OPTICAL CONSIDERATIONS

Consider the following patient:

Spectacle Rx:  -3.00 D. sphere
K-readings: 43.00 @ 180; 43.75 @ 090

With a spherical rigid lens on the eye there would be 0.75 D.C. (43.75-43.00) created by the lacrimal lens.  However, there is no cylinder in the spectacle correction.  Thus, the rigid lens would create 0.75 D. of residual astigmatism.

With a hydrogel lens on the eye, it would conform to the cornea and no lacrimal lens cylinder would be created and thus no residual astigmatism would be present.

This patient would be best corrected with a spherical hydrogel lens.