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Jonathon B Young, Ali Bakhshinejad, Christine Skumatz, Matthew Runquist, Iris S Kassem; Quantification of fibrin volume in a juvenile rabbit model of lensectomy using 9.4 Tesla magnetic resonance imaging. Invest. Ophthalmol. Vis. Sci. 2019;60(9):6113.
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© ARVO (1962-2015); The Authors (2016-present)
Juvenile rabbits have robust postoperative inflammation and fibrin formation after lensectomy with intraocular lens (IOL) insertion. We sought to quantify the effect of tissue plasminogen activator (tPA) on the volume of fibrin using high-resolution 9.4 Tesla magnetic resonance imaging (MRI).
All experiments were approved and in compliance with the Animal Care and Use Committee of MCW. 9 juvenile (6-7 week old) New Zealand White rabbits had unilateral clear-cornea lens extraction surgery with insertion of an acrylic IOL under anesthesia with isoflurane. Rabbits were examined under sedation postoperatively with slit lamp biomicroscopy. After exams on postoperative day 3 (POD3), either 25µg of recombinant rabbit tPA (n = 5) or balanced salt solution (control; n = 4) was injected into the anterior chamber. On POD4, rabbits were examined and then euthanized with eyes harvested and placed in fixative. At least 1 week later, eyes were placed in an agarose gel, and scanned using a 9.4T MRI system for ex vivo imaging. 3 blinded examiners manually measured fibrin volume (sum of area x slice thickness) on MRI using Horos Project software. tPA versus control eyes were compared using a two-tailed t-test. Automated quantitation of the fibrin clot using an Otsu algorithm was applied to 7 of 9 eyes.
The volume of fibrin in tPA-treated eyes was significantly smaller with 0.397 ± 0.665mm3, while the scar volume of control eyes was 2.80 ± 1.08mm3 (unpaired t-test; p < 0.01). Automated segmentation of the scar in 4 tPA-treated eyes was 0.110 ± 0.220 mm3, and 0.75 ± 0.256 mm3 in 3 control eyes. There was no statistical difference between automated versus manual measurements (paired t-test; p > 0.05). Automated segmentation volumes were lower compared to observer volumes in 6 of 7 measurements.
9.4 Tesla ex vivo MRI imaging allows for quantification of the fibrin scar in a rabbit model of lensectomy with IOL implantation. This initial study reveals a significantly lower volume of fibrin following 25µg of tPA administration compared to control eyes. Further development of automated software may be useful for objective fibrin volume measurement of pharmacologic therapies for postoperative scar formation.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
A) Slit-lamp image of a control rabbit eye B) Ex vivo MRI image C) Automated segmentation area of fibrin
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