GP Lens Management Guide – 7

Diagnostic Toric Fitting

The most accurate method of fitting is with a diagnostic fitting set. Contact your CLMA member laboratory for fitting set information. Typically, these lenses are fit like spherical lenses (i.e., often 0.12 – 0.50D flatter than “K”). A spherical over-refraction is performed and the over-refraction is added to the diagnostic lens powers to obtain the final lens powers.

For example:

  • Ks: 42.50 @ 180; 45.50 @ 090
  • Refraction: -3.75 -3.50 x 180
  • (at corneal plane): -3.75 -3.00 x 180
  • Diagnostic Lens: 42.00/45.00D; Plano/-3.00D
  • Over-Refraction: -3.25DS 20/20
  • Final Order: 42.00/45.00D; -3.25/-6.25D

When there is little to no physiological residual astigmatism, a spherical over-refraction (as above) will result in good visual acuity; this lens is termed a spherical power effect or SPE bitoric as it can rotate on the eye without affecting vision. Photo demonstrates a Good Bitoric fit.

If the patient has significant residual astigmatism, it can be managed by performing a sphero-cylindrical over-refraction and adding the over-refraction to the diagnostic lens power per meridian. This lens is often termed a cylinder power effect or CPE bitoric. If it rotates on the eye, vision may be compromised; fortunately, this rarely is a problem.

For example:

  • Ks: 42.50 @ 180; 45.50 @ 090
  • Refraction: +1.00 -4.00 x 180
  • Diagnostic Lens: 42.00/45.00D; Plano/-3.00D
  • Over-Refraction: +1.50 -1.00 x 180
  • Add: +1.50 to Plano in the 180 Meridian, +0.50 to -3.00D in the 90 Meridian
  • Final Order: 42.00/45.00D, +1.50/-2.50D

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