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Presbyopic Correction ThroughNegative Spherical Aberration
Seema Somani
Presbyopic Correction Through NegativeSpherical Aberration
The symptoms ofmoderate presbyopiacan be alleviatedby introducingcontrolled amounts ofnegative sphericalaberration. Thetreatment trades best-focus image for greaterdepth of focus.
By Seema Somani, PhD
Positive NegativeZero
Refresher: What is “Spherical Aberration(SA)”?
PositiveParaxial power <Peripheral power
Negative
Paraxial power >Peripheral power
Paraxial power =Peripheral power
Zero
Presbyopia can be mitigated byincreasing the eye’s depth of focusProblem
Accommodation loss creates a fixed-focus system with symptoms of blurry images formost of the object distances.
SolutionIntroduce a controlled amount of negative spherical aberration to achieve longer depthof focus.
Methods
Optical simulations were used to designand test long depth of focus in a model eye
Anterior Cornea parameters
Radius (mm)
Conic Const
2nd order coef
4th order coef
6th order coef
8th order coef
Basic model 7.8 -0.5 0 0 0 0 Aspheric model 7.71 -0.5 -0.000816 0.000825 -0.000231 0.000019
The model eye wasoptimized to achieve thebest focus of the objectat infinity
Pupil Diameter = 6mm
AnteriorCornea
PosteriorCornea
Lens
Retina
Results
Through-focus spot diagrams show thatimage quality is more consistent withnegative SA
Spot diagram isanalogous to PSF
Model eye wasoptimized for thebest focus of anobject at infinity
Focus
Object moves closerObject moves farther
away
2 m 2 m
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 10 20 30 40 50 60
Radius in microns (1micron ~ 0.2arcmin)
En
erg
y F
rac
tio
n
SA ZeroInfinity
SA NegativeInfinity
The Encircled Energy of an eye with negativeSA changes less for far and near objects thanthe eye with zero SA
For both far and near objects, the PSF of aneye with negative SA changes less than an eyewith zero SA.
0
0.05
0.1
0.15
0.2
0.25
0.3
-10 -5 0 5 10Position in microns (1micron ~ 0.2arcmin)
Geometric polychromatic point spread function was calculated using 3wavelengths – 450, 550, and 650 nm.
SA Zero;Obj Inf
SA Negative;Obj Inf
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
-0.075 -0.05 -0.025 0 0.025 0.05 0.075Shift from focus in mm
MTF
at 5
0 cy
/mm
MTF of an eye with negative SA showsless variability for far and near objects
FocusObject moves closer
Zero
Negative
Conclusions
Simulations with a model eye show thatreduction in image quality (contrast andsharpness) is slower with negativespherical aberration than when nospherical aberration is present.
0
0.05
0.1
0.15
0.2
0.25
0.3
-10 -5 0 5 10Position in microns (1micron ~ 0.2arcmin)
Controlled amounts of sphericalaberration can mitigate moderatepresbyopia by trading best-focus imagequality for longer depth-of-focus.
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