Research On Optical Design Method For Portable Fundus Camera

A large number of capillaries are distributed on the human retina and are the onlycapillaries that can be directly observed in human body. The quick and direct observation ofretinal capillaries with fundus camera provides an important way for diagnosis of diabetes,coronary heart disease, hypertension and many other diseases, so fundus camera is anindispensable ophthalmological instrument in modern medicine. And development ofportable fundus camera, which is beneficial to promote the retinal screening to the remoteareas, is of great significance.By considering the physiological and optical characteristics of the human eye, a novelportable fundus camera with liquid lens to compensate the ametropia of human eyes isproposed and developed for the first time. Since the calculation method of this novel zoomsystem is not developed, we propose to use Gaussian Brackets method to deduce the relatedformula between the power of the liquid lens and the diopter of eyes. The paraxial opticalsystem of the fundus camera with ophthalmophantom is calculated and set up by using thecommercial optical design software of Code V.To eliminate the strong stray light caused by corneal center and make full use of lightenergy, the annular stop in conventional illumination systems is replaced by a fiber-coupled,ring-shaped light source that forms an annular beam. Besides, a polarized light source isused, and an analyzer plate is placed after beam splitter in the imaging system to block thelight reflected from the lenses and cornea. Simulation results in LightTools show that theillumination uniformity at the fundus exceeds90%, and the stray light is within1%.Finally, a proof-of-concept prototype which has a field of view of50o, workingdistance of40mm, and overall length of220mm is developed. Experiment is carried out todemonstrate the diopter compensation capability of the system, in which fundus images ofophthalmophantom at different diopters are captured. The results show that the camera canbe adapted to eyes whose diopter range from-10D to+10D by using liquid lens. Theexperimental results also show that ghost images and stray light have been greatly reducedto a level that professional diagnostic will not be interfered with. This compact system withliquid lens liquid lens can remarkably simplify the optomechanical structure whilemaintaining a good diopter-adjusting performance.