Epithelial thickness after hyperopic LASIK: three-dimensional display with Artemis very high-frequency digital ultrasound

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.

To Investigate the Changes in Corneal Curvature and Its Correlation with Corneal Epithelial Remodeling After Trans-PRK and FS-LASIK

PURPOSE

To evaluate curvature changes in different regions and their correlation with corneal epithelial remodeling in myopic patients undergoing femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and transepithelial refractive keratectomy (Trans-PRK) after surgery.

METHODS

One hundred and sixty-three patients (163 right eyes) undergoing Trans-PRK and LASIK were evaluated for up to 6 months using anterior segment optical coherence tomography (OCT) to measure the epithelial thickness and corneal topography to measure corneal curvature in different areas (2 mm, 5 mm, and 7 mm). We calculated the curvature ΔK (ΔK = preoperative - postoperative), ΔK5-2 (ΔK5-2 = K5mm - K2mm), ΔK7-5 (ΔK7-5 = K7mm - K5mm), and the epithelial thickness ΔET5-2 (ΔET5-2 = ET5mm - ET2mm) and ΔET7-5 (ΔET7-5= ET7mm - ET5mm).

RESULTS

Corneal curvature flattened in each region of the two groups (all p < 0.001) and gradually steepened during the follow-up period. The Trans-PRK group flattened more significantly within 2 mm and 5 mm, while the FS-LASIK group at 7 mm. Both groups of ΔK decreased over time. Both groups of ΔK5-2 and ΔK7-5 gradually decreased during the follow-up period (P5-2=0.025 and P7-5 < 0.001 for Trans-PRK, P5-2 = 0.011 and P7-5 < 0.001 for FS-LASIK). The corneal epithelium of the two groups gradually thickened during the follow-up period, with Trans-PRK significantly thickening in the central and peripheral regions and FS-LASIK in the central and paracentral regions. There is a significant correlation between the ΔK5-2 and ΔET5-2, ΔK7-5 and ΔET7-5 (all r > 0.37, p < 0.001).

CONCLUSIONS

All groups showed significant curvature flattening after surgery and gradually steepening during the follow-up period. The corneal epithelium thickness in both groups of 17 regions became thicker,. In contrast, Trans-PRK group showed more significant thickening to the periphery and the central 5 mm area of the FS-LASIK. This study indicates a significant positive correlation between differences in epithelial thickening in different regions and differences in curvature changes in the corresponding areas PRK, FS-LASIK, curvature, corneal epithelial thickness.

Association of Changes in Thickness of Limbal Epithelial and Stroma with Corneal Scars Detected by High-Resolution Anterior Segment Optic Coherence Tomography

AIM

To investigate the corneal central and limbal thickness in cornea scar patients using high-resolution anterior segment optical coherence tomography (AS-OCT) and to determine the changes in the limbal region due to the corneal scar. Also, to evaluate tear film parameters in scar patients.

METHODS

Thirty patients with central corneal scar and 30 control subjects. The control subjects were healthy individuals who came to our clinic for routine ophthalmological examination. They were enrolled in this matched case-control study. Central epithelial thickness (ET), stromal thickness (ST), limbal epithelial thickness (LET), and limbal stromal thickness (LST) were analyzed using high-resolution AS-OCT. For evaluation of the ocular surface, the following techniques were used: tear break-up time (BUT) employing standard sterile strips of fluorescein sodium, Schirmer test-I (SCH), and the Ocular Surface Disease Index (OSDI) Questionnaire.

RESULTS

The mean central ET of the patient group was 51.5 ± 12.4 µm, while the mean central ET of the control group was 59.2 ± 9.0 µm. There was a statistically significant difference between patients and controls (p = 0.008). The mean LST of the patients was 747.9 ± 115.7 µm, and the mean LST of the controls was 726.3 ± 79.7 µm. There was a statistically significant difference between patients and controls according to BUT (p = 0.009) and SCH (p = 0.04). However, there was no significant difference between OSDI results of patients and controls (p = 0.08).

CONCLUSION

Corneal monitoring with high-resolution AS-OCT is a simple, noninvasive, useful technique for corneal scar patients. Cornea scars cause decreased ET. This result could be associated with lower tear film parameters in scar patients. The scar length is associated with higher intraocular pressure (IOP) values. Decreased LET and increased LST were detected in scar patients.

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.].

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.

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.

Cataract surgery following refractive surgery: Principles to achieve optical success and patient satisfaction

A growing number of patients with prior refractive surgery are now presenting for cataract surgery. Surgeons face a number of unique challenges in this patient population that tends to be highly motivated to retain or regain functional uncorrected acuity postoperatively. Primary challenges include recognition of the specific type of prior surgery, use of appropriate intraocular lens (IOL) power calculation formulas, matching IOL style with spherical aberration profile, the recognition of corneal imaging patterns that are and are not compatible with toric and/or presbyopia-correcting lens implantation, and surgical technique modifications, which are particularly relevant in eyes with prior radial keratotomy or phakic IOL implantation. Despite advancements in IOL power formulae, corneal imaging, and IOL options that have improved our ability to achieve targeted postoperative refractive outcomes, accuracy and predictability remain inferior to eyes that undergo cataract surgery without a history of corneal refractive surgery. Thus, preoperative evaluation of patients who will and will not be candidates for postoperative refractive surgical enhancements is also paramount. We provide an overview of the specific challenges in this population and offer evidence-based strategies and considerations for optimizing surgical outcomes.

Corneal epithelial remodeling induced by combined small incision lenticule extraction and accelerated corneal collagen crosslinking for myopia

PURPOSE

To evaluate the changes of the corneal epithelial thickness (ET) profile induced by combined small incision lenticule extraction and accelerated corneal collagen crosslinking (SMILE-xtra) for myopia compared with the standard small incision lenticule extraction (SMILE).

SETTING

Nuri Eye Hospital, 61, Dunsan-ro, Seo-gu, Daejeon, 35233, Korea.

DESIGN

Retrospective cross-sectional study.

METHODS

Thirty-one myopic eye undergoing SMILE-xtra and control group of 36 myopic eyes undergoing SMILE were retrospectively analyzed. Spectral-domain optical coherence tomography (CIRRUS™ HD-OCT 5000, ZEISS, Dublin, CA) was used to measure corneal ET of 17 zones within the central 7-mm zone at preoperative, postoperative 1 month, 3 months and 6 months. Postoperative ET alterations were analyzed for correlation with treatment parameters.

RESULTS

There was no difference in preoperative mean age, postoperative MRSE, visual acuity, and ablation depth between the two groups, and there was a significant difference in preoperative central corneal thickness. Both groups showed the greatest increase in corneal ET in the paracentral area on the inferotemporal area, respectively, for 6 months. The preoperative MRSE and the ablation depth showed significant correlation with the postoperative epithelial thickening in mid-peripheral sectors in both groups, and significant negative correlations in paracentral sectors only in SMILE-xtra group.

