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Results for “Corneal Topography”

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At least 19 recordsLinked to original sources

PubMed2004

Corneal topography in corneal refractive therapy (CRT): a 1-month follow-up.

PURPOSE: To evaluate visual outcome and corneal shape change during the first month of wearing corneal refractive therapy (CRT) reshaping contact lenses to correct myopia in otherwise healthy eyes. METHODS: Twenty-nine eyes were fit with Paragon CRT contact lenses, which were worn nightly. Before and after CRT fitting, uncorrected visual acuity was measured, and corneal topography was performed and evaluated with the Holladay Diagnostic Summary EyeSys 2000 Videokeratoscope. To evaluate the visual outcome, refractive yield (achieved/attempted correction) was calculated and accounted for distance or monovision. RESULTS: Uncorrected visual acuity improved in all patients. In 1 month, refractive yield was 96.7%. Corneal uniformity index and predicted corneal acuity index were maintained, and the Q value changed from -0.08 to +0.38 (P < 0.05). CONCLUSIONS: CRT lenses are effective in improving visual acuity. They significantly changed the corneal from prolate to oblate while maintaining corneal quality.

Adult↗

PubMed1996

[Use of the confocal laser scanning method for determining corneal topography and corneal tissue effects in refractive corneal surgery].

Refraction of the cornea head been generally measured with ophthalmometers or computer disk keratometers. We therefore used a confocal laser scanning system for measurement of the corneal topography. Enucleated tonicized pig eyes were measured before and after laser thermokeratoplasty (LTK). The topographical data were used to determine refraction and refractive change; the data were stored digitally. The single images and their differences were displayed on a PC. Unlike conventional ophthalmometry, confocal laser scanning can demonstrate the topographical shape, showing the overall topography of the cornea and local corneal effects, e.g., coagulation, mechanical lesions or high-energy laser effects. Topographical laser scanning has proven to be a generally useful method of determining refraction and surface alterations in corneal refractive surgery.

Animals↗

PubMedDate not supplied

Computerized corneal topography of furrow corneal degeneration.

PURPOSE: To analyze the corneal topography features of furrow corneal degeneration. SETTING: Western Galilee-Nahariya Medical Center, Nahariya, Israel. METHODS: Computer-assisted corneal topography analysis of two patients with furrow corneal degeneration was obtained and studied. RESULTS: The typical appearance of circumferential peripheral thinning in the lucid interval between the limbus and corneal arcus indicated a clinical diagnosis of furrow corneal degeneration. The corneal topography maps showed central flattening and excentric localized steepening. A step of 1.50 diopters was seen central to the peripheral furrow. CONCLUSION: Keratometry and noncomputerized keratoscopy are insufficient methods of evaluating the topographic features of furrow corneal degeneration. Computer-assisted corneal topography showed steepening and central flattening that may be attributed to the thinned peripheral circumference.

Aged↗

PubMedDate not supplied

Repeatability of corneal topography: the "corneal field".

BACKGROUND: The purpose of this study was to determine the interoccasion repeatability of keratometry, photokeratography, and videokeratography and to describe the "corneal field," a scheme for explaining videokeratography results. METHODS: A single examiner obtained corneal curvature measurements with a keratometer, a photokeratoscope, and the TMS-1 in 29 adult patients on two occasions. RESULTS: Estimates for the repeatability of keratometry were +/- 0.49 and +/- 0.65 diopters (D) for the horizontal and vertical meridians respectively. The repeatability of photokeratography was +/- 0.90 and +/- 1.21 D. We presented a rational method for presenting numeric videokeratographic data by temporally and spatially averaging corneal curvature values and grouping them into 24 regions. The repeatability of videokeratography with the TMS-1 was +/- 0.50 D centrally, +/- 0.65 D paracentrally, and +/- 0.80 to +/- 1.00 D in the midperiphery. CONCLUSIONS: Repeatability of the photokeratoscope for central measurements is considerably worse than the keratometer. The repeatability of videokeratography is worse toward the periphery. Refractive surgeons and contact lens investigators need to be aware of these limitations so that true change can be distinguished from measurement error.

