Keratectomy Research Articles

Early visual and clinical outcomes of transepithelial photorefractive keratectomy versus transepithelial keratectomy with smart pulse technology for myopia

Abstract: PURPOSE: The purpose of this study was to compare early visual outcomes, epithelial healing, and stromal haze between transepithelial photorefractive keratectomy (Trans-PRK) using smart pulse technology (SPT) with traditional Trans-PRK. METHODOLOGY: This study is a retrospective, comparative study conducted at a private eye center in “Riyadh, Saudi Arabia,” investigating myopic patients who underwent either Trans-PRK with SPT (study group) or traditional Trans-PRK (control group). The patients were assessed preoperatively and followed up at 1 week and 2 months postoperatively. The main outcomes included uncorrected distance visual acuity (UDVA), corneal haze, and corneal epithelial defect. RESULTS: This study included 501 eyes, of them, 222 eyes (44.3%) underwent Trans-PRK with SPT. The UDVA in the study group was significantly better 1 week postoperatively (P < 0.05). For the 2-month follow-up visits, there was no significant difference between the groups. Epithelium healing and stromal haze were comparable in the two groups without significant differences between them. CONCLUSION: Transepithelial photorefractive keratectomy with SPT yielded better short-term visual outcomes than traditional Transepithelial photorefractive keratectomy.

Effect of Posterior Keratometry and Corneal Radius Ratio on the Accuracy of Intraocular Lens Formulas After Myopic LASIK/PRK.

To investigate the impact of back-to-front corneal radius ratio (B/F ratio) and posterior keratometry (PK) on the accuracy of intraocular lens power calculation formulas in eyes after myopic laser in situ keratomileusis (LASIK)/photorefractive keratectomy (PRK) surgery. A retrospective, consecutive case series study included 101 patients (132 eyes) with cataract after myopic LASIK/PRK. Mean prediction error (PE), mean absolute PE (MAE), median absolute error (MedAE), and the percentage of eyes within ±0.25, ±0.50, and ±1.00 diopters (D) of PE were determined. The Barrett True K-TK formula exhibited the lowest MAE (0.59 D) and MedAE (0.48 D) and the highest percentage of eyes within ±0.50 D of PE (54.55%) in total. In eyes with a B/F ratio of 0.70 or less and PK of -5.70 D or greater, the Potvin-Hill formula displayed the lowest MAE (0.46 to 0.67 D). The Barrett True-TK exhibited the highest prediction accuracy in eyes after myopic LASIK/PRK overall. However, for eyes with a low B/F ratio and flat PK, the Potvin-Hill performed best. [J Refract Surg. 2024;40(9):e635-e644.].

Lens Factor Choice in IOL Power Calculation after Laser Refractive Surgery: The Right Constant for Advanced Lens Measurement Approach (ALMA).

Background/Objectives: To evaluate the advanced lens measurement approach (ALMA) formula accuracy using different lens constants available on the user group for laser interference biometry (ULIB) and IOL Con platforms. Methods: In this retrospective, comparative, case-series study, 150 eyes of 160 patients with previous myopic Photorefractive Keratectomy (PRK) or laser-assisted in situ keratomileusis (LASIK), who underwent uneventful cataract surgery and IOL implantation, were examined. The ALMA formula was evaluated to calculate the refractive prediction error (PE), analysing four different categories of lens constants: both nominal and optimized A-Constant for SRKT, which are available on the ULIB and IOL Con platforms. An additional analysis was carried out in this study, evaluating if a decreased ULIB optimized constant (DUOC) with different fixed factors (-1.2 -1.3 -1.4 -1.5) could improve refractive outcomes. Median absolute error (MedAE) and percentage of eyes within ±0.50 and ±1.00 diopters (D) of prediction error were measured as the main outcomes. Results: Comparing the lens factors available on ULIB and IOL Con platforms, the ALMA formula reported a lower MedAE and higher percentages of eyes with a refractive PE within 1.0 D using ULIB nominal constants (all p < 0.05). Using DUOC (-1.3), and there was a statistically significant improvement of both MedAE and of the percentages of eyes with PE within ±0.50 D with the ALMA method compared to nominal ULIB constants (all p < 0.05). Conclusions: The impact of different lens factors in the IOL power calculation after myopic LRS should be carefully evaluated. The ALMA formula, in the absence of optimized constants by zeroing the mean error, should be used by subtracting 1.3 from the optimized ULIB constants available on the IOL Con website. This finding suggests further studies to test which of these constants could work better with the other post-refractive surgery formulas.

