Corneal ectasia after excimer surgery: biomechanical models and Mandelbrot fractal theory

Session Details

Session Title: Moderated Poster Session: Refractive

Session Date/Time: Saturday 05/09/2015 | 14:00-15:00

Paper Time: 14:00

Venue: Poster Village: Pod 1

First Author: : A.Kachanov RUSSIA

Co Author(s): :    S. Nikulin   S. Bauer   B. Zimin        

Abstract Details

Purpose:

To evaluate the frequency of corneal ectasia after excimer laser surgery and try to explain such complication by using biomechanical models and Mandelbrot theory.

Setting:

St.-Petersburg brunch of Sv. Fyodorov “Eye Microsurgery Clinic”, St.-Petersburg, Russia.

Methods:

We reviewed our consecutive more than 60500 cases of excimer laser surgery including LASIK /88%/ and PRK /12%/. There were 58% of women and 42% of men of our study. Follow-up period was up to 16 years. The age of all patients was from 18 to 74 years. Some of them had hyperopia with manifest refractive spherical-equivalent (MRSE) up to 6,5D, and the others had myopia with MRSE from –1,0D to –22,0D. All patients had a standard ophthalmic examination including corneal topography (TMS-3 Autotopographer, “TOMEY; and especially PENTACAM, “Oculus”), aberrometry (WASCA, “Carl Zeiss Meditec”) etc.

Results:

There was NOT corneal ectasia in the groups after PRK and hyperopic LASIK. The age of the patients with post-op corneal ectasia ranged from 18 up to 48 years. 42 eyes (0,078%) had corneal ectasia after myopic LASIK. There was virtually no difference between the degree of myopia and the frequency of post-LASIK ectasia. Preoperative characteristics of the eyes, which further caused keratectasia, were within normal limits. According to our models after LASIK RST remains just over 50% of its original thickness. But after PRK cornea remains more uniform and resistant to mechanical stress, because it remains approximately 80% of its original thickness.

Conclusions:

After LASIK cornea becomes more irregular and more “chaotic”, than after PRK and it's not possible confidently predict the development of corneal ectasia after excimer surgery. We can suppose, that after myopic LASIK cornea can behave like a strange attractor according to Mandelbrot fractal theory. Biomechanical models and fractal theory may help to understand post-op corneal ectasia phenomenon.

Financial Interest:

NONE