What is the real IOP?
Clinical relevance of 24hrs intraocular pressure monitoring
Dr. Arthur Sit emphasizes the significance of circadian IOP fluctuations since it is a significant risk factor for glaucoma progression. IOP is highest at night in most individuals in physiologic positions. He suggested that the primary mechanism of this finding was due to decreased uveoscleral flow and a decrease in the outflow facility. This compensates for decreased aqueous humor production, thus leading to an IOP spike at night time. The advancement of multiple devices i.e., implantable intraocular IOP sensors and hand-held IOP reader promises continuous 24-hour IOP monitoring.
Home monitoring and target pressure
In this talk, Dr. Tony Realini states the importance of home monitoring of IOP. Occasional IOP measurement of IOP at 2-4 times per year is not sufficient for glaucoma management. A rebound tonometer can be a useful tool for home tonometry since the is no need for anesthesia or visible dyes, automated endpoint detection, digital measurement display, potable for patient self-use, and disposable contact components. Moreover, His recent studies suggested that portable rebound provides good reproducibility thus enabling better detection of IOP changes and potential measurement of nighttime supine IOP.
Diurnal IOP changes: body and head position or activities
Dr. Yong Woo Kim suggests that IOP varies with circadian rhythm and with lifestyle-related exogenous factors. Particularly, IOP increases in the supine, lateral decubitus, prone, or lower head position with the neck in flexed or extended state. His recent study reported that greater time of decubitus posture during sleep was associated with NTG. Breath holding, Valsalva maneuver, and obstructive sleep apnea may lead to an IOP increase, but further investigation is needed.
He suggests that exploring the mechanism of diurnal IOP variation may help us understand the mechanism of glaucoma, and further studies are needed to investigate the causal relationship between diurnal IOP spikes and glaucoma development and progression.
Biomarker of IOP
In this talk, Dr. Ernst Tamm highlights that a biomarker for increased trabecular meshwork outflow resistance and subsequent IOP elevation is the increased stiffness of tissues residing within 1㎛ of Schlemm’s canal luminal surfaces. This region correlates to the thickened extracellular matrix fibrils that connect endothelial cells of Schlemm’s canal with JCT cells. An increase in integrin-mediated cell-matrix contracts may be the reason for the increase in inner wall stiffness in POAG.
IOP of NTG patients is truly low?
Dr. Kengo Ikesugi emphasized that we need to take precautions when we diagnose normal tension glaucoma (NTG) based on the following four reasons. First, NTC can be confused with other diseases such as coloboma, and autosomal dominant optic atrophy. Second, Intraocular pressure is difficult to measure due to various ocular conditions (i.e., thin or thick cornea, corneal edema). Third, variability and numerous sources of errors are possible for the current tonometry. Finally, IOP fluctuation may lead to a false diagnosis of NTG for patients with increased IOP.