Journal of Glaucoma:
Glaucoma in India: Estimated Burden of Disease
George, Ronnie MS; Ve, Ramesh S. MPhil; Vijaya, Lingam MS
Glaucoma Services, Medical and Vision Research Foundations, Chennai, India
Reprints: Lingam Vijaya, MS, Director, Glaucoma Services, Medical Research Foundation, Sankara Nethralaya, 18, College Road, Chennai, India-600 006 (e-mail: firstname.lastname@example.org).
Received for publication October 9, 2008; accepted September 26, 2009
Over the last decade the prevalence of glaucoma has been reported by the Vellore Eye Survey, Andhra Pradesh Eye Disease Study, Aravind Comprehensive Eye Survey, Chennai Glaucoma Study, and West Bengal Glaucoma Study. There have been some differences largely because of methodologic variations. We use the reported age and gender stratified prevalence estimates from these studies and the Indian population census estimates to calculate the number of persons with glaucoma or at risk of the disease in the country. On the basis of the available data, we estimate that there are approximately 11.2 million persons aged 40 years and older with glaucoma in India. Primary open angle glaucoma is estimated to affect 6.48 million persons. The estimated number with primary angle-closure glaucoma is 2.54 million. Those with any form of primary angle-closure disease could comprise 27.6 million persons. Most of those with disease are undetected and there exist major challenges in detecting and treating those with disease. In the light of the existing manpower and resource constraints, we evaluate options for improving case detection rates in the country.
Glaucoma is the second leading cause of blindness worldwide. Twelve million persons worldwide are estimated to be blind because of the disease.1 With the exception of Asia, Primary open angle glaucoma (POAG) is far more common than Primary angle-closure glaucoma (PACG) worldwide.2 In Asia, population-based studies from China and India have reported that a significant percentage of the population suffer from angle-closure glaucoma.3–8 Foster and Johnson have estimated that an approximate of 28.2 million persons have angle-closure disease in China.3,4 Those at risk of angle-closure disease comprise a significant proportion of the adult population. PACG is a more blinding disease than POAG, at least in the Chinese population.3,4 There are differences in the rates of acute angle closure among persons of Indian origin and of Chinese origin.9 There is relatively little information about the burden of disease in India.
Over the last decade numerous population-based studies from India have emerged, prevalence of glaucoma and various eye diseases from the Vellore Eye Survey (VES),5 Andhra Pradesh Eye Disease Study (APEDS),8,10 Aravind Comprehensive Eye Survey (ACES),11 Chennai Glaucoma Study (CGS),6,7,12,13 and West Bengal Glaucoma Study (WBGS)14 have been published. These studies used differing methodology and diagnostic criteria for glaucoma (Table 1).
The first population-based glaucoma prevalence study in India was the Vellore Eye Study conducted in the town of Vellore in the state of Tamil Nadu in southern India.5 The VES was the first study to highlight the potentially large burden of angle-closure disease reporting that 10.3% of the population had occludable angles or angle-closure glaucoma.5 It confirmed the clinical suspicion that angle-closure disease was an important health problem in the country. A summary of the prevalence of primary glaucomas as reported by the various studies is provided in Tables 2 and 3.
There are methodologic differences between these studies that could account for some of the variability. The wide differences in angle closure disease prevalence could be technique related. Standard testing conditions (dim illumination, a shortened slit beam that does not fall on the pupil) and expertise with the technique are factors that potentially affect diagnosis. Studies that were carried out by persons with specialized glaucoma training have consistently reported higher rates of primary angle-closure suspects (PACS) and primary angle closure (PAC).5–7 We estimate the number of persons with glaucoma and angle-closure disease in India based on published prevalence studies.