Adult↗

PubMedDate not supplied

Characteristics of normal corneal topography using the EyeSys corneal analysis system.

PURPOSE: To study the parameters of corneal topography of normal eyes using the Corneal Analysis System (CAS, EyeSys Technologies) to determine the types and frequency of patterns and parameters. SETTING: University of Illinois Eye Center, Chicago, Illinois, USA. METHODS: Three independent, masked judges, using a forced-choice paradigm, classified corneal topography patterns into six categories on one randomly selected, normal eye of 100 persons who did not wear contact lenses. The patterns were defined by using the midpoint dioptric bin and a 0.50 diopter (D) steeper bin. RESULTS: The pattern frequency using the mid-dioptric bin was teardrop (6%), amorphous (11%), round (11%), symmetric bow tie (17%), asymmetric bow tie (1 %), kidney (22%), and oval (32%). Mean refractive and keratometric cylinders, respectively, were teardrop (0.13 and 0.15 D), amorphous (0.15 and 0.49 D), round (0.18 and 0.56 D), oval (0.21 and 0.56 D), kidney (0.51 and 0.72 D), and bow tie (1.18 and 1.82 D). Pattern frequency using the 0.50 D steeper bin was round (2%), oval (5%), teardrop (6%), kidney (15%), amorphous (17%), asymmetric bow tie (17%), and symmetric bow tie (37%). Mean refractive and keratometric cylinders, respectively, were round (0.13 and 0.32 D), amorphous (0.25 and 0.38 D), kidney (0.11 and 0.42 D), oval (0.40 and 0.59 D), teardrop (0.08 and 0.75 D), and bow tie (0.65 and 1.09 D). Mean flat and steep contours were 41.76 D (95% confidence interval [CI], 38.68 to 44.84 D) and 44.15 D (95% CI, 41.00 to 47.31 D), respectively. Mean contour range was 2.40 D (95% CI, 0.61 to 4.17 D). CONCLUSION: The data suggest that for 95% of normal corneas, corneal contours will be steeper than 38.50 D, flatter than 47.50 D, and have a contour range less than 4.25 D when using the EyeSys CAS.

Adolescent↗

PubMed1992

Clinical uses of corneal topography analysis.

Corneal topography analysis has become an indispensable tool in the evaluation and treatment of corneal disease. It is helping us understand the normal corneal shape and how it is altered in ectatic diseases, by contact lens wear, and by surgery. Topography analysis is also now being used in planning procedures to correct astigmatism and in the fitting of contact lenses.

Astigmatism↗

PubMed1997

Gaussian power with cylinder vector field representation for corneal topography maps.

The corneal maps displayed on commercially available corneal topography instruments are really one-dimensional, defining quantities only along a meridian, and ignoring shape information along any other direction. Both axial and instantaneous power have the drawbacks that there is a singularity at the center data point on the videokeratograph axis, and the computed powers and appearance of the corneal map change depending on the videokeratograph axis or on the location of asymmetries. We propose a new representation for corneal topography maps, Gaussian power with cylinder vector field, that has no singularity, and faithfully produces power values and corneal map patterns that are independent of videokeratograph axis or location of asymmetries.

Computer Simulation↗

PubMed1998

Corneal topography after cataract surgery using a clear corneal incision closed with one radial suture.

