Much glaucoma undetected in Thailand, study shows

Results of a population-based survey underscore glaucoma’s impact as a cause of visual impairment throughout Southeast Asia.

Many cases of glaucoma are undetected in Thailand, a recent study suggests. With an increase in the population over age 50 expected in the coming years, the number of undetected glaucoma cases is expected to rise as well, the authors say.

Rupert R. A. Bourne, BSc, FRCOphth, and colleagues at London’s Institute of Ophthalmology, conducted a population-based survey to determine the prevalence of glaucoma in Thailand and to evaluate its associated morbidity and ocular features.

Dr. Bourne told Ocular Surgery News in an e-mail interview that in Thailand glaucoma is the second most common cause of blindness after cataract. He noted 41% of all subjects in the study who had glaucoma were blind in at least one eye.

Additionally, 50% of the patients with primary angle-closure glaucoma (PACG) and 75% of patients with primary open-angle glaucoma (POAG) identified in the study had not been previously diagnosed.

“It highlights the fact that many cases of glaucoma are currently undetected in Thailand. In my opinion, glaucoma should definitely be addressed by [blindness prevention efforts],” Dr. Bourne said. “Certainly, awareness of undetected glaucoma should be promoted among ophthalmic personnel and the public at large. This is of particular importance given the aging population of Thailand. The number of males affected by glaucoma is expected to rise threefold, and fourfold for females, over the next 50 years. This is likely to impose a burden on the country in terms of costs of health care and costs to the individual and family.”

The authors of the study wrote: “The findings of this survey and these future projections emphasize the importance of glaucoma as a cause of visual impairment in Thailand and throughout Southeast Asia.”

Population-based study

From the Rom Klao district, about 35 km south of Bangkok, 701 patients were examined and included in the data analysis.

The authors noted that there was a significant difference in the number of men and women, as more women responded and were examined (P < .001).

Median vertical cup-to-disc ratio (CDR) among 498 patients who had normal suprathreshold visual fields was 0.45 with 97.5th and 99.5th percentiles of 0.72 and 0.86 respectively. The 97.5th percentile of CDR asymmetry was 0.21.

Mean and median IOP in patients with normal visual fields in both eyes, a total of 1,018 eyes, was 13.3 mm Hg.

Prevalence, mechanisms

Overall, 27 patients with glaucoma were identified, a prevalence of 3.8%. Of these, 16 (59%) were diagnosed with POAG, six (22%) with PACG and five (18%) with secondary glaucoma.

The authors reported that the number of male and female glaucoma cases suggested a preponderance of glaucoma among females. Following age standardization, no significant gender difference existed when all cases of glaucoma were considered. However, POAG was significantly more prevalent in women than men (P = .006).

Five (31%) POAG patients, three (50%) PACG patients and four (80%) secondary glaucoma patients had IOPs equal to or greater than the 97.5th percentile of the population with “normal” suprathreshold visual fields.

According to the study, another 22 patients were diagnosed as having primary angle-closure (PAC). Of these, 14 patients had peripheral anterior synechiae (PAS) in at least one eye and eight patients had IOPs greater than the population 97.5th percentile. Only one patient had both PAS and raised IOP.

The prevalence of glaucoma increased with age for both men and women. In patients age 50 to 59 years, 2.6% of men and 1.2% of women had glaucoma. This increased to 6.8% of men and 10.1% of women among patients age 70 years or older.

The ratio of POAG to PACG in this study (3.2:1) compared to a study of Singapore Chinese (1.6:1) and an Indian study (2.4:1), reflects findings closer to the glaucoma incidence study in Singapore, the authors said. In that study, Malays and Indians were found to be at a lower risk of symptomatic PAC in comparison to the Chinese population. It also reflects the findings of a hospital-based study in Thailand where the incidence of PACG was much lower than in Singapore Chinese.

Causes of blindness

Overall, 54 patients were unilaterally blind and 14 were bilaterally blind on presentation. Following refractive correction, 43 patients were unilaterally blind and nine remained bilaterally blind.

According to the study, cataract was the most common cause of blindness, causing unilateral blindness in 23 (53%) patients and bilateral blindness in five (55.5%) patients.

Glaucoma was the second leading cause of unilateral blindness. It caused blindness in five (12%) patients, while trauma resulting in secondary glaucoma caused three cases (7%).

For Your Information:

• Rupert R. A. Bourne, BSc, FRCOphth, can be reached at the Department of Epidemiology and International Eye Health, Institute of Ophthalmology, 11-43 Bath St., London, EC1V 5EL, England; (44) 20-7850-158001; fax: (44) 20-7250-3207; e-mail: rupert_bourne@hotmail.com.

Reference:

Bourne, RRA, Sukudom P, et. al. Prevalence of glaucoma in Thailand: A population based survey in Rom Klao district, Bankok. Br J Ophthalmol. 2003;87:1-6.