Ophthalmic fundus camera design based on freeform surface for reducing refractive error sensitivity

The eye has a remarkably complex structure and biomechanics. An imbalance between the forces acting on several muscles and the tissue properties may alter or even preclude vision. With the widespread use of electronics, refractive errors have become a common problem, making clear fundus imaging difficult. To overcome this challenge, freeform surfaces have emerged as a potential solution, enabling compact, low-cost, and user-friendly systems that are insensitive to refractive errors. We propose a fundus camera based on a freeform surface that can image the fundus without the influence of refractive errors. A special front lens was designed to image the pupil on a freeform lens that can realize phase modulation. The system performs well providing a field of view of 40∘ and a pupil diameter of 3 mm for refractive errors ranging from -5D to +5D. The volume of the system was less than 35 mm × 35 mm × 135 mm.