Review of Laser Vision Correction (LASIK, PRK and SMILE) with Simultaneous Accelerated Corneal Crosslinking - Long-term Results

Comparative Analysis of Corneal Wound Healing: Differential Molecular Responses in Tears Following PRK, FS-LASIK, and SMILE Procedures

BACKGROUND/OBJECTIVES

In this study, we aimed to analyze the changes in the expression profiles of selected messenger RNAs (mRNAs) and their encoded proteins in the tears of patients undergoing photorefractive keratectomy (PRK), femtosecond-assisted laser in situ keratomileusis (FS-LASIK), and small-incision lenticule extraction (SMILE) procedures.

METHODS

A total of 120 patients were divided into three groups based on the laser vision correction (LVC) procedure: PRK, FS-LASIK, or SMILE. Tear samples were collected preoperatively and at 1, 7, 30, and 180 days postoperatively. The expression levels of selected messenger RNAs (mRNAs) and proteins were analyzed by using reverse transcription quantitative polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA), respectively.

RESULTS

PRK and FS-LASIK elicited significantly stronger biological responses than SMILE. Interleukin-15 (IL-15) expression increased notably in the PRK and FS-LASIK groups, with mRNA levels reaching fold changes of 4.65 ± 0.65 and 4.99 ± 0.28, respectively, on day 1, compared with only 2.09 ± 0.23 in the SMILE group. Vascular endothelial growth factor A (VEGFA) levels were also elevated in the PRK (2.98 ± 0.23 fold change) and FS-LASIK groups (3.45 ± 1.09 fold change) on day 1, while the SMILE group showed minimal fluctuations. The protein concentration analysis based on the ELISA confirmed these trends, with IL-15 levels peaking at 54.2 ± 2.5 pg/mL in the PRK group and 52.8 ± 3.1 pg/mL in the FS-LASIK group, compared with 32.4 ± 1.9 pg/mL in the SMILE group on day 1. Similarly, VEGFA protein concentrations were the highest in the PRK (72.4 ± 4.1 pg/mL) and FS-LASIK patients (69.5 ± 3.8 pg/mL) on day 1 but remained low in the SMILE patients (45.6 ± 2.3 pg/mL). By day 180, gene expression and protein levels in all groups had stabilized, returning to near-preoperative values.

CONCLUSIONS

PRK and FS-LASIK induced more pronounced molecular and protein-level changes during corneal wound healing than the less invasive SMILE procedure, indicating stronger biological responses. These findings suggest that tailored postoperative care based on the specific procedure could optimize healing and patient outcomes. However, further research with larger sample sizes and longer follow-ups is needed to confirm these observations and develop personalized treatment strategies.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Collagen is crucial target protein for scleral remodeling and biomechanical change in myopia progression and control

In recent decades, the prevalence of myopia has been on the rise globally, attributed to changes in living environments and lifestyles. This increase in myopia has become a significant public health concern. High myopia can result in thinning of the sclera and localized ectasia of the posterior sclera, which is the primary risk factor for various eye diseases and significantly impacts patients' quality of life. Therefore, it is essential to explore effective prevention strategies and programs for individuals with myopia. Collagen serves as the principal molecule in the extracellular matrix (ECM) of scleral tissue, consisting of irregular collagen fibrils. Collagen plays a crucial role in myopia progression and control. During the development of myopia, the sclera undergoes a thinning process which is primarily influenced by collagen expression decreased and remodeled, thus leading to a decrease in its biomechanical properties. Improving collagen expression and promoting collagen crosslinking can slow down the progression of myopia. In light of the above, improving collagen expression or enhancing the mechanical properties of collagen fibers via medication or surgery represents a promising approach to control myopia.

[Clinical outcomes of SMILE Xtra for myopia correction]

PURPOSE

This study assesses the treatment outcomes of patients with thin corneas and/or borderline corneal topography who underwent combined refractive surgery using the SMILE Xtra technique.

MATERIAL AND METHODS

The study included 53 patients (105 eyes) with myopia and a risk of developing keratectasia according to the Randleman criteria. All patients underwent prophylactic crosslinking following the SMILE procedure by introducing riboflavin solution into the corneal pocket, followed by ultraviolet irradiation according to the SUB-400 protocol with additional acceleration. The results were evaluated using data from Scheimpflug analyzer, analysis of corneal biomechanical properties, optical coherence tomography (OCT), and standard ophthalmological examinations. Follow-up lasted up to 12 months.

