Unilateral Granular Type 2 Corneal Dystrophy With Exacerbation After LASIK

PURPOSE

The aim of this study was to report a case of unilateral granular corneal dystrophy type 2 (GCD2) with exacerbation after bilateral laser in situ keratomileusis (LASIK).

METHODS

Clinical evaluation, Scheimpflug imaging, anterior segment optical coherence tomography (AS-OCT), cytology, and genetic testing were used to confirm the diagnosis of unilateral GCD2 with exacerbation after bilateral LASIK. Detailed literature review for possible unilateral GCD2 presentations was performed.

RESULTS

A 54-year-old White woman presented with blurred vision in her left eye and a history of bilateral LASIK performed 8 years before. Examination revealed dense opacities in the left cornea only, which were confirmed to be confined to the LASIK interface and adjacent corneal stromal tissue, as determined by AS-OCT. The patient underwent flap lift, interface debris removal, and stromal bed phototherapeutic keratectomy. Cytological analysis showed eosinophilic corneal stromal deposits that stained with trichrome stain and were congophilic on Congo red stain. Genetic testing was positive for heterozygous GCD2 transforming growth factor β-induced gene ( TGFBI ), c.371G>A, p.R124H mutation. There were no opacities identifiable in the right eye on serial slit-lamp examination, Scheimpflug imaging, or OCT imaging at 4 or 8 years after bilateral LASIK. Literature review failed to identify any previous reports of unilateral GCD2.

CONCLUSIONS

This is the first known reported case of unilateral granular corneal dystrophy type 2. LASIK is contraindicated in eyes with corneal stromal dystrophies related to mutations in TGFBI as both flap creation and laser ablation can exacerbate visually significant opacity formation. Scheimpflug and AS-OCT imaging are useful to identify opacities in GCD2.

Subclinical Keratoconus Detection and Characterization Using Motion-Tracking Brillouin Microscopy

PURPOSE

To characterize focal biomechanical alterations in subclinical keratoconus (SKC) using motion-tracking (MT) Brillouin microscopy and evaluate the ability of MT Brillouin metrics to differentiate eyes with SKC from normal control eyes.

DESIGN

Prospective cross-sectional study.

PARTICIPANTS

Thirty eyes from 30 patients were evaluated, including 15 eyes from 15 bilaterally normal patients and 15 eyes with SKC from 15 patients.

METHODS

All patients underwent Scheimpflug tomography and MT Brillouin microscopy using a custom-built device. Mean and minimum MT Brillouin values within the anterior plateau region and anterior 150 μm were generated. Scheimpflug metrics evaluated included inferior-superior (IS) value, maximum keratometry (Kmax), thinnest corneal thickness, asymmetry indices, Belin/Ambrosio display total deviation, and Ambrosio relational thickness. Receiver operating characteristic (ROC) curves were generated for all Scheimpflug and MT Brillouin metrics evaluated to determine the area under the ROC curve (AUC), sensitivity, and specificity for each variable.

MAIN OUTCOME MEASURES

Discriminative performance based on AUC, sensitivity, and specificity.

RESULTS

No significant differences were found between groups for age, sex, manifest refraction spherical equivalent, corrected distance visual acuity, Kmax, or KISA% index. Among Scheimpflug metrics, significant differences were found between groups for thinnest corneal thickness (556 μm vs. 522 μm; P < 0.001), IS value (0.29 diopter [D] vs. 1.05 D; P < 0.001), index of vertical asymmetry (IVA; 0.10 vs. 0.19; P < 0.001), and keratoconus index (1.01 vs. 1.05; P < 0.001), and no significant differences were found for any other Scheimpflug metric. Among MT Brillouin metrics, clear differences were found between control eyes and eyes with SKC for mean plateau (5.71 GHz vs. 5.68 GHz; P < 0.0001), minimum plateau (5.69 GHz vs. 5.65 GHz; P < 0.0001), mean anterior 150 μm (5.72 GHz vs. 5.68 GHz; P < 0.0001), and minimum anterior 150 μm (5.70 GHz vs. 5.66 GHz; P < 0.001). All MT Brillouin plateau and anterior 150 μm mean and minimum metrics fully differentiated groups (AUC, 1.0 for each), whereas the best performing Scheimpflug metrics were keratoconus index (AUC, 0.91), IS value (AUC, 0.89), and IVA (AUC, 0.88).

CONCLUSIONS

Motion-tracking Brillouin microscopy metrics effectively characterize focal corneal biomechanical alterations in eyes with SKC and clearly differentiated these eyes from control eyes, including eyes that were not differentiated accurately using Scheimpflug metrics.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

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.

The Most Cited Modern Articles in Refractive Surgery (2010-2020)

PURPOSE

To provide a comprehensive analysis of the most highly cited modern articles in refractive surgery, those published between 2010 and 2020, and compare these results to a list of the most highly cited articles in refractive surgery from all timepoints.

METHODS

The Scopus database was searched for articles pertaining to refractive surgery using multiple search terms to identify the top 100 most cited articles in refractive surgery published between 2010 and 2020. Articles were reviewed for relevance and ranked based on total citations accrued.

