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Dan Schwartz Ophthalmology, UCSF. Robert Grubbs Chemistry, Caltech. Sculpting Implants in situ : Light-Adjustable Intraocular Lens. Julie Kornfield, Bob Grubbs Division of Chemistry & Chemical Engineering, Caltech. Jagdish Jethmalani & Chris Sandstedt Calhoun Vision.

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Julie Kornfield, Bob Grubbs Division of Chemistry & Chemical Engineering, Caltech

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Dan Schwartz

Ophthalmology, UCSF

Robert Grubbs

Chemistry,

Caltech

Sculpting Implants in situ: Light-Adjustable Intraocular Lens

Julie Kornfield, Bob Grubbs

Division of Chemistry & Chemical Engineering, Caltech

Jagdish Jethmalani & Chris Sandstedt

Calhoun Vision


  • Cataract Treatment:

    • extraction

    • replacement with an intraocular lens (IOL)

  • 14 million implants/yr. worldwide

  • Current IOLs:

Cornea

Retina

Lens

Pupil

Sclera

Motivation

The Problem: Imperfections in wound healing and lens positioning create refractive errors (farsightedness, nearsightedness and astigmatism).


Clinical Need

  • Cataract surgery is the most commonly performed surgery in patients over 65

  • 50% of patients require spectacles afterward

    • Defocus, Lateral Displacement, Post-Operative Astigmatism (Unpredictable Wound Healing), Rotation.

  • 98% of these are within ± 2 D.


Matrix

Macromer

[High mol. wt. poly(siloxane)]

[Low mol. wt. poly(siloxane)]

Design Principles for New Polymers

Photopolymerizable

end groups

Photoinitiator

(Light sensitive)

==>

-Low glass transition temperature (-125 C)

-Relatively rapid diffusionÆability to modify shape on large length scale

-Non-volatile

-Insoluble in water


hn

hn

Light-induced changes in shape and refractive index

Spatially resolved irradiation

"locking"

==>

==>

Irradiation profile controlled by:

-Transmission mask,

-Spatial light modulator, or

- Rastered laser

-Once the desired shape is achieved, blanket irradiation makes it permanent


CCD Camera

Test

Sample

100 µm

pinhole

He:Ne Laser

f=40 mm

f=125 mm

Ronchi Ruling

300 Lines/inch

Simple Characterization of Lenses

  • Optical Quality

  • Controllable Shape Changes

  • Effective Photolocking

  • Permanent Shape After “Locking”

  • Prior to Adjustment, not altered by Ambient Light


Example of Power Change

Ronchi Interferogram

Before Irradiation:

Lens quality matches current IOLs

Ronchi Interferogram

After Irradiation

Irradiate 2 min with 2 mW/cm2 at 325nm, allow 3 hr for diffusion:

Focal length reduced from 11mm to 4mm!


0.00

-0.50

Diopters

-1.00

-1.50

D

0

20

40

60

Adjustments occur Overnight

  • 12 hours after adjustment is performed, the desired lens power is achieved.

  • 48 hours after adjustment is performed, irradiation of the entire lens makes it permanent.

time post irradiation (hours)

Experiments performed at Calhoun Vision.


Biocompatibility of Material & Irradiation: in vivo evaluation in rabbit

Two weeks after surgery and irradiation, the eye is “quiet”.

Explanted lens for evaluation.

Calhoun Vision and Dr. Nick Mamalis at the University of Utah, Salt Lake City, Utah


Adjustments in vivo are Precise and Predictable

Animal-to-animal variability is small.

Dose-response relationship measured in the lab holds in vivo, too.

Calhoun Vision and Dr. Nick Mamalis at the University of Utah, Salt Lake City, Utah


Astigmatic

adjustment

Increase

lens power

Decrease

lens power

Precise Myopic, Hyperopic & Astigmatic Adjustments

Control orientation & magnitude.

Dose-Response Experiments performed at Calhoun Vision.


Standard Slit-Lamp Footprint

User Friendly Software

Texas Instruments Digital Micromirror Device

Unlimited Flexibility for Lens Modifications

Clinical Implementation

Digital Light Delivery System

Designed & Manufactured with Carl Zeiss Meditec AG

Developed by Zeiss Meditec and Calhoun Vision.


Digital Mirror Device Projects Any Desired Intensity Profile

To decrease lenspower

To Increase lenspower

To correct astigmatism


It works in rabbits, but does it work in people?

Initial clinical experiments (on blind eyes) did not give the predicted adjustment.

Why?

Literature on the human cornea was inadequate:

Transmission values from 30% to 75% were reported

No information on lateral variations in transmission

Careful experiments on human donor corneas:

Transmission values from 56% to 58% were found

Attenuation is greater near the perimeter


Results in Clinical Trials

Precise, predictable adjustments are achieved in patients.


