Reshaping procedures for the surgical management of corneal ectasia

A bibliometric and citation network analysis of crosslinking

Purpose: Research on crosslinking has focused mainly on trying to slow the progression of keratoconus. The objective of this bibliometric analysis is to determine the relationships between the different publications and authors. As well as to identify the different areas of research on crosslinking. Methods: Web of Science (WOS) was the database for the search of publications for the period 1972 to December 2023, using the terms: crosslinking, cross-linking, ocular, vision, visual, cornea, ectasia AND Keratoconus. The analysis of the publication was performed using the CitNetExplorer, VOSviewer and CiteSpace software. Results: 7161 publications and 59415 citation networks were found. The year with the most publications is 2021, a total of 571 (7.97%) publications and 135 citation networks. The most cited publication was "Riboflavin/ultraviolet-a-induced collagen crosslinking for the treatment of keratoconus" published by Wollensak et al. in 2003, with a citation index of 1780. Using the Clustering function, five groups were found that cover the main research areas in this field: keratoconus, corneal transplantation, cataracts, corneal inflammation and axial growth. Conclusion: The treatment of keratoconus continues to be the topic of interest in this area of research. However, in recent years there has been an increase in research on how crosslinking helps to slow down axial growth.

Correlation between Corneal Volume and Corneal Biomechanics and Corneal Volume Significance in Staging and Diagnosing Keratoconus

Purpose

To investigate the relationship between corneal volume (CV) at different zones and corneal biomechanics in keratoconus (KC) along with the significance of CV in diagnosing and staging KC.

Methods

This prospective clinical study included 456 keratoconic eyes (Group B) and 198 normal eyes (Group A). Using the topographic KC classification method, Group B was divided into subgroups based on severity (mild, moderate, and severe). The CVs of the 3 mm, 5 mm, and 7 mm zones and biomechanical parameters were obtained by Pentacam and Corvis ST. The diagnostic utility of multirange CVs at different disease stages and severity was determined using a receiver operating characteristic (ROC) curve analysis.

Results

The CV of the 7-mm zone had the strongest correlation with A1V, A2T, PD, DA ratio max (2 mm), DA ratio max (1 mm), ARTh, integrated radius, SPA1, and CBI (p < 0.01). The CVs of the Group B subgroups were significantly lower than those of Group A for each diameter range (p < 0.05). There were significant differences between the severe, mild, and moderate subgroups for the 3 mm zone (p < 0.05, all). The 3 mm zone CV exhibited better diagnostic ability in each group for distinguishing KC from the normal cornea (Groups A vs. B: area under the ROC curve (AUC) = 0.926, Groups A vs. B1: AUC = 0.894, Groups A vs. B2: AUC = 0.925, Groups A vs. B3: AUC = 0.953).

Conclusion

The CV significantly decreased in keratoconic eyes. Progressive thinning in the 3 mm zone may be a valuable measurement for detecting and staging KC. Combining the CV examination with corneal biomechanical information may effectively enhance the ability to detect KC.

SMAD4-Dependent Signaling Pathway Involves in the Pathogenesis of TGFBR2-Related CE-like Phenotype

(1) Background: Our previous data indicated that disturbance of the Transforming Growth Factor beta (TGFB) signaling pathway via its Type-2 Receptor (TGFBR2) can cause a Corneal Ectasia (CE)-like phenotype. The purpose of this study is to elucidate whether the SMAD4-dependent signaling pathway is involved in the TGFBR2-related CE-like pathogenesis. (2) Methods: Smad4 was designed to be conditionally knocked out from keratocytes. Novel triple transgenic mice, KerartTA; Tet-O-Cre; Smad4flox/flox (Smad4kera-cko), were administered with doxycycline (Dox). Optical Coherence Tomography (OCT) was performed to examine Central Corneal Thickness (CCT), Corneal Radius, Anterior Chamber and CE-like phenotype and compared to the littermate Control group (Smad4Ctrl). (3) Results: The OCT revealed normal cornea in the Smad4Ctrl and a CE-like phenotype in the Smad4kera-cko cornea, in which the overall CCT in Smad4kera-cko was thinner than that of Smad4Ctrl at P42 (n = 6, p < 0.0001) and showed no significant difference when compared to that in Tgfbr2kera-cko. Furthermore, the measurements of the Anterior Chamber and Corneal Radius indicated a substantial ectatic cornea in the Smad4kera-cko compared to Smad4Ctrl. The H&E staining of Smad4kera-cko mimics the finding in the Tgfbr2kera-cko. The positive immunostaining of cornea-specific marker K12 indicating the cell fate of cornea epithelium remained unchanged in Smad4kera-cko and the Proliferating Cell Nuclear Antigen (PCNA) immunostaining further indicated an enhanced proliferation in the Smad4kera-cko. Both immunostainings recapitulated the finding in Tgfbr2kera-cko. The Masson's Trichrome staining revealed decreased collagen formation in the corneal stroma from both Smad4kera-cko and Tgfbr2kera-cko. The collagen type 1 (Col1a1) immunostaining further confirmed the reduction in collagen type 1 formation in Smad4kera-cko. (4) Conclusions: The aforementioned phenotypes in the Smad4kera-cko strain indicated that the SMAD4-dependent signaling pathway is involved in the pathogenesis of the CE-like phenotype observed in Tgfbr2kera-cko.

Oxygen-supplemented and topography-guided epithelium-on corneal crosslinking with pulsed irradiation for progressive keratoconus

PURPOSE

To investigate the effects of customized topography-guided epithelium-on crosslinking (epi-on CXL) with oxygen supplementation on procedural efficacy and corrected distance visual acuity (CDVA) in patients with progressive keratoconus (KC) at 1 year.

SETTING

Private eye clinic, Brisbane, Australia.

DESIGN

Retrospective, single-center, nonrandomized case series.

METHODS

Topography-guided epi-on CXL using the Mosaic system was performed on patients with progressive KC. Oxygen goggles; transepithelial riboflavin; and pulsed, high UV-A irradiance (1 second on, 1 second off; 30 mW/cm2) were applied to enhance oxygen kinetics and bioavailabilities of riboflavin and UV-A. Guided by baseline topography, a higher UV-A dose (15 J/cm2) was applied to the area of steepest anterior curvature with decreasing fluence (as low as 7.2 J/cm2) toward the outer 9 mm. Postoperative CDVA and maximum keratometry (Kmax) were evaluated.

RESULTS

102 eyes (80 patients) were followed for 11.5 ± 4.8 months. At the latest follow-up, mean CDVA (logMAR), mean K, and Kmax (diopters [D]) improved from 0.18 ± 0.28, 46.2 ± 3.8, and 53.0 ± 5.67 at baseline to 0.07 ± 0.18, 45.8 ± 3.7, and 51.9 ± 5.56, respectively (P < .001). 3 eyes (3%) lost more than 1 CDVA line, and another 3 eyes (3%) had increased Kmax greater than 2 D. 43 eyes were followed for at least 12 months (n = 43): mean CDVA, mean K, and Kmax improved from 0.19 ± 0.33 logMAR, 46.5 ± 3.5 D, and 53.6 ± 5.67 D to 0.07 ± 0.17 logMAR, 46.0 ± 3.5 D, and 52.33 ± 5.49 D, respectively (P ≤ .002). No complications were observed.

CONCLUSIONS

Tailoring oxygen-supplemented epi-on CXL with differential UV-A energy distributions, guided by baseline topography, in patients with KC seems to be safe and effective. At 1 year, study reports sustained improved CDVA and corneal stabilization.

Assessment of Health Disparities and Barriers to Accessing Keratoconus and Crosslinking at a Tertiary Referral Center

PURPOSE

The aim of this study was to determine the barriers to accessing the crosslinking service in Auckland, New Zealand.

METHODS

This was a prospective 1-year study of patients at Auckland District Health Board. Studied parameters included age, sex, body mass index, ethnicity, New Zealand Deprivation (NZDep; an area-based measure of socioeconomic status, 1 = low deprivation-10 = high deprivation) score of residence, disease severity (maximum keratometry and thinnest corneal thickness), attendance, distance travelled, car ownership, employment status, and visual outcomes. Statistical analysis was performed using independent t tests, Pearson correlation, independent samples ANOVA, MANCOVA, and binomial logistic regression.

RESULTS

Four hundred fifty-four patients with keratoconus were analyzed and had a mean age of 24.1 ± 0.8 years, mean body mass index of 33.0 ± 9.7 kg/m 2 , and 43% were female. Pacific Peoples consisted 40.2% of the population; Māori 27.2%; Europeans 21.2%; Asian 9.9%; and Middle Eastern, Latin American, and African (MELAA) 1.3%. The mean distance travelled was 12.5 ± 9.5 km, NZDep score was 6.8 ± 2.6, and attendance was 69.0 ± 42.5%. The lowest attendance was observed in Pacific Peoples (58.9%) and the highest was in Asians (90%) ( P = 0.019). The mean worst-eye visual acuity at attendance was 0.75 ± 0.47 logMAR (6/35). Unemployment was associated with worse best-eye visual acuity at FSA ( P = 0.01) and follow-up ( P < 0.05). Māori and Pacific Peoples had the highest NZDep ( P < 0.001), were younger at presentation ( P = 0.019), had higher disease severity ( P < 0.001), and worse visual acuity ( P < 0.001).