BACKGROUND AND OBJECTIVE: To determine whether corneal topography and visual recovery are affected by suturing a temporal, clear corneal incision for cataract surgery. PATIENTS AND METHODS: Forty-one consecutive phacoemulsification patients (39 eyes) had a 3.2-mm incision sutured with one 10-0 nylon, radial suture removed after 1 postoperative week. Visual acuity (VA) and corneal topography, including best fit sphere (BFS), best fit cylinder (BFC), principle meridian, topographic irregularity (TI), and vector-corrected astigmatism (VCA), were measured preoperatively and 1 day, 1 week, and 1 month postoperatively. Two-tailed t tests and Pearson correlations were calculated. RESULTS: From the preoperative measurement to 1 week postoperatively, VA improved, BFS (P = .005) and TI (P = .033) increased, and VCA shifted with-the-rule. From 1 week to 1 month postoperatively, BFS (P = .012) and TI (P = .002) decreased. BFC and its direction did not change. Almost all measures were significantly correlated. CONCLUSION: The benefits of sutureless surgery on corneal topography and visual recovery are not degraded by using a suture to prevent wound leakage.

Aged↗

PubMedDate not supplied

Corneal topography parameters after superior clear corneal incision cataract surgery in arcus lipoides.

PURPOSE: To compare changes in corneal topographic parameters after cataract surgery in eyes with different severities of arcus lipoides. METHODS: Fourty eyes of 40 patients (23 women, 17 men, age 71.3+/-20.4 years, range 40 to 89 years) were studied prospectively in a consecutive, non-interventional, comparative series of cases. Eyes were classed in three groups (0 to 2) according to the assessed grade of arcus lipoides (none, <180 degrees, >180 degrees). Corneal topography (Tomey TMS-2) was performed preoperatively and at 1 and 10 days and 1 and 3 months following cataract surgery (superior 4.0 mm clear corneal incision, no suture). Keratometric astigmatism (Dcyl), surface regularity index (SRI), surface asymmetry index (SAI), and potential visual acuity (PVA) were evaluated for the different groups and time-points, using the Kruskal-Wallis, Wilcoxon, and Mann-Whitney statistical tests. RESULTS: No significant preoperative difference was found in mean Dcyl, SRI, or PVA; preoperative SAI was lower in Group 1. Postoperatively Dcyl was increased at day 1 in Groups 1 and 2, and remained higher in Group 2 until month 1. At month 3 significant differences among Groups 0, 1, and 2 disappeared. CONCLUSIONS: The 4.0 mm superior clear corneal incision is a safe method for cataract surgery in the presence of arcus lipoides. This procedure induces greater corneal astigmatism, surface irregularity, and lower PVA in the early postoperative period in cases with arcus lipoides than in normal corneas. Concerning final results, wound healing was not affected by greater severity of arcus lipoides, although stabilization of the corneal surface tended to be slower.

Adult↗

PubMed1998

Corneal topography in LASIK.

Corneal topography plays an important role in laser in situ keratomileusis (LASIK). Preoperative screening permits the detection of keratoconus and other corneal shape anomalies that may be a contraindication for refractive surgery. Monitoring the progress of the surgical outcome with topography is helpful to detect postoperative complications such as decentration and clinically significant irregular astigmatism. LASIK compares favorably with PRK for the treatment of low to moderate myopia in terms of early achievement of refractive stability, but induction of modest amounts of irregular astigmatism can be a concern.

Astigmatism↗

PubMed2006

Evaluation of keratoconus in Asians: role of Orbscan II and Tomey TMS-2 corneal topography.

