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Michael Hynes, Matthew Bujak, Emmanuel Cherin, Stuart Foster; Design of a subtarsal ultrasonic transducer for mild hyperthermia of meibomian glands treating Dry Eye Disease. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):297.
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© ARVO (1962-2015); The Authors (2016-present)
Dry Eye Disease (DED) is a disorder of the ocular surface that commonly causes pain and low vision, and is typically treated by mild hyperthermia, elevating the tarsus and its meibomian glands by around 6 °C. However, the efficacy of home hyperthermia treatments is debatable, due to the strong tarsal blood perfusion limiting the amount of heat reaching the inner tarsus. We present a design for a therapeutic ultrasonic device for hyperthermia treating DED in a clinical setting and results from preclinical experiments.
The device is composed of a contact lens with an internal air gap, and an ultrasonic transducer mounted inside the lens with an air backing (Fig 1). When powered on, the transducer heats the tarsus from the conjunctival epithelium. The air gap reflects acoustic energy away from the cornea due to the acoustic impedance mismatch between the transducer and the air backing, preventing direct ultrasonic heat deposition. A prototype was built from two 22 mm diameter scleral contact lenses and a 6.5 mm diameter PZT transducer. Hydrophone measurements were made of the acoustic intensity across scleral-abutting lens face. Hyperthermia experiments were performed on a 22 kg pig in vivo. The temperatures of the aqueous humour and marginal eyelid were measured by two embedded type E thermocouples in 4 separate hyperthermia trials. Histopathology was performed on the eyelid and eye tissues.
Acoustic intensity measurements found no evidence of ultrasonic energy propagating through the scleral-abutting lens face. In the eyelid, equilibrium temperature rises of 5-7 °C were achievable in within 15 minutes (Fig 2a). The temperature of the aqueous humour did not rise by more than 1.4 °C in any trial (Fig 2b). Histopathological examination of the treated and control eyelid and eye tissues showed no substantive difference.
The ultrasound device raised the temperature of the eyelid by the desired therapeutic amount typically required to faciltate meibum flow and improve dry eye. No acoustic energy reached the cornea, however heat diffusion raised the temperature of the aqueous humour by no more than 1.4 °C. No adverse histopathological changes were discerned from the treatment in either the eyelid or corneal tissues.
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