CONCLUSIONS

Poor attendance was seen in this cohort. Pacific Peoples and Māori presented younger with worse disease severity and visual acuity but also had the highest nonattendance. These results suggest that deprivation, factors associated with ethnicity, and unemployment are potential barriers to attendance.

Efficacy of enzyme‑induced collagen crosslinking on porcine cornea

The purpose of the present study was to investigate the effect of a new crosslinking (CXL) method, induced by enzymes, on porcine corneas. Corneal strip (10x3 mm) pairs obtained from 60 fresh porcine eyes were harvested and divided into four groups, Groups A-D. Each pair of corneal strips was incised from the central part of the same cornea; one was incubated in transglutaminase (Tgase) solution (microbial Tgase 2 produced by tissue engineering) and the other remained untreated as a control. CXL strips of Groups A-D were incubated with 2, 1, 0.5 and 0.25 U/ml Tgase solution, respectively at 37˚C for 30 min. After that, tensile strain measurements were performed for all strips. One cornea from each group was chosen randomly for hematoxylin and eosin, and Masson staining to identify histological morphology changes. The elastic modulus of treated corneas of Groups A-D were 6.56±2.93, 4.72±1.29, 5.24±2.13 and 3.48±1.60 MPa (mean ± SD), respectively at a strain of 20%, and had a 66, 43, 36 and -6% increase compared with those of their control strips. Compared with the control strips, the elastic modulus of the treated strips significantly increased in Groups A-C. The central corneal thickness of the treated corneas in Groups A-D were 1.54±0.14, 1.41±0.15, 1.47±0.11 and 1.43±0.13 µm, respectively; however, there was not a statistically significant difference compared with the control group. No reduction in corneal transparency was observed, and no obvious abnormalities were found in corneal morphology. CXL mediated by enzymes can lead to a notable enhancement in the biomechanical characteristics of the cornea while maintaining its structural integrity. Enzyme-induced CXL could be a new generation CXL method for strengthening the cornea.

Keratoconus Management in the Community: A Survey of Optometrists

OBJECTIVES

Defining the patterns of practice and referral criteria of optometrists within New Zealand to investigate the diagnosis and management of keratoconus.

METHODS

Optometrists recruited through the New Zealand Association of Optometrists, Cornea and Contact Lens Society of New Zealand, and private practices were invited to complete an anonymous survey.

RESULTS

Responses were received from 168 optometrists (representing 20.0% of the optometrist population). Half (48%) of optometrists had ≥15 years of experience, and 22% prescribed soft contact lenses daily, whereas only 6.4% prescribed rigid gas-permeable (RGP) lenses daily. The main barriers to prescribing RGPs were experience with fitting, low market demand, and patient discomfort. When referring to an ophthalmologist, 41% reported referring on progression of corneal parameters, 27% on initial diagnosis, 21% at no set time, and 10% with a reduction in visual acuity. Most optometrists (64%) would refer for possible surgery when visual acuity dropped between 6/9 and 6/12. Optometrists with greater experience were more likely to prescribe RGP lenses and co-manage patients with ophthalmologists. Ownership of a corneal imaging unit suggested an increased likelihood of prescribing RGP lenses but did not alter referral patterns.

CONCLUSION

This survey provides an overview of current practice and highlights the importance of optometrists in the diagnosis and management of keratoconus. There was a significant discrepancy in keratoconus management, regarding optical correction modality and referral criteria for ophthalmology review. Further interdisciplinary work is required between optometry and ophthalmology to standardize referral guidelines and enhance visual outcomes.

Comparing Repeatability and Agreement between Commonly Used Corneal Imaging Devices in Keratoconus

SIGNIFICANCE

Keratometry and pachymetry are important for diagnosis and monitoring of keratoconus. Many corneal imaging units exist, but comparison to determine repeatability and agreement is paramount for adequate keratoconus management in primary and secondary care.

PURPOSE

This study aimed to evaluate the repeatability and agreement of a Placido disc-based videokeratoscope (Melbourne, Victoria, Australia) used in primary care with spectral-domain optical coherence tomography (Optopol Technology, Zawiercie, Poland) and Scheimpflug corneal tomography (Oculus, Wetzlar, Germany) in secondary care.

METHODS

This was a prospective single-center study where one eye was randomized to have central corneal thickness;thinnest corneal thickness (TCT); and maximum, mean, steep, and flat keratometry (Kmax, Kmean, Ksteep, and Kflat, respectively), measured with all three devices. Three measurements were completed per device to assess intraobserver repeatability.

RESULTS

A total of 110 eyes from 110 patients with keratoconus were analyzed. Repeatability was best with the Pentacam for central corneal thickness, Kmax, Kmean, Ksteep, and Kflat parameters (precision, 9.21, 0.8, 0.38, 0.52, and 0.58). The Medmont had better repeatability than the Revo with Kmax, Kmean, Ksteep, and Kflat (precision, 1.41,1.35,1.43, and 1.59). Revo had the best repeatability with TCT (precision, 3.81). The intraclass correlation coefficient was >0.94 for all parameters in all devices. Agreement was generally poor between devices. However, there was good agreement between Pentacam and Medmont Kflat measurements ( P > .05).

CONCLUSIONS

Repeatability of keratometry parameters with the Pentacam and Medmont was greater than the Revo, suggesting a lower threshold for detecting change in anterior corneal parameters. The Revo had the greatest repeatability for TCT, suggesting a lower threshold for detecting thinning in disease progression and corneal-crosslinking safety. There was poor agreement between devices, and it is not recommended for them to be used interchangably.

Repeatability of Scheimpflug based corneal tomography parameters in advanced keratoconus with thin corneas

OBJECTIVE

To determine the repeatability limits of corneal tomography parameters in patients with advanced and moderately thin keratoconic corneas to assist in planning thickness-based procedural interventions.

METHODS

Prospective, single-centre, repeatability study. Three tomography scans using the Pentacam AXL were obtained from patients with keratoconus with thinnest corneal thickness (TCT) ≦400 µm (sub-400 group) and compared to those with TCT = 450-500 µm (450-plus group). Eyes with previous crosslinking, intraocular surgery, or acute corneal hydrops were excluded. Eyes were age and gender-matched. The within-subject standard deviations for flat keratometry (K1), steep keratometry (K2), maximal keratometry (Kmax), astigmatism and TCT were used to calculate respective repeatability limits (r). Intra-class correlation coefficients (ICC) were also analysed.

RESULTS

The sub-400 group comprised 114 eyes from 114 participants, and the 450-plus group comprised 114 eyes from 114 participants. In the sub-400 group, TCT was amongst the least repeatable parameters (33.92 µm; ICC 0.96), compared with the 450-plus group (14.32 µm; ICC 0.99, p < 0.01). In the sub-400 group, K1 and K2 of the anterior surface were the most repeatable parameters (r 3.79 and 3.22 respectively; ICC 0.97 and 0.98 respectively) compared with the 450-plus group (r 1.17 and 0.92 respectively; and ICC 0.98 and 0.99 respectively, p < 0.01).

CONCLUSIONS

The repeatability of corneal tomography measurements is significantly reduced in sub-400 keratoconic corneas when compared to 450-plus corneas. Repeatability limits should be carefully considered when surgical interventions are planned for such patients.

Combined Photorefractive Keratectomy and Corneal Cross-Linking for Keratoconus and Ectasia: The Athens Protocol

ABSTRACT

Customized photorefractive keratectomy with minimal tissue ablation combined with corneal cross-linking seems to be a long-term safe and effective strategy for anatomical and visual management of keratoconus, postsurgical ectasia, and other ectasia management. Multiple published studies, many with long-term follow-up, have supported the Athens Protocol and its various forms as a means to manage corneal ectatic disorders, which not only stabilize corneal shapes but also improve functional vision.

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.

Therapeutic non-ectasia applications of cornea cross-linking

Corneal cross-linking is a photopolymerization technique traditionally used to strengthen corneal tissue. Corneal cross-linking utilizes riboflavin (vitamin B2) as a photosensitizer and ultraviolet-A light (UVA) to create strong covalent bonds within the corneal stroma, increasing tissue stiffness. Multiple studies have demonstrated corneal cross-linking's effectiveness in treating corneal ectasia, a progressive, degenerative, and non-inflammatory thinning disorder, as quantified by key tomographic, refractive, and visual parameters. Since its introduction two decades ago, corneal cross-linking has surpassed its original application in halting corneal ectatic disease and its application has expanded into several other areas. Corneal cross-linking also possesses antibacterial, antienzymolytic and antioedematous properties, and has since become a tool in treating microbial keratitis, correcting refractive error, preventing iatrogenic ectasia, stabilising bullous keratopathy and controlling post keratoplasty ametropia. This review provides an overview of the current evidence base for the therapeutic non-ectasia applications of cornea cross-linking and looks at future developments in the field.

