a new definition of refraction: basics and beyond
DESCRIPTION
A New Definition of Refraction: Basics and Beyond. Austin Roorda, Ph.D. Unversity of Houston College of Optometry. First use of Optics as Vision Aids. reading stones from 1000 AD. 1284 Salvino D'Armate built the first spectacles which were used as reading glasses. - PowerPoint PPT PresentationTRANSCRIPT
A New Definition of A New Definition of Refraction:Refraction:
Basics and BeyondBasics and Beyond
Austin Roorda, Ph.D.
Unversity of Houston College of Optometry
First use of Optics as Vision AidsFirst use of Optics as Vision Aids
reading stones from 1000 AD1000 AD
1268 Roger Bacon discussed possibilities of magnification with lenses
Roger Bacon
1284 Salvino D'Armate built the first spectacles which were used as reading glasses
1451 Nicholas of Cusa uses negative lenses to cure myopia (nearsightedness)
Kepler
1604 Kepler describes the optics of near and far sightedness
1748: Benjamin Franklin invents the bifocal lens
1827: Sir George Biddel Airy invents spectacles for astigmatism
RetinoscopyRetinoscopy
PhoropterPhoropter
AutorefractorAutorefractor
Refraction SystemsRefraction Systems
AberrometersAberrometersVISX Wavescan
Summit Autonomous Custom Cornea
B&L Zywave
Wavefront Sciences Complete Optical Analysis System
TraceyTech Tracey 1
What is the Wavefront?What is the Wavefront?
converging beam=
spherical wavefront
parallel beam=
plane wavefront
What is the Wavefront?What is the Wavefront?ideal wavefrontparallel beam
=plane wavefront
defocused wavefront
What is the Wavefront?What is the Wavefront?parallel beam
=plane wavefront
aberrated beam=
irregular wavefront
ideal wavefront
What is the Wavefront?What is the Wavefront?
aberrated beam=
irregular wavefront
diverging beam=
spherical wavefront
ideal wavefront
What is the What is the Wave AberrationWave Aberration??diverging beam
=spherical wavefront wave aberration
-3 -2 -1 0 1 2 3
-3
-2
-1
0
1
2
3
Wavefront Aberration
mm (right-left)
mm
(su
peri
or-in
ferio
r)
Wave Aberration: DefocusWave Aberration: Defocus
Wave Aberration: AstigmatismWave Aberration: Astigmatism
-3 -2 -1 0 1 2 3
-3
-2
-1
0
1
2
3
Wavefront Aberration
mm (right-left)
mm
(su
peri
or-in
ferio
r)
-3 -2 -1 0 1 2 3
-3
-2
-1
0
1
2
3
Wavefront Aberration
mm (right-left)
mm
(su
peri
or-in
ferio
r)
Wave Aberration: ComaWave Aberration: Coma
-3 -2 -1 0 1 2 3
-3
-2
-1
0
1
2
3
Wavefront Aberration
mm (right-left)m
m (
supe
rior
-infe
rior)
Wave Aberration: All TermsWave Aberration: All Terms
How Do We Interpret the How Do We Interpret the Wave Aberrations?Wave Aberrations?
Wave Aberration Surface MapWave Aberration Surface Map
-2 -1 0 1 2
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
Wave Aberration Contour MapWave Aberration Contour Map
mm (right-left)
mm
(su
perio
r-in
ferio
r)
Breakdown of Zernike TermsBreakdown of Zernike Terms
-0.5 0 0.5 1 1.5 2123456789
1011121314151617181920
Zer
nik
e te
rmCoefficient value (microns)
astig.defocus
astig.trefoilcomacomatrefoil
spherical aberration
2nd order
3rd order
4th order
5th order
Root Mean SquareRoot Mean Square
2 2 2 22 0 2 12 2 2 3 .......RMS Z Z Z Z
astig
mat
ism te
rm
defo
cus t
erm
astig
mat
ism te
rm
trefo
il ter
m……
Point Spread FunctionPoint Spread Function
Point Spread Function vs. Pupil SizePoint Spread Function vs. Pupil Size
pupil images
followed by
psfs for changing pupil size
1 mm 2 mm 3 mm 4 mm
5 mm 6 mm 7 mm
Simulated ImagesSimulated Images
20/40 letters
20/20 letters
Strehl RatioStrehl Ratio
diffraction-limited PSF
Hdl
Heye
actual PSF
Strehl Ratio = eye
dl
H
H
Modulation Transfer Modulation Transfer FunctionFunction
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 50 100 150
spatial frequency (c/deg)
con
tra
st
Area under the MTF
20/20 20/10
Applications for AberrometryApplications for Aberrometry
Can we Build a Better Can we Build a Better Autorefractor?Autorefractor?
-0.5 0 0.5 1 1.5 2
1
234
567
89
10
111213
141516
171819
20
Ze
rnik
e t
erm
Coefficient value (microns)
astig.
defocus
astig.
trefoil
coma
coma
trefoil
spherical aberration
2nd order
3rd order
4th order
5th order
choose the spectacle
correction that minimizes the
second order Zernike terms
Can we Build a Better Can we Build a Better Autorefractor?Autorefractor?
perf
ect P
SF
choose the spectacle
correction that maximizes the
strehl ratio
defocus/astigmatism
Can we Build a Better Can we Build a Better Autorefractor?Autorefractor?
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
-1.4
-1.2 -1
-0.8
-0.6
-0.4
-0.2 0
0.2
0.4
0.6
0.8 1
Defocus (D)
Are
a un
der
MT
F (
0 -
50 c
/d)
choose the spectacle correction that maximizes the
area under the MTF
Can we Build a Better Can we Build a Better Autorefractor?Autorefractor?
• Challenge– RMS, Strehl, and MTF area are not
correlated
• Solution– population data (Rochester, Indiana)– early results suggest maximizing metrics
like the Strehl ratio works best
Aberrometric RefractionAberrometric Refraction
• conventional autorefractors are
accurate to ~ 0.5 D
• aberrometric autorefractor should
achieve ~ 0.1 D accuracy **
** ± 0.25 D is an acceptable correction error
Diagnosis of High-order Diagnosis of High-order AberrationsAberrations
Post - RKPost - RK Post - LASIKPost - LASIK
KeratoconusKeratoconus