Optical detection and imaging have wide applications in biomedicine and biological and chemical analyses. With continuing miniaturization effort to realize integrated microsystems, micro-scale optical components become more and more important. For any optical system, lenses are critical elements. In this talk, I will present our work on liquid microlenses. I will first introduce a few types of microlenses and microlens arrays, including tunable liquid microlenses actuated by temperature-, pH- and infrared light-responsive hydrogels, microlens arrays for light-field imaging, microcamera arrays mimicking compound eyes, and artificial reflecting superposition compound eyes. Then, I will discuss about potential applications of these lenses in medical instruments. I will describe miniaturized cameras capable of multiple viewpoints, prototype flexible endoscopes implementing infrared-light responsive liquid microlenses at their distal ends, and prototype multiple-camera laparoscopes.