Advances in 3D bioprinting technology for functional corneal reconstruction and regeneration

Corneal transplantation constitutes one of the major treatments in severe cases of corneal diseases. The lack of cornea donors as well as other limitations of corneal transplantation necessitate the development of artificial corneal substitutes. Biosynthetic cornea model using 3D printing technique is promising to generate artificial corneal structure that can resemble the structure of the native human cornea and is applicable for regenerative medicine. Research on bioprinting artificial cornea has raised interest into the wide range of materials and cells that can be utilized as bioinks for optimal clarity, biocompatibility, and tectonic strength. With continued advances in biomaterials science and printing technology, it is believed that bioprinted cornea will eventually achieve a level of clinical functionality and practicality as to replace donated corneal tissues, with their associated limitations such as limited or unsteady supply, and possible infectious disease transmission. Here, we review the literature on bioprinting strategies, 3D corneal modelling, material options, and cellularization strategies in relation to keratoprosthesis design. The progress, limitations and expectations of recent cases of 3D bioprinting of artifial cornea are discussed. An outlook on the rise of 3D bioprinting in corneal reconstruction and regeneration is provided.

Cataract surgery in Keratoconus revisited - An update on preoperative and intraoperative considerations and postoperative outcomes

PURPOSE

This review aims to evaluate and simplify the recent literature on preoperative surgical planning, intraoperative considerations, postoperative surprises, and their management in patients with keratoconus undergoing cataract surgery.

METHODS

A review of the literature was done to analyze all the pertinent articles on Keratoconus and cataract surgery.

RESULTS

The surgical planning of cataracts in eyes with keratoconus needs a multifaceted approach. Preoperatively, techniques such as cross-linking or the use of intra-corneal rings help stabilize the progression. Unreliable biometric measurements are a significant problem in keratoconus patients, especially in an advanced stage of the disease. It is better to consider actual K readings if the K value is less than 55D but for a K value, more than 55D using standard K values will prevent postoperative refractive surprises. For calculation of K values, an elevation-based device like pentacam gives better repeatability in mild to moderate cases whereas for advanced keratoconus none of the keratometers is reliable. Recently, the Kane keratoconus formula performed better in all stages of disease whereas previous studies showed good results with SRK/T formula is a mild and moderate disease. Monofocal intraocular lenses are a better choice in these patients. Toric lenses can be used in mild and stable keratoconus. Intraoperatively, the use of a customized RGP lens can overcome the challenge of image distortion and loss of visual perspective. Despite taking necessary measures, postoperative refractive surprise can occur and can be managed with IOL exchange or Secondary IOLs.

CONCLUSION

There is a spectrum of challenges in managing cataracts in keratoconus which makes thorough preoperative planning important for good surgical outcomes. Despite the measures, there might be post-operative surprises and the patients need to be informed regarding the same.

Cataract surgery in patients with underlying keratoconus: focused review

An underlying diagnosis of keratoconus (KC) can complicate cataract surgery. In this study, the results of a focused review of the literature pertaining to cataract surgery in patients with KC are detailed. Topics essential for the appropriate management of this patient population are discussed. First, the individual and shared epidemiology and pathophysiology of cataract and KC are reviewed. Then, the theory and approach to intraocular lens power calculation are discussed, highlighting particularities and pitfalls of this exercise when performed in patients with KC. Finally, several special-although not uncommon-management scenarios and questions are addressed, such as surgical planning in cases where corneal stabilization or tissue replacement interventions are also necessitated.

Analysis of visual and refractive results after wedge resection for high astigmatism after penetrating keratoplasty in keratoconus

PURPOSE

To analyze visual and refractive results after wedge resection to correct high astigmatism after penetrating keratoplasty (PK) for keratoconus.

SETTING

Cornea Unit of the Centro de Oftalmología Barraquer Barcelona, Spain.

DESIGN

A retrospective quasi-experimental, before and after study.

METHODS

Patients who developed high astigmatism or ectasia in the graft-host junction after PK were treated with wedge resection. The following variables were studied before the surgery, 1-year after and at the final visit: uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refractive and topographic astigmatism and spherical equivalent. Vectorial analysis of the astigmatism changes was performed.

RESULTS

Fifty-one eyes were included with a mean follow-up of 4.19 ± 3.09 years. Mean refractive astigmatism was 11.47 ± 3.57 diopters (D) pre-operatively and 4.79 ± 3.32 D at the final follow-up (p < 0.001). The mean centroid changed from 2.65 ± 11.82 D at 23 degrees preoperatively to 0.35 ± 5.86 D at 127 degrees postoperatively. Concerning spherical equivalent, the mean preoperative value was -3.10 ± 4.15 D and the mean postoperative value was -1.55 ± 3.41 D (p = 0.002). Mean pre-operative and final follow-up UDVA were 1.25 ± 0.27 and 0.84 ± 0.50 (p < 0.001). Mean Pre-op and final follow-up CDVA were 0.27 ± 0.19 and 0.24 ± 0.24.

CONCLUSIONS

Wedge resection is a useful surgical procedure to correct high astigmatism. It is a safe technique with moderate efficacy and may be considered as initial procedure of choice in high astigmatism due to long-term ectasia in the graft-host junction after PK for keratoconus.

Oxygen-supplemented transepithelial-accelerated corneal crosslinking with pulsed irradiation for progressive keratoconus: 1 year outcomes

PURPOSE

To investigate the effects of combining oxygen supplementation with enhanced UV-A light and increased riboflavin permeability in improving the efficacy of epithelium-on crosslinking (epi-on CXL).

SETTING

Private eye clinic in Brisbane, Queensland, Australia.

DESIGN

Retrospective single-center nonrandomized uncontrolled longitudinal cohort case series.

METHODS

Transepithelial CXL was performed on keratoconic eyes. Applications of an oxygen goggle and pulsed UV-A irradiation (1 second on, 1 second off) were used to enhance oxygen kinetics during epi-on CXL. Additional procedural modifications included the use of benzalkonium chloride and high UV-A irradiance level (30 mW/cm 2 ) to improve the stromal bioavailability of riboflavin and UV-A. The main efficacy outcomes were the changes in mean corrected distance visual acuity (CDVA) and safety over 12 months. Additional refractive and keratometry (K) outcomes were also observed.

RESULTS

53 eyes (38 patients) were included in this study. 12 months postoperatively, mean CDVA improved from a mean of 0.18 ± 0.2 at baseline to 0.07 ± 0.1 logMAR ( P < .0001). No statistically significant change was observed in maximum K (Kmax) and mean K, which were respectively 51.7 ± 5.8 diopters (D) and 46.4 ± 3.85 D at baseline and 51.2 ± 5.7 D ( P = .152) and 46.0 ± 3.84 D ( P = .06) 12 months postoperatively. Only 3 eyes experienced an increase of more than 2 D in Kmax; however, none of these eyes experienced a CDVA loss. There were no reported infections, corneal scarring, or other severe adverse effects.

CONCLUSIONS

Performing supplemental oxygen epi-on CXL with accelerated, pulsed UV-A irradiation in conjunction with riboflavin permeability enhancers resulted in improved CDVA ( P < .0001) and stable keratometry up to 12 months postoperatively with a good safety profile.

Corneal Crosslinking: Present and Future

Keratoconus is a progressive corneal thinning disorder that can lead to vision loss. In the last 2 decades, corneal crosslinking (CXL) has emerged as an effective method to halt the progression of keratoconus and reduce the number of patients requiring keratoplasty. The procedure has been adopted globally and has evolved to become a part of combination treatments to regularize the cornea and improve visual outcomes. CXL has even been extrapolated in managing other ocular pathologies such as progressive myopia, infectious keratitis, and bullous keratopathy. This review aims to summarize the current role of CXL in keratoconus and its alternative uses, and provide insights into future developments in this fast-developing field.

Flattening of Central, Paracentral, and Peripheral Cones After Non-accelerated and Accelerated Epithelium-off CXL in Keratoconus: A Multicenter Study

PURPOSE

To assess the flattening of central, paracentral, and peripheral cones following non-accelerated (non-A-CXL) and accelerated (A-CXL) epithelium-off corneal cross-linking with 10 times higher intensity.

METHODS

In this multicenter study of 200 eyes (100 in each group), following 10 minutes of soak time with riboflavin 0.1%, continuous CXL was performed for 30 minutes (intensity: 3 mW/cm², fluence: 5.4 J/cm²) in the non-A-CXL group and 3 minutes (intensity: 30 mW/cm², fluence: 5.4 J/cm²) in the A-CXL group. Anterior and posterior cone flattening were compared at 12 months. Multiple regression analysis was performed to establish correlation of age, sex, cone location, and preoperative maximum keratometry (Kmax) values with postoperative flattening at 12 months.

RESULTS

In the non-A-CXL and A-CXL groups, central cones were the steepest, followed by paracentral and peripheral cones. Both groups showed significant flattening in central (1.54 ± 1.94 and 1.09 ± 1.79 diopters [D]) and paracentral (0.62 ± 1.59 and 0.55 ± 0.98 D) cones only. In the non-A-CXL group, there was a positive correlation between postoperative flattening and preoperative Kmax values, whereas paracentral and peripheral cone locations were negatively related. In the A-CXL group, only paracentral location was negatively correlated to postoperative flattening and showed posterior cone steepening at 12 months.

CONCLUSIONS

Although central cones were the steepest in both groups, there was no difference in postoperative flattening between the groups for all cone locations. In the non-A-CXL group, postoperative flattening was proportional to preoperative Kmax values in central cones and was less with paracentral and peripheral locations. With A-CXL, postoperative flattening was less only with paracentral location. In the A-CXL group, significant posterior cone steepening was noticed only in paracentral cones. [J Refract Surg. 2022;38(5):310-316.].

