Simple retinal imaging system using a MEMS scanning mirror

Abstract

We have fabricated a simple and compact scanning laser optical system using microelectromechanical system (MEMS) scanner that can be incorporated into portable health monitoring devices. The two-dimensional (2-D) MEMS scanner used in this system is much smaller and light in weight compared to galvanometer scanners and polygon scanners used in the commercially available ophthalmic devices. MEMS scanners have many advantages and also limitations compared to galvanometer and polygon scanners. An easy to use and compact device is more useful for rapid alignment for measurement and data acquisition. Sensitivity of the system was quantified by measuring signal-to-noise ratio (SNR) for both high and low reflectivity materials. SNR was 10 for the high reflectance materials and about 4 for low reflectance materials, which is sufficient for biological imaging. Distortion generated using large scanning angle of 2-D MEMS scanner was corrected in real time by custom made LabVIEW program. Ocular safety is important to consider when using a laser for ophthalmic devices. We calculated the maximum permissible beam power for thermal damage and photochemical damage considering the specification of our system such as visual angle and wavelength of the laser beam. The measured laser intensity in the front of model eye was 6 μW, which is much smaller than the maximum permissible beam power recommended by the American National Standards Institute.