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Surgeon: Population of India may have increased risk of angle-closure glaucoma
Screening and prophylactic treatment of at-risk patients would be a great burden for the Indian health care system.
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Glaucoma is increasingly recognized as a major cause of ocular morbidity in India, but the country lacks the infrastructure and resources for detecting at-risk patients and treating the disease, according to one Indian ophthalmologist
Primary angle-closure glaucoma (PACG) is of particular concern in India because it may have an incidence equal to or greater than primary open-angle glaucoma (POAG), said Ravi Thomas, MD, of Hyderabad.
Dr. Thomas told Ocular Surgery News that population-based studies have reached differing conclusions regarding the incidence of PACG in India, and the discrepancies may be due to the differing definitions and methodologies used.
Whatever the differences, a large portion of the Indian population is known to have occludable angles, which predispose patients to PACG, he said.
“Clinically, in the hospital as well as in a prevalence study, it was felt that PACG was as common as primary open-angle glaucoma (POAG),” he said.
Further complicating the situation, few ophthalmologists in India specialize in glaucoma, and most of those who do practice in urban areas. Also, Dr. Thomas said, ophthalmology residents are not taught, and most Indian ophthalmologists do not routinely perform, the comprehensive eye examinations recommended in the Preferred Practice Patterns of the American Academy of Ophthalmology and other organizations. Because IOP measurements, gonioscopy and optic disc findings are needed to diagnose glaucoma, particularly PACG, cases are often missed.
“If the diagnostic test is not done, we can’t recognize the disease. In the absence of gonioscopy we will miss all the PACG and primary angle closure (PAC). If we catch the PACG with disc and field exam, without gonioscopy, we will label it as POAG,” Dr. Thomas said.
Population-based screening programs would be too expensive to be undertaken in a country with a population of more than 1 billion, he said.
“We should, however, do opportunistic screening and case detection. Whenever a patient sees an ophthalmic caregiver, the patient should undergo a complete ophthalmic examination, including IOP, fundus exam and if necessary visual field and gonioscopy. This will help identify a large proportion using existing resources,” Dr. Thomas said.
Population-based studies
It has been said that PACG causes more cases of blindness worldwide than POAG, Dr. Thomas noted. However, the natural history of occludable angles (in primary angle closure suspects, or PACS) and PAC is not clear because there have been few population-based studies on the natural history of PACS.
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He also noted that the type of PACG may differ among ethnic populations. For example, PACG among Chinese populations may be different from that seen in India. However, PACG as a whole is probably more common worldwide and causes more blindness than POAG, he said.
In a presentation during the International Glaucoma Symposium in Barcelona earlier this year, Dr. Thomas said angle closure may be more common in the West than previously thought. The Egna-Neumarkt Study, which included patients from a rural community in Italy, found that occludable angles were more frequent and the prevalence of PACG much higher than previously believed, accounting for approximately 25% of all glaucoma cases. Dr. Thomas noted that the study was actually screening for POAG, not looking for angle closure.
“A more appropriate conclusion might be that 25% of patients from that population referred for screening for open-angle glaucoma have angle closure,” he said in his presentation.
According to Dr. Thomas, the prevalence of glaucoma, including PACG, has been studied among varying Indian populations, but studies do not agree on the rate of progression to glaucoma or what risk factors indicate who is more at risk.
The Andhra Pradesh Eye Disease Survey found that PACG was more common than previously recognized, but POAG remained the most common form of glaucoma. The Vellore Eye Study, in contrast, described PACG as more than four times more prevalent than POAG.
“I feel that a lot of the differences can be explained by definitions and methodology. If we account for this, the results are more similar,” Dr. Thomas said.
Vellore Eye Study
In the Vellore Eye Study, Dr. Thomas and colleagues examined 972 randomly selected people from the population of Vellore, India. Occludable-angle PACS was defined as trabecular meshwork visible for less than 180° in an otherwise normal eye. Patients exhibited no peripheral anterior synechia with normal optic disc and IOP readings.
Primary appositional angle closure was defined as a PACS and raised IOP, but no peripheral anterior synechia (PAS). Primary synechial angle closure was similarly defined, with or without raised IOP, but also showing PAS. Presence of disc and visual field changes was not required.
PACG was defined as appositional or synechial angle closure with damage to the optic disc and visual field. Disc changes and visual field changes were mandatory for this diagnosis, he said.
At the start of the Vellore Eye Study, Dr. Thomas and colleagues identified 118 patients (10.5%) with occludable angles and 37 (3.8%) with PAC. These and 110 normal patients were invited to participate in 5-year follow-up. Of the PAC suspects in the study, 50 of the 118 patients returned for the 5-year follow-up examination. Of these, 38 had bilateral occludable angles and 12 had unilateral occludable angles.
In 2000, Dr. Thomas said, 22% of patients who were reexamined developed PAC. None developed an acute attack or disc or field changes.
“Compared to patients with open angles, primary angle-closure suspects with occludable angles have 24 times the risk of progression to angle closure,” he said during his IGS presentation.
Prophylactic treatment
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According to Dr. Thomas, laser peripheral iridotomy (LPI) — the current accepted treatment for PAC and PACG — has been suggested to treat all PACS (occludable angles) cases. However, such treatments must be based on the natural history of the disease as well as the risk of progression from angle closure to blindness, he said.
He said LPI has shown success with minimal complications in preventing progression to PAC. However, the cost of prophylactic LPIs would be a burden on the Indian health care system. Considering the prevalence of occludable angles, one in 10 people in the entire population of India above the age of 30 years would have to undergo LPI.
“PAC and PACG reflect pathology and have to be treated,” Dr. Thomas said. “The question is how to treat PACS. We cannot do iridotomies for all the PACS in the country, and neither could my small series identify features that mandated treatment.”
“I don’t think laser iridotomy is needed for all PACS,” he said. “Perhaps in special situations, like when repeated dilations are required for retinal examination or lasering, and there are social and socioeconomic considerations. We would have to buy YAG lasers for every district hospital. This naturally would overburden an already stressed and almost nonexistent delivery system.”
He said his study provided a natural experiment of LPI vs. no LPI in PAC. The small numbers prevented a statistically significant result, but clinically it would appear to confirm that iridotomy is beneficial, he added.
For Your Information:References:
- Ravi Thomas, MD, can be reached at the L.V.Prasad Eye Institute, L.V.Prasad Marg, Banjara Hills, Hyderabad - 500 034, India; (91) 40-2354-8267; fax: (91) 40-2354-8271; e-mail: ravithomas@lvpei.org.
- Bonomi L, Marchini G, et al. Prevalence of glaucoma and intraocular pressure distribution in a defined population. The Egna-Neumarkt Study. Ophthalmology. 1998;105:209-215.
- Dandona L, Dandona R, et al. Angle closure glaucoma in an urban population in southern India. Ophthalmology. 2000;107:1710-1716.
- Thomas R, George R, et. al. Five year risk of progression of primary angle closure suspects to primary angle closure: a population based study. Br J Ophthalmol. 2003;87:450-454.
- Jonas JB, Thomas R, et. Al. Optic disc morphology in south India: The Vellore eye study. Br J Ophthalmol. 2003;87:189-196.
- Thomas R, Parikh R, et. al. Population-based screening versus case detection. Indian J Ophthalmol. 2002;50:333-237.
- Thomas R, Paul P, Muliyil J. Glaucoma in India. J Glaucoma. 2003;12:81-87.