Minimum Epithelial Thickness Research Articles

Evaluation of corneal epithelial changes after corneal collagen cross-linking by using anterior segment optical coherence tomography

Background The thickness of the corneal epithelium can be precisely measured using anterior segment optical coherence tomography (AS-OCT). Aim This study aimed to conduct an AS-OCT evaluation of changes in the corneal epithelial thickness following collagen cross-linking (CXL). Patient and methods This prospective interventional study utilized 23 eyes from 13 cases who underwent treatment for progressive keratoconus (KC) with epi-off corneal CXL according to the Dresden’s Protocol. Results After 6 months postoperative the central minimum epithelial thickness (0.0–2.0 mm) showed a statistically significant increase, while the mid-peripheral (5.0–7.0 mm) showed a statistically significant decrease compared with the preoperative level. The central average epithelial thickness (0.0–2.0 mm) showed statistically nonsignificant increase, while the mid-peripheral and peripheral (5.0–7.0, 7.0–9.0 mm) showed a statistically significant decrease in comparison to the level before the operation. At 6 months postoperative, a decrease in Mean k was associated with statistically significant elevation in average central and paracentral epithelial thickness (0.0–2.0, 2.0–5.0 mm) as compared with the preoperative level (negative correlation). At 6 months postoperative, reduction in thinnest pachymetry was associated with statistically significant increase in central and paracentral average epithelial thickness (0.0–2.0, 2.0–5.0 mm) (negative correlation) as compared with the preoperative and 3 months postoperative. Conclusions With AS-OCT, it is simple to track changes in the epithelium over time. Epithelial remodeling occurs after CXL in the areas of protrusion and thinning. The thickness of the epithelium is greatest at the cone’s base and diminishes as one moves away from it.

Diagnostic Importance of OCT Pachymetry in Keratoconus.

To demonstrate changes in distance and near fusional vergence measured with prism bars, while compensating for present heterophoria using current ametropia correction. In addition, to determine the differences in values of the AC/A ratio determined by the heterophoric (calculation) and gradient methods. The basic sample includes 19 subjects with a mean age of 21.5 ±3.0 years (min. 18, max. 27). We used the Von Graefe technique for examination of distance and near phoria, and prism bars for examination of fusion vergences measured in prism diopters. We divided the basic cohort into six research sets according to the size of distance and near heterophoria. This was a cohort of patients with distance (D OR) and near orthophoria (N OR), a cohort of patients with distance (D EX) and near exophoria (N EX) and a set of patients with distance (D ES) and near esophoria (N ES). In the case of both groups with exophoria (distance, near) we found a statistically significant result only for negative fusion vergence (NFV). There was a statistically significant increase in NFV in the sample with distance and near exophoria (D EX, p = 0.01 and B EX, p = 0.02, respectively). In our study, we also demonstrated a statistically significant difference (p < 0.001) in the values of the AC/A ratio measured by the gradient and heterophoric methods. The values determined by the gradient method are lower (3.0 ±1.1 pD/D versus 5.8 ±0.9 pD/D) than by the heterophoric method. By comparing fusion vergence values in patients with exophoria and orthophoria, we demonstrated that in the presence of distance or near exophoria there is an increase in ipsilateral fusion vergence. In the case of an increase in ipsilateral fusion vergence, the finding was statistically significant both distance and near (p = 0.01 and p = 0.02, respectively). By contrast, we were unable to prove this fact in the group of patients with esophoria. In our study, we also demonstrated a statistically significant difference (p < 0.001) in the values of the AC/A ratio measured by the gradient and heterophoric methods. The values determined by the gradient method are lower (3.0 ±1.1 pD/D versus 5.8 ±0.9 pD/D) than by the heterophoric method.

