Quantitative evaluation of anterior segment parameters in the era of imaging

Purpose: To review the parameters for quantitative assessment of the anterior segment and iridocorneal angle and to develop a comprehensive schematic for the evaluation of angle anatomy and pathophysiology by high-resolution imaging. Methods: The published literature of the last 15 years was reviewed, analyzed, and organized into a construct for assessment of anterior segment processes. Results: Modern anterior segment imaging techniques have allowed us to devise new quantitative parameters to improve the information obtained. Ultrasound biomicroscopy, slit-lamp optical coherence tomography, and anterior segment optical coherence tomography provide high-resolution images for analysis of physiologic and pathologic processes. These include iridocorneal angle analysis (eg, angle opening distance, angle recess area, trabecular-iris space area), anterior and posterior chamber depth and area, iris and ciliary body cross-sectional area and volume, quantitative anatomic relationships between structures, and videographic analysis of iris movement and accommodative changes under various conditions. Modern devices permit imaging of the entire anterior chamber, allowing calculation of anterior chamber and pupillary diameters and correlating these with measurement of anterior chamber dynamics in light vs dark conditions. We have tabulated all reported anterior segment measurement modalities and devised a construct for assessment of normal and abnormal conditions. Conclusion: Quantitative measurement of static and dynamic anterior segment parameters, both normal and abnormal, provides a broad range of parameters for analysis of the numerous aspects of the pathophysiology of the anterior segment of the eye.