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      Effect of Pneumatic Suction Ring Placement on Intraocular Pressure in Cats

      Ophthalmic Research
      S. Karger AG
      Cat, Intraocular pressure, Pneumatic suction ring

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          Purpose: To determine the effect of placing a pneumatic suction ring on intraocular pressure (IOP) in the cat and to design an improved method to generate a stable elevation of IOP. Methods: A pneumatic suction ring was applied to the eye in cats while the IOP was monitored. Three groups of animals (10 per group) were used. A vacuum pressure of 450 mbar was applied in one step to eyes of group 1 (anesthetized) and to group 2 (euthanized) cats. In group 3 (anesthetized) cats, an initial vacuum pressure of 250 mbar was applied, followed by a vacuum of slowly increasing pressure at a rate of 5 mbar/min for a total of 40 min to 450 mbar. Results: After the one-step application of a vacuum (450 mbar) to the eyes of anesthetized cats (group 1), IOP peaked within the first minute from a basal value of 25 ± 2 mm Hg (mean ± SD) to 90 ± 7 mm Hg. It then rapidly decreased to 69 ± 2 mm Hg 5 min later and continued to decrease to 39 ± 4 mm Hg 40 min later. This sharp peak and decline of IOP were also observed in eyes of euthanized cats (group 2). The basal IOP of these eyes was 8 ± 1 mm Hg. It rose to 18 ± 2 mm Hg immediately after the application of vacuum pressure (450 mbar) and returned to the basal level 5 min later. In contrast, the eyes of group 3 receiving an initial vacuum of 250 mbar followed by a 5 mbar/min vacuum increment exhibited a rapid increase in IOP and a very stable plateau (mean IOP = 62–68 mm Hg), lasting the whole study period (40 min). Conclusion: IOP after a one-step application of a vacuum via a pneumatic suction ring is self-adjusting and declines rapidly over time. This decline in IOP can be overcome by a supplementary increment in vacuum pressure.

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          Flow of aqueous humor in the canal of Schlemm.

          A mathematical model is presented for the flow of aqueous humor in Schlemm's canal in the eye. The model introduces a canal segment between two collector channels as a rectangular channel with porous upper wall. Two cases have been considered in the model: (I) the inner porous wall of the canal is rigid; (II) the inner wall is collapsible. Analytical solution of the governing equation in case I is straightforward, whereas the nonlinear equation in case II is solved by an iterative procedure. Aqueous fluid pressure and flow profiles in the proposed model are drawn, and the effects of important parameters on these profiles are brought out and discussed. It is concluded that for case I, resistance to aqueous flow is influenced by the filtration constant of the trabecular and endothelial meshwork and that narrowing of the canal reduces outflow. In case II, an increase in intraocular pressure (IOP) or compliance coefficient of the canal inner wall increases the collapse of the canal, which offers increased resistance to flow resulting in the decreased flow whereas increasing filtration constant facilitates aqueous outflow. These theoretical results suggest that increased IOP or decreased rigidity of the inner wall may contribute to the development of increased resistance as observed in some cases of glaucoma and that increasing values of filtration constant may contribute to the facility of outflow increase.

            Author and article information

            Ophthalmic Res
            Ophthalmic Research
            S. Karger AG
            October 2001
            01 October 2001
            : 33
            : 5
            : 271-275
            Dean A. McGee Eye Institute, University of Oklahoma Health Science Center, Oklahoma City, Okla., USA
            55680 Ophthalmic Res 2001;33:271–275
            © 2001 S. Karger AG, Basel

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            Page count
            Figures: 4, References: 15, Pages: 5
            Original Paper

            Vision sciences,Ophthalmology & Optometry,Pathology
            Intraocular pressure,Cat,Pneumatic suction ring


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