Multiple Linear Regression Analysis of the Impact of Corneal Epithelial Thickness on Refractive Error Post Corneal Refractive Surgery

Study of corneal and retinal thicknesses at five years after FS-LASIK and SMILE for myopia

BACKGROUND

This study aimed to observe corneal and retinal thicknesses at 5 years after femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) for myopia, investigate the effect of epithelial remodeling on refractive status and visual quality, and compare retinal thicknesses among fundus tessellation grades.

METHODS

Patients who received FS-LASIK or SMILE 5 years before were enrolled in this cross-sectional study. After 1:1 propensity score matching, each surgical group obtained 177 patients (177 eyes). Examinations including visual acuity, refraction, corneal and retinal thicknesses, corneal higher-order aberrations (HOAs), and fundus photography were performed in this visit at 5 years after surgery. The Quality of Vision (QoV) questionnaire was used to assess visual symptoms and overall satisfaction. Corneal and retinal thicknesses between groups were compared, contributing factors were analyzed, and correlations with postoperative refractive status, HOAs, QoV scores and overall satisfaction were evaluated.

RESULTS

The discrepancy of epithelial thickness between central and pericentral zones in FS-LASIK group was larger than that in SMILE group, which was negatively correlated with postoperative spherical equivalent (SE), positively correlated with spherical aberration (all P < 0.05), but not correlated with QoV scores and overall satisfaction (all P > 0.05) in both surgical groups. There was no statistical difference in stromal thickness and total corneal thickness (all P > 0.05). Most annuluses of epithelial and stromal thicknesse were linearly related to preoperative SE (all P < 0.05). The macular thickness, ganglion cell complex thickness, and retinal nerve fiber layer thickness exhibited comparable values between two surgical groups and four fundus tessellation grades, with no significant association observed with postoperative SE (all P > 0.05).

CONCLUSION

The tendency that epithelial thickness in central zone was thicker than peripheral zone was more obvious at 5 years after FS-LASIK compared to SMILE. This uneven distribution of epithelial thickness might play a role in myopic regression and the changes in HOAs, especially in patients with high myopia, but it had little effect on patients' subjective visual quality and satisfaction. Retinal thicknesses were not affected by these two surgical methods, and they did not appear to be the clinical indicators for myopic regression or fundus tessellation progression.

Corneal Toxicity in Patients Treated by BELANTAMAB MAFODOTIN: How to Improve and Facilitate Patients Follow-Up Using Refractive Shift?

Purpose: Multiple myeloma (MM) is the second most common neoplastic blood disease worldwide. Belantamab mafodotin is a new antibody conjugate anti-B-cell maturation antigen effective against refractory myelomas. It induces intracorneal microcysts leading to refractive fluctuations. The aim of this study is to assess the value of monitoring refractive fluctuations based on the location of microcystic-like epithelial changes (MECs) to facilitate patient follow-up. Methods: This observational and multicentric study was conducted using data collected from several French centers contacted through secure email through a standardized data collection table. Results: The fluctuation of objective refraction in spherical equivalent confirms a significant myopic shift from peripheral to central forms. A decrease in the best-corrected visual acuity (BCVA), an increase in keratometry, and an increase in central epithelial pachymetry have also been observed when MECs migrate toward the center. Conclusion: The myopization found in our study in patients with central and paracentral MECs is consistent with current literature. Fluctuations in BCVA, keratometry, and epithelial pachymetry are also consistent. This study is the first real-world study and highlights heterogeneity in follow-up, emphasizing the need to establish multidisciplinary follow-up strategies. The analysis of refractive fluctuations appears to be a reproducible and noninvasive screening method that could facilitate patient follow-up without the need for consultation focused on corneal diseases.

Changes in Corneal Epithelial Thickness in Different Areas After Femtosecond Laser-Assisted LASIK in Patients With High Astigmatism

PURPOSE

To explore changes in corneal epithelial thickness (CET) after femtosecond laser-assisted laser in situ keratomileusis in patients with high astigmatism.

METHODS

CET was measured at every intersection of the concentric circles and specific axes using AngioVue optical coherence tomography (Angio-OCT) preoperatively and 1 month postoperatively. The average thickness of corneal central, paracentral, and peripheral regions was the mean of the points within the central 2, 2 to 5, and 5 to 7 mm areas, respectively. Correlation analysis was performed to investigate the association between CET along different axes and other preoperative and postoperative parameters.