PURPOSE: To evaluate the corneal topographic patterns of Asian patients with keratoconus (KC). DESIGN: Prospective observational case-control study. METHODS SETTING: Institutional. STUDY POPULATION: A total of 116 patients (both eyes included) with KC were recruited. The control group consisted of 70 laser in-situ keratomileusis (LASIK) candidates with myopia. Patients with previous ocular surgery and trauma were excluded. OBSERVATION PROCEDURE: Corneal topography was performed using the Tomey KC screening system (Topographic Modeling System, software version 2.4.2J, Tomey Corp, Nagoya, Japan) and Orbscan II corneal topography system (Bausch & Lomb Surgical, Orbtek Inc, Salt Lake City, Utah, USA). MAIN OUTCOME MEASURES: Videokeratographic variables were analyzed and the eyes were grouped into KC, KC suspect, and control groups. RESULTS: The corneal topographic patterns of 196 eyes were analyzed. The topographic patterns displayed by Tomey (TMS-2N) and Orbscan II were similar. The majority of eyes with KC (71.2%) and KC suspect (70%) had asymmetric bowtie patterns. Thirteen indices of TMS-2N were analyzed and the means of the indices were found to be significantly higher in eyes in the KC group than the KC suspect group (P < .001). Fourteen indices of Orbscan II were analyzed. Eyes in the KC suspect group had higher mean posterior elevation (46 +/- 17 microm), 3 mm irregularity (2.44 +/- 1.36 diopters [D]), 5 mm irregularity (2.61 +/- 1.19 D) and had thinner corneas (mean 504.4 +/- 40.4 microm) than normal eyes (26 +/- 8 microm, 1.05 +/- 0.37 D, 1.38 +/- 0.39 D, and 554.0 +/- 25.0 microm, respectively). CONCLUSION: Corneal topography pattern recognition combined with quantitative diagnostic indices is useful for the screening and classification of KC with the Orbscan II being more sensitive in screening for KC than TMS-2N.

Adolescent↗

PubMed1999

Differentiating contact lens induced warpage from true keratoconus using corneal topography.

PURPOSE: Superior corneal flattening associated with inferior corneal steepening is a videokeratoscopic topography pattern that usually describes both keratoconus and contact lens induced warpage. To differentiate these two conditions topographically, we analyzed ten different corneal topographic shape variables and found that two distinct conditions were described. Three unique measurements of corneal geometry: shape factor (SF), irregularity (CIM), and apical toricity (TKM) were analyzed and evaluated as an additional method for differentiating these two conditions. METHODS: A retrospective series of 100 eyes with a medical diagnosis of either contact lens induced warpage or true keratoconus were mapped using the Humphrey Atlas Corneal Topographer (San Leandro, CA) and their individual topographic indices were analyzed in an attempt differentiate the two conditions with videokeratoscopy. Variables included Flat Keratometry Reading, Maximum Axial Curvature, Maximum Tangential Curvature, Corneal Astigmatism, Corneal Shape Factor, Reference Sphere, Corneal Irregularity Measure (CIM), Maximum Elevation, and Mean Reference Toric K (TKM). All patients wore rigid gas permeable contact lenses. RESULTS: True keratoconic eyes had steeperflat K readings (46.9+/-3.7 D vs. 43.04+/-1.18 D; P<6.3E-13) with greater variations in maximum axial curvature (54.1+/-4.76 D vs. 43.6+/-1.5 D; P<2.4E-15) and maximum tangential curvature (55.1 7+/-4.56 D vs. 47.7+/-1.5 D; P<5.4E-16) than did eyes with contact lens induced warpage. The amount of corneal toricity (-3.43+/-2.29 D vs. -1.33+/-0.88 D; P<1.5E-07) was also greater for true keratoconus. True keratoconic eyes had larger and more variable shape factors (0.61+/-0.26 vs. 0.02+/-0.13; P<2.5E-19) and CIM's (2.30+/-1.16 vs. 1.03+/-0.37; P<7.5E-10) than those with contact lens induced warpage. Steeper reference spheres (47.58+/-3.55 D vs. 43.6+/-0.37 D; P<2.2E-10), greater maximum elevation over their respective reference spheres (15.51+/-9.91 microns vs. 6.2+/-3.0 microns; P<8.1E-08) and steeper, more variable toric mean reference spheres (51.88+/-4.01 D vs. 43.82+/-1.82 D; P<3.9E-17) are also present in true keratocon us. True keratoconic eyes can be separated from contact lens induced warpage eyes with a sensitivity of 98%, while identification of contact lens induced warpage demonstrates 94% specificity using corneal topography. CONCLUSIONS: While contact lens induced warpage and true keratoconus exhibit similar corneal topography patterns (superior flattening and inferior steepening), they demonstrate two uniquely different geometric shapes that can be readily differentiated using the various corneal shape indices of videokeratoscopy with a high degree of accuracy and specificity.

