We evaluated the corneal topography of 109 eyes which have 1 diopter or more astimatism, with computer-assisted videokeratography(Eye Sys CAS). There was 11% with round pattern, 17.4% with oval pattern, 49.5% with symmetric bow-tie pattern, 19.3% with assymmetric bow-tie pattern, 2.8% with irregular pattern. 70% of subjects had right and left eyes classified into the same group. There was statistically significant difference among the patterns for keratometric astigmatism and difference among the groups which were classified by the location of the area of highest refractive power for keratometric and total astigmatism. The mean angular separation between flat and steep meridian was 89.2 degrees and ranged from 78.61 degrees to 100.67 degrees. The mean residual astigmatism was 0.547 diopter. In the with-the rule astigmatism type, when the total astigmatism less than 1.89 diopter, residual astigmatism neutralize the corneal astigmatism, but when the total astigmatism increase more than 1.89 diopter, residual astigmatism tend to increase the total astigmatism.
Astigmatism* ; Classification* ; Corneal Topography*

In the evaluation of tear film stability based on corneal topography, a pretreatment algorithm for tear film video was proposed for eye movement, eyelash reflection and background interference. First, Sobel operator was used to detect the blur image. Next, the target image with highlighted ring pattern was obtained by the morphological open operation performed on the grayscale image. Then the ring pattern frequency of the target image was extracted through the Hough circle detection and fast Fourier transform, and a band-pass filter was applied to the target image according to the ring pattern frequency. Finally, binarization and morphological closed operation were used for the localization of the ring pattern. Ten tear film videos were randomly selected from the database and processed frame by frame through the above algorithm. The experimental results showed that the proposed algorithm was effective in removing the invalid images in the video sequence and positioning the ring pattern, which laid a foundation for the subsequent evaluation of tear film stability.
Algorithms ; Cornea ; Corneal Topography ; Tears

Many devices using in LASIK and PRK remake to minimize side effect. Fixation devices(EK-Fixation devices:Sejong Medical, Korea)and Holder(Global Fixation ring multiple teeth 13 mm diameter:Katena, USA; below holder)are made to minimize side effect called Ablation Decentration. Our study aims at evaulating the effect of using Fixation devices and Holder after LASIK. Corneal topography was used to anaylze centration in groups of patients:15 had LASIK using Fixation devices, 23 had LASIK using Holder, 20 had LASIK not using Fixation devices and Holder. Mean amount of decentration in topography of group of LASIK using Fixation devices was statistically significantly decreased in pre-operation(0.220+/-0.158)compared with 0.083+/-0.055 in post operation(P=0.017). In LASIK using Holder, mean amonut of decentration in topography in pre-operation(0.214 +/-0.124)was statistically significantly decreased compared with 0.146+/-0.071 in pre-peration, too(P=0.044). But mean amount of decentration in topography in LASIK not using Fixation devices and Holder, 0.156+/-0.100 in pre-operation was not statistically significantly different from 0.200+/-0.178 in post-operation. In LASIK groups using Fixation devices, mean amount of decentration in topography was significantly decreased comparing with other groups(P=0.010). And then, mean amount of decentration in topography from preoperative cornea center to postoperative cornea center using Fixation devices was 0.243+/-0.109, using Holder was 0.248+/-0.154 compared to control group(0.267+/-0.163). Groups using Fixation devices and Holder was significantly decreased comparing with other groups (P=0.010). In conclusion, Fixation devices and Holder are made to minimize side effect called Ablation Decentration in our study.
Cornea ; Corneal Topography ; Keratomileusis, Laser In Situ* ; Tooth

PURPOSE: This study was aimed to evaluate the efficacy of an eye-tracking system, in terms of the amount of decentration. Comparison was made between two LASIK groups operated with and without the use of eye-tracking system. METHODS: An eye-tracking system was used in 41 eyes(Group 1) and patient fixation alone without an eye-tracking system in 41 eyes(Group 2). Corneal topography(Humphrey ATLAS(TM) Corneal Topography System; Zeiss Humphrey Systems, Dublin, California, U.S.A.) was performed before surgery and 3 months postoperatively. The amount of ablation decentration was measured on the difference map obtained from the axial map. RESULTS: The mean +/-SD of decentration was 0.38 +/-0.23 mm in group 1, and 0.49 +/-0.24 mm in group 2(p=0.047). The amount of decentration was graded as follows: grade I(<0.5 mm); Grade II(0.5~1.0 mm); Grade III(>1.0 mm). Grade I, there was a significantly less decentration in group 1(p=0.037). For grade II, however, there was no significant difference between the two groups(p=0.766). CONCLUSIONS: Using eye-tracking system alone may not be effective in decreasing moderate decentration. Good fixation of the patients seemed to be as effective as an eye tracking system in achieving good ablation centration.
California ; Corneal Topography ; Humans ; Keratomileusis, Laser In Situ*