Prospective Objective Analysis of Corneal Haze Following Customized Transepithelial PRK Without Mitomycin C Combined With Accelerated Corneal Cross-Linking Versus Corneal Cross-Linking Alone.

To compare haze and refractive outcomes in patients undergoing combined accelerated corneal cross-linking (A-CXL) and selective wavefront-guided transepithelial photorefractive keratectomy (WG-transPRK) without mitomycin C (MMC) versus those undergoing A-CXL. This prospective study analyzed 95 eyes (86 patients) with progressive keratoconus from October 2018 to October 2022. The first group underwent CXL combined with corneal or ocular WG-transPRK (CXL+PRK, n = 52), targeting higher order aberrations (HOAs). The second underwent CXL only (n = 43), both following the same accelerated CXL protocol without MMC on the SCHWIND Amaris laser platform (SCHWIND eye-tech-solutions). Baseline and postoperative evaluations (1, 3, 6, and 12 months) included uncorrected (UDVA) and corrected (CDVA) distance visual acuity, manifest refraction, tomography, corneal HOAs, and optical coherence tomography (OCT) scans. A patented machine learning algorithm objectively detected and quantified stromal haze on OCT scans in grayscale units. In both groups, anterior corneal haze reflectivity and subepithelial haze peaked at 3 months postoperatively, then progressively decreased at 6 and 12 months. Haze did not differ between groups at any time point. By 12 months, CDVA increased by 2.5 lines in the CXL+PRK group (P < .001) and by 0.7 lines in the CXL group (P = .10), and maximum keratometry decreased from 51.70 ± 5.10 to 47.90 ± 7.90 diopters (D) (CXL+PRK group) (P < .001) and from 51.20 ± 5.10 to 50.30 ± 4.60 D (CXL group) (P = .004). Corneal HOAs decreased in both groups but more in the CXL+PRK group. Combining CXL with WG-transPRK without MMC does not result in increased haze when compared to A-CXL alone. This combined approach achieves greater improvements in visual, topographic, and aberrometric parameters. [J Refract Surg. 2024;40(9):e583-e594.].

Transepithelial Photorefractive Keratectomy versus Conventional Photorefractive Keratectomy in treatment of Myopia and Compound Myopic Astigmatism (Comparative Study)

Transepithelial Photorefractive Keratectomy versus Conventional Photorefractive Keratectomy in treatment of Myopia and Compound Myopic Astigmatism (Comparative Study)

Comparative outcomes of mechanical and transepithelial PRK on the same excimer laser: A contralateral eye study.

Compare refractive results between mechanical PRK (mPRK) and transepithelial PRK (tPRK) with WaveLight Allegretto EX500 excimer laser system (Alcon Laboratories, Fort Worth, TX, USA). Department of Ophthalmology of the Federal University of Sao Paulo, Brazil. Prospective and randomized study. In 151 eyes of 73 patients with astigmatism and myopia, both eyes had similar refraction before surgery, with a maximum of 15-µm difference in ablation who underwent mPRK in one eye and tPRK in the contralateral eye. The mean age of the patients in this study was 31.45 ± 6.97 years (range, 22 to 54 years). A comparison was made with all variables between the two groups, and we found that UDVA and SE were worse in the tPRK group at six months than in the mPRK group. In the mPRK group, there was a higher frequency in the +/- 0.50 range and a lower frequency in the +/- 1.50 range. In the tPRK group, however, there was a lower frequency in the +/- 0.50 range and a higher frequency in the +/- 1.50 range. Concerning gain or loss of lines of sight, there was no association between the two groups (chi-square test, p = 0.887). Both mPRK and tPRK appear to have similar safety. However, mPRK was associated with significantly better UDVA and SE six months post-operatively.

