Efficacy of a contact lens sensor for monitoring 24-h intraocular pressure related patterns

Abstract

Purpose: To study performance of a contact lens sensor (CLS) for 24-hour monitoring of IOP-related short-term patterns and compare with IOP obtained by pneumatonometry.

Methods: Prospective clinical trial. Thirty-one healthy volunteers and 2 glaucoma patients were housed for 24 hours in a sleep laboratory. One randomly selected eye was fitted with a CLS (Triggerfish, Sensimed, Switzerland), which measures changes in ocular circumference. In the contralateral eye, IOP measurements were taken using a pneumatonometer every two hours with subjects in the habitual body positions. Heart rate (HR) was measured 3 times during the night for periods of 6 minutes separated by 2 hours. Performance of CLS was defined in two ways: 1) recording the known pattern of IOP increase going from awake (sitting position) to sleep (recumbent), defined as the wake/sleep (W/S) slope and 2) accuracy of the ocular pulse frequency (OPF) concurrent to that of the HR interval. Strength of association between overall CLS and pneumatonometer curves was assessed using coefficients of determination (R2).

Results: The W/S slope was statistically significantly positive in both eyes of each subject (CLS, 57.0 ± 40.5 mVeq/h, p<0.001 and 1.6 ± 0.9 mmHg/h, p<0.05 in the contralateral eye). In all, 87 CLS plots concurrent to the HR interval were evaluated. Graders agreed on evaluability for OPF in 83.9% of CLS plots. Accuracy of the CLS to detect the OPF was 86.5%. Coefficient of correlation between CLS and pneumatonometer for the mean 24-h curve was R2 = 0.914.

Conclusions: CLS measurements compare well to the pneumatonometer and may be of practical use for detection of sleep-induced IOP changes. The CLS also is able to detect ocular pulsations with good accuracy in a majority of eyes.

Trial registration: ClinicalTrials.gov NCT01390779.

Conflict of interest statement

Competing Interests: The authors received funding from Sensimed AG. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials.

Figures

Fig 1. CONSORT flow chart.

Fig 2. Twenty-four-hour IOP pattern measured in CLS (1B) and pneumatonometer eye (1A) (N = 30).

Coefficient of determination between the two eyes was R2 = 0.956. Pneumatonometer data were collected sitting during the diurnal/wake period and supine during the nocturnal/sleep period.

Fig 3. Example of 30-second plot with the CLS (contact lens sensor) with the patient asleep.

The oscillating signal represents diastolic to systolic variations in IOP due to heart activity, referred to as OPF.

Fig 4. Example of 24-h CLS pattern recorded in a study subject.

The red line represents the wake/sleep (W/S) slope as determined from 1 hour pre- to 1 hour post-sleep.

Fig 5. Calculation of wake/sleep (W/S) slope as determined from 1 hour pre- to 1 hour post-sleep with CLS (blue).

For the pneumatonometer means (red), actual relative time is not used, but rather one point before, one point closely following and one point after “lights off time”, with a two hour difference between each.