Transcript Slide 1

Measurement of Higher Order Aberrations in
Contact Lenses
James J. Butler
Pacific University
Physics Department
Forest Grove, OR
Matt Lampa
Pacific University
College of Optometry
Forest Grove, OR
Pacific University Physics Department
Pacific University Physics
• Small, liberal arts
college setting ~ 1500 undergraduates
• Innovative teaching
• All physics majors have senior
capstone research experience
• Faculty connected with College of Optometry
Physics Department Optics Tools
• Nd:YAG pumped OPO laser system
• Continuously tunable from 420 nm
to 2500 nm
• 4 ns pulses @ 10 Hz repetition rate
• Shack-Hartmann wavefront sensor
• Zernike representations of tilt, defocus,
astigmatism, coma, spherical, and
higher order aberrations
• 39 x 31 element lenslet array provides
λ/50 wavefront sensitivity over a
6 mm x 5 mm aperture
Optics Research in the Physics
Department
• Optical Limiting
– collaboration with Naval
Research Laboratory
– eye and sensor protection
– scope sights, binoculars, and
fiber optic systems
– must operate at visible and
infrared wavelengths
Lens
• “nonlinear absorbers” - increase
absorption as irradiance of
incident light increases
Capillary fiber
Incident
Light 
• capillary fiber makes high
irradiance beam interact with
nonlinear absorber for large distance
Nonlinear Core
Optical Limiting Experimental Setup
P.C. Running
LabVIEW
Energy Detector
Frequency Doubled Nd:YAG Laser or
Nd:YAG pumped OPO
Energy Ratiometer
Sample Holder
Fiber Cladding
8%
Pick Off
Energy Detector
or
CCD camera
Objective
Core
Objective
Nonlinear Transmission at 1050 nm
Relative Transmission
Energy out of core (nJ)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.0
90
80
70
60
50
40
30
20
10
0
0.1
1.0
10.0
100.0 1000.0
Energy coupled into core (nJ)
1 nJ into core
0
100
200
Energy coupled into core (nJ)
300 nJ into core
300
Contact Lens Aberrations
A new collaboration between Dr. Butler and Dr. Lampa
Initial Funding:
Pacific Research Institute for Science and Mathematics
Collaborator:
Shannon Soper – physics major, Pacific University
Wavefront Aberrations
Ideal Image Formation
Spherical wavefronts
Real image point
Real object point
Real Image Formation
exit pupil
of optical
system
Ideal (paraxial)
image plane
ideal
wavefront
ideal image
point
aberrated
wavefront
Wavefront aberrations quantified
using Zernike polynomials
http://wyant.optics.arizona.edu/
zernikes/zernikes.htm
Wavefront Aberrations Notes
• Piston, tilt, and power (defocus) are ignored in discussions of aberrations
• 2nd order Zernike polynomials – astigmatism
• 3rd order Zernike polynomials – coma & trefoil
• 4th order Zernike polynomials – spherical, secondary astigmatism, & tetrafoil
astigmatism
coma
spherical
Contact Lens Aberrations
• Liang et al. (1994) measured aberrations of 2 uncorrected eyes
Eye type
2nd
order
(μm)
3rd
order
(μm)
4th
order
(μm)
-1.5 D myope
1
0.5
0.3
emmetrope
0.8
0.8
0.2
• Dietze et al. (2003) measured spherical aberration (4th order Zernike) of 17 eyes
Eye type
Uncorrected (μm)
myope
(up to -8.5 D)
-0.1 to +0.4
emmetrope
-0.1 to +0.2
hyperope
(up to +4.5 D)
-0.05 to +0.6
• SA of off-eye soft contact lenses theoretically
calculated and ranged from about -0.2 to +0.1 μm
(approximately linear with lens power)
• Change in SA of eyes wearing soft contact lenses
approximately equal to calculated SA of off-eye soft
contact lenses (although theory was consistently
below measured)
More Contact Lens Aberrations
• Lu et al. (2003) measured Zernike aberrations up to 5th order for 54 myopic eyes (-2 to -8 D)
Average RMS
aberrations
2nd
order
(μm)
3rd
order
(μm)
4th
order
(μm)
5th
order
(μm)
uncorrected
0.75
0.35
0.2
0.3
Soft contact lens
corrected
0.8
0.4
0.25
0.4
Hard contact lens
corrected
0.5
0.3
0.2
0.3
• Numbers in red significantly different
than uncorrected
• Eye conforms to hard lens shape
leading to reduction in 2nd order
(astigmatism)
• Increase in high order aberrations for
soft contact lens correction not
explained
• Off-eye aberrations of lenses not
measured
• Jeong et al. (2005) and Kollbaum et al. (2008) measured aberrations of off-eye contact
lenses in a wet cell but did not compare to on-eye lenses
• Bakaraju et al. (2010) developed sophisticated bench-top model eye that could be used to
compare on-eye and off-eye contact lens aberrations but no reports have been made yet.
Proposed Work
• Develop physical model eye that closely matches optical characteristics of
actual eye
- Use gelatin with appropriate water content to obtain n ~ 1.37 (Dr. Dan
Boye, Physics Department, Davidson College)
- Gelatin promises to allow the fabrication of model eye with appropriate
refractive index and any desired optical properties (e.g. astigmatism,
keratoconus, etc.)
• Carefully measure and characterize aberrations of physical model eyes
• Measure and characterize aberrations of various contact lenses (single vision
and multifocal) off-eye using a wet cell.
• Measure aberrations of physical model eyes with contact lenses in place
• Determine a relationship between off-eye and on-eye aberrations of contact lenses
and characteristics of model eye
References
• J. Liang, B. Grimm, S. Goelz, and J.F. Bille, “Objective measurement of wave aberrations of the
human eye with the use of a Hartmann-Shack wave-front sensor,” Journal of the Optical Society of
America A, Vol. 11, pp. 1949-1957 (1994).
• H.H. Dietze and M.J. Cox, “On- and off-eye spherical aberration of soft contact lenses and
consequent changes in effective lens power,” Optometry and Vision Science, Vol. 80, pp. 126-134
(2003).
• F. Lu, X. Mao, J. Qu, D. Xu, and J.C. He, “Monochromatic wavefront aberrations in the human
eye with contact lenses,” Optometry and Vision Science, Vol. 80, pp. 135-141(2003).
• T.M. Jeong, M. Menon, and G. Yoon, “Measurement of wave-front aberration in soft contact
lenses by use of a Shack-Hartmann wave-front sensor,” Applied Optics, Vol. 44, pp. 4523-4527
(2005).
• P. Kollbaum, M. Jansen, L. Thibos, and A. Bradley, “Validation of an off-eye contact lens ShackHartmann wavefront aberrometer,” Optometry and Vision Science, Vol. 85, pp. E817-E828 (2008).
• R.C. Bakaraju, K. Ehrmann, D. Falk, A. Ho, and E. Papas, “Physical human model eye and
methods of its use to analyse optical performance of soft contact lenses,” Optics Express, Vol. 18,
pp. 16868-16882 (2010).