Corneal topography

PURPOSE: To determine the mean angle kappa and its determinants in the population of Tehran, Iran. METHODS: In a cross-sectional survey with random cluster sampling, a total of 442 participants aged> 14 years were selected from 4 municipality districts of Tehran for Orbscan acquisitions. Exclusion criteria were history of eye surgery for refractive errors, cataract or glaucoma, and use of topical medication or any type of contact lens at the time of the study. Mean angle kappa in different age and gender groups and its association with ...

Keratometry is currently achieved by projecting a circular mire onto the patient's cornea and analyzing the size and shape of its reflected image. The projection mires are decisive for the precision of the measurement. We have previously developed a keratometric module for slit lamps, and the development of four projection mires are presented. Mire 1 is composed of optical fibers and electrical cables; Mire 2, 48 LEDs; Mire 3, optical fibers and no electrical cables; and Mire 4, mechanical parts--cable free. Mires 2-4 provide accurate keratometry measurements at slit lamps. Mire 4 is the most adequate for the clinical environment.

Describes an automatic optical system that is attached to a slit lamp in order to provide automatic keratometry at low cost. The system consists of projecting a light ring as a target onto the patient's cornea as well as analysis of the deformation of the target in order to obtain the radius of curvature and the axis of the associated astigmatism. The reflected image of the target is displayed on a PC monitor, while dedicated software performs the analysis of the image, which provides the corneal keratometry

Purpose: To compare thickness measurements of the central 6.0 mm of the cornea obtained with the Orbscan® II topography system and topographical ultrasound pachymetry. Setting: School of Optometry, University of Santiago de Compostela, Galicia, Spain. Methods: In 24 right eyes, pachymetric measurements were taken at the center and 1.2 mm and 3.0 mm on the superior and inferior hemimeridians. A 1‐sample t test was applied to assess the significance of the relationship between Orbscan II and ultrasound methods. The relationship between the 2 was assessed by analyzing regression and plotting the differences against the mean corneal thickness. Orbscan II data were analyzed in 3 ways: (1) without the application of an acoustic equivalent correction factor; (2) with a correction factor of 0.92, as recommended by the manufacturer; (3) with correction using the equations derived in this study. The data were systematically compared with those of ultrasound pachymetry. Results: Before the cor...

To present the Tomographic and Biomechanical Index (TBI), which combines Scheimpflugbased corneal tomography and biomechanics for enhancing ectasia detection. Patients from different continents were retrospectively studied. The normal group included 1 eye randomly selected from 480 patients with normal corneas and the keratoconus group included 1 eye randomly selected from 204 patients with keratoconus. There were two groups: 72 ectatic eyes with no surgery from 94 patients with very asymmetric ectasia (VAE-E group) and the fellow eyes of these patients with normal topography (VAE-NT group). Pentacam HR and Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany) parameters were analyzed and combined using different artificial intelligence methods. The accuracies for detecting ectasia of the Belin/Ambrósio Deviation (BAD-D) and Corvis Biomechanical Index (CBI) were compared to the TBI, considering the areas under receiver operating characteristic curves (AUROCs). The random forest meth...

The present study was designed to evaluate the topography of a series of keratoconus patients. Using a computer-assisted videokeratography (Eye Sys) we determined the topographic findings of 85 eyes of 46 consecutive patients with keratoconus. We analysed some quantitative topographic parameters like: power at the apex, central corneal power, the amount of irregular astigmatism, distance between the apex and the visual axis, difference in central corneal power between the two eyes of the same individual and steepening of the inferior cornea compared with the superior cornea. Keratoconic topographic alterations were classified into two groups. Fifty seven of the cones (71%) could be described as peripheral with steepening of the cornea extending to the limbus. The remaining twenty three eyes (29%) had steepening confined to the central cornea. In many instances corneal topography was characterized by a high degree of nonsuperimposable mirror image symmetry (enantiomorphism) in the lo...

To compare treatments with wavefront optimized and custom-Q ablations. Two consecutive groups of eyes were treated for myopia and astigmatism with surface ablation. One group was treated with wavefront optimized ablation and the second group was treated with custom-Q ablation. Preoperative and 3-month postoperative Q-values, higher order aberrations, low contrast visual acuity, and classic outcome parameters were analyzed. The wavefront optimized ablation group was comprised of 46 eyes of 23 patients with a mean spherical equivalent refraction (SE) of -3.64 diopters (D) (range: -1.15 to -8.25 D); mean Q-value changed from -0.33 preoperatively to 0.06 postoperatively. The custom-Q ablation group was comprised of 42 eyes of 21 patients with a mean SE of -3.24 D (range: -1.47 to -8.00 D); mean Q-value changed from -0.36 preoperatively to -0.03 postoperatively. A statistically significant difference in postoperative change in Q-values (P = .049) between the two groups was noted, but the...

