16.5% had acuity <6/ 60-3/ 60 in the worse eye. Of those with unilateral moderate visual impairment, 79.7% had presenting distance visual acuity <6/18-6/30 in the worse eye, and the remaining 20.3% had acuity <6/ 30-6/ 60 in the worse eye.
The causes of unilateral visual impairment are shown in [Table:1]. For all levels of unilateral visual impairment considered together, the most common cause was refractive error (42.9%) followed by cataract (14.4%), corneal disease (11.5%), and retinal disease (11.2%). The causes for the majority of unilateral blindness were distributed between corneal disease (23.2%), cataract (22.5%), retinal disease (18%), optic atrophy (12.9%), and amblyopia (10%). The predominant cause of unilateral moderate visual impairment was refractive error (67%).
The univariate distribution of unilateral visual impairment for the demographic variables is shown in [Table:2]. The prevalence of both unilateral blindness and unilateral moderate visual impairment increased with increase in age. For unilateral blindness the prevalence increased steeply at age 30 years and beyond, and for unilateral moderate visual impairment it increased steeply at age 40 years and beyond. However, because a large proportion of the Hyderabad population is young,12 the absolute proportion of visual impairment in the younger age groups was high [Table:3]. The age of those having unilateral visual impairment due to cataract (mean 55.7 years, 95% confidence interval 49.6-61.7 years) was significantly more than those having unilateral visual impairment due to other causes (mean 43.1 years, 95% confidence interval 39.9-46.3 years).
Multivariate analysis revealed that higher age and lower socioeconomic status had significantly higher odds of having unilateral visual impairment [Table:4].
Population-based estimation of the magnitude and causes of bilateral and unilateral visual impairment would enable understanding of the eye-care needs in a population. We have recently reported data from APEDS, a population-based study, that bilateral blindness is estimated to be present in 1% of the population of Hyderabad, and bilateral moderate visual impairment in another 7.2%. The causes of this visual impairment were varied.
Data reported in this paper suggest that 3.8% of the population of Hyderabad may have unilateral visual impairment. This translates into approximately 1 out of 25 persons in the population. Though the prevalence of unilateral visual impairment increased with increase in age, because of a greater proportion of younger people in the population of Hyderabad compared to the rest of India, 20.2% of the total unilateral visual impairment was present in children (≤15 years old), 14.1% in those 16-29 years old, and another 36.2% in those 30-49 years old. This implies that the absolute proportion of unilateral visual impairment is high in children and in the productive years of adulthood. This may potentially have a significant effect on the development of children and the productivity of adults.
Multivariate analysis revealed that unilateral visual impairment was more likely to be present in those belonging to the lower socioeconomic strata. This trend is similar to that seen for bilateral visual impairment in this population,[1,2] and underscores the need for targeting this segment of the population in the efforts to reduce visual impairment.
Refractive error was responsible for 42.9% of the overall unilateral visual impairment, 6.5% of unilateral blindness, and 67% of unilateral moderate visual impairment. These figures for cataract were 14.4%, 22.5%, and 9%, respectively. Corneal disease, retinal disease, optic atrophy, and amblyopia also contributed significantly to the unilateral blindness, and corneal and retinal diseases to the overall unilateral visual impairment. These data suggest that the causes of unilateral visual impairment in this urban population are varied, and like the causes of bilateral visual impairment,[1,2] are not limited to cataract. This issue is important because the eye-care policy of India currently focuses mostly on cataract which has led to the situation that other causes of visual impairment are not given adequate attention at the policy level. For example, refractive error is responsible for a large proportion of bilateral visual impairment in this urban population in India[1,2] and also unilateral visual impairment as shown by the data in this paper. However, this relatively easily treatable cause of visual impairment does not receive much "real" attention in the eye-care policy in our country. Perhaps it is time that this changes. Similarly, causes other than cataract and refractive error also contributed significantly to bilateral blindness and unilateral blindness (data in this paper) in this urban population in India, suggesting that we should start developing strategies for prevention and early treatment of these causes.
It would seem that in order to reduce visual impairment in India on a long-term basis, we would have to base our eye-care policy on sound current population-based data from well-designed epidemiologic studies.[14- Around the world, successful health policy is based on recent and reliable epidemiologic data, and is continually refined on the basis of new epidemiologic data. The logic of this is quite straightforward. Unless we know reliably and in some detail about the various aspects of a problem, its resolution cannot be well planned.
In conclusion, the varied causes of bilateral visual impairment in this population reported earlier,[1,2] and the varied causes of unilateral visual impairment in this population reported in this paper, suggest that from a public health perspective we should start giving more serious attention to causes of visual impairment other than cataract if long-term reduction in visual impairment is to be achieved in India.
This study was supported by the Hyderabad Eye Research Foundation, Hyderabad, India. Rakhi Dandona is supported in part by the R.B. McComas and Hugh Noel puckle Scholarships from the University of Melbourne, Melbourne, Australia. The authors thank Professor Hugh R. Taylor for guidance in study design; Pyda Giridhar, V. Nagaraja Naidu, M.N.K.E. Prasad, and Kovai Vilas for mapping the selected blocks and recruiting and interviewing the participants.
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