Keratoconus Topography Research Articles

Reduced Retinal Blood Vessel Densities Measured by Optical Coherence Tomography Angiography in Keratoconus Patients Are Negatively Correlated with Keratoconus Severity.

Keratoconus (KC) is the most common corneal ectasia. Optical coherence tomography angiography (OCT-A) is a relatively new non-invasive imaging technique that allows the visualization and quantification of retinal and choriocapillary blood vessels. The aim of this study is to assess retinal and choriocapillary vessel density (VD) differences between KC patients and healthy controls and to investigate correlations between VD and KC severity. Fifty-two eyes were included in this exploratory study: twenty-six eyes from 26 KC patients and twenty-six eyes from 26 age- and gender-matched healthy controls. All patients underwent Scheimpflug corneal topography with Pentacam, axis lengths measurement and optical coherence tomography angiography (OCT-A). The thinnest spot in corneal pachymetry, maximum K (Kmax) and KC severity indices from the Belin/Ambrósio enhanced ectasia display (BAD) were also assessed. There was a distinct reduction particularly in the retinal VD of the superficial capillary plexus (SCP). Correlation analyses showed strong and moderate negative correlations between the VD in the macular SCP and BAD KC scores and between the SCP VD and Kmax. There was no difference in retinal thickness between the KC and healthy controls. With this study, further evidence for altered VD measurements by OCT-A in KC patients is given. For the first time, we demonstrated negative correlations between BAD KC scores and retinal blood vessel alterations. A major limitation of the study is the relatively small sample size. Since an artefactual reduction of the quantitative OCT-A measurements due to irregular corneal topography in KC must be assumed, it remains to be investigated whether there are also actual changes in the retinal microcirculation in KC.

Benefits of using corneal topography to choose subjective refraction technique in keratoconus (RE-CON): a prospective comparative crossover clinical study.

In prospective no-masking, comparative, crossover monocenter clinical trial, we aimed to evaluate whether the optimal subjective refraction technique varies with the keratoconus topography and to identify relevant topographic criteria. This study included 72 keratoconus eyes with impaired visual acuity. Each eye tested three methods of refraction (Jackson cylinder, astigmatism dial, stenopeic slit), resulting in three eyeglass lenses. Patients were assigned to the group corresponding to the eyeglass lens offering the best visual acuity. Five topographical characteristics were collected via the Pentacam: mean keratometry (Km), maximum keratometry (Kmax), distance from corneal center to Kmax (dKmax), Belin/Ambrosio Display (BAD_D), and index of surface variance (ISV). Forty-six eyes were included in the dial group (64.8%), 23 eyes in the cylinder group (32.4%), and only 2 eyes in the slit group (2.8%); thus, we only compared dial and cylinder groups. The main analysis retrieved a significant probability to choose dial technic for BAD_D (p = 0.024); when BAD_D is > 9.71 (ROC threshold), the positive predictive value (PPV) = 89.5%, and for ISV, p = 0.012; when ISV is > 77, PPV = 89.1%. The sub-analysis of patients with different visual acuities between cylinder and dial confirmed these results with slightly different thresholds: the probability to choose dial technic was for BAD_D, p = 0.03; when BAD_D is > 7.55, PPV = 90%, and for ISV, p = 0.0084; when ISV is > 71, PPV = 88.5%. Refraction method is linked to topographic indices ISV and BAD_D. A BAD_D > 7.55 indicates the dial method. In addition to keratoconus screening and diagnosis, this study suggests a new application of the topographer to select a suitable refraction method for eyeglass prescription. Study registered on the ClinicalTrials.gov database under n°: NCT04174209.

Corneal topography in keratoconus evaluated more than 30\xa0years after penetrating keratoplasty: a Fourier harmonic analysis

The aim of this observational study was to examine the characteristics of anterior and posterior corneal topography in keratoconic eyes more than 30 years after penetrating keratoplasty (PK). Patients who maintained clear grafts for more than 30 years after PK were included and divided into the keratoconus (KC) group or other diseases (Others) group, based on the primary indication. Twenty-six eyes of 26 patients were included. The KC group and the Others group included 14 eyes and 12 eyes, respectively. The KC group participants were younger at the time of surgery (P = 0.03). No differences were found in best-spectacle-corrected visual acuity, keratometric power, and central-corneal-thickness. Based on corneal topography using Fourier harmonic analyses, regular astigmatism in the anterior cornea was significantly larger (P = 0.047) and the spherical component in the posterior cornea was significantly lower (P = 0.01) in the KC group. The area under the receiver operating characteristic curve of the spherical component, regular astigmatism, asymmetry component, and higher-order irregularity were 66.07%, 63.10%, 57.14%, and 59.23%, respectively, in the anterior cornea and 80.65%, 52.98%, 63.10%, and 63.99%, respectively, in the posterior cornea. Our results suggested that Fourier harmonic analysis of corneal topography could be useful for patients with KC long after PK.

