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PubMed · 291207

Anterior segment applications of vitrectomy techniques.

Abstract

We have used vitrectomy instrumentation and techniques to treat a variety of conditions affecting the anterior segment, including: (1) Various conditions causing an occluded or inadequate pupillary space, (2) Complications of vitreous gel in the anterior chamber, (3) Growth of epithelium into the anterior chamber, (4) Selected indications for lens surgery, (5) Flat anterior chamber, (6) Total hyphaema. The vitrectomy methods provided improved capabilities, including controlled excision of intraocular tissues under optimum visualization using a closed-eye system with normal intraocular pressure and the ability to use accessory techniques such as intraocular diathermy. Although new difficulties are introduced by reliance on complex instrumentation and possible complications from excessive traction or use of large volumes of intraocular irrigating solution, our experience in using these techniques to treat selected anterior segment conditions has been, favourable.

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BibTeXRIS

R G Michels. 1978. Anterior segment applications of vitrectomy techniques.. https://pubmed.ncbi.nlm.nih.gov/291207/

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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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