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Editors Selection IGR 11-1
Examination methods: IOP 24 hrs
Comment by Christopher Girkin on:
15127 Effect of 24-hour corneal biomechanical changes on intraocular pressure measurement, Kida T; Liu JH; Weinreb RN, Investigative Ophthalmology and Visual Science, 2006; 47: 4422-4426
Kida et al . (1058) describe their study defining the 24-hour variation in intraocular pressure, corneal thickness, and corneal hysteresis in fifteen healthy volunteers. The importance of variations in intraocular pressure has been suggested for many years and has been well described in normal and glaucoma subjects in the Hamilton Glaucoma Center Sleep Laboratory. Their prior work demonstrating that peak pressures occur during the nocturnal period emphasize how limited our current clinical assessments are in defining one of the primary causative factors of glaucoma. Additionally, recent clinical trails and several studies have demonstrated the effect of corneal thickness on the risk of developing glaucoma and on the measurements of IOP. Prior work has also demonstrated a significant 24-hour variation in corneal thickness, presumably due to variations in corneal hydration. A relationship between corneal thickness and corneal biomechanical behavior as defined by hysteresis, which might also relate to the risk of glaucomatous progression, has also been demonstrated in other studies. However, no prior work has examined the relationship between corneal thickness, hysteresis, and IOP over the 24-hour period. The authors found that while both the IOP and corneal thickness peak during the nocturnal period, variation in corneal thickness could only explain a small proportion of the IOP increase seen at night (~ 0.66 mmHg) using available conversions and the phase timing was earlier for corneal thickness (peak from 1:30 to 5:30 AM) than for IOP (peak at 5:30 AM). Hysteresis showed no significant pattern of variation through the 24-hour period. The authors concluded that while corneal thickness does indeed increase at night, this has minimal if any impact the measurement of nocturnal IOP. The authors discuss that the study was limited to younger patients without glaucoma and that further study in older subjects and in patients with glaucoma would be important to determine if variation in corneal parameters can effect the 24-hour IOP measurement in these groups.
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