Corneal Ectasia After Excimer Laser Keratorefractive Surgery: Histopathology, Ultrastructure, and Pathophysiology

Factors associated with changes in posterior corneal surface following laser-assisted in situ keratomileusis

PURPOSE

To identify factors associated with changes in the posterior corneal curvature following laser-assisted in situ keratomileusis (LASIK).

METHODS

This retrospective study included myopic astigmatic eyes that underwent LASIK between January and December 2013 at Care-Vision Laser Center, Tel-Aviv, Israel. The average posterior keratometry was measured with the Sirius device at a radius of 3 mm from the center. The correlations between the surgically induced change in average posterior keratometry and preoperative parameters such as preoperative sphere, cylinder, spherical equivalent, central corneal thickness (CCT), refraction, Baiocchi Calossi Versaci (BCV) index, ablation depth, percent of tissue altered (PTA), and residual stromal bed (RSB) are reported.

RESULTS

A total of 115 eyes with a mean age of 32.5 ± 8.3 years (range 22-56 years) were included. Central corneal thickness (p < 0.005), preoperative sphere (p < 0.001), spherical equivalent (p < 0.005), and preoperative posterior inferior/superior ratio (p < 0.05) were all significantly correlated with the percentage of change in the mean posterior K. According to ranked stepwise multiple regression analysis, 22% of the variance of change in posterior K could be explained by the examined factors. The factors that remained significant were the percentage of change in posterior inferior/superior ratio, preoperative subjective sphere, and preoperative mean posterior K (for all, p < 0.001).

CONCLUSIONS

The percentage of change in posterior inferior/superior ratio, subjective sphere, and preoperative mean posterior K are all correlated with change in the mean posterior K after LASIK. Understanding of the variables that can influence posterior corneal changes following refractive surgery may play a role in the prevention of iatrogenic keratectasia.

Comprehensive Assessment of Posterior Corneal Asphericity Change Calculated by Tangential Radius of Curvature After FS-LASIK and SMILE

PURPOSE

To evaluate changes in posterior corneal asphericity (ΔQ) using the tangential radius of curvature after femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) procedures.

METHODS

One hundred twenty right eyes of myopic patients who underwent either FS-LASIK or SMILE procedures were analyzed using Sirius 3D corneal topography for assessment. The tangential radius was employed to calculate both preoperative and postoperative posterior corneal Q-values across each semimeridian. After both surgical interventions, the ΔQ value variations across the 360° semimeridional regions of the posterior corneal surface were compared.

RESULTS

A marked postoperative increase in the posterior corneal Q-value was documented. No significant differences were noted between the postoperative Q-values or ΔQ-values of the two surgical approaches. Among patients with moderate myopia, postoperative Q-value exhibited considerably lower increases and ΔQ-value significantly smaller than their counterparts with high myopia. Moreover, the fluctuation in ΔQ across semimeridional regions was less evident in patients with moderate myopia than in those with high myopia. Notably, the degree of ΔQ fluctuation across semimeridional regions was similar between both surgical categories. These data offer insights into variations in the posterior corneal surface after refractive surgeries depending on the degree of myopia, illuminating their clinical relevance.

CONCLUSIONS

Both FS-LASIK and SMILE introduce notable changes to posterior corneal asphericity among patients with different myopia intensities. Furthermore, the influence on the asphericity across the entire posterior surface is similarly distributed between FS-LASIK and SMILE techniques. [J Refract Surg. 2024;40(3):e133-e141.].

Five-year follow-up of a posterior chamber phakic intraocular lens with a central hole for correction of myopia

PURPOSE

To evaluate intermediate and long-term visual outcomes and safety of a phakic intraocular posterior chamber lens with a central hole (ICL V4c) for myopic eyes.

METHODS

Retrospective, consecutive case study of patients that uneventfully received a ICL V4c for myopia correction, with a 5-year postoperative follow-up. Department of Ophthalmology, Goethe University Frankfurt, Germany.

RESULTS

From 241 eyes that underwent ICL implantation, we included 45 eyes with a mean age at surgery of 33 years ± 6 (18-48 years), with a 5 years follow-up. CDVA improved from 0.05logMAR ± 0.15 CDVA preoperatively to  - 0.00 ± 0,07 at 5 years and did not change significantly from 3 to 5 years' time (p = 0.266). The mean spherical equivalent (SE) improved from -10.13D ± 3.39 to  - 0.45D ± 0.69. The change in endothelial cell count showed a mean decrease of 1.9% per year throughout the follow-up. Safety and efficacy index were 1.16 and 0.78, respectively. Cataract formation was seen in 2 of 241 eyes (0.8%), but in none of the 45 eyes that finished the 5-year follow-up.

CONCLUSIONS

Our data show a good intermediate and long-term stability, efficiency, and safety of ICL V4c phakic lenses in myopic eyes comparable to other known literature.

Anterior, Posterior, and Thickness Cornea Differences after Scleral Lens Wear in Post-LASIK Subjects for One Year

The aim of this study is to analyze the anterior and posterior corneal surface shape and the corneal thickness difference outcomes between before and after scleral lens (ScCL) wear in post-LASIK ectasia subjects for one year. Twenty eyes with post-LASIK ectasia wearing scleral lenses were evaluated in a visit before contact lens and after 1, 6, and 12 months. The study variables analyzed included the apex, nasal, temporal, inferior, and superior corneal thickness; the anterior and posterior surface corneal at corneal diameters of 8, 6, 4, and 2 mm, and high-contrast visual acuity. A statistically significant increment of corneal thickness (p < 0.05) was observed in the inferior area after 6 months and in the superior area in the 12-month follow-up after wearing ScCLs. The anterior corneal curvature presented a flattening and a statistically significant steepening (p < 0.05) in the central and peripheral radii, respectively, after one year. The posterior corneal curvature showed a significant (p < 0.05) steepening, which mainly affected the central region after one year. Despite these changes, high-contrast visual acuity with ScCL correction remained at the same values. The prolonged use of scleral lenses in post-LASIK subjects showed significant changes in the corneal curvature and thickness. These outcomes recommend more detailed and periodic topographic and vision quality checks to monitor the wear in ScCL patients.

Transepithelial corneal crosslinking with oxygen enhancement and pulsed light for progressive ectasia: one-year results

PURPOSE

To evaluate the efficacy and safety of transepithelial accelerated crosslinking (TE-ACXL) using pulsed light and supplemental oxygen.

METHODS

Thirty eyes of 30 consecutive patients with progressive keratoconus or post-LASIK ectasia were enrolled in a prospective non-comparative study conducted at the Magrabi Eye Center (Jeddah, Saudi Arabia). All eyes underwent TE-ACXL with supplemental oxygen. Primary outcome measures were the mean change in corrected distance visual acuity (CDVA) (logMAR) and maximum keratometry (max K) from preoperatively to 12 months postoperatively. Secondary outcome measures included change in manifest refractive spherical equivalent (MRSE), refractive cylinder, keratometry, symmetry index (SI), center-surrounding index (CSI) and ectasia index (EI) of the anterior and posterior corneal surfaces, corneal and epithelial thickness at corneal vertex and thinnest location, corneal densitometry, corneal high order aberrations (HOA) and endothelial cell density (ECD).

RESULTS

Mean age was 29.6 ± 8.2 years. At 1 year, the follow up rate was 93.3%. CDVA improved statistically significantly at 12 months (p = 0.027). Measures of corneal keratometry or pachymetry did not change significantly (p < 0.05). Postoperatively, a demarcation line was documented in 78.6% eyes at 1 month, and in 12 (42.9%) eyes at 12 months. The mean depth of the demarcation line was 341.9 ± 49.4 µm. Corneal densitometry increased significantly at 1- and 3-months (p < 0.05) and returned to normal levels at 6- and 12-months postoperatively.