RESULTS

The 100 most cited modern articles in refractive surgery were identified. The article with the most citations by Sekundo et al has garnered nearly 600 citations to date. Almost all articles (88%) included in the top 100 had 200 or more citations. Intraocular lens (34 articles), keratorefractive lenticule extraction (ie, small incision lenticule extraction) (27 articles), and laser in situ keratomileusis (17 articles) were the predominant topics. Aarhus University in Denmark generated the most articles (5), whereas numerous articles originated from multiple countries, including the United States (16), United Kingdom (10), France (8), Spain (8), China (7), and Germany (7).

CONCLUSIONS

This list provides a comprehensive assessment of the most cited modern articles in refractive surgery and demonstrates key focuses and trends in the field over the past decade. Intraocular lens and keratorefractive lenticule extraction were the primary topics. There was a broader representation of procedures, topics, authors, and country of origin as compared to prior work. [J Refract Surg. 2023;39(11):784-790.].

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.

Quantifying Corneal Topographic Astigmatism (CorT Total) in Keratoconic Eyes

PURPOSE

To determine optimal corneal regions from which to derive corneal topographic astigmatism (CorT) in kerato-conic eyes.

METHODS

In this retrospective study, potential measures of corneal astigmatism are calculated from raw total corneal power data (179 eyes from 124 patients) from a corneal tomographer. The measures are derived from annular corneal regions varying in both extent and center position, and evaluated according to the variability of the ocular residual astigmatism (ORA) in the cohort. This variability is quantified by the ORArms, which is the root-mean-squared distance of the ORAs from their summated vector mean in double angle space. The lower the ORArms, the better the corneal astigmatism measure corresponds to manifest refractive cylinder.

RESULTS

Corneal astigmatism measures derived from regions centered on corneal vertex had ORArms values (mild: 1.07 diopters [D], moderate: 1.61 D, severe: 2.65 D) as low or lower than other measures derived from regions centered on thinnest point, corneal apex (front or back), or pupil center. Corneal astigmatism measures derived from a region centered 30% of the way toward thinnest point from corneal vertex appeared to have even lower ORArms values (mild: 1.05 D, moderate: 1.45 D, severe: 2.56 D). None of the corneal astigmatism measures corresponded closely with manifest refractive cylinder for severe keratoconus (ORArms > 2.50 D).

CONCLUSIONS

For keratoconic eyes, the CorT should be derived from an annular region centered 30% of the way toward thinnest point from corneal vertex, although when the keratoconus is mild, a standard corneal-vertex-centered CorT performs just as well. [J Refract Surg. 2023;39(3):206-213.].

The Most Cited Articles and Authors in Refractive Surgery

PURPOSE

To provide a comprehensive analysis of the most highly cited articles and authors in refractive surgery.

METHODS

The Scopus database was searched for articles pertaining to refractive surgery using multiple search terms to identify the top 100 most cited articles in refractive surgery. A publicly available database of more than 100,000 scientists that provides standardized information on multiple variables resulting in a composite indicator (C score) was searched to identify refractive surgery authors. A refractive surgery-specific composite score was created using only the authors' publications that were directly related to refractive surgery.

RESULTS

The 100 most cited articles and 40 refractive surgery authors with the highest ranked C score were identified. The article with the most citations by Trokel et al has garnered nearly 800 citations to date. All articles included in the top 100 had 200 or more citations. The peak publication years were 1998 to 2001. Laser in situ keratomileusis (22), photorefractive keratectomy (18), and postoperative corneal ectasia and/or corneal biomechanics (16) were the most represented topics. Emory University generated the most articles (7) and the majority of publications (48%) originated in the United States. Steven E. Wilson, MD, had the highest refractive C score and Jorge L. Alió, MD, PhD, had the most refractive surgery articles and citations. Among all authors listed, the average number of refractive surgery publications was 97, with 35% of the group having more than 100 refractive surgery articles published. All authors on the list had more than 2,000 citations for their refractive surgery articles, whereas 38% had 4,000 or more citations.

CONCLUSIONS

This list provides a comprehensive assessment of the most cited articles and authors in refractive surgery and demonstrates key focuses and trends in the field over time. [J Refract Surg. 2023;39(2):78-88.].

Motion-tracking Brillouin microscopy for in-vivo corneal biomechanics mapping

Corneal biomechanics play a critical role in maintaining corneal shape and thereby directly influence visual acuity. However, direct corneal biomechanical measurement in-vivo with sufficient accuracy and a high spatial resolution remains an open need. Here, we developed a three-dimensional (3D) motion-tracking Brillouin microscope for in-vivo corneal biomechanics mapping. The axial tracking utilized optical coherence tomography, which provided a tracking accuracy better than 3 µm. Meanwhile, 10 µm lateral tracking was achieved by tracking pupils with digital image processing. The 3D tracking enabled reconstruction of depth-dependent Brillouin distribution with a high spatial resolution. This superior technical performance enabled the capture of high-quality mechanical mapping in vivo even while the subject was breathing normally. Importantly, we improved Brillouin spectral measurements to achieve relative accuracy better than 0.07% verified by rubidium absorption frequencies, with 0.12% stability over 2000 seconds. These specifications finally yield the Brillouin measurement sensitivity that is required to detect ophthalmology-relevant corneal biomechanical properties.

The Impact of Repetitive and Prolonged Eye Rubbing on Corneal Biomechanics

PURPOSE

To evaluate the effect of simulated repetitive eye rubbing on the corneal biomechanics of porcine eyes using an ex vivo model system.

