The present study compares three centering methods for excimer laser photorefractive keratectomy (PRK. VISX 20/20) by analyzing the corneal topography. The subjects were grouped according to three different centering methods used in the procedure: an ablation using a light reflex from the patient's cornea pursued by both eyes of the surgeon (Group 1, n = 49); an ablation using a red light reflex from the patient's cornea pursued by the surgeon's left eye only while the right eye remained closed (Group 2, n = 27); an ablation using the patient's center of the pupil pursued by the surgeon's left eye only while the right eye remained closed (Group 3, n = 21). The mean distance from the center of ablation zone to the center of the pupil were; 0.69 +/- 0.45 mm for Group 1, 1.05 +/- 0.48 mm for Group 2 and 0.63 +/- 0.28 mm for Group 3. The degree of deviation in Group 2 was significantly greater than in Group 1 or Group 3. The deviation was greater in the right eyes than the left eyes in Group 2 only. The decentration of the right eye in Group 2 was due to angle Kappa with misalignment of the fixation light and viewing tube containing reticule.
Adult ; Comparative Study ; Female ; Human ; Keratectomy, Photorefractive, Excimer Laser/methods* ; Male

Laser in situ kratomileusis(LASIK) is a prefered method to excimer laser photorefractive keratectomy (PRK) because the former cuts only corneal stroma, while the latter cuts corneal epithelium, Bowmans membrane, and stroma, LASIK is a complex procedure composed of corneal flap preparation and photo-ablation. In corneal flap preparation, two types, manual and automatic, of microkeratomes have been used. We experienced problems during and after LASIK procedure using a manual microkeratome in learning curve period(8 months) and criticized the problems to shorten a learning curve of manual microkeratome. One hundred eighty six myopic eyes treated with LASIK using manual microkeratome(MLK, SCMD, USA) from January 1997 to August 1997 by one operator(Joo) were subjects. Problems occurred in 24 eyes(12.9%) and consisted of hole in corneal flap (5 eyes), thin corneal flap(3 eyes), winkling of corneal flap (2 eyes), hinge inside optical zone of laser(3 eyes), haze of interface (3 eyes), and free corneal flap(8 eyes). Majority of complications occurred in the first 3 months and most complicated cases were preventable when the speed of microkeratome enhancement was slow in late series of study. It seems that a manual microkeratome takes longer learning curve than automated microkeratome. Therefore, to decrease the number of problem cases in learning curve of LASIK using manual microkeratome a didatic course, advices from experienced surgeons, and participation in wet lab would be mandatory.
Bowman Membrane ; Corneal Stroma ; Epithelium, Corneal ; Keratomileusis, Laser In Situ* ; Lasers, Excimer ; Learning Curve ; Methods ; Photorefractive Keratectomy

The excimer laser diopter correction has proven to be efficient and safe. This paper presents the principle of excimer laser refractive surgery. Based on analyzing the mathematics model of the human eye cornea, the authors have proposed a new model which can be used to proceed the myopia, hyperopia, astigmatism diopter correction. Also studied were the excimer laser's ablation mechanism and the flying-spot scanning technology. The research results have been directly applied to Ophthalmic excimer laser system. The correction of diopter is well improved.
Algorithms ; Cornea ; anatomy & histology ; Humans ; Keratomileusis, Laser In Situ ; methods ; Lasers, Excimer ; Models, Theoretical ; Photorefractive Keratectomy ; methods ; Refractive Surgical Procedures

To evaluate the relationship between ablation zone demm in PRK and 88.7% were decentered less than 0.75 mm in LASIK. The most meridional displacement was toward the superonasal quadrant; 46% in PRK and 51% in LASIK. There was less decentration in males, in the 2nd-operated eye, in older age, PRK, in larger ablation diameter, and in shallower ablation depth, but these differences were not statistically significant.
Adult ; Corneal Transplantation/methods* ; Factor Analysis, Statistical ; Female ; Human ; Keratectomy, Photorefractive, Excimer Laser* ; Laser Surgery* ; Male ; Middle Age ; Myopia/surgery* ; Pupil*

Photo refractive keratectomy (PRK) and laser Situ Keratomileusis (LASIK) have been used for over a decade and become popular in China. Principles and characteristics of eye trackers made by several famous foreign manufacturers are introduced in this paper and their developing direction in the future is pointed out too.
Cornea ; surgery ; Eye Movements ; Humans ; Keratomileusis, Laser In Situ ; instrumentation ; Lasers, Excimer ; Myopia ; surgery ; Photography ; instrumentation ; methods ; Photorefractive Keratectomy ; instrumentation ; Refractive Surgical Procedures ; Video Recording

The purposes of this study were to assess the expression patterns of heat shock proteins (Hsps), after eyeball heating or cooling, and to elucidate their relationships with corneal wound healing and intraocular complications after excimer laser treatment. Experimental mice were grouped into three according to local pretreatment type: heating, cooling, and control groups. The preconditioning was to apply saline eyedrops onto the cornea prior to photoablation. Following photoablation, we evaluated corneal wound healing, corneal opacity and lens opacity. Hsp expression patterns were elucidated with Western blot and immunohistochemical staining. The heating and cooling groups recovered more rapidly, and showed less corneal and lens opacity than the control group. In the heating and cooling groups, there were more expressions of Hsps in the cornea and lens than in the control group. These results were confirmed in the Hsp 70.1 knockout mouse model. Our study showed that Hsps were induced by the heating or cooling preconditioning, and appeared to be a major factor in protecting the cornea against serious thermal damage. Induced Hsps also seemed to play an important role in rapid wound healing, and decreased corneal and lens opacity after excimer laser ablation.
Animals ; Blotting, Western ; Cornea/pathology ; Heat ; Heat-Shock Proteins/biosynthesis ; Heat-Shock Proteins 70/genetics ; Immunohistochemistry ; Keratectomy, Photorefractive, Excimer Laser/*methods ; *Lasers ; Lens, Crystalline/pathology ; Mice ; Mice, Inbred C57BL ; Mice, Knockout ; Support, Non-U.S. Gov't ; Temperature ; Time Factors ; Wound Healing