RESULTS

Forty-two eyes of 28 patients were included. CET along the astigmatic (K1) and perpendicular (K2) axes in the central and paracentral areas increased (P < .001), whereas that along the K2 axis decreased in the peripheral area 1 month postoperatively (P = .001). The amount of CET change in the peripheral area between the K1 and K2 axes was significantly different (P < .001). In the central area, the change in CET along the K2 axis was positively correlated with ablation depth (r = 0.315, P = .042) and negatively with refractive power after surgery (r = -0.347, P = .024). In the peripheral area, the changes in CET along both K1 and K2 axes were negatively correlated with ablation depth (r = -0.431, P = .004; r = -0.387, P = .011, respectively).

CONCLUSIONS

Epithelial modeling differed between the different astigmatism axes after refractive surgery. The compensatory response of the corneal epithelium is more pronounced along the steeper axis. [J Refract Surg. 2024;40(4):e239-e244.].

The effect of incomplete blinking rate on corneal epithelial remodeling after trans-PRK surgery: a six-month study

Purpose

To evaluate the impact of incomplete blink rate on corneal epithelial thickness after transepithelial photorefractive keratectomy (Trans-PRK) surgery.

Methods

Trans-PRK patients were divided into two groups based on preoperative incomplete blinking rates, namely rates ≤0.5 (41 right eyes, group A) and rates >0.5 (65 right eyes, group B). We used anterior segment optical coherence tomography to measure the corneal epithelial thickness (CET) and lipiview to measure the number of blinks, incomplete blinking rate, and lipid layer thickness (LLT).

Results

In both groups, CET decreased at 1 week and 1 month, and the thicknesses in the IT, T, and ST regions exceeded the preoperative levels. Three months after Trans-PRK, the thickness exceeded the preoperative levels and continued to increase during subsequent follow-ups. The blinking times and LLT in both groups decreased at 1 week and gradually increased but did not return to preoperative levels. Group A maintained an incomplete blinking rate of over 0.5 at all postoperative periods. The incomplete blinking rate of group B remained above 0.5 postoperatively, although there was an improvement compared with preoperative rates. Both groups showed a correlation between changes in CET and incomplete blinking rate. There was a correlation between changes in LLT and the incomplete blinking rate after surgery.

Conclusion

Both groups showed uneven corneal epithelia thickening, which became more pronounced approaching the peripheral areas. In addition, changes in CET after surgery were positively correlated with the incomplete blinking rate in both patient groups. There was a negative correlation between postoperative LLT and incomplete blinking rate.

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.

The Impact of Corneal Epithelial Thickening and Inhomogeneity on Corneal Aberrations After Small Incision Lenticule Extraction

PURPOSE

To investigate the corneal epithelial remodeling profile after small incision lenticule extraction (SMILE), the correlated explanatory variables, and its potential impact on corneal higher order aberrations (HOAs).

METHODS

This single-center study prospectively evaluated 75 right eyes of 75 patients scheduled for SMILE. An anterior segment optical coherence tomography device was used to automatically obtain central 6-mm corneal epithelial thickness (ET), total corneal HOAs, and individual Zernike components before and after surgery. The ET inhomogeneity over the central 3- and 6-mm cornea was quantified with coefficient of variance (CV).

RESULTS

Both ET and CV significantly increased 1 month postoperatively (all P < .05). The stepwise multiple regression analysis showed that ET and CV were significantly correlated with preoperative ET and CV, respectively (all P < .01). The corrected spherical equivalent also significantly influenced ET and CV (all P < .01). Over the central 6-mm zone, the alterations of total corneal HOAs and individual Zernike components such as vertical coma (Z7) and spherical aberration (Z12, Z24) were significantly correlated with ET and CV (all P < .05).

CONCLUSIONS

The SMILE-induced epithelial remodeling involved both ET and ET inhomogeneity. The modulation was associated with preoperative and treatment parameters, and exerted a significant impact on corneal HOA alterations especially over the central 6-mm cornea. Together with the amount of correction and corneal curvature gradient change, preoperative assessment of ET and ET inhomogeneity might help predict postoperative epithelial remodeling. [J Refract Surg. 2023;39(1):23-32.].

Effect of corneal epithelial remodeling on visual outcomes of topography-guided femtosecond LASIK

PURPOSE

To assess the effect of epithelial remodeling on visual outcomes over a 9 mm diameter corneal surface after topography-guided laser in situ keratomileusis (LASIK) for myopia correction using spectral-domain anterior segment optical coherence tomography (AS-OCT).

SETTING

Outpatient clinical practice at the Stanford University Byers Eye Institute in Palo Alto, California.

DESIGN

Prospective nonrandomized observational study.

