Hyaluronidase treatment, collagen fibril packing, and normal transparency in rabbit corneas

Hyaluronidase treatment is the initial step of corneaplasty, a treatment under development that induces stromal softening and involves the application of a custom designed forming lens to achieve modification of refractive error. The purpose of this investigation was to examine changes in the arrangement of stromal collagen fibrils after hyaluronidase treatment.

Rabbit corneas were evaluated by slit-lamp microscopy at 0, 2 and 7 days after treatment and haze was assessed by subjective observation. Molecular and interfibrillar Bragg spacing of corneal collagen were measured from synchrotron x-ray scattering patterns. Transmission electron microscopy and digital image analysis were used to calculate radial distribution functions from the positions of collagen fibrils. The calculated fibril sizes and positions were also used to predict the transmission of visible light through these corneas.

Hyaluronidase-treated corneas were shown to have a decreased interfibrillar Bragg spacing of 15% to 21%. Fibril hydration did not change. Transparency of these corneas remained unaltered.

Hyaluronidase reduced the hydration of the corneal stroma, which led to a more compacted collagen fibril arrangement. This compression was predicted to cause a small reduction in the transmission of visible light through the cornea but not to a point likely to cause visual impairment.