Laser refraction correction surgeries

Laser refraction correction

Laser refraction correction
Supervisor: [ Dr. Andrey V. Larichev ]

$Laser refraction correction surgeries$

Figure. 1

$Example of calculation of a wavefront-guided refractive operation$

Figure. 2

Laser refractive surgery is widely used for correcting the refraction and astigmatism of human eyes, allowing the patients to get rid of glasses or contact lenses. Nowadays, these operations are applicable for myopic and hyperopic cases from -15 to +6 D, including cases complicated by cylinder up to 5 D (according to last FDA approvals). However, in more complex cases, when aberrations of the third order or higher cannot be neglected, or when no clinical correction data are available, the standard operations cannot be carried out. In such cases, wavefront-guided operations, also known as customized ablation operations, may be the way out.

The aberration data obtained with MultiSpot aberrometers are used to calculate customized operations (two of the instruments are under clinical tests at Tambov and Cheboksary branches of the S.Fyodorov Eye Microsurgery State Institute). High repeatability and accuracy of measurements permit treating cases caused by aberrations up to 6th order.

In cooperation with the operation laser manufacturer, Physics Instrumentation Center, our group develops new algorithms to calculate the operation profile, taking into account all aberrations measured, cornea topography data (if available), and specific laser characteristics affecting the operation procedure. An original algorithm controlling the laser shot sequence provides a unique possibility to reproduce the operational profile with a deviation not exceeding 1 um within the optical zone.

In complex cases, the surgeon can individually adjust the magnitudes of different aberration groups (like astigmatism, coma, spherical etc.) or eliminate them totally.

The algorithm takes into account the laser beam parameters, the dependence of the ablation on the incident angle, and the biophysical response of the cornea. A special attention has been paid to keep the conic constant intact, yet the surgeon can vary this parameter in order to diminish the overall ablation depth.

Since 2003, several hundreds of customized operations have been carried out. A significant improvement of the post-operational vision quality has been observed.

The poster [ Utility of dynamic aberrometry for acuity measurements and testing ] (in PDF, 1.55 Mb) contains more detailed information.

In Figure 1, a schematic of LASIK (Laser-Assisted In Situ Keratomileusis)-type surgery is shown. Other types of the laser refractive operations, which can be calculated from the wavefront data, include PRK (Photorefractive Keratectomy), LASEK (Laser Epithelial Keratomileusis), and Epi-LASIK.

Figure 2 is an example of calculation of a wavefront-guided refractive operation. The case is complicated by a large coma, which prevents standard lens correction and reliable measurements with the use of an autorefractor.

Selected publications:

M.G. Yablokov, V.A. Machehin, A.V. Doga, M.G. Kolotov, S.K. Vartapetov, A.V. Larichev, N.G. Irochnikov, Wavefront study results obtained with the first domestic aberrometer "MultiSpot 250", Oftalmokhirurgiya, №2 (2005) (In Russian)
A. Larichev, N. Iroshnikov, V. Maniahin, M. Yablokov, V. Sugrobov, Corneal asphericity after myopic correction with excimer lasers, 2nd International Topical Meeting on Physiological Optics, Granada University, Spain, October 2004. (poster)