Fig. 4. The measurement of depth optic canal and the sphenoid ridge from the pterion. AB is a vertical line drawn at the lateral margin of the optic canal. IP-L is the horizontal distance from the internal location of the pterion to the lateral margin of the optic canal. IP-SR is the linear distance from the internal location of the pterion to the lateral end of the sphenoid ridge. IP, internal location of the pterion; OC, optic canal; SR, a point on the lateral end of the sphenoid ridge.
