Glaucoma is a potentially blinding disease that affects 66 million persons worldwide. It is the second leading cause of blindness worldwide. The disease is characterized by typical changes in the optic nerve (the nerve that connects the eye to the brain) with associated visual field defects (the area seen by the eye). Since the outer portion of the visual field is the first to be affected and most types of glaucoma are asymptomatic the disease is often diagnosed once significant vision/field has been lost. Therefore, early diagnosis is essential so that treatment to halt/slow progression can be instituted.
Public health planning to develop strategies for early diagnosis and treatment of this disease in the population requires data on the prevalence, distribution and pattern of the disease. Existing data from India suggest that Indians have a different pattern of disease. Recent genetic studies from the West indicate that glaucoma has a hereditary component with specific genes identified from the affected persons. There is a paucity of such data from India . If such data were available it would be possible to identify persons at risk of developing the disease.
The Chennai Glaucoma study is a population-based study, designed with a view to gather information on the prevalence of glaucoma in rural and urban South India . The study, funded by Chennai Willingdon Corporate Foundation, commenced on 2 nd Nov 2000. Clinical work on the rural component started on 15 th June 2001. 7785 persons, above 40 years of age, from rural Tamil Nadu and Chennai city were examined at a special facility created at Sankara Nethralaya. 3924 subjects representing the rural south Indian population participated from 27 contiguous villages of Thiruvallur and Kancheepuram districts of Tamil Nadu. 3850 Urban subjects participated from 5 randomly chosen divisions from Chennai city.
Every patient underwent a detailed ophthalmic evaluation. Ophthalmic examination consisted of the following components/ tests:
(a) Ocular and medical history,
(b) Lensometry (Appasamy LM14 telescopic lensmeter, Chennai , India ) if necessary,
(c) Refraction and recording of best-corrected visual acuity using the Modified ETDRS chart (Light House Low Vision Products, New York , NY , USA ),
(d) Scanning Laser Polarimetry using the NFA GDx (GDx Version 1.0.16, Laser Diagnostic Technologies, San Diego , CA , USA )
(e) Frequency doubling perimetry using the Frequency Doubling Perimeter (Zeiss Humphrey Systems, Dublin , CA , USA )
(f) Corneal pachymetry using the DGH 550 Ultrasonic pachymeter (DGH Technology Inc., Exton , PA , USA )
(g) Slit lamp biomicroscopy, (Zeiss SL 130-Carl Zeiss, Jena , Germany )
(h) Applanation tonometry (Zeiss AT 030 Applanation Tonometer, Carl Zeiss, Jena , Germany )
(i) Gonioscopy, (Sussmann-type 4 mirror hand held gonioscope -Volk Optical Inc, Mentor, Ohio, USA)
(j) Ocular biometry (Alcon ultrasonic biometer - Ocuscan, Alcon laboratories Inc, Fort Worth , TX , USA ).
(k) Grading of lens opacities, (The Lens Opacities Classification System (LOCS II)
(l) Fundus examination, (Indirect ophthalmoscope - Appasamy Associates, Chennai , India )
(m) Optic disc and fundus photography ( Zeiss FF450-plus fundus camera with VISUPAC digital image archiving system - Carl Zeiss, Jena, Germany)
(n) Visual field – White on white ((Zeiss Humphrey Systems, Dublin , CA , USA )
All the abnormal features will be recorded using standard international classifications. Data collection also included assessment of socio-economic status, systemic and ocular history, and ophthalmic examination. In addition a detailed pedigree is taken from those identified to have glaucoma and family members are screened for the disease. Genetic analysis to identify risk factors for glaucoma is also being performed. The project was successfully completed by February 2004. The study has generated 27 peer reviewed publications.
The important findings of the study are:
1) Prevalence of primary open angle glaucoma in the rural population was 1.62%. The prevalence increased with increasing age and 98.5% were unaware that they had the disease.
2) Prevalence of primary angle closure disease (PACG + PAC) in the rural population: 1.58%. An additional 7% were at risk of developing angle closure glaucoma. A few important risk factors were shown to be associated with primary angle closure disease