Advice

Technology overview

Technology overview

This briefing describes the regulated use of the technology for the indication specified, in the setting described, and with any other specific equipment referred to. It is the responsibility of healthcare professionals to check the regulatory status of any intended use of the technology in other indications and settings.

About the technology

CE marking

The SENSIMED Triggerfish was CE-marked in May 2010 as a Class IIa medical device, under the description of 'medical device telemetry applications for recording IOP [intraocular pressure]-related patterns'. The sensor, antenna, data cable, software, and data recorder are included in this CE mark.

Description

The SENSIMED Triggerfish contact lens sensor is a minimally invasive medical device designed to provide continuous 24-hour recording of ocular dimensional changes (changes in the shape of the eye), related to intraocular pressure fluctuations.

The device has the following single-use components:

  • A disposable, soft, contact lens containing a sensor. The lens is made from pure silicone with an oxygen plasma surface treatment, and is worn for 24 hours. The sensor is 585 micrometres thick in the centre and 260 micrometres thick in the periphery. The contact lens diameter is 14.1 mm. The lens is available in 3 curvature radius sizes: 8.4 mm (steep), 8.7 mm (medium) and 9.0 mm (flat). It is fitted like an ordinary contact lens following appropriate measurements of the eye. The lens has an oxygen transmissibility of 119 Dk/t units, which exceeds the levels recommended for normal contact lenses in order to avoid hypoxia of the cornea.

  • A self-adhesive, flexible, disposable antenna which is placed on the skin around the eye for a single 24-hour period.

  • A booklet where the patient can record relevant information to help to understand the patterns recorded in ocular dimensional changes. This may include meal times or periods of sleep or physical activity.

  • A pouch that holds the recorder. This is single-use for hygiene reasons.

The SENSIMED Triggerfish also has the following reusable components:

  • A recorder which is worn around the person's neck in the pouch. Following a recording session, they attend a consultation with an ophthalmologist or optician, where the system is removed. After this consultation, the collected data is retrieved from the recorder, via the Bluetooth USB adapter.

  • A data cable which connects the antenna to the recorder.

  • The Bluetooth USB adapter which transfers data from the recorder to a computer.

  • The battery charger for the recorder.

  • Software for the clinician to visualise the results from the recording session.

The sensor works by measuring minute changes in the dimensions of the eye (the ocular dimensions) through a strain gauge in the contact lens. These patterns are the result of changes in the production and outflow of aqueous humour, combined with the biomechanical properties of the eye walls. Changes in both IOP and in ocular dimensions are caused by the same factors, and so it is assumed that the profiles are closely related. The manufacturer states that by measuring the patterns of ocular dimension changes, the SENSIMED Triggerfish can reveal changes in IOP over the course of 1 whole day and night. The sensor records for 30 seconds at 5 minute intervals over 24 hours. The information is transmitted wirelessly from the sensor to the antenna, and then transferred via a wire from the antenna to the recorder. At the end of a 24-hour recording session, data are transferred from the recorder via a Bluetooth adapter to a computer for analysis. A clinician views the data through computer software which filters out peaks and 'noise' caused by eye blinks.

Data from the sensor are measured in electrical units (millivolts) referenced against a starting value of 0 at each recording session. For this reason, data from the SENSIMED Triggerfish cannot be directly compared with results from currently used IOP measurement devices such as Goldmann Applanation Tonometry (GAT), which measure pressure in millimetres of mercury (mm Hg). Furthermore, the SENSIMED Triggerfish produces a qualitative profile of relative intraocular pressure peaks and patterns over 24 hours, whereas GAT gives definitive IOP values at a fixed time point. SENSIMED Triggerfish is not designed to replace definitive IOP measurements (in mm Hg) with a contact tonometer such as GAT.

Intended use

The SENSIMED Triggerfish device is indicated for continuous recording of IOP-related patterns in ocular dimensions for up to 24 hours in people with glaucoma, at risk of glaucoma, or with suspected high intraocular pressure. The safety and tolerability of the device has only been evaluated in adults aged over 18 years.

The manufacturer states that IOP-lowering medication (eye drops) can be administered as usual by people wearing the sensor, and that sterile artificial tears can be used to hydrate the eye if needed. The manufacturer also states that people wearing a hearing aid can use the SENSIMED Triggerfish, and that it is not contraindicated in pregnant or lactating women.

According to the manufacturer's instructions for use, the SENSIMED Triggerfish should not be used by people with:

  • active eye disease, eye injury or eye abnormality affecting the cornea, conjunctiva, or eyelids

  • a history of eye or eyelid infections including blepharitis and sties

  • a history of adverse effects associated with wearing contact lenses, including intolerance and abnormal ocular response to contact lenses

  • active inflammation or infection of the eye

  • corneal vascularisation

  • insufficiency of lachrymal secretion

  • corneal hypoesthesia

  • a known allergy to silicone

  • skin irritations, certain allergies, eczema, or other indications against wearing patches.