RESULTS

The preoperative spherical equivalent of refraction was -4.09±1.30 D, and postoperative measurements on day 1, day 7, and at 1, 3, 6, and 12 months were: -0.08±0.64; 0.1±0.53; 0.2±0.48; 0.05±0.52; -0.29±0.47; 0.1±0.49 D, respectively. On day 1, uncorrected visual acuity (UCVA) increased to 0.78±0.17, rising to 0.94±0.11 by day 7, and remained stable throughout the follow-up. Mean keratometry values preoperatively were 44.32±1.3 D, and 40.89±1.65 D on day 1, with no statistically significant changes throughout the follow-up. Central corneal thickness decreased from 528.30±28.71 μm preoperatively to 459.32±28.92 μm on day 1 and 440.54±29.12 μm on day 7. Patient complaints of blurred vision on day 1 were associated with mild corneal edema due to residual riboflavin and energy load from UV treatment; these symptoms resolved by day 7. No regression of refractive results or keratectasia was observed throughout the follow-up period.

CONCLUSION

SMILE Xtra can be used for myopia correction in cases with an increased risk of postoperative keratectasia in patients with thin corneas and/or borderline corneal topography readings.

Development of interface haze after femtosecond laser-assisted in situ keratomileusis with accelerated corneal crosslinking: a case series

BACKGROUND

Femtosecond laser-assisted in situ keratomileusis (FS-LASIK) with accelerated corneal crosslinking (FS-LASIK Xtra) is a recent procedure to achieve safer corneal ablation in myopic patients with borderline corneal thickness. Despite its well-accepted effectiveness, the development of remarkable interface haze is a potential concern but has rarely been reported and discussed.

METHODS

We report for the first time a case series of 11 eyes of 7 patients who developed typical interface haze 1-3 months after FS-LASIK Xtra for the correction of myopia with astigmatism, with intensity grades ranging from 0.5 + to 3 + at the time of onset.

RESULTS

The preclinical spherical diopters of the 7 patients ranged from - 2.25 D to - 9.25 D and cylindrical diopters ranged from - 0.25 D to - 2.50 D. The haze tended to be self-limiting, and topical anti-inflammatory therapy was given to moderate and severe cases, who responded well to treatment.

CONCLUSIONS

The development of clinically significant interface haze is a relatively rare complication after FS-LASIK Xtra but tends to have a higher incidence and intensity compared to conventional stromal surgery such as FS-LASIK. Timely treatment and close follow-up are essential to patients undertaking FS-LASIK Xtra.

Combined simultaneous photorefractive keratectomy and collagen cross-linking in keratoconus suspect patients

PURPOSE

To evaluate the safety and efficacy of combined simultaneous photorefractive keratectomy (PRK) with collagen cross-linking (CXL) in keratoconus suspects (KCS).

METHODS

This was a retrospective, non-randomized study of KCS patients who underwent combined simultaneous PRK with CXL. The efficacy, safety, refractive outcomes, and corneal wavefront aberration changes were assessed after the surgery and compared with existing preoperative data.

RESULTS

Fifty-six eyes of 28 patients, including 20 females (71.4%), with a mean age of 30.92±4.09 years, were enrolled. The mean follow-up was 19.46±8.48 months (range: 7-35). At the conclusion of the study, mean uncorrected distance visual acuity LogMAR improved from 0.89±0.44 preoperatively to 0.04±0.09 postoperatively (P<0.001). In addition, a statistically significant corneal flattening was observed postoperatively, with a decrease in manifest refraction. A statistically significant increase was found in higher-order aberrations (P<0.001), horizontal coma (P<0.001), and spherical aberration (P<0.001) compared with preoperatively. Postoperatively, 41% exhibited refractive astigmatism of 0.50 diopter (D) or less; 83.8% showed 1.00 D or less.

CONCLUSION

The results of our study indicate that combined simultaneous PRK with CXL can be a safe and effective method for treating refractive instability in KCS patients.

