Epithelial thickness in the normal cornea: three-dimensional display with Artemis very high-frequency digital ultrasound

A 6-Month Follow-Up Comparative Study of Single-Step Transepithelial Photorefractive Keratectomy (Trans-PRK) Using the StreamLight Software with and without Epithelial Thickness Customization

Purpose

To compare corneal aberrometry, densitometry, and refractive outcomes of single-step Transepithelial Photorefractive Keratectomy (Trans-PRK) with and without epithelial thickness customization.

Patients and Methods

This was a prospective, interventional, randomized controlled study. Patients undergoing Trans-PRK using the WaveLight EX500 laser with StreamLight software (Alcon Laboratories, Forth Worth, TX, USA) were randomly assigned to control (55 µm standard epithelial thickness) or customized (thinnest point of epithelial thickness for each patient) groups. MS-39 (CSO, Italy) anterior segment optical coherence tomography was used to measure the epithelial thickness. Inclusion criteria were spherical equivalent <6 diopters (D), astigmatism <4D, and CDVA 20/25 or better. The assessments were at baseline and 6 months post-op: visual acuity, refraction, aberrometry, and corneal densitometry.

Results

108 eyes were enrolled, [control group (n=56) and customized group (n=52)]. Mean epithelial ablation thickness in the customized group was 54.81±3.56µm (p=0.470 vs control group). Both groups experienced significant postoperative increases in higher-order aberrations (HOA) and spherical aberrations, with no significant intergroup differences. Mean HOA RMS (µm) of the frontal cornea and total cornea increased by 0.27, and 0.29, respectively, in the control group, and 0.26 and 0.28, respectively, in the customized group (p<0.001 for all). Mean change in spherical aberrations in the frontal cornea and total cornea was 0.23µm (p<0.001) and 0.25µm (p<0.001), in the control group, and 0.19µm (p<0.001) and 0.20µm (p<0.001), in the customized group. Mean corneal densitometry in anterior cornea decreased by 0.63GSU (p=0.021) and 1.18GSU (p<0.001) in the control and customized groups. In the posterior cornea, it increased by 1.67GSU (p=0.004) and 0.38GSU (p=0.006).

Conclusion

No significant differences in refractive and aberrometry outcomes between control and customized Trans-PRK groups, with corneal densitometry changes not affecting visual acuity.

Inter-zonal epithelial thickness differences for early keratoconus detection using optical coherence tomography

PURPOSE

To develop and test a parameter for early keratoconus screening by quantifying the localized epithelial thickness differences in keratoconic eyes.

METHODS

The cross-sectional study included 189 eyes of 116 subjects in total: 86 eyes of 54 keratoconus patients with bilateral ectasia and 40 eyes of 20 healthy subjects in the parameter-development dataset and 42 eyes of 21 keratoconus patients with asymmetric ectasia and 21 eyes of 21 healthy subjects in the parameter-validation dataset. Epithelial thickness maps were obtained using anterior segment optical coherence tomography and the inter-zonal epithelial thickness differences were calculated. The developed parameter was tested in keratoconus patients with asymmetric ectasia.

RESULTS

Compared to healthy controls, the inferior-temporal and global inter-zonal epithelial thickness differences were higher not only in eyes with tomographically significant keratoconus (median [interquartile range] of 4.42 [3.13] µm vs. 0.78 [0.42] µm, p < 0.001, and 3.05 [1.51] µm vs. 1.07 [0.26] µm, p < 0.001, respectively), but also in tomographically normal keratoconus fellow eyes (1.36 [0.85] µm vs. 0.78 [0.42] µm, p = 0.005, and 1.31 [0.32] µm vs. 1.07 [0.26] µm, p = 0.01, respectively). The inferior-temporal inter-zonal epithelial thickness differences had an area under the receiver operating characteristic curve (95% confidence interval) of 0.991 (0.972-1) for detecting tomographically significant keratoconus and 0.749 (0.598-0.901) for differentiating between tomographically normal keratoconus fellow eyes and healthy controls.

CONCLUSIONS

The inter-zonal epithelial thickness differences are increased in keratoconus fellow eyes which still have a normal Scheimpflug corneal tomography, and therefore may serve as a useful parameter to detect early ectatic changes.

Assessment of corneal epithelial thickness mapping by spectral-domain optical coherence tomography

Background

To assess corneal epithelial-thickness (ET) mapping resulting from spectral-domain-optical-coherence-tomography (SD-OCT) by analysing its repeatability and reproducibility and its utility for screening corneal-refractive-surgery (CRS) candidates.

Methods

ET was measured in 25-sectors by two-operators. Intra-subject-standard-deviation, coefficient-of-repeatability (CoR) and coefficient-of-variability (CoV) were calculated to evaluate repeatability. Reproducibility was evaluated using a Bland-Altman analysis. Scheimpflug-tomography, refraction, visual acuity, and patient history were used to make a decision on eligibility for CRS. After this decision, the surgeon was shown the patient's ET map and was asked to reconsider his analysis. The percentage of screenings that changed after evaluating the ET maps was determined.

Results

Forty-three eyes with normal corneas (CRS-group) and 21 eyes not suitable for CRS (non-CRS-group) were studied. For the CRS-group, CoR ranged from 2.03 (central) to 19.73 μm (outer-inferonasal), with the central-sector showing the highest repeatability (CoV: 1.53-1.80%). For the non-CRS-group, CoR ranged from 3.82 (central-middle-superonasal) to 13.42 μm (middle-inferotemporal), with the inner-superonasal-sector showing the highest repeatability (CoV: 2.86-4.46%). There was no statistically significant difference between operators (p > 0.01). In the CRS-group, the outcomes showed a narrow 95% limits-of-agreement (LoA) for the central-and inner-nasal-sectors (about 4 μm), and wider for the inner-superior, outer-superotemporal and outer-inferonasal (about 10-14 μm). In the non-CRS-group, they were for the outer superonasal (about 4 μm), and for the middle-inferotemporal and outer-temporal (about 10 μm), respectively. Candidacy for CRS changed in 7.82% of patients after evaluation of the ET maps, with all of them screened-out.

Conclusion

The SD-OCT provided repeatable and reproducible corneal ET measurements and may alter candidacy for CRS.

Clinical trial registration

German Clinical Trials Register: https://drks.de/search/en/trial/DRKS00032797, identifier: DRKS00032797.

In vitro and ex vivo models of microbial keratitis: Present and future

Microbial keratitis (MK) is an infection of the cornea, caused by bacteria, fungi, parasites, or viruses. MK leads to significant morbidity, being the fifth leading cause of blindness worldwide. There is an urgent requirement to better understand pathogenesis in order to develop novel diagnostic and therapeutic approaches to improve patient outcomes. Many in vitro, ex vivo and in vivo MK models have been developed and implemented to meet this aim. Here, we present current in vitro and ex vivo MK model systems, examining their varied design, outputs, reporting standards, and strengths and limitations. Major limitations include their relative simplicity and the perceived inability to study the immune response in these MK models, an aspect widely accepted to play a significant role in MK pathogenesis. Consequently, there remains a dependence on in vivo models to study this aspect of MK. However, looking to the future, we draw from the broader field of corneal disease modelling, which utilises, for example, three-dimensional co-culture models and dynamic environments observed in bioreactors and organ-on-a-chip scenarios. These remain unexplored in MK research, but incorporation of these approaches will offer further advances in the field of MK corneal modelling, in particular with the focus of incorporation of immune components which we anticipate will better recapitulate pathogenesis and yield novel findings, therefore contributing to the enhancement of MK outcomes.

Comparative outcomes of mechanical and transepithelial PRK on the same excimer laser: A contralateral eye study

PURPOSE

Compare refractive results between mechanical PRK (mPRK) and transepithelial PRK (tPRK) with WaveLight Allegretto EX500 excimer laser system (Alcon Laboratories, Fort Worth, TX, USA).

SETTING

Department of Ophthalmology of the Federal University of Sao Paulo, Brazil.

DESIGN

Prospective and randomized study.

METHODS

In 151 eyes of 73 patients with astigmatism and myopia, both eyes had similar refraction before surgery, with a maximum of 15-µm difference in ablation who underwent mPRK in one eye and tPRK in the contralateral eye. The mean age of the patients in this study was 31.45 ± 6.97 years (range, 22 to 54 years).

RESULTS

A comparison was made with all variables between the two groups, and we found that UDVA and SE were worse in the tPRK group at six months than in the mPRK group. In the mPRK group, there was a higher frequency in the +/- 0.50 range and a lower frequency in the +/- 1.50 range. In the tPRK group, however, there was a lower frequency in the +/- 0.50 range and a higher frequency in the +/- 1.50 range. Concerning gain or loss of lines of sight, there was no association between the two groups (chi-square test, p = 0.887).

CONCLUSION

Both mPRK and tPRK appear to have similar safety. However, mPRK was associated with significantly better UDVA and SE six months post-operatively.

Comparison between a new transepithelial PRK vs. conventional alcohol-assisted PRK: Corneal densitometry and aberrometry study

PURPOSE

To describe and compare corneal densitometry, subjective refraction, visual acuity, and corneal higher order aberrations (HOA) after corneal refractive surgery using either alcohol-assisted photorefractive keratectomy (aaPRK) or single-step transepithelial PRK (tPRK).