METHODS

The average rubbing force that patients with keratoconus apply to their eyelids was previously determined. Fresh porcine eyes with eyelids were either exposed to 10,500 rub cycles from a custom-built eye rubbing machine that rubbed with a similar force to knuckle human eye rubbing (n = 33) or no rubbing at all (control; n = 37). A total of 10,500 rubs are equivalent to 1 year of rubbing six times daily, five movements per rub. The corneal biomechanical properties of these eyes were then tested by measuring the elastic modulus of 5-mm strips.

RESULTS

The elastic modulus at the range of 1% and 5% of strain was 1.219 ± 0.284 and 1.218 ± 0.304 N/mm² in the eye rubbing group and the no-rub control group, respectively. Corneal stiffness was similar in both groups (P = .984).

CONCLUSIONS

The threshold to induce biomechanical changes (purely by eye rubbing) must be higher than 10,500 rubbing movements, suggesting that occasional eye rubbing may not affect corneal biomechanics in normal eyes, and likely only triggers keratoconus progression in predisposed corneas. Further in vivo studies assessing the impact eye rubbing has on inflammatory activity and the biomechanical properties of weakened corneas is warranted. [J Refract Surg. 2022;38(9):610-616.].

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.

Cogan syndrome masquerading as corneal ectasia

Purpose

To report a case of Cogan syndrome that presented with the appearance of bilateral asymmetric corneal ectasia on Scheimpflug tomography.

Methods

Case Report and Literature Review.

Results

A 43-year-old woman previously diagnosed with keratoconjunctivitis sicca and presumed keratoconus presented with seven months of episodic eye pain and progressive bilateral blurry vision with new onset bilateral monocular diplopia. Review of symptoms were significant for tinnitus, vertigo, and sensorineural hearing loss that began many months after her initial presentation for visual symptoms. Scheimpflug tomography showed asymmetric focal steepening on anterior curvature with corresponding focal total corneal thinning, focal posterior elevation, and abnormal ARTMax (205 OD, 103 OS) and BAD-D (2.75 OD, 5.6 OS) values. Clinical examination was notable only for faint anterior corneal stromal inflammation without neovascularization, but there was significant corresponding focal hyperreflectivity on anterior segment optical coherence tomography (OCT) examination with focal epithelial hypertrophy rather than thinning. Given the combined findings of interstitial keratitis and sensorineural hearing loss the patient was diagnosed with Cogan syndrome. She responded well to topical steroids and systemic immunosuppressive therapy, with near resolution of her abnormal topographic and tomographic findings and resolution of monocular diplopia in both eyes.

Conclusions

Cogan syndrome should be suspected for any patient with corneal stromal findings and associated with vertigo and/or hearing loss. Anterior segment optical coherence tomography (OCT) can distinguish between ectatic and inflammatory diseases and may help make the appropriate diagnosis in subtle cases.

High-Fluence Accelerated Epithelium-Off Corneal Cross-Linking Protocol Provides Dresden Protocol-Like Corneal Strengthening

Purpose

To assess whether optimized technical settings for accelerated epithelium-off corneal cross-linking may lead to increases in biomechanical stiffness similar to the benchmark 30-minute epithelium-off Dresden protocol.

Methods

Three-hundred porcine eyes were divided equally into six groups for analysis. All samples underwent epithelial debridement and soaking with 0.1% iso-osmolar riboflavin solution for 20 minutes. Corneal cross-linking (CXL) was performed using epithelium-off protocols varying in acceleration and total fluence (intensity in mW/cm² * time in minutes, total fluence in J/cm²): standard (S)-CXL (3*30, 5.4), accelerated (A)-CXL (9*10, 5.4), A-CXL (9*13'20″, 7.2), A-CXL (18*6'40″, 7.2), and A-CXL (18*9'15″, 10). Control corneas were not irradiated. The elastic modulus of 5-mm wide corneal strips was measured as an indicator of corneal stiffness.

Results

All irradiated groups had significantly higher elastic modulus than controls (P < 0.05), with a stiffening effect of 133% S-CXL (3*30, 5.4), 122% A-CXL (9*10, 5.4), 120% A-CXL (9*13'20″, 7.2), 114% A-CXL (18*6'40″, 7.2) and 149% A-CXL (18*9'15″, 10). The high-fluence accelerated epithelium-off protocol (18*9'15″, 10) showed the highest stiffening effect. Elastic modulus at 5% strain (1%-5% strain) showed significant differences between A-CXL (18*9'15″, 7.2) and three other accelerated protocols: A-CXL (9*10, 5.4; P = 0.01), A-CXL (9*13'20″, 7.2; P = 0.003), and A-CXL (18*6'40″, 10; P = 0.0001).

Conclusions

An accelerated high-fluence epithelium-off CXL protocol (18 mW/cm² for 9'15″) was identified to provide a significantly greater stiffening effect than any other accelerated protocols and is indistinguishable from the Dresden protocol, with accelerating irradiation times ranging from 30 to 9 minutes; by combining gentle acceleration with higher fluence, such a protocol does not require supplemental oxygen.

Translational Relevance

This A-CXL (18*9'15″, 10) protocol has the potential to become a new standard in epithelium-off CXL, delivering Dresden protocol-like strengthening over a shorter period.

Individualized Corneal Cross-linking With Riboflavin and UV-A in Ultrathin Corneas: The Sub400 Protocol

PURPOSE

To determine whether corneal cross-linking (CXL) with individualized fluence ("sub400 protocol") is able to stop keratoconus (KC) progression in ultrathin corneas with 12-month follow-up.

