Plasminogen activator activity and inhibition in rabbit tears after photorefractive keratectomy Adrienne Csutak a , David M. Silver a,b, * , Jo ´zsef To ˝zse ´r c , Andrea Facsko ´ a , Andra ´s Berta a a Department of Ophthalmology, Faculty of Medicine, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary b Applied Physics Laboratory, The Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MA 20723-6099, USA c Department of Biochemistry and Molecular Biology, Faculty of Medicine, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary Received 17 March 2003; accepted in revised form 18 August 2003 Abstract Plasminogen activator is a normal component of tear fluid that plays a role in corneal wound healing processes. This work examines whether inhibitor-induced low levels of plasminogen activator activity (PAA) during corneal re-epithelialization after excimer laser photorefractive keratectomy (PRK) correlates with the eventual occurrence of haze in rabbit eyes. Tear samples were collected with glass capillaries from 16 eyes of eight New Zealand rabbits, using i.m. injection of pilocarpine hydrochloride for stimulation. Tears were collected before and after PRK surgery, and then daily for 5 days, and every fourth day thereafter for 3 months. Both eyes underwent PRK treatment. One eye of each rabbit was treated as a control while the contralateral eye was treated with aprotinin, a serine protease inhibitor, over the first 7 days. PAA in the tear samples was measured by a spectrophotometric method using human plasminogen and chromogenic peptide substrate S-2251. For the eight control eyes after PRK, the PAA values were significantly lower (day 1) and higher (days 2 and 3) than the equilibrium PAA ðp , 0·001Þ: The corneas remained clear in each of these control eyes. For the eight contralateral aprotinin-treated eyes after PRK, the PAA values on days 1 – 7 were significantly lower than the equilibrium PAA (p , 0·001). All eight of these aprotinin-treated eyes developed corneal haze after 2 months. There was no significant difference ðp ¼ 0·06Þ between control and aprotinin-treated eyes for the equilibrium PAA after 19 days. We conclude that a corneal wound healing abnormality (haze) develops in rabbit eyes after PRK when PAA levels are reduced using aprotinin for a week following PRK. q 2003 Elsevier Ltd. All rights reserved. Keywords: plasminogen activator; photorefractive keratectomy; refractive surgery; corneal wound healing; rabbit tears 1. Introduction The cornea is responsible for two-thirds of the refracting power of the eye, making it a candidate for surgical procedures aimed at refractive correction. The qualities of the wounds made by the ArF excimer laser suggested the concept of using such a laser to directly photoablate the cornea after removal of the epithelial layer (Marshall et al., 1986). The effect is to reprofile the surface of the cornea, defining a new anterior radius of curvature, thereby altering the optical power of the cornea. Marshall et al. (1986) termed this technique photorefractive keratectomy (PRK). The procedure is a reasonably safe, effective and predictable technique for correcting low to moderate myopia. Never- theless, the most frequently reported complications include glare, haloes, difficulty with night vision, decreased contrast sensitivity, transient increases in intraocular pressure, mild subepithelial haze and myopic regression (Chan et al., 1997; Hadden et al., 1999). Numerous laboratory investigations, principally utilizing rabbit and monkey models, have generally demonstrated rapid and stable re-epithelialization over the area of excimer laser ablation. After injury, reformation of the basement membrane and anchoring fibril network is necessary for tight adhesion of the epithelium to the stroma, and the healing epithelium must synthesize and assemble these structures (Gipson et al., 1987, 1989). After mechanical keratectomy wounding, full re-assembly of the adhesion complex generally requires 1–2 months in rabbits (Gipson et al., 1989). In both rabbit and monkey eyes, the ablation 0014-4835/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. DOI:10.1016/j.exer.2003.08.012 Experimental Eye Research 77 (2003) 675–680 www.elsevier.com/locate/yexer * Corresponding author. Dr David M. Silver, Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723-6099, USA. E-mail address: david.m.silver@jhuapl.edu (D.M. Silver).