The Aotearoa Research Into Keratoconus Study: Geographic Distribution, Demographics, and Clinical Characteristics of Keratoconus in New Zealand

PURPOSE

To investigate the epidemiologic, demographic, and basic clinical characteristics of individuals with keratoconus managed by optometrists in New Zealand (NZ)/Aotearoa.

METHODS

A prospective, longitudinal, nationwide, survey protocol was completed for every patient with keratoconus who underwent a consultation with participating optometrists in a 2-year period. Data for each patient included date of birth, sex, self-reported ethnicity, new or previous diagnosis, uncorrected (UCVA) and best-corrected visual acuity (BCVA), type of refractive correction required to obtain BCVA and keratometric readings obtained using keratometry or computerized topography.

RESULTS

One thousand eight hundred sixty-nine cases were identified, with a mean age of 41.0 ± 15.7 years, 56.4% being men, and 87.3% with previous diagnosis. The distribution of cases was skewed toward Auckland (41.6%), Waikato (21.3%), Wellington (16.8%), and Bay of Plenty (13.3%). Self-reported ethnicities were predominantly NZ European (54.4%), Māori (24.7%), and Pacific Peoples (15.5%), disproportionate to the general population profile (74.0%, 14.9%, and 7.4% respectively). Most eyes (64.3%) were managed with rigid contact lenses (corneal lens in 34.2%). The mean K-mean was 49.0 ± 5.7 D. The mean UCVA was 6/42 and BCVA was 6/9. Māori and Pacific Peoples had both the highest K-mean and proportions of eyes graded stage IV on the Amsler-Krumeich scale.

CONCLUSIONS

The results indicate that keratoconus is relatively common in NZ with at least 1869 patients managed by optometrists in 2 years. Most eyes had mild to moderate disease; however, Māori and Pacific Peoples seem to have greater disease severity. An ethnic predilection is apparent, with Māori and Pacific Peoples overrepresented relative to their population proportions, reinforcing a long-held clinical suspicion.

Prospective one year study of corneal biomechanical changes following high intensity, accelerated cornea cross-linking in patients with keratoconus using a non-contact tonometer

PURPOSE

To characterize corneal biomechanical properties utilizing a dynamic ultra-high-speed Scheimpflug camera equipped with a non-contact tonometer (CorVis ST, CST) in keratoconic corneas following continuous high intensity, high irradiance corneal cross-linking.

DESIGN

Prospective longitudinal single-centre study at a tertiary referral center.

METHODS

Corneal biomechanical properties were measured in patients with progressive keratoconus undergoing high intensity (30 mW/cm2), high irradiance (5.4 J/cm2), accelerated corneal cross-linking with continuous exposure to ultraviolet-A for 4 min. CST was used to assess corneal biomechanical properties pre-operatively and at 1, 3, 6 and 12 months post-operatively. CST output videos were further analyzed using several previously reported algorithms.

RESULTS

A total of 25 eyes of 25 participants were examined. The mean age of participants was 20.9 ± 5.3 years; 56% were male and 80% were of Māori or Pacific Island origin. Energy absorbed area (mN mm), was the only significantly changed parameter compared to baseline at all time points measuring 3.61 ± 1.19 preoperatively, 2.81 ± 1.15 at 1 month (p = 0.037), 2.79 ± 0.81 (p = 0.033) at 3 months, 2.76 ± 0.95 (p = 0.028) at 6 months and 2.71 ± 1.18 (p = 0.016) at 12 months.

CONCLUSIONS

The significant difference between the pre and post-operative energy absorbed area appears to reflect changes in corneal viscous properties that occur following corneal cross-linking.

Visual and Refractive Outcomes of Toric Implantable Collamer Lens Implantation in Stable Keratoconus After Combined Topography-Guided PRK and CXL

PURPOSE

To evaluate the safety and efficacy of toric implantable Collamer lens (ICL) (STAAR Surgical) implanted at least 6 months after combined topography-guided photorefractive keratotomy (TG-PRK) and corneal cross-linking (CXL) in keratoconus.

METHODS

This retrospective study included 46 eyes with keratoconus of 31 patients who underwent toric ICL implantation after previous TG-PRK+CXL. Patients were examined for uncorrected (UDVA) and corrected (CDVA) distance visual acuity, flat and steep keratometry, and manifest refraction spherical equivalent preoperatively and 12 months postoperatively.

RESULTS

At 12 months postoperatively, there was a statistically significant improvement in visual and refractive outcomes (all P < .001). Mean UDVA improved to 0.17 ± 0.14 logMAR (vs 1.00 ± 0.38 logMAR preoperatively) and mean manifest refraction spherical equivalent improved to -0.32 ± 1.42 diopters (D) (vs -7.35 ± 5.20 D preoperatively). At 12 months, 63% of eyes achieved UDVA of 20/32 or better and 60.9% of eyes were within ±0.50 D of manifest refraction spherical equivalent. Mean refractive astigmatism improved from -2.90 ± 2.21 D preoperatively to -1.47 ± 1.46 D at postoperative 12 months (P < .001), with 30.4% and 45.7% of eyes having a postoperative astigmatic error within ±0.50 and ±1.00 D, respectively. No complications were observed.

CONCLUSIONS

Toric ICL implantation was found to be safe and effective for the correction of myopia and myopic astigmatism in patients with stable keratoconus who had undergone TG-PRK+CXL, as revealed by the statistically significant improvement in visual and refractive outcomes at 12 months after toric ICL implantation. [J Refract Surg. 2021;37(12):824-829.].

Membranous Extracellular Matrix-Based Scaffolds for Skin Wound Healing

Membranous extracellular matrix (ECM)-based scaffolds are one of the most promising biomaterials for skin wound healing, some of which, such as acellular dermal matrix, small intestinal submucosa, and amniotic membrane, have been clinically applied to treat chronic wounds with acceptable outcomes. Nevertheless, the wide clinical applications are always hindered by the poor mechanical properties, the uncontrollable degradation, and other factors after implantation. To highlight the feasible strategies to overcome the limitations, in this review, we first outline the current clinical use of traditional membranous ECM scaffolds for skin wound healing and briefly introduce the possible repair mechanisms; then, we discuss their potential limitations and further summarize recent advances in the scaffold modification and fabrication technologies that have been applied to engineer new ECM-based membranes. With the development of scaffold modification approaches, nanotechnology and material manufacturing techniques, various types of advanced ECM-based membranes have been reported in the literature. Importantly, they possess much better properties for skin wound healing, and would become promising candidates for future clinical translation.

Keratoconus detection of changes using deep learning of colour-coded maps

Objective

To evaluate the accuracy of convolutional neural networks technique (CNN) in detecting keratoconus using colour-coded corneal maps obtained by a Scheimpflug camera.

Design

Multicentre retrospective study.

Methods and analysis

We included the images of keratoconic and healthy volunteers’ eyes provided by three centres: Royal Liverpool University Hospital (Liverpool, UK), Sedaghat Eye Clinic (Mashhad, Iran) and The New Zealand National Eye Center (New Zealand). Corneal tomography scans were used to train and test CNN models, which included healthy controls. Keratoconic scans were classified according to the Amsler-Krumeich classification. Keratoconic scans from Iran were used as an independent testing set. Four maps were considered for each scan: axial map, anterior and posterior elevation map, and pachymetry map.

Results

A CNN model detected keratoconus versus health eyes with an accuracy of 0.9785 on the testing set, considering all four maps concatenated. Considering each map independently, the accuracy was 0.9283 for axial map, 0.9642 for thickness map, 0.9642 for the front elevation map and 0.9749 for the back elevation map. The accuracy of models in recognising between healthy controls and stage 1 was 0.90, between stages 1 and 2 was 0.9032, and between stages 2 and 3 was 0.8537 using the concatenated map.

Conclusion

CNN provides excellent detection performance for keratoconus and accurately grades different severities of disease using the colour-coded maps obtained by the Scheimpflug camera. CNN has the potential to be further developed, validated and adopted for screening and management of keratoconus.

Prospective Clinical Study of Keratoconus Progression in Patients Awaiting Corneal Cross-linking

PURPOSE

Keratoconus progression should be treated with corneal cross-linking (CXL) in a timely manner. This study aimed to investigate patient factors associated with keratoconus progression between time of listing and at time of CXL.

METHODS

Prospective observational study at a tertiary center. Ninety-six eyes of 96 patients with keratoconus. Demographic, clinical, and tomographic parameters were analyzed to determine the risk factors for keratoconus progression. Analyzed tomographic indices included steepest keratometry, average keratometry, cornea thinnest point, index of surface variance, index of vertical asymmetry, keratoconus index, center keratoconus index, index of height asymmetry, and index of height decentration.

RESULTS

A total of 38 eyes (39.6%) were found to have keratoconus progression during an average waiting time of 153 ± 101 days. There were significant differences in preoperative tomographic parameters such as index of surface variance (111.3 ± 36.6 vs. 88.3 ± 31.8; P = 0.002), index of vertical asymmetry (1.1 ± 0.4 vs. 0.9 ± 0.4; P = 0.005), keratoconus index (1.31 ± 0.12 vs. 1.22 ± 0.11; P < 0.001), and index of height decentration (0.16 ± 0.07 vs. 0.11 ± 0.06; P = 0.015) between eyes that progressed and those that remained stable. There were no significant differences in steepest keratometry, average keratometry, cornea thinnest point, and center keratoconus index. Multivariate analysis did not reveal age, presence of atopy/atopic keratoconjunctivitis, eye rubbing, or waiting time to be a significant risk factor for progression; however, Maori ethnicity was a risk factor (odds ratio = 3.89; P = 0.02).