Allogenic Lenticular Implantation for Correction of Refractive Error and Ectasia: Narrative Review

INTRODUCTION

Intrastromal lenticule implantation is a promising treatment option for corneal pathologies, from refractive error to ectasia. In this narrative review, we intend to feature up-to-date literature supporting the use of lenticular tissue, a compelling method that can be customized for a variety of applications, providing an additional source of donor tissue for treating corneal diseases.

METHODS

We searched databases PubMed, Mendeley, and Scopus last accessed 10 May 2023, for literature on stromal lenticules and narrowed based on relevance. Review articles, animal studies, ex vivo studies, and book chapters were excluded, while assessable and relevant articles published in English were included.

RESULTS

Storage methods from using fresh lenticules to dehydration have proven successful, with cryopreservation maintaining structure and cellular viability for up to 10 years. Successful use of lenticules for treatment of numerous pathologies including corneal ectasias, hyperopia, and presbyopia with additional insight into the treatment of corneal ulcers and perforations are highlighted in this narrative review.

CONCLUSION

Lenticular implantation is an innovative and advantageous treatment for various ocular pathologies, offering increased bioavailability, flexibility, and customization for patients. They can treat previously untreatable diseases and serve as a replacement for synthetic implants, with promising outcomes worldwide. Lenticular implantation has the potential to become a leading approach in ophthalmologic surgery. Further studies should aim to provide evidentiary support for a standardization of lenticule banking.

Femtosecond-laser-assisted Small Incision Lenticule Extraction to Treat Refractive Error: A Narrative Review

With the approval of the Federal Drug Agency of the USA in 2018, femtosecond laser-assisted small incision lenticule extraction (SMILE) became an officially available option in several countries including Saudi Arabia to treat myopia and astigmatism. Intense marketing by industries has placed both clients and corneal surgeons into a dilemma of the plus and minuses of this option. Although several reviews compare SMILE to other conventional methods, especially laser in situ keratomileusis, this narrative review perhaps for the first time offers a detailed summary of this procedure and compares two sets of published literature, by authors from China and other countries. The efficacy and safety of SMILE seem to outnumber the complications and high cost of the investment. Its long-term usefulness for treating high myopia and hyperopia is still a matter of research.

Use of corneal cross-linking beyond keratoconus: a systemic literature review

PURPOSE

The success of corneal collagen cross-linking in altering keratoconus' clinical course has driven a search for further uses of this procedure. This literature review aims to analyze the scientific evidence available for the benefit of cross-linking in the management of ophthalmic diseases other than progressive keratoconus or ectasia induced by corneal refractive procedures.

METHODS

A systemic literature review.

RESULTS

We reviewed 97 studies. We found that collagen cross-linking can limit the progression of several other corneal ectasias, thus reducing and limiting the need for keratoplasty. Collagen cross-linking also can reduce the refractive power of the cornea and can be considered for a moderate degree of bacterial keratitis or when the organism is unidentified, which is refractive to antibiotics alone. However, the comparative rarity of these procedures has limited the extent of evidence. In fungal, Acanthamoeba, and herpes virus keratitis, the evidence is inconclusive of the safety and efficacy of cross-linking.

CONCLUSION

Current clinical data is limited, and laboratory data has not fully correlated with published clinical data.

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.

Post-LASIK dry eye disease: A comprehensive review of management and current treatment options

Laser-assisted in situ keratomileusis (LASIK) is a unique corneal stromal laser ablation method that uses an excimer laser to reach beneath corneal dome-shaped tissues. In contrast, surface ablation methods, such as photorefractive keratectomy, include removing epithelium and cutting off the Bowman's layer and the stromal tissue of the anterior corneal surface. Dry eye disease (DED) is the most common complication after LASIK. DED is a typical multi-factor disorder of the tear function and ocular surface that occurs when the eyes fail to produce efficient or adequate volumes of tears to moisturize the eyes. DED influences quality of life and visual perception, as symptoms often interfere with daily activities such as reading, writing, or using video display monitors. Generally, DED brings about discomfort, symptoms of visual disturbance, focal or global tear film instability with possible harm to the ocular surface, the increased osmolarity of the tear film, and subacute inflammation of the ocular surface. Almost all patients develop a degree of dryness in the postoperative period. Detection of preoperative DED and committed examination and treatment in the preoperative period, and continuing treatments postoperatively lead to rapid healing, fewer complications, and improved visual outcomes. To improve patient comfort and surgical outcomes, early treatment is required. Therefore, in this study, we aim to comprehensively review studies on the management and current treatment options for post-LASIK DED.

