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.