Keratoconus is a chronic and progressive non-inflammatory ectatic disorder characterized by corneal thinning and irregular corneal topography, and its pathgenesis is a hot topic.A suitable animal model of keratoconus is still lacking, which limits the progress of relevant research.Corneal ectasia is a main anatomical basis of keratoconus, so we assume that keratoconus model could be constructed by simulating corneal ectasia.

This study was to investigate the influence of collagenase type Ⅱ on biomechanical responses detected by corneal visualization Scheimpflug technology (Corvis ST) and the feasibility of construction of rabbit model of corneal ectasia using collagenase type Ⅱ.

This study protocol was approved by Ethic Committee of Peking University First Hospital and followed the Statement about experimental animal use and care from Association for Research in Vision and Ophthalmology (ARVO). Keratectasia models were established in 10 right eyes of 10 New Zealand white rabbits by soaking 8 mm-diameter central cornea using collagenase type Ⅱ solution prepared by PBS solution containing 15% dextran (200 μl of 5 mg/ml) for 30 minutes after epithelial debridement, and only 200 μl PBS solution containing 15% dextran was used in the same way in the left eyes as controls.The average corneal curvature (Km) and central corneal thickness (CCT) were measured with hand-held electronic corneal curvature meter and corneal ultra-sonic pachymetry respectively before modeling and 14 days after modeling.Corneal biomechanical parameters and intraocular pressure were measured in vivo by using Corvis ST at day 14 after modeling.The rabbits were sacrificed at day 14 after modeling, and corneal sections were prepared for hematoxylin-eosin staining and transmission electron microscopic examination.

There were no significant differences in Km and CCT between model group and control group before modeling (Km: [48.28±2.29]D vs.[48.82±1.63]D; CCT: [356.50±19.13]μm vs.[356.20±21.66]μm; both at P>0.05). The Km increased to (48.87±2.27)D and CCT decreased to (340.40±19.84)μm at day 14 after modeling, which were significantly different from (46.86±1.47)D and (367.80±23.38)μm ( both at P<0.01). The maximal deformation amplitude of model group and control group was (1.25±0.07)mm and (1.15±0.13)mm, respectively, showing a considerable difference between them (t=2.65, P<0.05). No significant differences were found in applanation 1/2 time, applanation 1/2 length, applanation velocity, radius of curvature and peak distance between the two groups (all at P>0.05). The morphology and ultrastructure examinations revealed that the arrangement of collagen fibers was loose and disorder and the interfiber space was enlarged in comparison with control group.

Collagenase type Ⅱ can lower corneal biomechanical properties.Soaking of cornea with collagenase type Ⅱ may be a potential way to establish a keratectasia animal model.

Biomechanical properties; Cornea/pathology; Collagenase type Ⅱ; Deformation amplitudes; Keratoconus; Keratectasia/chemical induced; Rabbits; Corneal visualization Scheimpflug technology