Outcomes of Photorefractive Keratectomy in Patients Who Underwent Keratoplasty

&amp;lt;i&amp;gt;Purpose&amp;lt;/i&amp;gt;: To assess the efficacy of photorefractive keratectomy (PRK) in patients who underwent corneal transplantation, and to determine the influencing factors. &amp;lt;i&amp;gt;Methods&amp;lt;/i&amp;gt;: The present study was a retrospective chart review research that was conducted at Dhahran Eye Specialist Hospital between 2014 and 2017. &amp;lt;i&amp;gt;Results&amp;lt;/i&amp;gt;: Seventy-nine eyes were included in the study. The mean BCVA showed an improvement of two lines post-PRK as compared to that before PRK (0.73 ± 0.1 and 0.54 ± 0.2, respectively). There was a statistically significant decrease in the cylindrical value postoperatively as compared to that preoperatively (−2.15 ± 1.4 and−3.25 ± 1.8, respectively; p &amp;lt; 0.001). However, there was no statistically significant difference in spherical equivalent and sphere. Three eyes (4%) developed postoperative complications. There was a medium positive correlation between residual stroma and achieved spherical equivalent (SE) (r = 0.305, p = 0.006), as well as between optical zone and postoperative uncorrected visual acuity (r = 0.350, p = 0.001), in addition to post SE (r = 0.307, p = 0.006). However, the depth of ablation showed a medium negative correlation with achieved SE (r = −0.375, p = 0.001). &amp;lt;i&amp;gt;Conclusion&amp;lt;/i&amp;gt;: PRK may be an option for correcting refractive errors in patients who underwent keratoplasty. The optical zone and residual stromal thickness have a positive correlation with the effects of the outcomes, whereas the depth of ablation has a negative correlation with the outcomes.

Comparison between a new transepithelial PRK vs. conventional alcohol-assisted PRK: Corneal densitometry and aberrometry study.

To describe and compare corneal densitometry, subjective refraction, visual acuity, and corneal higher order aberrations (HOA) after corneal refractive surgery using either alcohol-assisted photorefractive keratectomy (aaPRK) or single-step transepithelial PRK (tPRK). We conducted a retrospective and observational study. We analyzed 120 right eyes from 120 healthy consecutive myopic patients who underwent aaPRK or tPRK to correct myopia of up to 6 diopters and astigmatism of up to 2 diopters. The WaveLight EX500 excimer laser (Alcon Laboratories, Inc.) was used in all cases. Visual acuity, subjective refraction, and Pentacam AXL® measurements were performed at the preoperative visit and at 6-months follow-up visit. Pentacam AXL® software was used to assess corneal optical density in various annuli for different corneal depths and anterior corneal HOA (6 mm area of analysis). Preoperative spherical equivalent values were similar between groups preoperatively (-3.07 ± 1.52 and -3.38 ± 1.46 in the aaPRK and tPRK groups, respectively). There were no statistically significant differences in visual acuity and postoperative refraction between groups. Postoperative corneal densitometry did not show statistically significant differences in any of the areas studied and both surgical procedures obtained similar results. However, analysis of HOA showed statistically significant differences between the techniques (1.42 ± 0.39 and 1.80 ± 0.62 for the aaPRK and tPRK groups, respectively; p = 0.000). Both aaPRK and single-step tPRK gave comparable visual, refractive, and corneal density outcomes. Some differences were observed in HOA but were not clinically relevant.

Comparative analysis of surgically induced astigmatism following cataract surgery: influence of previous myopic correction and corneal parameters.