METHODS

Visual acuity, including uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA), 5% and 25% contrast sensitivity CDVA, manifest refraction, and corneal epithelial thickness after topography-guided femtosecond LASIK were analyzed. Corneal epithelial thickness was mapped across 13 sections and 3 concentric zones using AS-OCT preoperatively and at 1 month, 3 months, 6 months, and 12 months postoperatively.

RESULTS

60 eyes of 30 patients with a mean age of 32.8 years (range 23 to 52 ± 7.03 years) undergoing myopic LASIK correction were assessed. In eyes with complete follow-up data (n = 30), mean preoperative UDVA was logMAR 1.48 ± 0.45 and logMAR -0.11 ± 0.08 at postoperative 12 months. Mean preoperative CDVA was logMAR -0.08 ± 0.11 and logMAR -0.13 ± 0.07 at 12 months. Linear mixed modeling demonstrated a significant correlation between improvement in UDVA and decreased superior and nasal corneal epithelial thickness and between improvement in CDVA and increased central epithelial thickness 12 months postoperatively.

CONCLUSIONS

Improvement in UDVA and CDVA at 12 months after topography-guided femtosecond LASIK was correlated with nonuniform epithelial remodeling, including epithelial thickening in the central zone and thinning in the superior and nasal sections as measured by AS-OCT.

Refractive Shifts and Changes in Corneal Curvature Associated With Antibody-Drug Conjugates

PURPOSE

Antibody-drug conjugates (ADCs) are a class of cancer drug wherein some are associated with corneal abnormalities, but there is a dearth of published information on refractive shifts in patients receiving ADCs. Here, we evaluated the dynamics of refractive error and keratometry readings in patients with ADC-related keratopathy and microcyst-like epithelial changes (MECs).

METHODS

This study is a retrospective case series including 58 eyes of 29 patients with ADC-related keratopathy from a single tertiary care cancer referral center (MSKCC). One eye (29 total) was randomly assigned for statistical analysis. In addition, a subset analysis of MEC location-refractive error correlation was performed on 20 eyes. Clinical records including slitlamp examination, indirect ophthalmoscopy, calculated spherical equivalence (SE), keratometry, and visual acuity were recorded at baseline, during, and off treatment.

RESULTS

A subset analysis of MEC location-refractive error correlation of 20 eyes revealed the following: Peripheral MECs were significantly associated with hyperopic shifts (P value < 0.001) and paracentral/central associated with myopic shifts (P value < 0.001). In the full cohort and on drug, the greatest change in SE from baseline was myopic (68%, as high as -4.75 D) and hyperopic (32%, as much as +3.75 D). Eighty-nine percent had a change in vision from baseline while on drug, but at the 3-month follow-up off drug, SE and vision returned to baseline in 33% and 82% of eyes.

CONCLUSIONS

Peripheral MECs were significantly associated with hyperopic shifts, and paracentral/central MECs were associated with myopic shifts. While on drug, most eyes had a myopic refractive shift, which corresponded with corneal steepening.

Evaluation of Wide Corneal Epithelial Remodeling after Small Incision Lenticule Extraction (SMILE) with Wide-Field Optical Coherence Tomography

Purpose

This study aims to assess the corneal epithelial remodeling within a 9 mm diameter zone induced by small incision lenticule extraction (SMILE) and evaluate its relationship with the refractive outcomes.

Methods

A total of 64 eyes of 64 patients were included. Wide-field optical coherence tomography (OCT) was used to measure the epithelial thickness (ET) across a 9 mm diameter area, preoperatively, and after one day, one week, one month, three months, and six months postoperatively. The ET changes were compared among the different time points and analyzed zones.

Results

The ET increases from one week to three months and stabilized from three months to six months. Compared to the preoperative values, the mean ET changes at six months in central (2 mm), paracentral (2-5 mm), mid-peripheral (5-7 mm), and peripheral (7-9 mm) zones were 4.37, 4.36, 1.61, and -1.59 μm, respectively. The correlation between the epithelial thickening and the amount of myopia correction was positive in central (P = 0.001) and paracentral zones (P < 0.001) and negative in peripheral zone (P = 0.006). The intended diameter of the optical zone was negatively related to epithelial hyperplasia in the central (P = 0.020) and paracentral zone (P = 0.006), and the correlation was positive in the mid-peripheral zone (P = 0.001). The epithelial thickening of central zone (P = 0.012) and the difference of mean ET between central and paracentral zone (P = 0.020) were negatively related to the spherical equivalent at six months.

Conclusion

An asymmetric lenticule-like pattern of epithelial remodeling occurred in 9 mm diameter cornea at six months after myopic SMILE. The epithelial remodeling may affect the refractive outcomes of SMILE.

