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Instruments and techniques for anterior chamber implants.

Abstract

The widely used white-to-white + 1 method was investigated clinically for its accuracy in choosing implant length. This method allowed the surgeon to open one implant per case in approximately 65% of cases. The basic concept of adding 1 mm to the clear corneal diameter was then investigated with cadaver eyes. The concept was found to be quite inaccurate. An anterior chamber ruler is described that allows the surgeon to open one implant per case in 95% of cases. An implant ruler for checking the length of the implant and the plane of the feet also is described. An implant positioner is described that inserts the distal feet, inserts the proximal feet, checks the implant fit, and changes the axis if necessary.

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BibTeXRIS

J R Karickhoff. 1980. Instruments and techniques for anterior chamber implants.. https://doi.org/10.1001/archopht.1980.01020040117018

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Model of pulsatile-flow of aqueous humor through the iris-lens canal.

PURPOSE: To present a model of pulsatile-flow of aqueous humor from posterior (PC) to anterior chamber (AC) and to analyze the sensitivity of this novel model in detecting typical high risk conditions predisposing to pupillary block. METHODS: The model assumes noncontinuous flow of aqueous 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 2 events of aqueous ejection there is no actual flow through this canal. Pupillary pumping rate (PPR) was calculated from the aqueous flow rate and the calculated volume of iris-lens canal. RESULTS: PPR values were generated by incorporating pupillary diameter (1 to 8 mm), aqueous flow rate (1 to 2.5 microL/min), and iris-lens canal width (0.5 to 2 mm) and height (3-9 microm) in numerical experimentation with the present model. 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. 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 at simulated light-dark transition in eyes of patients with clinically narrow angles and ultrasound biomicroscopy evidenced pupillary block. CONCLUSIONS: Upon the incorporation of real ultrasound biomicroscopy measurements 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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