DESIGN

Retrospective, interventional case series.

METHODS

Thirty-nine eyes with progressive KC and corneal stromal thicknesses from 214 to 398 μm at the time of ultraviolet irradiation were enrolled. After epithelium removal, ultraviolet irradiation was performed at 3 mW/cm² with irradiation times individually adapted to stromal thickness. Pre- and postoperative examinations included corrected distance visual acuity (CDVA), refraction, Scheimpflug, and anterior segment optical coherence tomography imaging up to 12 months after CXL. Outcome measures were arrest of KC progression at 12 months postoperatively and stromal demarcation line (DL) depth.

RESULTS

Thirty-five eyes (90%) showed tomographical stability at 12 months after surgery. No eyes showed signs of endothelial decompensation. A significant correlation was found between DL depth and irradiation time (r = +0.448, P = .004) but not between DL depth and change in K_max (r = -0.215, P = .189). On average, there was a significant change (P < .05) in thinnest stromal thickness (-14.5 ± 21.7 μm), K_max (-2.06 ± 3.66 D) and densitometry (+2.00 ± 2.07 GSU). No significant changes were found in CDVA (P = .611), sphere (P = .077), or cylinder (P = .915).

CONCLUSIONS

The "sub400" individualized fluence CXL protocol standardizes the treatment in ultrathin corneas and halted KC progression with a success rate of 90% at 12 months. The sub400 protocol allows for the treatment of corneas as thin as 214 μm of corneal stroma, markedly extending the treatment range. The DL depth did not predict treatment outcome. Hence, the depth is unlikely related to the extent of CXL-induced corneal stiffening but rather to the extent of CXL-induced microstructural changes and wound healing.

The biology of corneal cross-linking derived from ultraviolet light and riboflavin

Over the past 20 years, corneal crosslinking (CXL) has been used by surgeons to halt progression in eyes with keratoconus. We reviewed the literature regarding the mechanism of action of CXL, the role of each of its components the strong biologic reaction, and their effects on cell interaction, proteins involved, wound healing, and cytotoxic reaction. CXL surgery involves a photochemical response in which ultraviolet light at a given wavelength and riboflavin participate. The combination of irradiation with UVA light and riboflavin leads to an intense process of apoptosis of keratocytes in the anterior stroma. Differences in light irradiation, as well as the importance of riboflavin and its vehicle, were also detailed. The surgery creates additional chemical bonds between the amino terminals of the collagen side chains and the proteoglycans of the extracellular matrix. A photosensitization reaction catalyzed by riboflavin classically involves the production of singlet oxygen. Microstructure studies show changes in the size of the fibril and potentially in the interfibrillar space, that the most significant changes related to the stiffening effect of CXL occur in the anterior third of the cornea and that short irradiation times, especially below 5 min, may not have the same biological effect. Changes in the riboflavin vehicle, with the incorporation of Hydroxypropyl methylcellulose as a carrier, can lead to faster diffusion and a more intense photochemical reaction. These are findings that can impact the optimal adjustment of irradiation time according to the riboflavin (and its carrier) used. Many studies have suggested that CXL is safe and effective in the standard and accelerated protocols that have been used by surgeons. After the initial depletion of anterior keratocytes, keratocyte density seems to return to average 6-12 months after surgery when corneas are examined with the confocal microscope.

Assessment of the mechanical forces applied during eye rubbing

Background

To determine the average amount of mechanical forces applied to the lids of keratoconus patients during eye rubbing.

Methods

Fifty-seven patients (41 male, 16 female, average age 34.8 years) with a clinically and topographically diagnosed keratoconus and a history of eye rubbing were prospectively asked to perform their individual eye rubbing movement on a high-precision balance. The type of eye-rubbing movement and the force applied, represented in newtons (N), were recorded and analyzed.

Results

We detected three different types of eye rubbing. Rubbing with the fingertip was most frequent (51%), followed by rubbing with the knuckle (44%) and rubbing with the fingernail (6%). Each type of eye rubbing showed different average forces, with knuckle type eye rubbing applying significantly more force (9.6 ± 6.3 N) on the lids than fingertip (4.3 ± 3.1 N) and fingernail (2.6 ± 3.3 N) types (p < 0,001 and p = 0,016, respectively).

Conclusions

There were major variations in the force exerted on the lids, depending on the type of eye rubbing employed. This data will help determine the forces that need to be applied in future experimental eye rubbing models.

Corneal Epithelial Thickness Mapping After Photorefractive Keratectomy for Myopia

PURPOSE

To evaluate the longitudinal changes in epithelial thickness after photorefractive keratectomy (PRK) and correlate these with refractive changes.

METHODS

This prospective study included 52 eyes of 52 candidates for myopic PRK. Along with standard ophthalmic examinations, corneal epithelial thickness mapping by anterior segment optical coherence tomography was performed. Epithelial thickness maps of 9-mm diameter were divided into 25 sectors, including a central 2-mm zone and eight octants within para-central (2 to 5 mm), midperipheral (5 to 7 mm), and peripheral (7 to 9 mm) annular zones. All PRK treatments were performed using the Technolas Teneo 317 model 2 excimer laser (Bausch & Lomb, Rochester, NY) and an aspheric profile with a 6-mm diameter optical zone. Follow-up was at 1, 3, and 6 months.

