Implantable Optofluidic Sensor for Assessment of Intraocular Pressure

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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.
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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.

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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)

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Methods

• Sensor mechanism consists of a sealed system of
  two fluid 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 ?
  705nm the upper layer emits wavelength ? 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

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Methods
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Results
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.
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Results
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.
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Results
(A)
(B)
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.
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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)

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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