Evolution of corneal epithelial remodeling after myopic laser in situ keratomileusis surgery measured by anterior segment optical coherence tomography combined with Placido disk

Purpose:

To investigate patterns of short- and long-term variations in corneal epithelial thickness (CET) after myopic laser in situ keratomileusis (LASIK) using anterior segment optical coherence tomography (AS-OCT) combined with Placido disk-based topography.

Methods:

In this retrospective study, 36 subjects (72 eyes) who underwent LASIK myopic surgery and 53 healthy subjects (106 eyes) who served as controls were enrolled. AS-OCT (MS-39) was performed in all patients before, 1 day, 1 month, and 6 months after surgery. Statistical analysis was performed to analyze CET changes over time after LASIK and to detect patterns of definitive CET remodeling compared to healthy subjects. Multivariate analysis was performed to look for possible predictors of final CET.

Results:

There was no statistically significant difference between groups in terms of demographic and anterior segment parameters (all P > 0.05). After LASIK, all sectors and rings got thicker over time (1.62–8.32 μm; P < 0.01). Except for the central sector, all areas achieved the thickest CET value one day after surgery with a progressive epithelial thinning between 1 and 6 months of follow-up. Changes on CET occurred independently of the grade of myopia before LASIK or final refraction (P > 0.05). None of the clinical variables studied, including diopters corrected, were found to be correlated with final CET (P > 0.05).

Conclusion:

Independent of anterior segment parameters and diopters corrected, CET becomes thicker after LASIK surgery. Central and inner ring sectors thicken more than those more peripheral. CET remodeling after myopic LASIK should be taken into consideration when planning refractive surgery.

Identification of Key Contributive Compounds in a Herbal Medicine: A Novel Mathematic—Biological Evaluation Approach

A pattern or syndrome in response to a multicomponent system is the actual target of herbal medicine treatment. However, it is a substantial challenge to fill the gap between a contributive compound profile in herbal medicine (especially a formula) and its biological features. This study aims to establish a feasible component‐mining strategy, which provides a strong prediction of key compounds in support of experimental and clinical observations. Given interdisciplinary scope of life science and mathematical statistics, the relationship between chemical profile and bioactivities is measured by a model termed mathematical prediction bioactivity, in which gray relational analysis, multiple linear/non‐linear regression analysis (including t‐distributed stochastic neighbor embedding), and radial basis function analysis are involved. R language programming‐dependent analysis is adopted with add‐on packages, including UniDOE, Factoextra, FactoMineR, Factanal, Rtsne, and Nnet. By using this assessment method in a biological experiment, it is identified that 6‐shogaol extracted from Ginger‐Coptis formula (a herbal formula) is beneficial for diabetic retinopathy (DR) treatment. The study provides both a novel compound 6‐shogalol for DR treatment and a new strategy for mining key contributors in a multicomponent system.

Corneal Epithelial Thickness Changes Following SMILE for Myopia With High Astigmatism

PURPOSE

To evaluate the corneal epithelial thickness (CET) profile changes after small incision lenticule extraction (SMILE) surgery for myopic astigmatism correction of greater than 2.00 diopters (D).

METHODS

This prospective observational study included 40 eyes (23 patients) treated with SMILE for myopia with cylinders of -2.25 to -4.50 D. Along with standard ophthalmic examinations, CET maps with a diameter of 9 mm were measured by high-resolution spectral-domain optical coherence tomography preoperatively and postoperatively. Correlations between the degree of residual astigmatism and the difference in CET values between preoperative flat and steep meridians were analyzed.

RESULTS

The CET showed significant changes in the central (2 mm), paracentral (2 to 5 mm), midperipheral (5 to 7 mm), and peripheral (7 to 9 mm) zones 6 months after SMILE (P < .001). Among the regions, the CET in the paracentral zones displayed the largest increase (9.75%) with the highest average thickness (57.29 µm). Moreover, symmetrical regional epithelial thickening at the preoperative astigmatism axis was observed in the midperipheral zones. The difference in CET between preoperative flat and steep meridians in the mid-peripheral zones continuously increased from postoperative 1 day to 6 months. This difference was positively correlated with the residual cylinder errors at 6 months postoperatively (r = -0.334, P = .035).

CONCLUSIONS

The 9-mm diameter CET in eyes with high astigmatism significantly increased 6 months after SMILE. Additionally, the difference in CET between preoperative flat and steep meridians in midperipheral zones may be related to astigmatic undercorrection in SMILE. [J Refract Surg. 2021;37(4):224-230.].