Corneal strength change and keratocan expression of corneas during the healing of penetrating injury in rabbits

Abstract

Background Corneal walleye formation is a result of excessive corneal wound healing. Controlling the corneal trauma or excessive healing reaction after operation of penetrating corneal trauma is a focus in the study of corneal wound healing. Objective This study was to investigate the changes of corneal strength and the expression of keratocan, a marker of corneal stroma, after corneal penetrating injury operation, and to determine the optimal removal time of corneal suture. Methods Full-thickness incisions of 5 mm along the vertical diameter were done at the central cornea on 80 eyes of 80 six-month-old New Zealand rabbits in this study. Then the incisions were interruptedly sutured with 10-0 nylon thread to establish the corneal wound healing models. Each 4 rabbits were sacrificed in 1 week, 2, 3, 4, 5, 6, 7, 8 weeks after operation, respectively, and the central corneal stripes were prepared with the size of 7 mm×5 mm. The mean maximal strength of the corneal bands was measured by uniaxial tensile test with electroforce3220-AT biomachanics machine. Then, each 6 whole corneas were obtained at the above time points, and the dynamic changes of keratocan mRNA expression in the specimens were detected by reverse trancription PCR (RT-PCR). The care and use of the animals followed the rules of ARVO. Results The mean maximal strength of corneal stripes was 0, (1.007±0.041), (1.991±0.034), (2.512±0.030), (3.630±0.049) and (4.935±0.004) MPa in 1 week, 2, 3, 4, 5, 6 weeks after modeling, and the corneal strength values from 3 weeks through 6 weeks were significantly enhanced in comparison with the value at the adjacent before timepoint (q=6.35, 7.54, 8.21, 5.86, all at P<0.01). The relative expression levels (absorbance) of keratocan mRNA in the corneas were 0.869±0.015, 0.779±0.065, 0.621±0.027, 0.460±0.018, 0.393±0.057 and 0.255±0.045 in 1 week, 2, 3, 4, 5, 6 weeks after operation, and each value was lower than that of the adjacent before timepoint (q=5.24, 5.61, 7.49, 4.75, 5.47, all at P<0.01). The intensity of corneal stripes and the expression levels of keratocan mRNA in the corneas were stable in 7 weeks and 8 weeks after operation. Conclusions The dynamic change of corneal strength during the repair of penetrating corneal injury is associated with the down-regulation of keratocan in cornea. Rabbit cornea reaches a maximal strength capacity in 6 weeks after penetrating injury, therefore, it is the optimal time to remove suture. Key words: Ocular trauma; Cornea/physiopathology; Biomechanics; Corneal stroma/cytology; Fibrosis; Reverse transcriptase PCR