A Novel Contact Lens Sensor System for Continuous Intraocular Pressure Monitoring: Evaluation of Accuracy in Human Eyes

Abstract

Purpose: To evaluate the accuracy of intraocular pressure (IOP) monitoring by a novel contact lens sensor system (CLS) in human eyes.

Design: Cross sectional study.

Participants: Eighty eyes of 80 participants were recruited and divided into 3 groups: (1) 40 normal eyes; (2) 30 eyes with primary open-angle glaucoma (POAG) or ocular hypertension (OHT) with normal IOP (<21 mmHg), including 27 POAG eyes and 3 OHT eyes; and (3) 10 POAG/OHT eyes with high IOP (≥21 mmHg), comprising 4 POAG eyes and 6 OHT eyes.

Methods: Participants wore the CLS to enable continuous monitoring of IOP while they assumed both seated and supine positions, with each position maintained for 10 minutes. Intraocular pressure was also measured by the Goldmann applanation tonometer (GAT) while participants were seated and the Perkins applanation tonometer (PAT) in supine, both before and after CLS wear.

Main outcome measures: The average IOP measured by CLS during the final 1-minute of seated and supine positions was compared with IOP measured by GAT and PAT before and after CLS wear. Also, intraclass correlation coefficient and Bland-Altman analyses were performed.

Results: No significant differences were found between pre-CLS GAT and CLS in normal eyes or between all comparisons in POAG/OHT eyes with high IOP (P > 0.5). Contact lens sensor system IOP was higher than pre-CLS PAT and post-CLS GAT/PAT IOP in normal eyes (P < 0.01), and higher than pre-CLS GAT and post-CLS PAT in POAG/OHT eyes with normal IOP (P < 0.05). All IOP differences were within ± 2 mmHg. Intraclass correlation coefficient showed moderate to very strong consistency (0.51 ≤ r ≤ 0.95, P < 0.05) except for that between sitting CLS and post-CLS GAT in POAG/OHT eyes with high IOP. Bland-Altman analysis showed that over 80% of points were within ± 5 mmHg and over 60% within ± 3 mmHg.

Conclusions: With good agreement in IOP measurement compared with applanation tonometry in seated and supine positions, across normal and POAG/OHT eyes, the CLS can be used for fairly accurate continuous IOP monitoring.

Financial disclosures: Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Keywords: Contact lens; Continuous tonometry; Glaucoma; Intraocular pressure.

Figure 1

Images of the CLS and IOP measurement. A, The constitute of the CLS. B, Contact lens in an eye. C, Participant wearing the CLS. CLS = contact lens sensor system; IOP = intraocular pressure.

Figure 2

The flow chart of the trial and IOP was continuously monitored by CLS. Participants receiving IOP measurement using applanation tonometers and the CLS. A, The flow chart of participants receiving IOP measurements using applanation tonometers and the CLS. B, Continuous IOP curve of a participant measured by CLS and mean IOP extracted from the curve for comparative analysis. CLS = contact lens sensor system; GAT = Goldmann applanation tonometer; IOP = intraocular pressure; PAT = Perkins applanation tonometer.

Figure 3

Comparisons of IOP values measured by CLS, pre-CLS, and post-CLS GAT/PAT. CLS = contact lens sensor system; GAT = Goldmann applanation tonometer; IOP = intraocular pressure; PAT = Perkins applanation tonometer. ∗P < 0.05; ∗∗P < 0.01; ∗∗∗P < 0.001.

Figure 4

Correlation of IOP values measured between CLS and applanation tonometry. A, sitting CLS IOP versus pre-CLS GAT IOP in normal group. B, sitting CLS IOP versus post-CLS GAT IOP in normal group. C,D, supine CLS IOP versus pre- and post-CLS PAT IOP in normal group. E,F, sitting CLS IOP versus pre- and post-CLS GAT IOP in patient group with normal IOP. G,H, supine CLS IOP versus pre- and post-CLS PAT IOP in patient group with normal IOP. I,J, sitting CLS IOP versus pre- and post-CLS GAT IOP in patient group with high IOP. K,L, supine CLS IOP versus pre- and post-CLS PAT IOP in patient group with high IOP. CLS = contact lens sensor system; GAT = Goldmann applanation tonometer; IOP = intraocular pressure; PAT = Perkins applanation tonometer.

Figure 5

Bland–Altman plot of means against the difference between the IOP values measured by CLS and applanation tonometry. Bland–Altman plot comparing the CLS and applanation tonometry. The x-axis represents the mean of the 2 methods, and the y-axis represents the difference between the 2 methods (CLS–applanation tonometry). The solid line represents the mean difference, whereas the dashed lines represent the 95% limits of agreement (mean difference ± 1.96 standard deviation). The red lines represent the limits of agreement at ±3 mmHg, and the blue lines represent ±5 mmHg. CLS = contact lens sensor system; GAT = Goldmann applanation tonometer; IOP = intraocular pressure; PAT = Perkins applanation tonometer.