CONCLUSIONS

It is significant as the first study to compare corneal epithelial remodeling between SMILE and SMILE with accelerated corneal collagen crosslinking. The SMILE-xtra with the relatively large corneal ablation did not show a significant difference in the pattern of corneal epithelial remodeling compared to the SMILE group.

Corneal Higher Order Aberrations and Epithelial Remodeling With Femtosecond Laser-Assisted LASIK Topography-guided and Customized Asphericity Ablation in the Contralateral Eye: A Randomized, Double-Blind, Prospective Study

PURPOSE

To evaluate refractive results, corneal higher order aberrations (HOAs), and epithelial remodeling in the preoperative and postoperative period of regular corneas that had topography-guided femtosecond laser-assisted laser in situ keratomileusis (LASIK) (Contoura WaveLight; Alcon Laboratories, Inc) and compare them with the contralateral eye that underwent ablation customized by asphericity (Custom-Q WaveLight; Alcon Laboratories, Inc) in myopic eyes with or without astigmatism.

METHODS

A prospective, randomized, and double-blind study was conducted. Patients underwent preoperative and postoperative epithelial mapping and corneal tomography to assess the epithelial thickness map, HOAs of the corneal anterior surface, visual acuity, and refractive evaluation.

RESULTS

This study enrolled 96 normal eyes of 48 patients. Uncorrected distance visual acuity of 20/20 or better was achieved in 97% of patients and gains in corrected distance visual acuity and effectiveness in correcting refractive astigmatism were similar in both techniques. Seventeen sectors of the corneal epithelium map were assessed by spectral-domain optical coherence tomography and no significant differences were found between techniques preoperatively and postoperatively (P > .05). HOA root mean square, coma Z3±1, trefoil Z3-3, and tissue consumption exhibited statistically significant between-technique differences (P < .05).

CONCLUSIONS

The Contoura and Custom-Q techniques were similar with respect to refractive and visual outcomes after 3 months, as well as in epithelial remodeling. The Contoura provides lower postoperative HOA root mean square, coma Z3±1, and trefoil Z3-3 values, but the techniques showed no differences in the correction of the corneal astigmatic wavefront component and in the spherical aberration after 3 months. [J Refract Surg. 2023;39(11):751-758.].

Visual outcomes and corneal densitometry after allogenic and autologous lenticule intrastromal keratoplasty for the correction of moderate-to-high hyperopia

AIM

This study aimed to evaluate the visual outcomes and corneal densitometry (CD) after allogenic lenticule intrastromal keratoplasty (AL-LIKE) and autologous lenticule intrastromal keratoplasty (AU-LIKE) for the correction of moderate-to-high hyperopia.

METHODS

Ten subjects (14 eyes) underwent AL-LIKE and eight (8 eyes) underwent AU-LIKE. Patients were examined preoperatively and 1 day, 1 month, and 6 months postoperatively. The visual outcomes and CD for both surgical methods were evaluated.

RESULTS

No postoperative complications were observed with either method. The efficacy index was 0.85±0.18 and 0.90±0.33 in the AL-LIKE and AU-LIKE groups, respectively. The safety indices were 1.07±0.21 and 1.25±0.37 in the AL-LIKE and AU-LIKE groups, respectively. The CD values of the anterior, central, and posterior layers in the AL-LIKE group increased significantly at 1 day postoperatively (all P < 0.05). The CD values of the anterior and central layers remained significantly higher than the preoperative values at 6 months postoperatively (all P < 0.05). The CD values of the anterior layer in the AU-LIKE group increased significantly 1 day postoperatively (all P < 0.05) and decreased to preoperative values (all P > 0.05) 1 month postoperatively.

CONCLUSION

Both AL-LIKE and AU-LIKE exhibit good efficacy and safety in correcting hyperopia. However, AU-LIKE may have a smaller affected area and faster recovery time than those associated with AU-LIKE related to changes in corneal transparency.

Long-term results of hyperopic ablations using alcohol-assisted PRK and FS-LASIK: comparative study

PURPOSE

To evaluate the long-term visual and refractive outcomes of hyperopic excimer ablation using alcohol-assisted photorefractive keratectomy (PRK) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK).

SETTING

American University of Beirut Medical Center, Beirut, Lebanon.

DESIGN

Retrospective, matched comparative study.

METHODS

Eyes that underwent alcohol-assisted PRK were compared to matched eyes that underwent FS-LASIK. All patients were followed up for at least 3 years after surgery. The refractive and visual outcomes of each group were compared at different postoperative time points. The main outcome measures were spherical equivalent deviation from target (SEDT), manifest refraction, and visual acuity.

RESULTS

83 eyes underwent alcohol-assisted PRK and 83 matched eyes underwent FS-LASIK. Preoperative manifest refraction spherical equivalent was 2.44 ± 1.18 diopters (D) and 2.20 ± 0.87 D ( P = .133) in the PRK and FS-LASIK groups, respectively. Preoperative manifest cylinder was -0.77 ± 0.89 D and -0.61 ± 0.59 D ( P = .175) for the PRK and LASIK groups, respectively. 3 years postoperatively, SEDT was 0.28 ± 0.66 D and 0.40 ± 0.56 D for the PRK and LASIK groups, respectively ( P = .222), whereas manifest cylinder was -0.55 ± 0.49 D and -0.30 ± 0.34 D for PRK and LASIK, respectively ( P < .001). The mean difference vector was 0.59 ± 0.46 for PRK and 0.38 ± 0.32 for LASIK ( P < .001). 13.3% of PRK eyes and 0% of LASIK eyes had >1 D of manifest cylinder ( P = .003).

CONCLUSIONS

Both alcohol-assisted PRK and FS-LASIK are safe and effective for the treatment of hyperopia. PRK induces slightly more postoperative astigmatism than LASIK. Larger optical zones and recently introduced ablation profiles that lead to a smoother ablation surface might improve the clinical results of hyperopic PRK.

A Novel Role for Corneal Pachymetry in Planning Cataract Surgery by Determining Changes in Spherical Equivalent Resulting from a Previous LASIK Treatment

Objectives

To provide a metric to differentiate between hyperopic and myopic ablation of a prior LASIK treatment based on the corneal pachymetry profile after laser vision correction (LVC).

Methods

Pachymetry data were retrospectively recovered from patients who had previous LASIK for refractive purposes between 2019 and 2020. Patients with any corneal disorder were excluded. Ablation spherical equivalent was predicted from the central to semiperipheral corneal thickness (CPT) ratio, both values were provided by using the Pentacam user interface software (UI), and values were computed from extracted raw pachymetry data.

