Anterior Chamber Area Research Articles

Determinants of Angle Width in Chinese Singaporeans

To investigate determinants of angle width and derive mathematic models to best predict angle width. Population-based, cross-sectional study. A total of 1067 Chinese subjects aged ≥40 years. Participants underwent gonioscopy, A-scan biometry, and imaging by anterior segment optical coherence tomography (ASOCT, Carl Zeiss Meditec, Dublin, CA). Customized software (Zhongshan Angle Assessment Program, Guangzhou, China) was used to measure ASOCT parameters. Linear regression modeling was performed with trabecular-iris space area at 750 μm (TISA750) and angle opening distance at 750 μm (AOD750) from the scleral spur as the 2 dependent angle width variables. By using a combination of ASOCT and biometric parameters, an optimal model that was predictive of angle width was determined by a forward selection regression algorithm. Validation of the results was performed in a separate set of community-based clinic study of 1293 persons aged ≥50 years. Angle width and biometric parameters. The mean age (standard deviation) of the population-based subjects was 56.9 (8.5) years, and 50.2% were male. For TISA750, the strongest determinants among ASOCT and A-scan independent variables were anterior chamber volume (ACV, R(2)=0.51), followed by anterior chamber area (ACA, R(2)=0.49) and lens vault (LV, R(2)=0.47); for AOD750, these were LV (R(2)=0.56), ACA (R(2)=0.55), and ACV (R(2)=0.54). The R(2) values for anterior chamber depth and axial length were 0.39 and 0.27 for TISA750, respectively, and 0.46 and 0.30 for AOD750, respectively. An optimal model consisting of 6 variables (ACV, ACA, LV, anterior chamber width [ACW], iris thickness at 750 μm, and iris area) explained 81.4% of the variability in TISA750 and 85.5% of the variability in AOD750. The results of the population-based study were validated in the community-based clinic study, where the strongest determinants of angle width (ACA, ACV, and LV) and the optimal model with 6 variables were similar. Angle width is largely dependent on variations in ACA, ACV, and LV. A predictive model comprising 6 quantitative ASOCT parameters explained more than 80% of the variability of angle width and may have implications for screening for angle closure.

Anterior segment optical coherence tomography changes post laser peripheral iridotomy in primary angle closure suspects in an Asian population

AbstractPurpose Multiple modalities have been used to image the anterior chamber angle. We quantified changes in novel parameters associated with angle closure, namely anterior chamber area (ACA) and volume (ACV); anterior chamber width (ACW); lens vault (LV) and iris thickness, area and curvature using ASOCT, in a cohort of primary angle closure suspects (PACS) after laser peripheral iridotomy (LPI).Methods A prospective study of primary angle closure suspects > 50 years of age after LPI. ASOCT images (Visante, Carl Zeiss Meditec, Dublin, CA) from 176 subjects were analyzed quantitatively using customized software, before and 1 week after LPI.Results The mean age of the 176 participants was 63.0 ± 7.3 year and majority of the subjects were Chinese (95.5%) and women (76.7%). After LPI, the angle width opened significantly with increase in mean angle opening distance [AOD 500, 0.11 vs. 0.18 mm, p< 0.001), trabecular iris surface area (TISA500, 0.06 vs. 0.08 mm², p< 0.001) and angle recess area (ARA, 0.12 vs. 0.17 mm², p< 0.001). Mean ACA (14.9 vs. 16.0 mm², p< 0.001) and ACV (91.6 vs. 103.0 mm³, p< 0.001) increased significantly after LPI, but there was no change in ACW (11.21 vs. 11.24 mm, p = 0.3), anterior chamber depth (2.16 vs. 2.17 mm, p = 0.16) or LV (783.6 vs. 788.6µm, p = 0.72). Mean iris curvature was reduced (0.375 vs. 0.180 mm, p< 0.001) after LPI, but there was no significant change in iris thickness or area.Conclusion LPI results in a significant increase in the angle width in subjects with narrow angles. ACA and ACV increased after LPI but there was no change in ACD, ACW, LV or iris thickness and area. The increase in ACA/ACV is attributed to be due to decreased iris curvature after LPI.