CONCLUSION

TE-ACXL with oxygen supplement is effective at halting the progression of corneal ectasia for at least 1 year and can be a refractive neutral procedure.

Motion-Tracking Brillouin Microscopy Evaluation of Normal, Keratoconic, and Post-Laser Vision Correction Corneas

PURPOSE

To characterize focal biomechanical differences between normal, keratoconic, and post-laser vision correction (LVC) corneas using motion-tracking Brillouin microscopy.

DESIGN

Prospective cross-sectional study.

METHODS

Thirty eyes from 30 patients (10 normal controls [Controls], 10 post-LVC, and 10 stage I or II keratoconus [KC]) had Scheimpflug and motion-tracking Brillouin microscopy imaging using a custom-built device. Mean, maximum (max) and minimum (min) Brillouin shift, spatial standard deviation, and max-min values were compared. Min values were correlated with local Brillouin values at multiple Scheimpflug imaging locations.

RESULTS

Mean (P < .0003), min (P < .00001), spatial standard deviation (P < .01), and max-min (P < .001) were significantly different between the groups. In post hoc pairwise comparisons, the best differentiators for group comparisons were mean (P = .0004) and min (P = .000002) for Controls vs KC, min (P = .0022) and max-min (P = .002) for Controls vs LVC, and mean (P = .0037) and min (P = .0043) for LVC vs KC. Min (area under the receiver operating characteristic = 1.0) and mean (area under the receiver operating characteristic =  0.96) performed well in differentiating Control and KC eyes. Min values correlated best with Brillouin shift values at the thinnest corneal point (r2 = 0.871, P = .001) and maximum keratometry value identified in the tangential curvature map (r2 = 0.840, P = .002).

CONCLUSIONS

Motion-tracking Brillouin microscopy effectively characterized focal corneal biomechanical alterations in LVC and KC and clearly differentiated these groups from Controls. Primary motion-tracking Brillouin metrics performed well in differentiating groups as compared with basic Scheimpflug metrics, in contrast to previous Brillouin studies, and identified focal changes after LVC where prior Brillouin studies did not.

Ten-year follow-up of corneal cross-linking and refractive surface ablation in patients with asymmetric corneal topography

Purpose

Compare the safety and efficacy of wavefront-guided photorefractive keratotomy (PRK) 6 months after cross-linking (CXL) to wavefront-guided PRK alone for refractive correction in patients with bilateral asymmetric corneal topography.

Methods

Prospective randomized clinical trial with 16 patients (32 eyes). CXL with subsequent PRK after 6 months in one eye, and PRK alone was performed in contralateral eyes. The follow-up was 10 years. We analyzed visual outcomes, Scheimpflug topography, and corneal haze evaluation.

Results

Eyes in the PRK group showed better results than in the CXL + PRK group. Mean postoperative CDVA was 0.044 logmar (SD, 0.073) in the PRK group and 0.1 logmar (SD, 0.21) in the CXL + PRK group, the mean sphere was + 0.21 (SD, 0.6) D in the PRK group and 0.87 (SD, 2.3) D in the CXL + PRK group, and mean SE was -0.35 (SD, 0.65) D in the PRK group and 0.62 (SD, 2.32) D in the CXL + PRK group. In one patient, a steepening of 2.5 D and a thinning of 17 μm occurred in PRK alone group. Two patients in the CXL + PRK group presented corneal haze. The overall complication rate was 18,75% (haze and ectasia).

Conclusion

Non-simultaneous CXL and PRK procedures yielded good refractive results, but worse than those obtained with PRK alone. Although one patient in the PRK group developed corneal ectasia, the CXL + PRK group had a higher loss of vision lines, indicating less safety.

Patient-Reported Outcomes With Wavefront-Guided Laser in Situ Keratomileusis (PROWL) Study Outcomes From a Single Institution

PURPOSE

To determine patient-reported outcomes after laser in situ keratomileusis (LASIK) using wavefront-guided technology at a single institution.

METHODS

In this prospective observational study, 62 participants underwent examination and questionnaire at baseline, 1 month, and 3 months after surgery. The questionnaire included questions from validated questionnaires and new items to assess patient satisfaction with current vision and LASIK surgery, and existence/degree of visual symptoms.

RESULTS

At month 1, patients reported an improvement in far vision (P = .01), activity limitations (P ≤ .001), and less worry about vision (P ≤ .001), as well as new visual symptoms, including halos (P ≤ .001) and double images (P = .03). At month 3, patients still noted an improvement in near vision (P = .05), far vision (P ≤ .001), activity limitation (P ≤ .001), and worry (P ≤ .001) along with halos (P = .05), double images (P = .01), and dry eye (P = .01). A total of 3.3% of patients at month 1 and 0% at month 3 had difficulty performing any activity due to symptoms, and 34.6% and 25.0% of patients reported decreased quality of life at months 1 and 3, respectively.

CONCLUSIONS

After LASIK, patients experience new visual symptoms. Patients have high rates of satisfaction overall but with some patients reporting a decrease in quality of life 1 month after surgery; quality of life improves by postoperative month 3, with 25% patients reporting a decrease in visual well-being after surgery. [J Refract Surg. 2023;39(3):198-204.].

Corneal Biomechanics Losses Caused by Refractive Surgery

Recent advances, specifically in the understanding of the biomechanical properties of the cornea and its response to diseases and surgical interventions, have significantly improved the safety and surgical outcomes of corneal refractive surgery, whose popularity and demand continue to grow worldwide. However, iatrogenic keratectasia resulting from the deterioration in corneal biomechanics caused by surgical interventions, although rare, remains a global concern. On one hand, in vivo biomechanical evaluation, enabled by clinical imaging systems such as the ORA and the Corvis ST, has significantly improved the risk profiling of patients for iatrogenic keratectasia. That is despite the fact the biomechanical metrics provided by these systems are considered indicators of the cornea's overall stiffness rather than its intrinsic material properties. On the other hand, new surgical modalities including SMILE were introduced to offer superior biomechanical performance to LASIK, but this superiority could not be proven clinically, creating more myths than answers. The literature also includes sound evidence that tPRK provided the highest preservation of corneal biomechanics when compared to both LASIK and SMILE. The aim of this review is twofold; to discuss the importance of corneal biomechanical evaluation prior to refractive surgery, and to assess the current understanding of cornea's biomechanical deterioration caused by mainstream corneal refractive surgeries. The review has led to an observation that new imaging techniques, parameters and evaluation systems may be needed to reflect the true advantages of specific refractive techniques and when these advantages are significant enough to offer better protection against post-surgery complications.

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.

Normative Values for Corneal Tomography and Comparison of Both Eyes in Young Saudi Males with 20/20 Vision Using Pentacam-HR Scheimpflug Imaging

Purpose

Anterior segment evaluation using Scheimpflug imaging with the Pentacam scanner allows the acquisition of a plethora of information. It aids in screening and diagnosing corneal pathologies and determining suitability for keratorefractive procedures. This research has significant benefits in terms of establishing normative tomographic values, which is crucial in countries where Keratoconus (KC) is more prevalent, especially among young age group, along with aiding future research in the field of refractive surgery by providing relevant normative data.

Methods

A retrospective review of digital corneal tomography images for a group of medically and ophthalmologically free males aged between 18 and 21 years with 20/20 unaided distant visual acuity was performed.