CONCLUSIONS

A significant proportion of eyes were found to be progressing while waiting for CXL. A risk stratification score for patients awaiting CXL may reduce the risk of progression.

Repeatability of corneal and epithelial thickness measurements with anterior segment optical coherence tomography in keratoconus

PURPOSE

To investigate the repeatability in corneal thickness (CT) and epithelial thickness (ET) measurements using spectral domain anterior segment optical coherence tomography (AS-OCT, REVO NX, Optopol) in keratoconus, and examine the effect of corneal crosslinking (CXL) on repeatability.

METHODS

A cross-sectional study of 259 eyes of 212 patients with keratoconus attending the corneal disease clinic at a university hospital tertiary referral center were enrolled. Two groups were analysed: eyes with no prior history of CXL (Group A) and eyes with prior CXL (Group B). Repeatability of measurements was assessed using the intraclass correlation coefficient (ICC) and coefficient of variation (CV).

RESULTS

In Group A, central corneal thickness (CCT) was 472.18 ± 45.41μm, and the ET was found to be the thinnest in the inferior-temporal aspect at 51.79 ± 5.97μm and thickest at the superior-nasal aspect at 56.07 ± 5.70μm. In Group B, CCT was 465.11± 42.28μm, and the ET was the thinnest at the inferior-temporal aspect at 50.63 ± 5.52μm and thickest at the superior aspect at 56.80 ± 6.39μm. When evaluating CT measurements, ICC was above 0.86 and 0.83 for Group A and Group B respectively. When evaluating ET measurements, ICC was above 0.82 for both groups. CXL had no statistically significant impact on the repeatability of measurements.

CONCLUSIONS

AS-OCT provides repeatable CT and ET measurements in the central and peripheral cornea in patients with keratoconus. Repeatability is not affected by a history of CXL.

Postoperative Corneal Epithelial Remodeling After Intracorneal Ring Segment Procedures for Keratoconus: An Optical Coherence Tomography Study

PURPOSE

To assess epithelial corneal remodeling by anterior segment optical coherence tomography (AS-OCT) after intracorneal ring segments (ICRS) implantation in keratoconic eyes.

METHODS

This prospective observational study included patients with keratoconus receiving ICRS of different arc lengths according to their tomographic pattern. AS-OCT and corneal topography (Scheimpflug camera) were performed before and 1, 3, and 6 months after surgery. Corneal pachymetry mapping was performed and total corneal and epithelial thicknesses (3-mm central and 16 points on 6-mm zone) were measured over the pupil center using AS-OCT. Topographic parameters were also assessed.

RESULTS

A total of 68 keratoconic eyes were analyzed (Amsler-Krumeich stages 1 to 4) in four groups of 17 eyes: 210° ICRS, 320° ICRS, double 160° ICRS, and single 160° ICRS. Corneal pachymetry mapping revealed that epithelial thickness increased significantly in the internal zones juxtaposed to the ICRS without smoothing during the postoperative period (P < .05). Mean maximum epithelial thickness increased from 67 ± 6 to 79 ± 7 µm for 210° ICRS, 66 ± 9 to 82 ± 4 µm for 320° ICRS, 63 ± 6 to 78 ± 7 µm for double 160° ICRS, and 62 ± 5 to 77 ± 5 µm for single 160° ICRS (P < .0001). Significant epithelial thickening at the apex of the cone was observed in all groups (P < .05).

CONCLUSIONS

Significant epithelial thickening occurs after ICRS implantation adjacent to the ICRS to compensate for the ridge created with a thickening of epithelium over the cone due to regularization of the stromal surface. [J Refract Surg. 2021;37(6):404-413.].

Measurement of In Vivo Biomechanical Changes Attributable to Epithelial Removal in Keratoconus Using a Noncontact Tonometer

PURPOSE

To compare the biomechanical properties of the cornea after epithelial removal in eyes with keratoconus undergoing corneal cross-linking.

METHODS

Prospective interventional case series at a university hospital tertiary referral center. Corneal biomechanical properties were measured in patients with keratoconus undergoing corneal cross-linking, immediately before and after epithelial debridement by using a dynamic ultrahigh-speed Scheimpflug camera equipped with a noncontact tonometer.

RESULTS

The study comprised 45 eyes of 45 patients with a mean age of 19.6 ± 4.9 years (range 14-34). The cornea was found to be 23.7 ± 15.7 μm thinner after epithelial removal (P < 0.01). Corneal stiffness was reduced after epithelial removal as demonstrated by a significant decrease of parameters such as stiffness parameter A1 (12.31, P < 0.01), stiffness parameter-highest concavity (2.25, P < 0.01), A1 length (0.13 mm, P = 0.04), highest concavity radius of curvature (0.26 mm, P = 0.01), highest concavity time (0.22 ms, P = 0.04) and an increase in A1 velocity (-0.01 m/s, P = 0.01), A1 deformation amplitude (-0.03 mm, P ≤ 0.01), A1 deflection length (-0.32 mm, P < 0.01), A2 deformation amplitude (-0.03 mm, P = 0.01), and A2 deflection length (-1.00 mm, P < 0.01). There were no significant differences in biomechanical intraocular pressure (0.15 mm Hg, P = 0.78), deformation amplitude (0.03, P = 0.54), maximum inverse radius (-0.01 mm, P = 0.57), and whole eye movement length (-0.02 mm, P = 0.12).

CONCLUSIONS

Dynamic ultrahigh-speed Scheimpflug camera equipped with a noncontact tonometer offers an alternative method for in vivo measurements of the epithelial layer's contribution to corneal biomechanical properties. Our results suggest that corneal epithelium may play a more significant role in corneal biomechanical properties in patients with keratoconus than previously described.

Repeatability and agreement of biometric measurements using spectral domain anterior segment optical coherence tomography and Scheimpflug tomography in keratoconus

Purpose

To compare the repeatability and agreement in biometric measurements using Spectral Domain Anterior Segment OCT (AS-OCT, REVO-NX, Optopol) and Scheimpflug tomography (Pentacam-AXL, Oculus) in keratoconus.

Methods

Prospective case series at a university hospital tertiary center. Axial length (AL), anterior chamber depth (ACD), central corneal thickness (CCT), and thinnest corneal thickness (TCT) were measured using both devices in patients with keratoconus. Three groups were analyzed: eyes with no prior crosslinking or contact lens wear (Group A), eyes with prior crosslinking (Group B), and eyes with prior contact lens wear (Group C). Repeatability and agreement of measurements were analyzed.

Results

The study comprised of 214 eyes of 157 subjects. In Group A (n = 95 eyes), Group B (n = 86 eyes), and Group C (n = 33 eyes), intraclass correlation coefficient (ICC) was higher than 0.90 for all examined parameters, except for ACD readings in Group A with the REVO-NX (ICC = 0.83). Differences in ACD, TCT, and CCT were significantly different between the two devices for Groups A, B and C (p<0.05). AL measurements differed significantly in Groups A and B (p<0.05) but not in Group C (p = 0.18). Repeatability did not vary significantly between Groups A, B, or C in any parameter with both devices (p>0.05). There was poor agreement between the two devices across all parameters (p<0.05).

Conclusions

Both devices demonstrated good repeatability but poor agreement across AL, ACD, CCT and TCT measurements. There was no significant difference in repeatability in virgin eyes compared to eyes with prior crosslinking or contact lens wear, however, the interchangeable use of the two devices is not recommended.

Visual and Tomographic Outcomes of a 300° Arc-length ICRS Implantation in Moderate to Advanced Central Keratoconus

PURPOSE

To assess the outcomes of implanting a new 300° arc-length intrastromal corneal ring segment (ICRS) in moderate to advanced central hyperprolate keratoconus.

METHODS

Forty-two eyes with moderate to advanced central hyperprolate keratoconus were evaluated before and after implanting an inferior 300° ICRS (AJL Ophthalmic). The clinical measurements taken included manifest refraction, uncorrected (UDVA) and corrected (CDVA) distance visual acuity (logMAR scale), and corneal tomographic analysis (Sirius; Costruzioni Strumenti Oftalmici). Changes in the anterior and posterior corneal surfaces and the root mean square (RMS) for coma-like aberrations for a pupil size of 4.5 mm were evaluated. All examinations were performed before surgery and 6 months after surgery.

RESULTS

The mean UDVA improved from 1.12 ± 0.48 logMAR preoperatively to 0.73 ± 0.37 logMAR postoperatively (P < .0001). The mean CDVA changed from 0.33 ± 0.20 to 0.20 ± 0.11 logMAR (P < .0001). Postoperatively, the CDVA improved by two or more lines in 45.2% of the eyes and increased by one line in 19.04%, and none of the patients lost lines of CDVA. All of the anterior and posterior corneal tomographic parameters analyzed were significantly improved after surgery, except posterior flat keratometry, which remained unchanged. In 80.95% of the eyes, the postoperative mean keratometry was 50.00 diopters or less. The 6-month RMS for coma-like aberrations also declined significantly from 1.57 ± 0.68 to 1.06 ± 0.42 µm after surgery (P < .0001).

CONCLUSIONS

These results suggest that implanting a 300° arc-length ICRS is a safe and effective procedure for treating patients with moderate to advanced central hyperprolate keratoconus and clear cornea. [J Refract Surg. 2021;37(4):249-255.].

