We read with great interest the study by Mansouri et al titled “Continuous 24-Hour Monitoring of Intraocular Pressure Patterns With a Contact Lens Sensor: Safety, Tolerability, and Reproducibility in Patients With Glaucoma.”1 The authors describe their results about safety and tolerability of the contact lens sensor (CLS) Triggerfish (Sensimed AG) in 40 eyes of 40 patients either with glaucoma or suspected of having glaucoma. Safety and tolerability were good. We, too, could find the same satisfying results in our patients (so far 30 eyes, one of us [C.F.] 3 times).2 In addition, the authors studied the reproducibility of the measurements by repeating their examinations 1 week apart. The Pearson correlation showed an overall correlation of r = 0.59, determined as fair to good. We studied the reproducibility in only 5 subjects (young, healthy eyes; not for 24 hours, but for 2 hours) and found the same results.3 Besides safety, tolerability, and reproducibility, one very important quality is yet missing: the validity of the results gained by the CLS in young subjects as well as in elderly patients with and without glaucoma. Leonardi et al, the “inventors” of this CLS, (only) performed measurements in juvenile porcine eyes by inducing very short-acting spikes of intraocular pressure (IOP) (injection and ejection to ±10 mm Hg within 50 seconds4 or +3 mm Hg within 5 seconds5) and reported excellent results. We performed a similar experiment in 1 enucleated human eye but increased the IOP stepwise by 5 mm Hg using a pump for much longer periods (30 minutes). We could not obtain the expected stepwise profile by means of the CLS.6 No further experimental studies have been published on the validity of the results of the CLS so far. We therefore built a setup of 5 young subjects with healthy eyes in whom we measured the IOP in one eye with applanation tonometry and derived a profile from the second eye with the CLS simultaneously. We changed the position of the head and body (45 minutes upright, followed by 30 minutes supine, 20 minutes with the head and thorax down, and 30 minutes upright). Due to physiology, applanation tonometry showed an increasing slope when the subject was supine or with head and thorax down (Figure 1). In contrast, the CLS profiles did not follow the same shape. Some were flat, and some even went downward (Figure 2). We repeated these experiments under strictly identical conditions and obtained the same—unexpected and disappointing—results. The reasons for the missing validity remain unclear.3 View LargeDownload Figure 1. Mean intraocular pressure (IOP) after 45 minutes in the upright position followed by 30 minutes supine, 20 minutes with the head and thorax down, and again 30 minutes upright. The expected physiological increase and decrease were well demonstrated (5 right eyes, 5 measurements). View LargeDownload Figure 2. Mean values of the contact lens sensor (CLS) measurements in an arbitrary unit after 45 minutes in the upright position followed by 30 minutes supine, 20 minutes with the head and thorax down, and again 30 minutes upright. There were no comparable slopes to the graph gained by simultaneous applanation tonometry of the right eyes (5 left eyes, 27 measurements). We want to express our skepticism in interpreting the results of the CLS. Surprisingly, Mansouri even changed the therapy “immediately in two-thirds of the patients”7 owing to the Triggerfish profiles. Safety, tolerability, and reproducibility are not sufficient to judge a product as holding “the promise to improve glaucoma care.”1 Validity of the results is mandatory, at least in science. More studies are needed to prove this essential quality with this device. Also, the authors named the y-axis in their figure with 4 examples “IOP Pattern, mV.” Correctly it is a CLS pattern. Back to top Article Information Correspondence: Dr Faschinger, University Eye Clinic, Medical University, Auenbruggerplatz 4, 8036 Graz, Austria (email@example.com). Conflict of Interest Disclosures: Drs Faschinger and Mossböck have received expenses and fees for lectures from Alcon, Allergan, MSD, and Pfizer. References 1. Mansouri K, Medeiros FA, Tafreshi A, Weinreb RN. Continuous 24-hour monitoring of intraocular pressure patterns with a contact lens sensor: safety, tolerability, and reproducibility in patients with glaucoma. Arch Ophthalmol. 2012;130(12):1534-153922892888PubMedGoogle Scholar 2. Faschinger C, Mossböck G. Continuous 24 h monitoring of changes in intraocular pressure with the wireless contact lens sensor Triggerfish™: first results in patients [in German]. Ophthalmologe. 2010;107:918-92220535482PubMedGoogle ScholarCrossref 3. Faschinger C, Mossböck G, Krainz S. Validity and reproducibility of sensor contact lens profiles in comparison to applanation tonometry in healthy eyes [in German]. Klin Monbl Augenheilkd. 2012;229(12):1209-121423172649PubMedGoogle ScholarCrossref 4. Leonardi M, Leuenberger P, Bertrand D, Bertsch A, Renaud P. First steps toward noninvasive intraocular pressure monitoring with a sensing contact lens. Invest Ophthalmol Vis Sci. 2004;45(9):3113-311715326128PubMedGoogle ScholarCrossref 5. Leonardi M, Pitchon EM, Bertsch A, Renaud P, Mermoud A. Wireless contact lens sensor for intraocular pressure monitoring: assessment on enucleated pig eyes. Acta Ophthalmol. 2009;87(4):433-43719016660PubMedGoogle ScholarCrossref 6. Faschinger C, Mossböck G, Strohmaier C, et al. 24-Stunden-“Augendruck” Aufzeichnung mit Sensorkontaktlinse Triggerfish: von Euphorie zur Ernüchterung. Spektrum Augenheilkd. 2011;25(4):262-268Google ScholarCrossref 7. Mansouri K, Shaarawy T. Continuous intraocular pressure monitoring with a wireless ocular telemetry sensor: initial clinical experience in patients with open angle glaucoma. Br J Ophthalmol. 2011;95(5):627-62921216796PubMedGoogle ScholarCrossref
JAMA Ophthalmology – American Medical Association
Published: May 1, 2013
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