This retrospective study investigated the impact of corneal parameters on surgically induced astigmatism (SIA) in eyes with prior myopic correction undergoing cataract surgery. Department of Ophthalmology, San Marino Hospital, San Marino, Republic of San Marino. This case-control study analyzed existing data retrospectively, without randomization or masking. Eighty eyes divided in group 1 (40 eyes previous underwent refractive surgery for myopia) and group 2 ( 40 myopic eyes) that underwent cataract surgery with intraocular lens (IOL) implantation were included. SIA was calculated using values from the IOL Master Zeiss 700 and mean pupil power (MPP) derived from the CSO Sirius Topographer (based on 3mm pupil size) with vectorial analysis from doctor Hill software. No significant difference in SIA was observed between eyes with prior myopic photorefractive keratectomy and the control group (p > 0.05). SIA calculations using the IOL Master and CSO Sirius Tomographer yielded similar results. There was no significant correlation between SIA and axial length, corneal curvature, peripheral corneal thickness, or anterior chamber depth (p > 0.05). However, an inverse correlation was found between SIA and horizontal corneal diameter (p < 0.05). Corneal parameters, such as axial length, corneal curvature, peripheral corneal thickness, and anterior chamber depth, showed no significant influence on SIA. The inverse correlation between SIA and horizontal corneal diameter in study group suggests potential influence of white-to-white distance on SIA. These findings highlight the importance of considering corneal parameters for optimizing surgical outcomes.

Topography-guided photorefractive keratectomy combined with accelerated corneal collagen cross-linking versus cross-linking alone for progressive keratoconus: a long-term prospective cohort study.

To comprehensively compare the long-term outcome of the combined topography guided photorefractive keratectomy (TG-PRK) with accelerated corneal cross-linking (ACXL) and ACXL alone in eyes with progressive keratoconus. The analysis focused on the changes in the detailed corneal aberrometric values. This single-center, prospective cohort study included 28 patients (30 eyes) of the TG-PRK plus ACXL group and 14 patients (15 eyes) of the ACXL alone group. The mean duration of the follow-up was 44 ± 10.18 months (ranged from 31 to 65 months). The preoperative data and the postoperative measurement data at the last follow-up visit, including demographic data, uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction, corneal topography, pachymetry, aberrometry and densitometry were analyzed. The CDVA significantly improved in the TG-PRK plus ACXL group at the last follow-up visit (p = 0.006), while no significant improvement was found in the ACXL alone group (p = 0.432). The maximal keratometry of the anterior corneal surface (Kmax) of both groups significantly decreased at the last follow-up visit (p < 0.05). Compared with the ACXL alone group, the Kmax of the TG-PRK plus ACXL group showed a greater decline (p = 0.008). The total corneal aberrations, the corneal lower-order aberrations (LOAs), the corneal higher order aberrations (HOAs), the vertical coma and the spherical aberration (SA) at the 4.0 mm and 6.0 mm zone of the TG-PRK plus ACXL group significantly decreased at the last follow-up visit (all p < 0.05). The declines of the total corneal aberrations, the corneal LOAs, the corneal HOAs and the vertical coma at the 4.0 mm and 6.0 mm zone of the TG-PRK plus ACXL group were significantly higher than those in the ACXL alone group (p < 0.001). Compared with ACXL alone, combined TG-PRK with ACXL procedure had a significantly higher reduction in the corneal HOAs and better CDVA, while providing a similar long-term stability and safety. For progressive keratoconus patients with adequate corneal thickness, the combined procedure might be a recommended treatment option.

Ex Vivo Lenticule Customization for Stromal Lenticule Addition Keratoplasty.