PURPOSE: To evaluate device efficacy using the corneal curvature value. METHODS: Prospectively, 35 patients (70 eyes) were enrolled in the present study. Three sets of corneal curvature values were obtained using the autorefractor (RK-F1(R)), manual keratometer (OM-2(R)), partial coherence interferometry keratometer (IOL Master(R)), wavefront analyzer (KR-1W(R)), and videokeratography (Orbscan II(R)). Repeatability of each device was evaluated by coefficient of variation, standard deviation, and intraclass correlation coefficient. RM-ANOVA on ranks was used to compare the differences in corneal curvatures among the devices. The Bland-Altman plot was performed to assess measurement agreement among the devices. RESULTS: The coefficient of variation values from each device ranged from 2.92% (IOL master(R)) to 3.06% (Orbscan II(R)), and the values of intraclass correlation coefficient ranged from 0.965 (KR-1W(R)) to 0.997 (IOL master(R)). Compared with the manual keratometer, there was a maximum corneal curvature difference of 1.23 D in KR-1W(R), while the other devices had differences less than 0.82 D. CONCLUSIONS: When assessing corneal curvature, the repeatability values were similar among the 5 devices, although a difference greater than 1 D was observed when comparing the KR-1W(R) to the manual keratometer.
Corneal Topography ; Humans ; Interferometry ; Prospective Studies

PURPOSE: To compare corneal topographic changes using Orbscn II between keratoconus and keratoconus- suspected eyes. METHODS: Thirty-seven keratoconus eyes, 17 keratoconus-suspected eyes and 37 normal eyes were evaluated by using Orbscan II corneal topography. We compared central phachymetry, anterior elevation from best-fit sphere (BFS), posterior elevation from BFS, most protruded corneal thickness, central corneal thickness, anterior chamber depth, corneal diameter, and pupil size. RESULTS: Central pachymetry, anterior and posterior elevation from BFS, central corneal thickness, and anterior chamber depth were statistically significantly different between keratoconus and control eyes. Anterior elevation from BFS showed a significant difference between keratoconus-suspected and control eyes. There were statistically significant differences in central pachymetry, posterior elevation from BFS, central corneal thickness and most protruded corneal thickness between keratoconus and keratoconus-suspected eyes. Corneal diameter and pupil size showed no differences among the 3 groups. CONCLUSIONS: Suspected keratoconus eyes have a higher value of anterior elevation from BFS on Orbscan II topography as compared with control eyes. Central pachymetry, posterior elevation from BFS, central corneal thickness and most protruded corneal thickness may be helpful in distinguishing between keratoconus and keratoconus-suspected eyes.
Anterior Chamber ; Corneal Topography ; Keratoconus* ; Pupil

PURPOSE: To evaluate the efficacy of two excimer laser systems with eye-tracker in the term of decentration amount. METHODS: We performed LASIK with LaserScan LSX(TM) (group 1, 39 eyes) and Allegretto Wave(TM) (group 2, 94 eyes), both of which were equipped with eye-tracker. The amount of decentration was measured on a difference map that was obtained from preoperative and postoperative corneal topography, and was compared between the two groups. RESULTS: The amount of decentration was significantly higher in group 1 (0.39 +/- 0.22 mm) than in group 2 (0.29 +/- 0.18 mm) (p=0.018). When these groups were subdivided by preoperative spherical equivalent, in case of under -6.0 D, the amount of decentration between the two groups (0.31 +/- 0.16 mm in group 1, 0.28 +/- 0.15 mm in group 2, p=0.380), whereas in case of over -6.0 D, the amount of decentration was significantly higher in group 1 (0.48 +/- 0.26 mm) than in group 2 (0.30 +/- 0.21 mm) (p=0.020). CONCLUSIONS: Allegretto Wave(TM) showed better centration ability than LaserScan LSX(TM) and this superiority was more profound in highly myopic eyes.
Corneal Topography ; Keratomileusis, Laser In Situ* ; Lasers, Excimer