METHODS

We conducted a retrospective and observational study. We analyzed 120 right eyes from 120 healthy consecutive myopic patients who underwent aaPRK or tPRK to correct myopia of up to 6 diopters and astigmatism of up to 2 diopters. The WaveLight EX500 excimer laser (Alcon Laboratories, Inc.) was used in all cases. Visual acuity, subjective refraction, and Pentacam AXL® measurements were performed at the preoperative visit and at 6-months follow-up visit. Pentacam AXL® software was used to assess corneal optical density in various annuli for different corneal depths and anterior corneal HOA (6 mm area of analysis).

RESULTS

Preoperative spherical equivalent values were similar between groups preoperatively (-3.07 ± 1.52 and -3.38 ± 1.46 in the aaPRK and tPRK groups, respectively). There were no statistically significant differences in visual acuity and postoperative refraction between groups. Postoperative corneal densitometry did not show statistically significant differences in any of the areas studied and both surgical procedures obtained similar results. However, analysis of HOA showed statistically significant differences between the techniques (1.42 ± 0.39 and 1.80 ± 0.62 for the aaPRK and tPRK groups, respectively; p = 0.000).

CONCLUSIONS

Both aaPRK and single-step tPRK gave comparable visual, refractive, and corneal density outcomes. Some differences were observed in HOA but were not clinically relevant.

Use of High-Frequency Ultrasound for the Correlation of Epithelial Rete Peg Variation

OBJECTIVE

Rete pegs are projections of the oral epithelium into connective tissue. Their dimensions change during pathological conditions and may correlate with wound-healing status. Non-invasive, high-frequency ultrasound (US) may be able to capture these changes and aid in early detection of histopathological changes. The aim of this preclinical study is to correlate US images with histology and quantify epithelial layers at different tooth sites.

METHODS

Sagittal B-mode images of mid-facial and interproximal oral soft tissue sites were recorded in a preclinical minipig model using a linear array in second harmonic mode (12/24 MHz). Histology samples from the same locations were stained (hematoxylin and eosin), digitized and registered with US images. Manual annotations were used to measure distances D1 (thickness of epithelium on histology vs. hyperechoic zone on US) and D2 (sum of epithelial thickness and length of rete pegs on histology vs. sum of hyperechoic and hypoechoic zone on US) to statistically analyze them.

RESULTS

Ultrasonic-derived dimensions yielded a mean bias of -0.64 (55% coefficient of variance [COV]: -180 to +180 µm) and -12 µm (39% COV: -260 to +240 µm) for D1 and D2, respectively. Individualized analysis of D1 and D2 by tooth type showed similar tends in the ability to differentiate between epithelium at different tooth locations, on both histology and US.

CONCLUSION

Assessing soft tissue dimensions on a sub-millimeter scale using clinical imaging hardware is still a developing area. Future research might open doors for diagnosis of oral pathologies and abnormal wound healing, and may limit false-positive indications for biopsies.

Investigating the topographic effect of epithelium in myopic eyes with subtle topographic preoperative abnormalities

PURPOSE

To explore the topographic effect of the epithelium in keratoconus suspected (KCS) and in normal Placido classified corneas.

SETTING

Rothschild Foundation, Paris, France.

DESIGN

Prospective interventional case series.

METHODS

Anterior corneal specular Placido topography using OPD-Scan II was performed in 97 eyes of 67 patients undergoing photorefractive keratectomy for myopia, before and after epithelium removal. The differences in axial keratometry, asphericity, and astigmatism were computed.

RESULTS

After epithelial peeling, some Placido-normal classified corneas became KCS. Therefore, we have subdivided this group into 2 groups: one of normal classified corneas which stayed normal after epithelium removal (Group NN) and another of corneas that became KCS classified (Group NK). The mean difference in axial mean keratometry in the third central millimeter rings was +0.50 ± 0.24 diopters (D), 0.69 ± 0.31 D, and 0.49 ± 0.35 D and the mean difference in the magnitude of epithelial-induced astigmatism in the first central millimeter ring was 0.37 D × 89 degrees (positive cylinder), 0.54 D 86 degrees, and 0.52 D 86 degrees, respectively, in Group NN, NK, and KK (KCS corneas that stayed KCS). These differences were significant ( P < .0001). Preoperative keratometry was the only predictive factor differentiating Group NN from NK ( P < .001).

CONCLUSIONS

The epithelial layer tended to reduce the magnitude of the Bowman layer's astigmatism, prolateness, and keratometry, more importantly in Group NK. In the KK group, we found a similar trend as in normal eyes (Group NN). The epithelium would be able to mask Bowman layer's irregularities until a certain degree of severity.

Corneal Epithelial Thickness in Sjogren's Disease: A Pilot Study

Purpose

This study was to assess corneal epithelial thickness (CET) in patients with Sjogren's disease (SjD).

Methods

A retrospective chart review was conducted of SjD patients from September 2021 to January 2022. Patient demographics, unanesthetized Schirmer's test, serologic markers, and symptoms as measured by the Ocular Surface Disease Index (OSDI) were reviewed. Epithelial thickness from both eyes was measured using anterior segment OCT at the central 3mm and concentric 5mm, 7mm, and 9mm zones for the superior, temporal, inferior, and nasal corneal quadrants. Associations between corneal epithelial thickness with patient demographics, clinical characteristics, and symptoms were evaluated using regression models.

Results

Fifteen SjD patients (100% female) were included with a mean age of 58.4 years. Patients with Sjogren's disease had a significantly thinner superior corneal epithelium compared to the inferior epithelium (mean 47.7mm vs 53.1mm, p = 0.001). The epithelial thickness mean standard deviation (MSD) was significantly inversely correlated with the unanesthetized Schirmer test (r=-0.39, p = 0.005), suggesting that an overall variability of CET correlates with decreased aqueous tear production. SS-A, SS-B, ANA, and RF positivity were not associated with any measures of CET.

Conclusion

This pilot study suggests that there is significant superior versus inferior thinning of corneal epithelium in Sjogren's patients. There was a significant correlation between variability of corneal epithelial thickness and decreased tear production in Sjogren's patients. Further larger studies are needed to understand the relationship of CET with objective and subjective measurements of ocular surface disease.

Blepharoptosis and corneal epithelial thickness alterations, is there any relation?

BACKGROUND

To compare the epithelial thickness map of ptotic eyes of blepharoptosis patients with contralateral non- ptotic eyes.

METHODS

Unilateral blepharoptosis patients were enrolled consecutively. Patients were underwent full ophthalmologic examination and their demographic data such as age and gender and specific ptosis findings e.g. the cause and duration, MRD-1, and levator palpebralis superioris function were registered. Anterior segment imaging for epithelial thickness measurements was done using the Avanti RTVue-XR platform. The corneal epithelial thickness maps of ptotic and non-ptotic eyes were compared.

RESULTS

44 patients with unilateral blepharoptosis were included in the study. 27 (61.4%) of them were female and 17 (38.6%) cases were male. The mean of the patients' ages was 24.40 ± 15.16 years. Ptotic eyes had significantly thinner superior (p = 0.000), superior-temporal (p = 0.000) and superior-nasal (p = 0.005) sectors of the cornea and slightly thicker corneal epithelium (CE) in the inferior-nasal sector. The correlation of difference of superior-inferior CE was evaluated with different parameters including patient's age (p = 0.457), type of blepharoptosis (p = 0.786), duration of blepharoptosis (p = 0.477) and MRD1 (p = 0.248), but no correlation was found.

CONCLUSIONS

This study revealed that lid position in blepharoptosis may have effects on the corneal epithelial thickness map. Because of the lower position of upper eyelid, a thinning effect on superior corneal sectors may happen.

Epithelial thickness map-adjusted transepithelial photorefractive keratectomy for treatment of myopic astigmatism: 12-month results

PURPOSE

To evaluate the refractive results of Transepithelial Photorefractive Keratectomy (t-PRK) with the Technolas Teneo2 Excimer laser platform.

METHODS

In this retrospective comparative interventional case series, a total of 199 patients with myopia ranging from - 1 to - 7 diopters were enrolled and separated into three groups based on their target refraction of zero (group 1), - 0.25 (group 2), and - 0.5 diopters (group 3), respectively. The main outcome measure was post-operative cycloplegic refraction. Trans-PRK was performed using the Technolas Teneo2 Excimer laser. To prevent any remaining epithelium during stromal ablation, we adopted the thickest epithelial point in the 7 mm central map as the reference for Phototherapeutic keratectomy (PTK) depth. Patients were examined three and twelve months after the procedure, and the results were analyzed.

RESULTS

At the 12-month follow-up, uncorrected distance visual acuity was 20/20 in all patients. However, there was a significant difference in cycloplegic spherical equivalent refraction between the three groups. The 12-month post-operative spherical equivalent refraction was 0.90 ± 0.33 D, 0.79 ± 0.26 D, and 0.60 ± 0.19 D in groups 1, 2, and 3, respectively (P < 0.001; Kruskal-Wallis test). The rates of spherical equivalent refraction of more than 0.75 D were 58.3%, 39.1%, and 9.1% in the 0 D, - 0.25 D, and -0.50 D groups, respectively (P < 0.001; Chi-squared test).

CONCLUSIONS

The t-PRK with Technolas Teneo2 Excimer laser and epithelial thickness map adjustment of PTK induce a significant amount of residual hyperopia (> 0.75 D) in a large proportion of eyes with a target refraction of 0 or - 0.25, which is significantly reduced by using a target refraction of - 0.5.