Reported results from all population-based studies were considered for inclusion. For inclusion, the diagnostic criteria should have been IOP independent. Gonioscopy was required to have been part of the examination protocol for all subjects. Only those studies that included persons aged 40 years and older were included to generate estimates, as 128 million of the estimated 308 million person aged 40 years and above in the country are aged between 40 to 49 years. Age stratified prevalence estimates were available for all studies except the VES.5 Where available, age and gender stratified data were used to generate the estimates. The APEDS reported age stratified data.8,10 The reported male: female proportion among those affected with disease was applied to each age cohort to derive the gender distribution for glaucoma. The estimated age and gender stratified mid year population for India was obtained from US Census Bureau projections.16 As the rural urban distribution for the population was not available, the rural urban distribution of the population reported by the Indian census in 200117 was applied to the estimated mid year population of India for 2008 to derive approximate numbers of rural and urban residents in each age and gender subgroup. Percentage prevalence estimates age (and gender where available) adjusted to the estimated mid year population of India for 2008 are reported for the selected studies (Table 4). For estimation of disease burden in the country, the number of persons with disease were calculated using the reported age (and gender where reported) prevalence. The mean of the estimates for each age group were then used to arrive at the estimated population burden. Estimates were separately calculated for the rural and the urban populations based on the location in which each study was conducted.
As detailed age and gender stratified information on secondary glaucoma and ocular hypertension have not been reported, a rough estimate of the number of persons affected was derived from the percentage with secondary glaucoma. Those with pseudoexfoliation glaucoma were included as secondary disease.
Among the studies used to calculate prevalence estimates for POAG, the APEDS study definitions for definite glaucoma correspond to the Level 3 diagnosis on International Society of Geographical and Epidemiologic Ophthalmology (ISGEO) (Disc and field changes). The actual figures are likely to be higher. The ACES, POAG definitions included those with optic disc changes suggestive of glaucoma with visual field damage, in those without visual field data glaucomatous optic disc damage were considered sufficient for diagnosis. The overall estimated prevalence for POAG could possibly be an underestimate because of these reasons. The number of persons with POAG is estimated to be 6.48 (95% CI: 5.06-7.89) million (Table 5). The prevalence increased with age showing an exponential rise in the oldest age groups (Fig. 1). These figures are lower than those estimated by Quigley and Broman,2 however, there is a 95% CI's overlap.
The definitions of occludable angle and manifest PACG were again based on definitions suggested by the ISGEO15: PACS, an eye in which the posterior trabecular meshwork was not seen for more than 180 degrees on gonioscopy; PAC, an eye with PACS and peripheral anterior synechiae and/or elevated IOP without glaucomatous damage of the optic disc, iris whorling (distortion of the radially orientated iris fibres), “glaucomfleken” lens opacities, or excessive pigment deposition on the trabecular surface. PACG, PACS with evidence of glaucoma as defined by the ISGEO. PACG affects an estimated 2.54 (95% CI: 1.88-4.28) million persons. Those with some evidence of damage—raised IOP, peripheral anterior synechiae or glaucomatous disc, or field changes comprise 6.62 (95% CI: 4.78-9.41) million persons. The estimated total number of persons with angle closure disease is 27.66 (95% CI: 24.00-30.92) million (Table 6). The prevalence of PACG and PAC show a linear increase with age (Fig. 2). The figures for PACG are lower than those estimated by Quigley and Broman,2 however the 95% CI's overlap.
For angle closure disease only the CGS6,7 reported age wise data for all glaucoma subtypes using the ISGEO classification.18 The VES5 classified those with PAC and PACG as PACG, the APEDS8 classified those with IOP greater than 22 mm Hg or IOP disc and field changes in those with occludable angles as having PACG. This definition would include some of those now classified as PAC but would exclude those with synechial closure in the absence of raised IOP, disc, or field changes, potentially resulting in underestimation of the prevalence of PAC and PACG combined. The ACES11 defined PACG if it met at least 2 of these criteria: glaucomatous optic disc damage or glaucomatous visual field defects in combination with anterior chamber angle partly (9 clock hours) or totally closed, appositional angle closure, or synechiae in the angle along with the absence of signs of secondary angle closure.
