Study: High prevalence of cataracts continues

Issue: September 2008

G.V.S. Murthy

In India, nearly 74% of adults 60 years and older have cataracts or have undergone cataract surgery, according to a population-based study. Women have a significantly higher prevalence than men, and nuclear cataract is the most common type.

Age-related macular degeneration, however, was shown to be rare, a finding that may be partly attributed to India’s relatively short life expectancy.

The INDEYE Study, conducted in Delhi to represent northern India and Pondicherry to represent southern India, detailed the rates and risks of cataract and AMD.

G.V.S. Murthy, MBBS, MD, MSc, and other members of the research team presented preliminary study results at this year’s All India Ophthalmological Society conference in Bangalore.

In interviews with Ocular Surgery News, Dr. Murthy and fellow investigators Astrid E. Fletcher, PhD, Ravilla D. Ravindran, MD, and Badrinath Talwar, MD, discussed the prevalence of cataracts and AMD, and examined risk factors for cataracts.

Dr. Fletcher served as the principal investigator, with Drs. Murthy and Ravindran leading the investigation in Delhi and Pondicherry, respectively. Dr. Talwar assisted in the clinical examinations in Pondicherry.

Dr. Fletcher recalled investigators’ dismay upon encountering the high incidence of cataract amid ongoing initiatives to stem the disease.

“Despite all the efforts of the national program for the control of blindness in India, which have made a huge impact in many ways, our study, which was in the older population, the over 60s, still showed a high proportion of untreated cataracts,” she said.

Dr. Fletcher suggested that there may be insurmountable barriers in patients’ access to cataract surgery.

“It isn’t the cost of the surgery that is so much the problem, it may be other factors such as the costs of family members to accompany somebody to the hospital,” she said.

Study design and protocols

The INDEYE Study was conducted between 2004 and 2006. After administering a questionnaire, investigators selected 3,072 patients (1,460 men and 1,612 women) in Delhi and 3,257 patients (1,512 men and 1,745 women) in Pondicherry, Dr. Murthy said.

Patients underwent a clinical examination, anthropometry, visual acuity measurement, digital imaging of cortical and posterior subcapsular opacities, photography of nuclear opacities and fundus photography of the retina, macula and disc, Dr. Ravindran said.

The questionnaire was used to collect demographic and environmental data. Patients also gave blood samples that were tested for antioxidant levels.

Objectives and protocols for the INDEYE Study were tested in the Feasibility Study, a 2003 pilot survey conducted in a rural area of Haryana.

Before embarking on the INDEYE Study, investigators increased the target population age from 50 years, as used in the feasibility study, to 60 years and older, Dr. Murthy said.

Age and gender

The overall prevalence of cataract — including operated cataract — in those older than 60 years was 73.6% (75.2 % in Delhi and 72% in Pondicherry), Dr. Murthy said. Among patients older than 70 years, 81% of men and 85.8% of women in Delhi, and 61.2% of men and 68.5% of women in Pondicherry had fairly advanced nuclear cataracts, the study showed.

“Three out of every four individuals [aged older than 60 years] in this country do have a cataract,” Dr. Murthy said at the meeting. “That is the challenge. We know cataracts exist. We know cataract surgery rates are increasing in this country. We also know that significant proportions are still untreated.”

Among those 70 years and older, 11.8% of men and 13.9% of women in Delhi, and 14.7% of men and 18.2% of women in Pondicherry had cortical cataract. Also, 33.7% of men and 42% of women in Delhi, and 26.1% of men and 34.4% of women in Pondicherry had posterior subcapsular cataracts, he said.

Overall, women had a higher risk of having any cataract type, he said, attributing the disparity to women formerly having less access to cataract surgery than men.

“We find that as age increases, both among the men and women, both at the northern site as well as the southern site, you find that there is an increase in the prevalence of nuclear cataract,” he told OSN. “We know that the people whose eyes we couldn’t grade tended to be the older people who got the most severe opacities.”

Dense cataracts hindered imaging of lenticular opacities and retinal structures.

