FLEXIBLE ELASTOMER OPTICAL WAVEGUIDE FOR WHOLE-GLOBE SCLERAL CROSSLINKING

Moonseok Kim*, Sheldon J.J. Kwok*, Theo G. Seiler, Harvey H.. Lin, Eric Beck, Marleen Engler, Peng Shao, Theo Seiler, Irene Kochevar, Seok-Hyun (Andy) Yun

December 2016, International CXL Experts Meeting, Zurich, Switzerland

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Sclera crosslinking for myopia control

•  High prevalence of myopia needs to be addressed with more effective interventions

•  Altered sclera biomechanics has been identified in progression of pathologic myopia

•  Photochemical crosslinking is a promising technique to arrest scleral elongation and prevent myopia

2

The myopia boom. Nature 2015

The light delivery challenges

3

•  Whole globe sclera crosslinking (SXL) is challenging•  Sclera is anatomically difficult to access•  Uniform light delivery required around the

globe•  Miniature LEDs is a possibility, but they are

limited in flexibility and generate heat

•  We propose use of a flexible waveguide optimized for uniform light delivery into the sclera

The waveguide design

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1.  Flexible waveguide to wrap around the eyeball 2.  Requires n2 > 1.38 (sclera) enabling waveguiding by total internal

reflection 3.  Use of transparent material to minimize light absorption (loss) 4.  Uniform light delivery to scleral tissue through scattering loss

Air: n1 = 1.0 Fiber optic (laser input)

θc

Light extracted to sclera (n3 = 1.38)

n2

Fiber optic (laser input)

The waveguide design•  Made of transparent and flexible

PDMS (polydimethylsiloxane)

•  RIPDMS = 1.42 > RIsclera = 1.38

•  Dimensions•  Length= 70 mm•  Width= 5 mm•  Thickness ~ 1 mm

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Coupled 450 nm light

Wrapped around eye

3 0 0 4 5 0 6 0 0 7 5 0

6 0

7 0

8 0

9 0

1 0 0

W a v e le n g th (n m )

Tra

nsm

itta

nce

/cm

(%

) Wrapped around eye

The waveguide design

6

450 nm light

𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼∝ 𝐼𝐼𝑒−α𝐼𝐼𝑧

Light extracted to sclera 𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼

Fiber optic (laser input)

Flat waveguide à z

100

50

0

Ligh

t rem

aine

d (%

)

70350z, along length of waveguide (mm)

543210Approximate number of bounces

Flat waveguide𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼(%

)

The waveguide design

7

Tapering the waveguide compensates for exponential attenuation: less bounces in thicker region, more bounces in thinner regions

100

80

60

40

20

706050403020100z, along length of waveguide (mm)

Flat Tapered

𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼(%

)

Light extracted to sclera

Fiber optic (laser input)

Tapered waveguide à z (70 mm) width: 5 mm

1.5mm 0.5mm

Periscleral crosslinking with riboflavin and blue light

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•  Fresh porcine eyes stained with 0.5% riboflavin solution for 30 minutes

•  Illumination with 450 nm at 25-50 mW/cm2 for 30 minutes

•  Fluorescence intensity was monitored during SXL

•  Scleral strips were acquired after SXL and analyzed by tensiometry

450 nm excitation Riboflavin fluorescence

After photobleaching

0 9 0 1 8 0 2 7 0 3 6 00 .0

0 .5

1 .0

A n g le (D e g re e s )

I ex

t (n

orm

.)

T a p e r e d(1 .5 to 0 .5 m m )

F la t(1 m m )

Obtaining uniform light delivery

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Fluorescence distribution around the globe

Proximal Distal

Tensiometry results

10

Elastomer waveguide

Direct laser illumination

4 6 8 1 00 .0

0 .5

1 .0

1 .5

S tra in (% )

Str

ess

(M

Pa

)

W ith e la s to m e r w a v e g u id e

C o n tro l

D ire ct illum ina tion

50 mW/cm2

0

5

1 0

1 5

Yo

un

g's

mo

du

lus

at

8%

str

ain

(M

Pa

)

Control Directillumination

Elastomer waveguide

Prox

imal

(0° t

o 18

0 °)

Dis

tal

(180

° to

360°

)

•  SXL with blue light, 50 mW/cm2 resulted in a 1.8-fold increase in the Young‘s modulus at 8% strain•  No significant difference between direct illumination and with elastomer waveguide•  No significant difference between proximal (0° to 180°) and distal (180 ° to 360 °)

50 mW/cm2

0° 180°

Proximal

Distal

Tensiometry results

Conclusions & future work

•  We demonstrated periscleral crosslinking of porcine eyeballs with flexible elastomer waveguide resulting in a ~2-fold increase in Young’s modulus

•  Further optimization of waveguide geometry and irradiation parameters will improve light uniformity

•  Future experiments include SXL with waveguides in vivo

Acknowledgements

Funding from National Institutes of Health (NIH)The authors have patents and invention disclosures on related technologies