Posters

Theoretical analysis of the changes in spherical aberration after myopic and hyperopic LASIK, and implications in the selection of pseudophakic IOL asphericity

Poster Details

First Author: J.Caivache Anaya SPAIN

Co Author(s):    S. Fernandez Mota              

Abstract Details

Purpose:

The aim of this study is to analize, by computer simulation, the changes in corneal and total spherical aberration (SA) and Root Mean Square (RMS) of total aberrations after hyperopic and myopic LASIK, the influence of both, spherical or aspherical IOL implantation in such eyes, and to propose the most appropiate pseudophakic IOL (spherical or aspherical) based on the spherical aberration induced by previous LASIK .

Setting:

Clinica Baviera. Palma de Mallorca. España.

Methods:

A theoretical emmetropic eye based on the Navarro's Eye has been implemented in Zemax, introducing some changes in the asphericity factor Q of the internal optical surfaces, so that the values of total and corneal aberration resemble the average values obtained in real eyes. From this theoretical eye, axial length has been modified to simulate -2,00 D, -4,00 D and -6,00 D myopic eyes and +2,00 D, +4,00 D and +6,00 D hyperopic eyes. In each case, an emmetropic targeted LASIK has been simulated by modifying the corneal radius and Q of the anterior surface. The new postoperative corneal radius was obtained from preoperative radius and calculating the radius required for postoperative emmetropia, and the postoperative Q was obtained from the measured changes in Q in pre and postoperative real corneas with the ORBSCAN topograph, obtaining a linear regression curve relating the refraction change with the change in Q. For each simulated surgery, SA and total aberration for both, the cornea and the whole eye has been obtained with Zemax. Finally, a lens exchange with different spherical and aspherical lenses has been simulated in each postoperative LASIK eye, obtaining an aberrometric analysis of the new pseudophakic post-LASIK eye.

Results:

The myopic LASIK changes the cornea from prolata to oblate, changes the Q value from negative to positive, and increases the positive corneal SA, causing an increase in the total positive SA of the whole eye. The hyperopic LASIK increases the corneal prolaticity and changes the corneal SA from positive to negative, increases the negative Q value, causing an increment in the total negative SA of the whole eye. In absolute value, the SA increment is greater after hyperopic LASIK. After myopic post-LASIK IOL implantation, the greatest increment in SA absolute value occurs with a spherical IOL, and the lowest SA absolute value increment occurs with a aspherical lens (IOL SA= -0,26). After hyperopic post-LASIK IOL implantation, the greatest increment in SA absolute value occurs with a aspherical IOL (IOL SA= -0,26), and the lowest SA increment occurs with a spherical lens. In the simulation with Zemax, induced aberrations are highly pupil-dependent.

Conclusions:

To optimize the SA value, the best choice after miopic-LASIK is a negative SA aspherical IOL, and after hyperopic LASIK, the best choice is a spherical IOL. FINANCIAL INTEREST: NONE