People must not bathe, shower or swim while wearing the device because there is a risk of electric shock. They must not wear full metallic frame glasses and should limit the use of mobile phones and radios to minimise interference with the recording signal. People are also advised not to drive while wearing the sensor.

Setting and intended user

Having examined the patient's eye for contraindications (including a test of visual acuity, central corneal radius and thickness measurement, slit lamp examination [including the conjunctiva and cornea], and intraocular pressure tonometry), a clinician with appropriate training must fit the SENSIMED Triggerfish. Following eye measurements, the device should be fitted in the same way as a regular contact lens. An ophthalmologist or optometrist with appropriate training is needed to interpret the results of the SENSIMED Triggerfish.

Patients may follow their routine activities over the 24-hour period while the device records, including sleeping (but excluding driving or water-based activities, as described above).

Current NHS options

NICE's guideline on glaucoma recommends that GAT should be used to measure IOP in people with chronic open-angle glaucoma (COAG) or OHT, and those who are suspected of having COAG. GAT is a contact technique for measuring pressure in the eye, in which the patient is given anaesthetic eye drops before the pressure inside the eye is measured by applying force directly to the cornea. Non-contact devices that measure pressure in the eye are available, but GAT is considered to be the most accurate (Guidance on the referral of glaucoma suspects by community optometrists, Royal College of Optometrists 2010).

NICE's guideline on glaucoma recommends that as well as GAT, people with COAG, OHT or suspected COAG are offered central corneal thickness measurement, gonioscopy, standard automated perimetry for visual field testing, and optic nerve examination using a slit lamp. The results of these tests indicate the risk of OHT and glaucoma progression, and therefore the level of clinical supervision and treatment needed. The guideline recommends that people with OHT or suspected COAG are assessed at regular intervals (from every 4‑6 months for people at high risk of COAG to 12–24 months for people at low risk). Intervals for assessment of people with confirmed COAG are based on their risk of progression to sight loss, and range from every 2‑6 months to every 6–12 months. NICE recommends that an optometrist or ophthalmologist should perform GAT at every clinical assessment.

It is recognised in literature that IOP levels fluctuate throughout a 24-hour period. Some studies suggest that IOP values tend to peak at night (Bagga et al. 2009), whereas others report that peak IOP levels are reached in the morning (David et al. 1992). Because GAT measurements are usually taken during office hours, peak IOP levels may be missed or underestimated. Fluctuating IOP levels in themselves may contribute to glaucoma progression, although there remains uncertainty about this (Caprioli 2007).

Because the peak IOP value may be underestimated in a single appointment, some NHS patients are referred for phasing. At a phasing clinic, a patient's IOP is measured using GAT every hour or 2 hours throughout the span of a regular working day (Moodie et al. 2010). Full, 24-hour recording of IOP is not routinely conducted in the NHS and needs in‑patient care (NIHR Horizon Scanning Centre 2012).

NICE is not aware of other devices available to the NHS that have a similar function to the SENSIMED Triggerfish.

Costs and use of the technology

The following are list prices provided by the UK distributor of the SENSIMED Triggerfish device (Kestrel Ophthalmics) for July 2014 (excluding VAT):

  • Sensor (steep, medium, flat; single use): £750 for a box of 2

  • Antenna, packaged by pack of 3, left or right (single use): £54

  • Data recorder: £3350

  • Data cable: £534

  • Battery charger: £22

  • Software: £2000

  • Software update (per year): £680

  • Bluetooth USB stick: £17

  • Sleeve for recorder (single use, 25 units): £20

  • User manual: £20

  • Patient booklet (single use, to be given to each patient, 12 units): £4

  • Fitting guide for sensor: £2

  • Quick setup guide: £2

  • Carrying case: £150

From these list prices, it is estimated that each 24-hour use of the SENSIMED Triggerfish device would cost £424–£549 in single-use consumables, plus clinician time. The anticipated lifespan of the recorder and cable are not known, but both have 2-year warranty periods. Information from the manufacturer suggests that the battery supports at least 300 cycles of charge/discharge. Software updates are provided by the manufacturer with no additional charge.

The device calibrates automatically at start-up so no manual calibration is needed. No maintenance contracts are available; in the case of a faulty recorder, the UK distributor would provide a replacement.

The UK distributor offers training to NHS staff on how to use the SENSIMED Triggerfish device. Distributor representatives attend initial patient fitting sessions to resolve any issues.

The SENSIMED Triggerfish is intended as an adjunct to IOP measurement with tonometry techniques such as GAT. The following NHS tariffs for outpatient attendance (2013–14) relating to ophthalmic services have been provided for information (Payments by results tariff 2013–14):

  • First attendance, single professional: £106

  • First attendance, multi-professional: £108

  • Follow-up attendance, single professional: £60

  • Follow-up attendance, multi-professional: £87

No published costs were found for the cost of daytime or 24-hour phasing clinics.

