Experimental study using pig eyes for realizing ideal astigmatic keratotomy

Purpose. The effects of varying the incision length and depth were analyzed using pig eyes to acquire information for realizing an ideal method of ast igmatic keratotomy (AK), Methods. Single and paired arcuate incisions were made on pig corneas using a diamond knife. Incisions with varying lengths o f 40 degrees, 60 degrees, and 90 degrees were made with the incision depth fixed at 90% of corneal thickness. Next, paired incisions with varying inci sion depth from 20% to 95% of corneal thickness were made with the incision length fixed at 90 degrees. The changes in corneal shape were analyzed usi ng corneal topography and the degrees of astigmatic change were measured us ing a surgical keratometer. Results. For short single and paired incisions (40 degrees or 60 degrees in length), narrow areas of flattenings occurred, and steepenings were observed on both sides adjacent to the flattened area s. For long paired incisions of 90 degrees length, wide areas of flattening s and steepenings were observed with an approximately 1:1 coupling ratio, a nd a positive linear relationship between the incision depth and degree of astigmatic change was observed in the range of incision depth between 40% a nd 80% of corneal thickness. Conclusion. This experimental study suggests t hat for achieving ideal corneal sphericity after AK, long incisions coverin g the entire steep areas (paired 90 degrees incisions for regular astigmati sm) should be used and the degree of astigmatic correction may be controled by varying the incision depth.