Results

Data of 157 eyes of 81 patients were collected, of which data were analysed for 73 eyes of 73 patients to avoid concurrence of measurements in both eyes per subject (42% female; mean age 40.9; SD 12.8). The CPT ratio cutoff for distinction between myopic and hyperopic LASIK was 0.86 for Pentacam UI data. Sensitivity and specificity were 0.7 and 0.95, respectively. Accuracy increased with computation of the CPT ratio based on extracted raw data with sensitivity and specificity of 0.87 and 0.99, respectively. There was a marked linear correlation between the CPT ratio and the ablation spherical equivalent (R² = 0.93).

Conclusions

CPT ratio cutoffs can correctly classify if a cornea previously had a hyperopic versus myopic LASIK surgery and estimate the ablation spherical equivalent of such treatment. This could prove useful for increased accuracy of intraocular lens (IOL) calculations for patients with no historical data of their prior LVC surgery at the time of cataract surgery planning.

Does Adjunctive Under-flap CXL Reduce Regression for Hyperopic LASIK?

PURPOSE

To investigate whether adding accelerated under-flap corneal cross-linking to hyperopic laser in situ keratomileusis (LASIK-ufCXL) affects postoperative stability and regression, visual and refractive outcomes, and subjective quality of vision.

METHODS

This prospective comparative contralateral eye study included 51 patients with hyperopia (102 eyes) who received LASIK-ufCXL in the eye with highest defocus equivalent (DEQ) or randomized when DEQ equal, with the contralateral control eye receiving LASIK alone. After excimer ablation, 0.25% riboflavin was instilled on the stromal bed for 3 minutes. The flap was repositioned, followed by a total irradiation dose of 3.24 J ultraviolet A (UV-A) light administered to the corneal surface, using 18 mW/cm² UV-A for 3 minutes. Postoperative hyperopic regression (stability) was the primary outcome measure, defined by the difference in spherical equivalent (SEQ) at 1 week and 24 months postoperatively. Secondary measures reported uncorrected distance visual acuity, corrected distance visual acuity, cylinder vector analysis, subjective quality of vision, subjective night vision disturbances, and corneal haze.

RESULTS

At 24 months, the SEQ stability (P = .4273) and the magnitude of hyperopic regression (P = .5613) did not significantly differ between groups, with a small trend showing hyper-opic regression of 0.50 diopters or greater being less frequent in LASIK-ufCXL eyes. There were no significant differences in accuracy, efficacy, and safety (P > .05), with a small trend of more residual refractive astigmatism in the LASIK-ufCXL group (P = .3216, Cohen's d: -0.29). Subjective quality of vision trended inferior in LASIK-ufCXL eyes (P = .2237, Cohen's d: -0.25), with a greater haze grading (P = .0466, Cohen's d: 0.41).

CONCLUSIONS

Postoperative regression and stability were statistically equivalent between hyperopic LASIK vs LASIK-ufCXL, with identical safety. There were small clinical trends of lower efficacy, accuracy, and subjective quality of vision in LASIK-ufCXL eyes. [J Refract Surg. 2022;38(12):770-779.].

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.

Corneal Epithelium Asymmetry in Children With Atopy: The Effect of Hand Dominance

Purpose

To evaluate the effect of eye rubbing on the epithelial thickness profile in tomographically normal corneas by AS-OCT and to compare right and left eyes in right-handed children.

Methods

Thirty right-handed boys (mean age 11.2 years) with ocular allergy and history of eye rubbing were evaluated using Scheimpflug (Pentacam HR, Oculus Wetzlar, Germany) and anterior segment optical coherence tomography. Epithelial thickness (ET) and full corneal thickness (CT) parameters were compared between right and left eyes with a non-parametric Mann–Whitney test. A p-value lower than 0.05 was considered for statistical significance.

Results

No eyes had topometric nor tomographic criteria for keratoconus. The min-max ET was lower in right eyes (−2.8 µm vs −3.5; p = 0.02). The difference between inferior and superior (I-S) octants was lower in right eyes (1.1 µm vs 1.9 µm; p = 0.03) as a result of inferotemporal thinning. The highest ET difference was registered between nasal and temporal octants and was more pronounced in the right eyes (2 µm vs 3.1 µm; p < 0.001).

Conclusion

AS-OCT analyses reveal different epithelial thickness patterns between the eyes in young atopic patients, likely eye rubbers. Inferior and temporal epithelial thickness seem to be more affected by thinning in the eye on the side of the dominant hand.

The Impact of Epithelial Remodeling on Surgical Techniques Used in Topography-guided Surface Ablation in Irregular Corneas

PURPOSE

To analyze the optical consequences of epithelial remodeling in irregular corneas and their impact on the choice of different surface ablation techniques.

METHODS

Anterior corneal and stromal surface topographies and epithelial thickness maps were analyzed in 24 eyes with irregular corneal optics. On two of the eyes, four different surface ablation techniques were simulated: (1) conventional anterior topography-guided photorefractive keratectomy (PRK), (2) transepithelial phototherapeutic keratectomy (PTK), (3) transepithelial anterior topography-guided PRK, and (4) stromal topography-guided PRK.

RESULTS

Stromal surface topographies showed higher keratometric values, astigmatism, asphericity, and corneal higher order aberrations compared to topographies of anterior corneas covered by epithelium. Transepithelial anterior topography-guided PRK and stromal topography-guided PRK both resulted in regularized stromal surface, transepithelial PTK achieved partial regularization corresponding to the smoothing effect of the epithelial remodeling, and conventional anterior topography-guided PRK delivered after epithelial removal resulted in residual stromal surface irregularities.

CONCLUSIONS

The difference in optical landscapes between the stromal and anterior surfaces in irregular corneas will represent a source of error when anterior topography-guided treatments are delivered on the deepithelialized stroma, as in conventional PRK. In contrast, anterior topography-guided ablations performed as transepithelial PRK and stromal topography-guided PRK delivered after epithelial removal address the full stromal irregularity, whereas transepithelial PTK alone may be used when topography-guided treatments are not possible. The authors conclude topography-guided PRK of irregular corneas should lead to significantly improved regularization only if it includes the effect of epithelial remodeling. [J Refract Surg. 2022;38(8):529-537.].

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.

Understanding Corneal Epithelial Thickness Mapping

Corneal epithelial thickness (CET) and the regional variations in response to changes in corneal architecture and biomechanics have recently drawn the interest of corneal surgeons. Corneal epithelium possesses the tremendous capability of remodeling and changing its thickness. This remodeling of corneal epithelium takes place in response to underlying stromal irregularities which can result from a variety of corneal disorders including corneal ectasia. Measurement of CET can reveal the underlying stromal abnormalities and supplement in early diagnosis of corneal disorders especially corneal ectasia which has been one of the leading challenges in planning corneal refractive surgery. A significant number of patients ends up in ectasia after refractive surgery and the most common cause of this complication is the presence of preoperative subclinical keratoconus. Furthermore, postoperative complications of corneal refractive surgery are partly masked by epithelial remodeling and make the diagnosis and management difficult and extremely challenging. This leads not only to unpredictable visual and refractive outcome but also the need of multiple interventions to treat these complications. Although corneal tomography is considered as gold standard in the detection and diagnosis of corneal ectasia, a small number of subclinical cases may still go undetected. In this review, we have highlighted the underlying mechanism of epithelial remodeling, the devices and imaging modalities used to measure CET, and application of epithelial mapping in the diagnosis and management of various corneal disorders.

