The effect of various methods of eye immobilization on corneal topography.
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.


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.
Sher
N A
NA
Phillips Eye Institute, University of Minnesota Medical School, Minneapolis, USA.
Fundingsland
B R
BR
Bergin
A
A
Burba
T
T
Forber
S
S
DeMarchi
J
J
D003315:Cornea / Q000473:pathology*; D005403:Fixation, Ocular; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007646:Keratotomy, Radial; D009885:Ophthalmology / Q000379:methods*; D012030:Refractive Errors / Q000473:pathology; D054140:Refractive Surgical Procedures