Unilateral Real-Time Scheimpflug Videography to Study Accommodation Dynamics in Human Eyes

Abstract

Abstract: : Purpose: Development of a real-time Scheimpflug imaging system to understand the mechanism of accommodation (ACC); to characterize the factors leading to the age-related loss of accommodative amplitude in the living human eye. Methods: The system is based on the Nicholas Brown Scheimpflug system [Brit. J. Ophthal. (1972) 56, 624] and uses a 50 mm Nikkor Macro lens, which minimizes magnification derived image distortion. The system can acquire images at 40 frames per second and at sufficient resolution (1024 x 1024 pixels) to measure changes in lens shape and intraocular distances. ACC is induced by having the subject focus on a unique Floating Accommodation Stimulus (FAS) system. This allows stimulation of the same eye being imaged, preventing the loss of Scheimpflug alignment due to vergence. The FAS incorporates Badal optics so that the target stimulus appears to move towards and away from the subject without change in magnification. The refractive error of the subject is corrected by affixing corrective lenses on the FAS. The image stream from the camera is saved as an AVI file for analysis with custom software. The software tracks the lens movement and performs various intraocular measurements, including anterior chamber (ACR) depth, lens curvature, lens thickness and corneal thickness. Results: The camera is sufficiently light sensitive to enable clear imaging of the same eye presented with the ACC stimulus. Presentation of the ACC stimulus resulted in lens thickening and ACR shallowing that could clearly be seen in the Scheimpflug image. Scheimpflug images were obtained in 2 human subjects aged 22 and 26 years in response to an ACC stimulus. Conclusions: This dynamic Scheimpflug camera system can be used to collect data on human accommodation, to follow changes in anterior segment geometry and internal lens organization with accommodation and age, and to characterize the time dependence of these processes.  

Keywords: accommodation • imaging/image analysis: non-clinical • aging