The rates of OHT have been reported from the VES,5 APEDS,10 and ACES.11 There are wide variations in the reported rates. The APEDS10 reported the lowest rate of 0.42%(95% CI: 0.11,1.12%). There were 1.1%(95% CI: 0.84,1.41%) persons with OHT among those aged 40 years and older in ACES.11 The VES,5 reported that 3.08%(95% CI: 1.98,4.19%) were ocular hypertensive. Using the mean crude prevalence of 1.53% for OHT obtained from these studies, an estimated 4.7 million persons could be ocular hypertensive.
The rates of secondary glaucoma have been reported by some studies. The WBGS14 reported a rate of 0.08%, APEDS10: 0.21% in those aged 30 and above and 0.3% in the ACES.11 The ACES in addition, reported that 0.06% of those examined had absolute glaucoma and 0.44% had pseudoexfoliation glaucoma.18 The prevalence of pseudoexfoliation has also been reported by the CGS,19 and the APEDS.20 In the rural arm of the CGS, 1.38% of the population had glaucoma with aphakia or pseudophakia.21 An additional 0.49% had pseudoexfoliation glaucoma.20 On combining these reports the ACES19 reported a cumulative crude prevalence of 0.80% and the CGS19 1.87%. There is a wide range in the prevalence of reported disease. The mean crude prevalence (0.74%) was used to calculate crude estimates of those affected with secondary glaucoma, this was an estimated 2.28 million persons. The estimates for ocular hypertension and secondary glaucoma are crude and likely to be inaccurate as the age and gender wise data were not available for these conditions.
Blindness Owing to Glaucoma
Glaucoma is the second leading cause of blindness in the adult population in India. The proportion of those diagnosed to be bilaterally blind because of POAG in the APEDS,10 ACES,11 CGS (rural),12 CGS (Urban),13 and WBGS14 was 11.1%, 1.6%, 3.2%, 1.5%, and 5.2%, respectively. The corresponding figures for PACG for APEDS,8 CGS (rural),6 and CGS (Urban)7 were 16.6%, 2.9%, and 5.9%, respectively. The WBGS14 reported only 3 cases of PACG none of whom were blind. In those studies that reported significant rates of angle closure disease PACG caused between 1 and 4 times the proportion of blindness that POAG did. The proportion of those who were blind because of the disease was calculated for each study (Table 7). PACG on an average produced 2 times the proportion of bilateral blindness than POAG.
Detection of Disease
A vast majority of persons with glaucoma in India are undiagnosed. The ACES11 reported that 50% of those diagnosed to have POAG in their study cohort had undergone an eye examination by an ophthalmologist in the past. Less than 20% of them had been detected to have disease at the time of an earlier examination. Although none of them had undergone an examination in the year preceding the study examination, it is reasonable to assume that at least some of those diagnosed would have had apparent disease at the time of examination. One possible reason for the poor detection rates could be the overemphasis on IOP measurements in the diagnosis of glaucoma in India.22 “Normal” IOP (often measured using the Schiotz tonometer) is considered to preclude a diagnosis of glaucoma. Further more, the failure to detect glaucoma could be attributed to the lack of a comprehensive ophthalmic examination. All the population-based studies reported that a large proportion of those diagnosed to have POAG were actually measured to have IOP readings at presentation that were in the statistically normal range.12,13 Unless they have an optic nerve head evaluation they would remain undiagnosed. What is an even greater cause for concern is that among the 5 persons who were diagnosed to have glaucoma in the urban arm of the CGS, 2 (40%) actually had angle closure glaucoma.7 These are persons who were diagnosed to have glaucoma and were on treatment. Gonioscopy is recommended as a matter of routine for those diagnosed to have glaucoma. The misdiagnosis in these individuals indicates that gonioscopy is not routinely carried out for glaucoma patients or that it is not carried out with adequate training, perhaps secondary to poor primary training.23