A Standardized Protocol of Simultaneous Transepithelial Phototherapeutic Keratectomy (PTK) Followed by Corneal Collagen Crosslinking for Keratoconus

PURPOSE

To report outcomes in patients with progressive keratoconus who underwent a standardized protocol of transepithelial phototherapeutic keratectomy (t-PTK) laser followed by accelerated corneal collagen crosslinking (CXL).

METHODS

All patients with progressive keratoconus undergoing our protocol at a London clinic between 2019 and 2023 were included. The protocol involved t-PTK at 58-μm central ablation depth at a 9-mm treatment zone on the Schwind Amaris 1050RS platform. Preoperative K readings of 43.0D (both K1 and K2) were inputted for all cases. Patients then underwent CXL with a pulsed-light accelerated protocol (30 mW/cm2 for 8 minutes of UVA exposure time with 1 second on/1 second off).

RESULTS

Seventy-nine eyes from 55 patients were included with an average follow-up of 12 months (range 6-24 months). Both mean uncorrected distance visual acuity (UDVA) and best spectacle-corrected visual acuity improved significantly from 0.42 preoperatively to 0.29 postoperatively (P < 0.01) and 0.11 to 0.06 postoperatively (P < 0.01), respectively. The refractive cylinder reduced significantly from -3.07D to -2.63D (P < 0.05). The mean Km improved from 46.15D to 45.44D (P < 0.01) and mean Kmax from 54.03D to 52.52D (P < 0.01). 77% of eyes (n = 61) exhibited Kmax improvement postoperatively, and 56% showed an improvement in UDVA (n = 44). 16% (n = 13) had worsening of vision, but of these, only 1 patient had visual loss of more than 2 lines. No eyes had corneal haze reported at the final follow-up, and none required additional treatment.

CONCLUSIONS

This standardized simultaneous t-PTK and CXL protocol is safe and effective for the treatment of progressive keratoconus, providing visual, refractive, and topographic improvements.

Multi-modal imaging for the detection of early keratoconus: a narrative review

Keratoconus is a common progressive corneal disorder that can be associated with significant ocular morbidity. Various corneal imaging techniques have been used for the diagnosis of established cases. However, in the early stages of the disease, which include subclinical keratoconus and forme fruste keratoconus, detection of such cases can be challenging. The importance of detecting such cases is very important because early intervention can halt disease progression, improve visual outcomes and prevent postrefractive surgery ectasia associated with performing corneal refractive procedures in such patients. This narrative review aimed to examine several established and evolving imaging techniques for the detection of early cases of keratoconus. The utilization of combinations of these techniques may further increase their diagnostic ability.

Aspergillus fumigatus Hypoxia Adaptation Is Critical for the Establishment of Fungal Keratitis

Purpose

The poor visual outcomes associated with fungal keratitis (FK) underscore a need to identify fungal pathways that can serve as novel antifungal targets. In this report, we investigated whether hypoxia develops in the FK cornea and, by extension, if fungal hypoxia adaptation is essential for virulence in this setting.

Methods

C57BL/6J mice were inoculated with Aspergillus fumigatus and Fusarium solani var. petroliphilum via topical overlay or intrastromal injection. At various time points post-inoculation (p.i.), animals were injected with pimonidazole for the detection of tissue hypoxia through immunofluorescence imaging. The A. fumigatus srbA gene was deleted through Cas9-mediated homologous recombination and its virulence was assessed in the topical infection model using slit-lamp microscopy and optical coherence tomography (OCT).

Results

Topical inoculation with A. fumigatus resulted in diffuse pimonidazole staining across the epithelial and endothelial layers within 6 hours. Stromal hypoxia was evident by 48 hours p.i., which corresponded to leukocytic infiltration. Intrastromal inoculation with either A. fumigatus or F. solani similarly led to diffuse staining patterns across all corneal cell layers. The A. fumigatus srbA deletion mutant was unable to grow at oxygen levels below 3% in vitro, and corneas inoculated with the mutant failed to develop signs of corneal opacification, inflammation, or fungal burden.

Conclusions

These results suggest that fungal antigen rapidly drives the development of corneal hypoxia, thus rendering fungal SrbA or related pathways essential for the establishment of infection. Such pathways may therefore serve as targets for novel antifungal intervention.

A comparison of conventional and accelerated corneal crosslinking: corneal epithelial remodeling and in vivo confocal microscopy analysis

PURPOSE

To evaluate the effect of conventional and accelerated corneal crosslinking (CXL) on visual acuity, corneal topography, corneal epithelial thickness, and subbasal nerve morphology in progressive keratoconus patients.

METHODS

In this prospective and randomized study, twenty eyes of 20 patients were treated with conventional CXL (3 mW/cm2, 30 min, C-CXL) and 19 eyes of 19 patients were treated with accelerated CXL (9 mW/cm2, 10 min, A-CXL). The spherical equivalent, uncorrected visual acuity, best-corrected visual acuity, keratometric measurements, demarcation line measurement and epithelial thickness mapping analyses, and subbasal nerve morphology with in vivo confocal microscopy (IVCCM) were evaluated at baseline and at postoperative months 1, 3 and 6.

RESULTS

At postoperative 6 months, a significant improvement was observed in all keratometric values in both treatment groups (p < 0.05). All epithelial thickness indices, except central, temporal, and inferotemporal thickness, were reduced at 1 month postoperatively in both treatment groups. The epithelial map uniformity indices (standard deviation and difference between min-max thickness) were significantly lower than the baseline values at all time points after CXL in both treatment groups (p < 0.001). Compared with the preoperative values, there was a significant decrease in all IVCCM parameters at 1 month postoperatively (p < 0.05). At 6 months postoperatively, corneal nerve fiber density and corneal nerve branch density recovered to preoperative values in the A-CXL group, whereas corneal nerve regeneration was not complete in the C-CXL group.

CONCLUSION

Both conventional and accelerated CXL treatments appear to be effective in halting the progression of KC. Corneal epithelial irregularity slightly improves after CXL. The regeneration of subbasal nerves is faster after A-CXL treatment.

Epithelial thickness remodeling after small incision lenticule intrastromal keratoplasty in correcting hyperopia measured by RTVue OCT

PURPOSE

To characterize the in vivo corneal epithelial thickness (CET) remodeling profile in a population of eyes after small incision lenticule intrastromal keratoplasty (SMI-LIKE) for hyperopia.

METHODS

The CET profile was measured by RTVue-100 Fourier-domain OCT system across the central 6-mm diameter of the cornea of 17 eyes from 12 subjects (five males and seven females) who accepted corneal stromal lens implantation surgery for correcting hyperopia. The CET were measured at positions with a radius of 0-1.0 mm, 1.0-2.5 mm (divided into eight quadrants) and 2.5-3.0 mm (divided into eight quadrants) from the corneal center. Corneal maximum simulated keratometry (Km) was measured by Pentacam HR anterior segment analyzer to analyze CET changes. The examination data of subjects were collected in four time periods, which were preoperative, short-term postoperative (one week after surgery), mid-term postoperative (the last review within 3-6 months after surgery), and long-term postoperative (the last review over 1-2.5 years after surgery). The changes of CET were compared and analyzed in the four time periods.

RESULTS

Mean CET in 0-1.0 mm, 1.0-2.5 mm and 2.5-3.0 mm of the cornea decreased in one week after surgery, respectively, as compared to CET in the preoperative period, which turned from 55.06 ± 0.82 μm、54.42 ± 0.75 μm、53.46 ± 0.60 μm to 51.18 ± 1.05 μm (P = 0.005), 49.38 ± 0.70 μm (P = 0.000), 51.29 ± 0.59 μm (P = 0.025). In the mid-term postoperative period, mean CET in 0-1.0 mm and 1.0-2.5 mm areas kept thinner than mean CET in the preoperative period, CET in 0-1.0 mm is 50.59 ± 0.76 μm (P = 0.000),CET in 1.0-2.5 mm is 50.23 ± 0.57 μm (P = 0.000), while mean CET in 2.5-3.0 mm area recovered to the same thickness as the preoperative level, which is 54.36 ± 0.66 μm (P = 1.000), until the long-term period, CET stabilized in the above doughnut pattern.

CONCLUSIONS

After stromal lenticule implantation for hyperopia, CET showed a remodeled form of thinning in the 0-2.5 mm area and thickening in the 2.5-3.0 mm area, and remained stable within one year after surgery.

Clinical Applications of Anterior Segment Optical Coherence Tomography: An Updated Review

Since its introduction, optical coherence tomography (OCT) has revolutionized the field of ophthalmology and has now become an indispensable, noninvasive tool in daily practice. Most ophthalmologists are familiar with its use in the assessment and monitoring of retinal and optic nerve diseases. However, it also has important applications in the assessment of anterior segment structures, including the cornea, conjunctiva, sclera, anterior chamber, and iris, and has the potential to transform the clinical examination of these structures. In this review, we aim to provide a comprehensive overview of the potential clinical utility of anterior segment OCT (AS-OCT) for a wide range of anterior segment pathologies, such as conjunctival neoplasia, pterygium, scleritis, keratoconus, corneal dystrophies, and infectious/noninfectious keratitis. In addition, the clinical applications of AS-OCT (including epithelial mapping) in preoperative planning and postoperative monitoring for corneal and refractive surgeries are discussed.

