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Editors Selection IGR 11-1

Clinical Examination Methods: 24-h IOP Monitoring: Effect of Body Posture

Comment by John Liu on:

72600 Twenty-four hour intraocular pressure monitoring with the SENSIMED Triggerfish contact lens: effect of body posture during sleep, Beltran-Agulló L; Buys YM; Jahan F et al., British Journal of Ophthalmology, 2017; 101: 1323-1328

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When patients slept with a 30-degree head-up wedge pillow, intraocular pressure (IOP) readings taken every two hours were significantly lower compared to a flat sleep body position. In the current study, investigators used the Sensimed Triggerfish contact lens sensor to monitor the related IOP change pattern in 12 patients with progressive glaucoma. The new results surprisingly did not corroborate the anticipated IOP elevation during the sleep period or the IOP-lowering effect due to the head-up sleep body position. The authors noticed a significant baseline drift upward. However, the correlation between the sensor output signals and the Goldmann IOP readings, taken before the contact lens fitting and after the removal of contact lens, was absent. These observations cast doubt on the use of this contact lens sensor to evaluate individual IOP changes in glaucoma patients. For all the study participants except one, polysomnography showed obstructive sleep apnea. It is known that obstructive sleep apnea reduces the nocturnal IOP elevation. Without the anticipated nocturnal IOP elevation, variation of experimental data could overshadow a small IOP-lowering effect and the frequently observed baseline drift became relatively prominent. Since the sensor is embedded in silicone material, not hydrogel, it is impossible to determine the corresponding applanation IOP over the contact lens. By design, the sensor software uses the first output signal as the set point for baseline. Physiological environment when the sensor first lands on the corneal-conjunctival surface and when the sensor has been sitting on the corneal-conjunctival surface for 24 hours may be very different.

The new results surprisingly did not corroborate the anticipated IOP elevation during the sleep period or the IOP-lowering effect due to the head-up sleep body position

For example, time-dependent changes in the sensor temperature and the tightness of fit associated with circular conjunctival pressure mark may contribute to the 24-hour baseline drift. There is no evidence that these confounding factors have been appropriately addressed in the senor's engineering design. While the current study cautions the use of this new technology beyond the indication of determining 24-hour IOP peak timing, the study affirms that more research is needed to develop the contact-lens based IOP sensor as a clinically useful tool for glaucoma management.

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