The prevalence of both cataract and glaucoma increase with age and a person who undergoes cataract surgery is unlikely to follow-up for a routine evaluation for glaucoma because of poor awareness about the disease and poor access to eye care facilities.24 Robin et al25 report that from the ACES only one third had undergone an eye examination at any time in their lives, yet three fourths of persons aged 40 years or older in this rural population required eye care services. Among those with established glaucoma in a clinic-based study, Lee et al26 found knowledge and perceptional barriers among glaucoma patients in south India to be the reason for missed visits in nearly 40% of those with poor follow-up among those studied. If this is the awareness level among those with glaucoma, awareness levels among those without established disease are likely to be worse.27
Thomas et al have in a recent article highlighted the lamentable state of residency training in a south Indian state.28 Despite the provision of equipment to ophthalmology departments and training to the trainers after an initial survey; a vast majority of residency programs, in the state that they surveyed, continued to provide substandard training when evaluated 8 years later. Although there are a number of hospitals that provide specialist fellowship training in various subspecialties, only a small proportion of those who complete residency do further training. Those who have received inadequate residency training are far more likely to provide inadequate levels of care to their patients for the duration of their professional career.28
In India there were an estimated 25 glaucoma specialists in 2001.29 On the basis of the existing full fledged glaucoma training programs in the country, we estimate that less than 100 additional specialists have been trained. Even with a diagnosis rate of less than 10%, keeping in mind the significant burden of disease in the country, it is apparent that most glaucoma is currently being managed by the 12,000 general ophthalmologists. Well trained General ophthalmologists are capable of managing glaucoma appropriately; improving residency training to acceptable standards would automatically ensure better detection rates in the community. There is also a huge disparity in the quality of training for ophthalmic assistants and optometrists in the country.30 The duration of training for an optometry degree or diploma ranges from 6 months to 4 years with similar variations in the quality of training. The optometrist is a primary contact for many of those who require spectacles. With few exceptions, most optical dispensaries offer no additional examination beyond refraction and spectacle prescription.30
These disparities in training are reflected in the wide variability in the quality of eye care services available. There are well equipped and staffed tertiary eye care centers with facilities comparable with that in any developed country. At the other end of the spectrum, there are eye care centers that do not have access to or do not use a slit lamp. A majority of ophthalmologists practicing in these centers have little or no exposure to currently acceptable standards of glaucoma diagnosis or care. Availability of equipment in the absence of the required skills for its use or in the interpretation of its results is another situation as described by Thomas et al.22,29
Rural urban disparities in availability of eye care services compound the problem. More than 70% of the Indian population resides in villages. Only 25% of ophthalmologists practice in rural India. The 1:100,000 ophthalmologist: population ratio for India is therefore, much worse in rural India.31 Women have been reported to have poorer access to eye care services in India.32 From our estimates, marginally fewer women have POAG as compared with men, however angle closure disease is far more common in women (17.1 million) as opposed to men (10.6 million). This inequality in access to care could potentially result in greater morbidity from glaucoma among women.
Another, perhaps more immediate, technique of improving detection rates would be to incorporate, into the cataract surgical program, components of a glaucoma examination.22,29 The cataract surgical program in the country targets the same age group of patients who are at risk for glaucoma and has reasonably good coverage in rural India too. Ensuring that even a significant percentage of those who are examined as part of a cataract surgical initiative, are evaluated for glaucoma would improve detection rates significantly. A state sponsored mandate that required measurement of IOP, anterior chamber depth, angle assessment and optic disc evaluation for all those who pass through cataract screening would, if implemented on the ground, provide a fillip to both detection rates and improve the average quality of an eye examination.
