Topographical analysis without considering the epithelium effect can result in an incorrect assessment, affecting the accuracy of any topography guided treatment. Methods: Five eyes of 5 patients with progressive keratoconus submitted to CXL according to the original Dresden protocol. Corneal topography was performed before and during the procedure immediately after epithelium removal and values of keratometry: K1, K2, mean K Km , maximum corneal apical curvature Kmax , corneal thickness and corneal astigmatism were evaluated. Results: The average values of corneal curvature before and after epithelial remove were: K1:
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Topographical analysis without considering the epithelium effect can result in an incorrect assessment, affecting the accuracy of any topography guided treatment.
Methods: Five eyes of 5 patients with progressive keratoconus submitted to CXL according to the original Dresden protocol. Corneal topography was performed before and during the procedure immediately after epithelium removal and values of keratometry: K1, K2, mean K Km , maximum corneal apical curvature Kmax , corneal thickness and corneal astigmatism were evaluated. Results: The average values of corneal curvature before and after epithelial remove were: K1: In central corneal thickness there was seen a reduction of Conclusion: There was seen a significant increase in the values of Kmax, K2 and mean K.
This study demonstrates the masking effect of corneal epithelium on corneal curvature in keratoconus. The authors declare no conflicts of interests.
Keratoconus is a bilateral, noninflammatory and slowly progressive corneal ectasia characterized by thinning and increased corneal curvature. Retrospective study carried out in the Cornea section of the Ophthalmology Service of Centro Hospitalar do Porto, Portugal, between March and September with 5 eyes of 5 patients with progressive keratoconus subjected to CXL according to the original Dresden protocol.
Patients or legal guardians provided an informed consent about the procedure and study, as well as permission to use clinical information for research purposes. Of the selected cases, four were in stage I and one in stage II of the Amsler-Krumeich classification.
The progression of keratoconus was defined by at least one of the following criteria in the last 12 months, and consecutive cases that met the following inclusion criteria were selected: increase of 1. The acquisitions not reaching this quality parameter were discarded, and the test was repeated until obtaining quality captations.
The values of curvature of the central cornea - K1, K2, average K Km , point of maximum curvature Kmax , superior, inferior, nasal and temporal curvatures and pachymetry values 3mm from the center on anterior sagittal curvature maps, and anterior corneal astigmatism were evaluated, and demographic data was also collected.
The values are presented as average and standard deviation of the average. The normality of the results was evaluated by the Shapiro-Wilk test. The Wilcoxon test was used for paired samples for statistical analysis. The average age of our sample was The average values of corneal curvature before and after removal of the epithelium can be seen in table 1, where a statistically significant increase after removal of the epithelium in the average value of K2 from A statistically significant increase of 4.
These differences were observed in all patients evaluated. The analysis of the differences in keratometric values of K1 and superior, inferior, nasal and temporal curvatures at 3mm from the corneal center showed no statistically significant differences after removal of the epithelium Table 1.
Regarding pachymetric changes - table 2 - central pachymetry showed an average reduction of central corneal pachymetry of The analysis of pachymetric alterations in the different quadrants - superior and inferior temporal and superior and inferior nasal, 3mm from the center of the cornea — showed statistical difference in all of them except in the inferior temporal quadrant Table 2.
No complications, in particular infectious, were observed during the exams and procedures. A quality capture of all patients was possible for export and treatment. The corneal tomography curvature maps show a significant increase in the keratometric values in the more curved meridian in the central 3mm, point of maximum curvature and average curvature without epithelium with non-significant reduction of the pachymetry value in the apex zone inferior temporal after the removal of the epithelium.
Figures 1A and B. In the present study, 5 eyes with progressive keratoconus were submitted to CXL according to the original Dresden protocol. After removal of the corneal epithelium in eyes with keratoconus, an increase in the average curvature Km , apical curvature, Kmax and K2 was detected.
Pachymetric alterations were also observed showing smaller epithelial thicknesses in the localization of the apex in the keratoconus eyes evaluated.
The epithelium affects the refractive power of the cornea, and consequently contributes to the total refractive power of the eye. Besides, the epithelial thicknesses of the points with the highest keratometric indexes were lower than in the flatter points. All of these signals show the effect of the epithelium in the total refractive power of the cornea, thus playing a regularizing role of stromal ectasia to induce a mask effect on the real curvature of the cornea in patients with keratoconus.
Intraoperative keratometric changes of the epithelium were already analyzed in vivo by Vinciguerra et al. As in our study, they observed an increase in the apical keratometric index Kmax and in keratometry of the more curved meridian K2 after removal of the epithelium. These results were then proposed as signs of the mask effect and regularization of the corneal epithelium in the irregularities of the corneal stroma.