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.

Three-Year Outcomes of Under-flap Stromal Bed CXL for Early Post-LASIK Ectasia

PURPOSE

To investigate the 36-month clinical outcomes of under-flap stromal bed CXL (ufCXL) and report on its ability to stabilize post-laser in situ keratomileusis (LASIK) ectasia.

METHODS

This case series included 20 eyes with diagnosed early post-LASIK ectasia treated with ufCXL. Inclusion criteria were early, mild post-LASIK ectasia, defined as new-onset postoperative manifest refraction cylinder of 1.50 diopters (D) or less, with new topographic inferior steepening consistent with ectasia, uncorrected distance visual acuity of 20/40 or better, and corrected distance visual acuity of 20/25 or better. The existing LASIK flap was lifted, 0.25% isotonic riboflavin was applied directly to the stromal bed, the flap was repositioned, and 18 mW/cm² ultraviolet light was applied for 5 minutes to the corneal flap surface. Post-ufCXL ophthalmic data were compared to pre-ufCXL baseline measurements.

RESULTS

Visual outcomes were maintained pre-ufCXL to 36 months post-ufCXL, with preserved safety index (P = .6545), efficacy index (P = .4980), spherical equivalent accuracy (P = .1536), defocus equivalent accuracy (P = .1032), central corneal thickness (P = .5196), and corneal irregularity indices at 3 mm (P = .8548) and 5 mm (P = .3399). Refractive astigmatism significantly decreased from 0.83 to 0.55 D pre-ufCXL to post-ufCXL (P = .0439), as did maximum keratometry from 42.40 to 42.00 D pre-ufCXL to post-ufCXL (P = .0420). The ufCXL demarcation line depth was 336 ± 21 µm post-ufCXL, with normal endothelial cell density (2,574 ± 203 cells/mm²). Only 1 of 20 eyes showed evidence of progression of 1.00 D in maximum keratometry.

CONCLUSIONS

The ufCXL procedure shows promise in stabilizing early post-LASIK ectasia. Visual function, refractive astigmatism, maximum keratometry, and corneal irregularity indices were statistically maintained at 36 months postoperatively. [J Refract Surg. 2022;38(8):511-519.].

Visual and Topographic Outcomes of Corneal Collagen Cross Linking for Post LASIK Ectasia

Purpose

To assess the topographic and visual outcomes of corneal cross-linking (CXL) for post-LASIK ectasia.

Methods

A retrospective case series of patients who had progressive post-LASIK ectasia, with at least 2 years of follow-up. They had epithelium-off CXL. Topographical and visual changes were recorded.

Results

The study included 21 eyes of 11 patients. At month 24, the final logMAR corrected distance visual acuity (CDVA) and spherical equivalent (SE) were stable compared to baseline (0.16, and −2.0 diopter (D), respectively). The final Kmean and Kmax were 42.5 and 47.4 D, respectively. Stability or improvement in CDVA, SE, and Kmax was seen in 17 eyes (81%). Significant corneal thinning was seen (438 vs 457 microns, p = 0.003). Thinning by 2% or more was seen in 12 eyes (57.1%). Failure of CXL was seen in 4 eyes (19%). No other ocular complications were seen.

Conclusion

CXL for post LASIK ectasia is a safe and effective modality. Despite corneal thinning, there was stability or improvement in topographic parameters and CDVA over the 2-year follow-up period.

Comparison of Long-Term Outcomes and Refractive Stability following SMILE versus SMILE Combined with Accelerated Cross-Linking (SMILE XTRA)

Purpose

To compare the long-term safety, efficacy, predictability, and refractive stability following SMILE versus SMILE combined with accelerated cross-linking (SMILE XTRA), and to specifically study the regression patterns following the two procedures.

Methods

This retrospective study included 54 eyes of SMILE and 54 eyes of SMILE XTRA treated for normal and borderline cases of myopia/myopic astigmatism, respectively, based on certain predefined topographic features and risk factors. Patients in both the groups were matched for age and refractive error. The mean postoperative follow-up for the SMILE group was 22.18 ± 10.41 months and the SMILE XTRA group was 21.81 ± 10.19 months.