Results

A total of 1272 subjects (2544 eyes) were included. Findings revealed a mean maximal corneal curvature (Kmax) of 42.91 ± 1.40D (range 36.90–47.80D). The mean flat keratometry (K1) was 41.87 ± 1.31D (range 36.00–46.40D). The mean steep keratometry (K2) was 42.66 ± 1.35D (range 36.70–47.60D). The mean corneal astigmatism (CA) was 0.79 ± 0.37D (range 0.00D-2.30D). The mean central corneal thickness (CCT) was 558.53 ± 33.84 μm (range 421–677 μm). The mean thinnest corneal location thickness (TCLT) was 551.64 ± 34.08 μm (range 417–669μm). The mean corneal diameter (CD) and anterior chamber depth (ACD) were 12.13 ± 0.39 mm (range 10.50–13.60 mm) and 3.12 ± 0.29 mm (range 2.08–4.08 mm), respectively. The median differences between both eyes of the same subject were as follows: kmax difference of 0.20D (IQR 0.1–0.4); K1, K2 and CA difference of 0.20D (IQR 0.1–0.3) for all 3 parameters; CCT and TCLT difference of 5.00 μm (IQR 3.0–9.0) and 6.00 μm (IQR 3.0–10.0), respectively; CD difference of 0.10 mm (IQR 0.0–0.1); and ACD difference of 0.04 (IQR 0.02–0.06).

Conclusion

We believe our data can aid in establishing normative tomographic values and acceptable differences between both eyes. Our data may also help detect subtle corneal pathology and be useful for researchers and innovators in the field of ophthalmology.

Accuracy of the Preoperative Predicted Percentage of Tissue Altered Calculation in Refractive Surgery Planning for Myopic LASIK

PURPOSE

To determine the reliability of the percentage of tissue altered (PTA) calculation as part of the planning strategy for myopic laser in situ keratomileusis (LASIK) by comparing the estimated PTA provided by preoperative calculation to the postoperative PTA actually achieved in microkeratome-assisted myopic LASIK.

METHODS

This retrospective study included 3,624 eyes of 3,624 patients who underwent mechanical microkeratome-assisted LASIK surgery for myopic correction. The calculated preoperative PTA values based on the planned flap thickness and ablation depth were compared with the actual achieved postoperative PTA using the difference of corneal central thickness postoperatively for assessing the achieved ablation depth and the intraoperative ultrasound-assisted flap thickness measurement. Regression analysis was performed to reveal preoperative parameters that might influence PTA calculation accuracy.

RESULTS

The mean difference between the estimated and achieved PTA was 0.451 ± 3.45% (P < .001) (95% CI: 0.3708 to 0.5322) with a preoperative and postoperative mean PTA of 31.07 ± 4.07% and 31.52 ± 5.78%, respectively. The differences between the achieved and planned maximum ablation depth and flap thickness were 4.32 ± 13.70 µm (P < .001) and -1.61 ± 13.66 µm (P < .001), respectively.

CONCLUSIONS

Although a statistically significant difference was found between the preoperative calculated PTA and actually achieved PTA, the difference in PTA value (less than 1%) was clinically non-significant and indicated a highly reliable metric for preoperative refractive surgery planning. [J Refract Surg. 2022;38(7):422-427.].

Five-year stability of posterior corneal surface after small incision lenticule extraction for high myopia

Background

To study the 5-year changes in the posterior corneal surface after small incision lenticule extraction (SMILE) for high myopia.

Methods

Eighty eyes received SMILE was included in this prospective study. They were allocated into two groups based on the spherical equivalent: high myopia (40eyes, -7.49 ± 0.70D) and moderate myopia (40eyes, -4.43 ± 0.87D). Certain points of posterior corneal elevation (the central point (PCE), thinnest point (PTE), maximal point (PME), and in various corneal areas) were evaluated using a Scheimpflug camera (Pentacam; Oculus GmbH, Germany) preoperatively and at 6 months and 5 years after surgery.

Results

All surgeries were completed uneventfully and no ectasia was developed throng the observation. The safety index and efficacy index were 1.14 and 1.03 in the high myopia group, and 1.16 and 1.06 in the moderate myopia group, respectively. Most of the calculated values in the high myopia group showed a slight increase at 6 months but decreased at 5 years. At 5 years postoperatively, the value of the PTE was significantly lower than at baseline in both groups (P ≤ 0.047); a statistical difference was also revealed in the PME in the moderate group with slight changes (10.15 ± 3.01 μm vs. 11.60 ± 4.33 μm, P = 0.002); no statistical significance was observed in other calculated values (P ≥ 0.067). Similarly, no significant linear correlation was noted between changes in all values and the residual bed thickness either (P ≥ 0.057).

Conclusions

SMILE causes no protrusion in posterior corneal surface for correction of high myopia at the follow-up visit of 5 years.

Combined accelerated collagen crosslinking and sub-Bowman's keratomileusis in high myopic eyes: a comparison between total ultraviolet energy dose

AIM

To compare the safety, efficacy, and predictability outcomes of combined sub-Bowman's keratomileusis (thin flap laser in situ keratomileusis [LASIK]) and accelerated crosslinking (CXL) using two different irradiation durations.

METHODS

A retrospective comparative study of patients with percent tissue altered ≥35%, undergoing simultaneous CXL during sub-Bowman's keratomileusis were recruited. Following riboflavin application, they underwent ultraviolet-A (UVA) irradiation (18 mW/cm²) for either 2 min (total energy 2.16 J/cm²) or 3 min (total energy 3.24 J/cm²). Visual and refractive outcomes were compared between follow-up visits during the first year postoperatively. Demarcation line and endothelial cell count were evaluated, respectively, at 1 and 3 months postoperatively.

RESULTS

The baseline characteristics were similar between the 40 eyes/patients treated using the 2-min protocol and the 33 eyes/patients treated with the 3-min protocol (p ≥ .114). Uncorrected distance visual acuity and corrected distance visual acuity were significantly better for eyes treated with the shorter irradiation protocol on Day 1 (p ≤ .030) and Month 1 (p ≤ .040) postoperatively; these differences diminished by Month 3 (p ≥ .070). Likewise, the efficacy index was higher during the first postoperative week for the 2-min protocol (p ≤ .043). At 1 year, the proportion of eye attaining within 0.5 D of target refraction was 80.0% and 84.8% for the 2-min and 3-min protocols, respectively (p = .590). The corresponding corneal stromal demarcation line depth and endothelial cell density changes were comparable between the two groups (p = .311 and 0.899, respectively).

CONCLUSIONS

A comparable volume of crosslinked corneal tissue can be achieved by using a shorter UVA irradiation duration. Additional duration of UVA irradiation could lead to delay in visual rehabilitation after simultaneous sub-Bowman's keratomileusis and CXL.

Three-Year Follow-Up of Posterior Corneal Elevation in Thin Corneas After Small Incision Lenticule Extraction

Purpose

To evaluate the changes in posterior corneal elevation in thin corneas after small incision lenticule extraction (SMILE).

Methods

In this prospective study, 97 eyes of 97 patients undergoing SMILE were recruited. Eyes were categorized into the following groups based on the preoperative minimum central corneal thickness (CCT): group A (37 eyes, 480–499 μm), group B (30 eyes, 500–529 μm), and group C (30 eyes, 530–560 μm). The posterior corneal surface was measured with a Pentacam over a 3-year follow-up period. Changes in the posterior corneal elevation at the central point (PCE), thinnest point (PTE), and predetermined area were measured.

Results

No iatrogenic keratectasia was observed during the follow-up period. The mean changes in PCE, PTE, and the inferior area in group A were 1.14 ± 3.40 μm, −0.11 ± 3.20 μm, and −0.26 ± 1.23 μm, respectively (P ≥ 0.125). Although statistically significant change in the central-4 mm area was noted, the value was quite small (0.98 ± 1.67 μm) and was not higher than that in the other two groups (P = 0.003). For all three groups, the elevation remained stable or showed a backward change in the central annulus, while there was a small forward displacement in the 6-mm optical zone. In group A, changes in elevation values yielded negative statistical correlations with residual bed thickness and CCT (P ≤ 0.006) (except for the inferior area, the 4-mm and 6-mm optical zone).

Conclusions

With a strict preoperative assessment, SMILE achieved good safety and efficacy in correcting myopia in thin corneas and enabled a stable posterior corneal surface over a 3-year follow-up period.

