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Contact Lens Sensor Triggerfish –
What Do We Know?
Deputy of the Head of the Department of Ophthalmology Medical University, Graz, Austria
M ultiple measurements of the intraocular pressure (IOP) at different times during the day and at night provide information on the
peak and trough values, and the number and magnitude of short- and long-term fluctuations. Goldmann applanation tonometry
(GAT) is generally used only once or a few times during office hours. The ideal would be a safe, well-tolerated, and valid 24-
hour measurement. The contact lens sensor Triggerfish ® (SENSIMED AG, Lausanne, Switzerland) is claimed to measure changes in corneal
curvature induced by changes in IOP. After animal experiments, multiple studies in healthy and glaucoma patients were performed, in some
cases revealing good correlation with tonometer values, in others poor or no correlation at all. The interpretation of the 24-hour profiles is not
standardised, and there is no agreement upon definition of a fluctuation. Comparability between mmHg and an electrically measured value
cannot be established. Despite the fact that safety and tolerability of the device are good, the absence of definitive validation of the results
means that the product cannot yet be recommended for daily clinic or office use. This product is also no longer marketed as providing ’24-
hour IOP profile’ or ‘continuous monitoring of IOP fluctuation’, but now rather as recording a ’24-hour profile of ocular dimensional changes’.
Keywords Intraocular pressure, sensor contact lens, strain
gauge, validity of “pressure” profile
Disclosure: Christoph Faschinger received honoraria
for lectures from Allergan and AMO. Editorial assistance
was provided by Sven Obholzer, MD in translating work.
No funding was received in the publication of this article.
This study involves a review of the literature and did not
involve any studies with human or animal subjects
performed by any of the authors.
Open Access: This article is published under the
Creative Commons Attribution Noncommercial License,
which permits any non-commercial use, distribution,
adaptation and reproduction provided the original
author(s) and source are given appropriate credit.
Received: 25 July 2016
Accepted: 1 August 2016
Citation: European Ophthalmic Review,
2016;10(2):113–6 Corresponding Author: Christoph Faschinger,
Auenbruggerplatz 4, A-8036 Graz, Austria.
The main risk factor for glaucoma damage is an intraocular pressure (IOP) above an undeterminable
threshold value for an individual patient. The IOP is not constant but is subject to multiple
physiological and pathological fluctuations. These can vary in magnitude and duration, for example,
the pulsation of retinal vessels, Valsalva manoeuvre, changes from upright to supine position, and
circadian rhythm. The reference standard to determine IOP is Goldmann applanation tonometry
(GAT), which is usually performed only once and seldom multiple times during office hours. This
only gives information of a few seconds out of 86,000 seconds in a day, and as such decreases the
value of information gained. Measurements in sleep laboratories are cumbersome. In addition to
this there is still critical discussion about weather fluctuations pose an additional independent risk
factor for glaucoma progression. 1,2
Multiple IOP measurements take time and the repeated topical anaesthetic used with GAT may
damage the cornea. An alternative would be multiple or alternating IOP measurements with
non-contact or other tonometers, which however are not the reference standard. Similar to non-
invasive 24-hour electrocardiogram (continuous) or blood pressure measurements (intermittent),
continuous IOP measurement would perhaps provide additional important information. This idea
was seemingly realised with the contact lens sensor (CLS) Triggerfish ® (SENSIMED AG, Lausanne,
Switzerland). This medical device received CE certification in 2008 and American Food and Drug
Administration (FDA) approval in 2016.
The review describes the current state of knowledge about this medical device, especially
discussing the question whether an application in daily clinical or office use for diagnosing and
therapeutic monitoring of glaucoma patients is necessary and/or recommended.
Contact lens sensor Triggerfish – product description
The theory published by Leonardi et al., was, that IOP could be measured indirectly by a strain
gauge embedded in a contact lens. 3 The basis for this theory was that the corneal curvature in
the limbal area (diameter of the strain gauge at 11.5 mm) changed with variation in IOP, and that
this could be measured. Two circular strain gauges made from platinum-titanium (7 µm) and a
loop antenna made from gold (30 µm) for data transfer and a microchip (50 µm) for wireless data
management were embedded in a silicone contact lens (diameter 14.2 mm), through a complicated
manufacturing process. For better patient tolerance it was coated with an oxygen plasma. Power
is supplied by the recorder and an antenna which is stuck around the orbit. Measurements are
taken at 5 minute intervals for 30 seconds, within these 30 seconds 10 times with 300 datasets.
The gained data are transferred wirelessly via this antenna to a recorder which is worn around the
waist. During the 24-hour measurement period spectacles with metal frames must be avoided,
but all other normal daily activities should be performed and documented in a diary. This is with
the exception of activities that include moisture and water (e.g. swimming, showering etc.) and
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