Results

At the end of follow-up, the mean sphere, cylinder, and SE reduced to −0.03, −0.09, and −0.08 D in the SMILE group and −0.06, −0.15, and −0.13 D in the SMILE XTRA group. 96% and 93% eyes remained within ±0.50 D in SMILE and SMILE XTRA groups, respectively, and 94% eyes maintained an UDVA of 20/20 or better in the SMILE as well as SMILE XTRA groups. Safety and efficacy indices for the SMILE group were 1.03 and 1.00. For the SMILE XTRA group, the safety and efficacy indices were 1.00 and 0.99. No eye in either group had postoperative ectasia or enhancement performed for significant residual refractive error.

Conclusion

Both the SMILE and SMILE XTRA groups exhibited comparable visual outcomes, safety, and efficacy. Contrary to the belief, combination of prophylactic CXL with SMILE did not result in a hyperopic shift in the long term. No eye in either group encountered postoperative ectasia; however, further follow-up is suggested to establish the long-term effects on refractive and corneal stability following SMILE XTRA, as all the eyes treated in this group were borderline.

Case Report: Dislocation Into Vitreous Cavity and Removal of a Posterior Chamber Phakic Intraocular Lens

Purpose:

To report a rare case of delayed dislocation of a novel posterior chamber phakic intraocular lens into the vitreous cavity, which was successfully treated by a reformed technique.

Case Presentation

A 29-year-old female received Ejinn phakic refractory lens (EPRL) implantation to correct her high myopia. Spontaneous dislocation into the vitreous cavity occurred 26-months post-operatively without traumatic history. Pars plana vitrectomy combined with cutting the EPRL into two equal pieces was performed to remove the dislocated EPRL.

Conclusion

Dislocation into the vitreous cavity of EPRL can be successfully and easily removed by our reformed technique. Concerns about zonules-related complications pre-operatively, intraoperatively, and post-operatively must be raised in the practice of EPRL implantation.

Evaluation of Corneal Endothelium after Myopic Laser-Assisted In Situ Keratomileusis (LASIK) with Accelerated Cross-Linking (CXL) in Diabetic Patients

Purpose:

To study the effect of LASIK with accelerated CXL on corneal endothelium in myopic diabetic patients.

Methods:

A prospective comparative interventional case series study on 120 eyes of 60 myopic patients treated with LASIK with accelerated CXL. They were divided into two groups; group A included 60 eyes of diabetic patients, group B included 60 eyes of non-diabetic patients. Corneal endothelium was evaluated by specular microscope preoperatively and after 3 and 6 months postoperatively.

Results:

The endothelial cells density (ECD) showed statistically significant changes after 3 and 6 months postoperatively (p-value <0.001) in group A while group B showed statistically significant changes after 3 months without significant change after 6 months (p-value= 0.103), both groups had improved to near preoperative levels, with no significant differences between them at the end of 6 months follow-up (p-value = 0.219). Regarding pleomorphism, there was a significant change in group A during 6 months follow-up (p-value <0.001) with no significant change in group B (p-value= 0.884), and in comparing both groups, there was a significant change at the end of 6 months follow-up (p-value <0.001). Regarding polymegathism, there was a significant change in group A during 6 months follow-up (p-value <0.001) with no significant change in group B after 3 (p-value= 0.178) and 6 (p-value= 0.866) months follow-up, and in comparing both groups, there was a significant change at the end of 6 months follow-up (p-value <0.001).

Conclusion:

LASIK with accelerated CXL is safe on corneal endothelium in diabetic myopic patients but needs to follow up for a long period.

Incidence of Ectasia After SMILE From a High-Volume Refractive Surgery Center in India

PURPOSE

To report the incidence of ectasia after small incision lenticule extraction (SMILE) in a high-volume refractive surgery center in India.

METHODS

To derive the incidence of ectasia after SMILE, all eyes that underwent SMILE or SMILE Xtra (SMILE combined with prophylactic accelerated corneal cross-linking) from November 2012 to August 2019 were retrospectively analyzed. Furthermore, these cases were classified as being "normal" or "borderline" based on certain predefined criteria. Only eyes with a minimum follow-up of 12 months were included.