Repeatability of ANTERION in subjects with keratoconus

Aims/Purpose: The aim of this study was to study the repeatability of ANTERION in subjects diagnosed with keratoconus.Methods: The subjects selected had a previous diagnosis of keratoconus. These subjects were divided into three groups, according to the keratoconus treatment: subjects without treatment, intrastromal ring implantation and crosslinking. Subjects with pathologies with ophthalmological repercussion or previous surgeries were excluded.Three measures were performed with ANTERION in patients with keratoconus to evaluate the repeatability. These exams were performed with Cataract and Metricts module; therefore, six measurements were performed per patient and eye.Results: The parameters that showed values of coefficient of variation (CV) >5% in all the evaluated groups were: the vertical coma value, the difference between the thickness of the inferior–superior stroma and the eccentricity of the anterior and posterior corneal surface. In the groups with intrastromal ring segments and crosslinking, a CV >5% was obtained in the measurements of the minimum epithelial thickness and in the difference between the inferior–superior epithelial thickness. In the crosslinking and untreated groups, a CV >5% was obtained in the horizontal coma value. In the groups with intrastromal ring segments and without treatment, a CV >5% was obtained in the corneal RMS value and in the Score, which gives a value of the degree of keratoconus.The subjects implanted with intrastromal rings segments, a CV >5% was obtained in the measurements of the epithelial thickness at the point of greatest thickness.Conclusions: A parameter was considered to show low repeatability when its CV was >5%. The topographic measurements of K corneal and elevation values show good repeatability in subjects diagnosed with keratoconus. However, ANTERION shows a low repeatability in aberrometric values, and in measurements related to the stage and progression of the keratokonus.

Corneal and Epithelial Thickness Mapping: Comparison of Swept-Source- and Spectral-Domain-Optical Coherence Tomography.

Objective To compare the results and repeatability of the corneal thickness (CT) and epithelial thickness (ET) maps provided by Enhanced Spectral-Domain-Optical Coherence Tomography with those of Spectral-Domain-OCT in normal eyes. Methods 30 normal eyes of 30 patients were assessed by 3 trained operators with ESD-OCT and SD-OCT. Results The central and minimum ET obtained with both devices were correlated: central ET, r = 0.86, p < 0.05; minimum ET, r = 0.72, p < 0.05. Compared with SD-OCT, ESD-OCT tended to underestimate these figures by 1.4 and 1.9 μm on average. The central and minimum CT obtained with both devices were strongly correlated: central CT, r = 0.994, p < 0.05; minimum CT, r = 0.995, p < 0.05. ESD-OCT tended to overestimate these figures by 11 and 14 μm on average. Repeatability was good for both devices with a mean coefficient of variation of measurements <6% for ET and <2% for CT. Interoperator variability (standard deviation and COV) was significantly higher for ESD-OCT than for SD-OCT for all local epithelial thicknesses and significantly lower for the central CT and several local corneal thicknesses, whereas no significant differences between both technologies were found for the central and minimum ET and the minimum CT. Conclusion ESD-OCT and SD-OCT provide reproducible measurements of CT and ET in normal corneas with a strong correlation between both technologies. However, both technologies are not interchangeable when the main thickness parameters (i.e., central and minimum CT and minimum ET) are used for diagnosing early keratoconus or calculating the expected residual stromal bed thickness before corneal refractive surgery or anterior lamellar keratoplasty.

Anterior segment-optical coherence tomography for evaluation of the epithelium thickness profile in keratoconic corneas and normal corneas

Purpose This study intends to compare the characteristic distributive epithelial pattern by Fourier-domain anterior segment-optical coherence tomography (AS-OCT) corneal mapping between keratoconic and normal eyes. Patients and methods This prospective case–control study included 51 participants who were divided into two groups: study group A (formed of 50 eyes of 26 keratoconic participants) and control group B (50 eyes of 25 healthy controls of matched age and sex with group A). Maps of corneal epithelial statistics within central 5 mm [S: 2–5 mm (superior), I: 2–5 mm (inferior), minimum, maximum, SD (topographic variability), minimum−maximum], and the total corneal pachymetry maps were assessed by the Fourier-domain AS-OCT system and imaged by Scheimpflug imaging corneal topography for both groups. Results For group A of keratoconic corneas, the attained results are as follows: the mean of epithelial thickness at the center was 50.1±7.98 µm, superior 56.01±6.98 µm, inferior 48.73±5.97 µm, minimum 39.95±9.11 µm, maximum 62.92±8.85 µm, minimum−maximum −22.01±10.91 µm, and topographic variability 6.9±4.2 µm. For group B of healthy control eyes, the mean of epithelial thickness at the center was 52.71±3.71 µm, superior 52.29±3.32 µm, inferior 53.42±3.11 µm, minimum 48.89±3.71 µm, maximum 55.92±3.47 µm, minimum−maximum −6.3±3.51 µm, and topographic variability 1.53±0.82 µm. All variables of epithelial thickness between the two groups are significant (P&lt;0.01). In comparing the epithelial map of keratoconus (KCN) with the control group, the epithelium was found to be thicker at the maximum (+7 µm) and superior location (+3.72 µm), but thinner at the minimum (−8.94 µm) and the inferior (−4.69 µm) with highly significant differences in both minimum−maximum (−15.71) and topographic variability (+5.37). Moreover, in KCN, the point of minimum epithelial thickness was in accordance with the minimum point of the total corneal thickness and the maximum point of back elevation. Conclusion The mapping for epithelial thickness utilizing AS-OCT could be a promising tool in KCN diagnosis.

