An Experimental Study Of Effects Of Different Irrigating Height On Ocular Tissue In Vitrectomy

ObjectiveTo observe the effects of different irrigating heights on rabbit cornea and retina in vitrectomy, discuss suitable irrigating heights in order to provide theoretical basis for clinical application.Material and methodsTwenty-four adult pigmented rabbits(2.0～2.5kg)were selected, of which the anterior segment and fundus of eyes were normal. The rabbits were randomly divided into 4 groups, group A, group B, group C and group D. 4 groups were performed with vitrectomy at the height of 70cm, the operation lasted for 15 minutes. After operation, the irrigated heights of group A, group B and group C kept 40cm, 70cm, 90cm respectively. Group D kept normal intraocular pressure, as control group. All of the groups were observed for 1.5h. Incisions in sclera and bulbar conjunctiva were stitched up.The corneal edema was observed respectively under operating microscope, intraocular pressure was measured preoperation, in operation and postoperation. Corneal thickness was measured with ultrasonic pachymetry. Corneal endothelial cell density was measured with no-contacting specular microscopy and computerized digitizer. Functional changes of retina were investigated by recording visual evoked potentials (VEP) and electroretinograms (ERG). The eyeballs were enucleated for histopathological examinations of the cornea and retina. Apoptosis of retinal ganglion cells were tested with TUNEL technique.All the original data were expressed by (x|—)±s. Self-comparison t-test and one-way analysis of variance was used for analysis of all results.Results1. Observing corneal condition under operating microscope indicated: corneal oedema weren't found in group A and group D. The time of corneal oedema occurred was 58.20±9.32minutes after irrigation in group B. The time of corneal oedema occurred was 30.30±7.38minutes after irrigation in group C. Corneal oedema didn't reach four quadrants in group B. Corneal oedema were found in all eyes of group C and reached four quadrants, epithelial blisters arising from the corneal epithelial layer.2. Intraocular pressure measure indicated: the intraocular pressure respectively were 29.40±1.28mmHg, 51.43±0.90mmHg, 66.09±1.35mmHg, 15.45±2.21mmHg. With lifting the irrigating height, intraocular pressures were elevated.3. Corneal thickness examination indicated: compared the corneal thickness of group B and group C between preoperation and postoperation, the difference was statistical significant (P < 0.05); The corneal thickness of group A between preoperative and postoperative, there was no statistical significance (P>0.05). With lifting the irrigating height, corneal edema aggravated.4. Corneal endothelial cell density examination indicated: After operation, compared the corneal endothelial cell density between group C and group D, the difference was statistical significant (P<0.05). The corneal endothelial cell density between group A , group B and group D, there was no statistical significance (P> 0.05).5. Electrophysiologic studies (EPS) indicated: After operation, compared group B, group C with group D, group B and group C showed statistically significant changes of amplitudes and potent periods of a-wave, b-wave, P₂ -wave (P<0.05); group A with group D, group A didn't show statistically significant changes of amplitudes and potent periods of a-wave, b-wave, P₂-wave (P>0.05). At four hours after operation, compared every irrigating height group with D group, there was no statistical significance (P> 0.05).6. Observing cornea and retina under the light microscope indicated: there were no obvious changes in group A under light microscope. In group B, corneal epithelium cells became edematus and disordered, stroma layer became edematus and obviously thickened. In group C, corneal epithelium cells became edematus and disordered more obviously,there were cavitation in cells. In group B and group C, Every layer of retina became disordered, retinal ganglion cells and inner nuclear layer cells decreased in the mumber and there were cavitation in ganglion-cell layer.7. Observing the apoptosis of retinal ganglial cells: in slices of retina of every group, there were no TUNEL positive cell.Conclusions1. The height of irrigating affected directly on intraocular pressure in vitrectomy. With the increase of the irrigating height, intraocular pressure arised, accordingly the structure and function of cornea and retina were injured. Especially when the irrigating height was 90cm, cornea become edematus easily, the retinal gangion cells were injured easily, the retinal function declined temporarily after irrigating for 1.5h. When the irrigating height was 70cm, the structure and function of cornea and retina were injured, the degree of injure was less than that of the height of 90cm.2. Maintain a suitable irrigating height and assure flow of irrigating using apparatus infusions, make intraocular pressure keep at a little higher intraocular pressure level to assure the operation succeed and avoid injuring cornea and retina.