Evaluation of keratoconus progression and visual improvement after intrastromal corneal ring segments implantation: A retrospective study

OBJECTIVE

To investigate the role of ICRS in halting keratoconus progression in a large sample of patients.

METHODS

A retrospective, non-comparative, interventional study based on the review of medical records of patients diagnosed with keratoconus who underwent Ferrara corneal ring segment implantation. A retrospective chart analysis study of 123 operated eyes with follow-up ranging from 3 to 16 years (mean 5.3 ± 3.6 years) was performed. This study was carried out at Ocular Surgery Unit, São Paulo, Brazil. All topographic data were obtained from Pentacam (Oculus, Arlington, USA). The same surgeon performed all surgeries, and the Ferrara ICRS nomogram was used for ICRS selection in all cases.

RESULTS

Corrected distance visual acuity, keratometry, and topographic astigmatism improved in most cases, with statistical significance. In 42 eyes (53.8%), there was an increase in K1 or K2, and in 36 (46.2%), there was a reduction or maintenance in K1. Considering a difference higher than 1 D, between 3-month post-surgery and final visit (group 3), 32 eyes (41%) showed an increase, and 46 eyes (59%) ended equal or below this value.

CONCLUSION

The implantation of ICRS showed improvement in visual and keratometric indexes. The majority of patients did not increase more than one diopter in keratometric values after ICRS implantation. ICRS may be effective for slowing disease progression, especially in older patients.

Intracorneal circular ring implant with femtosecond laser: Pocket versus tunnel

PURPOSE

To evaluate and compare visual and refractive outcomes after implantation of the intracorneal continuous ring 360° arc (ICCR) versus the intracorneal ring segment 340° arc (ICRS) using femtosecond laser for central keratoconus.

SETTING

Research Department, Oftalmosalud, Instituto de Ojos, Lima, Peru.

METHODS

Randomized study that included 40 eyes of 32 patients diagnosed with central keratoconus between November 2014 and March 2015. Twenty eyes had an implantation of ICCR (MyoRing, Dioptex GmbH, Austria) through an intrastromal pocket and 20 eyes had an implantation of ICRS (Keraring, Mediphacos, Brazil) through an intrastromal tunnel. Both procedures were performed with a femtosecond laser (LDV Z6 model, Ziemer Ophthalmic Systems AG). Visual acuity (VA), refraction, and Scheimpflug imaging analysis were performed pre- and postoperatively at 1 month and 1 year. Comparisons of means were performed using the Student's t-test.

RESULTS

At 1 year, uncorrected VA improved 0.77 LogMAR (p < 0.001) in the ICCR group and 0.79 LogMAR (p = 0.01) in the ICRS group; mean sphere improvement was 5.13 Diopters (D) in the ICCR group and 6.27 D in the ICRS group (p < 0.001 both); mean Steeper Keratometry improvement was 4.24 D in the ICCR group and 5.53 D in the ICRS group (p < 0.001 both). In the ICCR group, mean decrease in the pachymetry at the thinnest point of the cornea was 32.16 µm (p = 0.01), and in the ICRS group, mean increase was 4.2 µm at 1 year (p = 0.61).

CONCLUSION

Intracorneal continuous ring 360° arc (ICCR) and intracorneal ring segment 340° (ICRS) are effective treatments for central keratoconus. No significant differences between rings were found on visual acuity, refraction, and keratometry improvement.

Impact of contact lens wear on epithelial alterations in keratoconus

PURPOSE

The purpose of this study was to characterize the central epithelial thickness (CET) of penetrating keratoplasty corneal specimens obtained from patients with keratoconus (KC) and correlate the histological patterns with their clinical history.

METHODS

Ex vivo histological imaging was performed to measure CET and total corneal thickness (TCT) in 56 patients with KC. Microscopic slides from penetrating keratoplasty corneal specimens, stained with hematoxylin and eosin were evaluated using bright field microscopy. CET and TCT were measured, and morphological features were studied. Clinical history regarding duration of KC prior to surgery and length of and tolerance to contact lens wear were compared and analyzed.

RESULTS

The microscopic slides of all patients available for follow up (n=48) were analyzed and CET and TCT were measured. The histological evaluation revealed 3 distinctive epithelial patterns. Pattern 1 with central hypertrophic and hydropic changes (n=19) measured 70.89±25.88μm in CET and 308.63±100.74μm in TCT; Pattern 2 (n=14) had not changed, similar to normal epithelium CET and TCT measuring 36.5±7.02μm and 260.14±87.93μm respectively. Pattern 3 (n=15) demonstrated thinner central epithelium characterized by atrophy and focal hydropic changes measuring 19.93±4.60μm and 268.00±79.39μm in CET and TCT respectively (all p<0.0001). The presence of Pattern 2 characterized by similar to normal CET was correlated with the duration of the condition (R=0.600, p=0.030). There was a significant difference in the length of CL wear comparing those with patterns 1 and 2 versus 3 (least no. of CL years) (p=0.05 and p=0.33 respectivelly).

CONCLUSIONS

Patients with advanced disease have various central corneal epithelial changes detected with histology. Although each central epithelial pattern type was distinctive comparing the 3 patterns, there was no correlation with years of CL wear but only with the duration of the condition.

Case Report: Successful Corneal Crosslinking in a Patient with Corneal Ectasia Associated with Stevens-Johnson Syndrome

SIGNIFICANCE

Corneal ectasia can be a complication of Stevens-Johnson syndrome. When detected in a timely manner, corneal crosslinking can be a safe treatment. This is an important association to highlight that early diagnosis and treatment can prevent the need for invasive surgical procedures such as keratoplasty.

PURPOSE

This study aimed to report a successful accelerated epithelium-off corneal crosslinking in a rare case of corneal ectasia secondary to Stevens-Johnson syndrome.

CASE REPORT

A 25-year-old Indian man presented with a progressive visual acuity decline 5 years after an acute episode of Stevens-Johnson syndrome secondary to penicillin ingestion. Serial tomography scans confirmed the diagnosis of corneal ectasia. After the preparation of the ocular surface, which was deemed to have a mild degree of limbal stem cell deficiency, with frequent preservative-free lubrication and steroid use, accelerated epithelium-off crosslinking was performed with 4 minutes of continuous ultraviolet-A exposure at 30 mW/cm2 and a total energy dose of 7.2 J/cm2. Complete re-epithelialization was observed at 72 hours after crosslinking with no complications. Corneal tomography 15 months after treatment showed stabilization of ectasia, with improvement in visual acuity.

CONCLUSIONS

Corneal ectasia is a rare but important complication of Stevens-Johnson syndrome. Accelerated epithelium-off crosslinking treatment can be considered in patients with a compromised ocular surface after Stevens-Johnson syndrome. Pre-operative optimization of the ocular surface and vigilant monitoring in the early post-operative period are recommended for the prevention of complications.

Blended Natural Support Materials-Collagen Based Hydrogels Used in Biomedicine

Due to their unique properties-the are biocompatible, easily accessible, and inexpensive with programmable properties-biopolymers are used in pharmaceutical and biomedical research, as well as in cosmetics and food. Collagen is one of the most-used biomaterials in biomedicine, being the most abundant protein in animals with a triple helices structure, biocompatible, biomimetic, biodegradable, and hemostatic. Its disadvantages are its poor mechanical and thermal properties and enzymatic degradation. In order to solve this problem and to use its benefits, collagen can be used blended with other biomaterials such as alginate, chitosan, and cellulose. The purpose of this review article is to offer a brief paper with updated information on blended collagen-based formulations and their potential application in biomedicine.

[Intraocular correction of ametropia in patients with keratoconus]

This review was conducted due to the growing number of patients with keratoconus requiring cataract surgery and the complexity of surgical planning. The article reviews preoperative planning, intraoperative options, and postoperative management, which can help obtain high functional results. Treatment of cataracts in keratoconic eyes requires a multifaceted approach. In some cases, in the preoperative period, interventions such as crosslinking and implantation of intrastromal segments or corneal ring may be required to ensure stable keratometry values for accurate intraocular lens (IOL) calculations. The use of stabilizing procedures prior to optical biometrics can assist in preoperative lens selection and provide predictable surgical outcomes. To achieve targeted refraction and reduce unwanted optical effects, it is necessary to take a critical approach when choosing the type of lens (toric, monofocal). This is due to the appearance of aberrations of different order after preliminary surgical interventions on the cornea. The intraoperative decision plays important role in choosing the position of the corneal incisions, how to use sutures for wound adaptation, choosing scleral approaches to minimize possible postoperative complications. In the postoperative period, the degree of irregular astigmatism and the need for rigid gas-permeable or scleral lenses should be assessed.

Intrastromal corneal ring segment implantation in paracentral keratoconus with perpendicular topographic astigmatism and comatic axis

PURPOSE

To evaluate the outcomes of implanting intrastromal corneal ring segment (ICRS) using two different strategies in a specific paracentral keratoconus phenotype.

METHODS

Eighty-nine eyes with paracentral keratoconus with perpendicular topographic astigmatism and comatic axes were evaluated before and after implanting a 150° arc-length ICRS. Patients were divided into two groups according to the axis where the ICRS was implanted: Group I: comatic axis and Group II: flat topographic axis. Uncorrected (UDVA) and corrected (CDVA) distance visual acuities, refractive errors, and root mean square (RMS) for coma-like aberration were recorded. The postoperative follow-up was 1 year.

