June 2015
Volume 56, Issue 7
Free
ARVO Annual Meeting Abstract  |   June 2015
Laser refractive surgery centration: visual axis or line-of-sight?
Author Affiliations & Notes
  • Daniel R Neal
    Research and Development, AMO WaveFront Sciences, LLC, Albuquerque, NM
  • Thomas D Raymond
    Research and Development, AMO WaveFront Sciences, LLC, Albuquerque, NM
  • Wei Xiong
    Research and Development, AMO WaveFront Sciences, LLC, Albuquerque, NM
  • Richard James Copland
    Research and Development, AMO WaveFront Sciences, LLC, Albuquerque, NM
  • Footnotes
    Commercial Relationships Daniel Neal, Abbott Medical Optics (E), Zeiss Meditec (P); Thomas Raymond, Abbott Medical Optics (E); Wei Xiong, Abbott Medical Optics (E); Richard Copland, Abbott Medical Optics (E)
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2015, Vol.56, 3914. doi:
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    • Get Citation

      Daniel R Neal, Thomas D Raymond, Wei Xiong, Richard James Copland; Laser refractive surgery centration: visual axis or line-of-sight?. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3914.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract
 
Purpose
 

Since the eye is not a centered optical system, there has been a debate over the correct location for centering a laser refractive surgical treatment. The cornea has a well-defined axis and center and yet it is not co-located with the pupil. It has been observed in some cases that aberrations may be induced for a decentered pupil.

 
Methods
 

Aberrations were modeled centered on the cornea with different amounts of induced aberrations. These were compared to published literature results for induced aberrations for four different laser platforms.

 
Results
 

The models indicate that there is a significant coupling between spherical aberration and coma for off-axis pupils if the spherical aberration (SA) is assumed to be centered on the cornea. This matches the clinical results for the cornea centered laser systems, but not the results for the pupil centered systems. For a typical (6 mm pupil) -0.37 um RMS corneal spherical aberration induced by a conventional LASIK treatment, the resulting coma is 0.37 um for a centered pupil verses 0.62 um for a decentered pupil. Using only the spherical aberration term and centering the treatment on the corneal vertex, the simulation predicted 0.35 um RMS coma, in excellent agreement with the clinical results.

 
Conclusions
 

The desired centration is more a property of the design of the laser delivery system than of the eye itself. While the eye may have a significant coupling between aberrations on the cornea and on the pupil, the individual laser system may take these effects into account. Residual errors may be due, in part, to remodeling of the epithelial layer after healing, and hence be somewhat unpredictable.  

 
Figure 1 - Optical simulation of induced coma caused by decentered pupil with corneal-vertex-centered spherical aberration. The corneal aberration was 0.25 um RMS over 6mm pupil and the predicted coma was 0.35 um RMS for a 0.6 mm decentration.
 
Figure 1 - Optical simulation of induced coma caused by decentered pupil with corneal-vertex-centered spherical aberration. The corneal aberration was 0.25 um RMS over 6mm pupil and the predicted coma was 0.35 um RMS for a 0.6 mm decentration.
 
 
Figure 2 - Simulation of various aberrations as a function of pupil decentration. Spherical aberration does not change with decentration, however, coma and astigmatism can change significantly, even for fairly small decentrations.
 
Figure 2 - Simulation of various aberrations as a function of pupil decentration. Spherical aberration does not change with decentration, however, coma and astigmatism can change significantly, even for fairly small decentrations.

 
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