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V.J. Rubinstein, B.M. DeBroff; IOP Changes Associated with Variable OVD Filling of the Anterior Chamber Through a Self-Sealing Corneal Incision . Invest. Ophthalmol. Vis. Sci. 2003;44(13):198.
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Purpose: To evaluate the effect of variable anterior chamber filling with OVD's (ophthalmic viscoelastic device) on intraocular pressure. Methods: Nineteen human cadaver eyes were evaluated. Each eye had balanced-salt saline injected through the pars-plana until the IOP was normalized (12-24mmHg) as measured by Shiotz tonometry. A BD Edge head stilleto 0.9 mm knife was then used to create a self-sealing corneal paracentesis approximately one mm from the limbus at the plane of the iris. Viscoat was injected into the anterior chamber so that the anterior chamber was uniformly filled, but not deepened. The IOP was then measured by Shiotz tonometry. Additional Viscoat was then injected into the anterior chamber so that there was complete filling with deepening of the anterior chamber and until Viscoat refluxed from the paracentesis site. The IOP was measured again by Shiotz tonometry. Results: Prior to OVD injection the mean IOP was 20.1 mmHg (SD 4.48). During testing, when Viscoat "just filled" the anterior chamber the mean IOP of tested eyes was 31.84 mmHg (SD 6.49). By contrast, when there was forceful regurgitation of Viscoat through the incision site, the mean IOP was 81.95 mmHg (SD 19.78). Paired T test analysis was performed. The baseline IOP compared to IOP when anterior chamber was "just filled" gave a p-value of 2.84 x 10 -7. Baseline IOP compared to maximally filled anterior chamber gave a p-value of 1.78 x 10 -9. The IOP with "just filled" anterior chamber compared to maximally filled anterior chamber gave a p-value of 1.3 x 10 -10. Conclusions: Ophthalmologists often create a paracentesis incision for cataract surgery as their first step and then inject OVD to deepen the anterior chamber prior to creating the main incision. A self-sealing corneal wound can trap viscoelastic within the anterior chamber and forceful injection of viscoelasitc has been shown by this study to significantly elevate the intraocular pressure. This elevated intraocular pressure may be sufficient to cause occlusion of the retinal vasculature, decrease perfusion to the ciliary body and optic nerve head and decrease corneal clarity. All of these situations can compromise visual acuity and limit the surgical outcome. Forceful injection of OVD should be avoided as an initial step of clear cornea phacoemulsification to avoid dangerous elevation of intraocular pressure.
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