Contact Lenses↗

PubMed1999

Corneal topography in patients with congenital ptosis.

PURPOSE: To determine the effect of congenital ptosis on corneal shape, and to assess the role of these topographic changes in the development of amblyopia. METHODS: Twenty-two patients with congenital ptosis were examined and a corneal topographic examination performed in both the ptotic and normal eyes. The qualitative corneal classification was done according to the colour-coded topographic maps. The surface regularity index (SRI) and the surface asymmetry index (SAI) were used as quantitative descriptors of the study. RESULTS: Ptotic eyes had an increased incidence of astigmatism, bow tie pattern on corneal topography, corneal asymmetry (SAI, p < 0.05) and corneal irregularity (SRI, p < 0.05). Lack of mirror-image symmetry with the fellow eye was higher in amblyopic eyes. CONCLUSION: Eyes with congenital ptosis have an increased incidence of astigmatism and a bow tie pattern on corneal topography. These features are associated with the presence of amblyopia.

Adolescent↗

PubMed2007

Nomogram, corneal topography, and final prescription relations for corneal refractive therapy.

PURPOSE: To analyze the relationships between the first diagnostic lens and the lens finally prescribed for corneal refractive therapy with Paragon CRT and to correlate them with corneal topography, and refractive parameters. METHODS: The files of 86 patients who were successfully fitted with corneal refractive therapy using Paragon CRT were reviewed. Differences between diagnostic vs. finally prescribed lens parameters of base curve radius (BCR), return zone depth (RZD) and landing zone angle (LZA), as well as the number of lenses required to achieve the final fit were correlated with corneal topographic parameters and attempted refraction. RESULTS: There were statistically significant differences between CRT parameters for the first lens suggested by the nomograms and the lens finally prescribed (Wilcoxon signed ranks, p<0.05). On average, those changes did not achieve 1 full step difference (i.e., 0.10 mm for BCR and 25 microm for RZD). Only LZA achieved a full step change (1 degrees). According to our data, 92% of the fittings were achieved by changing only two parameters or less. The majority of changes required were within+/-1 step of the initially selected (96% for BCR, 99% for RZD, and 100% for LZA). Changes in lens parameters are related with some ocular parameters, but mainly with first lens parameters. RZD was the parameter requiring more changes. The amount of change in RZD was correlated with steep keratometry, BCR, and RZD of the first lens. CONCLUSIONS: Nomograms used for lens selection with Paragon CRT have a high first-fitting success with a relatively simple fitting procedure. Correlations between final lens parameters and ocular and initial lens parameters obtained in this study can assist clinicians to anticipate the level of difficulty in achieving optimal fitting with Paragon CRT sigmoid contact lens for corneal refractive therapy and the most frequent changes needed to achieve it.

Adolescent↗

PubMed1996

Application of a modified keratometer in the study of corneal topography on Chinese subjects.

A corneal topography study was carried out on Hong Kong Chinese subjects using a modified keratometer. The Chinese corneal topography measured by this modified keratometer was similar to other studies using the Wesley-Jessen Photo Electronic Keratoscopy (PEK) System 2000. The mean p-values along the horizontal meridian and the vertical meridian were 0.82 and 0.87, respectively. A negative correlation was found between the p-value and the central corneal radius along the horizontal meridian which may indicate that a steeper central cornea will have a greater p-value. However, the correlation coefficient of 0.56 was not too certain for this conclusion to be drawn. A difference of 0.04 was found between the horizontal p-value and the vertical p-value, which may be a result of the tight lid tension along the vertical meridian. This modified keratometer can be considered as an inexpensive instrument for the study of corneal topography.