The large number of persons with undiagnosed angle closure disease in the country poses a daunting challenge. It is impractical to consider treating all those with PACS in the country. In addition to the low risk of progression,33 the inadequate information on the natural history of disease are reasons why the Asia Pacific Guidelines for glaucoma management do not advocate a YAG iridotomy (YAG LPI) in all those with PACS.34 Ongoing laser intervention studies in PACS, in China and Singapore, would provide information on the risks and benefits of treatment.35 Removal of the crystalline lens would prevent progression among those with PACS. An active cataract surgical program will make some inroads in those with PACS and significant cataract. However with existing reported disparities in the quality of cataract surgery,36–38 the surgical complications in eyes with angle closure disease are likely to be greater in those eye care facilities that have poorer outcomes.
However, there is a need to treat PAC and PACG.34 Here again, detection rates are dependent on the performance of a comprehensive eye examination and on gonioscopy skills. These need to be taught in our residency and optometry training programs.28,30 The van Herick39 technique alone is reasonably specific in diagnosing a narrow angle.40,41 It is easy to carry out but requires the availability of a slit lamp.39 Low-cost instruments available in the country provide a potential way forward in including this as routine protocol.
Treatment of POAG could be either medical or surgical.42 The availability of low-cost glaucoma medications is widespread.29 With sustained economic growth a larger proportion of the population would be able to afford medication. Cost considerations often dictate that lower cost brands are prescribed, there are concerns about the suboptimal concentration of antibiotic eye drops available and inappropriate environmental conditions for their storage.43,44 Inequivalence of the glaucoma generic equivalents is another cause for concern.45 Sleath et al24 report, in a survey of glaucoma patients from south India, 20 % had to travel for half an hour or longer to purchase their medication and 9% required to travel more than 2 hours to purchase their medication. A majority of those who participated in this study (60%) were urban residents; the access to pharmacies is likely to be much poorer in rural India. Primary surgery for glaucoma is an attractive alternative to those who have poor access to care and are unlikely to be able to undergo regular examinations.42 This could be incorporated into cataract surgical programs keeping in mind that marginally poorer outcomes have been reported for combined cataract and trabeculectomy surgery.46 However, on a mass scale the risk of surgical complications in both the early and late postoperative period, with a trabeculectomy is different from that for cataract surgery and postoperative protocols for trabeculectomy would need to be independent of those developed for cataract.45,47 The significant lifetime risk of bleb related infections47 should be weighed against the lifetime risk of blindness secondary to glaucoma. Treatment would need to be individualized on a case to case basis.
Rates for secondary glaucoma are sketchily reported for the Indian population. They range from 0.08% to 1.39%. The actual rates are likely to be higher. Secondary glaucoma may be responsible for a greater proportion of blindness as compared with primary disease. Improved cataract surgical services would potentially reduce the burden of iatrogenic surgery related glaucoma.21
The blindness rates reported for India are lower than those reported by Foster and Johnson3,4 These may, in part, be because of the low rates of acute angle closure in the country pointing to a more chronic form of the disease. Seah et al have reported that Indians had only half the hospital admission rates for acute angle closure as compared with the population of Chinese origin.9 The small number of individuals blind in each study results in wide confidence intervals for blindness rates and may contribute to the reported variations in prevalence.
On the basis of the available data, we estimate that there are approximately 11.2 million persons aged 40 years and older with glaucoma in India. An additional 28.1 million people have ocular hypertension, PACS, or PAC. Every eighth individual or nearly 40 million of the estimated 309 million people, aged 40 years or older in the country have glaucoma or are at risk of the disease.
Before community-based glaucoma and detection programs are planned, it is important to ensure that those who come into contact with an eye care professional, for any reason, are offered a comprehensive eye exanimation. Sensitizing the public at large of the importance of undergoing these investigations (eg, with applanation, gonioscopy, 3-dimensional stereoscopic optic nerve evaluation, and perimetry) is probably the best way of ensuring that we as eye care providers are under pressure to follow appropriate examination techniques as a routine.
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