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M. Abdulrazik; Model of Pulsatile-Flow of Aqueous Humor Through the Iris-Lens Canal for the Prediction of Clinical Conditions Predisposing to Pupillary Block. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1280.
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To present a model of pulsatile-flow of aqueous humor from the posterior- (PC) to the anterior-chamber (AC), and to analyze the ability of this model to predict high risk clinical conditions predisposing to pupillary block.
The model assumes non-continuous flow of aqueous humor through the iris-lens canal. Aqueous that fills the canal will be ejected toward the AC-side of the canal at certain time intervals, and between two events of aqueous ejection there is no actual flow through this canal. The PC-AC pressure gradient indicator of the present model is the pupillary pumping rate (PPR). PPR was calculated from the aqueous flow rate and the calculated volume of iris-lens canal ([PPR] = [aqueous flow rate] / [volume of iris-lens canal]).
PPR values were generated by incorporating pupillary diameter (PD, 1 to 8 mm), aqueous flow rate (AFR, 1 to 2.5 µl/min) and iris-lens canal width (w, 0.5 to 2 mm) and height (h, 3 to 9 µm) in numerical experimentation with the present model algorithm ([PPR] = [AFR] / [Pi . h . w . (w+PD)]). PPR showed inverse dependence on iris-lens canal height and pupillary diameter and was directly proportional to aqueous flow rate, in agreement with the steady-flow model of Silver and Quigley (J Glaucoma. 2004;13(2):100-7). However, contrary to the steady-flow model, PPR showed inverse dependence on iris-lens canal width and predicted the anticipated PC-AC pressure gradient changes in eyes of patients with clinically narrow angles and ultrasound biomicroscopy (UBM) evidenced pupillary block when their UBM measurements of the iris-lens contact width (w) were used (Figure 1).
Upon the incorporation of clinical UBM measurements of the iris-lens contact width in numerical experimentations with both models, the present pulsatile-flow model, contrary to the steady-flow model, showed good predictability of PC-AC pressure gradient changes in a typical condition predisposing to pupillary block.
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