The first task in any retinal fundus image processing is to detect the optical disk, as this is the prime location in a fundus image from where all the retinal blood vessels originate. In this paper, a faster method to detect retinal optical disk is proposed that uses mean intensity value of retinal image to detect the center of optical disc, which can be used in retinal image based person authentication system or retinal disease diagnosis. A candidate based approach on the green channel of an RGB fundus image is used to detect optical disc center location. The system has been successfully tested on several publicly available standard databases, namely: DRIVE, MESSIDOR, VARIA, VICAVR and DIARETDB_01 and produced 97.5%, 97.8%, 94%, 93.1% and 86.5% accuracies respectively. It is observed that, if lower recognition accuracy is accepted (from 100% to 97.5%) on DRIVE database, the detection speed increases from 7 seconds to 2 seconds per image, which is faster than any other previous methods with such high accuracies.