The presence of Relative Afferent Pupillary Defect (RAPD) indicates serious ocular disease, if untreated may lead to loss of vision. Swinging Flash Test (SFT) has been a traditional way of testing for RAPD for decades, quantification of RAPD, its reliability and accuracy is still not a reality. In this study, a novel Pupilometer device is proposed which uses custom-built hardware and software to perform the test to determine the RAPD at an early stage. The hardware of the device consists of components to produce a light stimulus into each eye and record the response of the pupils to the stimulus with a high-resolution camera. A Graphical User Interface (GUI) developed is responsible for the timing of the stimulus, processing the recorded response of the pupil in calculating the area of the pupil through image segmentation and analysis. RAPD test was conducted on 30 patients who are diagnosed with RAPD by using the pupilometer designed. The Pupil area of 30 RAPD patients has shown to be significant with p<0.001 in the diagnosis of RAPD