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C. J. Roberts, A. M. Mahmoud, M. D. Twa, H. J. Karol, P. A. Weber, H. Kanngiesser; Comparison of PASCAL Dynamic Contour Tonometry Using a Standard Slip-lamp Mounted Device, a Handheld Configuration, and a Contact Lens Mounted Sensor: Implications for Continuous 24 Hour IOP Monitoring. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1254.
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The ability to monitor 24 hour intraocular pressure (IOP) is important for Glaucoma diagnosis and treatment. However, currently only discrete measurements in awake subjects can be performed. The purpose of the current study is to evaluate a pressure sensor mounted in a contact lens which interfaces to a PASCAL Dynamic Contour Tonometer (DCT).
Preliminary testing was performed on 4 eyes, with acquisition of 5 replicate measurements using each of three configurations of the PASCAL DCT: 1) the PASCAL DCT in its standard, slit-lamp mounted configuration, 2) a hand-held configuration that uses a PASCAL contour tip mounted in a standard Perkins tonometer that is connected by wire to the DCT signal processor, and 3) a rigid gas-permeable contact lens embedded PASCAL pressure sensor that was connected by wire to the DCT signal processor. Measurements with a quality index of 3 or better were analyzed. Analysis of variance was performed to compare the measurements obtained with the three configurations of both intra-ocular pressure (IOP) and ocular pulse amplitude (OPA).
The mean values of IOP and OPA using the standard configuration were 16.1+1.1 mmHg and 2.6+0.2 mmHg, respectively. The mean values of IOP and OPA using the hand-held configuration were 16.5 +1.4 mmHg and 3.1+0.1 mmHg, respectively. The mean values of IOP and OPA using the contact lens were 18.1 +1.5 mmHg and 3.0+1.1 mmHg, respectively. These values were not significantly different (IOP: p=0.08; OPA: p=0.63), due to the small n in this feasibility study.
The trend toward higher IOP measurements with the contact lens sensor compared to the other two configurations may be due to a fixed contact area between the lens and cornea that is bigger than the self adjusting contact area between normal eyes and the standard contour tip. A bigger contact area may provoke an initial increase in measured IOP. Long term measurements are needed to show if this is a transient effect. Further product development may also enable wireless connection with data acquisition electronics, which has the potential to provide continuous IOP measurements during normal activities, including sleep.
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