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.

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.].

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.

[Regression and ablation profiles in corneal refractive surgery]

Regression after corneal refractive surgery is a complex phenomenon which seems inevitable. The choice of surgical technique has very little influence on regression for low myopia or myopic astigmatism. However, LASIK and SMILE are the two techniques of choice in the correction of high myopia. LASIK is also better for the correction of hyperopia, hyperopic astigmatism and mixed astigmatism. Intraoperatively, the choice of a wide optical zone and adherence to a thick residual stromal bed provide stability. Regression may also be reduced by modulating anti-inflammatory therapy, treating dry eye, and using mitomycin C in PKR. In all cases, obtaining keratometry during patient follow-up helps to identify the cause of the regression. The objective of this review is to synthesize recent data from the literature on regression in refractive surgery as a function of the ablation profiles used.

[Refractive surgery for hyperopia]

Hyperopia is a refractive error in which light is focused behind, instead of on, the retina. Clear vision can be obtained by accommodation, but in the long run, this results in eye strain. Hyperopia can be classified as low [≤2.00 diopters (D)], moderate (2.00-4.00 D) and high (>4.00 D). Detailed preoperative evaluation is necessary and essential to obtain good postoperative results. Various surgical techniques can be proposed to correct this ametropia. The main techniques used act either by modifying the corneal curvature with the Excimer laser or by implanting a phakic intraocular lens. The anatomical peculiarities of the hyperopic eye (small corneal diameter, short axial length, narrow anterior chamber or large kappa angle) make refractive surgery for hyperopia a considerable challenge. Large optical ablation zones now allow correction of high hyperopia by reducing the risks of optical aberrations and regression. The patient must be informed and understand the postoperative course, which differs from that of surgery for myopia.

Coma Influence on Manifest Astigmatism in Coma-Dominant Irregular Corneal Optics

PURPOSE

To evaluate the influence of coma on manifest refractive cylinder (MRC) in eyes with coma-dominated corneal optics and suggest alternative guidelines for surgical planning of astigmatism correction in topography-guided ablation and toric intraocular lens (IOL) exchange surgery.

METHODS

Twelve eyes with coma-dominant corneal optics and low lenticular astigmatism were selected. The astigmatism remaining after subtraction of total corneal astigmatism (TCA) and lenticular astigmatism from MRC, termed discrepant astigmatism, was calculated and correlated to corneal coma at the anterior surface. Refractive and topography data were then used to simulate topography-guided refractive surgery (topography-guided group) in 7 eyes and lenticular exchange surgery with toric intraocular lens (IOL) implantation (toric IOL group) in 5 eyes. The estimated postoperative MRC after correction of TCA or MRC for each group was compared.

RESULTS

The axis and amplitude of discrepant astigmatism correlated strongly with the axis and amplitude of coma. In the topography-guided group, where topography-guided ablation eliminated corneal higher order aberrations (HOAs), TCA-based correction led to less estimated postoperative manifest astigmatism than MRC-based correction. In the toric IOL group, where removal of the crystalline lens did not affect corneal HOAs, MRC-based correction via toric IOL implantation led to less estimated postoperative astigmatism than TCA-based correction.

CONCLUSIONS

Discrepant astigmatism in eyes with coma-dominant corneal optics correlates with coma. In such eyes, treating TCA, along with corneal HOAs, instead of MRC, seems appropriate in topography-guided treatments, whereas treating MRC may be a better choice in lenticular exchange surgery with toric IOL implantation, where corneal HOAs are not treated. [J Refract Surg. 2021;37(4):274-282.].

Corneal Epithelial Thickness Profile in Healthy Portuguese Children by High-Definition Optical Coherence Tomography

Introduction and Objective

To evaluate corneal epithelial thickness (ET) and corneal thickness (CT) profiles in healthy eyes of Portuguese children and provide information to establish the first normative Caucasian database for these age group.

Methods

Sixty healthy eyes of 60 children aged between 8 and 18 were evaluated using the Cirrus high-definition optical coherence tomography device. The average ET and CT were assessed using Cirrus Review Software with predefined concentric corneal ring-shaped zones. Specific regions of ET (central, superior, inferior, temporal, nasal, superonasal, inferotemporal, superotemporal and inferonasal) were also assessed. The mean ET, the mean CT and the difference of ET in corresponding octants were compared by gender. Correlations between central epithelial thickness (CET), age and refractive error were evaluated.

Results and Discussion

The average ET was lower in the peripheric zones, whereas the average CT was higher. ET was thinner in the superior area than in the inferior (p<0.05). ET was thicker in boys than in girls (p<0.05), but CT did not differ. CET was not correlated with older age or refractive error.

Conclusion

Optical coherence tomography analysis of ET reveals that it is thinner in the periphery, where the CT is thicker. Unlike CT, ET seems to be influenced by gender. ET profile proved to be a useful tool in keratoconus diagnosis and subclinical keratoconus detection in adults. As epithelial changes occur early in the disease and keratoconus is more aggressive in pediatric population, a normative database of ET profile could contribute to enhance early recognition of the disease in this age group.

Sterile Excimer Laser Shaped Allograft Corneal Inlay for Hyperopia: One-year Clinical Results in 28 Eyes

Purpose: This study aimed to evaluate the one-year clinical results of an allograft corneal inlay (ACI) implantation in a case series of 28 hyperopic eyes of 16 patients.Methods: Patients with manifest refraction spherical equivalent (MRSE) between +1.00 and +6.00 D and having a cylindrical refraction of less than 1 D were included in this prospective study. The refractive powers of excimer laser-shaped ACIs were determined based on the refractive error of the individual subject's eyes. After the creation of a femtosecond flap, the inlays were centered on the pupillary axis. Visual acuities, refractive results, and other clinical findings were reported for the 6- and 12-month follow-up exams.Results: The mean age of the patients included in the study was 36.2 ± 12.4 years (range 22-65 years). The mean pre-operative MSRE of 3.6 ± 1.51 D decreased to 0.21 ± 0.56 D (P < .001). The uncorrected distance and near visual acuity increased from 0.33 ± 0.22 and 0.17 ± 0.13 to 0.75 ± 0.22 (P < .001) and 0.72 ± 0.19 (P < .001), respectively. The corrected distance visual acuity remained unchanged (pre-OP: 0.79 ± 0.22; post-OP: 0.80 ± 0.21; P = .916), and the corrected near visual acuity increased from 0.78 ± 0.22 to 0.84 ± 0.20 (P = .003). The mean K-value and central corneal thickness increased from 42.57 ± 0.81 D and 557.5 ± 43.0 µm to 44.8 ± 1.4 D (P < .001) and 597.1 ± 58.1 µm (P < .001), respectively. No significant postoperative complications such as diffuse lamellar keratitis, epithelial ingrowth, or decentralization were observed.Conclusion: Excimer laser-shaped ACI offers an alternative treatment modality for patients with hyperopia. Acceptable visual results and similar regression rates were observed with ACI implantation compared with other laser refractive procedures.

