Fig. 2.

(a) Schematic of the cylindrical lens effect (astigmatism) caused by a small glass tube. (b and c) Simulated astigmatism ratio before and after correction: (b) as a function of inner diameter for a given tube wall thickness (i.e., 45 μm) and (c) as a function of wall thickness for a given inner tube diameter (i.e., 250 μm). The ray tracing analysis shows that the two-step method (i.e., filling the tube with index matching fluid and flattening the outer surface) could well correct the cylindrical lens effect.