RESULTS

Of the total 7,024 eyes analyzed, 6,619 eyes underwent SMILE, of which 10 eyes developed ectasia at a mean interval of 21.3 months, making the incidence of ectasia after SMILE 0.15%. Of these 10 eyes with ectasia, 2 eyes had normal preoperative topography, whereas the remaining 8 eyes were borderline as per the predefined criteria. Retrospective data analysis revealed that 6,025 of 7,024 eyes were normal and thus suitable for a standard SMILE procedure, whereas 999 eyes were borderline, of which 594 eyes underwent SMILE and 405 eyes underwent SMILE Xtra. The incidence of ectasia in borderline eyes undergoing SMILE was 0.80% (8 of 999) versus 0% (none) for borderline eyes undergoing SMILE Xtra (chi square, P < .05).

CONCLUSIONS

The incidence of ectasia after SMILE in the early postoperative period was 0.15%, with borderline eyes accounting for most cases. Borderline eyes treated with SMILE Xtra did not progress to ectasia, potentially suggesting a protective role of simultaneous CXL. [J Refract Surg. 2021;37(12):800-808.].

Changes in Corneal Biomechanical Properties in PRK Followed by Two Accelerated CXL Energy Doses in Rabbit Eyes

PURPOSE

To evaluate whether photorefractive keratectomy (PRK) combined with the two commonly delivered energy doses in accelerated corneal cross-linking (A-CXL) could help the cornea maintain its preoperative stiffness level.

METHODS

A total of 72 corneas of 36 healthy white Japanese rabbits were randomly divided into four equal groups. The groups included an untreated control group and three that had undergone PRK. After tissue ablation, one of the latter three groups (PRK group) was left untreated, whereas the other two were exposed to riboflavin (0.22% concentration by volume) and ultraviolet-A (370 nm) with the same irradiation (30 mW/cm2) but different CXL energy doses of 1.8 J/cm2 (PXL group) and 2.7 J/cm2 (PXH group). Dynamic Scheimpflug analyzer (Corvis ST; Oculus Optikgeräte GmbH) measurements of stiffness parameter at first applanation (SP-A1), Stress-Strain Index (SSI), and other dynamic corneal response parameters were taken 3 days preoperatively and 1 month postoperatively. Subsequently, ex vivo inflation testing was performed and the tangent modulus of each specimen was estimated using an inverse analysis process.

RESULTS

In comparison to the control group, the tangent modulus at a stress of 10 kPa decreased by 8.9% in the PRK group and increased by 10.6% and 22.4% in the PXL and PXH groups, respectively. SP-A1 decreased postoperatively in the PRK group (P < .05), indicating an overall stiffness reduction of -7.4, -3.5, and -5.3 mm Hg/mm in PRK, PXL, and PXH groups, respectively. The material stiffness parameter SSI remained almost unchanged in the PRK group (P = .989), increased slightly in the PXL group (8.3%, P = .077), and increased significantly in the PXH group (11.1%) (P < .05).

CONCLUSIONS

Biomechanical deterioration following PRK was significant and could not be fully compensated for by ACXL with either 1.8 or 2.7 J/cm2 doses. The increased value of corneal overall stiffness was higher in A-CXL with 2.7 J/cm2 energy than with 1.8 J/cm2 energy. [J Refract Surg. 2021;37(12):853-860.].

Association between Iris Biological Features and Corneal Biomechanics in Myopic Eyes

PURPOSE

Iris biological features such as surface features and profile characteristics reflected the development of iris stroma and microvessels. Iris vessels and microcirculation are still lack of effective detection methods, and we can directly observe only the iris surface biological characteristics. This cross-sectional study evaluated the association between iris surface biological features and corneal biomechanics in young adults with myopia.

METHODS

We recruited 152 patients with myopia aged ≥18 years, from the Eye Hospital of Wenzhou Medical University, who had complete Corneal Visualization Scheimpflug Technology (Corvis ST) data and graded iris surface features. Iris surface features included crypts, furrows, and color measured from digital slit lamp images. The biomechanical properties of the cornea were assessed using Corvis ST. Only 1 eye of each participant was randomly selected for analysis. Associations between the iris surface features and corneal biomechanics were analyzed using linear regression models. The grade of iris crypts, furrows, and color and corneal biomechanical parameters measured with Corvis ST was the main outcome measures.

