Transcript Implantable Optofluidic Sensor for Assessment of Intraocular Pressure

Implantable Optofluidic Sensor for
Assessment of Intraocular Pressure
Christina Antonopoulos MD, Mostafa Ghannad-Rezaie, Nikos Chronis
PhD, Shahzad Mian MD
W.K. Kellogg Eye Center and Department of Mechanical Engineering
University of Michigan, Ann Arbor, Michigan
The authors of this poster have received research funding from the
National Institutes of Health (Grant 1R21NS062313 ).
The authors hold no proprietary interest in the material presented
herein.
Abstract
Purpose: To develop an implantable opto-fluidic IOP sensor that enables long-term continuous
monitoring of intraocular pressure.
Methods: The design consists of an implantable MicroElectroMechanical Systems (MEMS)
pressure sensor that converts IOP variations into spectral signals in the near infrared (NIR)
region (700 nm-900 nm). The sensor integrates a pressure-tunable elastomeric microlens with a
Quantum Dot (QD) bilayer, each layer having a distinct emission wavelength. A collimated NIR
laser beam, focused through the microlens into the QD bi-layer, induces fluorescent excitation of
the bilayer.
Results: IOP variations can cause changes in the focal length of the microlens which result in
changes in the ratiometric fluorescent intensity emitted by the bilayer. Intraocular implantation
may occur with: (1) iris fixation, (2) integration into intraocular lenses, (3) integration into
keratoprosthesis devices.
Conclusion: An implantable, opto-fluidic sensor can enables long-term, continuous IOP
monitoring, and is small in size when compared to the other pressure transducers. This device
will be used for ex vivo and in vivo testing to establish safety and efficacy.
Purpose
 To develop an implantable opto-fluidic
intraocular pressure sensor that enables
long-term, continuous monitoring of
intraocular pressure
 To successfully implant the device into the
optic of an intraocular lens, keratoprosthesis
or iris-sutured for stand-alone monitoring for
use in clinical scenarios in which frequent IOP
monitoring is critical (advanced glaucoma) or
otherwise unfeasible (keratoprosthetic eyes)
Methods:
 Sensor mechanism consists of a sealed system of two fluid
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chambers covered by thin elastomeric membranes; one acts as
a deflectable membrane and the other as a microlens coupled
with a tunable Quantum Dot (QD) bilayer.
When external pressure (intraocular pressure, IOP) is applied
the deflectable membrane deflects downwards and by virtue of
fluid displacement induces a convex deflection of QD bilayer.
The microlens focal length remains constant.
A collimated near infrared (NIR) laser beam, focused through
the microlens onto the QD bilayer induces fluorescent excitation
of the bilayer; the lower layer emits light at wavelength λ =
705nm; the upper layer emits wavelength λ = 800 nm
IOP variations cause QD bilayer position to change in the focal
plane, bringing the upper layer out of focus and the lower layer
in focus and therefore changes in the ratiometric fluorescent
intensity emitted by the bilayer.
The signals are send back to the external unit for self-read-out
Methods
Results
20
1.2 um X 1.2 um
1.0um X 1.0um
0.8um X 0.8 um
1.4um X 1.4um
18
16
Displacment(um)
14
12
10
8
6
4
2
0
5
10
15
20
25
Pressure (mmHg)
30
35
40
45
Figure 1: Intraocular pressure versus deflection of deflectable membrane (square, silicone nitride, 297nm thickness) or differing
sizes. The external pressure is increased from 1mmHg to 45mmHg. The experiment is repeated for six membranes of each size,
all with identical fabrication. The deflection at maximum external pressure ±4.5% and ±3% for the largest and smallest
membranes, respectively.
Results
3500
3000
1.5
intensity
2500
2000
1500
1000
705nm
data1
800nm
data2
1.25
0
200
400
600
800
wavelength (nm)
1000
1200
2500
705nm/800nm
data3
intensity
1
2000
1500
1000
500
3500
0
200
3000
.75
400
600
800
wavelength (nm)
1000
1200
2500
intensity
ratio
500
2000
1500
1000
500
.5
0
200
400
600
800
wavelength (nm)
1000
1200
Intensity
.25
4,000
3,000
2,000
1,000
0
-10
0
10
20
30
Pressure (mmHg)
40
50
Figure 2: The intensity and ratio of light emitted by the Quantum Dot channels as a function of intraocular pressure. The lens
focuses on the 800nm QD monolayer at atmospheric pressure. As external pressure is increased, the membrane deflects and
moves the 705 nm layer and 800nm layer into and out of the focal plane, respectively. Therefore, the ratio of the signal
intensities of the 705nm QD layer and the 800nm QD layer increases. We repeated the experiment for six identically
fabricated devices. There is up to ±6% variation in the ratio of channel across devices. The ratio change is statistically
significant for 6mmHg change.
Results
1.35
0.55
1.3
0.5
1.2
ratio
ratio
1.25
1.15
0.45
0.4
1.1
Device 1
Device 2
Device 3
1.05
1
Device 1
Device 2
Device 3
0.35
0.3
0
5
10
15
20
25
0
5
10
15
day
day
(A)
(B)
20
25
Figure 3: Long-term response of three identical devices submersed for three weeks in water. Each device response is
recorded every 3 days to 20mmHg (A) and 40mmHg (B). A variation in the ratio of ±5% and ±6% is observed for 20mmHg
and 40mmHg external pressure, respectively.
Discussion
 We are developing an implantable, opto-fluidic
sensor that (i) enables long-term, continuous IOP
monitoring, (ii) is small in size, and (iii) is theoretically
safely implantable into the eye
 Safe implantation in the eye will theoretically
generated a data set of continuous IOP
measurements to enhance the management of any
form of glaucoma
 Our device is applicable to patients with glaucoma,
ocular hypertension, glaucoma suspects, patients in
whom prior anterior segment surgery precludes
measurement or monitoring of IOP (e.g.
keratoprosthetic eyes)
Conclusions
 An implantable, opto-fluidic sensor can
potentially enable valuable, long-term,
continuous IOP monitoring for clinicians
 Future goals include in vivo testing to
establish safety and efficacy and implantation
into intraocular lenses and keratoprostheses