RESULTS

Repeated thickness measures before and after PRK at different follow-up times showed a significant difference in thickness separately in various zones (P < .001). A significant decrease in thickness was seen 1 month after PRK in all zones. Afterward, epithelial thickening continued in all zones and reached the preoperative thickness in the midperipheral and peripheral zones 6 months later, whereas the thickness in the central 5-mm zone was significantly thicker than before surgery. There was also a significant correlation between changes in spherical equivalent and epithelial thickness from before to 6 months postoperatively in the paracentral and peripheral zones.

CONCLUSIONS

There was a marked decrease in the epithelial thickening pattern at 1 month after PRK, with gradual thickening at 3 and 6 months. Changes in epithelial thickness and spherical equivalent were significant only for the para-central peripheral zone. [J Refract Surg. 2019;35(10):632-641.].

Analysis of cases and accuracy of 3 risk scoring systems in predicting ectasia after laser in situ keratomileusis

PURPOSE

To identify risk factors for ectasia after laser in situ keratomileusis (LASIK) by comparing the accuracy of the Ectasia Risk Score System (ERSS), Screening Corneal Objective Risk of Ectasia (SCORE) Analyzer, and percentage of tissue altered (PTA) in predicting the occurrence of ectasia.

SETTING

Multiple centers in 8 countries.

DESIGN

Retrospective case series.

METHODS

Previously unpublished post-LASIK ectasia cases were analyzed. Consecutive patients who had LASIK performed at least 5 years previously with no resultant ectasia were used as controls. Axial maps from preoperative Orbscan IIz topographies were analyzed in a masked fashion, and examination files tested with the SCORE Analyzer. The PTA values and ERSS scores were generated using available preoperative and perioperative data. Only eyes with subjectively identified normal preoperative topography were tested with the PTA. Threshold values for the SCORE, ERSS, and PTA were more than or equal to 0, 4, and 40, respectively.

RESULTS

Ectasia occurred in 31 eyes (22 patients); 79 eyes (44 patients) were used as controls. In all eyes, the sensitivity and specificity for predicting ectasia, respectively, were 67.7% and 79.7% for the ERSS and 64.5% and 100% for the SCORE. In eyes with normal topography (ectasia group, 12 eyes; controls, 64 eyes), the PTA yielded sensitivity of 33.3% and specificity of 85.9%. The area under the receiver operating characteristic curve was highest for SCORE (0.911) followed by the ERSS (0.844) and PTA (0.557).

CONCLUSIONS

The SCORE was most predictive of ectasia, achieving the best specificity; the ERSS had the best sensitivity. Further studies are required to validate the PTA as a screening metric for ectasia.

Custom air puff-derived biomechanical variables in a refractive surgery screening setting: Study from 2 centers

PURPOSE

To assess the ability of air puff-derived biomechanical variables to predict surgeon-perceived candidacy for laser in situ keratomileusis (LASIK).

SETTING

Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, and Emory Eye Institute, Emory University, Atlanta, Georgia, USA.

DESIGN

Retrospective case series.

METHODS

Data were collected from refractive surgery screening examinations by 2 surgeons at 2 centers. Disqualified cases (19 eyes and 28 eyes from each surgeon) were judged not to be candidates based on available data including standard variables from the Ocular Response Analyzer. Controls consisted of LASIK candidates (n = 26 and 23). Three custom biomechanical variables not available during screening were calculated and compared by group and surgeon.

RESULTS

The hysteresis loop area was significantly different between disqualified cases and controls for both surgeons (Surgeon 1: controls, 121.50 ± 25.38 [SD], disqualified, 107.62 ± 18.50, P = .04; Surgeon 2: controls, 135.89 ± 22.47, disqualified, 106.11 ± 16.40, P < .001). The area under the curves of the receiver operating characteristics and the cutoff values were statistically significant for the concavity minimum and hysteresis loop area for Surgeon 1 and for all variables except concavity minimum for Surgeon 2. The hysteresis loop area had the highest odds ratio (Surgeon 1, 4.48, Surgeon 2, 20.00). Adjusted R² in best-subsets regressions were 40.2% for Surgeon 1 and 62.9% for Surgeon 2.

CONCLUSIONS

The hysteresis loop area was predictive of which patients were disqualified for LASIK at different sites. Certain measures of the corneal dynamic response to an air puff might serve as correlates to clinically perceived ectasia risk.

Depth-Dependent Reduction of Biomechanical Efficacy of Contact Lens-Assisted Corneal Cross-linking Analyzed by Brillouin Microscopy

PURPOSE

To determine the relative impact of contact lens- assisted corneal cross-linking (CACXL) and standard protocol CXL (CXL) on regional corneal stiffness using Brillouin microscopy.

METHODS

CXL and CACXL were performed on 30 intact fresh porcine eyes (15 per group). Depth profile of stiffness variation and averaged elastic modulus of anterior, middle, and posterior stroma were determined by Brillouin maps. Corneas were cut into strips to conduct mechanical stress-strain tests after Brillouin microscopy to evaluate stiffness difference between CXL and CACXL. Each eye served as its own control.

RESULTS

CXL had a greater impact on corneal stiffness, with a maximum increase of 5.74% compared to 3.99% for CACXL (P < .001). CXL increased longitudinal modulus by 7.8% in the anterior, 1.7% in the middle, and -0.7% in the posterior regions compared to CACXL, which increased longitudinal modulus by 5.5% in the anterior (P < .001), 1.2% in the middle (P = .15), and -0.4% in the posterior regions (P = .60). Mechanical stress-strain tests showed that at 10% strain averaged Young's modulus was 5 MPa for CXL and 2.97 MPa for CACXL (P < .001).

