Three dimensional analysis of the optic nerve head is important in the detection and treatment of eye diseases, particularly glaucoma. In glaucoma, the fluid pressure within the eye increases. Since there is a wide variability in people's sensitivity to elevated pressure, it is not possible to predict which eye will be damaged by a given pressure. The side effects of treatment preclude treating everyone with elevated pressure. However, those eyes susceptible to elevated pressure slowly begin to show erosion of the optic nerve head. The erosion process progresses very slowly and imperceptibly. By the time it can be detected visually, permanent visual loss has often occurred.