Graft epithelial mapping following penetrating keratoplasty using anterior segment optical coherence tomography

AIM: To evaluate the changes in corneal epithelial thickness in corneal grafts following penetrating keratoplasty (PK) using anterior segment optical coherence tomography (AS-OCT), and to determine the role of epithelial thickness mapping in the early detection of graft rejection. METHODS: This prospective comparative observational study included 20 patients (20 eyes) who underwent PK as study group and 16 patients (16 eyes) as control group. Corneal epithelial thickness mapping using AS-OCT was performed at 2wk, 1 and 3mo postoperatively. The parameters of epithelial thickness and distribution at the 3mo were compared to 16 patients (16 eyes) with allograft rejection following PK. RESULTS: There was significant decline in the superior, inferior, maximum, and minimum epithelial thickness values of the study group at 1mo compared to 2wk (P=0.0004, 0.0001, 0.0001, 0.04 respectively) with no significant differences at 3mo compared to 1mo (P=0.4, 0.1, 0.8) respectively. Percentage of reduction in epithelial thickness was significantly higher than that of stromal thickness at 1mo compared to 2wk (P=0.04). The epithelial thickness maps showed a similar pattern of epithelial thickness distribution in the study group and in the rejection group showing considerable corneal edema. However, the allograft rejection group showed irregular pattern of epithelial thickness distribution in patients showing relatively higher central corneal thickness (CCT) as measured by pachymetry map. CONCLUSION: Quantitative assessment of graft epithelial remodeling following PK shows early changes that contribute to significant corneal graft thickness changes. Changes in corneal epithelial thickness and pattern of distribution could be used as an indicator for corneal graft rejection.

Correlation between pigmented arc and epithelial thickness (COPE) study in orthokeratology-treated patients using OCT measurements.

To determine the intensity of corneal pigmented arc in orthokeratology (ortho-k)-treated children, and its correlation with key epithelial thickness measurements obtained by anterior segment optical coherence tomography (AS-OCT). This study is a retrospective case series. Medical records of children who received ortho-k treatment for myopia control in our hospital were reviewed. Intensity of ortho-k-associated pigmented arc and its correlation with key epithelial thickness parameters in the central 7-mm-diameter zone obtained by AS-OCT was examined. The subjects were further divided into apparent and unapparent pigmented arc groups for severity comparison. The mean age of children was 11.4 years, and the incidence of corneal pigmented arc was 92.2% after lens wear for a mean duration of 21.2 months. Intensity of pigmented arc was found to be significantly correlated with key epithelial thickness parameters, including maximum and minimum epithelial thickness (Spearman's rank correlation coefficient (rs) = 0.404, P = 0.003; rs = - 0.426, P = 0.002, respectively), the difference between them (Min-Max) (rs = -0.624, P < 0.001) and standard deviation (rs = 0.659, P < 0.001). Significant correlation between intensity of pigmented arc and ortho-k target power (rs = 0.454, P = 0.001) was found. Comparison between the two groups showed significant difference in the same key epithelial thickness parameters. Children receiving ortho-k treatment tended to develop pigmented arcs. Significant correlation between intensity of pigmented arc and key epithelial thickness parameters was observed. AS-OCT can be a useful tool for predicting intensity of pigmented arc in ortho-k-treated children.

Corneal Epithelial Remodeling After Standard Epithelium-off Corneal Cross-linking in Keratoconic Eyes.

To evaluate remodeling of the corneal epithelium after epithelium-off corneal cross-linking (CXL). In this prospective single-center study, 93 eyes of 93 patients with progressive keratoconus underwent standard CXL. The maximum keratometry was assessed before and after CXL with Scheimpflug imaging, and the epithelial thickness profile across the central 5 mm of the cornea was assessed with spectral-domain optical coherence tomography anterior segment imaging. The mean patient age was 27 ± 11 years; 76 patients (81%) were male and 17 (19%) were female. Between baseline and 6 months after CXL, the mean corneal maximum keratometry flattened from 58.90 to 57.80 diopters (P < .0001). The mean minimum epithelial thickness increased slightly (from 41 ± 6 to 42 ± 7 μm, P = .12), whereas the mean maximum epithelial thickness decreased slightly (from 65 ± 6 to 64 ± 7 μm, P = .067), reducing the net difference between the minimum and maximum epithelial thickness (from 24 ± 9 to 22 ± 9 μm, P = .0023). The difference between the minimum and maximum epithelial thickness was strongly positively correlated with the maximum keratometry reading at baseline (R2 = 0.38) and at 6 months after CXL (R2 = 0.59). Epithelium-off CXL resulted in modest regularization of the epithelial thickness profile across the central 5 mm of the cornea at 6 months. This could slightly mask flattening of the underlying stroma. [J Refract Surg. 2018;34(6):408-412.].

