OPTICAL CONSIDERATIONS

Consider the following patient:

Spectacle Rx: -3.00 = -0.50 x 180
K-reading: 43.00 @ 180; 43.25 @ 090

With a spherical rigid lens on the eye a 0.25 D. of cylinder would be corrected (43.00 and 43.25 D. K-readings).  Since a 0.50 D.C. is required the patient would have a 0.25 D.C. uncorrected with the spherical, non-flexing spherical rigid lens.  We say this patient has 0.25 D. of residual astigmatism.

With a spherical hydrogel lens on the eye there would be 0.50 D.C. uncorrected.  This patient, thus, has 0.50 D. of residual astigmatism.

Most patients can do well with no visual or asthenopic problems with a 0.50 D. of residual astigmatism.  Many do not have a problem with 0.75 D.  However, with 1.00 D. or more of residual astigmatism, the use of a toric lens or some other method to correct it should be considered.

In this case either a spherical rigid or spherical hydrogel would be options.