Primary Effect Of Laser In-situ Keratormileusis On Retinal Nerve Fiber Layer

OBJECTIVE:The study evaluated primary effect of LASIK on configuration and function of eye ball through the measurement of eye axial length, average retinal nerve fiber layer(RNFL) thickness and mean defect(MD) of visual field preoperatively and postoperatively.METHODS:1. The length of eye axis, the depth of anterior chamber and the length of vitreous body of 8 eyes of 4 rabbits were measured by A-ultrasound before the operation and during the negative pressure suction respectively.2. The length of eye axis , the depth of anterior chamber and the length of vitreous body of 9 eyes of 5 patients were measured by A-ultrasound before the surgery and during the negative pressure suction.3. These data were analyzed by paired-samples T test.4. Twenty-five eyes of 13 patients with myopia under -6.00 diopters were enrolled. All LASIK surgery was performed by the same surgeon. The examination of confocal scanning laser ophthalmoscopy(heidelberg retina tomography, HRT) and computerized perimetry was performed beforesurgery and 1 day, 1 week and 1 month after surgery. HRT measured the average retinal nerve fiber layer(RNFL) thickness and the RNFL cross sectional area . Computerized perimetry measured the Mean defect(MD) of visual field.5. These data were analyzed by one-way ANOVA.RESULTS:1. The length of eye axis and vitreous body of rabbits and patients became longer, the depth of anterior chamber became shorter in the negative pressure suction compared to the preoperative measurement.2. There were statistically significant differences (P<0.05) at Iday and 1 week after surgery on the average retinal nerve fiber layer(RNFL) thickness and the RNFL cross sectional area compared to the preoperative measurement. There were no statistically significant differences(P>0.05) at 1 month after surgery on the RNFL thickness and the RNFL cross sectional area compared to the preoperative measurement.3. There were no statistically significant (P>0.05) differences between preoperative and postoperative values on the mean defect of visual field (MD) in computerized perimetry.CONCLUSIONS:1. Configuration of eyes could be affected by vaccum suction. The length of eye axis and vitreous body of rabbits and patients became longer, the depth of anterior chamber became shorter during the negative pressure suction.2. There was thinning in the retinal nerve fiber layer after LAS IK, but these changes appeared to be temporary. The most possible cause for thosechanges was increased intraocular pressure( IOP) induced by the negative pressure suction. It would become the same as preoperative thickness until 1 month after surgery.3. The time of negative pressure suction should be decreased at our best during the LASIK surgery, so the damage of the configuration and function of retinal nerve fiber layer may be avoided.