The true corneal power following RK, ALK, PRK, and LASIK is challenging to measure directly, using methods such as keratometry or corneal topography.
Keratometry and topography assume a normal relationship between the anterior and posterior corneal curvatures, measuring the anterior corneal radius.
Incisional keratorefractive surgery for myopia flattens both the anterior corneal radius and the posterior corneal radius. Ablative keratorefractive surgery for myopia flattens the anterior corneal radius but leaves the posterior corneal radius mostly unchanged.
Standard keratometry measures an intermediate area and extrapolates the central power based on some broad assumptions. For this reason, keratometry, autokeratometry, and simulated keratometry by topography will typically overestimate central corneal power, following keratorefractive surgery for myopia. Failure to keep this important fact in mind will often result in an unexpected and unpleasant post-operative hyperopic surprise.
| Double K Formula Corrections Learn how 2-variable IOL power calculation formulas may be another source of errors following keratorefractive surgery. Lacking the Holladay 2 formula, instead you can use the “Double K” correction method in conjunction with the SRK/T, Hoffer Q, or Holladay 1 formulas. |
| Hyperopic LASIK and PRK IOL Calculations How to estimate the central corneal power following hyperopic LASIK or PRK. |
| Myopic LASIK IOL Calculations How to estimate the central corneal power following myopic LASIK. |
| Radial Keratotomy (RK) IOL Calculations How to estimate the central corneal power following radial keratotomy (RK). |
Keep in mind that the above methods provide an estimate of the true central corneal power and may not be entirely accurate. Currently, these techniques represent the most effective clinical methods available. Hopefully, in the future, we may have a more precise and less time-consuming method for measuring these challenging eyes.
