How Does Previous Refractive Surgery Affect IOL Power Calculation?
Refractive surgeries such as LASIK, LASEK, and RK cause changes in the shape of the cornea that can result in errors with the normal formulas used to choose the intraocular lens power for cataract surgery. The formulas depend on a normal central corneal structure which is changed by refractive surgeries.
Standard Intraocular Lens Power Calculations
The standard intraocular lens (IOL) power calculation uses the curvature of the cornea, the axial length (size of the eye), and some formulas use the anterior depth.
The pie-shaped cuts in the cornea cause a central flattening of the cornea like a plateau on top of a mountain. The typical methods of measuring the cornea are unable to accurately measure the curvature of the cornea which is a major component used to determine the power of the intraocular lens to be used. Typically the chosen intraocular lens will not be a high enough power to correct the vision after surgery.
These laser procedures remove a portion of the anterior surface of the cornea and therefore change the relationship between the anterior surface of the cornea and the posterior surface of the cornea. This causes an alteration in that ratio resulting in errors choosing the intraocular lens power.
Methods for Helping Choose the Best IOL Power
The best possible data that can be obtained is vitally important in making sure the proper strength of the intraocular lens is obtained.
This instrument measures the anterior and posterior surface of the cornea. It also calculates a true central curvature of the cornea.
This instrument measures the anterior and posterior surface of the cornea. Lens opacities may limit its ability to measure the posterior corneal surface.
This is a new instrument that measures the eye using laser optical technology.
ASCRS and Alcon Formula
This formula was developed by Warren Hill M.D., Li Wang M.D. PhD., and Douglas Koch M.D. and is used by many eye doctors to calculate the intraocular lens power in people who have had prior corneal refractive surgery.
It is very important that anyone who has a refractive corneal operation to keep a copy of their medical records. The pre-surgery eye exam information is an important piece of the information used to help calculate the intraocular lens power. You may not develop cataracts for many years after your refractive surgery and your medical records may not be available. Technology is constantly improving and you can still have a good result from cataract surgery even if you have had a prior corneal refractive procedure.