2020–2021 BCSC Basic and Clinical Science Course™
13 Refractive Surgery
Chapter 11: Considerations After Refractive Surgery
Intraocular Lens Calculations After Refractive Surgery
Eyes With No Preoperative Information
When no preoperative information is available, the hard contact lens method can be used to calculate corneal power. This method is not very useful in clinical practice. The best-corrected visual acuity (BCVA; also called corrected distance visual acuity, CDVA) needs to be at least 20/80 for this approach to work. First, a baseline manifest refraction is performed and then a plano hard contact lens of known base curve (power) is placed on the eye, and another manifest refraction is performed. If the manifest refraction does not change, then the cornea has the same power as the contact lens. If the refraction is more myopic, the contact lens is steeper (more powerful) than the cornea by the amount of change in the refraction; the reverse holds true if the refraction is more hyperopic. For example:
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Current spherical equivalent manifest refraction: –1.00 D
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A hard contact lens of known base curve (8.7 mm) and power (37.00 D) is placed
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Overrefraction: +2.00 D
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Change in refraction: +2.00 D – (–1.00 D) = +3.00 D
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Calculation of corneal power: 37.00 D + 3.00 D = 40.00 D
Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.