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Ryan A. Vasan, Nathan M. Radcliffe; In vivo Measurement of Conjunctival Thickness over Glaucoma Tube Implants using Anterior Segment Ocular Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5048.
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© ARVO (1962-2015); The Authors (2016-present)
High definition anterior segment optical coherence tomography (AS-OCT) has been used for imaging various anterior segment structures. We sought to determine whether this technique could be used to measure the conjunctival thickness overlying the tube of a glaucoma drianage device. Specifically, we sought to use AS-OCT to measure conjunctival thickness overlying the extraocular portion of the glaucoma tube implants and to measure in vivo internal tube diameter.
In this retrospective study we included patients who had undergone glaucoma drainage implant surgery who also had AS-OCT imaging using the Cirrus 4000 HD-OCT (Carl Ziess Meditec, Dublin, CA). AS-OCT scans were acquired using the 5-line raster protocol with the upper eyelid elevated. Scans were oriented perpendicular to the tube. The thickness of the conjunctiva as well as the internal diameter of the tube lumen were measured using the on-screen measuring tool. We recorded patient variables including age, sex, central corneal thickness, number of glaucoma drops used, time since surgical procedure, type of implant and patch graft used, and any concurrent surgery performed.
We included 11 implants of 10 eyes of 7 patients. Of these patients, 3 were men and 4 were women. The average age was 67 years (42-82). Two patients had Boston Type I Keratoprostheses (KPro), both performed after implantation of the tube shunts. One of the two KPro patients had two separate glaucoma drains in the same eye. Of the 11 implants, 1 was a Molteno (Molteno Ophthalmic Limited, Dunedin, New Zealand]), 2 were Baerveldt (Abbott Medical Optics Inc., Santa Ana, CA) and 8 Ahmed (New World Medical, Inc., Rancho Cucamonga, CA). The conjunctival thickness measurements average 195μ (76-448μ, SD 116μ). The average internal diameter of the tube lumen was 300μ (264-360μ, SD 35μ). Differentiation of tube type yielded average lumen of 352μ for Molteno, 278μ for Baerveldt, and 290μ for Ahmed. The average CCT was 550μ, average number of drops used was 2.5, and of the 11 tubes, 8 had pericardial patch grafts and 3 were unknown.
AS-OCT can be successfully used to accurately measure conjunctival thickness overlying glaucoma tube implants as well as the internal tube diameter in vivo. Monitoring this quantifiable data longitudinally in patients may have a role in managing patients at risk for or with a history of conjunctival erosion.
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