Original Article
Prevalence and Associated Risk Factors of Glaucoma in Aligarh, India – A population based study
Anees Ahmad,1  Syed Zulfequar Ahmad,2 Najam Khalique,1  Mohammad Ashraf,3 Yasir Alvi4
Department of Community Medicine, J.N. Medical College, AMU, Aligarh, India
Department of C.G.H.S., Lucknow, India
Department of Ophthalmology, J.N. Medical College, AMU, Aligarh, India
Department of Community Medicine HIMSR, Hamdard Univerisity New Delhi

Corresponding Author
Yasir Alvi (MD Assistant Professor)
Department of Community Medicine
HIMSR, Hamdard Univerisity, New Delhi
Email id: yasiralvi13@gmail.com


Background: Glaucoma is one of the most common causes of blindness. Being irreversible, its early detection and management are utmost important. With increasing life expectancy, the prevalence of glaucoma is expected to rise. We did this study to find the prevalence of glaucoma among middle-aged and elderly population and to find out its associated factors. 
Methods: A community based cross-sectional study among rural and peri-urban area of Aligarh was done for a duration of one year. A trained ophthalmologist interviewed and examined 680 patients with a detailed eye examination. Intraocular pressure (IOP) was measured by Keeler pulsair non-contact tonometer, confirm by applanation tonometry. Anderson criteria were used to diagnose glaucomatous visual field defect. 
Results: In our study population, a total of 31 subjects were diagnosed as glaucoma in either one or both eyes. The overall prevalence of glaucoma was found to be 4.6%. About equal distribution of type of glaucoma, i.e. Primary Open Angle Glaucoma (POAG), Primary Angle Closure Glaucoma (PACG) and Normotensive Glaucoma (NTG) was observed in our study participants. The prevalence of glaucoma was found to be significantly associated with increasing age, positive family history as well as a history of angle closure. 
Conclusion: The prevalence of glaucoma is higher in the population of Aligarh. Its association with increasing age, positive family history and history of angle-closure may give us clues for early detection. Screening for glaucoma during middle age especially among person with a positive family history or angle-closure would help us early diagnosing and management of this irreversible disease.

Glaucoma is the leading cause of irreversible blindness worldwide and World Health Organization ranks it as second most common cause of blindness worldwide after cataract.1 It is estimated that the global burden of glaucoma  to be 60 million and it would be 79.6 million by 2020, with almost half of them Asian.2  In terms of prevalence, the global prevalence of glaucoma is estimated at 3.54%.3 The studies showing the prevalence of glaucoma between 0.94% to 4.73% among them in various part of Asia4,5 with angle-closure glaucoma being more frequent among Asian populations. The prevalence is expected to rise. 
India with increasing greying of the population, is expected to become the second largest home of glaucoma by 2020. The estimated prevalence of glaucoma cases in India is reported to be 11.9 million.6 This prevalence of glaucoma in India is not the same at every place, with varying prevalence among different populations and subgroups having rate of being 2.3 – 4.7%.7,8,9  In regards to subtype, Indian population have an equal proportion of Primary open-angle (POAG) and Primary closed-angle glaucoma (PACG). 
Glaucoma is a multifactorial condition resulting from progressive optic neuropathy and visual field loss. These changes are often slow and many glaucoma patients do not know about their underlying glaucomatous eye. Chennai Glaucoma Study as well as Aravind comprehensive eye survey, observed that more than 90% cases of glaucoma were undiagnosed and were identified only at the time of study.10,11 They have proposed periodic screening of high-risk population for diagnosing the disease at an early stage. As glaucoma types and risk factors varies from population to population, we did this study to shed a light on its patter in western part of Uttar Pradesh. Considering the paucity of community glaucoma studies, we conducted this study with the objectives of finding out the prevalence of glaucoma and its associated factor among adults aged 40 years and above in the rural and peri-urban area of Aligarh.

Materials and Methods
A community-based cross-sectional study was conducted for a period of one year from July 2015- June 2016 among middle age and elderly population at field practise area of Rural Health Training Centre (RHTC) and Urban Health Training Centre (UHTC), Department of Community Medicine, JN Medical College, AMU, Aligarh. Inclusion criteria were people aged 40 years and above, resident of registered household (UHTC and RHTC) and who gave consent for interview and examination. Those who were severely ill or who did not give the consent were excluded from the study.

