Quantitative Measurement of Iris Curvature and Its Application in Evaluating the Changes in Iris Curvature in Primary Angle Closure Suspect

Objective: To evaluate the accuracy of the quantitative measurement of iris curvature by Rhinoceros and to assess the changes iniris curvature in primary angle closure suspect after laser periphery iridectomy (LPI). Methods: This was a prospective study. Sixteen patients (16 eyes) with primary angle closure suspect (PACS) who planned to undergo LPI treatment in Taizhou Municipal Hospital were selected. The anterior segment images of different axes were captured by Allegro Oculyzer. The curvature radius of the anterior iris surface was quantitatively measured by Rhinoceros 5.0. The repeatability of image capturing and image measurement was assessed. The iris curvature of the patients with PACS was compared before and after LPI. Sixteen normal persons (16 eyes) matched for age, sex, and pupil size were selected as the control group. The iris curvature was compared between the PACS and control groups. The correlation between iris curvature and central anterior chamber depth, anterior chamber volume and peripheral anterior chamber depth at 6 mm in the PACS group were analyzed. The correlation between changes in iris curvature and central anterior chamber depth, anterior chamber volume, and 6 mm peripheral anterior chamber depth before and after LPI treatment were also analyzed. A paired t test, independent t test and Pearson correlation coefficient were used for statistical analysis. Results: The coefficient of variation of anterior segment image capturing was 3.02%. The coefficient of variation of anterior segment image measurement was 2.54%. The radius of the iris curvature in the PACS group was 7.81±1.63 mm, which increased to 9.20±2.22 mm after LPI (t=-9.45, P<0.001). The radius of the iris curvature in the control group was 9.99±4.00 mm. The difference between the PACS group and control group was statistically significant (t=-5.69, P<0.001). After correction for the central anterior chamber depth, there was a correlation between the iris curvature radius in the direction of 0° (r=0.879, P<0.001), 90° (r=0.684, P=0.005), 180° (r=0.619, P=0.014), 270° (r=0.740, P=0.002) and the peripheral anterior chamber depth at 6 mm in the corresponding directions. After the treatment with LPI, except for the direction of 270° (r=0.453, P=0.078), there was a correlation between the changes in iris curvature in the direction of 0° (r=0.693, P=0.003), 90° (r=0.560, P=0.024), 180° (r=0.580, P=0.019) and the changes in peripheral anterior chamber depth at 6 mm in the corresponding directions. Conclusions: This quantitative measurement of iris curvature has good accuracy and repeatability. It can be used for the early diagnosis and quantitative evaluation of the therapeutic effect of PACS. Key words: iris curvature; quantitative measurement; primary angle closure suspect