Change in corneal curvature induced by surgery

The first section deals with the mechanisms by which sutures, incisions and intracorneal contact lenses produce a change in corneal curvature. To clarify the mechanisms by which incisions and sutures produce astigmatism, we made incisions and placed sutures in the corneoscleral limbus of human eye bank eyes (chapter 2). The changes in corneal curvature were studied by central keratometry and by shadowgraph photography of the corneal contour. A radial corneal suture induces astigmatism by tissue compression. A radial anterior suture comprises more tissue on the outside than on the inside of the cornea. This moves the epithelial side of the cornea posteriorly towards the center of the globe. This posterior displacement decreased the sagittal depth of the cornea, so that the depth of the anterior chamber decreased slightly. The center of the cornea steepened in the meridian of the suture. This can be illustrated by holding a card between the thumb and first two fingers and applying pressure to make the card arch over the palm. When the forefinger of the other hand presses down near the arched card, this area moves toward the palm like limbal tissue near a suture and the arch of the central area of the card increases; resembling the steepening of the central cornea. With this theory we can understand the mechanism by which sutures produce corneal astigmatism after cataract surgery. Incisions in the anterior layers of the cornea weaken the mechanical stability. The intraocular pressure then causes the wound to gape arid outward bulging of the cornea. The central corneal curvature flattens. Corneal incisions are clinically used with radial keratotomy, an operation for the correction of myopia. It is one of the techniques of refractive corneal surgery. Refractive corneal surgery (chapter 3) constitutes of surgical techniques to change the corneal power so that the patient can see better without contact lenses or glasses. All these techniques are irreversible which led us to try and find a method that would be reversible. We found it to be possible to flatten the central corneal curvature of human eye bank eyes by radial interrupted nylon sutures (chapter 4).