Tanu Sharma, B. Optom

Optometrist, Vision Eye Centre, New Delhi, India


A glaucoma is a group of disorders that usually happens when fluid builds up in front of the eye that extra fluid increases the Intraocular Pressure in the eye which damages the optic nerve. (1)

This article is all about the various ways of measuring Intra Ocular Pressure (IOP) beyond the tonometry procedure for 24 hours.

Multiple measurements of the intraocular pressure 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 is generally used only once or a few times during office hours as a part of Diurnal variation measurement. (2)

To avoid all these problems Swiss Company has introduced a Contact lens sensor (CLS) for the detection of IOP-related changes in the eye.

Figure 1: Illustration of Triggerfish contact lens
(Pic Courtesy: https://new-glaucoma-treatments.com/the-sensimed-triggerfish-sensor-device/)

SENSIMED Triggerfish CLS is a non-invasive wireless soft contact lens that is designed to take automated recordings of IOP – related patterns for up to 24 hours. The CLS is a soft disposable contact lens containing a sensor that sits on the anterior surface of the eye like an ordinary lens, and it is made from pure silicone with an oxygen plasma surface treatment to avoid drying with an oxygen transmissibility of 119 dk/t unit to avoid hypoxia sensor is 585 μm thick in the center and 260 μm thick at the periphery with a diameter of 14.1 mm after the lens is fitted, a self-adhesive, flexible, disposable antenna is placed on the periorbital region for a single 24-hr period and a data cable connects the antenna to the recorder which is worn in a pouch. (3)The Triggerfish CLS takes 300 strain gauge readings over a 30-second period every 5 minutes, for a total of 86,400 data points over a 24-hour period and the data are sent via Bluetooth connection to a computer for analysis. Of note, the data points are measured in millivolts or “millivolt equivalents” and are relative to the very first measurement, which is taken as zero. (3)

One study suggests that the correlation between IOP measurements taken by Tonopen and the IOP profile measured by SENSIMED CLS in the contralateral eye of patients undergoing laparoscopic colorectal surgery is poor. In addition, there were a small but significant number of patients who were unable to tolerate the contact lens. (4)

Another study explained that the Triggerfish CLS is a safe and well-tolerated device for monitoring IOP-related patterns in healthy and glaucomatous individuals.

One study conflicts that Triggerfish CLS is safe and provides reproducible results and recent studies suggest a myriad of potential indications for Triggerfish CLS, .including predicting glaucomatous progression and predicting the efficacy of glaucoma treatment. (5)

One of the studies suggests that during 24-hours measurement there was no signal drift and very low noise. Patients are concerned about electronic devices possibly interfering with the measurement of contact lens sensors that use of their cordless telephone, smartphone or computer does not cause any problems. (6)

Another study explained that sleep position affects IOP as measured by Triggerfish in some patients with progressive glaucoma. The upward drift in Triggerfish output detected in >50% of the subjects requires further investigation to establish whether the increased output values over time are an artifact induced by the Triggerfish or a real change. (7)

Take Home Message

The Triggerfish CLS is a safe and well-tolerated device for monitoring IOP-related patterns in healthy and glaucomatous individuals although patients experience progressive vision loss despite seemingly normal office-measured IOP.

It showed that 24-hour recording with sensimed triggerfish leads to improved clinical outcomes for patients, such as control of IOP, progression from ocular hypertension to glaucoma, or vision loss.



  1. https://www.aao.org/eye-health/diseases/what-is-glaucoma [Last accessed: 16th Dec 2022, 04:30 pm AEDT]
  2. Faschinger C. Contact Lens sensor triggerfish–what do we know?. Journal-Contact Lens Sensor Triggerfish–What Do We Know?. 2016.
  3. https://www.ophthalmologytimes.com/view/triggerfish-pressure-sensor-promising [Last accessed: 16th Dec 2022, 04:40 pm AEDT]
  4. Vitish‐Sharma P, Acheson AG, Stead R, Sharp J, Abbas A, Hovan M, Maxwell‐Armstrong C, Guo B, King AJ. Can the SENSIMED Triggerfish® lens data be used as an accurate measure of intraocular pressure? Acta ophthalmologica. 2018 Mar;96(2):e242-6.
  5. Dunbar GE, Shen BY, Aref AA. The Sensimed Triggerfish contact lens sensor: efficacy, safety, and patient perspectives. Clinical Ophthalmology (Auckland, NZ). 2017;11:875.
  6. Rabensteiner DF, Rabensteiner J, Faschinger C. The influence of electromagnetic radiation on the measurement behaviour of the triggerfish® contact lens sensor. BMC ophthalmology. 2018 Dec;18(1):1-5.
  7. Beltran-Agulló L, Buys YM, Jahan F, Shapiro CM, Flanagan JG, Cheng J, Trope GE. Twenty-four hour intraocular pressure monitoring with the SENSIMED Triggerfish contact lens: effect of body posture during sleep. British Journal of Ophthalmology. 2017 Oct 1;101(10):1323-8.