Figure 1.

Serial same eye comparison plots of applanation force (in grams) versus axial stromal displacement (in micrometers) of anterior and posterior corneal regions of interest for 4 eyes before and after corneal CXL. Anterior and posterior data are obtained simultaneously with OCE along a two-dimensional scan along the horizontal meridian. The difference in deformability under the same surface load can be seen by comparing the x-axis (displacement) position for the 2 regions along any y-axis (force) value (blue horizontal lines in post-CXL and blue circles in pre-CXL, where the differences for the later are too small to illustrate with a line). For example, in subject 1, the anterior stroma (burgundy) shows slightly greater displacement (higher deformability) than the posterior stroma (green) across most of the deformation curve. After CXL, the anterior stroma (blue) is far less deformed than the posterior stroma (orange), indicating a marked stiffening of the anterior stroma. Slopes are fit to each curve to characterize the overall force/displacement relationship for each region to yield a measure of axial stiffness (see text). The slope term is insensitive to slight differences in initial force/preload between the pre-CXL and post-CXL comparison, as can be seen in subject 3 (lower left), where there is a notable increase in the slope (stiffness) of the post-CXL anterior stroma in the latter portion of the perturbation sequence.