Synopsis

Careful preoperative assessment and suitable surgical design should be taken to ensure posterior corneal stability after SMILE in thin corneas.

Ectasia After Corneal Refractive Surgery: A Systematic Review

INTRODUCTION

The incidence of ectasia following refractive surgery is unclear. This review sought to determine the worldwide rates of ectasia after photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), and small incision lenticule extraction (SMILE) based on reports in the literature.

METHODS

A systematic review was conducted according to modified Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Publications were identified by a search of eight electronic databases for relevant terms between 1984 and 2021. Patient characteristics and preoperative values including manifest refractive spherical refractive equivalent (MRSE), central corneal thickness (CCT), anterior keratometry, postoperative residual stromal bed (RSB), and percent tissue altered (PTA) were summarized. In addition, annual rates of each refractive surgery were determined, and incidence of post-refractive ectasia for each type was calculated using the number of ectatic eyes identified in the literature.

RESULTS

In total, 57 eyes (70 eyes including those with preoperative risk factors for ectasia) were identified to have post-PRK ectasia, while 1453 eyes (1681 eyes including risk factors) had post-LASIK ectasia, and 11 eyes (19 eyes including risk factors) had post-SMILE ectasia. Cases of refractive surgery performed annually were estimated as 283,920 for PRK, 1,608,880 for LASIK, and 96,750 for SMILE. Reported post-refractive ectasia in eyes without preoperative identifiable risk factors occurred with the following incidences: 20 per 100,000 eyes in PRK, 90 per 100,000 eyes in LASIK, and 11 per 100,000 eyes in SMILE. The rate of ectasia in LASIK was found to be 4.5 times higher than that of PRK.

CONCLUSION

Post-refractive ectasia occurs at lower rates in eyes undergoing PRK than LASIK. Although SMILE appears to have the lowest rate of ectasia, the number of cases already reported since its recent approval suggests that post-SMILE ectasia may become a concern. Considering that keratoconus is a spectrum of disease, pre-existing keratoconus may play a larger role in postoperative ectasia than previously accounted for in the literature.

Mechanical Properties of Bioengineered Corneal Stroma

For the majority of patients with severe corneal injury or disease, corneal transplantation is the only suitable treatment option. Unfortunately, the demand for donor corneas greatly exceeds the availability. To overcome shortage issues, a myriad of bioengineered constructs have been developed as mimetics of the corneal stroma over the last few decades. Despite the sheer number of bioengineered stromas developed , these implants fail clinical trials exhibiting poor tissue integration and adverse effects in vivo. Such shortcomings can partially be ascribed to poor biomechanical performance. In this review, existing approaches for bioengineering corneal stromal constructs and their mechanical properties are described. The information collected in this review can be used to critically analyze the biomechanical properties of future stromal constructs, which are often overlooked, but can determine the failure or success of corresponding implants.

Update and Review of Diagnosis and Management of Post-Refractive Surgery Ectasia

ABSTRACT

Post-Refractive Surgery Ectasia is a serious, sight-threatening, and highly - avoided complication seen after the following procedures: Laser in situ Keratomileusis, Photorefractive Keratectomy, Small Incision Lenticule Extraction, Radial and/or Arcuate Keratotomy. Specific risk factors may include age, corneal thickness, degree of refractive error, corneal topographic changes including irregular astigmatism, percent tissue ablation, and residual stromal bed. Biomarkers may be a new option to help indicate who is at greatest risk for ectasia. Visual aids including glasses or contacts lenses are often required to achieve optimal vision. Collagen crosslinking is the only treatment thought to stop progression of ectasia and prevent keratoplasty. Other surgical options may include topography-guided phototherapeutic keratectomy and intrastromal corneal ring segments. Ultimately an "ounce of prevention is a pound of cure" so careful preoperative screening and ultimately offering the safest and most effective treatments for patients is arguably the most important job of the refractive surgeon.

Factors associated with changes in posterior corneal surface following photorefractive keratectomy

PURPOSE

To identify factors associated with changes in the posterior cornea curvature following laser refractive surgery.

MATERIALS AND METHODS

This retrospective study included myopic astigmatic eyes that underwent PRK between January 2013 and December 2013 at Care-Vision Laser Centers, Tel-Aviv, Israel. The average posterior K was measured with the Sirius device at a radius of 3 mm from the center. The correlations between the surgical induced change in average posterior k and preoperative parameters such as central corneal thickness (CCT), refraction, Baiocchi Calossi Versaci index (BCV), ablation depth, percent tissue altered (PTA), and residual stroma bed (RSB) were analyzed.

RESULTS

A total of 280 eyes with a mean age of 24.9 ± 6.1 years (range, 18-47 years were included in this study. The mean PTA was 14.8 ± 6.0%. A greater change in posterior K was found in females (p = 0.01), smaller treatment zones of 6.0 mm (p = 0.02) and PTA > 20% (p < 0.001). A lower CCT (r =  - 0.24, p < 0.001), higher myopia (r =  - 0.34, p < 0.001), higher astigmatism (r =  - 0.17, p < 0.001), higher total BCV (r = 0.13, p = 0.03), lower back BCV (r =  - 0.12, p = 0.05), higher front BCV (r = 0.16, p = 0.01), higher posterior I-S ratio (r = 0.16, p = 0.01), and a lower RSB (r =  - 0.42, p < 0.001) were all significantly correlated with percentage of change in mean posterior K. In ranked stepwise multiple regression analysis, 26.2% of the variance of change in posterior K could be explained by the examined factors. The factors that remained significant were PTA (p < 0.001), CCT (p = 0.001), and posterior I-S ratio (p = 0.001). PTA alone accounted for 15% of the variance in posterior K changes in multivariate analysis.

CONCLUSIONS

Understanding of factors affecting a change in posterior cornea after refractive surgery may have an important practical value for the prevention of iatrogenic keratectasia. Preoperative CCT, posterior I-S ratio, and PTA were significantly associated with changes in posterior K after PRK. PTA was the strongest predictor of posterior corneal changes (p < 0.001).

Corneal densitometry in patients with keratoconus undergoing intrastromal Ferrara ring implantation

OBJECTIVE

Evaluation of central corneal densitometry changes following Ferrara corneal ring segment implantation in patients with keratoconus, especially the correlation between corneal densitometry and keratometry.

METHODS

Retrospective, non-comparative, interventional study based on the review of medical records of patients diagnosed with keratoconus who underwent Ferrara corneal ring segment implantation. Pre and post-operative corneal densitometry measurements obtained with Pentacam HR (Oculus, Wetzlar, Germany) were analyzed. The follow-up time was 3 months, and data comparison was made, using specific statistical analysis, with the data of 3 months postoperatively.

RESULTS

The study sample consisted of 43 eyes of 36 patients. The mean corrected visual acuity improved from 0.82 LogMAR preoperatively (SD ± 0.33) to 0.19 LogMAR (SD ± 0.13) postoperatively. The mean spherical equivalent varied from -4.63 (SD ± 3.94) preoperatively to -2.16 (SD ± 2.63) postoperatively. Asphericity varied from -0.69 (SD ± 0.32) preoperatively to -0.27 (SD ± 0.31) postoperatively. The mean maximum K was 54.01D (SD ± 3.38) preoperatively and 51.50D (SD ± 2.90) postoperatively. The mean anterior densitometric value was 18.26 (SD ± 2.03) preoperatively and 17.66 (SD ± 1.84) postoperatively.

CONCLUSION

Corneal densitometry is an interesting technology that should be studied in keratoconus patients. Our results suggest that the corneal densitometry in the cornea's anterior layer reduces after ICRS implantation and correlates with corneal keratometry. Further studies should be performed to increase the knowledge in this field.

