Background: Accurate, predictable, and safe refractive surgery requires immobilization of the eye. We measured the effects of current eye fixation techniques on human cadaver eyes.
Materials and methods: Central to our study was a device specially designed to secure cadaver eyes and stabilize intraocular pressure. Topographical measurements were made with a modified Model 2 Corneal Analysis System (EyeSys Technologies, Houston, Tex) mounted vertically to allow analysis of a cadaver eye mounted in the artificial orbit. The effect on human cadaver eyes of six fixation instruments was assessed: forceps, U-shaped fixation forceps, a full Hofman-Thornton ring, a VISX vacuum fixation ring, a Meditec suction ring, and a new instrument, the Eye Fixation Speculum.
Results: The circular vacuum fixation rings caused minimal distortion, resulting in less than 1.00 diopter (D) of change. Forceps and U-shaped fixation forceps, which apply force at one or two points, caused significantly more distortion. Single-point fixation forceps distorted the cornea at the point of application a mean of +5.50 +/- 3.50 D, and, at 180 degrees from the point of instrument application, a mean of +2.00 +/- 1.90 D. U-shaped forceps apply force at two points, 90 degrees and 270 degrees, from the axis of instrument application. At these axes, the cornea was distorted a mean of +9.40 +/- 3.70 D and +8.30 +/- 3.10 D, respectively.
Conclusions: Single- and multi-point fixation instruments, due to an asymmetric application of fixation force, significantly distort the cornea. Ring fixation instruments, which apply a more equally distributed force, cause less distortion.