Sample size 
We calculated the sample size from the formula given below assuming the prevalence of glaucoma as 3.5% based on prominent prevalence studies in India,  and with absolute precision of 2% and 95% confidence interval and a design effect of two. The sample size came out to be 649. Taking non-responses rate into account, the final sample size was increased to 700. Probability proportion to size (PPS) systematic random sampling was done to draw the desired sample from each area with 410 from rural and 290 from peri-urban. 

Study procedure
A predesigned & pretested questionnaire was used to collect data from the study population. It elicits socio-demographic information along with detailed eye examination. Socio-economic status was assessed by Modified BG Prasad classification, 2016.12 Study instruments included Landort ‘C’ chart for visual acuity, +1 D lens, Keeler ‘Pulsair easy eye’ non-contact tonometer, Appasamy Applanation tonometer, direct ophthalmoscope, slit lamp, gonioscope, and automated perimeter (24-2 SITA standard, Zeiss-Humphrey Visual Field Analyzer). A preliminary eye examination was done at home and those in whom glaucoma was suspected or whose uncorrected visual acuity was <3/60, were referred to ophthalmology OPD at RHTC/UHTC for further evaluation.

Operational definition
1. High Intraocular pressure: 
Pressure  > 21mm of Hg in either eye.
Difference of more than 6 mm Hg in both eyes.

2. Significant Disc changes:
Vertical cup disc ratio > 0.6 in either eye.
Asymmetry of cup disc ratio > 0.2.
Other disc changes like polar notch, hemorrhages on or near the disc, thinning of neuroretinal rim.

3. Glaucoma diagnosis
Any two of the three features
High Intraocular pressure
Significant Disc changes 
Glaucomatous field defect (Anderson criteria)

Figure 1: Type of glaucoma among the study population

Statistical Analysis
Data were tabulated and analysed by using SPSS ver.21.13 Descriptive data were presented as frequency, graph, mean and percentage. Categorical data were analysed by chi-square test or Fisher exact test, whenever applicable. All tests were two-tailed, and a p-value of = 0.05 was considered significant. 
Ethical Considerations
The study was approved from the Institutional Ethics and Research Advisory Committee, Faculty of Medicine, Aligarh Muslim University, Aligarh. Informed consent from all the participant was taken before the study. They were assured that the personal information received would be kept confidential. Proper health education and adequate counselling were provided to all the subjects. Referral for any subject found to have glaucoma or any other ailment was done for further management.

Among the total 700 patients selected, only 680 patients completed the whole questionnaire and were finally analyzed as 20 participants refused or dropout before the complete examination and were excluded from the study. The final analysis was done on 281 urban and 399 rural participants. 

Socio-demographic and clinical characteristics
Among the total of 680 study participants, 267 (38.3%) were males and 413 (60.7%) were females. The mean age of the participants was 55.0 ± 11.56 years ranged from 40 – 102 years. The majority of participants were in the age group 40-50 years. Majority of them were married (80.0%) and Hindu (54.0%) by religion. The educational status of the study population was very poor, with more than half of them (63.8%) being illiterate. The study population consisted mostly of housewives 392 (57.6%) and only 237 (34.8%) were employed leaving 51 (7.5%) unemployed or retired. Majority of the participants belonged to lower socio-economic classes with 329 (48.4%) and 277 (33.4%) in class V and class IV respectively. (Table 1) 

Mean IOP observed among individual 1360 eyes was found to be 13.61 ± 4.17 mm Hg, with glaucomatous and non-glaucomatous population was 20.24 ±10.75 and 13.23 ± 3.03 mm Hg respectively. Majority of eyes have normal anterior chamber depth while 29% of them had a shallow angle with two subjects classified as isolated Primary Angle Closer without glaucomatous changes. The mean CD ratio observed in study eyes was 0.335±0.095, the glaucomatous and non-glaucomatous population was 0.577±0.16 and 0.321 ± 0.07 respectively.

Prevalence of glaucoma
We observed a prevalence of 4.6% (31/680) of glaucoma in our study participants. About equal distribution of type of glaucoma, i.e. Primary Open Angle Glaucoma (POAG), Primary Angle Closure Glaucoma (PACG) and Normotensive Glaucoma (NTG) was observed in our study participants. The prevalence of POAG and PACG was 1.3% and 1.2% respectively while NTG and secondary glaucoma was found in 1.2% and 0.9% of the patients. The prevalence of glaucoma among our study participant was found to be significantly associated with increasing age, positive family history as well as the history of angle closure. We did not observe it be associated with other demographic factors like gender, religion, education as well as clinical factors like history of other chronic diseases (Table 2).

