Histologic evaluation of thermal effects in laser-thermokeratoplasty and corneal ablation

M. N. Asiyo-Vogel, R. Brinkmann, H. Notbohm, R. Eggers, H. Lubatschowski, H. Laqua, A. Vogel


Purpose: Thermal denaturation of corneal collagen plays an important role in refractive laser surgery - either by inducing collagen shlinkage as in laser-thermokeratoplasty (LTK), or by creating an unwanted damage zone as in corneal ablation, especially with infrared lasers. We investigated several histologic techniques with respect to their potential to differentiate the various degrees of thermal changes. Methods: Corneas of freshly enucleated porcine eyes were treated with a holmium laser (2.1 μm) to produce LTK lesions, or ablated with a Q-switched and a free-running Er:YSSG aser (2.70 μm), and a free-running Er: YAG laser (2.94 μm). The lesions were investigated by light microscopy using various staining methods, transmission electron microscopy, and polarisation microscopy after Sirius Red staining. Sirius-Red, a strongly elongated, birefringent molecule binding parallel to collagen molecules, was used to enhance corneal birefringence. Results: Routine light microscopy does not discriminate the various degrees of thermal damage The combination of Sirius-Red staining and polarisation microscopy allows to distinguish between a strongly coagulated zone and a transition zone to the normal tissue. Sirius-Red uptake is increased in both zones reflecting the availability of new binding sites. The central zone appears darker under polarisation than normal collagen due to a loss of birefringence. Intrinsic birefringence is strongly reduced, but form birefringence partly remains as long as some collagen fibrils are still intact. This interpretation was supported by the electron microscopic examination. The transition zone towards normal cornea shows increased birefringence, because the natural birefringence is largely preserved and enhanced by the increased Sirius-Red dye uptake indicating changes on a molecular level. Conclusion: Sirius Red offers an improved and simple histologic method for analysing thermal collagen changes. It may contribute to a better understanding of the working mechanisms of LTK and improve the analysis of thermal effects in corneal ablation.

Original languageEnglish
JournalInvestigative Ophthalmology and Visual Science
Issue number3
Pages (from-to)S571
Publication statusPublished - 15.02.1996

Research Areas and Centers

  • Academic Focus: Biomedical Engineering


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