RESULTS

The iris crypts were significantly associated with deflection amplitude at the first applanation (A1 DLA, β = 0.001, P = 0.013), A1 delta arc length (A1 dArcL) (β = -0.001, P = 0.01), maximum delta arc length (dArcLM) (β = -0.004, P = 0.03), and stiffness at the first applanation (SP-A1) (β = -2.092, P = 0.016). The iris furrows were only associated with integrated radius (β = -0.212, P = 0.025). Iris color was found not related with corneal biomechanical parameters measured via Corvis ST.

CONCLUSIONS

Iris surface features were associated with corneal biomechanical properties in myopic eyes; more iris crypts were associated with lower corneal stiffness while more extensive furrows were related with higher corneal stiffness. Iris crypts and furrows may provide useful information on corneal biomechanical properties in myopic eyes.

Radiobiological effects and medical applications of non-ionizing radiation

Radiation is used in medicine to diagnose and treat diseases but it can also cause harm to the body by burning or mutation. This depends on whether the radiation is ionizing or nonionizing. Despite its vast applications in surgery, dermatology and cosmetics, little is taught and thus known about non-ionizing radiation. This review article discusses the fundamentals of non-ionizing electromagnetic radiations. The main aim is to extensively explain the different types of non-ionizing radiation. This will equip students and medical personnel with knowledge on different medical applications and expose them to a variety of specializations in medicine that utilize non-ionizing radiation. The article discusses the physics, hazard, means of protection and medical application of each type of radiation: ultraviolet radiation, light (both visible light and LASER), infrared radiation, microwaves and extremely low frequency radiation separately. It presents these terms in a simple manner that avoids rigors mathematics and physics, which makes them comprehensible for medical students. The development of new diagnostic and therapeutic approaches could also lead to increased hazards to the body unless they are treated with precaution. If not adequately monitored, a significant health risk may be posed to potentially exposed employees. Hence proper dosage should be used for non-ionizing radiation. This is only possible through understanding of the risks/benefits of these radiations by studying the physics and radiobiological effects of each individual radiation.

Severe long-term progressive corneal remodeling after bilateral simultaneous prophylactic crosslinking and topography-guided surface ablation with mitomycin

To report a case of a 20-year-old woman who developed massive and progressive corneal remodeling in both eyes after bilateral PRK with mitomycin and CXL as an elective refractive procedure for mild keratoconus. The patient had 6 years of follow up, initially presenting with focal steepening of up to 20 diopters on both eyes one-and-a-half- years postoperatively that spontaneously reversed over the next five years while the high order aberrations worsened. At the present time, the patient depends on bilateral scleral contact lenses for her day-to-day activities. The use of combined elective PRK with mitomycin and prophylactic CXL could lead to progressive corneal deformation. Additional reports would help to establish the role of this combination procedure among the armamentarium to visually rehabilitate patients with keratoconus.

Biomechanics of Ophthalmic Crosslinking

Crosslinking involves the formation of bonds between polymer chains, such as proteins. In biological tissues, these bonds tend to stiffen the tissue, making it more resistant to mechanical degradation and deformation. In ophthalmology, the crosslinking phenomenon is being increasingly harnessed and explored as a treatment strategy for treating corneal ectasias, keratitis, degenerative myopia, and glaucoma. This review surveys the multitude of exogenous crosslinking strategies reported in the literature, both "light" (involving light energy) and "dark" (involving non-photic chemical processes), and explores their mechanisms, cytotoxicity, and stage of translational development. The spectrum of ophthalmic applications described in the literature is then discussed, with particular attention to proposed therapeutic mechanisms in the cornea and sclera. The mechanical effects of crosslinking are then discussed in the context of their proposed site and scale of action. Biomechanical characterization of the crosslinking effect is needed to more thoroughly address knowledge gaps in this area, and a review of reported methods for biomechanical characterization is presented with an attempt to assess the sensitivity of each method to crosslinking-mediated changes using data from the experimental and clinical literature. Biomechanical measurement methods differ in spatial resolution, mechanical sensitivity, suitability for detecting crosslinking subtypes, and translational readiness and are central to the effort to understand the mechanistic link between crosslinking methods and clinical outcomes of candidate therapies. Data on differences in the biomechanical effect of different crosslinking protocols and their correspondence to clinical outcomes are reviewed, and strategies for leveraging measurement advances predicting clinical outcomes of crosslinking procedures are discussed. Advancing the understanding of ophthalmic crosslinking, its biomechanical underpinnings, and its applications supports the development of next-generation crosslinking procedures that optimize therapeutic effect while reducing complications.

