In the AO retinal imaging system, the aberration measurement and retinal imaging have different requirements for the size of the illumination area on the fundus. For retinal imaging, a large field size is always advantageous, but it should be noted that the imaging FOV is restricted by the isoplanatic angle of the human eye. If the imaging FOV is greater than the isoplanatic angle, then the adaptive compensation effect will be lost.28–30 However, the illumination spot projected on the retina should be a “point source” to ensure the wavefront sensing accuracy. If the illumination area on the fundus is too large, the light spots on the SH-WFS will link to each other and result in detection error, as shown in Fig. 2. To solve this problem, two light sources (one for wavefront sensing and one for retinal imaging) can be used. There was only one light source in our system, however, and the size of the illumination area on the fundus for the wavefront sensing is the same as that for the retinal imaging. To ensure the detection accuracy of the SH-WFS, the illumination spot on the fundus in our previous experiment was approximately 0.75-deg for both the retinal imaging and wavefront sensing.19 To enlarge the FOV of the retinal imaging without decreasing the wavefront sensing accuracy of the SH-WFS, a modified mechanical shutter was used to control the FOV. The shutter was conjugated to the fundus with a hole in the shutter center, as shown in the dotted-line box on the left of the shutter in Fig. 1. The size of the illumination area on the fundus can be adjusted by changing the clear aperture of the shutter. When ocular aberrations were detected, the shutter was closed. The size of the illumination area on the fundus was restricted by the small hole in the shutter. The smaller hole of the shutter for wavefront sensing can be easily determined. First, the size of the laser spot projected on the fundus should be smaller than the isoplanatic patch of human eye, and meanwhile, the light spot on the SH-WFS could not link to each other. In the experiment, the diameter of the small hole was 0.9 mm and results in an approximately 0.4-deg illumination spot on the fundus. The shutter was open for the retinal imaging, and the illumination spot size was increased to 1.7-deg, which was approximately equal to the isoplanatic angle of the human eye.