Corneal Epithelial Thickness Mapping: A Major Review

The corneal epithelium (CE) is the outermost layer of the cornea with constant turnover, relative stability, remarkable plasticity, and compensatory properties to mask alterations in the underlying stroma. The advent of quantitative imaging modalities capable of producing epithelial thickness mapping (ETM) has made it possible to characterize better the different patterns of epithelial remodeling. In this comprehensive synthesis, we reviewed all available data on ETM with different methods, including very high-frequency ultrasound (VHF-US) and spectral-domain optical coherence tomography (SD-OCT) in normal individuals, corneal or systemic diseases, and corneal surgical scenarios. We excluded OCT studies that manually measured the corneal epithelial thickness (CET) (e.g., by digital calipers) or the CE (e.g., by confocal scanning or handheld pachymeters). A comparison of different CET measuring technologies and devices capable of producing thickness maps is provided. Normative data on CET and the possible effects of gender, aging, diurnal changes, refraction, and intraocular pressure are discussed. We also reviewed ETM data in several corneal disorders, including keratoconus, corneal dystrophies, recurrent epithelial erosion, herpes keratitis, keratoplasty, bullous keratopathy, carcinoma in situ, pterygium, and limbal stem cell deficiency. The available data on the potential role of ETM in indicating refractive surgeries, planning the procedure, and assessing postoperative changes are reviewed. Alterations in ETM in systemic and ocular conditions such as eyelid abnormalities and dry eye disease and the effects of contact lenses, topical medications, and cataract surgery on the ETM profile are discussed.

Evaluation of the effect of artificial tears on corneal epithelial thickness changes after photorefractive keratectomy

PURPOSE

This study aimed to evaluate the corneal epithelial thickness changes after photorefractive keratectomy (PRK) and the impact of long-term artificial tear usage on epithelial thickness changes in these patients.

METHODS

This study was performed on 71 patients (142 eyes) without dry eye disease who received PRK for myopic refractive correction. The corneal epithelial thickness profile was obtained before, one, three, and six months after surgery using anterior segment optical coherence tomography. Patients were randomly divided into two groups: group A, who received preservative-free artificial tears post-surgery, and group B, who did not receive artificial tears.

RESULTS

The epithelial thickness decreased universally in the first month and then increased in the 3- and 6-month follow-ups. Group A had a significantly thicker epithelium in central, paracentral, and midperipheral zones compared with group B in the 3-month follow-up. In the 6-month follow-up, no significant differences were detected between groups. At the last follow-up, the central, paracentral, and midperipheral zone epithelial thicknesses in all patients were significantly higher than preoperative values, but peripheral zone thickness only increased to preoperative values.

CONCLUSIONS

Patients using artificial tears showed a faster thickening, especially in the central and paracentral zones, but there were no significant differences between the two groups in the final follow-up. Artificial tear usage may increase the rate of the epithelial remodeling process in post-PRK patients without significantly altering the final epithelial thickness profile. Further studies are warranted to evaluate the influence of different factors on epithelial remodeling.

The Effect of Upper Eyelid Blepharoplasty on Corneal Tomography and Epithelial Profile

Introduction

Upper tarsal mechanical forces influence corneal epithelial thickness profile, which could modulate corneal astigmatism. Upper eyelid blepharoplasty reduces upper tarsal strength and may have an impact on ocular surface. The aim of this study is to evaluate the effect of upper eyelid blepharoplasty on corneal epithelial thickness profile, astigmatism and aberrations.

Methods

Patients with dermatochalasis underwent bilateral upper eyelid blepharoplasty. Anterior segment optical coherence tomography (AS-OCT) (Zeiss Cirrus 5000 HD-OCT) and Pentacam (Oculus, Wetzlar Germany) were performed before surgery and in the 8th postoperative week. Corneal epithelial thickness, keratometry, aberrations and asphericity were considered for statistical purposes. Only right eyes were considered. A p-value lower than 0.05 was considered significant.

Results

Thirty eyes of 30 patients were included. The degree of astigmatism did not change after surgery (0.95D vs 0.83D, p=0.23). The difference between preoperative and postoperative steepest axis was 3.1° (p=0.04) with a tendency to change toward the vertical meridian. Mean epithelial thickness was higher in the inferior region both pre- and postoperatively and did not change. ET in the superior octant was lower (42 µm vs 45 µm, p<0.01) and the difference between inferior and superior octants (I-S) was higher (7 µm vs 3 µm, p<0.001) before surgery. There were no statistically significant changes in corneal aberrations (p=0.52) and asphericity (p=0.41) after surgery.

Conclusion

Our results support that upper tarsus pressure influences epithelial thickness profile and, consequently, the corneal steepest keratometry. These results lead us to postulate that upper eyelid blepharoplasty may influence biometric and keratometric measurements.

Current microfluidic platforms for reverse engineering of cornea

According to the World Health Organization, corneal blindness constitutes 5.1% of global blindness population. Surgical outcomes have been improved significantly in the treatment of corneal blindness. However, corneal transplantation is limited by global shortage of donor tissue, prompting researchers to explore alternative therapies such as novel ocular pharmaceutics to delay corneal disease progression. Animal models are commonly adopted for investigating pharmacokinetics of ocular drugs. However, this approach is limited by physiological differences in the eye between animals and human, ethical issues and poor bench-to-bedside translatability. Cornea-on-a-chip (CoC) microfluidic platforms have gained great attention as one of the advanced in vitro strategies for constructing physiologically representative corneal models. With significant improvements in tissue engineering technology, CoC integrates corneal cells with microfluidics to recapitulate human corneal microenvironment for the study of corneal pathophysiological changes and evaluation of ocular drugs. Such model, in complement to animal studies, can potentially accelerate translational research, in particular the pre-clinical screening of ophthalmic medication, driving clinical treatment advancement for corneal diseases. This review provides an overview of engineered CoC platforms with respect to their merits, applications, and technical challenges. Emerging directions in CoC technology are also proposed for further investigations, to accentuate preclinical obstacles in corneal research.

Lateral Transport During Membrane Permeation in Diffusion Cell: In Silico Study on Edge Effect and Membrane Blocking

Membrane transport in diffusion cell studies is not one-dimensional from the donor to the receptor. Lateral diffusion within the membrane into the surrounding clamped region can lead to edge effect. Lateral diffusion can also affect the impact of an object blocking the membrane in a diffusion cell. The effects of lateral transport on permeation across a two-layer membrane in diffusion cells were investigated in this study under edge effect and membrane blocking conditions that could be encountered in previous gingiva and hypothetical skin permeation studies. Model simulations of time-dependent and steady-state transport were performed using COMSOL Multiphysics. The simulations indicated edge effect could increase the steady-state flux across the membrane up to 35% with a relatively thick membrane and small diffusion cell opening (e.g., gingiva study). The edge effect decreased when the relative thickness and permeability of the major barrier (top layer in the two-layer membrane) decreased. When the membrane was partially blocked by an object, lateral diffusion within the membrane could mitigate its impact: e.g., when the object was in the receptor, the impact caused by membrane blocking was reduced more than half. Therefore, membrane lateral transport should be considered under certain circumstances in permeation studies using diffusion cells.

Descemet Membrane Endothelial Keratoplasty (DMEK) Reduces the Corneal Epithelial Thickness in Fuchs' Patients

Fuchs' endothelial corneal dystrophy (FECD) is the occurrence of corneal edema due to endothelial cell dystrophy. Descemet membrane endothelial keratoplasty (DMEK) is considered to be the gold standard of treatment. The aim of this study was to investigate the changes in the corneal epithelial thickness of FECD patients before and after DMEK and to compare these results with a healthy control cohort. In this retrospective analysis, 38 eyes of patients with FECD that were treated with DMEK and 35 healthy control eyes received anterior segment optical coherence tomography (OCT; Optovue, XR-Avanti, Fremont, CA, USA). The corneal epithelial thicknesses in different locations were analyzed and compared between the preoperative, postoperative, and control cohorts. The median follow-up time was 9 months. There was a significant degression of the mean epithelial thickness after DMEK in the central, paracentral, and mid-peripheral zones (p < 0.01) of the cornea. The total corneal thickness and stromal thickness decreased significantly as well. No significant differences were observed between the postoperative and control cohorts. In conclusion, the FECD patients had an increased epithelial thickness compared to the healthy controls, which decreased significantly after DMEK and reached thickness levels comparable to those of healthy control eyes. This study emphasized the importance of distinguishing between the corneal layers in anterior segment pathologies and surgical procedures. Moreover, it accentuated the fact that the structural alterations in FECD extend beyond the corneal stroma.

Repeatability of corneal pachymetry and epithelial thickness measurements with spectral-domain optical coherence tomography (SD-OCT) and correlation to ocular surface parameters

PURPOSE

To assess the repeatability of corneal pachymetry and epithelial thickness measurements with spectral-domain optical coherence tomography (SD-OCT) and identify correlations between epithelial thickness and ocular surface parameters.

METHODS

Adults who happened to have prolonged computer use were recruited, excluding those with conditions interfering with corneal measurements or tear production. All subjects filled in the ocular surface disease index (OSDI) questionnaire. Three consecutive measurements of central and peripheral corneal and epithelial thickness were performed with SD-OCT (RTVue XR). Schirmer test I and tear film break-up time (TBUT) were performed. Repeatability was evaluated with intraclass correlation coefficient (ICC), coefficient of variation and repeatability limit. Spearman correlation was used for non-parametric variables.

RESULTS

113 eyes of 63 subjects were included in the study. ICC was ≥ 0.989 for all corneal and ≥ 0.944 for all epithelial pachymetry segments. The best repeatability was found centrally and the worst superiorly both for corneal and epithelial measurements. Central epithelial thickness was weakly correlated with Schirmer test I (rho = 0.21), TBUT (rho = 0.02), OSDI symptoms and OSDI score (rho <|0.32|). OSDI symptoms and OSDI score were weakly correlated with Schirmer test I (rho <|0.3|) and TBUT (rho <|0.34|).