원추각막의 각막지형도 분석

원추각막의 각막지형도 분석

Corneal topography in keratoconus: state of the art.

The morphological characterization of the cornea using corneal topographers is a widespread clinical practice that is essential for the diagnosis of keratoconus. The current state of this non-invasive exploratory technique has evolved with the possibility of achieving a great number of measuring points of both anterior and posterior corneal surfaces, which is possible due to the development of new and advanced measurement devices. All these data are later used to extract a series of topographic valuation indices that permit to offer the most exact and reliable clinical diagnosis. This paper describes the technologies in which current corneal topographers are based on, being possible to define the main morphological characteristics that the keratoconus pathology produces on corneal surface. Finally, the main valuation indices, which are provided by the corneal topographers and used for the diagnosis of keratoconus, are also defined.

Repeatability of placido-based corneal topography in keratoconus.

To determine and compare the repeatability of a Placido-based corneal topography (Oculus Keratograph) in a sample of healthy and keratoconus eyes. The corneal topography, determined using the Oculus Keratograph, of 25 healthy and 25 keratoconus eyes was assessed three consecutive times. A single randomized eye was included per patient. Coefficient of variation (CV) of the eccentricity, corneal diameter, index of surface variance, index of vertical asymmetry, keratoconus index (KI), smallest sagittal curvature radius (Rmin), aberration coefficient, and maximum corneal power and minimum corneal power (diopters) in the 3.0-mm zone in addition to the maximum corneal power point (MCPP) (diopters) were calculated and compared between healthy and keratoconus eyes. Healthy eyes showed lower topographic values (p < 0.05) than keratoconus eyes, except with regard to the Rmin value. Corneal diameter (p = 0.45) was similar in both groups. All variables showed good CVs in healthy and keratoconus eyes (maximum corneal power [0.21 and 0.47%, respectively], minimum corneal power [0.19 and 0.36%], MCPP [0.22 and 0.77%], corneal diameter [0.27 and 0.33%], index of surface variance [4.82 and 3.10%], index of vertical asymmetry [7.05 and 3.80%], KI [0.29 and 0.72%], Rmin [0.53 and 0.78%], and aberration coefficient [0 and 4.00%]) except for the eccentricity CV (5.79 and 14.53%, respectively). Statistically significant differences (p < 0.05) between healthy and keratoconus groups were found for all variables, except with respect to the MCPP, eccentricity, corneal diameter, KI, and Rmin (p > 0.07). The Oculus Keratograph provides repeatable measurements of corneal topography in healthy and keratoconus eyes. These results could improve the topographical diagnosis of keratoconus, thus aiding in patient management.

Comparison of front-surface corneal topography and Bowman membrane specular topography in keratoconus

To define the contribution of the corneal epithelium in corneal topography in keratoconus and discuss the implications regarding combined topography-guided photorefractive keratectomy and corneal collagen crosslinking (CXL). French National Reference Center for Keratoconus, Bordeaux, France. Case series. Specular topographies were performed before and immediately after epithelial removal during conventional CXL surgery in patients with keratoconus. The study included 1 eye with forme fruste keratoconus, 4 eyes in Krumeich stage I, and 3 eyes in stage II. The mean simulated maximum keratometry (K) increased by 2.87 diopters (D) after epithelial removal. The mean effective refractive power increased by a mean of 4.01 D and the astigmatic refractive power, by a mean of 2.17 D. The difference in mean axis deviation was not significant. The mean inferior-superior ratio irregularity index increased 1.51 units. All K and refractive readings except astigmatic refractive axis were significantly increased after epithelial removal. All regularity indices increased significantly without the epithelium. The amplitude of variations in K readings made it difficult to predict the refractive changes after custom laser photoablation based on epithelial-based topography. The astigmatism refractive axis did not change significantly; therefore, this axis could be useful for astigmatic corrections, whereas the spherical component would not be useful. Topographic changes after epithelial removal can be important but not intuitive in keratoconus eyes. This should be considered in custom topography-guided photoablation strategies when attempting to correct refractive errors at the time of CXL.