Post-LASIK Ectasia Versus Keratoconus: An In Vivo Confocal Microscopy Study

PURPOSE

To examine and compare corneal cellular and subbasal nerve (SBN) characteristics in post-laser-assisted in situ keratomileusis ectasia (PLE) corneas, normal post-laser-assisted in situ keratomileusis corneas (PLC), keratoconus (KC) corneas, and normal virgin corneas (NC).

METHODS

In this cross-sectional comparative study, 18 PLE eyes of 11 patients, 18 PLC of 15 cases, 32 KC eyes of 32 patients, and 29 NC of 29 subjects were assessed using in vivo confocal microscopy. The density of the basal epithelial cell (BEC), anterior keratocyte, posterior keratocyte, and endothelial cell layers, as well as the characteristics of SBN fibers, was compared between the 4 groups.

RESULTS

The density of the BEC and anterior and posterior keratocyte layers was significantly lower in KC compared with NC (-650 ± 190, P = 0.013; -181 ± 39, P < 0.001; and -36 ± 11, P = 0.021, respectively). However, there was no significant difference between PLE and PLC regarding these parameters (all Ps ≥ 0.6). Mean SBN parameters, including central corneal nerve branch density, nerve fiber length, total branch density, and nerve fiber area, were significantly lower in KC compared with NC and in PLE compared with PLC (all Ps ≤ 0.021).

CONCLUSIONS

The pathophysiology of PLE seems to differ from KC. Apparent changes in the BEC and anterior and posterior keratocytes associated with KC were not observed in PLE. However, SBNs seem to be involved in both conditions.

Corneal Crosslinking for Progressive Keratoconus and Corneal Ectasia: Summary of US Multicenter and Subgroup Clinical Trials

Purpose

The multicenter studies reviewed were designed to evaluate the safety and efficacy of corneal collagen crosslinking (CXL) for the treatment of progressive keratoconus and corneal ectasia after laser refractive surgery. The results of these studies led to approval by the United States Food and Drug Agency for both conditions in 2016. This paper reviews these studies, as well as single-center substudies investigating other aspects of crosslinking outcomes.

Methods

As part of prospective, randomized, controlled clinical trials, the treatment group received standard CXL, and the sham control group received only riboflavin ophthalmic solution. The primary efficacy criterion was maximum keratometry (K_max) 1 year after CXL. Secondary outcomes were corrected distance visual acuity (CDVA) and uncorrected distance visual acuity (UDVA). Safety and adverse events were analyzed. In single-center substudies, corneal topography, ocular aberrations, corneal haze measurements, corneal thickness, corneal biomechanics, subjective visual function, and outcomes predictors were also investigated. This paper presents a general review of the design and outcomes of crosslinking in these studies.

Results

In the crosslinking treatment group, K_max flattened by 1.6 diopters (D) and 0.7 D in eyes with keratoconus and ectasia, respectively. In both studies, there was continued progression in the control group. The CDVA improved by an average of 5.7 logMAR letters (LL) in the keratoconus treatment group and by 5.0 LL in the ectasia group. In both studies, corneal haze was the most frequently reported crosslinking-related adverse finding. This was most prominent at 1 month and generally returned to baseline between 3 and 12 months. In general, corneal topography, ocular aberrations, and subjective visual function improved after crosslinking.

Conclusions

In the US multicenter trials, CXL was shown to be safe and effective in stabilizing K_max, CDVA, and UDVA in eyes with progressive keratoconus or corneal ectasia.

Translational Relevance

Corneal crosslinking was originally developed in the laboratory at the University of Dresden in the late 1990s. The combination of ultraviolet-A light and riboflavin was found to be the most effective of a number of different modalities tested to increase the biomechanical strength of the cornea. The clinical study design for the US multicenter clinical trials of crosslinking demonstrated the safety and effectiveness of this technique for treatment of progressive keratoconus and corneal ectasia, bringing this important advancement to patients in the United States.

Selective transepithelial ablation with simultaneous accelerated Corneal Cross-linking for corneal regularization of keratoconus: the STARE-X Protocol

Purpose

To evaluate the changes in refractive outcomes and corneal aberrations in central and paracentral keratoconus after Selective transepithelial topography-guided photorefractive keratectomy combined with Accelerated Corneal Collagen Cross-Linking (STARE-X).

Settings

Centro polispecialistico Mediterraneo, Siena Crosslinking Center and University of Messina (Italy).

Design

Prospective, interventional, multi-centric study.

Methods

One hundred eyes of 100 patients underwent STARE-X protocol. Patients were subdivided into 2 groups: Group 1 with cone located within the central 3-mm zone (50 eyes); and Group 2 (50 eyes) with cone located outside the central 3-mm zone. Follow-up was two years at least for all eyes. Outcome parameters included uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA). Corneal tomography and corneal wavefront aberrations were assessed and compared before and two years after the treatment.

Results

At 2 years UDVA, CDVA improved, as well as sphere, cylinder, K-max reduced after treatment in both groups (p<.001 respectively). Moreover, a statistically significant reduction was observed of total High-Order Aberrations Root Main Square (HOA RMS), Coma RMS and Spherical Aberration (SA RMS) in both groups (p<.001 respectively). However, CDVA improved more in Group 1 than in Group 2 (p<.02).

Conclusion

The STARE-X protocol demonstrated effective results in halting keratoconus progression and improving corneal regularity with a safe and effective profile. STARE-X improved both visual acuity and corneal aberration at 2 years. Longer follow-up studies are warranted to observe further long-term CXL flattening effect on the cone.

Fibril density reduction in keratoconic corneas

This study aims to estimate the reduction in collagen fibril density within the central 6 mm radius of keratoconic corneas through the processing of microstructure and videokeratography data. Collagen fibril distribution maps and topography maps were obtained for seven keratoconic and six healthy corneas, and topographic features were assessed to detect and calculate the area of the cone in each keratoconic eye. The reduction in collagen fibril density within the cone area was estimated with reference to the same region in the characteristic collagen fibril maps of healthy corneas. Together with minimum thickness and mean central corneal refractive power, the cone area was correlated with the reduction in the cone collagen fibrils. For the corneas considered, the mean area of keratoconic cones was 3.30 ± 1.90 mm². Compared with healthy corneas, fibril density in the cones of keratoconic corneas was lower by as much as 35%, and the mean reduction was 17 ± 10%. A linear approximation was developed to relate the magnitude of reduction to the refractive power, minimum corneal thickness and cone area (R² = 0.95, p < 0.001). Outside the cone area, there was no significant difference between fibril arrangement in healthy and keratoconic corneas. The presented method can predict the mean fibril density in the keratoconic eye's cone area. The technique can be applied in microstructure-based finite-element models of the eye to regulate its stiffness level and the stiffness distribution within the areas affected by keratoconus.

Quasi-Static Optical Coherence Elastography to Characterize Human Corneal Biomechanical Properties

Purpose

Quasi-static optical coherence elastography (OCE) is an emerging technology to investigate corneal biomechanical behavior in situations similar to physiological stress conditions. Herein OCE was applied to evaluate previously inaccessible biomechanical characteristics of human corneal tissue and to study the role of Bowman's layer in corneal biomechanics.

Methods

Human corneal donor buttons (n = 23) were obtained and Descemet's membrane and endothelium were removed. In 11 corneas, Bowman's layer was ablated by a 20 µm stromal excimer laser ablation. Buttons were mounted on an artificial anterior chamber and subjected to a pressure modulation from 10 to 30 mm Hg, and back to 10 mm Hg, in steps of 1 mm Hg. At each step, a spectral-domain optical coherence tomography scan was obtained. Displacements were analyzed by optical flow tracking, and strain over the entire stromal depth was retrieved from the phase gradient of the complex interference signal.

Results

During pressure increase, corneal tissue moved upward (486–585 nm/mm Hg) but did not fully recover (Δ= 2.63 to 8.64 µm) after pressure decrease. Vertical corneal strain distribution was negative in the anterior and positive in the posterior cornea, indicating simultaneous corneal compression and expansion, respectively. Bowman's layer caused minor localized differences in corneal strain distribution.