Anatomical and Visual Outcomes after LASIK Performed in Myopic Eyes with the WaveLight® Refractive Suite (Alcon® Laboratories Inc., USA)

Purpose

To evaluate changes in corneal anatomy and quality of vision following LASIK refractive surgery for mild to high myopia using the WaveLight® Refractive Suite (Alcon® Laboratories Inc., USA). Setting. Rothschild Foundation, Paris, France.

Design

Prospective interventional case series.

Methods

We examined 60 myopic eyes (average SE −4.5 D, from −9.3 to −0.75 D) of 30 patients from 21.3 to 38.7 years old. Pachymetry, keratometry, Q factor, corneal aberrations, visual acuity (VA), contrast sensitivity, dry eye assessment, and quality of vision were measured preoperatively, one day (D1), and 1, 3, and 6 months postoperatively.

Results

6 months postoperatively, keratometry became flatter, and the Q factor became more oblate (from −0.18 ± 0.08 to +0.19 ± 0.06). Pachymetry decreased by 117.9 ± 62.2 µm at D1 and increased by 37.87 ± 32.6 µm between D1 and M6. Refraction was emmetropic at D1 and remained stable thereafter. Six months after surgery, VA was slightly but nonsignificantly improved (<0.05 log MAR), whereas contrast sensitivity remained unchanged. Quality of vision was not affected by surgery and was more related to dry eye symptoms than to corneal HOAs (r² = 0.49; p < 0.001 vs. r² = 0.03; p < 0.001).

Conclusions

LASIK surgery for moderate to high myopia, performed with the WaveLight® Refractive Suite, showed good postoperative outcomes, with demonstrated safety, predictability, efficiency, and stability. This is probably due to well-controlled spherical aberration and the use of large optical zones. Besides, we can assume that the patients' quality of vision depends more on the postoperative dry eye disease generated by the laser than on the induced HOAs.

Longitudinal Epithelial Thickness Profile Changes 18 Months After Photorefractive Keratectomy

PURPOSE

Long-term evaluation of corneal epithelial thickness (ET) profile changes after photorefractive keratectomy (PRK) using Fourier-domain anterior segment optical coherence tomography.

METHODS

Three hundred twenty-six eyes of 163 patients were included in this prospective observational study. The corneal epithelial map was obtained across a 9-mm diameter area of the cornea before and up to 27 months after surgery. ET was assessed in 25 sectors and 4 annular zones (central 2 mm, paracentral 2-5 mm, midperipheral 5-7 mm, and peripheral 7-9 mm).

RESULTS

There was a significant reduction in mean ET in all zones 1 month after PRK. Subsequently, ET increased in all annular zones. The change in mean ET became stable in the midperipheral and peripheral zones at 3 to 6 months and in the central zone at 12 months, and it continued to increase in the paracentral zone even after 18 months after surgery. The ET was 3.40 μm and 4.05 μm in the central and paracentral zones at 6 months, respectively. Postoperative spherical equivalent changed significantly only from 1 to 3 months (P < 0.04). There was a significant correlation between postoperative spherical equivalent at month 1 and ET change in the paracentral and midperipheral zones (P < 0.027).

CONCLUSIONS

There is a significant reduction in ET 1 month after myopic PRK with a gradual thickening thereafter until it reaches stability at 12 months in the central zone. However, it continues to change even after 18 months in the paracentral zone. The greatest thickening is in the paracentral zone, followed by the central zone.

Impact of the Reference Point for Epithelial Thickness Measurements

PURPOSE

To analyze the implications of different reference points on the read-out of epithelial thickness mapping.

METHODS

A simulation for changing the reference point from normal-to-the-surface tangent to parallel vertical sections quantifying its effect on the read-out of epithelial thickness mapping has been developed. The simulation includes a simple modeling of corneal epithelial profiles and allows the analytical quantification of the differences in the read-out from normal-to-the-surface tangent to parallel vertical sections epithelial thickness mapping.

RESULTS

The difference in the read-out between parallel vertical sections and normal-to-the-surface tangent epithelial thickness mapping increases for steeper corneas, but it is not largely affected by asphericity. The difference increases for thicker epithelia.

CONCLUSIONS

The reference point for determining the readout of epithelial thickness mapping should be taken into account when interpreting output. Using conventional epithelial thickness map readings (normal-to-the surface tangent) in transepithelial ablations (representing close to parallel vertical sections) may result in induced refractive errors that can be quantified using simple theoretical simulations, because the center-to-periphery progression of the corneal epithelial profile deviates from the progression of the ablated one. Adjustments for the epithelial thickness read-out or, alternatively, for the target sphere can be easily derived. [J Refract Surg. 2020;36(2):200-207.].

Surgical options for retreatment after small-incision lenticule extraction: Advantages and disadvantages

Since the inception of small-incision lenticule extraction (SMILE), many surgeons have speculated the lack of an adequate and standard retreatment procedure will impede its popularity. However, more than 1 million patients worldwide have had this surgery, with visual outcomes nearly equivalent to current laser in situ keratomileusis (LASIK) results. With the procedure's growing popularity, some patients will inevitably have a postoperative residual refractive error from regression, overcorrection, undercorrection, and astigmatic induction and will require retreatment. To our knowledge, literature reviewing major retreatment options is limited. Options include surface ablation, thin-flap LASIK, secondary small-incision lenticule extraction, and a cap-to-flap procedure (CIRCLE) in which a femtosecond laser is use to create cuts that convert the small-incision lenticule extraction cap into a LASIK flap. This review discusses major advantages and disadvantages of these options and compares the visual outcomes based on the existing literature. An algorithmic approach created from this analysis is presented to guide retreatment decision-making.

Six-Month Outcomes After High Hyperopia Correction Using Laser-Assisted In Situ Keratomileusis With a Large Ablation Zone

PURPOSE

To evaluate refractive and visual outcomes of laser-assisted in situ keratomileusis (LASIK) to treat high hyperopia using an aberration-neutral profile and large ablation zone.