Some studies have been carried out with the objective of detecting epithelial features or patterns in keratoconus corneas, and currently the corneal epithelium thickness and distribution profiles are proposed as useful in the diagnosis of keratoconus. The mask effect of the epithelium is thus supported by the statistically significant differences between the pachymetry and keratometry values before and after epithelial removal observed in the present study, in which pachymetric and keratometric alterations were analyzed at 3mm from the cornea center, a location including the cone apex in all patients.
Despite the results reported, there are some limitations in our study. First, the small number of patients evaluated. Secondly, the thickness of the epithelium evaluated was obtained with a subtraction technique which is not a direct measure such as optical coherence tomography OCT or ultra-high frequency ultrasonography. Finally, the calculation of the thickness of the epithelium by this technique has limitations, presenting lower values in the present study than those already described in corneas with keratoconus.
One of the possible uses of this knowledge and evaluation is in treatments guided by topography to treat the true corneal topography, and despite the greater difficulty of capture in the examination, all the patients of the present study showed quality capture for export and treatment.
However, in spite of these limitations we believe that the present study provides valid information on the effect of corneal epithelium in corneal topography in patients with keratoconus corroborating what is previously described in the literature. Thus, the authors recommend this approach to all patients with progressive keratoconus who do not have contraindication to CXL.
The present study showed topographic and pachymetric variations in patients with keratoconus, showing that the corneal epithelium affects the corneal curvature with a regularization effect of the stroma irregularity masking its true value and severity. With the removal of the epithelium, a statistically significant increase was observed in the values of Kmax, K2 and Kmedian. These differences may be partly explained by the nonuniform distribution of the epithelium in the irregular corneas, being thinner in the more curved areas of the stroma, with higher keratometric indexes, namely in the apex as demonstrated.
As a result, the epithelium behaves as a regularizing factor of true stromal ectasia. Thus, the evaluation of corneal tomography without considering the effect of the epithelium may induce a poor diagnosis, evaluation and classification of keratoconus, affecting the accuracy of any topographic treatment or even hiding the progression of the disease. Declaration of financial interests: The authors have no proprietary or commercial interest in any materials discussed in this project.
Original Articles Revista vol. Introduction Keratoconus is a bilateral, noninflammatory and slowly progressive corneal ectasia characterized by thinning and increased corneal curvature. Methods Retrospective study carried out in the Cornea section of the Ophthalmology Service of Centro Hospitalar do Porto, Portugal, between March and September with 5 eyes of 5 patients with progressive keratoconus subjected to CXL according to the original Dresden protocol.
Results The average age of our sample was Discussion In the present study, 5 eyes with progressive keratoconus were submitted to CXL according to the original Dresden protocol. Conclusion The present study showed topographic and pachymetric variations in patients with keratoconus, showing that the corneal epithelium affects the corneal curvature with a regularization effect of the stroma irregularity masking its true value and severity.
Rabinowitz YS. Surv Ophthalmol. Superior keratoconus. Keratoconus evaluation using the orbscan topography system. J Cataract Refract Surg. Biomechanical properties of keratoconus and normal corneas. Exp Eye Res. Histochemical studies of keratoconus. Curr Eye Res. Changes in collagen orientation and distribution in keratoconus corneas.
Invest Ophthalmol Vis Sci. Epithelial thickness in the normal cornea: three-dimensional display with Artemis very high-frequency digital ultrasound. J Refract Surg. Epithelial, stromal, and total corneal thickness in keratoconus: three-dimensional display with artemis very-high frequency digital ultrasound.
Reinstein DZ, Archer T. Combined Artemis very high-frequency digital ultrasound-assisted transepithelial phototherapeutic keratectomy and wavefront-guided treatment following multiple corneal refractive procedures. Correlation between epithelial thickness in normal corneas, untreated ectatic corneas, and ectatic corneas previously treated with CXL; is overall epithelial thickness a very early ectasia prognostic factor?
Clin Ophthalmol. Intraoperative and postoperative effects of corneal collagen cross-linking on progressive keratoconus. Arch Ophthalmol. Refractive index of the human corneal epithelium and stroma. Vogt A. Textbook and atlas of atlas of slit lamp microscopy of the living eye. Bonn, Germany: Wayenborgh Editions; Refractive and topographic errors in topography-guided ablation produced by epithelial compensation predicted by 3D Artemis VHF digital ultrasound stromal and epithelial thickness mapping.
Optics of the corneal epithelium. Refract Corneal Surg. Thickness mapping of the cornea and epithelium using optical coherence tomography.
Optom Vis Sci. Corneal and epithelial thickness in keratoconus: a comparison of ultrasonic pachymetry, Orbscan II, and optical coherence tomography. Revista Brasileira de Oftalmologia. Revista vol.