RESULTS

Mean UDVA (logMAR) changed from 0.49 ± 0.37 preoperatively to 0.30 ± 0.32 6 months afterwards (p < 0.001) in the group I and from 0.53 ± 0.34 to 0.37 ± 0.35 (p < 0.001), in the group II. Mean CDVA in group I changed from 0.11 ± 0.18 preoperatively to 0.06 ± 0.14 6 months after surgery (p < 0.001). In group II the improvement did not reach statistical significance (from 0.09 ± 0.10 to 0.07 ± 0.09; p = 0.06). No eyes lost lines of CDVA in group I. Eight eyes (15.7%) lost lines of CDVA in group II. The spherical equivalent decreased after surgery in both groups (p < 0.001). The RMS for corneal coma-like aberration only decreased in the group I (p < 0.001).

CONCLUSION

Both strategies provided safe and effective visual and refractive outcomes in the specific keratoconus phenotype analyzed. The orthopedic strategy provided better visual outcomes than the refractive one.

Histological Patterns of Epithelial Alterations in Keratoconus

Purpose

The purpose of this study was to confirm the presence of specific patterns of epithelial response in corneal buttons from keratoconus patients.

Methods

This was a retrospective and descriptive study. 90 penetrating keratoplasty specimens obtained from patients diagnosed with keratoconus were evaluated using bright-field microscopy. Morphologically identifiable characteristics including epithelial cell density and epithelial thickness were analyzed on hematoxylin and eosin- (H&E-) and periodic acid of Schiff- (PAS-) stained slides.

Results

Three distinctive patterns of epithelial alteration of the central cornea were established. Pattern 3, in which the central epithelium was as thick as peripheral epithelium, was the commonest (44.4%), followed by the pattern 2, defined as central epithelium thinner than periphery epithelium (38.9%), and the uncommonest pattern was number 1, with central epithelium thicker than the periphery (16.7%).

Conclusions

Three distinctive histologic patterns that could potentially have a diagnostic and prognostic value in keratoconus patients were found.

Measurement of refractive, wavefront, topographic, and keratometric changes attributable to epithelial removal in keratoconus

OBJECTIVE

The corneal epithelium is able to mask topographic and keratometric abnormalities of the underlying Bowman layer in keratoconus, but its contribution to refractive and wavefront parameters has not yet been studied. This study compared the refractive and aberrometric features of the corneal epithelium and Bowman layer in eyes with keratoconus before and after epithelial debridement.

METHODS

Corneal refractive and wavefront variables were measured in patients with keratoconus undergoing corneal crosslinking-immediately before and after epithelial debridement using a third-generation combined corneal topographer, autorefractor, and aberrometer.

RESULTS

After epithelial debridement, there were significant changes in spherical equivalent (-1.37 D; p < 0.01) and asphericity (-0.64; p = 0.03). The mean difference in the magnitude of epithelium-induced astigmatism in the 3rd and 5th central millimeter rings was 0.44 ± 3.20 D × 8 and 0.43 ± 2.75 D × 21 (positive cylinder), respectively. Corneal astigmatism axis shifted in the against-the-rule orientation after epithelial debridement. There were no significant changes in any corneal higher-order aberration parameter after epithelial debridement (p > 0.05).

CONCLUSIONS

In eyes with keratoconus, epithelial debridement increased the magnitude of anterior corneal prolateness and tended to increase astigmatism and shift its axis toward the against-the-rule orientation. This study supports the notion that the corneal epithelium smooths underlying Bowman layer irregularity in keratoconus.

Safety, Efficacy, and Predictive Factors of Conventional Epithelium-Off Corneal Crosslinking in the Treatment of Progressive Keratoconus

Purpose

To report predictive factors of outcome of conventional epithelium-off corneal crosslinking (CXL) in the treatment of progressive keratoconus.

Methods

This is a monocentric observational retrospective study conducted at Eye and Ear International Hospital, Lebanon. All patients with progressive keratoconus who underwent CXL between January 2008 and January 2016, with minimal 3-years follow-up were included. Primary treatment outcomes were maximum keratometry (K max), best-corrected distance visual acuity (CDVA), and failure. Failure was defined as an increase of 1.00 diopters (D) or more in K max and/or an increase of 0.1 logMAR or more in CDVA and conversion to corneal transplantation. Statistical analysis was done to identify predictors of treatment success. Univariate and multivariate analyses were performed to determine the correlations between baseline parameters and outcomes, and an equation for predicting K max and CDVA was created.

Results

156 eyes of 102 patients were enrolled. The mean age was 23.85 ± 6.52 years. Failure occurred in 31 eyes (19.87%). Gender and thinnest pachymetry did not have any impact on postoperative outcomes. Concerning the CDVA outcome, multivariate analysis showed that a better preoperative CDVA was associated with higher improvement in CDVA, and higher baseline K max and higher posterior mean K were associated with a worse outcome CDVA. Regarding postoperative K max, a higher baseline K max, a worse baseline CDVA, and a younger age were associated with less flattening postoperatively.

Conclusion

CXL is a safe and effective method in treating progressive keratoconus. However, the clinical benefits can differ among patients, and in our series, a nonnegligible number of cases show a continued progression of their ectasia. Further studies to identify predictors of postoperative progression prior to the procedure could help sort out good responders to treatment.

Changes in higher order aberrations after central corneal regularization - a comparative two-year analysis of a semi-automated topography-guided photorefractive keratectomy combined with corneal cross-linking

Background

The optical quality in progressive keratoconus deteriorates due to ectasia and distortion of the corneal shape and optics. While corneal cross-linking (CXL) aims at stopping disease progression, “CXL-Plus” combines CXL with excimer laser ablation to improve visual function. Central Corneal Regularization (CCR) represents a therapeutic excimer laser modality specifically designed to smoothen the ectatic corneal shape and to reduce higher order aberrations (HOA). We set out to compare CXL-Plus, consisting of CXL combined with CCR, with CXL by itself for patients with progressive keratoconus.

Methods

Retrospective 2-year matched group analysis of patients who either underwent CXL-Plus (n = 28) or CXL as a sole procedure (n = 28) for progressive keratoconus. Main outcome parameters were HOA, visual function and tomographic results 12 and 24 months postoperatively.

Results

After 12 months, the total HOA root mean square wavefront error was reduced from 0.79 ± 0.30 to 0.40 ± 0.19 μm (CXL-Plus; p <  0.0001) and changed from 0.71 ± 0.28 to 0.73 ± 0.36 μm (CXL; p = 0.814). Uncorrected distance visual acuity improved from 0.70 ± 0.35 to 0.36 ± 0.29 logMAR (CXL-Plus; p = 0.0002) and from 0.65 ± 0.39 to 0.46 ± 0.37 logMAR (CXL; p = 0.067), translating to gains of three or more lines in 50% (CXL-Plus) and 36% (CXL) of patients. The steepest keratometry value (Kmax) regressed by 5.84 D (CXL-Plus; p <  0.0001) and 0.66 D (CXL; p = 0.752). For none of the investigated parameters a statistically significant change could be shown between 12 and 24 months.

Conclusions

CXL-Plus in the form of a CCR reduces HOA and Kmax more effectively than CXL as a sole procedure.

Reliability of the Evidence Addressing Treatment of Corneal Diseases: A Summary of Systematic Reviews

Importance

Patient care should be informed by clinical practice guidelines, which in turn should be informed by evidence from reliable systematic reviews. The American Academy of Ophthalmology is updating its Preferred Practice Patterns (PPPs) for the management of the following 6 corneal diseases: bacterial keratitis, blepharitis, conjunctivitis, corneal ectasia, corneal edema and opacification, and dry eye syndrome.

Objective

To summarize the reliability of the existing systematic reviews addressing interventions for corneal diseases.

Data Source

The Cochrane Eyes and Vision US Satellite database.

Study Selection

In this study of published systematic reviews from 1997 to 2017 (median, 2014), the Cochrane Eyes and Vision US Satellite database was searched for systematic reviews evaluating interventions for the management of any corneal disease, combining eyes and vision keywords and controlled vocabulary terms with a validated search filter.

Data Extraction and Synthesis

The study classified systematic reviews as reliable when each of the following 5 criteria were met: the systematic review specified eligibility criteria for inclusion of studies, conducted a comprehensive literature search for studies, assessed risk of bias of the individual included studies, used appropriate methods for quantitative syntheses (meta-analysis) (only assessed if meta-analysis was performed), and had conclusions that were supported by the results of the systematic review. They were classified as unreliable if at least 1 criterion was not met.

Main Outcomes and Measures

The proportion of systematic reviews that were reliable and the reasons for unreliability.

Results

This study identified 98 systematic reviews that addressed interventions for 15 corneal diseases. Thirty-three of 98 systematic reviews (34%) were classified as unreliable. The most frequent reasons for unreliability were that the systematic review did not conduct a comprehensive literature search for studies (22 of 33 [67%]), did not assess risk of bias of the individual included studies (13 of 33 [39%]), and did not use appropriate methods for quantitative syntheses (meta-analysis) (12 of 17 systematic reviews that conducted a quantitative synthesis [71%]). Sixty-five of 98 systematic reviews (66%) were classified as reliable. Forty-two of the 65 reliable systematic reviews (65%) addressed corneal diseases relevant to the 2018 American Academy of Ophthalmology PPPs; 33 of these 42 systematic reviews (79%) are cited in the 2018 PPPs.

