This chapter considers the design and functionality of flood-illumination adaptive optics (AO) ophthalmoscopes. A vision science AO system, similar to AO systems used in astronomy and communications, comprises four main components: a retinal beacon light source, a wavefront sensor (WFS), a control computer, and a wavefront corrector (WFC). The chapter discusses different designs of AO imaging instruments, each offering different benefits, such as flood-illuminated AO, AO-scanning laser ophthalmoscopy, and AO-optical coherence tomography systems. Lenses in AO ophthalmoscopes are usually off-the-shelf precision achromats that have been corrected for various aberrations, for example, spherical aberration and coma, as well as longitudinal chromatic aberration. A WFC in an AO ophthalmoscope is positioned in a plane that is conjugate to the pupil of the eye. The total number of actuators, in combination with the number of lenslets in the WFS, determines the correctable number of modes of an AO system. The vast majority of current flood-illuminated AO ophthalmoscopes are custom-built laboratory-based research systems.