CONCLUSION

RTVue XR measurements of corneal and epithelial thickness are highly repeatable in all segments. The lack of correlation between epithelial thickness and ocular surface parameters could suggest the assessment of epithelial integrity with reliable methods such as SD-OCT.

Corneal Epithelial Thickness Changes After Topical Treatment of Dry Eye Disease in Primary Sjögren Syndrome

Purpose

To evaluate the changes on epithelial thickness before and after topical treatment in primary Sjögren syndrome-associated dry eye disease (SS-DED).

Methods

This was a prospective study that included referred women with SS-DED and healthy age-matched controls. Corneal epithelial thickness was evaluated using high-definition anterior segment optical coherence tomography (Cirrus 5000 HD-OCT) in the baseline first consultation, and four weeks after treatment with preservative free 1mg/1mL sodium hyaluronate. Schirmer test 1 (ST1), tear break-up time (TBUT), tear meniscus height (TMH), SICCA Ocular Surface Score (SICCA OSS) and Ocular Surface Disease Index (OSDI) were evaluated. Statistical significance was defined as p-value <0.05.

Results

The study included 40 eyes, 20 with SS-DED and 20 controls. At baseline, SS-DED patients had lower ST1 (11.1 ± 2.2mm vs 14.1 ± 3.1mm, p<0.01), faster TBUT (9.1 ± 1.8s vs 13.2 ± 1.1s, p<0.01) and lower TMH (211.2 ± 68.4 µm vs 217.2 ± 60.1µm; p<0.01) than the control group, whereas SICCA OSS and OSDI were higher (p<0.01). The superior epithelium was thinner in SS-DED group (41.1 ± 3.2 µm vs 43.1± 2.3 µm, p<0.01). After treatment, ST1, TBUT, TMH, SICCA OSS, and OSDI improved (p<0.01), and superior epithelium thickened (p<0.01) in the SS-DED group.

Conclusion

Treatment with sodium hyaluronate improved ST1, TBUT, TMH, SICCA-OSS, and OSDI score. Superior epithelium tends to be thinner in SS-DED but becomes thicker with treatment. Our results seem to illustrate the morphological changes in the corneal epithelium in DED, which could be further recognized as a clinical biomarker of SS-DED.

Twelve-month outcomes of single-step transepithelial photorefractive keratectomy for moderate hyperopia and hyperopic astigmatism

BACKGROUND

Conventional mechanical or alcohol-assisted photorefractive keratectomy (PRK) techniques for correction of hyperopia and hyperopic astigmatism were associated with inconsistent results. The aim of this study is to evaluate the 12-month visual and refractive outcomes of the relatively new single-step transepithelial photorefractive keratectomy (TE-PRK) for moderate hyperopia and hyperopic astigmatism.

METHODS

This is a prospective interventional study. Forty-eight eyes of 30 patients with moderate hyperopia or hyperopic astigmatism with a cycloplegic spherical equivalent refraction (SEQ) between 2.0 and 4.5 diopters (D) underwent single-step StreamLight® TE-PRK using EX500 excimer laser (Alcon Laboratories, USA). The main outcome measures were recorded at 6 and 12 months postoperatively including assessment of logarithm of the minimum angle resolution (logMAR) uncorrected and corrected distance visual acuity (UDVA, CDVA), cycloplegic refraction, corneal topographic changes as well as post-PRK peripheral haze grading.

RESULTS

The mean preoperative cycloplegic SEQ was significantly reduced from 3.21 ± 0.61 D to 0.35 ± 0.04 D and 0.41 ± 0.04 D at 6 and 12 months, respectively (P < 0.001). The mean preoperative UDVA significantly improved from 0.53 ± 0.02 logMAR to 0.07 ± 0.01 logMAR and 0.08 ± 0.01 logMAR at 6 and 12 months, respectively (P < 0.001) while the mean preoperative logMAR CDVA showed non-significant change over time throughout the study (P = 0.135). At the end of the study, 41 eyes (85.4%) achieved UDVA of 20/25 or better and no eye lost any lines of CDVA. Thirty-eight eyes (79.1%) had a postoperative cycloplegic cylinder of 0.5 D or less at 12 months. The mean preoperative mean keratometry showed significant increase at 6 and 12 months postoperatively (P < 0.001) while there was no significant change between the two postoperative visits denoting topographic stability (P = 0.058). The mean postoperative Q value at 6 and 12 months showed a significant prolate shift (P < 0.001). No haze was observed in 62.5% and 85.4% of the enrolled eyes at 6 and 12 months, respectively.

CONCLUSIONS

Single-step StreamLight® TE-PRK for moderate hyperopia and hyperopic astigmatism achieved acceptable visual and refractive outcomes.

TRIAL REGISTRATION

(Clinicaltrials.gov): NCT05261685, 2 March 2022, retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT05261685.

Comparison of Vision Correction and Corneal Thickness at 180-Day Follow-Up After Femtosecond Laser-Assisted In-Situ Keratomileusis (FS-LASIK), Photorefractive Keratectomy (PRK), and Small Incision Lenticule Extraction (SMILE): A Study from a Single Center in Poland of 120 Patients with Myopia

BACKGROUND This study from a single center in Poland included 120 patients with myopia, and the aim was to compare vision correction and corneal thickness at the 180-day follow-up after femtosecond laser-assisted in-situ keratomileusis (FS-LASIK), photorefractive keratectomy (PRK), or small incision lenticule extraction (SMILE). MATERIAL AND METHODS The effectiveness and safety of laser vision correction (LVC) procedures were evaluated by determining pre- and post-procedure uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) values on the Snell chart. Twenty patients with diagnosed mild myopia (sphere maximum -3.0 diopters D; cylinder maximum 0.5 D) were qualified for PRK surgery. Fifty patients with diagnosed intolerance (sphere maximum -6.0 D; cylinder maximum 5.0 D) were eligible for the FS-LASIK procedure. Fifty patients with diagnosed myopia (sphere maximum -6.0 D cylinder 3.5 D) were qualified for the SMILE procedure. RESULTS Regardless of which procedure was performed, both UDVA and CDVA improved significantly postoperatively (P<0.05). In addition, the UDVA and CDVA values were similar in the postoperative period (P>0.05). For each procedure, the EI was no less than 0.94. Regardless of which type of LVC procedure was performed, CET at the center and 1.5 mm from the center in 4 meridians thickened, and this change was not statistically significant over the observation period (P>0.05). CONCLUSIONS Our analysis demonstrated similar effectiveness of the 3 methods - PRK, FS-LASIK, and SMILE - in patients with mild and moderate myopia.

[TransPRK in general anesthesia-An alternative for anxious patients]

OBJECTIVE

The aim was to analyze and compare the refractive results of anxious patients treated with transepithelial photorefractive keratectomy (TransPRK) while under general anesthesia (ITN) versus patients treated under local anesthesia (TRO).

MATERIAL AND METHODS

The TransPRK treatment was performed with the AMARIS 1050 RS laser (SCHWIND eye-tech-solutions GmbH, Kleinostheim, Germany) in a group of patients with ITN and a group of patients, treated as usual with TRO. The method used an aspheric aberration neutral ablation profile, as well as SmartPulse technology and 7D eyetracking. In ITN propofol and rocuronium were injected intravenously. The artificial respiration was via a resuscitation bag after intubation with a laryngeal mask. To achieve pain insensitivity in the group of patients in TRO three drops of Conjucain Edo 0.4% were instilled at intervals of a few minutes. Follow-up examinations were performed after 1 and 4 days and after 1 and 3 months.

RESULTS

A total of 35 consecutive TransPRK laser treatments under ITN were retrospectively compared with a group of 699 eyes treated with TransPRK under TRO in the period from February 2017 to December 2021. The preoperative sphere had a range of -5.50 to -1.0 dpt, the average cylinder was 1.19 dpt and cylinders were treated up to 4.75 dpt. The results after 3 months follow-up showed a predictability of 100% eyes within the target correction of less than 0.5 dpt in ITN and in TRO 97%. The astigmatic correction showed 91% of eyes in ITN with less than 0.5 dpt and an angle of error of 83% within ±5°. In TRO 96% of eyes showed astigmatic correction with less than 0.5 dpt and an angle of error of 77% within ±5°. After 3 months 83% of eyes treated in ITN reached a visual acuity of 1.0 or more and 84% of eyes treated in TRO.

CONCLUSION

The TransPRK performed in ITN led to equal refractive results than when treated as usual in TRO. For anxious patients there is the possibility of laser vision correction in ITN. Because of shorter treatment time and accordingly shorter time under general anesthesia, TransPRK is an advantage for LASIK surgery.

Corneal Epithelial Thickness Mapping in the Diagnosis of Ocular Surface Disorders Involving the Corneal Epithelium: A Comparative Study

PURPOSE

The purpose of this study was to analyze the role of corneal epithelial thickness (ET) mapping provided by spectral domain optical coherence tomography in the diagnosis of ocular surface disorders (OSDs) involving the corneal epithelium.

DESIGN

This was a retrospective comparative study.

