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Cathy Y. Li, Alicia C. How, Yu Xiang George Kong, Evelyn O'Neill, Jonathan G. Crowston, Michael Coote; Raised Pressure Alters Tissue Hydraulic Permeability In Implant Capsules Post Glaucoma Surgery In Rabbit. Invest. Ophthalmol. Vis. Sci. 2011;52(14):637.
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Critical to the success of glaucoma filtration surgery is the management of fluid flow in the filtration area. This study aims to investigate the influence of intraocular pressure elevation (IOP) on in vivo changes in tissue hydraulic permeability of filtration capsule.
Modified filtration surgery with single-late paediatric Molteno implant was performed on anaesthetized New Zealand White rabbits (n=20). Implant was placed in the superotemporal quadrant of the left eye and the fellow eye was used as control.Tissue hydraulic permeability study was performed one week after the procedure by cannulating the internal ostium of the drainage tube through the anterior chamber. Permeability was calculated by measuring fluid flow rate required to maintain a pressure of 15 mmHg. Subsequently, animals were randomized to either (1) no pressure challenge group (n=10) or (2) pressure challenge group (n=10) where an elevated pressure of 25 mmHg for 30min was applied through the cannulated ostium. Tissue hydraulic permeability study was repeated at week 4 followed by harvest of tissue capsule for histological analysis. Statistics performed using Student’s t-test.
Hydraulic permeability one week after implant surgery was 1.218 ± 0.373 mm/min/mmHg. At week 4, group that had no pressure challenge showed little change in hydraulic permeability (1.629 ± 0.539 mm/min/mmHg, P>0.05). However group that had pressure elevation showed marked decline in hydraulic permeability (0.438 ± 0.495 mm/min/mmHg, P<0.05). These changes were associated with increase capsule fibrosis on histology.
Tissue hydraulic permeability is a reliable measure of filtration ability of the filtration area. Early exposure to elevated pressure alters tissue hydraulic permeability of the filtration capsule and may reduce likelihood of eventual success of the filtration surgery.
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