For decreasing light loss and diminishing the aberrations of the optical system, an open-loop adaptive optics (AO) system for retinal imaging in vivo is introduced. Taking advantage of the ability of young human eyes to accommodate, there was only one single curved mirror to make the pupil of the eye conjugate with the wavefront corrector and the wavefront sensor. A liquid crystal spatial light modulator (LC-SLM) was adopted as the wavefront corrector because the LC-SLM can be made in a small size to match the sensor. To reduce a pair of lenses or focusing mirrors, the wavefront corrector and sensor are positioned in the noncommon path. The system adopts open-loop control and the high-precision LC-SLM guarantees the effectiveness of the AO system. The designed field of view is 1° on the retina (about 300 μm). The image quality was simulated with different mirror surface types, including circular, parabolic, and hyperbolic. A hyperbolic mirror with conic constant −1.07, which is close to −1, could best eliminate the aberrations. Theoretical analysis showed that the optical throughput of this system was at least 22.4% higher than that of a standard transmission AO system. In a practical experiment, a parabolic mirror was positioned in the optical path. Images of the cone photoreceptors and the capillary vessels were obtained successfully. This system simplifies the optical setup in comparison to the commonly used 4F systems while still guaranteeing the effectiveness of AO to correct the ocular aberrations.