Experimental modification of the corneal curvature by means of scleral surgery

Most surgical procedures for correcting astigmatism are done on the cornea. The present article shows the modification of the corneal curvature by scleral surgery. The experiments were conducted on rabbit eyes. The most spherical eyes were chosen according to the keratometric measurements. A geometrical analysis of the astigmatism shows that beginning with an ellipse (image of an astigmatic eye in the corneascope), by modifying the main radii of the ellipse, while the perimeter is maintained constant a perfect circle is thus obtained. This analysis enables us to calculate the amount of sclera surgery required to obtain a given correction for a given degree of astigmatism. Four scleral procedures were investigated: folds, resections, imbrications, and sclerotomies; the results show that the first three procedures steepen the meridian where the surgery is performed while flattening simultaneously the ortogonal meridian. The main advantages of scleral surgery vs corneal surgery for correction of astigmatism are: (a) the cornea remains untouched, (b) the surgical area will be protected by the conjunctiva, (c) the stitches are left permanently, and (d) larger astigmatic errors can so be corrected.