Conclusions

Corneal strain distribution is more complex than previously assumed, with a fundamental difference in mechanical response between the anterior and posterior stroma. Clinically, OCE technology might be used to monitor the progression of corneal ectatic diseases and to determine the success of corneal cross-linking.

Comparison of Corneal Biomechanical Properties between Post-LASIK Ectasia and Primary Keratoconus

Purpose

To compare the corneal biomechanical properties between post-LASIK ectasia and primary keratoconus.

Methods

A total of 42 eyes of 42 patients with matching age and central corneal thickness (CCT) were divided into two groups according to diagnosis of post-LASIK ectasia (PLE group; n = 21; age range: 22–47 years) and primary keratoconus (KC group; n = 21; age range: 21–47 years). The corneal biomechanical properties were assessed using Scheimpflug-based technology (Corvis ST; Oculus Optikgeräte, Wetzlar, Germany). The paired t-test and linear regression analysis were performed.

Results

The PLE group had significantly higher mean stiffness parameter at the first applanation (SP-A1; 76.65 ± 21.66 vs 52.72 ± 13.65, p ≤ 0.001) and mean stress-strain index (SSI) (SSI: 0.78 ± 0.16 versus 0.64 ± 0.12, p=0.001) than the KC group. SP-A1 was positively correlated with CCT in the PLE group (Pearson's r = 0.816, p ≤ 0.001), but not in the KC group (Pearson's r = −0.014, p=0.952). No statistical correlation was observed between SSI and CCT in either group (Pearson's r = 0.292, p=0.199, and Pearson's r = 0.004, p=0.985, respectively).

Conclusions

In our case series, KC manifested more severe than PLE in biomechanical properties. Since SSI measurements were independent of corneal thickness, it can be used for corneal biomechanical assessment.

Evaluating the Ectasia Risk Score System in Cancelled Laser In Situ Keratomileusis Candidates

Purpose

To evaluate the ectasia risk score system in cancelled laser in situ keratomileusis (LASIK) candidates at an academic hospital.

Methods

LASIK candidates who had been cancelled by a surgeon considering the patient age, preoperative central corneal thickness, residual stromal bed thickness, or preoperative manifest refraction spherical equivalent were retrospectively reviewed, and their Randleman ectasia risk score system score was calculated.

Results

The mean ectasia score of 194 eyes (97 patients) was 4.5 ± 2.67; 40 (20.6%), 46 (23.7%), and 108 (55.7%) eyes were classified as low-, moderate-, and high-risk eyes, respectively. The topography was abnormal in 69% of the patients. The mean manifest refraction spherical equivalent, central corneal thickness, and estimated residual stromal bed thickness were 4 (+0.50 to –15.50) diopters, 520 (439 to 608) µm, and 312.38 (61.5 to 424.12) µm, respectively. The main cause of cancellation in low- and moderate-risk patients (86 eyes) was the presence of unstable refractive error in the past year.

Conclusion

Although promising, some other criteria, such as stable refraction, should be added to this scoring system to achieve greater practicality since a main cause of cancelling LASIK candidates in this study was the presence of unstable refraction.

A Prospective Comparison of Wavefront-Guided LASIK versus Wavefront-Guided PRK After Previous Keratorefractive Surgery

Purpose

To compare the results of retreatment with wavefront-guided LASIK versus wavefront-guided PRK for residual refractive error following previous myopic keratorefractive surgery.

Methods

In this prospective study, 32 eyes of 28 patients after prior myopic keratorefractive surgery underwent retreatment with flap-lift wavefront-guided LASIK (n = 12) or wavefront-guided PRK (n = 20) for residual refractive error. Safety, efficacy, predictability, and wavefront outcomes were evaluated.

Results

At last follow-up, both LASIK and PRK retreatment resulted in similar improvement in visual acuity with respective mean ± standard deviation (SD) uncorrected distance visual acuity of −0.07 ± 0.11 logMAR and −0.06 ± 0.13 logMAR (p = 0.87). In the study, 16.7% of LASIK and 33.3% of PRK eyes gained one or more lines of best-corrected distance visual acuity (CDVA), while 16.7% and 9.5% of eyes lost one or more lines of CDVA with LASIK and PRK, respectively. One hundred % of LASIK eyes and 89.5% of PRK eyes were within ± 0.50 diopters of emmetropia. Wavefront analysis demonstrated similar reductions in total RMS error higher-order aberrations (p = 0.84) with no difference in coma, trefoil, or spherical aberration between eyes undergoing LASIK or PRK retreatment.

Conclusion

Wavefront-guided LASIK and wavefront-guided PRK following previous keratorefractive surgery demonstrate similar safety, efficacy, and predictability with comparable wavefront outcomes.

Simulation of the biomechanical effects induced by laser in situ keratomileusis (LASIK) for different levels of ablation in normal corneas

PURPOSE

To employ a finite element (FE) stress model to simulate laser in situ keratomileusis (LASIK) surgery and its biomechanical consequences.

METHODS

The basic geometrical model we used for the cornea was patient-specific on which we manually incorporated seven simulations: three simulations evaluating the effect of a 120, 140 and 180 μm flap (without ablation); three simulations evaluating ablation depths of 40, 80 and 120 μm (with a 120 μm flap); and one control model, without any simulated surgical intervention.

RESULTS

In all simulations, stress values were greatest in the centre of the cornea. Furthermore, when comparing the different treatments, stress values were highest in the cornea with the deepest ablation, and were lowest in the non-treated cornea. Specifically, peak effective stresses were 0.031, 0.028 and 0.025 MPa in 120, 80 and 40 µm ablation depths, respectively.

CONCLUSIONS

In our model, the depth of tissue penetration using ablation or flap creation was correlated with tissue loads-the thinner the residual stromal bed is, the greater are the stresses occurring as a result of the same IOP.

RELEVANCE

We based our model geometry on patient specific scans, allowing for customisation of the treatment to the patient's corneal structure.

Longitudinal evaluation of posterior corneal power by anterior segment optical coherence tomography 18 months following photorefractive keratectomy

PURPOSE

To investigate the change in anterior, posterior, and net corneal power more than 18 months after photorefractive keratectomy (PRK) by RTVue anterior segment optical coherence tomography (OCT).

SETTING

Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran.

DESIGN

Prospective observational study.

METHODS

PRK was performed using Technolas TENEO 317 laser platform. Anterior, posterior, and net corneal power was measured by the RTVue-XR anterior segment OCT system with the Pachymetry + Cpwr scan pattern at baseline and months 1, 3, 6, 12, 18, and more than 18 (up to 27) after PRK.

RESULTS

Three hundred twenty-six eyes of 163 patients (61 men [37.4%], 102 women [62.6%]; mean age 29.71 years; range 18.5 to 46.5 years) were enrolled in this study. Mean preoperative spherical equivalent was -3.15 ± 1.50 diopter (D) (range -8.37 to -0.62 D). The mean change in net corneal power was 3.052 D, 3.281 D, 3.324 D, 3.114 D, 3.446 D, and 3.972 D at months 1, 3, 6, 12, 18, and more than 18 postoperatively compared with baseline, respectively (P < .001 for all comparisons). The mean change in posterior corneal power at postoperative visits compared with baseline was not statistically significant (P > .1) except for 1 month postoperatively, which increased by 0.13 D (P < .001). Changes in posterior corneal power were not correlated with any of the preoperative clinical and Scheimpflug variables.

CONCLUSIONS

Posterior corneal power did not change for more than 18 months after PRK, except for an early small increase at 1 month postoperatively.

