The Change of Eyeball Contour and Factors Affecting Corneal Flap using Automated Microkeratome in LASIK

PURPOSE: To evaluated the effect of suction ring on eyeball contour and its influence on the corneal flap made in LASIK(laser in situ keratomileusis). METHODS: We measured corneal thickness and axial length of 47 eyes, before and during application of the suction ring, in those which had undergone LASIK. The diameter and thickness of corneal flap made with Automated Corneal Shaper(R) were also measured in operation room. RESULTS: When applying suction ring while making a corneal flap, corneal thickness and axial length were decreased significantly(p<0.05), and the diameter of the flap was decreased as preoperative corneal curvature decreased(p<0.05). CONCLUSIONS: Careful attention is needed not to give an eyeball unnecessary pressure which may result in intraocular damage or flap complications such as free cap especially when their corneal curvature is too flat.

Change of intraocular pressure, corneal flap and thickness by automated corneal shaper(R) in porcine eye

PURPOSE: To evaluate the performance of Automated Corneal Shaper(R)(ACS) METHODS: we analysed the changes in intraocular pressure, axial length and corneal thickness and its influence on corneal flap following keratectomy by ACS in 20 porcine eyes. RESULTS: Corneal flap was made by ACS with plate 160, and its size and thickness were measured. With the suction ring application, intraocular pressure rised from 17.0 +/-1.96 mmHg to 62.0 +/-11.8 mmHg (p=0.001), while corneal thickness and axial length were decreased from 1090 +/-75.1 micro meter to 1074 +/-73.7 micro meter(p=0.001) and from 19.94 +/-0.89 to 19.72 +/-0.73 mm (p=0.028) respectively. Thickness of corneal flap was 122 +/-23.9 micro meter and its diameter was 8.3 +/-0.15 mm in average. CONCLUSION: special attention is required during LASIK (laser in situ keratomileusis) with Automated Corneal Shaper(R) in order to prevent intraocular damage by abrupt rise in intraocular pressure and change of eyeball contour.

Use of modified suction ring in LASIK / 眼科新进展

Objective　To evaluate the effect of modified suction ring in laser in situ keratomileusis(LASIK) for special eyeballs.Methods　Those eyeballs that couldn't be sucked successfully with regular suction ring were performed with modified suction ring, and the characteristic of those eyes was analyzed.Results　Fifteen eyes of 9 cases were included in this study and were sucked successfully with modified suction ring with intact corneal flap.Eight eyes of 5 cases had small corneal power especially in the peripheral section. The corneal power in the peripheral section of 7 eyes was less than 41D. Corneal diameter of 1 eye was 9.5mm and 6 eyes of 3 cases had small palpebral fissure.Conclusions　The modified suction ring is safe and effective for those eyes with flat cornea, small corneal diameter and small palpebral fissure.

Factors Affecting the Thickness of Suction Ring in LASIK

PURPOSE: Suction ring is needed to fix the cornea during LASIK procedure. But if we choose the suction ring inappropriately, we meet the various problems such as conjunctival edema, conjunctival hemorrhage, ocular pain, and prolongation of operation time. To investigates various factors affecting the thickness of suction ring(1-4) in LASIK procedure. METHODS: We performed LASIK procedure by using SCMD microkeratome and VISX STAR laser on 398 eyes from Dec. 1996 to Feb. 1999. We compared difference on pachymetry, keratometry, corneal diameter, spherical equivalent according to the thickness of suction ring and analyzed these factors with One-Way ANOVA test. RESULTS: The results are that keratometry affected size of suction ring significantly. The flap size and hinge size are affected by size of suction ring significantly, but others did not show significant results. CONCLUSIONS: These results suggest that we need to choose the size of suction ring according to keratometry during LASIK procedure for decreasing various complications.

The Effects of LASIK-Related Negative Pressure on the Microcirulation of Optic Nerve and Retina

It is known that intraocular pressure becomes elevated over 65 mmHg when using a suction ring or fixation ring during LASIK. We intended to find out if transient elevation of IOP alters the microcirculation of the optic disc and retina. 10 patients were enrolled in this study. LASIK was performed on one eye using a suction ring and fixation ring. The other eye was used as a control. Heidelberg Retina Flowmetry[HRF] was performed preoperatively, postoperatively 1 day, 1 week, 3 weeks, and 3 months, respectively and analysis was done at the nasal and temporal neuroretinal rim, peripapillary retina, and optic cup. There was a statistically significant increase of flow at all sites on postoperative 1 day. Furthermore, increased flow was continued until postoperative 3 weeks at the temporal neuroretinal rim. However, the flow was normalized to the preoperative level by 3 months in all measured areas. No differences of flow were found when compared to the control eyes in each site.

A Case of Acute Central Stromal Melting after LASIK

LASIK is an effective and exact procedure to correct myopic refractive error but fatal complication may be happened during making corneal flap using microkeratome. We report a patient who developed acute central stomal melting following LASIK on postoperative day 4. This complication was treated by lifting the flap and scraping the interface of corneal flap & central stroma with a metal blade. After 4 months, overcorrected hyperopic refractive error was retreated with excimer laser ablation and patient recovered successful visual acuity. The pathogenesis of this case is not completely understood. Corneal endothelium and central cornea stroma may be mechanically damaged due to excessive suction ring application during LASIK procedure. Interface epithelial ingrowth may be associated with early postoperative inflammation and infection of corneal flap may produce proteinase which melts corneal flap. If corneal flap melting happens after LASIK procedure, early surgical debridement of melting stroma and proper reattachment of the flap may be needed.