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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
1
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
4
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
5
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
8
• 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
9
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