To determine amount of surgically induced outcome of 3.5mm clear corneal incisin, 30 eyes(30 patients) were evaluted retrospectively. Corneal curvature was measured using cmputerized videokeratography, and the induced astigmatism was calculated with using the Holladat-Cravy-Koch formula. The corneal flattening was significantly more prominent at distances of 0.5, 1.5 and 2.5mm along 90-degree meridian and 270 degree meridian at one week 1 month postoperatively but decreased at 6 months. Surgically induced astigmatism was -0.5D at one week, -0.12D at 1 month, and -0.13D at 6 month in groups using keratometry and in group using toography. At 1 month postoeratively surgically induced astigmatism in topography was statically sigmificant(p<0.05).
Astigmatism ; Cataract* ; Corneal Topography* ; Retrospective Studies

PURPOSE: To evaluate the effect of reverse geometry lens (RGL) on correction of moderate degree myopia and cornea in patients of moderate-degree myopia. METHODS: 48 eyes of 82 eyes were chosen to wear reverse geometry lens and the remaining 34 eyes were fitted with rigid gas permeable (RGP) lens. The subjects were tested three days, one, two weeks, one, two and three months after fitting the lens. Uncorrected visual acuity, manifested refractive error, corneal thickness and corneal endothelial cell count were evaluated. corneal topography were performed. RESULTS: The uncorrected visual acuity was increased at 0.05 LogMAR after two weeks. and manifested refractive error decreased during the first months, thereafter stabilizing to -0.2 D (diopters). Corneal thickness was 540.4 micrometer and 583.0 micrometer in the center and mid-periphery, decreased to 505.2 micrometer and 572.7 micrometer, respectively, three months after RGL fitting (p<0.05). Endothelial cell count was 2663.5 cells/mm2 and 2541.5 cells/mm2 in the center and mid-periphery, 3 months after RGL fitting and endothelial cell count was not significantly different compared with that of pre-fitting. There was no statistical difference between RGL fitting group and RGP fitting group in the change of corneal endothelial cell count. CONCLUSIONS: RGL was found to be effective in correction of moderate-degree myopia. It had minimal effect on corneal endothelium, in short-term usage, however, the change of corneal thickness suggests that RGL fitting may effect on corneal epithelium and stroma.
Cornea* ; Corneal Topography ; Endothelial Cells ; Endothelium, Corneal ; Epithelium, Corneal ; Humans ; Myopia* ; Refractive Errors ; Visual Acuity

PURPOSE: To unveil the etiology, pathogenic mechanism and the clinical significance of the corneal iron line through various clinical aspects of the corneal iron line. METHODS: This study included 45 eyes of 39 patients who visited the Department of Ophthalmology in Chungnam National University Hospital between April 2011 and March 2014. Anterior segment of the eye was photographed during the diagnostic process. The medical history of the patient was investigated and corneal topography was performed to discover the relationship between the position of the corneal iron line and the curvature of the corneal surface. RESULTS: The corneal iron line was identified in various corneal diseases such as herpetic stromal keratitis and; corneal ulcer. The average age of patients was 57.8 years. Corneal topography was performed in 12 patients and a connection was found between the curvature of the corneal surface and the position of corneal iron line at 75%. During the research period, corneal disease progressed and associated corneal iron line became clearer in 2 eyes. However, there was no repositioning or new appearance in different areas. The corneal iron line was not associated with visual acuity and the shape varied in accordance with the accompanying corneal disorder. The location where the tears repeatedly accumulate was associated with corneal surface. CONCLUSIONS: Based on the occurrence location and the shape of the corneal iron line, we could understand that the occurrence of corneal iron line is associated with the past and current corneal surface irregularities, which verified the validity of the tear pooling hypothesis. Therefore, this result can aid in establishing the diagnosis and treatment plan when the corneal iron line is discovered during clinical practice.
Chungcheongnam-do ; Corneal Diseases ; Corneal Topography ; Corneal Ulcer ; Diagnosis ; Humans ; Iron* ; Keratitis ; Ophthalmology ; Tears ; Visual Acuity