By Gail F. Schwartz, MD
This study measured IOP patterns with a contact lens sensor (CLS) during repeated continuous 24-hour monitoring in patients with suspected or established glaucoma, and found that use of the device was safe and tolerable, with fair to good reproducibility. The authors conclude that continuous 24-hour IOP monitoring with this device may be useful in the management of patients with glaucoma.
The authors believe this is the first study to investigate the reproducibility of IOP patterns during repeated 24-hour periods in patients with established and suspected glaucoma. The potential for 24-hour IOP measurement without artificial settings, such as sleep labs, would prove invaluable for glaucoma care. The contact lens measurement is analogous to a Holter monitor. Further validation is clearly needed.
The study included 40 patients with glaucoma or suspected glaucoma. They participated in two 24-hour IOP monitoring sessions at a one-week interval using a CLS (Sensimed). Patients pursued daily activities, and sleep behavior was not controlled. Some patients were on IOP-lowering drops and some were not.
The main adverse events were blurred vision (82 percent), conjunctival hyperemia (80 percent) and superficial punctate keratitis (15 percent). While incidence of conjunctival hyperemia was high, its intensity was graded as mild in 94 percent of patients. In all but one patient, hyperemia was transient and disappeared shortly after removal of the CLS, while in the remaining patient, it lasted up to three days. Hyperemia itself was not associated with other safety findings or discomfort.
The mean (SD) visual analog scale score was 27.2 (18.5) mm during the first monitoring session and 23.8 (18.7) mm during the second (P = 0.22). Overall correlation between the two sessions was 0.59 (0.51 for those not taking glaucoma medication and 0.63 for those on glaucoma medication; P = 0.12).
Since the device is integrated into a soft contact lens (SCL), it may be subject to adverse events similar to those known to occur with any SCL used for vision correction. The electronic circuitry and other integrated elements of the CLS can be a potential source of additional complications.
The authors note that the only adverse events of note were blurred vision and conjunctival hyperemia. They say blurred vision is explained by (1) refractive power of the CLS itself; (2) orthokeratologic effect of the CLS as a result of its (intended) tight fit, which is demonstrated by the change in corneal curvatures and a mean reduction in best-corrected visual acuity by 0.17 (decimal scale) after CLS removal; and (3) potential disturbance of peripheral vision by CLS elements. Therefore, patients were advised to drive carefully or refrain from driving if possible.
Additional validation could be performed by measuring the same patient with drops and after a washout period, although we do not know for sure how much variability exists day-to-day even with consistent dosing. While the CLS could significantly impact clinical practice, it is still not as useful as an HbA1C test is for diabetes, in the sense that patients would be much more likely to be adherent during the contact lens period. Lack of adherence can be seen with the HbA1C but not with this methodology.