We did a study among middle age to elderly population to find out the prevalence of glaucoma as well as to observed any associated factors. We observed an overall prevalence of glaucoma to be 4.6%. The various type of glaucoma, with POAG, PACG and NTG in 1.3%, 1.2% and 1.2% of population respectively while secondary glaucoma was the found in 0.9% of the patients. The prevalence of glaucoma among our study participant was found to be significantly associated with increasing age, positive family history as well as the history of angle closure.
The prevalence of glaucoma from previous studies has varied results. It was observed to be 2.3 – 4.7%   in India, with a prevalence of 4.2% researchers from Agra, near to our study area9. Some Central and Southern studies have reported a lower prevalence of glaucoma in compare to North India.14  International studies have a wide range of rates of glaucoma, varied from 0.94% in Nepal to 13.8% among US citizen.15 It was reported to be 1.95% among the ethnic Indian living in Singapore.16 A meta-analysis estimated the global prevalence of glaucoma as 3.54%.16  Although comparing this prevalence is difficult because of differences in definition, methodology, diagnostic equipment, genetic and environmental predisposition of glaucom,17  we concluded the prevalence of glaucoma we observed on the higher side. Among subtypes of glaucoma, in India the POAG is a predominant subtype, with a prevalence of POAG varying from 1.26 – 4.32% and PACG in 0.15 – 1.11% among various Indian subpopulation.18  We observed a equal distribution of PACG  and POAG subtypes in our study. 
Among the associated factors, the presence of glaucoma increased with advancing age of the patients. As the development of glaucoma is associated with progressive optic neuropathy and visual field loss, which is expected to worsen with increasing age. Although we did our study among middle age to elderly population, the prevalence of glaucoma in elderly patients was very high in comparison to the middle age group (7.4% vs 1.6%). Similar increase in the prevalence of glaucoma with advancing age has been reported in several studies. Indian studies like Andhra  Pradesh Eye Disease Study, Aravind comprehensive eye survey and Central India Eye and Medical Study  found a significant association with age and glaucoma, so did others in, Barbados Eye Study, and European Glaucoma Prevention Study.19 With increasing age, due to the higher risk of ocular hypertension and gradual distraction of optical nerve, the risk of glaucoma also increases. Early detection and treatment would be highly beneficial to a country like India, where these patients often present very late stage.20 Among all the socio-demographic factors, apart from the age of the patients, higher prevalence of glaucoma was observed in urban population, females, and lower socio-economic class, but it was not found to be statistically significant. These findings support the observations of previous studies done across various part of India and other countries.21,22
Among other factors, we also observed a strong relation of positive history of angle closure in patients as well as family history with the presence of glaucoma. A positive family history of glaucoma is a known risk factor for future glaucoma.24 Genetic predisposition of glaucoma also documented in researches.23 The same study observed positive family history to carry a relative risk of 3.69 times for being diagnosed with Open Angle glaucoma in siblings.24 While another study documented that about half of all POAG having a positive family history, with first degree relatives having 9 times increased risk of developing glaucoma.25 Further, a study from Germany found those having positive family history not only diagnosed but they were also significantly younger at diagnosis than without it.26 Although a recent study from Saudi found no variation of prevalence of glaucoma with age group.27 Several researchers also found a significant association between the attack of angle-closure and development of primary angle closure glaucoma (PACG).28 The smaller limbal and axial anterior chamber depth are highly associated with angle closure and angle closure glaucoma.29 Being more common among Asians than Caucasians or African population, PACG patients often land up in glaucoma blindness more than any other subtype of glaucoma. Among Caucasian too, PACG development is considered as long-term outcomes after acute primary angle closure  As the majority of PACG sufferers are asymptomatic, presenting late, patients with angle closer should be regularly screened.30 Although, we found glaucoma to be higher among patients with a history of hypertension, it was not found to be statistically significant. Similarly, no significant association was found with a history of diabetes mellitus too. These findings support studies had reported hypertension or diabetes not being a risk factor for glaucoma.   An international study had contrasting findings.24 Similarly, another study reported systemic hypertension to be a risk factor for glaucoma development.31 This may be because of their clinic-based studies, which may not give real a picture in the community. In regards to diabetes mellitus too, its association with glaucoma is controversial.32

Our study highlights a higher prevalence of glaucoma in our field study. Apart from this, its association with increasing age and positive family history and angle-closure, screening for glaucoma especially among person with high risk should be introduced a part of general screening during middle age. Being the most common irreversible cause of blindness, early diagnosis and management of glaucoma would yield better prognosis.

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