Advanced Surface Ablation in Mild (Fruste) Keratoconus: A Case Report

Corneal ectasia is a complication of refractive surgery, and keratoconus is a contraindication to this type of procedure. Surface ablation may be an option for selected cases of mild keratoconus, with patient education being fundamental to this treatment as well as a complete evaluation of the cornea and optical properties of the patient. Here we report the clinical outcome of a patient 15 years after advanced surface ablation in a case of mild (fruste) keratoconus.

Evaluation of new Corvis ST parameters in normal, Post-LASIK, Post-LASIK keratectasia and keratoconus eyes

The aim of this study was to evaluate the distribution of new Corneal Visualisation Scheimpflug Technology (Corvis ST) parameters in normal, Post-laser in situ keratomileusis (LASIK), Post-LASIK keratectasia (KE) and keratoconus (KC) eyes, and explore the diagnostic ability of these parameters in distinguishing KE from LASIK eyes. Twenty-three normal eyes, 23 LASIK eyes, 23 KE eyes and 23 KC eyes were recruited in this study. The following new Corvis ST parameters were measured: Max Inverse Radius, deformation amplitude (DA) Ratio Max [2 mm], Pachy Slope, DA Ratio Max [1 mm], Ambrosio’s relational thickness horizontal (ARTh), Integrated Radius, stiffness parameter at first applanation (SP-A1) and Corvis biomechanical index (CBI). The general linear model, linear regression model, relation analysis and receiver operating characteristic (ROC) curve were performed. The Max Inverse Radius, DA Ratio Max [2 mm], Pachy Slope, DA Ratio Max [1 mm], Integrated Radius and CBI in LASIK eyes, KE eyes and KC eyes were higher than in normal eyes, while the ARTh and SP-A1 parameters were lower than in normal eyes. The KE eyes had higher Max Inverse Radius, DA Ratio Max [2 mm], Pachy Slope, DA Ratio Max [1 mm], Integrated Radius, and lower SP-A1 value than LASIK eyes (all P < 0.05). The central corneal thickness was related to the Pachy Slope (r = −0.485), ARTh (r = −0.766), SP-A1 (r = 0.618) in KE eyes (all P < 0.05). The area under the ROC curve of Integrated Radius, Max Inverse Radius, DA Ratio Max [2 mm] and SP-A1 were above 0.800 in identifying KE from LASIK eyes. Thus, the new Corvis ST parameters were different between LASIK and KE eyes, suggesting that they might be helpful in distinguishing KE eyes from LASIK eyes. However, a further multi-center and large sample study is necessary to confirm these findings.

Myopic Laser-Assisted Subepithelial Keratectomy (LASEK) outcomes using three different excimer laser platforms: a retrospective observational study

Background

To compare the visual and refractive outcomes after myopic LASEK using three different excimer lasers and standardized surgical and mitomycin C (MMC) application protocols.

Methods

In this retrospective, observational cohort study, we examined 122 eyes treated with Allegretto, 135 eyes treated with Esiris and 137 eyes treated with Technolas excimer lasers. All eyes were treated under the same surgical protocol, and a standardized MMC dosage was used. The three groups were refraction-matched, and both visual and refractive outcomes were evaluated at 1 and 7 days and 1 and 3 months after surgery.

Results

At 3 months postsurgery, Allegretto provided significantly better outcomes than Esiris and Technolas in terms of postoperative uncorrected distance visual acuity (UDVA) (1.11 ± 0.2 vs 1.01 ± 0.2 vs 0.98 ± 0.2) (P = 0.0001), corrected distance visual acuity (CDVA) (1.13 ± 0.2 vs 1.10 ± 0.1 vs 1.04 ± 0.2) (P = 0.0001), residual sphere (− 0.01 ± 0.2 vs + 0.29 ± 0.7 vs + 0.27 ± 0.6) (P = 0.0001), and efficacy index (0.99 ± 0.2 vs 0.90 ± 0.2 vs 0.91 ± 0.2) (P = 0.0004).

Conclusions

We found slightly better visual and refractive outcomes in the Allegretto group at 3 months post-op after LASEK with MMC to correct myopia.

[Search for genetic markers for precise diagnostics of keratoconus]

Keratoconus is a chronic disorder of the cornea, characterized by its progressive thinning, stretching, and conical protrusion. Diagnostics of subclinical keratoconus, as well as its early stages (forme fruste), is a complex problem. The presence of these forms of keratoconus in a patient is one of the reasons for the development of keratectasia after laser refractive surgery. Currently, the role of genetic factors in keratoconus development has been proven. This indicates the possibility of diagnostics of subclinical and forme fruste keratoconus using genetic markers. Knowledge about the patient's genetic susceptibility to keratoconus would allow correcting the tactics of treatment of refractive anomalies and avoiding serious side effects. The studies of causal mutations indicate the genetic heterogeneity of keratoconus, which complicates the development of a diagnostic panel. Selection of candidate variants from the currently known ones based on clear criteria may be one of the approaches for diagnostic markers search. In this review, we have analyzed articles on keratoconus markers in order to form a list of candidate variants for genotyping in the Russian population. The selection criteria took into account the complexes of symptoms in which a marker was found, populations in which a particular marker was investigated, the presence and results of replication studies. The analysis included markers in VSX1, SOD1, ZEB1, LOX, CAST, DOCK9, TGFBI, HGF, MAP3K19, KCND3, COL4A3, COL4A4, COL5A1, FNDC3B, FOXO1, BANP-ZNF469, MPDZ-NF1B, WNT10A genes. Based on the results of the analysis, the following candidate variants were selected for genotyping in the Russian population of patients with keratoconus: rs1536482 and rs7044529 in the COL5A1 gene, rs5745752 and rs2286194 in the HGF gene, rs4954218 in the MAP3K19 gene, rs4839200 near the KCND3 gene, rs2721051 near the FOXO1 gene, rs1324183 between the MPDZ and the NF1B genes, and rs121908120 in the WNT10A gene.

Spatially-resolved Brillouin spectroscopy reveals biomechanical abnormalities in mild to advanced keratoconus in vivo

Mounting evidence connects the biomechanical properties of tissues to the development of eye diseases such as keratoconus, a disease in which the cornea thins and bulges into a conical shape. However, measuring biomechanical changes in vivo with sufficient sensitivity for disease detection has proven challenging. Here, we demonstrate the diagnostic potential of Brillouin light-scattering microscopy, a modality that measures longitudinal mechanical modulus in tissues with high measurement sensitivity and spatial resolution. We have performed a study of 85 human subjects (93 eyes), consisting of 47 healthy volunteers and 38 keratoconus patients at differing stages of disease, ranging from stage I to stage IV. The Brillouin data in vivo reveal increasing biomechanical inhomogeneity in the cornea with keratoconus progression and biomechanical asymmetry between the left and right eyes at the onset of keratoconus. The receiver operating characteristic analysis of the stage-I patient data indicates that mean Brillouin shift of the cone performs better than corneal thickness and maximum curvature respectively. In conjunction with morphological patterns, Brillouin microscopy may add value for diagnosis of keratoconus and potentially for screening subjects at risk of complications prior to laser eye surgeries.

Transepithelial photorefractive intrastromal corneal crosslinking versus photorefractive keratectomy in low myopia

PURPOSE

To compare the outcomes of transepithelial photorefractive intrastromal corneal crosslinking (CXL) and photorefractive keratectomy (PRK) in eyes with low myopia.

SETTING

Purpan Hospital, Toulouse, France.

DESIGN

Prospective case series.

METHODS

Myopic patients with a manifest refraction spherical equivalent (MRSE) of -1.00 to -2.50 diopters (D) and a cylindrical component of plano to -0.75 D were included. The dominant eye had PRK (PRK eyes). The nondominant eye had transepithelial photorefractive intrastromal CXL with riboflavin (ParaCel Part 1 and 2), 30 mW/cm² pulsed ultraviolet-A irradiation centered on the pupil (Mosaic System) for 16 minutes and 40 seconds, and a supplemental oxygen delivery mask (CXL eyes). The primary outcome measure was the change in the MRSE. Other outcome measures were the uncorrected (UDVA) and corrected (CDVA) distance visual acuities, mean keratometry, and endothelial cell count (ECC) over a 6-month follow-up. Adverse events were assessed.

