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

• n eye aberration
• n eye aberration

measurement measurement

David Atchison and Neil David Atchison and Neil Charman 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 n Corneal flattening following myopic

Corneal flattening following myopic 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 n Custom ablation based on pre-operative

Custom ablation based on pre-operative 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 n Does the direction in which aberrations are

Does the direction in which aberrations are measured affect these measurements measured affect these measurements ie ie into- into- the-eye (Tracey) versus out-of-the-eye the-eye (Tracey) versus out-of-the-eye (Hartmann-Shack)? (Hartmann-Shack)?

n n What is the effect of the reference plane on

What is the effect of the reference plane on these measurements eg cornea versus entrance these measurements eg cornea versus entrance pupil? pupil?

n n How do these effects vary with the level of

How do these effects vary with the level of myopia or when myopia is corrected? myopia or when myopia is corrected?

Method Method

n n Eye modelling using axial ametropic eyes based

Eye modelling using axial ametropic eyes based

• n Navarro model eye. Reference height 3mm
• n Navarro model eye. Reference height 3mm

(6mm diameter) (6mm diameter)

n n Rigorous

Rigorous raytracing raytracing with wave aberrations with wave aberrations referenced to either the anterior corneal plane or referenced to either the anterior corneal plane or natural entrance pupil natural entrance pupil

n n Raytracing

Raytracing into eye from infinity or out of the eye into eye from infinity or out of the eye from the retina from the retina

n n Residual wave aberrations determined after

Residual wave aberrations determined after correction correction – – object at far point of eye or cornea

• bject at far point of eye or cornea

ablated ablated

Direction in which aberrations Direction in which aberrations are measured are measured

Spherical aberration increases as myopia increases Spherical aberration increases as myopia increases Effect of direction minimal Effect of direction minimal

Uncorrected myopia – referenced to cornea Myopia (D) 2 4 6 8 10 C 4 (microns) 0.22 0.24 0.26 0.28 0.30 0.32 0.34 0.36 Into eye Out of eye

Reference plane Reference plane

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

Uncorrected myopia - out of eye Myopia (D) 2 4 6 8 10 C 4 (microns) 0.22 0.24 0.26 0.28 0.30 0.32 0.34 0.36 Cornea Entrance pupil

Reference plane Reference plane

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

Myopia - out of eye Myopia (D) 2 4 6 8 10 C 4 (microns) 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Entrance pupil Spectacle lens

difference difference pupil pupil referenced referenced

• 9D
• 9D

myope myope

corneal corneal referenced referenced

emmetrop emmetrop e e

emme emme-

• trope

trope 9D 9D myope myope

m mm m

Effect of myopia correction Effect of myopia correction

• thin ideal lens at cornea
• thin ideal lens at cornea

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

Myopia - out of eye, corneal referenced Myopia (D) 2 4 6 8 10 C 4 (microns) 0.22 0.24 0.26 0.28 0.30 0.32 0.34 0.36 Uncorrected Corrected with thin lens

Effect of myopia correction Effect of myopia correction

• custom ablation
• custom ablation

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

Custom correction - out

• f eye

Myopia (D) 2 4 6 8 10 C 4 (microns) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 Entrance pupil Cornea

Conclusions Conclusions

n n Direction of wave aberration measurement

Direction of wave aberration measurement has minimal effects on estimated has minimal effects on estimated aberrations aberrations

n n Reference plane choice (cornea or pupil) is

Reference plane choice (cornea or pupil) is important for highly myopic eyes important for highly myopic eyes

n n Correcting the eye with ophthalmic

Correcting the eye with ophthalmic 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 n Correcting aberrations by ablation should

Correcting aberrations by ablation should 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