The purpose of this study was to explore the optimal shape of customized lenticules for stromal lenticule addition keratoplasty (SLAK) for off-centered ectasia. Two different methods to create ex vivo models of eccentric-keratoconus were investigated. Twelve human corneas were used to create model 1 by a hyperopic photorefractive keratectomy (PRK), and model 2 by masked phototherapeutic keratectomy (PTK) on the anterior corneal surface, whereas both types received myopic ablation of the posterior surface. Keratoconus models underwent a modified femtosecond laser (FSL) flap-cut to create stromal pockets. Sixteen human corneas underwent FSL dissection to obtain four lenticule types: type I (planar) and type II (negative) lenticules were used without modifications, whereas type III (customized-planar), and type IV (customized-negative) lenticules underwent further masked-PRK to obtain an asymmetric bow-tie shape. Topographic, aberrometric analysis, and anterior segment optical coherence tomography (AS-OCT) were performed in all recipient corneas before and after lenticule implantation. Keratoconus model was successfully reproduced. Tomographic analysis showed a significant inferiorly decentered corneal steepening with coherent stromal thinning. Model 2 reproduced better the curvature of real keratoconus. Lenticules type I implantation induced a homogeneous corneal thickening, type III produced higher thickening in the inferior half of the cornea. Type II determined a maximal peripheral pachymetric increase, with a gradual reduction toward the center, and type IV presented an asymmetric peripheral thickening. Topographic assessment showed a cone apex flattening in all cases, but it was significantly higher in types II and IV. Customized lenticules improved significantly corneal surface regularity regarding types I and II. The approach of customizing lenticules by increasing their asymmetry and tailoring the re-shaping effects, may improve SLAK outcomes in eccentric keratoconus.

Late Onset Corneal Haze Post Photorefractive Keratectomy

Introduction: Photorefractive keratectomy (PRK) is a surface ablation procedure to correct refractive errors. Regardless of the safety and efficacy, corneal haze may occur after PRK, and it remains one of the most feared complications because it can impair good visual outcomes. Case Presentation: A 20-year-old woman complained of blurred vision in her right eye (RE) after undergoing PRK elsewhere six months before admission with a history of refraction of S-12.75 C-1.75 x 10° preoperatively and S-0.75 postoperatively. Six-month postoperative uncorrected visual acuity (UCVA) was 0.01, best corrected visual acuity (BCVA) was 0.5 with S-7.00 C-0.75 x 50°. A slit lamp examination revealed grade three corneal haze. Anterior optical coherence tomography (OCT) showed the hyperreflective area with 132 μm deep into the stroma. The patient underwent phototherapeutic keratectomy (PTK) and mitomycin-C (MMC) treatment to a depth of 50 μm Ø6.5mm transition zone 0.5 mm. Two months later, UCVA was 0.2, BCVA was 0.63 with S-2.50 C-0.50 x 90°, and slit lamp examination revealed no haze remaining. Conclusions: This case illustrates the potential risk for corneal haze development, mainly when PRK is performed at greater treatment depths. However, with phototherapeutic keratectomy and mitomycin-C treatment, an excellent visual outcome and vision restoration can be obtained.

LASIK Versus PRK Based on Increased Risk of Corneal Haze: Assessing Current Decision-Making Capabilities of Six Artificial Intelligence Models in Refractive Surgery.

