The influences of The influences of reference plane and reference - PowerPoint PPT Presentation

The influences of The influences of reference plane and reference plane and direction of measurement direction of measurement on eye aberration on eye aberration measurement measurement David Atchison and Neil Charman David Atchison and Neil Charman Centre for Health Research Centre for Health Research Queensland University of Technology Queensland University of Technology Brisbane, Australia Brisbane, Australia Faculty of Life Sciences Faculty of Life Sciences University of Manchester, UK University of Manchester, UK

Background Background n Corneal flattening following myopic Corneal flattening following myopic n corneal ablation causes a reduction in corneal ablation causes a reduction in magnification between aperture stop (iris) magnification between aperture stop (iris) and entrance pupil and entrance pupil n Custom ablation based on pre-operative Custom ablation based on pre-operative n wavefront ablation across the entrance wavefront ablation across the entrance pupil will result in an incomplete correction pupil will result in an incomplete correction

Related Issues Related Issues n Does the direction in which aberrations are Does the direction in which aberrations are n measured affect these measurements ie ie into- into- measured affect these measurements the-eye (Tracey) versus out-of-the-eye the-eye (Tracey) versus out-of-the-eye (Hartmann-Shack)? (Hartmann-Shack)? n What is the effect of the reference plane on What is the effect of the reference plane on n these measurements eg cornea versus entrance these measurements eg cornea versus entrance pupil? pupil? n How do these effects vary with the level of How do these effects vary with the level of n myopia or when myopia is corrected? myopia or when myopia is corrected?

Method Method n Eye modelling using axial ametropic eyes based Eye modelling using axial ametropic eyes based n on Navarro model eye. Reference height 3mm on Navarro model eye. Reference height 3mm (6mm diameter) (6mm diameter) n Rigorous Rigorous raytracing raytracing with wave aberrations with wave aberrations n referenced to either the anterior corneal plane or referenced to either the anterior corneal plane or natural entrance pupil natural entrance pupil n Raytracing Raytracing into eye from infinity or out of the eye into eye from infinity or out of the eye n from the retina from the retina n Residual wave aberrations determined after Residual wave aberrations determined after n correction – – object at far point of eye or cornea object at far point of eye or cornea correction ablated ablated

Direction in which aberrations Direction in which aberrations are measured are measured 0.36 Uncorrected myopia – referenced 0.34 to cornea 0.32 0.30 0.28 (microns) 0 0.26 4 Into eye C 0.24 Out of eye 0.22 0 2 4 6 8 10 Myopia (D) Spherical aberration increases as myopia increases Spherical aberration increases as myopia increases Effect of direction minimal Effect of direction minimal

Reference plane Reference plane 0.36 Uncorrected myopia - out of eye 0.34 0.32 0.30 0.28 (microns) 0 0.26 4 Cornea C 0.24 Entrance pupil 0.22 0 2 4 6 8 10 Myopia (D) Spherical aberration increases as myopia increases – – Spherical aberration increases as myopia increases greater rate for the cornea than for the entrance pupil greater rate for the cornea than for the entrance pupil

Reference plane Reference plane 0.8 Myopia - out of eye 0.7 0.6 Entrance pupil Spectacle lens 0.5 (microns) 0.4 0 4 C 0.3 0.2 0 2 4 6 8 10 Myopia (D) Spherical aberration increases as myopia increases – – Spherical aberration increases as myopia increases much greater rate for spectacle plane than for entrance much greater rate for spectacle plane than for entrance pupil pupil

corneal pupil corneal pupil difference difference referenced referenced referenced referenced emmetrop emmetrop e e emme- - emme trope trope -9D -9D myope myope 9D 9D myope myope m m m m

Effect of myopia correction Effect of myopia correction - thin ideal lens at cornea - thin ideal lens at cornea 0.36 Myopia - out of eye, corneal 0.34 referenced 0.32 0.30 0.28 (microns) 0 0.26 4 Uncorrected C 0.24 Corrected with thin lens 0.22 0 2 4 6 8 10 Myopia (D) Spherical aberration increases as myopia increases – – Spherical aberration increases as myopia increases negligible difference between uncorrected and negligible difference between uncorrected and corrected conditions corrected conditions

Effect of myopia correction Effect of myopia correction - custom ablation - custom ablation 0.07 Custom correction - out 0.06 of eye 0.05 0.04 0.03 (microns) 0 0.02 4 Entrance pupil C 0.01 Cornea 0.00 0 2 4 6 8 10 Myopia (D) Correction of spherical aberration better when pre- Correction of spherical aberration better when pre- surgical aberrations measured relative to cornea than surgical aberrations measured relative to cornea than to entrance pupil to entrance pupil

Conclusions Conclusions n Direction of wave aberration measurement Direction of wave aberration measurement n has minimal effects on estimated has minimal effects on estimated aberrations aberrations n Reference plane choice (cornea or pupil) is Reference plane choice (cornea or pupil) is n important for highly myopic eyes important for highly myopic eyes n Correcting the eye with ophthalmic Correcting the eye with ophthalmic n correction has little effect on aberrations correction has little effect on aberrations (provided the plane of correction is (provided the plane of correction is unaffected) unaffected) n Correcting aberrations by ablation should Correcting aberrations by ablation should n be more complete if the original be more complete if the original aberrations are referenced to the cornea aberrations are referenced to the cornea rather than to the entrance pupil rather than to the entrance pupil