RESULTS

Nineteen patients were included. By 6 months, the mean MRSE had decreased by 0.72 D ± 0.42 (SD) in CXL eyes and by 1.35 ± 0.46 D in PRK eyes (P < .001). The mean change in UDVA was -0.35 ± 0.21 logarithm of the minimum angle of resolution (logMAR) in CXL eyes and -0.66 ± 0.19 logMAR in PRK eyes (P < .001). No complications were reported. The change in the ECC and CDVA was not statistically significant.

CONCLUSIONS

Photorefractive keratectomy provided better visual and refractive outcomes than transepithelial photorefractive intrastromal CXL. Transepithelial photorefractive intrastromal CXL, however, showed the potential refractive effect of CXL but with a limited magnitude of myopic correction.

Incidence and Clinical Characteristics of Post LASIK Ectasia: A Review of over 30,000 LASIK Cases

PURPOSE

To report the incidence of postoperative ectasia after laser in situ keratomileusis (LASIK).

METHODS

A retrospective case review of 30,167 eyes (16,732 patients) was conducted following LASIK between August 2007 and August 2015. The follow-up was between 2 and 8 years. Tomography was performed after 2 years postop. After identifying cases of ectasia, the charts of these patients were examined to identify any common factors that may have predisposed them to develop ectasia.

RESULTS

Ten eyes of seven patients developed post-LASIK ectasia. Eight eyes had been treated for myopia and myopic astigmatism, two eyes for mixed astigmatism. There were no cases of ectasia after LASIK for hyperopia. All 10 cases of ectasia had a flap that was created using the Moria M2 mechanical microkeratome (average flap thickness 118.15 ± 12.88 µm) and refractive error corrected using the Wavelight Allegretto excimer laser. Retrospectively, most prevalent risk factors were thin cornea (≤ 500 µm, 50% of cases), anterior topographic map irregularities (e.g., asymmetric bow tie, 40% of cases), Ectasia Risk Score > 3 (40% of cases), percent tissue thickness alteration ≥ 40% (20% of cases) and low residual stromal bed (≤ 300 µm, 30% of cases). One eye had no identifiable risk factors. In the retrospective chart review 14.97% (4,506) of all the eyes had similar risk factors to the cases that went on to develop ectasia.

CONCLUSION

The incidence of ectasia was 0.033% over 8 years. The incidence could be higher as some cases may destabilize beyond this period and some patients were lost to follow-up asymptomatic of any clinical signs. Other intrinsic factors may trigger the development of post LASIK ectasia. The current widely accepted risk factors are not sufficiently rigorous for screening out potential ectasia from developing after LASIK. There is a need to augment accuracy with higher sensitivity and specificity.

Tuck-in Lamellar keratoplasty with an lenticule obtained by small incision lenticule extraction for treatment of Post- LASIK Ectasia

Corneal ectasia is a rare but serious post-operative complication of LASIK. Our main aim was to describe and evaluate the efficacy and safety of tuck-in lamellar keratoplasty with an lenticule obtained by SMILE for treatment of Post LASIK Ectasia. Tuck-in lamellar keratoplasty was performed on three post-LASIK cornea ectasia patients (three eyes) with central corneal thickness less than 400 µm. Each patient was monitored for at least 12 months. Our primary outcomes measured pre and post-operatively included: Anterior segment optical coherence tomography(AS-OCT), corneal topography and monitored by slit-lamp microscopy. The mean total corneal thickness preoperatively and 1 day, 1 month, 3 months and 12 months post-op were 360.00 ± 32.07 µm, 590.00 ± 10.00 µm, 536.67 ± 11.54 µm, 523.33 ± 37.85 µm, 466.67 ± 41.63 µm. The mean lenticule implanted 1 day, 1 month, 3 months and 12 months post-op were 173.33 ± 41.63 µm,136.67 ± 25.16 µm, 133.33 ± 40.41 µm, 130.00 ± 17.32 µm. There was no evidence of immune rejection or other complications. Tuck-in lamellar keratoplasty with an lenticule obtained by SMILE seems to be a safe and alternative surgical approach in the treatment of post - LASIK cornea ectasia, especially for severe cases with cornea thickness less than 400 μm.

U.S. Multicenter Clinical Trial of Corneal Collagen Crosslinking for Treatment of Corneal Ectasia after Refractive Surgery

PURPOSE

To evaluate the safety and efficacy of corneal collagen crosslinking (CXL) for the treatment of corneal ectasia after laser refractive surgery.

DESIGN

Prospective, randomized, multicenter, controlled clinical trial.

PARTICIPANTS

One hundred seventy-nine subjects with corneal ectasia after previous refractive surgery.

METHODS

The treatment group underwent standard CXL, and the sham control group received riboflavin alone without removal of the epithelium.

MAIN OUTCOME MEASURES

The primary efficacy criterion was the change over 1 year of topography-derived maximum keratometry (K), comparing treatment with control groups. Secondary outcomes evaluated were corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA), manifest refraction spherical equivalent, endothelial cell count, and adverse events.

RESULTS

In the crosslinking treatment group, the maximum K value decreased by 0.7 diopters (D) from baseline to 1 year, whereas there was continued progression in the control group (1.3 D difference between treatment and control, P < 0.0001). In the treatment group, the maximum K value decreased by 2.0 D or more in 14 eyes (18%) and increased by 2.0 D or more in 3 eyes (4%). The CDVA improved by an average of 5.0 logarithm of the minimum angle of resolution (logMAR) letters. Twenty-three eyes (32%) gained and 3 eyes (4%) lost 10 or more logMAR letters. The UDVA improved 4.5 logMAR letters. Corneal haze was the most frequently reported crosslinking-related adverse finding.

CONCLUSIONS

Corneal collagen crosslinking was effective in improving the maximum K value, CDVA, and UDVA in eyes with corneal ectasia 1 year after treatment, with an excellent safety profile. CXL is the first approved procedure to diminish progression of this ectatic corneal process.

In vivo confocal microscopy and tear cytokine analysis in post-LASIK ectasia

AIM

Corneal keratectasia is one of the complications associated with laser in situ keratomileusis (LASIK) that results in vision impairment. The pathogenesis of post-LASIK ectasia (PLE) remains underexplored. We report the tear cytokine profile and in vivo confocal microscopy (IVCM) findings in eyes with PLE.

METHODS

This retrospective study included age-matched 7 (14 eyes) post-LASIK controls (PLCs) and 6 (12 eyes) PLE subjects. Corneal topography was used to categorise the subjects into PLC and PLE groups. Ocular Surface Disease Index (OSDI) scores obtained were based on standard questionnaire and IVCM images were used to determine corneal dendritic cells density (DCD) and sub-basal nerve plexus morphology. Inflammatory cytokines/chemokines in the tears were quantified using flow cytometry based cytometric bead array.

RESULTS

Pentacam-based scores, OSDI scores and corneal DCD were significantly (p<0.05) higher in patients with PLE compared with PLC. Discomfort-related subscale of OSDI score exhibited a positive correlation with total corneal DCD in the PLE cohort. The fold difference of chemokine (C-C motif) ligand/monocyte chemotactic protein-1 (CCL2/MCP1) (3.4±0.6) was found to be significantly (p<0.05) higher in the PLE cohorts and a positive correlation between CCL2/MCP1 levels and total corneal DCD was also observed in the PLE cohort.

CONCLUSION

The current study found a significant difference in the tear film cytokine profile between normal and PLE eyes. Presence of increased corneal dendritic cells and altered tear cytokines suggests an ongoing inflammatory response in PLE.