To investigate the current decision-making capabilities of 6 different artificial intelligence (AI) models by assessing their refractive surgery recommendations (laser in-situ keratomileusis [LASIK] or photorefractive keratectomy [PRK]) for a theoretical patient with a history of keloid formation. Claude-2 (Anthropic, 2023), GPT-4 (OpenAI, 2023), GPT-3.5 (OpenAI, 2022), Gemini 1.0 (Google DeepMind, 2023), Microsoft Copilot (Microsoft AI, 2023), and Google-PaLM (Google AI, 2022) underwent three systematic queries to determine the most appropriate surgical plan (LASIK or PRK) for a theoretical patient with an increasing manifest refraction of -3.50, -5.00, and -7.00 diopters (D) in both eyes, an uncomplicated ocular examination, and history of keloid formation. They were then tasked with providing published scientific references to support their responses. The AI models' recommendations were compared to those of a group of 6 experienced ophthalmologists, serving as a benchmark. The group of ophthalmologists unanimously recommended LASIK (6/6 ophthalmologists), in contrast to the unanimous initial recommendation for PRK from the AI models (6/6 models). Of the 42 references provided by the AI models, 55% were fictitious and 45% were authentic. Only 1 of the 6 models altered its initial recommendation to LASIK when presented with the same patient with a history of keloid formation but with increasing severity of myopia (-3.50 to 5.00 to 7.00 D). It is evident that current AI models lack the critical-thinking abilities required to accurately analyze and assess apparent risk factors in clinical scenarios, such as the risk of corneal haze after PRK at higher levels of myopia, particularly in cases with a history of keloid formation. [J Refract Surg. 2024;40(8):e533-e538.].

Refractive Surgery Patient Characteristics Associated With Satisfaction Scores.

To determine factors influencing patient satisfaction scores in recipients of refractive surgery. In this prospective survey-based study, patients who had refractive surgery at an outpatient refractive clinic completed a survey of selected questions from the Press Ganey survey and the National Eye Institute Visual Function Questionnaire-25. Correlation between patient-specific variables and survey questions were assessed using Student's t-tests. Fifty-three patients were recruited over a 3-year period. Most were male (55%) and middle aged (mean age: 34 years). Eleven percent underwent photorefractive keratectomy surgery and the rest had laser in situ keratomileusis, with no complications. Twenty-four percent of surveyed patients reported mild to moderate eye pain postoperatively, with the rest reporting no pain. All patients reported a full score for overall satisfaction. This study found persistent high patient satisfaction score across a variation of characteristics, suggesting that optimal scores are mainstay after refractive surgery procedures with excellent visual outcomes, independent of patient clinical and sociodemographic characteristics. [J Refract Surg. 2024;40(8):e539-e543.].

Comparative Analysis of Combined Topography-Guided Photorefractive Keratectomy and Corneal Crosslinking in Progressive Versus Stable Keratoconus.

To perform a comparative analysis of visual, refractive, and tomographic outcomes of combined topography-guided photorefractive keratectomy (TG-PRK) and corneal crosslinking (CXL) in patients with progressive versus stable keratoconus. Longitudinal retrospective case-control study. Patients with keratoconus submitted to simultaneous TG-PRK and CXL were included, with a minimum follow-up of 12 months up to 3 years. According to predefined disease progression criteria, patients were considered as progressive or stable. A total of 101 eyes from 93 patients were included, 62 considered progressive and 39 stable keratoconus. All baseline characteristics were similar between groups, except for age at surgery (progressive: 23.40 ± 4.22 years; stable: 35.97 ± 9.09; P < 0.001). Logarithm of the minimum angle of resolution CDVA improved significantly in progressive (baseline: 0.48 ± 0.24; 12 months: 0.33 ± 0.29; P < 0.001) and stable (baseline: 0.51 ± 0.24; 12 months: 0.28 ± 0.21; P < 0.001) patients, with no differences between groups. Maximum keratometry decreased significantly in progressive (baseline: 59.18 ± 5.63 diopters; 12 months: 54.73 ± 5.95; P < 0.001) and stable (baseline: 57.77 ± 5.02; 12 months: 53.59 ± 4.20; P < 0.001) patients, with no differences between groups. Index of surface variance significantly improved in progressive (baseline: 109.18 ± 31.74 diopters; 12 months: 94.11 ± 34.11; P < 0.001) and stable (baseline: 102.87 ± 29.52; 12 months: 86.95 ± 27.21; P < 0.001) patients, with no differences between groups. Other tomographic outcomes were also similar between groups. Pachymetry significantly decreased after surgery but remained stable throughout the follow-up. Combined TG-PRK and CXL is a safe and effective procedure for improving CDVA and regularizing the cornea, with comparable visual, refractive, and tomographic outcomes in both progressive and stable keratoconus. Combined TG-PRK and CXL may be added to the armamentarium of therapeutic tools for visual rehabilitation in patients with stable keratoconus.

