Prevalence of glaucoma in Thailand: a population based survey in Rom Klao District, Bangkok

Abstract

Aim: To determine prevalence, demography, mechanism, and visual morbidity of glaucoma in urban Thai people.

Methods: 790 subjects aged 50 years or older from Rom Klao district, Bangkok, Thailand, were enumerated in a population based cross sectional study. Each subject underwent the following investigations: visual acuity, visual field testing, slit lamp examination, applanation tonometry, gonioscopy, and an optic disc examination after mydriasis. Main outcome measures included visual acuity (logMAR), visual fields, intraocular pressure (IOP), gonioscopic characteristics, vertical cup/disc ratio (VCDR), prevalence of types of glaucoma. Glaucoma was diagnosed on the basis of optic disc appearance and visual field defects. In eyes in which the optic disc could not be examined, glaucoma was diagnosed when visual acuity was <3/60 and either IOP >99.5th percentile or there was evidence of previous glaucoma surgery.

Results: 701 subjects were examined (response rate 88.7%). In eyes with "normal" suprathreshold visual fields, the mean IOP was 13.3 mm Hg (97.5th percentile = 20 mm Hg). The 97.5th and 99.5th percentiles of VCDR were 0.72 and 0.86 respectively. Of the 701 subjects examined in the clinic, 27 had glaucoma (3.8%, 95% CI: 2.5 to 5.6), 16 had primary open angle glaucoma (POAG, prevalence 2.3%, 95% CI: 1.3 to 3.7), six were primary angle closure glaucoma (PACG, prevalence 0.9%, 95% CI: 0.3 to 1.9), and five were secondary glaucoma (SecG, prevalence 0.7%, 95% CI: 0.2 to 1.7). Among the 43 unilaterally blind subjects, glaucoma was the cause in five subjects (12%). One subject was bilaterally blind due to glaucoma (prevalence 11%, 95% CI: 0.3 to 61.9). 28 people (4%) were glaucoma suspects on the basis of optic disc appearance and six on the basis of visual fields only. 98 subjects (14%) had "occludable angles" in either eye, 22 of whom had primary angle closure (PAC, prevalence 3.1%, 95% CI: 1.9 to 4.7); 14 had peripheral anterior synechiae in either eye and eight had ocular hypertension (OHT).

Conclusions: POAG accounted for 67% of all glaucoma, PACG 21%, and secondary glaucomas 12%. Glaucoma was the second most common cause of severe unilateral visual loss.

Figure 1

The “normal” distribution of intraocular pressure (in subjects with normal suprathreshold visual fields in both eyes; right and left eyes included).

Figure 2

The prevalence of primary open angle glaucoma (POAG) with age in Thailand (diamonds) and Singapore (squares), presented with the assumed prevalence made by Quigley in 1996 (crosses).

Figure 3

The relative proportion of primary glaucoma attributable to POAG, PACG, and SecG found in Mongolia and Singapore (unpublished data from Foster PJ, 2000), Thailand (current study), India (unpublished data from Dandona L, 2000) and Ireland. All data are directly standardised to the urban population of Thailand.

Figure 4

The projected number of people in Thailand affected by glaucoma from year 2000 until year 2050 (demographic data obtained from age and sex specific country population data9). Figures given were calculated using age and sex specific glaucoma prevalence figures for all glaucomas from Table 5 (squares, men; diamonds, women).