METHODS

Institutional settings are as follows. Study population includes 303 eyes with an OSD and 55 normal eyes (controls). Observation procedures include spectral domain optical coherence tomography with epithelial mapping in the central 6 mm. Main outcome measures include ET map classification (normal, doughnut, spoke-wheel, localized/diffuse, and thinning/thickening patterns) and ET data and statistics (minimum, maximum, and SD). A quantitative threshold was determined with receiver operating curves to distinguish pathological from normal corneas. Sensitivity and specificity of classification and quantitative data were calculated using all eyes to assess the ability to distinguish corneas with a given corneal disorder from other conditions.

RESULTS

Classification of full agreement between 3 readers was obtained in 75.4% to 99.4% of cases. Main OSD features were keratoconus (135 eyes), doughnut pattern (sensitivity/specificity = 56/94%), and max-min ET ≥ 13 μm (84/43%); limbal deficiency (56 eyes), spoke-wheel pattern (66/98%), and max-min ET ≥ 14 μm (91/59%); epithelial basement membrane dystrophy (55 eyes), inferior thickening pattern (55/92%), and central ET > 56 μm (53/81%); dry eye (21 eyes), superior thinning pattern (67/88%), and minimal ET ≤ 44 μm (86/48%); pterygium (10 eyes), nasal thickening pattern (100/86%), and nasal ET > 56 μm (80/71%); and in situ carcinoma (11 eyes), max ET > 60 μm (91/60%), and ET SD >5 μm (100/58%).

CONCLUSIONS

The epithelial map pattern recognition combined with quantitative analysis of ET is relevant for the diagnosis of OSDs and for distinguishing various OSDs from each other. Deep learning analysis of big data could lead to the fully automated diagnosis of these disorders.

Applications of epithelial thickness mapping in corneal refractive surgery

In this review, we discuss the applications of epithelial thickness mapping in corneal refractive surgery. The review describes that the epithelial thickness profile is nonuniform in the normal eye, being thinner superiorly than inferiorly and thinner temporally than nasally. It is postulated that this is due to the eyelid forces and blinking action on the superior cornea. Changes in the epithelial thickness profile have been found to be highly predictable, responding to compensate for changes in the stromal curvature gradient, using the eyelid as an outer template. This leads to characteristic changes in the epithelial thickness profile that can be used for early screening in keratoconus, postoperative monitoring for early signs of corneal ectasia, and for determining whether further steepening can be performed without the risk of apical syndrome following primary hyperopic treatment. Compensatory epithelial thickness changes are also a critical part of diagnosis in irregular astigmatism as these partially mask the stromal surface irregularities. The epithelial thickness map can then be used to plan a trans-epithelial photorefractive keratectomy treatment for cases of irregularly irregular astigmatism.

Epithelial thickness mapping for corneal refractive surgery

PURPOSE OF REVIEW

As more devices become available that offer corneal epithelial thickness mapping, this is becoming more widely used for numerous applications in corneal refractive surgery.

RECENT FINDINGS

The epithelial thickness profile is nonuniform in the normal eye, being thinner superiorly than inferiorly and thinner temporally than nasally. Changes in the epithelial thickness profile are highly predictable, responding to compensate for changes in the stromal curvature gradient, using the eyelid as an outer template. This leads to characteristic changes that can be used for early screening in keratoconus, postoperative monitoring for early signs of corneal ectasia, and for determining whether further steepening can be performed without the risk of apical syndrome following primary hyperopic treatment. Compensatory epithelial thickness changes are also a critical part of diagnosis in irregular astigmatism as these partially mask the stromal surface irregularities. The epithelial thickness map can then be used to plan a trans-epithelial PRK treatment for cases of irregularly irregular astigmatism. Other factors can also affect the epithelial thickness profile, including dry eye, anterior basement membrane dystrophy and eyelid ptosis.

SUMMARY

Epithelial thickness mapping is becoming a crucial tool for refractive surgery, in particular for keratoconus screening, ectasia monitoring, hyperopic treatment planning, and therapeutic diagnosis and treatment.

Corneal Epithelial Remodeling as a Cause of Chalazion-Induced Hypermetropia

PURPOSE

The importance of the corneal epithelium and its role in influencing the refractive state of the eye is well established, as is the association between periocular mass lesions, such as chalazia, and changes in corneal refractive status. This case report provides new evidence linking these 2 phenomena.

METHODS AND RESULTS

A 74-year-old man presented with gradual onset of blurred vision in his right eye. Examination revealed a large central right upper lid chalazion, with associated hypermetropic shift. Corneal topography showed central corneal flattening, and anterior segment optical coherence tomography epithelial thickness mapping showed central focal epithelial thinning. The chalazion was treated with incision and drainage and subsequent LipiFlow thermal pulsation treatment. At 3- and 4-month review, corneal epithelial thickness and topographic changes were seen to normalize, with a corresponding return toward emmetropic refractive status.

CONCLUSIONS

Chalazia can cause reversible corneal epithelial remodeling and should be considered as a differential diagnosis in cases of unexplained vision loss and changes in refractive status.

Heidelberg Anterion Swept-Source OCT Corneal Epithelial Thickness Mapping: Repeatability and Agreement With Optovue Avanti

PURPOSE

To assess the repeatability of corneal epithelial thickness mapping in virgin, post-laser refractive surgery (PLRS), and keratoconic eyes using a novel swept-source optical coherence tomographer (SS-OCT), and to determine the agreement of the measurements with a validated spectral-domain (SD) OCT.

METHODS

Analysis of 90 virgin, 46 PLRS, and 122 keratoconic eyes was performed. Three consecutive measurements of each eye were acquired with the Anterion SS-OCT and Avanti SD-OCT devices, and averages of the epithelial thickness mapping were calculated in the central 2-mm zone and in the 2- to 5-mm and 5- to 7-mm diameter rings. The repeatability was analyzed using pooled within-subject standard deviation (Sw). The agreement was assessed by Bland-Altman analysis and paired t tests.

RESULTS

The repeatability ranges of the Anterion and Avanti epithelial thickness mapping measurements were Sw: 0.60 to 1.36 µm and Sw: 0.75 to 1.96 µm, respectively. The 95% limits of agreement of the Anterion and Avanti were 0.826 to 8.297. All values of the thickness measurements with the Anterion were lower than those of the Avanti, with the mean differences being 4.06 ± 1.81, 3.26 ± 2.52, and 3.68 ± 2.51 µm in virgin, PLRS, and keratoconic eyes, respectively (P < .001 for all).

CONCLUSIONS

The repeatability of the Anterion's epithelial thickness mapping was higher than that of the Avanti. In terms of the agreement between the Anterion and Avanti, the epithelium measured by the Anterion was always thinner than that of the Avanti, making their interchangeable use unsuitable without corrections. [J Refract Surg. 2022;38(6):356-363.].

Clinical outcomes of single-step transepithelial photorefractive keratectomy and off-flap epipolis-laser in situ keratomileusis in moderate to high myopia: 12-month follow-up

BACKGROUND

To compare the quantitative and qualitative optical outcomes of single-step transepithelial photorefractive keratectomy (TPRK) and off-flap epipolis-laser in situ keratomileusis (Epi-LASIK) in moderate to high myopia.

METHODS

In this prospective self-control study, we included patients with moderate to high myopia who were randomized to undergo TPRK in one eye and Epi-LASIK in the other eye. Twelve-month follow-up results for visual acuity, refraction, ocular high-order aberrations, contrast sensitivity, postoperative pain, epithelial healing, and haze grade were assessed.

RESULTS

A total of 64 eyes (32 patients) were enrolled in the study. More eyes completed re-epithelialization in the TPRK group than in the Off-flap Epi-LASIK group 3-4 days postoperatively, while all eyes completed re-epithelialization by 7 days. More eyes achieved a visual acuity (both UDVA and CDVA) of better than 20/20 in the TPRK group than in the Off-flap Epi-LASIK group. The ±0.50 D predictability for correction of the spherical equivalent (SE) was higher in the eyes of the TPRK group (91%) than in those of the off-flap Epi-LASIK group (80%) 12 months after surgery. No significant differences in ocular aberrations, including coma, spherical, and trefoil, were found between the two groups at 12 months. There were also no significant differences in visual acuity, contrast sensitivity, pain, and haze grading between the two groups.

CONCLUSIONS

Both TPRK and off-flap Epi-LASIK are safe, effective, and predictable treatments for moderate to high myopia with comparable surgical outcomes.

TRIAL REGISTRATION

This study was retrospectively registered on ClinicalTrial.gov ( NCT05060094 , 17/09/2021).

Role of Different Types of Contact Lenses in Epithelial Thickness

OBJECTIVE

To evaluate the potential role of different types of contact lenses, such as soft (SCL), hard (HCL), and mini scleral (SCCL), in corneal epithelial thickness with anterior segment optical coherence tomography (AS-OCT).

METHODS

In this cross-sectional study, patients who used contact lens at recent 6 months were recruited consecutively from September 2019 to October 2019, and the epithelial thicknesses of the cornea were obtained by AS-OCT and compared with control subjects who did not use contact lens.

RESULTS

In total, 184 eyes (115 subjects) were included; of them, 75 eyes were keratoconic (KCN) and 109 eyes were nonkeratoconic (non-KCN). Twenty eyes in KCN and 79 eyes of non-KCN group had no history of contact lens use and were included for comparison with KCN and non-KCN contact lens users, respectively. Mean duration of contact lens wearing was 75.63±50.42 months. The epithelial thickness of non-KCN SCL group was thinner than that of non-KCN control subjects all over the cornea, whereas the epithelium of non-KCN HCL was thinner at central site as well as nasal and temporal paracentral and midperipheral areas. Epithelial thickness of the KCN HCL group was not different from the KCN control subjects in all sectors. The KCN SCCL group had thinner epithelium at nearly all peripheral sectors as well as inferior, inferotemporal, inferonasal, and nasal midperipheral sectors compared with KCN control subjects.