Adopting Machine Learning to Automatically Identify a Suitable Surgery Type for Refractive Error Patients

efractive error is a visual impairment that arises when the ocular anatomy hinders the proper focusing of light onto the retina, the light-sensitive tissue layer located at the posterior region of the eye. This condition poses difficulties in achieving clear vision. Refractive error stands as the prevailing kind of visual impairment. The objective of this study is to classify two surgical approaches utilized in the treatment of refractive defects. Two commonly performed refractive surgeries are Photo-Refractive Keratectomy (PRK) and Laser-Assisted In-Situ Keratomileusis (LASIK). Artificial Intelligence (AI) encompasses a specific branch known as Machine Learning (ML), which is the focal point of this investigation. ML is dedicated to the advancement and use of algorithms that possess the capacity to acquire knowledge from data and enhance their predictive capabilities without explicit programming. The present study employs sophisticated ML methods to classify different types of refractive defect surgeries using a dataset of 124 samples obtained from Al-Rabee Hospital in Iraq, specifically focusing on corneal topography data. Two ML approaches, namely K-Nearest Neighbor (KNN) and Artificial Neural Network (ANN), are employed to predict the kind of refractive defect surgery. The findings produced from the experiment demonstrated an accuracy rate of 90.32% for the KNN algorithm and a perfect accuracy rate of 100% for the ANN algorithm. Additionally, the KNN algorithm exhibited a sensitivity of 90% and a specificity of 90.54%. The study’s findings indicate that the ANN classifier outperforms the KNN classifier.

Brillouin Biosensing of Viscoelasticity across Phase Transitions in Ovine Cornea.

Noninvasive in situ monitoring of viscoelastic characteristics of corneal tissue at elevated temperatures is pivotal for mechanical property-informed refractive surgery techniques, including thermokeratoplasty and photorefractive keratectomy, requiring precise thermal modifications of the corneal structure during these surgical procedures. This study harnesses Brillouin light scattering spectroscopy as a biosensing platform to noninvasively probe the viscoelastic properties of ovine corneas across a temperature range of 25-64 °C. By submerging the tissue samples in silicone oil, consistent hydration and immiscibility are maintained, allowing for their accurate sensing of temperature-dependent mechanical behaviors. We identify significant phase transitions in the corneal tissue, particularly beyond 40 °C, likely due to collagen unfolding, marking the beginning of thermal destabilization. A subsequent transition, observed beyond 60 °C, correlates with collagen denaturation. These phase transformations highlight the cornea's sensitivity to both physiologically reversible and irreversible viscoelastic changes induced by mild to high temperatures. Our findings underscore the potential of the Brillouin biosensing technique for real-time diagnostics of corneal biomechanics during refractive surgeries to attain optimized therapeutic outcomes.

Effect of Ablation Depth on the Endothelial Status of Eyes of Myopic Patients Undergoing Transepithelial Photorefractive Keratectomy: A Retrospective Study in Saudi Arabia.

The aim of this study was to correlate ablation depth on corneal endothelial cell (EC) indices following transepithelial photorefractive keratectomy (TPRK) in Saudi myopic patients. This was a retrospective cohort study of myopic eyes treated with TPRK. The changes in EC density and other indices were noted one week (W1) and 12 weeks (W12) after TPRK, which was the primary outcome. The laser ablation depth (AD) was correlated to the EC indices. The preoperative factors were also correlated to the outcomes using regression analysis to review predictors of change in the EC density. We had 120 eyes of 60 myopic patients operated on for TPRK. The mean of maximum AD (Adm) and central AD (ADc) were 110.3±23.7 µ and 108.8±24.4 µ, respectively. The median change in EC count at W1 and W12 were -9.5 (interquartile range (IQR) -33.0, 17.0) and -3.0 (IQR -29.3, 13.3), respectively. The ADm was negatively correlated to a change in EC density at W1 (Wilcoxon (Z) =-2.7, P = 0.006) and at W12 (Z = -3.74, P <0.001). ADm (Kruskal-Wallis (K-W) test (P) = 0.167), ADc (K-W P = 0.08), central corneal thickness (K-W P = 0.65), and use of mitomycin-C (K-W P = 0.357) were not significant predictors of the change in EC density at W1. None of the variables significantly influenced the change in EC density at W12. The corneal ablation depth for TPRK is correlated to changes in EC density at W1 and W12 after TPRK.

