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Sumit Dhingra, Ian Eames, Andre Nicolle, Vladimir Taban, Steve Brocchini, Peng T. Khaw; The Effect Of Scleral Flap Shape And Size On Aqueous Flow And Pressure Following Trabeculectomy: Implications From Mathematical And Physical Modelling. Invest. Ophthalmol. Vis. Sci. 2011;52(14):651.
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To predict the consequences of the shape and size of a scleral flap on both the aqueous flow distribution and the pressure difference across the flap following trabeculectomy. Posterior flow has been shown to result in more diffuse non-cystic blebs.
Two modelling methods were applied: the first used a numerical method to calculate the flow between the flap and sclera; the second approach used a enlarged physical model of the flap. Three flap shapes of different aspect ratios were considered: rectangular, triangular and semi-circular.
The calculations show that the pressure difference across the flap depends on the shortest dimension of the flap. Scleral flaps with larger surface areas always generate a larger pressure difference. Figure 1a shows the variation of flux ratio R (a measure of the flow away from limbus to the total flow) for both rectangular and triangular flaps. The symbol (x,o) correspond respectively to rectangular and triangular flaps. For W/L=2, R=1/2 as half the total fluid moves posteriorly. If W/L2. Figure 1b shows that as the aspect ratio of the rectangular and triangular flaps increases from 1 to 6, the decrease in the pressure difference is not significant.
The pressure difference across the scleral flap after trabeculectomy and aqueous flow away from the limbus are important in the formation of posterior diffuse blebs. Wider flaps may be preferential as they increase posterior flow. For flaps with aspect ratios <2, triangular flaps may result in more posterior flow. Theoretical and physical biomodelling may be useful techniques in improving surgical methods.
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