Post Keratorefractive Surgery.

The true corneal power following RK, ALK, PRK and LASIK is difficult to measure by any form of direct measurement, such as keratometry, or corneal topography.

Keratometry and topography assume a normal relationship between the anterior and posterior corneal curvatures, and measure 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 very broad assumptions. For this reason, keratometry, autokeratometry and simulated keratometry by topography will typically over-estimate 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.

Keep in mind that the above methods will give an estimation of the true central corneal power and may not be exact. At present, these techniques represent the best clinical methods available. Hopefully, in the future we may have a more accurate, and less time-consuming, method for measuring these challenging eyes.