Prevalence of Glaucoma and Normative Data of Ocular Biometry in Elderly Population in Bangkok

Study Design and Population The Bangkoknoi Model Eye Project is a population-based cohort study conducted in 42 communities within the Bangkoknoi district, a suburban area of Bangkok, Thailand. Ethical approval was obtained from the Institutional Review Board of the Siriraj Hospital Faculty of Medicine, Mahidol University (COA No. SI 077/2024) according to the principles of the Declaration of Helsinki. The study was prospectively registered to Thai Clinical trial registration on July 19, 2023.

The project was partially funded by the National Health Security Office (NHSO), the Siriraj Social Responsibility Fund, and the Siriraj Research Development Fund (grant number R016733016), Siriraj Hospital Faculty of Medicine, Mahidol University.

The BANMOP community network management team, consisting of researchers and local coordinators, organized meetings with community leaders to facilitate the implementation of the study. The study was communicated through community leaders and the Bangkoknoi District Bureau to encourage voluntary participation. Using a convenience sampling approach, people aged ≥50 years from the 42 communities were invited to participate.

All examinations were performed using a mobile ophthalmic survey unit established at each community site, including community centers and schools, between April and August 2024.

Medical and Ocular History Participants were interviewed to obtain medical and ocular history, including previous eye diseases, ocular trauma, previous or current ophthalmic treatments or surgeries, and systemic comorbidities such as diabetes mellitus, hypertension, and dyslipidemia.

Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA) were measured using standardized protocols. Automated refraction was performed using an autorefractometer (AR-610; Nidek Co., Ltd., Tokyo, Japan). Blindness was defined as a BCVA worse than logMAR 1.3 (Snellen equivalent <3/60).

Intraocular Pressure and Posterior Segment Imaging Intraocular pressure (IOP) was measured by experienced technicians using a noncontact pneumotonometer (CT-60 computerized tonometer; Topcon Ltd., Tokyo, Japan). At least three measurements were obtained for each eye and the mean value was used for analysis.

Color fundus photographs of the macula and optic disc were obtained using a fundus camera (CR6-45NM; Canon Inc., Tokyo, Japan). Spectral-domain optical coherence tomography (SD-OCT; Heidelberg Engineering, Germany) was performed to image the optic nerve head and macula using standard acquisition protocols. Because additional examinations, including Goldmann applanation tonometry (GAT), glaucoma module premium edition OCT (GMPE), and dark-room anterior segment OCT (AS-OCT), were not feasible for all participants within the constraints of a community-based mobile survey, these investigations were performed in a subset of participants using a convenience sampling approach. Comprehensive slit-lamp biomicroscopy was performed by ophthalmologists. Goldmann applanation tonometry (GAT) was performed by glaucoma specialists in the selected subset of participants.

Anterior Segment Assessment The depth of the anterior chamber was initially assessed using the van Herick method. Eyes with a peripheral anterior chamber depth less than one-quarter of the corneal thickness underwent gonioscopy, performed by experienced ophthalmologists using a 4-mirror goniolens. Anterior segment optical coherence tomography (AS-OCT) was performed under standard room lighting conditions to evaluate anterior chamber angle parameters, anterior chamber depth (ACD), central corneal thickness (CCT) and lens thickness (LT). Dark-room AS-OCT imaging was also performed in a subset of participants selected using convenience sampling.

Glaucoma Definition and Classification Glaucoma suspects were defined as individuals with suspicious glaucomatous features of the optic nerve head, including a cup-to-disc ratio >0.6, inter-eye asymmetry >0.2, localized neuroretinal rim loss, defects of the retinal nerve fiber layer, and/or IOP >21 mmHg (confirmed by GAT) with or without the corresponding SD-OCT abnormalities. All suspected glaucoma patients were referred to Siriraj Hospital for further evaluation, including Humphrey visual field (HVF) testing (SITA 24-2) and comprehensive examination by glaucoma specialists for definitive diagnosis. Glaucoma was defined by the presence of glaucomatous optic neuropathy (structural evidence) with corresponding glaucomatous defects of the visual field (functional evidence), and/or elevated IOP >21 mmHg measured by GAT. Glaucoma was classified as primary open-angle glaucoma (POAG), normal tension glaucoma (NTG), primary angle-closure glaucoma (PACG) and secondary glaucoma. Gonioscopy was performed in all cases of glaucoma, suspected glaucoma, and cases with angle-closure using the modified Shaffer grading system. Open angle glaucoma was defined by an open anterior chamber angle on gonioscopy.

Normal-tension glaucoma (NTG) was defined as glaucomatous optic neuropathy in eyes with open angles and untreated IOP <21 mmHg. Ocular hypertension (OHT) was defined as IOP >21 mmHg without structural or functional glaucomatous damage.

Primary angle-closure disease (PACD) was defined as an occludable or closed anterior chamber angle, characterized by invisibility of ≥180° of the posterior trabecular meshwork on gonioscopy. PACD was further classified into primary angle-closure suspect (PACS), primary angle closure (PAC), and primary angle-closure glaucoma (PACG).

Secondary glaucoma was defined as glaucoma with an identifiable underlying cause. Pre-existing glaucoma cases were confirmed based on current glaucoma medications or review of medical records at Siriraj Hospital.

Statistical analysis was performed using SPSS for Windows, version 29.0 (SPSS Inc., Chicago, Illinois, USA). Continuous variables were summarized as mean ± standard deviation (SD), while categorical variables were presented as frequencies and percentages. Comparisons of proportions between groups were performed using the chi-square test or Fisher's exact test, as appropriate. Logistic regression models were used to evaluate associations between the presence of glaucoma and potential risk factors, including continuous variables (e.g., intraocular pressure) and categorical variables (e.g., unilateral blindness). The agreement between continuous variables were compared using intraclass correlation coefficient. All P values are 2-sided, and statistical significance was defined as P < 0.05.