Distinguishing between contact lens warpage and ectasia: Usefulness of optical coherence tomography epithelial thickness mapping

To distinguish between corneal ectasia and contact lens-related warpage by characteristic patterns on corneal topography and optical coherence tomography (OCT) epithelial thickness maps. Casey Eye Institute, Portland, Oregon, USA. Prospective and retrospective case series. Axial and mean power maps were obtained on corneal topography systems. Epithelial thickness maps were generated using RTVue OCT. A sector divider was applied to all maps. The locations of the minimum epithelial thickness, maximum epithelial thickness, maximum axial power, and maximum mean power were determined based on sector averages. Agreement was defined as the extremums occurring in the same or adjacent sectors. Twenty-one eyes with keratoconus, 6 eyes with forme fruste keratoconus (better eye of asymmetric keratoconus), and 15 eyes with contact lens-related warpage were identified. The keratoconus and forme fruste keratoconus eyes had coincident topographic steepening with epithelial thinning. The locations of minimum epithelial thickness and maximum axial power agreed in 90% of the keratoconic eyes, while the minimum epithelial thickness and maximum mean power agreed in 95% of them. Conversely, the warpage eyes had coincident topographic steepening with epithelial thickening and normal pachymetry maps. The locations of maximum epithelial thickness and maximum axial power agreed in 93% of the warpage eyes, while the maximum epithelial thickness and maximum mean power agreed in all warpage eyes. Results show that epithelial thickness maps and corneal topographic maps are powerful synergistic tools in evaluating eyes with abnormal topography and can help differentiate between keratoconus and nonectatic conditions.

Corneal epithelial thickness mapping using Fourier-domain optical coherence tomography for detection of form fruste keratoconus

To determine whether optical coherence tomography (OCT) epithelial mapping can improve the detection of form fruste keratoconus. French National Eye Hospital, Paris 6 Pierre & Marie Curie University, Paris, France. Retrospective comparative study. Eyes with normal corneas, form fruste keratoconus, moderate keratoconus, or severe keratoconus were assessed using Fourier-domain OCT (RTVue 5.5), scanning-slit corneal topography (Orbscan IIz), and rotating Scheimpflug camera (Pentacam Comprehensive Eye Scanner). Several parameters provided by the software or derived from elevation maps, OCT pachymetric maps, and OCT epithelium parameters were evaluated and compared between the 4 groups. The study involved 145 eyes. There were no significant differences in the keratometry (K) value, inferior-superior value, keratoconus index, central K index, and topographic keratoconus classification indices between the form fruste keratoconus group and the control group (P>.05). Form fruste keratoconic corneas had less epithelial thickness in the thinnest corneal zone than normal corneas, and greater epithelial thickness in the thinnest corneal zone than keratoconic corneas (P<.005). The epithelial thickness in the thinnest corneal zone in form fruste corneas was located inferiorly (P<.005) and corresponded with the zone of minimum epithelial thickness and maximum posterior elevation (P<.005). The receiver operating characteristic curve analysis showedgood overall predictive accuracy of the epithelial thickness in the thinnest corneal zone, with a 52 μm threshold value for discriminating form fruste keratoconic corneas from normal corneas. The epithelial thickness in the thinnest corneal zone and its location provided by the OCT epithelial mapping might be useful for the early diagnosis of form fruste keratoconus. No author has a financial or proprietary interest in any material or method mentioned.

OCT corneal epithelial topographic asymmetry as a sensitive diagnostic tool for early and advancing keratoconus.

