Retinal traction in vitro. Biophysical aspects.

I The forces required to detach the retina from the pigment epithelium and the subsequent structural changes were studied toith a device that produced retinal traction at different rates over localized, equatorial areas of freshly enucleated owl monkey and albino rabbit eyes. Sloio traction (0.2 to 0.8 mm. per minute) produced higher and larger retinal detachments and bigger tears in both types of experimental animals. Medium traction rates (8.5 and 21.5 mm. per minute) resulted in lower and smaller detachments and smaller retinal tears. Above these rates (42.5 to 425.0 mm. per minute), the choroid separated grossly from the sclera. The ratio of traction force and height of detachment was proportional to the logarithm of the traction speed for slow and medium traction speeds. Structural studies showed that the separation of the retina occurred mainly between the two layers, at a traction rate of 0.2 mm. per minute, and at a level of the pigment epithelium at the rate of 8.5 mm. per minute. The structural changes and the force requirements during retinal detachment by traction in vitro are explained on the basis of the rheologic properties of the cementing substance between the retina and pigment epithelium.