RELATIVE STRENGTH OF SCLERAL CORNEAL AND CLEAR CORNEAL INCISIONS CONSTRUCTED IN CADAVER EYES

Square scleral corneal, square clear corneal, and rectangular clear co rneal incisions were constructed in six cadaver eyes that had no previ ous intraocular surgery. The 3.2 mm or smaller wounds had sutureless c losures. To determine their relative abilities to resist leakage and i ris prolapse, eyes were tested at external pressures of up to 525 poun ds per square inch (psi) at one of two intraocular pressure (IOP) rang es: 10 to 15 mm Hg or 20 to 25 mm Hg. The square scleral corneal (3.2 mm x 3.2 mm) and square clear corneal wounds (3.2 mm x 3.2 mm, 2.0 mm x 2.0 mm, 1.0 mm x 1.0 mm) withstood external pressure without effect at both IOP ranges, up to the maximum 525 psi. This level of external pressure was far greater than pressures withstood by rectangular clear corneal wounds, especially the wound usually constructed in clinical practice (3.2 mm x 2.0 mm), which leaked and demonstrated iris prolaps e at 13 psi at the lower IOP. The square clear corneal wounds that wer e stable at 525 psi, however, are either clinically impractical (visua l axis encroachment from 3.2 mm x 3.2 mm wound) or not technologically feasible until the size of phacoemulsification tips and intraocular l enses can be further reduced. Thus, of the procedures for small incisi on cataract surgery presently in use, the square scleral corneal incis ion with 1.5 mm internal corneal lip appears to offer greater stabilit y and safety than the conventional rectangular clear corneal incision (3.2 mm x 2.0 mm).