Persistent Haze and Disorganization of Anterior Stromal Collagen Appear Unrelated Following Phototherapeutic Keratectomy

Abstract

PURPOSE: The theoretical effects on corneal transparency induced by changes in collagen fibril packing following phototherapeutic keratectomy were compared to changes in objective measurements of haze. METHODS: Phototherapeutic keratectomy was performed on the right eyes of four young rabbits; left eyes were used as controls. Postoperative slit-lamp measurements of haze were taken at regular intervals up to 19 months. Wounded stromas were studied by synchrotron x-ray diffraction to calculate the average interfibrillar spacing of the collagen fibrils. These data were combined with transmission electron microscope measurements, and the summation of scattered fields method was used to predict the transmission of visible light. RESULTS: Objective measurements of haze were higher than the baseline control throughout the study. Electron micrographs of anterior stroma in 8-month-old wounds displayed irregularly spaced and poorly organized fibrils and x-ray diffraction indicated larger mean interfibrillar spacing compared to the controls. However, the predicted transmission of visible light through the anterior stromal scar tissue was not significantly different than normal. CONCLUSIONS: Following phototherapeutic keratectomy, anterior corneal collagen fibrils were more widely spaced and unevenly organized than in the normal rabbit cornea. However, this did not cause a significant loss of transparency and was therefore unlikely to contribute to haze.