Introduction: The iris positioning procedure is a crucial step in order to obtain a natural gaze of the custom ocular prosthesis. Some of the existing methods to produce precise and symmetrical iris orientation on the custom ocular prosthesis are quite complicated and required considerable time. This clinical report describes an easy and simple iris positioning technique by using an optical vernier interpupillary distance (IPD) ruler.Case Description: A 70-year-old male patient wanted to replace his old ill-fitting ocular prosthesis. He also refused long and frequent clinical visits. On diagnostic examination, post-enucleation socket syndrome was found on left orbital. The ocular impression tray was made immediately from clear self-cured acrylic resin, which was formed manually by fingers and placed on the tip of a disposable syringe. Afterwards, the ocular impression was taken by using light body polyvinyl-siloxane material. Wax pattern resulted from split cast technique was used to determine the center of iris position by using optical vernier IPD ruler. Blank sclera was obtained and the medio-lateral of iris on the normal eye was measured and transferred to the blank sclera by using optical vernier IPD ruler. The iris was marked and evaluated for its orientation and symmetry.Discussion: Subjective assessment by visual may bias the clinician to obtain precise iris position on the custom ocular prosthesis. Therefore, objective measurement for determining iris position is essential. Optical vernier IPD ruler is an accurate appliance/tool with millimeter scales and has movable frame to adjust the distance between the eyes. Furthermore, it is affordable, easy to use and recommended for clinical usage, especially in determining iris position.Conclusion: Simple method of iris positioning by using optical vernier IPD ruler can be an alternative way to produce acceptable custom ocular prosthesis and it took only a minute to obtain the objective measurement of iris orientation in this case.