METHODS

This was a retrospective, consecutive observational case series at Helios Ophtalmologie, St. Jean-de-Luz, France. One hundred forty-six consecutive eyes of 77 patients who underwent LASIK with mechanical microkeratome to correct hyperopia with correction in the maximum hyperopic meridian strictly higher than +5 D (mean + 6.6 ± 1.0 D) were included. Procedures were performed with an Amaris 750S excimer laser (Schwind eye-tech-solutions GmbH, Kleinostheim, Germany) using an aberration-neutral profile, a 6.7 ± 0.1 mm optical zone, and a 9.2 ± 0.1 mm total ablation zone. Refractive results, predictability, safety, and efficacy were evaluated at 6 months postoperatively.

RESULTS

At 6 months postsurgery, the mean manifest refraction spherical equivalent was -0.06 ± 0.83 D and the mean cylinder was 0.42 ± 0.35 D. Sixty-six percent of eyes were within ±0.50 D of the attempted spherical equivalent correction. Six months postoperatively, 60% of eyes achieved an uncorrected distance visual acuity of 20/20 or better. Ten percent of eyes lost 1 line of corrected distance visual acuity and 4% gained a line. No eyes lost more than 2 Snellen lines of corrected distance visual acuity at any follow-up.

CONCLUSIONS

High hyperopia correction with LASIK using an aberration-neutral profile and large ablation zone provides good efficacy, safety, predictability, and visual outcomes.

Longitudinal and Regional Non-uniform Remodeling of Corneal Epithelium After Topography-Guided FS-LASIK

PURPOSE

To observe the epithelial remodeling over a 9-mm diameter cornea induced by topography-guided femtosecond laser-assisted in situ keratomileusis (FS-LASIK) for myopia correction using spectral-domain optical coherence tomography (SD-OCT).

METHODS

Forty-three eyes of 22 patients who underwent topography-guided FS-LASIK for myopic correction were included. The "Pachymetrywide" scan pattern was used to generate the epithelial thickness map using SD-OCT preoperatively and 1, 3, and 6 months postoperatively. Epithelial thickness was compared and analyzed by section and zone.

RESULTS

Compared to the preoperative values, the change in the average epithelial thickness in the central, paracentral, and mid-peripheral zones was 2.09, 4.53, and -0.87 µm at 1 month; 3.00, 4.61, and -0.97 µm at 3 months; and 3.28, 4.55, and -0.81 µm at 6 months postoperatively, respectively. From 1 to 3 months postoperatively, the central epithelial thickness changed significantly (P = .021), whereas the epithelial thickness in the paracentral (P = .973) and mid-peripheral (P = .996) zones stabilized. No significant epithelial thickness change was observed in the zones between 3 and 6 months postoperatively (all P > .05). The epithelial thickness in the paracentral inferotemporal section increased by 12.7% at 6 months after surgery. The central epithelial hyperplasia showed no correlation with the change in postoperative manifest refraction spherical equivalent (P = .313).

CONCLUSIONS

After topography-guided FS-LASIK, the 9-mm diameter epithelial thickness showed a longitudinal and regional non-uniform redistribution. Central epithelial remodeling stabilized more slowly. The greatest increase in epithelial thickness was observed in the paracentral inferotemporal section. This epithelial remodeling did not cause refractive regression. [J Refract Surg. 2019;35(2):88-95.].

Outcomes for Hyperopic LASIK With the MEL 90® Excimer Laser

PURPOSE

To report the outcomes of laser in situ keratomileusis (LASIK) for hyperopia using the Triple-A ablation profile with the MEL 90 excimer laser (Carl Zeiss Meditec, Jena, Germany).

METHODS

This retrospective analysis included 1,383 eyes treated by LASIK for hyperopia using the Triple-A ablation profile with the MEL 90 at London Vision Clinic, London, United Kingdom, between September 2013 and December 2016. Inclusion criteria were attempted hyperopic correction of +0.25 diopters (D) or higher and corrected distance visual acuity (CDVA) of 20/40 or better. Patients were observed for 1 year after surgery. Standard outcomes analysis was performed.

RESULTS

One-year data were available for 1,350 (97%) eyes. Mean attempted spherical equivalent refraction (SEQ) was +2.77 ± 1.34 D (range: +0.13 to +6.50 D) and mean cylinder was -0.67 ± 0.66 D (range: 0.00 to -5.00 D). Mean age was 54 ± 11 years (range: 21 to 75 years), and 57% were female. Postoperative spherical equivalent was ±0.50 D in 73% and ±1.00 D in 93% of eyes. Uncorrected distance visual acuity was 20/20 or better in 75% of eyes, relative to 93% with preoperative CDVA of 20/20 or better. One line of CDVA was lost in 17% of eyes and two lines were lost in 0.6% of eyes. There was a clinically insignificant but statistically significant increase (P < .01) in contrast sensitivity at 3 and 6 cycles per degree (cpd) and no change for 12 and 18 cpd.

CONCLUSIONS

LASIK for hyperopia with the MEL 90 excimer laser was found to satisfy accepted criteria for safety, efficacy, and stability. [J Refract Surg. 2018;34(12):799-808.].

Repeatability and Reproducibility of Corneal Epithelial Thickness Mapping With Spectral-Domain Optical Coherence Tomography in Normal and Diseased Cornea Eyes

PURPOSE

To evaluate the performance of the epithelial thickness mapping (ETM) of the iVue spectral-domain optical coherence tomography (SD-OCT) device (Optovue Inc, Fremont, California, USA) in normal and diseased cornea eyes.

DESIGN

Reliability and validity analysis.

METHODS

Sixty eyes of 60 subjects were recruited for the study, which included normal subjects (n = 12) and patients with corneal diseases (12 patients each: dry eye syndrome [DES], contact lens wear, post-laser refractive surgery, and keratoconus). Three repeated scans were acquired on 3 iVue SD-OCTs with device-designated operators from consented subjects. Each subject was scanned on each device. Repeatability (based on random error of repeated scans) and reproducibility (including the random error and the instrument/operator variability) were assessed based on spatial zones derived from a 6-mm-diameter corneal ETM centered on the pupil and compared between the groups.

RESULTS

Fifty-nine eyes qualified for final analysis. Seventy-one of 598 acquired scans (11.9%) were excluded owing to scan quality concerns. The percentage of disqualified scans was similar across normal (10.7%) and diseased eyes (12.1%). Of 527 qualified scans, 40 (7.6%) scans required manual edits of the segmentation lines. Repeatability and reproducibility results were similar, indicating minimal device/operator variability for both groups. Repeatability and reproducibility were similar in all subgroups of cornea patients, excluding the DES group, for which reproducibility was significantly lower (range 3.2%-5.5% for DES patients and 1.1%-2.9% for normal subjects).

CONCLUSIONS

The iVue SD-OCT provides good corneal ETM repeatability and reproducibility in normal and diseased cornea eyes through all map zones.