CONCLUSIONS

Both CACXL and standard protocol CXL induced significant corneal stiffening primarily concentrated in the anterior cornea. CACXL leads to less stiffening compared with CXL. An attenuated but continuous stiffening effect can be observed through the whole cornea for both CACXL and CXL, although CACXL has a smaller stiffness gradient. [J Refract Surg. 2019;35(11):721-728.].

Biomechanical Impact of Localized Corneal Cross-linking Beyond the Irradiated Treatment Area

PURPOSE

To investigate the stiffening effect of localized corneal cross-linking (L-CXL) within and beyond the irradiated region in three dimensions.

METHODS

Ten porcine eyes were debrided of epithelium and incrementally soaked with 0.1% riboflavin solution. Using a customized, sharp-edged mask, half of the cornea was blocked while the other half was exposed to blue light (447 nm). The three-dimensional biomechanical properties of each cornea were then measured via Brillouin microscopy. An imaging system was used to quantify the optimal transition zone between cross-linked and non-cross-linked sections of the cornea when considering light propagation and scattering.

RESULTS

A broad transition zone of 610 µm in width was observed between the fully cross-linked and non-cross-linked sections, indicating the stiffening response extended beyond the irradiated region. Light propagation and the scattering induced by the riboflavin-soaked cornea accounted for a maximum of 25 and 159 ± 3.2 µm, respectively.

CONCLUSIONS

The stiffening effect of L-CXL extends beyond that of the irradiated area. When considering L-CXL protocols clinically, it will be important to account for increased stiffening in surrounding regions. [J Refract Surg. 2019;35(4):253-260.].

Distinguishing Highly Asymmetric Keratoconus Eyes Using Dual Scheimpflug/Placido Analysis

PURPOSE

To identify the best metrics or combination of metrics that provide the highest predictive power between normal eyes and the clinically unaffected eye of patients with highly asymmetric keratoconus using data from a Dual Scheimpflug/Placido device.

DESIGN

Retrospective case-control study.

METHODS

Combined Dual Scheimpflug/Placido imaging was obtained from the Galilei G4 device (Ziemer Ophthalmic Systems AG, Port, Switzerland) in 31 clinically unaffected eyes with highly asymmetric keratoconus and 178 eyes from 178 patients with bilaterally normal corneal examinations that underwent uneventful LASIK with at least 1 year follow-up. Receiver operating characteristic (ROC) curves were generated to determine area under the curve (AUC), sensitivity, and specificity for 87 metrics, and logistic regression modeling was used to determine optimal variable combinations.

RESULTS

No individual metric achieved an AUC greater than 0.79. A combined model consisting of 9 metrics yielded an AUC of 0.96, with 90.3% sensitivity and 92.6% specificity. Among those 9 metrics included, 5 related to corneal pachymetry: Opposite Sector Index and Anterior Height BFS Z from the anterior surface, Asphericity and Asymmetry Index, Posterior Height BFS Z, and Posterior Height BFS X from the posterior surface. The strongest variable in the model was the thinnest point location on the horizontal (x) axis.

CONCLUSION

While individual metrics performed poorly, using a combination of metrics from the combined Dual Scheimpflug/Placido device provided a useful model for differentiating normal corneas from the clinically normal eyes of patients with highly asymmetric keratoconus. Pachymetry values were the most impactful metrics.

Corneal higher-order aberrations measurements: Comparison between Scheimpflug and dual Scheimpflug-Placido technology in keratoconic eyes

PURPOSE

To compare the difference and agreement of corneal higher-order aberrations (HOAs) in keratoconic eyes using Scheimpflug and dual Scheimpflug-Placido imaging systems.

SETTING

Emory University, Atlanta, Georgia, and the University of Southern California, Los Angeles, California, USA.

DESIGN

Retrospective between-devices reliability and agreement study.

METHODS

Patients diagnosed with keratoconus were evaluated sequentially by Scheimpflug and dual Scheimpflug-Placido devices. Differences, correlations, and agreement between values for total root mean square (RMS), trefoil, coma, and spherical aberration were analyzed, and Bland-Altman plots were generated.

RESULTS

Fifty eyes from 50 patients (31 men, 19 women) were evaluated. Trefoil at 30 degrees, spherical aberration, and total RMS were significantly different between groups (P < .05), whereas trefoil at 0 degrees and total coma values were not statistically different. There was a weak positive correlation between devices for trefoil at 0 degrees (r = 0.228), and a moderate positive correlation for trefoil at 30 degrees (r = 0.473), horizontal coma (r = 0.430), and for total corneal RMS (r = 0.637). Vertical coma (r = 0.816) and spherical aberration (r = 0.874) showed a strong positive correlation. The 95% limits of agreement (LoA) for absolute values were 1.963 μm for trefoil at 30 degrees, 2.449 μm for trefoil at 0 degrees, 3.530 μm for horizontal coma, 2.145 μm for vertical coma, 1.242 μm for spherical aberration, and 10.527 μm for RMS.

CONCLUSION

Significant differences were found between measurements of corneal HOAs generated by Scheimpflug and dual Scheimpflug-Placido devices in patients with keratoconus, with generally limited correlations and wide LoA. HOAs measurements from these devices should not be considered equivalent.