“That is a problem, which means that lens opacities are still a major problem in India,” Dr. Murthy said, adding that the number of fundus images that could not be graded increased with age.

Risk factors for cataracts

The study found that cooking fuel, midday sun, tobacco use and low levels of vitamin C were associated with a higher risk of cataracts.

“The one thing that had a very strong correlation in the study was the exposure to cooking fuel,” Dr. Ravindran said. “We looked in the South at the association of cataract with cooking fuel, and there’s a strong correlation of people having cataract if they’re using unclean fuel. The risk to the patient is about 1.8 times compared to using only clean fuel, like using only kerosene stoves or liquefied petroleum gas.”

Patients in Delhi had a 1.02 times higher risk from using unclean fuels. Also, residents of Pondicherry who always used unclean fuels had a 3.18 times higher risk of cataract, compared with a 1.41 times higher risk in Delhi.

Midday exposure to sunlight also proved to be a risk factor, they found.

The type and duration of tobacco use also played a role. For example, residents of Pondicherry who used tobacco at any time in their lives had a 1.63 times higher risk of cataract, compared with a 1.31 higher risk in Delhi. Tobacco chewing was more common in Pondicherry (35%), while bidis were more prevalent in Delhi (48%).

In Pondicherry, tobacco chewing elevated the risk of cataract 1.67 times. Bidis increased the risk of cataract in Delhi 1.3 times. Past hookah use also increased the risk of cataract in Delhi by 1.46, according to the study.

Dr. Fletcher said there is a link between cataracts and blood levels of antioxidants, particularly vitamin C.

“I’m struck by the fact that this older population in India has … low levels of vitamin C and what the implication is for the health,” she said. “Ophthalmologists tend to think of the eye, but there are all of these other important factors that relate to not just vitamin C and its relationship to the eye but also vitamin C and its possible effects on general health.”

Prevalence of AMD

Dr. Talwar discussed the significance of low AMD rates in the study and the difficulty in grading eyes for AMD because of the high prevalence of dense cataracts, which hampered photography of the fundus.

“The prevalence of late stage AMD is so low that we can’t really say for sure whether there was any kind of associated risk factor,” he said.

Dr. Fletcher said the current rate of late-stage AMD in the INDEYE population is 0.9%, or 1.1% to 1.2%, based on the number of eyes that could be graded. Eyes that could not be graded because of dense cataracts or corneal opacities were not included. The macula could not be graded in 27% of eyes.

Dr. Murthy partly attributed the low incidence of AMD to India’s short average life expectancy.

“To actually have AMD as a major problem, you have to live much longer than people, in general, live in India,” he said. “The proportion of the population over 70 is miniscule right now. Once the life expectancy increases, then obviously AMD would become a major problem.”

However, focusing on an age-specific portion of the population, not the entire population, gives a more reliable assessment of AMD rates, Dr. Fletcher said.

“I agree that we wouldn’t have had as many people over 80 as we would have in comparable Western populations, but as long as you’re quoting age-specific rates, it should be like for like,” she said.

Further data from the INDEYE Study, particularly on risk factors, are expected to be released in late 2008.

For more information:

Astrid E. Fletcher, PhD, can be reached at London School of Hygiene and Tropical Medicine, Room 108, Keppel St., London WC1E 7HT, United Kingdom; +44-20-7927-2253; fax: +44-20-7580-6897; e-mail: astrid.fletcher@lshtm.ac.uk.

G.V.S. Murthy, MBBS, MD, MSc, can be reached at Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110 029 India; +91-11-26588500; e-mail: gvsmurthy2000@yahoo.com.

Ravilla D. Ravindran, MD, and Badrinath Talwar, MD, can be reached at Aravind Eye Hospital, Cuddalore Main Road, Thavalakuppam, Pondicherry 605 007 India; +91-413-2619100; fax: +91-413-2618848; e-mails: rdr@pondy.aravind.org, badri@pondy.aravind.org.

Reference:

Murthy GV, Gupta SK, et al. Prevalence of lens opacities in North India: the INDEYE feasibility study. Invest Ophthalmol Vis Sci. 2007; 48:88-95.