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V. H. Barocas, R. Amini; Computational Simulation of Increased Iris-Lens Contact and Reverse Pupillary Block Caused by Repeated Blinking. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5550.
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To study how iris root rotation due to spontaneous blinking can lead to reverse pupillary block and change the iris contour and aqueous humor flow by using a computational model.
In our recent work (IOVS, 50:5288-5294, 2009) we showed theoretically that applying pressure on corneoscleral surface can lead to iris root rotation. In this study, we developed a finite element model of the anterior segment to show how the iris root rotation due to blinking changes the iris contour and the aqueous humor flow. The geometric and mechanical parameters of the model were based on published data. Blinking was modeled by posteriorly rotating the iris root in 80 ms and returning it back to the anterior in 200 ms. The frequency of blinking was one blink at every three seconds. To see the effect of rotation angle, four sets of simulation with maximum rotations of 2, 4, 6, and 8 degrees were performed. The pressure difference between the anterior and posterior chambers and the iris-lens contact were calculated from the simulation.
When the iris root rotation was up to 2 degrees, the maximum iris-lens contact increased gradually from 0.28 to 0.34 mm within eight blinks. After the eighth blink, the repetition of blinking did not make any significant changes in the maximum value of the iris-lens contact. Similarly, increased iris-lens contact was predicted when the iris root was rotated 4, 6, and 8 degrees (041, 0.47, and 0.54 mm respectively). When the iris root was rotated 6 and 8 degrees, the pressure difference between the anterior and posterior chambers dropped from 1.23 Pa to -0.86 and -1.93 Pa indicating the existence of reverse pupillary block.
Clinical studies (Ophthalmology, 102: 446-455, 1995 and Exp Eye Res, 86: 220-225, 2008) have shown that prevention of blinking leads to anterior drifting of the iris. In our work, we showed that the repetition of iris root rotation caused by blinking may be a possible reason for the iris to stay more towards the posterior under normal circumstances.
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