Geometric analysis of radial buckling.

Tension analysis along the retinal surface demonstrates the advantage of meridional buckles over limbal-parallel buckles. A cylindrical sponge generates tensional forces in the retina along the long axis of the buckle and perpendicular to it. The tension perpendicular to the sponge is positive, and the retina and retinal pigment epithelium stretch in that direction. The tension along the long axis is positive (stretching) when the buckle is less than 90 degrees arc length; and negative (compression), greater than 90 degrees for a 5-mm sponge. Consequently, retinal compression folds on the buckles occur for buckles of arc length greater than 90 degrees. These tension forces at right angles to each other explain the development of (1) concave retinal detachment or retinal folds off short limbal-parallel buckles, (2) retinal folds on long limbal-parallel buckles, and (3) fishmouthing of horseshoe tears overlying a limbal-parallel buckle. The buckle increases retinal surface area overlying the buckle. The significance of this is not clear, but it may explain the lessening or disappearance of compression folds on the buckle in time.