Association of Narrow Angles With Anterior Chamber Area and Volume Measured With Anterior-Segment Optical Coherence Tomography

To describe the measurement of anterior chamber area and anterior chamber volume by anterior-segment optical coherence tomography and to investigate the association of these parameters with the presence of narrow angles. This was a cross-sectional study of subjects aged at least 50 years without ophthalmic symptoms recruited from a community clinic. All participants underwent standardized ocular examination and anterior-segment optical coherence tomography. Customized software was used to measure anterior chamber area (cross-sectional area bounded by the corneal endothelium, anterior surface of iris, and lens within the pupil) and anterior chamber volume (calculated by rotating the anterior chamber area 360° around a vertical axis through the midpoint of the anterior chamber area). An eye was considered to have narrow angles if the posterior pigmented trabecular meshwork was not visible for at least 180° on gonioscopy with the eye in the primary position. A total of 1922 subjects were included in the final analyses, 317 (16.5%) of whom had narrow angles. Mean anterior chamber area (15.6 vs 21.1 mm(2); P<.001) and anterior chamber volume (97.6 vs 142.1 mm(3); P<.001) were smaller in eyes with narrow angles compared with those in eyes without narrow angles. After adjusting for age, sex, anterior chamber depth, axial length, and pupil size, smaller anterior chamber area (odds ratio, 53.2; 95% confidence interval, 27.1-104.5) and anterior chamber volume (odds ratio, 40.2; 95% confidence interval, 21.5-75.2) were significantly associated with the presence of narrow angles. Smaller anterior chamber area and anterior chamber volume were independently associated with narrow angles in Singaporeans, even after controlling for other known ocular risk factors.

Angle closure glaucoma: a mechanistic review

With recent advances in imaging techniques such as anterior segment optical coherence tomography and ultrasound biomicroscopy, there is a better understanding of nonpupil block mechanisms and novel risk factors contributing to the pathogenesis of angle closure glaucoma. Recent studies suggest that multiple anatomical and physiological factors interplay in the pathogenesis of angle closure glaucoma. The association of greater iris convexity, area and thickness with narrow angles could result in a more anterior bowing and crowding of the peripheral iris. Other novel anatomic parameters such as greater lens vault, smaller anterior chamber width, area and volume, independently increase the risk of having angle closure. Dynamic increase or lesser reduction in iris volume during dilation supports the theory of physiological predisposition to the disease process. Choroidal expansion has been demonstrated in untreated and treated, acute and chronic primary angle closure eyes. It remains unknown whether this finding is a cause or effect in this condition. With a wider availability of imaging tools and a better understanding of risk factors and mechanisms, clinicians maybe able to more accurately identify those at greater risk of developing angle closure disease and tailor their treatment according to the predominant factor(s) involved.

Angle Recess Area Decreases With Age in Normal Japanese

Purpose: To investigate prospectively the relationships between anterior chamber angle configuration and refractive error, axial length, age, and body height in the Japanese. Methods: We studied 65 eyes of 65 subjects (30 men, 35 women) who were either patients at the Ophthalmology Department of Mie University or volunteers. The 65 subjects underwent a complete eye examination, A-scan biometry, and ultrasound biomicroscopy. Images were exported to an IBM-compatible personal computer in PCX format. The angle recess area (ARA) was measured using a software program of our own design. Results: The ARA decreased with age in all quadrants of all eyes. In older individuals, the angle in the superior quadrant was significantly narrower than in the other quadrants. The ARA correlated directly with anterior chamber depth ( P < .001), axial length ( P < .001), and body height ( P = .003), and inversely with age ( P < .001) and refractive error ( P = .003) in pairwise analysis. Multivariate analysis revealed a significant association between ARA and anterior chamber depth ( P < .001), axial length ( P = .016), and younger age ( P = .043). Conclusions: The anterior chamber area narrows with age, especially in the superior quadrant. Narrowing of the angle in Japanese is associated with older age, shorter axial length, and shallower anterior chamber depth. We hypothesize that because of the increasing prevalence of axial myopia in younger Japanese, angle-closure glaucoma could become less common in Japan in the future.

Effect of pilocarpine on visual acuity and on the dimensions of the cornea and anterior chamber.

The effect of pilocarpine on visual acuity and on the dimensions of the cornea, anterior chamber, and lens were studied in two groups of subjects. Significant changes in ocular tension, corneal curvature, anterior chamber depth, and lens anterior radius were found in a group of 55 glaucomatous eyes as a result of pilocarpine treatment, but there was no change in corneal thickness. Out of 102 glaucomatous eyes 78 became relatively myopic, and this appears to be due to changes in the dimensions of the lens of the eye similar to those occurring in accommodation, as a result of the effect of the drug on the ciliary muscle. The effect of pilocarpine on anterior chamber depth, area, and volume was studied in 125 eyes using a photographic method, and a significant reduction in the dimensions of the anterior chamber was observed as a result of the administration of pilocarpine. A significant correlation between depth and volume was also noted and the implications of this are discussed.