Higher-order aberration measurements: Comparison between Scheimpflug and dual Scheimpflug-Placido technology in normal eyes

PURPOSE

To compare higher order aberrations (HOAs) in normal eyes between a Scheimpflug imaging system (Pentacam HR) and dual Scheimpflug-Placido imaging system (Galilei G4).

SETTING

Emory University, Atlanta, Georgia, and the University of Southern California, Los Angeles, USA.

DESIGN

Retrospective case series.

METHODS

Eyes screened for refractive surgery were evaluated sequentially using a Scheimpflug device and a dual Scheimpflug-Placido device. Differences, correlations, and agreement between values for total root mean square (RMS), trefoil, coma, and spherical aberration were analyzed, and Bland-Altman plots were generated.

RESULTS

One hundred five eyes of 105 patients (44 men, 61 women) were evaluated. Total RMS, coma, and trefoil were significantly different between groups (all P < .001), while spherical aberration values were not. There was moderate correlation between devices for trefoil (r = 0.475 to 0.652), coma (r = 0.574 to 0.651), and spherical aberration (r = 0.483) and a strong correlation for total cornea RMS (r = 0.817). There was no directional bias between groups. The 95% limits of agreement for absolute values was 0.039 μm for trefoil at 30 degrees, 0.405 μm for trefoil at 0 degree, 0.553 μm for horizontal coma, 0.545 μm for vertical coma, 0.318 μm for spherical aberration, and 0.617 μm for RMS.

CONCLUSIONS

A Scheimpflug imaging device and dual Scheimpflug-Placido imaging device generated statistically different values for total cornea HOAs; however, the correlation between devices was moderate to strong and there was reasonable agreement in all measures for normal eyes. Based on these findings, the devices appear functionally equivalent for clinical use, although caution is warranted for outcomes-based research protocols that report HOAs.

Distinguishing Highly Asymmetric Keratoconus Eyes Using Combined Scheimpflug and Spectral-Domain OCT Analysis

PURPOSE

To determine optimal objective, machine-derived variables and variable combinations from Scheimpflug and spectral-domain (SD) OCT imaging to distinguish the clinically unaffected eye in patients with asymmetric keratoconus (AKC) from a normal control population.

DESIGN

Retrospective case-control study.

PARTICIPANTS

Thirty clinically unaffected eyes with no physical findings on slit-lamp examination, no definitive abnormalities on corneal imaging, and corrected distance acuity of 20/20 or better from 30 patients with highly AKC eyes and 60 eyes from 60 normal control patients who had undergone uneventful LASIK with at least 2 years of stable follow-up (controls).

METHODS

Scheimpflug and SD OCT imaging were obtained in all eyes, and receiver operating characteristic (ROC) curves were generated to determine area under the curve (AUC), sensitivity, and specificity for each machine-derived variable and variable combination.

MAIN OUTCOME MEASURES

Distinguishing AKC eyes from controls as determined by AUC, sensitivity, and specificity.

RESULTS

No individual machine-derived metric from Scheimpflug or SD OCT technology yielded an AUC higher than 0.75. Combining 5 Scheimpflug metrics (index height decentration [IHD], index vertical asymmetry [IVA], pachymetry apex, inferior-superior value, and Ambrosio's Relational Thickness Maximum [ARTmax]) yielded the best Scheimpflug results (AUC 0.86, sensitivity 83%, specificity 83%). Combining 11 SD OCT thickness metrics (minimum-median, temporal outer, superior nasal outer, minimum, epithelium minimum-maximum, epithelial standard deviation, superior inner, superior outer, superior temporal outer, superior nasal inner, central) yielded the best SD OCT results (AUC 0.96, sensitivity 89%, specificity 89%). Combining 13 total Scheimpflug/SD OCT metrics yielded the best results overall (AUC 1.0, sensitivity 100%, specificity 100%). The most impactful variables in combined models included epithelial thickness variability and total focal corneal thickness variability from SD OCT and anterior curvature and topometric indices from Scheimpflug technology. No posterior corneal metrics were impactful in modeling.

CONCLUSIONS

Individual machine-derived metrics from Scheimpflug and SD OCT imaging poorly distinguished normal eyes from minimally affected eyes from patients with highly AKC. Combined SD OCT metrics performed better than combined Scheimpflug metrics. Combining anterior curvature and asymmetry indices from Scheimpflug with regional total thickness and epithelial thickness variability metrics from SD OCT clearly distinguished the 2 populations. Posterior corneal indices were not useful in distinguishing populations.

Bilateral, Asymmetric Keratoconus Induced by Thyrotoxicosis With Long-term Stability After Corneal Cross-linking

PURPOSE

To present a case of bilateral, asymmetric keratoconus presenting unilaterally after partial thyroidectomy with delayed presentation in the second eye after thyrotoxicosis, with disease stabilization following corneal cross-linking (CXL).

METHODS

Case report and literature review.

RESULTS

A 17-year-old girl with a history of Graves' disease underwent partial thyroidectomy without thyroid hormone replacement therapy with normal baseline ophthalmic examination of corrected distance visual acuity (CDVA) of 20/20 and no manifest astigmatism in either eye. At age 29 years, keratoconus manifested in the right eye and standard protocol CXL was performed. At age 40 years, the right eye remained stable after CXL, but keratoconus manifested in the left eye and epithelium-off accelerated CXL was performed with subsequent disease stabilization.

