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M. E. Arnoldussen, M. Shusterman, G. G. Gum, S. Sanislo, S. Hansen; Intraocular Pressure Measurement During Application of the Oraya I-Guide in Yucatan Mini-Swine. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3118.
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The purpose of this study was to measure the intraocular pressure during application of the Oraya I-Guide in Yucatan mini-swine. The I-Guide is a vacuum-coupled scleral lens designed for stabilization and precise manipulation of the eye and is used during radiotherapy treatment for age-related macular degeneration on the Oraya IRay system. While no radiation was delivered in this study, clinical parameters were simulated to evaluate IOP across a range of testing conditions.
Four eyes from mini-swine were subject to tests lasting approximately five minutes. For each eye, a pressure sensor catheter (Data Sciences International PA-C40) was inserted into the vitreous and monitored remotely by a receiver (DSI RMC-1). Application of the I-Guide was repeated using different levels of vacuum and applanation, both below and above the clinical standard. A spring attached to a force gauge was used to simulate applanation bias on the eye. A vacuum gauge (Supco DPG25V) placed inline with the I-Guide tubing was used to verify the suction levels.
The increase in IOP during application of the I-Guide results from the cornea conforming to the lens under an applied vacuum as well as the applanation force holding the eye stable. All tests showed a slight decrease in vacuum pressure over time, but were absolutely stable in terms of the I-Guide remaining coupled to the eye. In comparing vacuum levels at each applanation force, there is no significant difference between elevated IOP at normal vacuum versus the higher vacuum level. The maximum IOP levels generally occurred at the beginning or end of each procedure when the I-Guide was placed or removed. While these signals are real, they represent the effect of physical manipulation of the eye which is already known to cause transient changes in IOP.
The maximum IOP increase due to application of the I-Guide was recorded at 40.5 mmHg using a sensor inserted into the posterior chamber of pig eyes. Under normal conditions, the increase in IOP was well below 30 mmHg. Once the eye is captivated by the lens, the level of vacuum does not appear to have an impact on IOP. Additional forces applied to the eye, whether by the user applying the I-Guide or from the spring-loaded holder, cause a transient increase in IOP. These results show that the I-Guide is a safe patient interface for performing treatments on the IRay system.
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