Adult↗

PubMedDate not supplied

Terrien's marginal degeneration: corneal topography.

Computer-assisted corneal topographic analysis was used to evaluate the corneal contour of four patients with Terrien's marginal degeneration. The corneal topography in these patients was characterized by flattening over the areas of peripheral thinning produced by the disorder. When thinning was restricted to the superior and/or inferior areas of the peripheral cornea, there was a relative steepening of the corneal surface approximately 90 degrees away from the midpoint of the thinned area. This resulted in high against-the-rule or oblique astigmatism characteristic of the disorder. This common pattern is attributable to the frequency with which the superior and/or inferior peripheral cornea is preferentially involved in Terrien's marginal degeneration. In some patients, the central corneal topography may remain relatively spherical if the area of thinning is small or if the disorder extends around the entire circumference of the cornea.

Adult↗

PubMed1996

[Corneal distortion induced by speculum--studies with computer-assisted corneal topography].

The corneal distortion induced by the presence of an eyelid speculum was analysed by the Videokeratoscope-Eyesys Corneal Analysis System (EYESYS), with a Barraquer type speculum (B group) in 22 normal eyes and with a Kratz-Barraquer type speculum in 38 normal eyes (KB group). The following differences were evaluated in the 2 groups: intraocular pressure (IOP), refractive power, change in astigmatism of the Cravy method, and corneal refractive power before and after the specula were put in the interpalpebral fissure. Significant differences were found in the IOP in the KB group, in spherical equivalent in the B and KB groups, and in corneal refractive power in the B groups. Then the 38 eyes of the KB group were divided into two groups by the average level of proptosis and the average difference of IOP, and the corneal refractive power of the two groups was compared by statistical analysis. Significant difference was found in the direction of 0 degree/ 180 degrees in the group with higher than average proptosis and in the direction of 90 degrees/ 270 degrees in the group with higher than average difference in IOP. Multiple regression analysis suggested that higher grades of proptosis were related with steeper vertical meridians and that wider palpebral fissures were associated with steeper horizontal meridians. Multiple regression also showed that the speculum did not cause corneal distortion with the proper relation between level of proptosis and width of the palpebral fissure.

Adult↗

PubMed1998

Laser in situ keratomileusis assisted by corneal topography.

PURPOSE: To assess whether laser in situ keratomileusis (LASIK) assisted by corneal topography can successfully treat corneal irregularities or irregular astigmatism in patients with previous ocular surgery or ocular trauma. SETTING: University Eye Hospital, Klinikum Mannheim, Mannheim, Germany. METHODS: In a prospective clinical study, LASIK was performed in 23 eyes of 22 patients. Reasons for surgery were irregular astigmatism after penetrating keratoplasty or penetrating injury or corneal irregularity after previous excimer laser surgery. Excimer ablation was based on preoperative corneal topography data (Corneal Analysis System, EyeSys Technologies) using a proprietary algorithm (Topographic Assist LASIK, Chiron Vision). Follow-up was 6 months. RESULTS: Mean preoperative uncorrected visual acuity (UCVA) was 20/80 and mean best spectacle-corrected visual acuity (BSCVA), 20/35. Uncorrected visual acuity improved in all but two cases. Postoperatively, mean UCVA increased to 20/50; mean BSCVA was unchanged. No eye lost two or more lines of BSCVA. Postoperative topography showed less corneal irregularity in 81.3% of eyes; full correction was achieved in 19.4%. Four eyes (19.4%) needed re-treatment for undercorrection and three eyes (14.3%) for regression. CONCLUSION: Preliminary results indicate that the concept of topographic-assisted LASIK is feasible. However, most eyes were undercorrected and had regression. One reason might be that corneal topography underestimated corneal irregularity, causing significant undercorrection.

Adolescent↗