PurposeTo investigate epithelial thickness-distribution characteristics in a large group of keratoconic patients and their correlation to normal eyes employing anterior-segment optical coherence tomography (AS-OCT).Materials and methodsThe study group (n=160 eyes) consisted of clinically diagnosed keratoconus eyes; the control group (n=160) consisted of nonkeratoconic eyes. Three separate, three-dimensional epithelial thickness maps were obtained employing AS-OCT, enabling investigation of the pupil center, average, mid-peripheral, superior, inferior, maximum, minimum, and topographic epithelial thickness variability. Intraindividual repeatability of measurements was assessed. We introduced correlation of the epithelial data via newly defined indices. The epithelial thickness indices were then correlated with two Scheimpflug imaging-derived AS-irregularity indices: the index of height decentration, and the index of surface variance highly sensitive to early and advancing keratoconus diagnosis as validation.ResultsIntraindividual repeatability of epithelial thickness measurement in the keratoconic group was on average 1.67 μm. For the control group, repeatability was on average 1.13 μm. In the keratoconic group, pupil-center epithelial thickness was 51.75±7.02 μm, while maximum and minimum epithelial thickness were 63.54±8.85 μm and 40.73±8.51 μm. In the control group, epithelial thickness at the center was 52.54±3.23 μm, with maximum 55.33±3.27 μm and minimum 48.50±3.98 μm epithelial thickness. Topographic variability was 6.07±3.55 μm in the keratoconic group, while for the control group it was 1.59±0.79 μm. In keratoconus, topographic epithelial thickness change from normal, correlated tightly with the topometric asymmetry indices of IHD and ISV derived from Scheimpflug imaging.ConclusionSimple, OCT-derived epithelial mapping, appears to have critical potential in early and advancing keratoconus diagnosis, confirmed with its correlation with established Scheimpflug-derived asymmetry topometric indices.

In Vivo Three-Dimensional Corneal Epithelium Imaging in Normal Eyes by Anterior-Segment Optical Coherence Tomography

To evaluate the safety and efficacy of real-time measurement of corneal epithelial thickness and investigate the distribution characteristics in a large normal-eye population using a clinically available spectral-domain anterior-segment optical coherence tomography (AS OCT) system. Corneal epithelial thickness distribution and topographic thickness variability were clinically investigated using AS OCT imaging in 373 patients with normal, healthy eyes. Descriptive statistics investigated 3 sets of subgroups, male (n = 171) and female (n = 202), younger (n = 194) and older (n = 179), right eyes (n = 195) and left eyes (n = 197). Pupil center epithelial thickness repeatability was an average 0.88 ± 0.71 μm; a similar repeatability was noted for the superior, inferior, maximum, and minimum epithelial thickness. On average, the pupil center epithelial thickness was 53.28 ± 3.34 μm, superior 51.86 ± 3.78 μm, inferior 53.81 ± 3.44 μm, minimum 48.65 ± 4.54 μm, maximum 56.35 ± 3.80 μm, and topographic variability was 1.78 ± 0.78 μm. Small differences were noted between male (average center 54.10 ± 3.34 μm) and female (52.58 ± 3.19 μm) subjects. The topographic thickness variability seems to increase with age: younger group, 1.65 ± 0.83 μm; older group, 1.93 ± 0.90 μm (P = 0.173). We present a comprehensive investigation of corneal epithelial thickness distribution characteristics in a healthy, untreated human eye population by using in vivo, clinically available Fourier-domain AS OCT. The 3-dimensional epithelial maps reveal epithelial nonuniformity and provide a novel benchmark for future and comparative studies.

Effects of the chronic use of finasteride and doxazosin mesylate on the histomorphometric characteristics of the prostate: experimental study in rats

The objective of the present study is to evaluate the histomorphometric characteristics of the prostate of rats submitted to chronic (long-time) treatment with doxazosin mesylate, finasteride and both substances combined. Four groups of eight rats each were selected for this study and treated with saline solution (control), doxazosin mesylate, finasteride and combination of the drugs, during 10 months. After this time, the prostate was removed, weighed and sent for histological analysis. Prostate sections were stained with Masson trichrome. With an image analyzer, the percentage of smooth muscle, collagen, epithelium, acinar lumen and interstitial space was measured. Also, the minimum, medium and maximum epithelial thickness, number of acini per field, mean acinar area and the presence of papillary projections were evaluated. The mean prostate weight of rats treated with finasteride and combined treatment was lower when compared to the control group (P<0.05). Prostate from rats treated with finasteride alone had a lower percentage of the epithelial component and a smaller minimum epithelial thickness than the control group (P<0.05). The number of acini per field in the combined groups was higher than that observed in all other groups (P<0.05). Also, rats of the finasteride and combined groups presented a reduced number of papillary projections when compared to the other groups (P<0.05). Our study clearly showed the effects of finasteride on prostate tissue, and from a histomorphometric perspective, it was not able to detect any advantage of the combined treatment over the use of finasteride alone.