Systems and methods are provided herein that generally involve measuring a prostate or other object. In some embodiments, a finger clip having a roller ring or wheel rotatably mounted thereto is disposed within an inflatable membrane. The roller ring can include a measurement pattern positioned opposite to optical fibers configured to receive light reflected from the measurement pattern. A user can put on the finger clip, position the membrane in proximity to a rectal wall overlying a prostate, and inflate the membrane. As the user slides their finger across the inside of the membrane, which is pressed against the rectal wall, the roller ring can rotate with respect to the fibers such that the fibers move relative to the measurement pattern. A controller can sense light reflected through the fibers from the reference pattern and calculate or estimate various attributes of the prostate based on the reflected light.
