A system is disclosed that includes an optical fiber including a first optical module and a gate. The gate can be capable of moving between closed and opened states to form a slit. At least one storage medium can be included having encoded thereon executable instructions that, when executed by the at least one processor, cause the system to carry out a method including directing light from the first optical module through the slit onto the stone to form a pair of lines with a spacing between the pair of lines; and determining a size of the stone, based on a distance from a distal tip of the optical fiber and the spacing between the pair of lines.