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Soohyun Kim, Iman Jalilian, Vijay Krishna Raghunathan, Sara M Thomasy, Christopher J Murphy; Corneal biomechanics following intrastromal injection of hyaluronidase. Invest. Ophthalmol. Vis. Sci. 2018;59(9):524.
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© ARVO (1962-2015); The Authors (2016-present)
Glycosaminoglycans provide support and participate in maintaining the stringent spacing between to the collagen fibrils of the corneal stroma. Hyaluronidase (HYAL), an enzyme that degrades hyaluronan and chondroitin, has been explored for use in deep anterior lamellar keratoplasty and has been suggested that it would soften the stroma and documented to affect collagen fibril packing. The purpose of this study was to determine the effect of stromal injection of HYAL on corneal stiffness and the spatial arrangement of collagen fibrils.
HYAL (1000U/eye) was injected intrastromally (4 sites at 25 µl/site) to the right eye of 12 rabbits; an equal volume of BSS (vehicle) was injected in the left eye as a control. A complete ophthalmic examination and central corneal pachymetry was performed weekly up to 90 days post injection. Confocal microscopy and slit-lamp biomicroscopy were performed before injection and at days 0, 1, 3, 5, 7 and 90. Rabbits were euthanized at day 1 (n=4), day 7 (n=5), and day 90 (n=3) and the stiffness of the cornea was measured using atomic force microscopy. The arrangement and distance of the collagen fibrils were determined using transmission electron microscopy. ANOVA followed by Tukey’s multiple-comparison test was used for statistical analysis.
Corneal thickness after the HYAL injection significantly decreased between day 3 (323 ± 39 µm; P < 0.001) and day 35 (347 ± 23 µm; P < 0.001) compared to controls (361 ± 14 and 365 ± 21 µm, respectively). Corneal stiffness was biphasic in response initially stiffening the stroma and then softening at longer timepoints; day 1 (2.5 ± 1.9 kPa; P = 0.009), day 7 (3.1 ± 1.9 kPa; P < 0.001) and 90 days (1.2 ± 0.69 kPa; P < 0.001) compared to controls (1.8 ± 1.1, 2.4 ± 1.2 and 2.5 ± 1.4 kPa, respectively). Interfibrillar spacing was significantly reduced at days 1 and 7 (49.5 ± 4.5 and 44.6 ± 4.0 µm, respectively; P < 0.001) versus the controls (54.0 ± 3.8 and 57.4 ± 6.4 µm, respectively).
Intrastromal injection of HYAL increases corneal stiffness by reducing the spaces between collagen fibrils and subsequently decreasing corneal thickness at short timepoints after injection. However, a decrease in the stiffness of the cornea occurs with a concomitant return to normal thickness of the cornea at 90 days post HYAL injection. Thus, the effects of HYAL on corneal stiffness are complex and change over time.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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