Optical system design of a liquid tunable fundus camera based on Gaussian brackets method

A novel fundus camera with liquid tunable lens (LTL) to compensate the ametropia of human eye is designed and developed. The formula for the power of the LTL related to the diopter of eyes is deduced by Gaussian brackets method. The paraxial optical system of the fundus camera with ophthalmophantom is calculated and modeled. To enable the imaging beam to pass through the LTL without obscuration, the eye pupil and the LTL are conjugate with each other with respect to the lens system between them, and the lens system should have a magnification approximately to 1. To eliminate the stray light, the light source and the cornea are conjugate with each other in the illumination system, ring-shaped light source combined with polarized light is used. Besides, an analyzer plate is placed after the beam splitter to block the light reflected from the lenses and cornea. The fundus camera has a field of view of 50O, working distance of 40 mm, and overall length of 220 mm. Experiment is carried out to demonstrate the diopter compensation capability of the system, in which fundus images of ophthalmophantom at different diopters are captured, and these images are compared with those of the system where no LTL is adopted. The results show that by means of using LTL, the camera can adapt to eyes with diopter range from -10 D to +10 D (1 D=1 m^-1). This compact system with LTL can remarkably simplify the optomechanical structure while maintaining a good diopter-adjusting performance.