Greyscale image of a tetrafoil fourth-order Zernike correction, projected on a LAL using a digital mirror device

3-D rendering of the Fizeau interference fringes of the LAL 24 hrs after irradiation with the tetrafoil spatial intensity profile.

Arbitrary Wavefront Correction

C. Sandstedt (Calhoun Vision)


Restoring Distance & Near Vision

From the Eye Sight website of student Kyle Keenan at Steton Hall University.


Strategies for “Built-in Bifocals”

Diffractive lens on a Refractive lens

Multizone lens


Irradiate to Add Multiple Zones

1.9 mm central region

0.5 mm ring +2.3 D

Alternating Zones of ± 2 D

2.0 mm central region -2.5 D

and 0.6 mm ring +2.8 D

1.8 mm central region

0.6 mm ring +2.8 D

Experiments performed at Calhoun Vision.


Irradiate to Add a Diffractive Lens

Irradiance Profile

Phase Contrast Microscope Image

Wavefront Image


USAF Target Images

Calhoun Vision Diffractive LAL +3.2 D Add

Distance Focus G4 E3

Near Focus G4 E1

Alcon ReStor IOL (SN#: 893599.049) +3.5 D Add

Near Focus G4 E2

Distance Focus G4 E3


Irradiation Patterns

  • Non-linear Response = Complicated Profiles

  • Currently empirical

Cylinder

Tetrafoil

Need for a theoretical model for systematic design.


Predicting Shape Change:Is this a previously solved problem?

  • Well known:

    • Polymerization reaction kinetics

    • Diffusion processes in non-deforming media

    • Solid deformation caused by external forces

  • Not so well known:

    • Deformation driven by diffusion


Some Interesting Features

  • Deformation without external force

    • Mechanical loading is determined completely within the object

    • The “load” is imposed by spatially-resolved chemical reaction

    • Free surface boundary condition

  • No material enters or leaves

    • Deformation arises from redistribution of material within the object


Diffusion and Deformation in Polymeric Gels

  • Stress-Diffusion Coupling Model (SDCM)

    • T. Yamaue and M. Doi (2004)

    • Restricted to situations in which an externally applied load on a rigid bounding surface drives fluid out of the gel

  • Mixture Theory approach

    • J. Shi, K. R. Rajagopal, and A. Wineman (1981)

    • Externally imposed pressure-drop across the material drives flow through a slab

    • Requires some ad hoc assumptions regarding constitutive equations and boundary conditions

  • Variational approach

    • S. Baek and A. R. Srinivasa (2004)

    • Gel is swollen in a bath; can be generalized to other choice of closed system

    • Provides rigorous underpinning for the requisite constitutive equations and boundary conditions.


photopolymerization

0

1

diffusion

swelling

2

3

Important Processes

hn

global shape change


External Stimulus

incorporated via

f(x,0)

Pertinent Material Properties

Mmc f0[A] G0

F(x,t)

Deformation Gradient Tensor

Important Processes: Relevant Parameters

hn

f(x,t)


Inter-Relationships among the Processes

Material Specifications

hn

Mmc f0[A] G0

External Stimulus

Ii (x,t)

D

I(x,t)

f(x,t)

rm (x,t)

jm (x,t)

G(x,t)

F(x,t)

Global Shape Change

Internal Variables

Each arrow is a physical (and, therefore, mathematical) relation


Material Specifications

Mmc f0

G0

D

f(x,t)

jm (x,t)

Diffusion

hn

[A]

External Stimulus

Ii (x,t)

1) Diffusion

I(x,t)

rm (x,t)

G(x,t)

F(x,t)

Global Shape Change

Internal Variables


f(x,t)

F(x,t)

Swelling

Material Specifications

hn

Mmc f0[A] G0

External Stimulus

Ii (x,t)

D

I(x,t)

rm (x,t)

jm (x,t)

G(x,t)

2) Swelling

Global Shape Change

Internal Variables


Global Shape Change

Material Specifications

hn

Mmc f0[A] G0

External Stimulus

Ii (x,t)

D

I(x,t)

f(x,t)

rm (x,t)

jm (x,t)

G(x,t)

F(x,t)

3) Global Shape Change

Internal Variables


Conclusions & Future Directions

  • Photosensitive Elastomers for Remote Manipulation

    • Enable wavefront corrections for static abberrations

    • Function in air, vacuum and aqueous media

    • Present interesting theoretical mechanics questions

    • May find application in “labs-on-a-chip” or space-based optics

Acknowledgements

Robert Grubbs

Chemistry,

Caltech

Dan Schwartz

Ophthalmology, UCSF

“That Man May See” FoundationChartrand FoundationCalhoun Vision


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