Figure 2.

Dual beam interferometry system to separate components of IP and OOP strains. (a) A simplified version of test rig, data are collected individually from illumination with beam 1 and then beam 2 over two measurement cycles. The rotating stand enables rotation through 90° to obtain sensitivity in both the horizontal and vertical planes ensuring δx=δy. (b) The direction of different planes with reference to the corneal surface. (c) An example of wrapped interference fringes for vertical and horizontal shear. (d) Equations demonstrating how phase data from different illumination angles are manipulated to give separate components of strain.