A bipolar scleral diathermy unit measuring tissue temperature beneath the electrodes was used in 27 autopsy eyes to induce corneal curvature changes in order to modify corneal refraction. The optimal coagulation temperature was found to be between 65 degrees and 70 degrees C. The refractive effect was influenced by the distance of the electrodes (1 mm, 2 mm, 3 mm), their location ("limbal distance") and their position in reference to the limbus ("radial", "parallel"). The highest corneal curvature changes were observed with diathermy applied directly at the limbus or 1 mm distance from the limbus. The corneal meridian corresponding to the treated sclera regularly became significantly steeper and the untreated 90 degrees meridian flatter. Limbus parallel diathermy administered directly at the limbus showed a 0.91 mm increase in the corneal curvature with a 2 mm distance or a 0.34 mm increase with a 3 mm distance of both electrodes. Placing the electrodes radially or parallel of the limbus revealed greatest changes in corneal refraction using diathermy directly at the limbus or 1 mm distant from the limbus. The refractive effect decreased as the distance from the limbus increased. Corneal astigmatism could be decreased and increased in a quasi-controlled manner. Over-lapping diathermy offered the potential of gradually changing the corneal power. Histological sections showed that scleral collagen had only a superficial coagulation effect. Scleral diathermy offers great advantages in comparison to corneal incisions for the therapy of corneal astigmatism. Further investigations are in progress.
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