Effect of Astigmatism Treatment With Three Excimer Lasers After Photorefractive Keratectomy.

To compare astigmatism correction after photorefractive keratectomy (PRK) using three excimer laser devices, Alcon Wavelight EX500, Schwind Amaris 1,050, and Technolas Teneo317 M2. This retrospective study included 414 eyes from 414 subjects with a history of PRK performed using Alcon Wavelight (n=172), Schwind Amaris (n=122), and Technolas (n=120). Uncorrected & corrected distance visual acuity (UDVA & CDVA), and refractive status (spherical equivalent (SE) and vector analysis (J0 and J45)) were postoperatively recorded at the 6-month and 12-month examinations. The mean CDVA and J45 at 6-month and 12-month showed no statistically significant difference among the three different excimer lasers (P>0.05). There was a statistically significant difference in mean UDVA and J0 at 6-month and 12-month after PRK among the three groups, with no statistically significant difference between Alcon Wavelight and Schwind Amaris lasers, while both of the prior lasers showed a significant difference with the Technolas laser. The highest and lowest changes in the magnitude of J0 in 6-month and 12-month follow-ups were seen for the Alcon Wavelight and Technolas groups, respectively. Both Schwind Amaris and Technolas had a small hyperopic SE while the Alcon Wavelight's SE was minimally myopic. This difference in SE between Alcon Wavelight and both Schwind Amaris and Technolas reached statistical significance. While all three lasers performed well in reducing preoperative astigmatism; however, the Alcon Wavelight and Schwind Amaris were more effective in correcting astigmatism than the Technolas. The difference between the Alcon Wavelight and Schwind Amaris did not reach statistical significance.

Early elastic and viscoelastic corneal biomechanical changes after photorefractive keratectomy and small incision lenticule extraction.

To compare early changes in the corneal biomechanical parameters after photorefractive keratectomy (PRK) and small incision lenticule extraction (SMILE) and their correlations with corneal shape parameters. One hundred twenty four eyes received myopic PRK and SMILE for similar amounts of myopia. Corneal tomography with Pentacam HR, biomechanical parameters using Corvis ST, and Ocular Response Analyzer (ORA) were evaluated before and 2weeks after surgery. The change in each parameter was compared between groups, while the difference in central corneal thickness and cornea-compensated intraocular pressure measured before and after surgery were considered as covariates. A significant reduction was seen in the corneal stiffness parameter at first applanation, and an increase in deformation amplitude ratio (DAR), and integrated inverse radius (IIR) in both groups after surgery (p < 0.001) Changes in DAR, and IIR were significantly greater in the SMILE than in the PRK group (p < 0.001) Corneal hysteresis (CH) and corneal resistance factor(CRF) decreased in both SMILE and PRK groups after surgery, (p < 0.001) with no statistically significant difference between groups (p > 0.05) Among new Corvis ST parameters, DAR showed a significant correlation with changes in Ambrosio relational thickness in both groups (p < 0.05). Both techniques caused significant changes in corneal biomechanics in the early postoperative period, with greater elastic changes in the SMILE group compared to the PRK group, likely due to lower tension in the SMILE cap and thinner residual stromal bed in SMILE. There were no differences in viscoelastic changes between them, so the lower CH may reflect the volume of tissue removed.