The aim was to evaluate the anterior and posterior corneal aberrations provided by the Pentacam system in normal and early to moderate keratoconic eyes. Fifteen normal eyes (normal group, mean age 32.60 +/- 7.45 years) and 15 eyes with the diagnosis of keratoconus (keratoconus group, mean age 29.07 +/- 8.66 years) were included in this study. All eyes received a comprehensive ophthalmologic examination including corneal topographic analysis with the Pentacam system. Keratometric, best-fit sphere and corneal aberrometric data were recorded and analysed. Root mean square values (RMS) were calculated for primary coma and coma-like aberrations. Statistically significant differences were found in all anterior aberrometric parameters (all p < 0.02), except for horizontal primary and secondary coma Zernike terms (p = 0.61 and 0.72). Regarding posterior corneal surface, statistically significant differences among groups were found in primary spherical aberration, primary vertical coma, coma RMS and coma-like RMS (all p < 0.01). In the normal group significantly higher levels of primary vertical coma, spherical aberration, coma and coma-like RMS were found for the posterior corneal surface (all p < 0.04). In the keratoconus group, only significant differences among anterior and posterior corneal surfaces were found in coma RMS, coma-like RMS and vertical coma (all p < 0.01). These higher levels of aberrations for the posterior corneal surface do not agree with the theoretical optical properties of this surface. With the Pentacam system, higher levels of vertical coma, primary coma and coma-like aberrations are present in keratoconic eyes compared to normal eyes. The values provided by this device for posterior corneal aberrations are erroneous.

To report the incidence, visual and refractive outcomes, optical zone enlargement, and recentration using topography-guided CRS-Master TOSCA II software with the MEL 80 excimer laser (Carl Zeiss Meditec AG, Jena, Germany) after primary myopic laser refractive surgery. Retrospective analysis of 73 eyes (40 patients) with complaints of night vision disturbances due to either a decentration or small optical zone following a primary myopic laser refractive surgery procedure using the MEL 80 laser. Multiple ATLAS topography scans were imported into the CRS-Master software for topography-guided ablation planning. The topography-guided re-treatment procedure was performed as either a LASIK flap lift, a new LASIK flap, a side cut only, or photorefractive keratectomy. Axial curvature maps were analyzed using a fixed grid and set of concentric circles superimposed to measure the topographic optical zone diameter and centration. Follow-up was 12 months. The incidence of use in the population o...

The aim of this study was to analyze the effect of postcollagen crosslinking (CXL) haze on the measurement and repeatability of pachymetry and mean keratometry (Km) of four corneal topographers. Sixty eyes of sixty patients with progressive keratoconus who had undergone accelerated CXL (ACXL) underwent imaging with a scanning slit imaging device (Orbscan II) and three Scheimpflug imaging devices (Pentacam HR, Sirius, and Galilei). Post-ACXL haze was measured using the densitometry software on the Pentacam HR. Readings of the thinnest corneal thickness (TCT) and Km from three scans of each device were analyzed. Effect of haze on the repeatability of TCT and Km measurements was evaluated using regression models. Repeatability was assessed by coefficient of variation. Corneal densitometry in different zones affected the repeatability of TCT measurement of Orbscan (P < 0.05) significantly but not the repeatability of TCT with Pentacam HR and Sirius (P = 0.03 and 0.05, respectively). ...

Refractive procedures enjoy very high success rates and are among the most commonly performed elective surgeries in medicine. With better insights into preoperative screening, the overwhelming majority of cases have successful outcomes. Unfortunately, however, all refractive surgeons must appropriately manage unsuccessful cases. Unsuccessful refractive surgery procedures may relate to each step of the refractive surgery process: preoperative screening, surgical planning, intraoperative events, and postoperative biomechanical or healing anomalies. This paper reviews the management of unsuccessful laser-assisted in situ keratomileusis (LASIK) procedures, focusing on significant advances related to wavefront-guided therapeutic ablations.

To investigate agreement between a rotating Scheimpflug camera (Pentacam, Oculus Optikgeräte GmbH) and two corneal topographers (TMS-2 Topography System, Tomey; and Keratron Scout, Optikon 2000 SpA) in measuring the corneal power of normal eyes. The mean corneal powers calculated by simulated keratometry (SimK) with each topographer were compared to those provided by the Pentacam in 71 patients. Specifically, the corneal power values of the Pentacam included in this analysis were the SimK (calculated using the measured anterior corneal radius and standard keratometric index of 1.3375) and the True net power (calculated using the anterior and posterior corneal curvatures and Gaussian optics formula for thick lenses, where the actual refractive index of the air, cornea, and aqueous humor are entered). Bland-Altman plots were used to investigate agreement and analysis of variance (ANOVA) was performed to detect statistical differences. Although ANOVA did not disclose a statistically si...

To determine astigmatic changes by vector analysis and postoperative refractive and visual outcomes after implantation of the monofocal aspheric bitoric AT Torbi 709M toric intraocular lens (IOL). Three centers in Salzburg, Austria, and Alicante and San Sebastián, Spain. Prospective interventional case series. Preoperative and postoperative visual acuity, subjective and objective refractions, and corneal radii using a topographer were examined in all patients. All patients had postoperative examinations within the first week and at 6 to 12 weeks. Astigmatic changes were evaluated using the Alpins vector method based on 3 fundamental vectors as follows: target induced astigmatism (TIA), surgically induced astigmatism (SIA), and difference vector. The various relationships between these 3 vectors were calculated, providing an extensive description of the astigmatic correction achieved. Eighty-eight eyes (71 patients) were included. Postoperatively, refractive cylinder was reduced sign...