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S. Roy, A. Villamarin, M. Feusier, N. Stergiopulos; Outflow Facility and Compliance Measurements After Experimental Filtering Surgery in an Animal Model Using Microtubes. Invest. Ophthalmol. Vis. Sci. 2009;50(13):179.
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To evaluate the effect on the outflow facility and the compliance of the eyeball of a minimally invasive filtering surgery using a microtube, based on an animal model of glaucoma surgery.
Rabbit eyes freshly enucleated (< 4h) where canulated using a perfusion system. Using gradual infusion rates (2-10 µl/min) the intraocular pressure (IOP) was continuously recorded to obtain the outflow facility Δflow/ΔIOP before surgery. Compliance ΔVolume/ΔIOP was computed based on the lapse rate of the IOP profile. Under a constant pressure of 15 mmHg, the conjunctiva was then opened at the limbus, and a superficial scleral flap (1/3 full thickness) was dissected onto the cornea. A paracenthesis was made using a 30G needle through the sclera to enter anterior chamber. A V-50 Ex-PRESSTM microtube was inserted, and aqueous humour percolation ascertained before suturing back the scleral flap and the conjunctiva. The outflow and compliance of the eyeball measurements were repeated using the same methods.
Preoperatively the outflow facility was 0.42 ± 0.07 µl/min/mmHg and the compliance was 14.13 ± 4.03 µl/mmHg (n=5). After surgery and implantation of the microtube, the outflow facility went up to 1.63 ± 0.07 µl/min/mmHg, thus representing a resistance to the egress of aqueous humor 4 times lower than the control (p< 0.001). The compliance of the eyeball after completion of the superficial flap dissection and microtube insertion remained stable at 12.5 ± 2.21 µl/mmHg. The difference compared to the control before surgery was not statistically different (p>0.74).
Glaucoma generally results from an increase in the resistance to aqueous outflow. The biomechanics of the eyeball and the compliance are playing important roles in the strain imposed on the optic nerve head in case of ocular hypertension. The filtering surgery should not appreciably modify the biomechanics of the eye. The minimally penetrating glaucoma surgery using microtubes seems not to alter the compliance of the eyeball whereas the outflow facility is significantly increased to reduce the elevated IOP.
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