An imaging device may include single-photon avalanche diodes (SPADs). Each SPAD may be overlapped by multiple microlenses. The microlenses over each SPAD may include first microlenses having a first size over a central portion of the SPAD and second microlenses having a second size that is greater than the first size over a peripheral area of the SPAD. The second microlenses may be spherical microlenses or cylindrical microlenses. The first microlenses may be aligned with underlying light scattering structures to improve the efficiency of the light scattering structures. The second microlenses may partially overlap isolation structures to direct light away from the isolation structures and towards the SPAD.