Likely place in therapy

The SENSIMED Triggerfish is currently used in some NHS and private hospitals as part of research studies, and so its place in guiding treatment or improving monitoring is not clear.

The manufacturer suggests that the SENSIMED Triggerfish would be useful in cases where recording takes place before and after an intervention such as a change in medication or surgery. This may provide information on whether an intervention has been effective in lowering IOP.

The SENSIMED Triggerfish may also be of benefit where there is a suspicion that fluctuating IOP levels are contributing to disease progression, or where peak IOP levels are being missed during daytime measurements.

Specialist commentator comments

The specialist commentators were in agreement that continuous recording of IOP-related changes over 24 hours would give a more precise and reliable measurement of IOP compared with single clinic visits. It would also identify IOP-related patterns and this may allow clinicians to better assess patients' responses to treatment and adjust accordingly. Patients with fluctuating IOP readings across single clinic visits, and those with good IOP control, or normal-tension glaucoma, but worsening visual fields may benefit particularly from 24-hour IOP recording. This could potentially benefit patients by reducing the number of clinic visits needed. It may also suggest a more appropriate course of treatment and limit unnecessary treatment changes.

However, the specialist commentators noted that the SENSIMED Triggerfish device's place in managing glaucoma is uncertain: published studies are limited to small patient numbers, and the validity of SENSIMED Triggerfish as a method for measuring IOP-related patterns remains unproven. The device does not directly measure IOP, and agreement studies are needed to confirm the association between SENSIMED Triggerfish and a reference standard such as GAT. In addition, there is uncertainty about whether IOP fluctuations are indeed a risk factor for glaucoma. It was noted that factors influencing 'calibration' between SENSIMED Triggerfish and GAT are unlikely to be stable over time or between patients. Ultimately further studies are needed to support the use of the SENSIMED Triggerfish in managing glaucoma.

All specialist commentators agreed that the cost of the single-use SENSIMED Triggerfish device was high and that, on currently available evidence, its cost effectiveness cannot be determined.

It was noted that a clinician with experience in contact lens fitting should oversee placement of the device. Patients may be required to wait in the clinic following fitting of the contact lens, which could impact resource use and service throughput. A specialist commentator noted that tests of visual acuity, central corneal thickness and radius measurements, slit lamp examination, and IOP would be routine in a NHS glaucoma clinic, and so may not need to be repeated during fitting of the device.

Various factors relating to the material the lens is made of (such as oxygen transmissibility, thickness and wettability) are related to the likelihood of adverse effects occurring. Correct fitting of the lens is important to prevent adverse effects and ensure accurate corneal curvature measurements. It was noted that measurements made by the device may be complicated by factors such as blinks, eye movement, corneal hydration and oxygenation, although the manufacturer states that the SENSIMED Triggerfish software can filter the effects of blinking out of the measurements. As such, more information is needed on lens parameters and fitting considerations.

A specialist commentator suggested that there may be more adverse effects with the SENSIMED Triggerfish than with general contact lenses. Another specialist commentator was uncertain about whether the lens can be cleaned with soft lens solution or saline if dropped during fitting. The manufacturer clarified that a lens should not be used if its sterility cannot be guaranteed, for example if it has been dropped. A specialist commentator noted that it was unclear whether the device could be used following trabeculectomy or aqueous shunt glaucoma surgery. The manufacturer stated that it is possible to use the SENSIMED Triggerfish device in some people who have had these procedures, depending on the position of the bleb, as advised by the physician.

The manufacturer's list of contraindications was considered to be extensive and may limit the population in whom the device can be used. Metallic framed spectacles are common among people in whom the SENSIMED Triggerfish is likely to be used, and this contraindication may affect people's daily activities while wearing the device. Moreover, further detail is needed on the contraindication of 'insufficiency of lachrymal secretion' because this is more common in older people.

Equality considerations

NICE is committed to promoting equality and eliminating unlawful discrimination. We aim to comply fully with all legal obligations to:

  • promote race and disability equality and equality of opportunity between men and women

  • eliminate unlawful discrimination on grounds of race, disability, age, sex, gender reassignment, pregnancy and maternity (including women post-delivery), sexual orientation, and religion or belief, in the way we produce our guidance (these are protected characteristics under the Equality Act 2010).

Age is a protected characteristic defined in the Equality Act (2010). Older people are at increased risk of developing glaucoma; improved management of pressure in the eye may reduce the risk of vision loss and therefore improve quality of life.

Vision loss may be classified as a disability which is a protected characteristic defined in the Equality Act (2010). Improved management of IOP may reduce the risk of vision loss and therefore improve quality of life.

People of African-Caribbean family origin are at increased risk of COAG.

People of Asian family origin are at increased risk of acute angle-closure glaucoma.