Outcomes of Re-treatment by LASIK After SMILE

PURPOSE

To report the outcomes of LASIK re-treatments after small incision lenticule extraction (SMILE).

METHODS

Retrospective review of all eyes to have undergone a re-treatment by LASIK after primary SMILE between September 2013 and January 2016. Thin-flap LASIK was used in most cases as long as sufficient tissue was available for safe flap creation between the maximum epithelial thickness and minimum cap thickness. Otherwise, the SMILE interface was converted into a LASIK flap by the Circle technique or side cut only. The multivariate nomogram for LASIK re-treatments was used, including sphere, cylinder, age, and primary spherical equivalent (SEQ) as variables. Patients were observed for 1 year after surgery and standard outcomes analysis was performed.

RESULTS

A total of 116 LASIK re-treatments were performed in a population of 2,643 consecutive SMILE procedures, indicating a re-treatment rate of 4.39%. Mean attempted SEQ was -0.05 ± 0.99 diopters (D) (range: -1.88 to +1.50 D). Mean cylinder was -0.70 ± 0.55 D (range: 0.00 to -2.25 D). Postoperative uncorrected distance visual acuity was 20/20 or better in 81% of eyes, for a population with corrected distance visual acuity (CDVA) of 20/20 or better in 95% before re-treatment. Mean postoperative SEQ relative to the target was +0.19 ± 0.49 D (range: -0.88 to +2.13 D), with 74% within ±0.50 D. Mean postoperative cylinder was -0.29 ± 0.24 D (range: 0.00 to -1.25 D). There was one line loss of CDVA in 15% of eyes, but no eyes lost two or more lines. There was a small increase in contrast sensitivity (P < .05). Overcorrection was identified in myopic re-treatments (n = 20) of -1.00 D or more; mean postoperative SEQ was +0.59 ± 0.64 D (range: -0.63 to +2.13 D).

CONCLUSIONS

Re-treatment after SMILE by LASIK achieved excellent visual and refractive outcomes, although these results indicate that myopic LASIK retreatment after primary myopic SMILE requires a different nomogram than for myopic LASIK re-treatment after primary myopic LASIK. [J Refract Surg. 2018;34(9):578-588.].

Three-year outcomes after high hyperopia correction using photorefractive keratectomy with a large ablation zone

Aim

To evaluate refractive and visual outcomes of photorefractive keratectomy (PRK) to treat high hyperopia using an aberration-neutral profile and large ablation zone.

Methods

This was a retrospective, consecutive observational case series at the Oftalmika Eye Hospital, Bydgoszcz, Poland. We included 51 consecutive eyes of 34 patients who underwent alcohol-assisted PRK to correct hyperopia within the range of +3.6 to +6.15 D (mean+4.61±0.67 D). Procedures were performed with an Amaris 750S excimer laser (Schwind eye-tech-solutions GmbH, Kleinostheim, Germany) using an aberration-neutral profile and a 10 mm total ablation zone. Refractive results, predictability, safety and efficacy were evaluated 3 years postoperatively.

Results

At 1-year postsurgery, the mean manifest refraction spherical equivalent (MRSE) was −0.002±0.43 D and mean cylinder was −0.181±0.31 D, while the values were +0.09±0.46 D and −0.15±0.26 D, respectively, at 2 years (MRSE p<0.001) and +0.15±0.44 D and −0.15±0.26 D, respectively, at 3 years (MRSE p<0.001). 78% of eyes were within ±0.50 D of the attempted spherical equivalent correction. Three years postoperatively, 22% of eyes lost one line of corrected distance visual acuity and 27% gained a line or two. The change in the mean corneal spherical aberrations for the 6 mm zone was from 0.27±0.07 to 0.08±0.13 µm.

Conclusions

High hyperopia correction with PRK using an aberration-neutral profile and large ablation zone provides good efficacy, safety, predictability and visual outcomes. Relatively low change of corneal spherical aberrations and low increase of hyperopia in the first three postoperative years were observed.

Femtosecond Laser-Assisted LASIK With and Without the Adjuvant Use of Mitomycin C to Correct Hyperopia

PURPOSE

To compare the visual and refractive results of femtosecond laser-assisted LASIK (FS-LASIK) with and without the adjuvant use of mitomycin C (MMC) to correct hyperopia.

METHODS

A total of 152 consecutive hyperopic eyes were included in this retrospective, observational cohort study, comparing 76 eyes treated with FS-LASIK + MMC with 76 age- and refraction-matched eyes treated with FS-LASIK without MMC. Visual and refractive results were evaluated 1 day, 1 week, and 1, 3, 6, and 15 months postoperatively.

RESULTS

Preoperative mean spherical equivalent was +3.27 diopters (D) versus +3.50 D in the MMC and no MMC groups, respectively (P > .05). Three months postoperatively, uncorrected distance visual acuity was significantly better in the MMC group (0.93 ± 0.2) than in the no MMC group (0.87 ± 0.2) (P = .01). The residual spherical equivalent was significantly lower in the MMC group (+0.18 ± 0.40 D) than in the no MMC group (+0.42 ± 0.50 D) (P = .01). Fifteen months postoperatively, including re-treated eyes, no significant differences were found in uncorrected distance visual acuity, corrected distance visual acuity, and residual refraction. Slightly better outcomes were found in the MMC group in terms of efficacy, safety, and predictability; however, these small differences were not statistically significant. The incidence of re-treatments during the 15-month follow-up was significantly lower in the MMC group than in the no MMC group (6.6% vs 10.5%, respectively) (P = .01).

CONCLUSIONS

FS-LASIK with or without the intraoperative use of MMC is safe and effective to correct hyperopia. However, slightly better refractive outcomes and a lower incidence of re-treatments were observed when intraoperative MMC was used, at least in a 15-month follow-up. [J Refract Surg. 2018;34(1):23-28.].

A comprehensive review on contact lens for ophthalmic drug delivery

With the prevalence of electronic devices and an aging population, the number of people affected with eye disease is increasing year by year. In spite of a large number of eye drops on the market, most of them do not perform sufficiently, due to rapid clearance mechanisms and ocular barriers. To enhance drug delivery to the eye, a number of novel formulations for ocular diseases have been investigated over recent decades, aiming to increase drug retention and permeation while also allowing for sustained drug release over prolonged periods. The contact lens, initially used to correct visual acuity and beautify female eyes, is one such novel formulation with outstanding potential. Recently, contact lenses have been extensively used for ocular drug delivery to enhance ocular bioavailability and reduce side effects, and are particularly suitable for the treatment of chronic diseases, and thus are of interest to ophthalmic scientists. This review summarizes contact lens classification, methods of preparation, strategies for integrating drugs into lenses, in vitro and in vivo studies, and clinical applications. This review also discusses the current state of ocular drug therapy and provides an outlook for future therapeutic opportunities in the field of ocular drug delivery.