Quantitative OCT-based corneal topography in keratoconus with intracorneal ring segments

Custom high-resolution high-speed anterior segment spectral domain Optical Coherence Tomography (OCT) was used to characterize three-dimensionally (3-D) corneal topography in keratoconus before and after implantation of intracorneal ring segments (ICRS). Previously described acquisition protocols were followed to minimize the impact of the motions of the eye. The collected set of images was corrected from distortions: fan (scanning) and optical (refraction). Custom algorithms were developed for automatic detection and classification of volumes in the anterior segment of the eye, in particular for the detection and classification of the implanted ICRS. Surfaces were automatically detected for quantitative analysis of the corneal elevation maps (fitted by biconicoids and Zernike polynomials) and pachymetry. Automatic tools were developed for the estimation of the 3-D positioning of the ICRS. The pupil center reference was estimated from the segmented iris volume. The developed algorithms are illustrated in a keratoconic eye (grade III) pre- and 30 days post-operatively after implantation of two triangular-section, 0.3-mm thick Ferrara ring segments. Quantitative corneal topographies reveal that the ICRS produced a flattening of the anterior surface, a steepening of the posterior surface, meridional differences in the changes in curvature and asphericity, and increased symmetry of the anterior topography. Optical distortion correction through the ICRS (of a different refractive index from the cornea) allowed accurate pachymetric estimates, which showed increased thickness in the ectatic area as well as in peripheral corneal areas. Automatic tools allowed estimation of the depth of the implanted ICRS ring, as well as its rotation with respect to the pupil plane. Anterior segment sOCT provided with fan and optical distortion correction and analysis tools is an excellent instrument for evaluating and monitoring keratoconic eyes and for the quantification of the changes produced by ICRS treatment.

Corneal Curvature after Penetrating Keratoplasty before and after Suture Removal: A Comparison between Keratoconus and Fuchs’ Dystrophy

Purpose: To assess the differences concerning corneal curvature and visual acuity after penetrating keratoplasty (PKP) comparing keratoconus (KC) and Fuchs’ dystrophy (FUCHS). Methods: Inclusion criteria for this prospective, comparative, interventional study were: (1) one surgeon, (2) central round nonmechanical excimer laser PKP without previous surgery, (3) FUCHS (n = 35) or KC (n = 52), (4) standardized graft size (7.5–8.0 mm) and technique, 16-bite double running cross-stitch suture. In 69% of FUCHS, a triple procedure was performed. The main outcome measures were: keratometric astigmatism, surface regularity index, surface asymmetry index, keratometric central corneal power and best-corrected visual acuity before (1.2 ± 0.4 years) and after suture removal (1.8 ± 0.6 years). Results: Astigmatism did not differ significantly between KC and FUCHS (p > 0.1) before (3.3 dpt vs. 3.5 dpt median) and after suture removal (2.5 dpt vs. 3.0 dpt). Surface regularity index and surface asymmetry index were significantly higher in FUCHS than in KC (p < 0.001) at both time stages. Central power was significantly greater in KC than in FUCHS (p < 0.001) with sutures in place. Due to a significant steepening in FUCHS and flattening in KC, this difference was no longer present after suture removal. Visual acuity in KC exceeded that in FUCHS before (0.68 vs. 0.60) and even more after suture removal (0.86 vs. 0.60; p < 0.001). Conclusions: In KC, keratometric astigmatism is not higher than in FUCHS after PKP. After suture removal, graft topography in KC and FUCHS may be expected to regularize and the excessive corneal flattening in FUCHS to normalize in the mid-term.

The Corneal Topography of Keratoconus

This article is the sixth in a series which describes the role of corneal topography and highlights its value in different clinical settings. It illustrates and describes the variety of topographical patterns seen in keratoconus. The importance of screening for sub-clinical cases prior to refractive keratoplasty and the development of software and statistical indices designed to detect, diagnose and monitor the progression of the disease are discussed. The article illustrates the limitations of placido-disc based systems in obtaining accurate information in severely affected eyes with surface irregularities. The possible clinical applications of videokeratoscopy in the management of keratoconus are reviewed.

Measurement of corneal topography in keratoconus

A new method is described for calculating the topography and curvature of an irregularly shaped cornea. Vertical planes of light are projected onto the cornea and points in x, y, z space are calculated from the light images on the corneal surface. A matrix of points is produced on the cornea and a mathematical surface is fitted to them. Using differential geometry theory, curvature values are calculated to find the corneal apex position, apex curvature and curvature change away from the apex. Typical results, in the form of a contour map, are shown for normal corneas and corneas with mild to severe keratoconus. The method gives an accurate quantitative measurement of keratoconic and other irregular corneas.

Computer-Assisted Corneal Topography in Keratoconus

Using a computer-assisted video-keratoscope, we determined the topographic findings of 14 eyes of 10 patients with keratoconus. None of these patients had worn contact lenses for at least one year prior to examination and were thus free of contact lens-induced topographical alterations. Two patterns commonly seen included inferior steepening more prominent temporally, and central steepening with a superimposed asymmetric bowtie pattern. When compared with normal eyes three quantitative parameters were significantly different (p less than 0.001): central corneal power, difference in corneal power between fellow eyes in the same patients, and steepening of the inferior cornea compared with the superior cornea. Study of the topography in keratoconus using this technique may prove useful for documenting the pattern of involvement of the anterior corneal surface and providing new insights into the pathogenesis of this condition.