Conclusions and Relevance

One in 3 systematic reviews addressing interventions for corneal diseases are unreliable and thus were not used to inform PPP recommendations. Careful adherence by systematic reviewers and journal editors to well-established best practices regarding systematic review conduct and reporting might help make future systematic reviews in eyes and vision more reliable.

Accelerated, Pulsed Collagen Cross-Linking versus the Dresden Protocol in Keratoconus: A Case Series

PURPOSE

The aim of our study was to compare the depth of the demarcation line developing in the cornea after the standard Dresden protocol versus the accelerated, pulsed, epithelium-off corneal collagen cross-linking (CXL).

METHODS

This was a nonrandomized, retrospective case series. Patients with progressive keratoconus were treated with either the standard Dresden protocol (Group 1) or accelerated, epithelium-off CXL using the Avedro (Waltham, MA, USA) device (Group 2). The accelerated CXL protocol involved 18 min of pulsed ultraviolet-A (20 mW/cm2, 7.2 J/cm2, pulsed pro-file: 1 s on, 2 s off). The depth of the demarcation line was measured about 3 months postoperatively.

RESULTS

Fifty-nine eyes of 35 subjects were included in the analysis. Group 1 consisted of 19 eyes, and Group 2 of 40 eyes. The mean age of the participants was 22.21 years in Group 1 and 26.55 years in Group 2 (p = 0.184). The mean preoperative K value was 44.89 D in Group 1 and 45.20 D in Group 2 (p = 0.768). The depth of the demarcation line was 322.50 μm in Group 1 and 319.95 μm in Group 2 (p = 0.937).

CONCLUSIONS

The demarcation line depth was not statistically significantly different between the two protocols. The significance of the demarcation line depth has not been fully clarified in the literature. Our results support the contention that these two techniques may have similar structural outcomes and ef-ficacies in the treatment of keratoconus.

Optical coherence elastography by ambient pressure modulation for high-resolution strain mapping applied to patterned cross-linking

The purpose of this study was to develop a novel non-contact optical coherence elastography (OCE) approach to measure laterally and axially highly resolved corneal strain distribution at different stages of patterned corneal cross-linking (CXL). Freshly enucleated rat eyes were obtained and prepared for accelerated patterned CXL treatment with distinct ultraviolet (UV) patterns (central, peripheral, bow-tie irradiation). Each cornea was measured repeatedly, in three different conditions: (i) virgin, (ii) after epithelial debridement and 0.5% hypo-osmolar riboflavin instillation for 30 min, and (iii) after patterned CXL at 9 mW cm-2 for 10 min. For biomechanical assessment, the corneal deformation response to an ambient pressure variation of -2 mmHg was recorded by OCE. Strain maps were obtained from phase and magnitude changes in the complex optical coherence tomography signal. Virgin corneas presented negative strain (-2.7 ± 1.1‰) in the anterior cornea and positive strain (1.9 ± 1.3‰) in the posterior cornea. A pronounced shift towards positive strains in the anterior cornea (particularly in UV-irradiated regions) was observed after CXL. Patterned UV irradiation induced localized strain alterations closely matching the geometry of the irradiation pattern. This study demonstrates the possibility of non-contact OCE by ambient pressure modulation, which could substantially improve the early diagnosis of corneal degeneration, advance research in small-animal eyes and refine in vitro mechanical investigation.

Efficacy and Safety of Transglutaminase-Induced Corneal Stiffening in Rabbits

Purpose

To evaluate the biomechanical efficacy and safety of in vivo microbial transglutaminase (Tgases)-induced corneal crosslinking in a rabbit model.

Methods

A total of 34 white New Zealand rabbits were divided into two groups, a biochemistry group and a photochemistry group. The right eye of every rabbit was treated and left eyes served as negative controls. In the biochemistry group, a 1 U/mL solution of crosslinking agent microbial Tgases (Tgases CXL) was applied to the corneal surface, while in the photochemistry group, clinical ultraviolet A-riboflavin crosslinking (UVA/RF CXL) was used. Efficacy and safety evaluated on the 14th day after the procedures. Twelve pairs of corneal strips were harvested from the eyes of 12 euthanized rabbits in every group, and uniaxial tensile tests were performed to evaluate ex vivo biomechanical effects. The CXL-treated eye to its corresponding untreated eye ratio of tangent modulus were calculated. Another five pairs of corneal button were excised from euthanized animals in every group for corneal stroma and endothelium staining to evaluate changes in keratocyte distribution and endothelial cell damage.

Results

In tensile tests, tangent modulus was statistically higher in the Tgases CXL groups under 1.0 MPa (26.59 ± 4.54 vs. 21.47 ± 4.72 MPa, P = 0.04) and 1.5 MPa (29.75 ± 5.01 vs. 20.47 ± 6.63 MPa, P = 0.00). The tangent modulus ratio of Tgases group (1.72 ± 1.0 vs. 1.05 ± 0.22, P = 0.04) was significantly higher than that of UVA/RF under 1.5-MPa stress. The distribution of keratocytes in the corneal stroma and the morphologies of endothelial cells were similar in Tgases CXL-treated and untreated corneas. However, in the UVA/RF CXL group, keratocytes in the anterior half of stromal thickness were lost, and clear endothelial cell apoptosis was observed.

Conclusions

Tgases-CXL effectively stiffened the cornea and caused no damage to the endothelium and keratocytes in the cornea. This crosslinking method could be useful as a next-generation treatment for corneal ectasia and could replace CXL of photochemistry.

Translational Relevance

These findings may give a new hope to biomechanically compromised corneal disease due to mechanical forces, such as corneal ectasia and keratoconus. A next-generation treatment to these corneal diseases due to mechanical forces may be designed based on the new findings.

Comparison of corneal biomechanical properties following penetrating keratoplasty and deep anterior lamellar keratoplasty for keratoconus

IMPORTANCE

Keratoplasty is a surgical procedure to create a more regular optical surface following biomechanical weakening of the cornea in keratoconus. The ideal keratoplasty procedure should also restore corneal biomechanics to that of the healthy cornea.

BACKGROUND

This study aimed to evaluate and compare the biomechanical properties of corneas following penetrating keratoplasty (PKP) and predescematic deep anterior lamellar keratoplasty (DALK) to those of healthy eyes.

DESIGN

Prospective cross-sectional study.

PARTICIPANTS

Two cohorts of post-keratoplasty eyes (42 eyes with PKP and 27 eyes with DALK) with each other, and with a cohort of 152 healthy eyes.

METHODS

All eyes were examined by slit-lamp biomicroscopy, tomography, anterior segment-OCT and non-contact tonometry CorVis ST (CST).

MAIN OUTCOME MEASURES

CST biomechanical parameters, maximum corneal deformation (MCD) and corneal energy dissipation were compared between keratoplasty techniques, and with healthy eyes.

RESULTS

The mean age of participants with PKP and DALK were 35 ± 13.7 and 36.1 ± 12.6 years, respectively. None of the CST parameters were significantly different between PKP and DALK eyes. However, when compared to healthy corneas, numerous parameters were significantly different for both keratoplasty techniques. Of note, MCD was significantly higher in PKP compared to DALK and healthy corneas, after controlling for co-factors.

CONCLUSIONS AND RELEVANCE

Neither type of keratoplasty technique utilized in keratoconus completely restored corneal biomechanical properties to that of healthy corneas. However, PKP resulted in a greater number of parameters significantly different to healthy corneas, compared to DALK.

Differential Regional Stiffening of Sclera by Collagen Cross-linking

Purpose: Corneal collagen cross-linking by ultraviolet light activation of riboflavin has been used clinically to enhance corneal stiffness. We sought to determine if cross-linking differentially affects scleral regions.Methods: Adjacent, parallel strips of sclera were cut from superolateral, superomedial, inferolateral, and inferomedial quadrants of posterior and equatorial sclera of 12 human cadaver eyes. One of each pair served as control while the other was cross-linked by immersion in 0.1% riboflavin and 365 nm exposure at 6 mW/cm² irradiance for 30 min. Behavior of strips was characterized using a microtensile load cell. Preloaded strips were imaged using orthogonally mounted cameras and optical coherence tomography to determine specimen dimensions including cross-sectional area. Tension was measured during 0.1 mm/s constant rate elongation.Results: Young's modulus (YM), the slope of the relationship relating tensile stress to strain, was calculated at 8% strain, and increased significantly after cross-linking (P < .001). In posterior sclera, mean (± standard error of mean, SEM) YM is increased in the superolateral, superomedial, inferolateral, and inferomedial quadrants by 46 ± 15%, 32 ± 11%, 67 ± 20%, and 53 ± 11%, respectively. In equatorial sclera, YM is increased by 139 ± 43%, 68 ± 27%, 143 ± 92%, and 68 ± 14%, respectively. The YM of pooled equatorial quadrants increased significantly more than that of the pooled posterior quadrants.Conclusions: Scleral collagen cross-linking by ultraviolet activation of riboflavin differentially increases scleral YM more in the equatorial than posterior sclera, and most in the lateral, equatorial sclera. Cross-linking might be used to arrest progressive myopia or to prevent staphyloma formation.