Refractive regression after laser in situ keratomileusis

Uncorrected refractive errors are a leading cause of visual impairment across the world. In today's society, laser in situ keratomileusis (LASIK) has become the most commonly performed surgical procedure to correct refractive errors. However, regression of the initially achieved refractive correction has been a widely observed phenomenon following LASIK since its inception more than two decades ago. Despite technological advances in laser refractive surgery and various proposed management strategies, post-LASIK regression is still frequently observed and has significant implications for the long-term visual performance and quality of life of patients. This review explores the mechanism of refractive regression after both myopic and hyperopic LASIK, predisposing risk factors and its clinical course. In addition, current preventative strategies and therapies are also reviewed.

LASIK for the Correction of High Hyperopic Astigmatism With Epithelial Thickness Monitoring

PURPOSE

To evaluate outcomes of high hyperopic LASIK using the MEL 80 excimer laser (Carl Zeiss Meditec, Jena, Germany).

METHODS

Retrospective analysis of 830 consecutive high hyperopic LASIK procedures using the MEL 80 excimer laser and either the VisuMax femtosecond laser (Carl Zeiss Meditec) or zero compression Hansatome microkeratome (Bausch & Lomb, Rochester, NY). Inclusion criteria were attempted hyperopic correction of +4.00 diopters [D] or higher in one axis and corrected distance visual acuity (CDVA) of 20/20 or better. Patients were observed for a minimum of 1 year. Epithelial thickness monitoring by Artemis very high-frequency (VHF) digital ultrasound (ArcScan Inc., Morrison, CO) was used to evaluate potential for further steepening as a re-treatment.

RESULTS

One-year data were available for 785 eyes. Mean attempted spherical equivalent refraction (SEQ) was +4.52 ± 0.84 D (range: +2.00 to +6.96 D) for the primary treatment and mean cylinder was 1.05 ± 0.86 D (range: 0.00 to 5.25 D). Mean age was 50 ± 12 years (range: 18 to 70 years) and 61% were women. Postoperative SEQ was ±0.50 D in 50% and ±1.00 D in 77% of eyes after primary treatment. After re-treatment, 67% of eyes were within ±0.50 D and 89% were within ±1.00 D. Uncorrected distance visual acuity was 20/20 or better in 76% of eyes after final treatment. One line of CDVA was lost in 25% of eyes and two lines were lost in 0.4%. There was a clinically insignificant but statistically significant decrease (P < .05) in contrast sensitivity (CSV-1000) by less than 1 log unit at 3 and 6 cycles per degree (cpd) and by 1 log unit at 12 and 18 cpd. Diurnal fluctuation in refraction was identified in 2 eyes, proven by VHF digital ultrasound to be due to diurnal epithelial remodeling overnight and unrelated to maximum postoperative keratometry induced.

CONCLUSIONS

LASIK for hyperopia by cumulative treatment of up to +8.33 D with the MEL 80 excimer laser was found to satisfy accepted criteria for safety, efficacy, and stability when applying specialized protocols, including epithelial monitoring. [J Refract Surg. 2017;33(5):314-321.].

Higher-Order-Aberrations Following Hyperopia Treatment: Small Incision Lenticule Extraction, Laser-Assisted In Situ Keratomileusis and Lenticule Implantation

Purpose

To compare the postoperative higher-order-aberrations (HOAs) after hyperopic small incision lenticule extraction (SMILE), hyperopic laser-assisted in situ keratomileusis (LASIK), and lenticule implantation for correction of hyperopia.

Methods

Eighteen monkeys were divided to six groups: +2.00 D and +4.00 D hyperopic SMILE, +2.00 D and +4.00 D hyperopic LASIK (n = 6 eyes for each), and lenticule implantation with a −2.00 D and −4.00 D lenticule (n = 3 eyes for each). The corneal HOAs were evaluated preoperatively and 3-month postoperatively.

Results

At 3-month postoperatively, the spherical aberrations significantly increased toward negative direction in all +4.00 D groups (all P < 0.05). There was a significant change toward more negative values in the third-order vertical coma in the SMILE +4.00 D and LASIK +4.00 D groups (P = 0.026 and P = 0.036, respectively). There were also significant changes in the third-order horizontal trefoil (P = 0.034) and oblique secondary astigmatism (P = 0.012) in the LASIK +4.00 D group. In the eyes that underwent +4.00 D lenticule implantation, the fourth-order horizontal quatrefoil significantly increased (P = 0.029). In low hyperopia correction (+2.00 D), treatment with lenticule implantation tended to have less changes in HOAs, compared to the other two groups.

Conclusions

In hyperopic SMILE, hyperopic LASIK or lenticule implantation surgery, significant induction of third- and fourth-order HOAs were seen in moderate hyperopia correction but not in low hyperopia correction. In low hyperopia treatment, lenticule implantation might offer a favorable trend in the aspect of HOAs.

Translational Relevance

The results provided the knowledge of surgically induced HOAs and understanding of the effects of surgery in different types of hyperopic correction.

Mechanisms of Optical Regression Following Corneal Laser Refractive Surgery: Epithelial and Stromal Responses

Laser vision correction is a safe and effective method of reducing spectacle dependence. Photorefractive Keratectomy (PRK), Laser In Situ Keratomileusis (LASIK), and Small-Incision Lenticule Extraction (SMILE) can accurately correct myopia, hyperopia, and astigmatism. Although these procedures are nearing optimization in terms of their ability to produce a desired refractive target, the long term cellular responses of the cornea to these procedures can cause patients to regress from the their ideal postoperative refraction. In many cases, refractive regression requires follow up enhancement surgeries, presenting additional risks to patients. Although some risk factors underlying refractive regression have been identified, the exact mechanisms have not been elucidated. It is clear that cellular proliferation events are important mediators of optical regression. This review focused specifically on cellular changes to the corneal epithelium and stroma, which may influence postoperative visual regression following LASIK, PRK, and SMILE procedures.

Combined application of prophylactic corneal cross-linking and laser in-situ keratomileusis - a review of literature

Laser in-situ keratomileusis (LASIK) is safe and effective laser refractive procedures in treating refractive errors. However, regression of treatment and iatrogenic keratectasia remain to be a major concern, especially in treating thin cornea with high ametropia. Collagen cross-linking (CXL) is an effective method in stopping keratoconus progression through increasing the biomechanical strength of the cornea. Adjuvant cross-linking to refractive procedures can theoretically help prevent regression and reduce the risk of keratectasia development by increasing the mechanical stability of cornea. During the procedure, riboflavin is directly applied to the corneal stroma, thereby reducing the need of de-epithelialization as in the conventional protocol for keratoconus. Currently, there is still no consensus regarding the indication of CXL during refractive procedure, nor any standardized treatment protocol. This article aims to summarize the current evidence regarding the use of adjuvant CXL in LASIK.