Abstract: An optical viewing system for use by bicycle riders and the like to increase the field of vision thereof includes headgear for supporting the system on the head of the user and an optical viewing accessory attached to the headgear. The optical viewing accessory has a pair of prisms thereon mounted for pivotal movement between retracted and extended positions. In their retracted positions, the prisms do not interfere with the direct line of sight of the user. However, in their extended positions, the prisms intersect the direct line of sight of the user and the internal reflection and refraction of the prisms allow the user to view objects located at positions at an angle, approximately ninety degrees, from the direct line of sight. The pivotal movement of the optical viewing accessory is activated under the influence of gravity as the head of the user is manipulated alternatively between the erect and prone positions.