CONCLUSIONS

This case demonstrates the association between thyrotoxicosis and keratoconus and the bilateral nature of keratoconus, and highlights the potentially asymmetric presentation of thyroid-induced keratoconus. CXL had a long-term stabilizing effect over 10 years despite the ongoing effects of thyroid gland dysfunction. [J Refract Surg. 2018;34(5):354-356.].

Epithelial remodeling after corneal crosslinking using higher fluence and accelerated treatment time

PURPOSE

To evaluate changes in regional corneal epithelial thickness after corneal crosslinking (CXL) using higher fluence (7.2 J/cm²) and accelerated treatment time (4 minutes) in eyes with progressive keratoconus using spectral-domain optical coherence tomography (SD-OCT) and to correlate focal epithelial and focal anterior curvature changes.

SETTING

Academic medical center in the United States.

DESIGN

Prospective case series.

METHODS

Patients had anterior segment SD-OCT (RTVue-100) with focal stromal and epithelial measurements and Scheimpflug imaging before and 1, 3, 6, and 12 months after accelerated CXL.

RESULTS

Twenty-seven eyes from 20 patients were evaluated. Before the accelerated CXL, the epithelium was thinnest in the inferior inner and outer temporal regions, whereas at 12 months postoperatively, the epithelium was significantly thinned in multiple inferior and nasal regions by 1.1 to 3.2 μm (P < .05, all measurements), with no significant changes from 6 to 12 months. Epithelial thickness standard deviation across the central 6.0 mm was significantly reduced by 3 months (1.4 μm, P = .09) and remained stable at 12 months (P = .009). Change in epithelial thickness was poorly correlated to change in anterior curvature (r = -0.035).

CONCLUSIONS

Significant epithelial remodeling occurred after accelerated CXL in eyes with progressive keratoconus, with improved regularity across the central 6.0 mm, by 6 months after treatment. There was poor correlation between focal epithelial thickness and anterior curvature changes, with wide variability between patients. Establishing the pattern of epithelial remodeling after CXL might help optimize future custom treatment protocols.

Prevalence of keratoconus in paediatric patients in Riyadh, Saudi Arabia

Background/aim

Keratoconus (KC) is a ectatic corneal disorder with marked progression during childhood and puberty that may lead to severe visual loss. In addition to KC prevalence, estimate shows major geographical variations; recent studies using Scheimpflug technology are in contrast to the 1980s and 1990s literature. The present study aims to determine the prevalence of KC in paediatric patients in Riyadh, Saudi Arabia (KSA).

Methods

This prospective, cross-sectional, observational, multicentre study collected data from paediatric patients from 6 years and 21 years of age who were seen at multiple non-ophthalmic emergency departments within KSA. Bilateral corneal measurements were performed using a rotational Scheimpflug corneal tomography system. Two masked examiners established the diagnosis of KC using both objective and subjective screening criteria. Cohen’s kappa coefficient (κ) was used to qualitatively analyse the interexaminer agreement.

Results

There were 522 patients (1044 eyes) evaluated, with an average age of 16.8±4.2 years (range 6–21 years). KC prevalence was 5.56% for examiner 1 and 3.83% for examiner 2. The κ was 0.81 (almost perfect agreement), with discrepancy in nine cases, which were jointly evaluated and consensus obtained. Final KC prevalence was 4.79% (95% CI 2.96 to 6.62) or 1:21 patients.

Conclusions

The prevalence of KC among paediatric patients in the KSA is considerably higher than numbers reported from earlier studies and from similar studies in other countries. This increase might be due to geographical variations in disease prevalence or due to the ability of screening technology to detect undiagnosed KC with greater accuracy.

Advanced Surface Ablation With a New Software for the Reduction of Ablation Irregularities

PURPOSE

To compare visual outcomes and postoperative aberrations after surface ablation performed with a 750-Hz versus a 1,050-Hz excimer laser coupled with an ablation software designed to reduce corneal surface irregularity.

METHODS

Retrospective comparative trial of myopic eyes that had refractive surgery consecutively treated with transepithelial advanced surface ablation with a 750-Hz excimer laser (750 group) versus a 1,050-Hz excimer laser coupled with the Smart Pulse Technology ablation software (SPT group). The SPT algorithm is a laser pulse technology software aimed at reducing surface irregularity of the stromal bed at the end of treatment. The authors evaluated the effect of this smoothing on final visual acuity. Patients were observed for 6 months.

RESULTS

A total of 139 eyes in the 750 group and 40 eyes in the SPT group were evaluated. Epidemiological and preoperative refractive data of the two groups were comparable. Uncorrected distance visual acuity improved with time and was significantly better in the SPT group (-0.04 ± 0.61 logMAR for the SPT group vs 0.02 ± 0.78 logMAR for the 750 group) (P < .001). At 6 months, 55% versus 21% achieved 20/16 or better (P = .005) and 90% versus 65% achieved 20/20 or better (P = .019) visual acuity in the SPT and 750 groups, respectively. Corrected distance visual acuity improved with time and appeared to be influenced by group (P = .054), with better results in the SPT group. Coma and trefoil improved significantly with time in a similar manner in both groups.

CONCLUSIONS

Surface ablation with the 1,050-Hz excimer laser and SPT software, aimed at reducing the final superficial stromal irregularity, led to improvement of 6-month uncorrected visual acuity. [J Refract Surg. 2017;33(2):89-95.].