Corneal Cross-Linking for Keratoconus: Current Knowledge and Practice and Future Trends

Corneal collagen cross-linking (CXL) with riboflavin is an accepted universal standard of care for our keratoconus patients with progressive disease. It has been a game changer in how we manage keratoconus. Early diagnosis and treatment is essential in paediatric patients as younger patients progress more rapidly and have poorer transplant outcomes. There is an ongoing debate around standard, accelerated, and transepithelial protocols of CXL, the role of CXL, and the combination of laser refractive surgery. Future developments will improve CXL safety and efficacy and the scope of utilization, but we must be careful not to leap too far ahead with clinical applications before publication of basic science research and good clinical results with standardized protocols.

Refractive surgery with simultaneous collagen cross-linking for borderline corneas - A review of different techniques, their protocols and clinical outcomes

Simultaneous corneal cross-linking (CXL) has been proposed as an adjunct therapy to corneal refractive procedures to prevent future ectasia, especially when performed in borderline corneas. This review analyses the currently available literature (minimum follow-up 6 months) on corneal refractive surgery and simultaneous CXL (PRK Xtra, LASIK Xtra, and SMILE Xtra) to evaluate the overall results including the safety, efficacy, and potential complications associated with these procedures. A comprehensive literature search of various electronic databases (PubMed, PubMed Central, Cochrane database, and MEDLINE) was performed up to 20^th May 2020. Four relevant studies were found for PRK Xtra, 12 for LASIK Xtra, and 3 for SMILE Xtra. The total number of eyes included in this review was 1,512: 294 for PRK Xtra, 221 for PRK-only, 446 eyes for LASIK Xtra, 398 eyes for LASIK-only, 91 for SMILE Xtra and 62 for SMILE-only. Current literature suggests that refractive surgery and simultaneous CXL is generally safe and delivers comparable results in terms of visual and refractive outcomes than refractive surgery alone. However, there is no consensus on a standard cross-linking protocol, and complications such as diffuse lamellar keratitis, central toxic keratopathy, and corneal ectasia following Xtra procedures have been reported. It is therefore suggested that surgeons exercise caution in case-selection and counsel their patients regarding the potential risks and benefits with Xtra procedures. Also, further studies are required to standardize the UV-A irradiation protocols and to evaluate the long-term effect on safety, refractive predictability, and stability of these procedures.

Three-Year Outcomes of Simultaneous Accelerated Corneal Crosslinking and Femto-LASIK for the Treatment of High Myopia in Asian Eyes

Purpose

To determine the long-term visual outcomes of simultaneous femtosecond laser-assisted laser in situ keratomileusis (femto-LASIK) and accelerated cross-linking (CXL) [LASIK Xtra] for the treatment of high myopia.

Patients and Methods

All 163 consecutive eyes of 85 patients who underwent LASIK Xtra for the treatment of high myopia and/or myopic astigmatism (spherical equivalent ≥ −6.00 D) in Singapore National Eye Centre from the years 2013 to 2017 were included in this retrospective case series. Post-operative follow-up was up to 3 years.

Results

Of the 163 eyes, 67 were followed up for 1 year (mean 12.9 months), 69 for 2 years (mean 24.0 months) and 43 for 3 years (mean 36.4 months). Overall mean follow-up was 22.8 months (9–46 months). The mean pre-operative spherical equivalent (SE) was −8.60 ± 1.47 D [range: −11.75 to −4.75] (n = 163) and mean attempted correction SE was −8.84 ± 1.41 D [range: −11.88 to −5.25]. Most eyes (>95%) maintained an uncorrected distance visual acuity of 6/12 or better over 3 years. Visual outcomes were predictable with ≥95% of eyes achieving a SE correction within ± 1D of attempted correction over 3 years. There was a mild regression in SE refraction over 3 years with a mean of −0.10 ± 0.45 D three years post-operatively (p = 0.03). The safety index was >1.05 at 3 years follow-up. There were no significant post-operative complications though 24 eyes had mild haze and 2 eyes had grade 1 diffuse lamellar keratitis that resolved within 1 month.

Conclusion

Our 3-year LASIK Xtra results show favorable safety, efficacy, predictability and stability outcomes in Asian patients with high myopia.