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Louis Yang, Phil Chen; Determination Of Optimal Intraocular Baerveldt Tube Position Using Post Mortem Enucleated Globes. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2646.
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© ARVO (1962-2015); The Authors (2016-present)
To determine ideal Baerveldt glaucoma implant tube position using sectioned globes
Intact enucleated globes were obtained through Sightlife eye bank. Each globe was inflated to physiologic IOP using balanced salt solution via 30 gauge needle through the pars plana. The axial length was measured. Anterior chamber (AC) depth was assessed using Van Herick method with a portable slit lamp. Caliper was used to mark the superior limbus at 1.0, 1.5, and 2.0 mm behind the conjunctival insertion. A 23-G needle was used to enter the AC either parallel to iris, or angled slightly anteriorly, and a segment of ligated Baerveldt tube was placed into the anterior chamber. This was repeated for each marking. Tube length and position in the AC was noted through the surgical microscope and portable slit lamp. Each globe was then sectioned through a sagittal incision to observe entry site in the angle. A 23-G needle was inserted from the intraocular side of the AC just above the iris insertion, and the exit site on the scleral surface was recorded.
8 globes (4 pairs) were used, 6 phakic and 2 pseudophakic. Axial length ranged from 22.9-24.0 mm. Van Herick measurement of AC depth ranged from moderate to deep. Baerveldt tubes were found in various positions ranging from peripheral cornea to ciliary sulcus, depending on angle of entry and distance from the conjunctival insertion. Sagittal sections confirmed these positions. "Ideal placement," with tube in AC without tube tip-iris touch at slit lamp, and through trabecular meshwork on sagittal section, was found most frequently at 1.5 mm and 2.0 mm. Tube length of 2-3 mm beyond the insertion site resulted in adequate and short tube length in the AC. Insertion of 23-G needle "inside-out" resulted in exit ranging from 1.0 mm to 2.5 mm behind the conjunctival insertion, with most being between 1.5 and 2.0 mm.
Sectioned globes show optimal intraocular tube position requires a 1.5-2.0 mm entrance site behind conjunctival insertion to avoid peripheral cornea. This was confirmed with "inside-out" needle placement. Angle of entrance greatly influenced tube position; strict "parallel to the iris" placement with good AC position usually resulted in peripheral corneal tube entry. This may contribute to late corneal decompensation.
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