CONCLUSION

The corneal epithelium was thinner at the peripheral zones in KCN SCCL users; at both peripheral and central zones in non-KCN SCL users and in central zones in non-KCN HCL users.

[Corneal epithelial thickness in keratoconus patients compared to healthy controls]

BACKGROUND

In keratoconus (KC) a progressive deformation and thinning of the cornea occurs. In contrast to Scheimpflug-based examinations, optical coherence tomography (OCT) can precisely measure the corneal layers separately, allowing separate analyses of corneal epithelial and corneal stromal thicknesses.

AIM OF THIS WORK

The aim of this work was to analyze the corneal epithelial thickness measured by optical coherence tomography (OCT) in patients with KC in comparison to the corneal epithelial thickness in healthy subjects. The diagnostic value of the observed changes was evaluated.

MATERIAL AND METHODS

In a retrospective analysis 125 eyes of patients with KC and 140 eyes of healthy subjects were included. Corneal measurements were performed by OCT (Optovue, XR-Avanti, Fremont, CA, USA). Corneal stromal thicknesses and corneal epithelial thicknesses in different locations were measured and analyzed.

RESULTS

There were significant differences in stromal and epithelial thickness measurements. Of the derived epithelial thickness parameters four showed a good discriminatory power between healthy controls and KC patients (area under the curve in the receiver operating characteristic analysis > 0.7).

CONCLUSION

Patients with KC showed an altered epithelial thickness compared to healthy controls. The derived calculated parameters based on corneal epithelial thickness can distinguish between KC and a healthy cornea.

A new method for the in vivo identification of degenerated material property ranges of the human eye: feasibility analysis based on synthetic data

This paper proposes a new method for in vivo and almost real-time identification of biomechanical properties of the human cornea based on non-contact tonometer data. Further goal is to demonstrate the method's functionality based on synthetic data serving as reference. For this purpose, a finite element model of the human eye is constructed to synthetically generate full-field displacements from different data sets with keratoconus-like degradations. Then, a new approach based on the equilibrium gap method combined with a mechanical morphing approach is proposed and used to identify the material parameters from virtual test data sets. In a further step, random absolute noise is added to the virtual test data to investigate the sensitivity of the new approach to noise. As a result, the proposed method shows a relevant accuracy in identifying material parameters based on full-field displacements. At the same time, the method turns out to work almost in real time (order of a few minutes on a regular workstation) and is thus much faster than inverse problems solved by typical forward approaches. On the other hand, the method shows a noticeable sensitivity to rather small noise amplitudes rendering the method not accurate enough for the precise identification of individual parameter values. However, analysis show that the accuracy is sufficient for the identification of property ranges which might be related to diseased tissues. Thereby, the proposed approach turns out promising with view to diagnostic purposes.

Determining the Utility of Epithelial Thickness Mapping in Refractive Surgery Evaluations

PURPOSE

To determine the impact of corneal epithelial thickness maps on screening for refractive surgery candidacy in a single refractive surgical practice.

DESIGN

Comparison of screening methods.

METHODS

A total of 100 consecutive patients who presented for refractive surgery screening were evaluated. For each patient, screening based on Scheimpflug tomography, clinical data, and patient history was performed and a decision on eligibility for laser in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), and small incision lenticule extraction (SMILE)was independently made by 2 masked examiners. Examiners were then shown patients' epithelial thickness maps derived from optical coherence tomography (OCT). The percentage of screenings that changed after evaluating the epithelial thickness maps, with regard to candidacy for surgery, and ranking of surgical procedures from most to least favorable was determined.

RESULTS

Candidacy for corneal refractive surgery changed in 16% of patients after evaluation of the epithelial thickness maps, with 10% of patients screened in and 6% screened out. Surgery of choice changed for 16% of patients, and the ranking of surgical procedures from most to least favorable changed for 25% of patients. A total of 11% of patients gained eligibility for LASIK, whereas 8% lost eligibility for LASIK. No significant difference was found between the evaluations of the 2 examiners.

CONCLUSIONS

Epithelial thickness mapping derived from optical coherence tomography imaging of the cornea altered candidacy for corneal refractive surgery, as well as choice of surgery, in a substantial percentage of patients in our practice, and was thus a valuable tool for screening evaluations. Overall, the use of epithelial thickness maps resulted in screening in a slightly larger percentage of patients for corneal refractive surgery.

Corneal Epithelial Mapping Characteristics in Normal Eyes Using Anterior Segment Spectral Domain Optical Coherence Tomography

Purpose

The detailed mapping characteristics of the corneal epithelial thickness (CET) in normal eyes from a Middle Eastern population were investigated in relation to age, sex, intraocular pressure, and keratometric power (K).

Methods

A retrospective cross-sectional and analytical study was conducted using spectral domain optical coherence tomography (OCT). We calculated the CET in 124 subjects in 17 zones within a 6 mm circle. Exclusion criteria included subjects with dry eyes, keratoconus, previous eye surgery, glaucoma, and irregular corneas.

Results

A total of 124 individuals was composed of 64 males and 60 females. The mean age of this population was 45.52, ranging from 18 to 79 years. The central CET was thicker in the central 2 mm than the other zones of the cornea except the nasal, inferior-nasal, inferior and inferior-temporal zones, respectively. Males have thicker CET than females in all zones except in the peripheral nasal zone. We found a positive and significant correlation between age and CET in the central, superior-peripheral, inferior-paracentral, and inferior-temporal paracentral zones. Additionally, a medium-positive correlation was detected between increasing age and the variability of epithelial spectral domain in different zones. No link between CET and intraocular pressure was found.

Conclusions

This study analyzed 17 CET zones within the central 6 mm, where the central epithelium is resistant to aging. The CET was thinner superiorly than inferiorly. This may help in decision-making in refractive procedures and in the prediction of corneal diseases.

Translational Relevance

OCT novel algorithms are noninvasive methods for measuring CET and have been demonstrated to be useful in refractive surgery planning and follow-up, as well as a robust tool for diagnosing potential corneal ectasia.

A cross-sectional study to compare the normal corneal epithelial thickness in various age groups of Indian population using 9 mm wide optical coherence tomography scans

Purpose:

To compare the corneal epithelial thickness among various age groups of normal Indians with 9-mm-wide optical coherence tomography scans.

Methods:

This cross sectional, observational study recruited patients in the age groups of 5–20 years (group 1), 21–35 years (group 2), 36–50 years (group 3), and more than 51 years (group 4). They underwent a detailed ophthalmic examination and were excluded if found to have any ocular surface or intraocular disease (except cataract and refractive error), undergone any ophthalmic surgery, corneal topography changes suggestive of corneal ectasias, or been continuously using any topical medication in either eye for a period of 3 months or more with the last instillation being within 1 month of inclusion in the study. Corneal epithelial thickness (CET) was measured using anterior segment optical coherence tomography (AS-OCT). The CET data from 25 sectors in each eye were analyzed for each age group.

Results:

There were 71 subjects in group 1, 76 subjects in group 2, 59 subjects in group 3, and 57 subjects in group 4. The mean (± standard deviation) ages in the groups 1, 2, 3, and 4 were 14.04 ± 5.10, 26.63 ± 4.71, 42.66 ± 3.92, and 61.65 ± 7.47 years, respectively. The central corneal thickness in all age groups was comparable. Maximum variance in CET parameters was seen in superior cornea.

Conclusion:

Central corneal thickness remains fairly stable over various age groups. The maximum variance in CET over age is seen in superior cornea. The findings from the Indian population correlate well with racially and geographically distinct subjects.

Wide Corneal Epithelial Thickness Mapping in Eyes With Topical Antiglaucoma Therapy Using Optical Coherence Tomography

Purpose

The purpose of this study was to assess the corneal epithelial thickness (CET) of the 9-mm diameter zone in patients treated using topical antiglaucoma medications and to evaluate the factors associated with CET changes.

Methods

Seventy-five patients treated using topical antiglaucoma medications and 65 healthy subjects were included in this cross-sectional study. Each patient completed the Ocular Surface Disease Index (OSDI) questionnaire and underwent examinations including the Schirmer I test, tear breakup time (TBUT), and fluorescein staining. CET mapping of the 9-mm diameter zone was performed using RTVue XR. The CET of the different analyzed zones was compared between groups. The relationship between CET and confounding factors was investigated.

Results

The patient group had a significantly shorter TBUT, shorter Schirmer I test, and greater fluorescein staining than those of the control group (all P < 0.05). The mean CET of patients with glaucoma was significantly lower than that of controls in the central, paracentral, mid-peripheral, and peripheral zones (all P < 0.001). Age affected the CET in the paracentral, mid-peripheral, and peripheral zones (all P < 0.01). The number of medications affected the CET in the central, paracentral, and mid-peripheral zones (all P < 0.05). The duration of treatment affected the CET in the central and peripheral zones (all P < 0.05).

Conclusions

Use of topical IOP-lowering medications leads to epithelial thinning in the 9-mm diameter zone in glaucomatous eyes. Epithelial protection should be considered in older patients and patients treated with multiple medications from the early stages of long-term topical antiglaucoma therapy.

Translational Relevance

The 9-mm diameter CET mapping by using widefield optical coherence tomography (OCT) can be a valuable and convenient method to assess the ocular surface damage in patients with topical antiglaucoma therapy.

