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Robotic Assisted Cannulation of Occluded Retinal Veins.
PURPOSE: To develop a methodology for cannulating porcine retinal venules using a robotic assistive arm after inducing a retinal vein occlusion using the photosensitizer rose bengal. METHODOLOGY: Retinal vein occlusions proximal to the first vascular branch point were induced following intravenous injection of rose bengal by exposure to 532nm laser light delivered by slit-lamp or endolaser probe. Retinal veins were cannulated by positioning a glass catheter tip using a robotically controlled micromanipulator above venules with an outer diameter of 80μm or more and performing a preset piercing maneuver, controlled robotically. The ability of a balanced salt (BSS) solution to remove an occlusion by repeat distention of the retinal vein was also assessed. RESULTS: Cannulation using the preset piercing program was successful in 9 of 9 eyes. Piercing using the micromanipulator under manual control was successful in only 24 of 52 attempts, with several attempts leading to double piercing. The best location for cannulation was directly proximal to the occlusion. Infusion of BSS did not result in the resolution of the occlusion. CONCLUSION: Cannulation of venules using a robotic microassistive arm can be achieved with consistency, provided the piercing is robotically driven. The model appears robust enough to allow testing of therapeutic strategies aimed at eliminating a retinal vein thrombus and its evolution over time
SLO image (left) and corresponding OCT image of the retina pre and post induction of a vein occlusion.
<p>OCT showing the site of a venous occlusion. A- prior to the induction of a thrombus. B- shortly after the creation of a venous occlusion, the outer diameter of the vein increases in size. An area of hyperfluorescence appears in the upper portion of the vascular lumen corresponding to the area of fibrin deposition within the thrombus (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0162037#pone.0162037.g007" target="_blank">Fig 7</a>). In the lower portion, the area of hypofluorescence corresponds to a dense meshwork of erythrocytes, platelets and inflammatory cells. An associated serous detachment is also present, often appearing within 30 minutes of the induction of the occlusion. In panel C, 14 days after the induction of the thrombus, there is still retinal inflammation present as witnessed by hyper reflective dots in the retina and the vitreous. A partial posterior vitreous detachment is present containing a number of inflammatory cells and residual debris. The area around the vein is thinned as the outer retinal layers are reduced in size.</p
Surgical set-up used to operate the animals.
<p>The Preceyes micromanipulator is positioned for this intervention for the right eye of a pig. The motion controller is handled by the surgeon, from the temporal side of the eye within the surgical field and well within reach of the eye itself. The surgeon remains in his standard operating room position. In his left hand, he is holding a handheld endoilluminator (free hand).</p
Hematoxylin-eosin stain (A-5x, B-10X) of an occluded vessel.
<p>Damage to the surrounding retina and underlying choroid is clearly visible following laser extending beyond the limits of the vascular wall. However, the vascular lumen is occluded with limited damage to the vessel wall. Extensive choroidal hemorrhage indicates that considerable damage was also induced in the choroidal circulation.</p
Retrograde filling of the retinal veins with BSS+ proximal to a vein occlusion.
<p>The black arrow shows the retrograde fill, while the red arrowhead the location of the occlusion.</p
Day 14 fluorescein angiogram showing the presence of collateral vessels.
<p>Day 14 following a rose bengal induced venous occlusion in a pig eye. The formation of collateral vessels adjacent to the site of occlusion is clearly evident in this late frame angiogram. The site of occlusion is indicated by the arrow.</p
Design schematic of the micromanipulator.
<p>Shown are the the various axes of rotation and degrees of freedom (DOF). The parallelogram mechanism kinematically constrains the instrument pivot to the entry point into the eye.</p
Green epifluorescence (A 20X, B 10X) and H&E stain (C: 20X, D:10X) of a laser induced vascular occlusion.
<p>The eye was collected within 2 hours of the occlusion. Epifluorescence in the green channel confirms the presence of fibrin while the remainder of the thrombus is composed of a network of platelets and erythrocytes and inflammatory cells.</p