Central corneal thickness and intraocular pressure in a Mongolian population.

OBJECTIVE: The purpose of the study was to quantify the variation of central corneal thickness (CCT) in an east Asian population and to examine its relationship to estimates of intraocular pressure (IOP) made with an applanation tonometer. DESIGN: The study design was a cross-sectional, population-based survey. PARTICIPANTS: One thousand two-hundred forty-two residents of Hövsgöl Province, Mongolia, 10 to 87 years of age participated. MAIN OUTCOME MEASURES: The CCT was measured using an optical pachymeter in all subjects. The IOP was measured using a, Goldmann-type applanation tonometer in subjects 40 years of age and older. RESULTS: There was a highly significant decrease in CCT with age: 5 microns/decade in men and 6 microns/decade in women (both, P < 0.0001). A highly significant positive correlation was identified between IOP and CCT. Linear regression analysis suggests that between the ages of 40 and 80 years, an increase in CCT of 10 microns is associated with an increase in IOP measurements of 0.18 mmHg in right eyes (95% confidence interval, 0.12-0.25) and 0.24 mmHg in left eyes (95% confidence interval, 0.17-0.31). The authors calculate that interindividual differences in CCT may produce a difference in measured IOP of between 2.3 and 3.1 mmHg. CONCLUSIONS: Variation in CCT is a significant source of variation in IOP measurements between individuals. The authors suggest that measurement of corneal thickness should be considered when assessing IOP as a risk factor for glaucoma in east Asians.

Anterior chamber depth in Mongolians: variation with age, sex, and method of measurement.

PURPOSE: To document anterior chamber depth in a Mongolian population and quantify the variation in this parameter attributable to age, sex, and method of measurement. METHOD: Depth of the anterior chamber was measured by optical pachymetry in 1,242 subjects aged 10 to 87 years. Figures for "true" anterior chamber depth were calculated by subtracting central corneal thickness from the distance between the anterior corneal epithelium and anterior lens capsule. A-mode ultrasound was also used to measure the distance from anterior corneal epithelium to anterior lens capsule in 94% (942) of subjects aged 40 years and older. These ultrasound data were compared with measurements of the same distance obtained by optical pachymetry. RESULTS: Mean anterior chamber depth in women was more shallow than in men of all ages (ANOVA, P < .0001), although this difference varied according to age. Mean anterior chamber depth decreased with age and was most accurately represented by a cubic function of age. This change was maximal between the ages of 30 and 60 years and equaled 0.15 mm per decade in men and 0.21 mm per decade in women. Mean depth of the anterior chamber measured by ultrasound was significantly less than the equivalent optical measurement (difference of 0.14 mm in right eyes, P < .001). CONCLUSIONS: Mean anterior chamber depth in Mongolians decreases with age and is more shallow in women than in men. Ultrasound and optical methods of anterior chamber depth measurement yield significantly different results and are therefore not directly comparable.

Glaucoma in Mongolia. A population-based survey in Hövsgöl province, northern Mongolia.

OBJECTIVES: To determine the prevalence of glaucoma and suspect glaucoma, and to classify the cases detected according to mechanism. DESIGN: A population-based prevalence study. SETTING: Rural and urban locations in Hövsgöl province, northern Mongolia. PARTICIPANTS: Nine hundred forty-two (94.2%) of 1000 individuals 40 years of age and older were examined. MAIN OUTCOME MEASURE: Primary angle-closure glaucoma was diagnosed in subjects with previous acute or intermittent symptoms of angle closure and in individuals with an occludable angle and an intraocular pressure greater than 19 mm Hg or a glaucomatous visual field. RESULTS: The prevalence of manifest primary angle-closure glaucoma was 1.4% (14 subjects). The prevalence of gonioscopically occludable angles was 6.4% (64 subjects, including those with glaucoma). Primary open-angle glaucoma was diagnosed in 5 subjects (prevalence, 0.5%). As all these subjects were older than 60 years, the prevalence became 2.1% for this age group. Three cases (prevalence, 0.3%) of secondary open-angle glaucoma were detected. No cases of secondary angle-closure glaucoma were diagnosed. The prevalence of blindness was 1.2% (12 subjects), and primary glaucoma accounted for one third of these cases (4 subjects). CONCLUSIONS: We confirmed glaucoma as a major public health problem in northern Mongolia. Primary angle-closure glaucoma is more prevalent than primary open-angle glaucoma, supporting clinic-based data from other east Asian countries. Among the subjects examined, 97 (9.7%) had either manifest, latent, or suspect glaucoma. Neighboring populations may be similarly affected owing to a shared genetic heritage.