Effects of long-term soft contact lens wear on corneal epithelial thickness after small incision lenticule extraction

The present study investigated changes in corneal epithelial thickness after small incision lenticule extraction (SMILE) in patients with long-term preoperative soft contact lens (SCL) wear, the impact of SCL wear on the efficacy of surgical outcomes and the effects of long-term SCL wear on postoperative corneal aberrations. Patients were assigned to three groups according to the duration of SCL wear: Group A, the non-SCL-wearing group; group B, those with SCL wear ≤1 year; and group C, those with SCL wear >1 year. Epithelial thickness was recorded in nine zones by anterior segment optical coherence tomography across a 5-mm diameter before surgery and at 1 week, and 1, 3 and 6 months post-surgery. Corneal epithelial thickness and corneal aberrations among the three groups were compared, as well as the effects of changes in corneal epithelial thickness on postoperative visual acuity and manifest refraction. No significant differences were noted with regard to age or preoperative spherical equivalent among groups A (22 eyes), B (17 eyes) and C (18 eyes). Preoperative corneal epithelial thickness in the inferonasal, inferior and inferotemporal zones was thinner in group B compared with that in group A, and corneal epithelial thickness was thinner in all nine zones in group C compared with that in group A (P<0.05). At all follow-up time points, in the central, nasal, inferonasal, inferior, inferotemporal and temporal areas, the epithelial thickness was thinner in group C compared with that in group A (P<0.05). At 3 months postoperatively, the epithelial thickness was thinner in the inferonasal and inferior sectors in group C compared with that in group B (P<0.05), and at 6 months postoperatively, the epithelial thickness in the inferior region was thinner in group C compared with that in group B (P<0.05). There were no significant differences in visual acuity or manifest refraction among the three groups at all postoperative time points. The total higher-order aberrations were greater in group C compared with those in group A for all time points (P<0.05) and were greater in group C at 1 and 3 months postoperatively compared with those in group B (P<0.05). The spherical aberrations at 3 and 6 months postoperatively were greater in group C compared with those in group A (P<0.05). The coma aberrations were greater in group C compared with those in groups A and B for all time points (P<0.05). In conclusion, long-term SCL wear will result in corneal epithelial thinning, which does not impact visual acuity or manifest refraction after SMILE.

Corneal dellen development after strabismus surgery

This study aimed to evaluate the frequency of corneal dellen development, the healing process, and associated factors that affecting the development and healing of corneal dellen formation after strabismus surgery. In this retrospective study, the records of 714 eyes of 1264 patients who underwent limbal approach strabismus surgery between January 2005 and January 2020 were examined and 47 eyes of 44 patients with corneal dellen were included in the study. Demographic features, ophthalmological examination findings, dellen occurrence and healing time, dellen localization, and the type of surgery were obtained from the medical records of the patients. Corneal dellen development rate was found to be 3.7%. A moderate positive correlation was determined between both mean dellen occurrence time (r = 0.387, p = .007), and mean dellen healing time (r = 0.376, p = .014) with age. In patients who underwent monocular two muscle surgery had significantly higher rates of dellen formation compared to patients who underwent single muscle surgery (p˂0.001). Corneal dellen was significantly higher in eyes undergoing single muscle rectus resection surgery than single muscle rectus recession surgery (p < .001). It was observed that corneal dellen developed more frequently after resection surgery, developed earlier in younger patients, and heals later in elderly patients. Therefore, patients can be followed up closely, keeping in mind the development of dellen, especially after resection surgery.

Two-Step Transepithelial Photorefractive Keratectomy with WaveLight EX500 Platform for Adolescents and Adults with Low to Moderate Myopia: A 12-Month Comparative Evaluation

Purpose

To compare the visual and refractive results obtained after two-step TransPRK using an EX500 excimer laser for low to moderate myopic correction in adolescents and adults.

Patients and Methods

Retrospectively, 91 eyes of 52 patients were categorized into four groups based on age and level of myopia. The demographics, data of efficacy, safety, predictability, stability, and post-operative complications were evaluated at 1, 3, 6, and 12 months post-operatively.

Results

At 1-month, adolescents with low myopia achieved the highest mean efficacy index (P =0.034). The efficacy indices continuously increased during the 1-year follow-up in all groups, except in adolescents with moderate myopia. The highest safety and efficacy indices were recorded in adolescents with low myopia at 1-year. Post-operative spherical equivalent within ±0.50 D at 1 year was 48.75% of all treated eyes; however, the final mean refractive spherical equivalent (MRSE) was under-corrected in all groups. By month 3, the percentage of eyes that had grade 0.5 haze was most prevalent in adolescents with moderate myopia (P <0.001).

Conclusion

two-step TransPRK using an EX500 proved to be an effective, predictable, stable and safe procedure for the correction of low to moderate myopia with or without astigmatism at 1 year. Adolescents with low myopia achieved the best-post-operative UDVA, efficacy and safety indices. Adolescents tolerated night visual problems and dry eye symptoms better than adults.

Microstructure characteristics of cornea of some birds: a comparative study

Background

Light is the critical factor that affects the eye's morphology and auxiliary plans. The ecomorphological engineering of the cornea aids the physiological activities of the cornea during connections between photoreceptor neurons and light photons. Cornea was dissected free from the orbit from three avian species as ibis (Eudocium albus), duck (Anas platyrhynchus domesticus) and hawk (Buteo Buteo) and prepared for light and scanning electron microscopy and special stain for structural comparison related to function.

Results

The three investigated avian species are composed of three identical layers; epithelium, stroma, and endothelium, and two basement membranes; bowman's and Descemet’s membrane, separating two cellular layers, except for B. buteo which only has a Descemet’s membrane. The corneal layers in the investigated species display different affinity to stain with Periodic Acid Schiff stain. The external corneal surface secured by different normal epithelial cells ran from hexagonal to regular polygonal cells. Those epithelial cells are punctured by different diameter microholes and microplicae and microvilli of various length. Blebs are scarcely distributed over their surface. The present investigation utilized histological, histochemical and SEM examination.

Conclusions

The study presents a brief image/account of certain structures of cornea for three of Avian’s species. Data distinguish the anatomic structures of the owl's eye. The discussion explains the role of some functional anatomical structures all through the vision.

Clinical outcomes of transepithelial PRK using SCHWIND AMARIS laser platform with actual versus default epithelial thickness values

PURPOSE

to investigate the clinical outcomes of transepithelial photorefractive keratectomy (tPRK) with actual epithelial thickness versus default software values.

METHODS

eighty-three patients with refractive spherical error of -1.50 to -7.00 diopters (D), and refractive astigmatism up to 4.00 D were consecutively enrolled and divided into two groups: group 1 undergone tPRK with actual central and peripheral epithelial thickness input in right eyes, group 2 undergone tPRK with actual central and 10 μm higher peripheral epithelial thickness in right eyes, left eyes underwent tPRK with default protocol in both groups. Outcome measures were induced refractive error, achieved optical zone (OZ), and wasted stromal tissue.

SETTING

Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, IranDesign: prospective controlled study.

RESULTS

Mean ± SD of induced spherical equivalent (SE) was +0.15 ± 0.39 D and +0.01 ± 0.35 D in right and left eyes of group 1 (p=0.01), and +0.04 ± 0.22 D and +0.03 ± 0.23 D in right and left eyes of group 2 (p=0.75), respectively. There was no statistically significant difference between wasted tissue between right and left eyes in group 1 and group 2 (p=0.77 and p=0.49, respectively). OZ contraction was significantly higher in right compared to left eyes in group 1 (p=0.05), but not in group 2 (p=0.95).

CONCLUSION

In tPRK, refractive outcomes, wasted tissue, and OZ contraction depend little on pre-existing corneal epithelial thickness in corneas with normal range epithelial thickness. However, OZ contraction may be a concern in lower amount of ablations.

Topo-Pachimetric Accelerated Epi-On Cross-Linking Compared to the Dresden Protocol Using Riboflavin with Vitamin E TPGS: Results of a 2-Year Randomized Study

In the present study (clinical trial registration number: NCT05019768), we compared the clinical outcome of corneal cross-linking with either the standard Dresden (sCXL) or the accelerated custom-fast (aCFXL) ultraviolet A irradiation protocol using riboflavin–D-α-tocopheryl poly(ethylene glycol)-1000 succinate for progressive keratoconus. Fifty-four eyes of forty-one patients were randomized to either of the two CXL protocols and checked before treatment and at the 2-year follow-up. The sCXL group was subjected to CXL with 30 min of pre-soaking and 3 mW/cm² UVA irradiation for 30 min. The aCFXL group was subjected to CXL with 10 min of pre-soaking and UVA irradiation of 1.8 ± 0.9 mW/cm² for 10 min ± 1.5 min. In both groups, a solution of riboflavin–vitamin E TPGS was used. Uncorrected distance visual acuity, corrected distance visual acuity, pachymetry, Scheimpflug tomography, and corneal hysteresis were performed at baseline and after 24 months. Both groups showed a statistically significant improvement in corrected distance visual acuity, and keratometric and corneal hysteresis compared to baseline conditions; no statistically significant differences in outcomes between the two groups were observed. Improvement in refractive, topographic, and biomechanical parameters were observed after sCXL and aCFXL, making the riboflavin–VE-TPGS solution an effective option as a permeation enhancer in CXL procedures. Deeper stromal penetration of riboflavin could be complemented by photo-protection against UVA and free radicals formed during photoinduced processes.