Postoperative Corneal Ectasia Research Articles

Correction of Internal Astigmatism Using Toric Scleral Contact Lens after Implantable Collamer Lens Surgery

Purpose: We present a case of internal astigmatism correction using a toric scleral contact lens in a patient with high myopia after implantable collamer lens (ICL) surgery.Case summary: A 45-year-old man presented with a significant decrease in visual acuity despite previous ICL surgery. Initial attempts to fit a corneal rigid gas permeable contact lens to the left eye were unsuccessful due to fitting challenges. Subsequently, the use of a spherical scleral contact lens effectively corrected corneal astigmatism but failed to address internal astigmatism, thereby limiting improvement in visual acuity. Postoperative corneal ectasia and ICL rotation were suspected to be the underlying causes of this astigmatism. The introduction of a front toric scleral lens resulted in a significant improvement in visual acuity and sustained comfort throughout the 3-month follow-up period.Conclusions: The use of toric scleral lenses can significantly improve visual acuity and provide exceptional comfort in cases where corneal morphology and lens position change after ICL surgery. This modality presents a promising alternative for future consideration.

Progress of corneal morphological examination combined with biomechanical examination in preoperative screening for keratorefractive surgery.

Although corneal refractive surgery has been proven to be excellent in terms of safety and effectiveness, the reduction of postoperative corneal ectasia remains one of the most concerned topics for surgeons. Forme fruste keratoconus (FFKC) is the most important factor that leads to postoperative corneal ectasia, and common preoperative screenings of the condition include corneal morphology examination and corneal biomechanical examination. However, there are limitations to the single morphological examination or biomechanical examination, and the advantages of the combination of the two have been gradually emerging. The combined examination is more accurate in the diagnosis of FFKC and can provide a basis for determining suspected keratoconus. It allows one to measure the true intraocular pressure (IOP) before and after surgery and is recommended for older patients and those with allergic conjunctivitis. This article aims to discuss the application, advantages, and disadvantages of single examination and combined examination in the preoperative screening of refractive surgery, so as to provide a certain reference value for choosing suitable patients for surgery, improving surgical safety, and reducing the risk of postoperative ectasia.

The Most Cited Articles and Authors in Refractive Surgery.

To provide a comprehensive analysis of the most highly cited articles and authors in refractive surgery. The Scopus database was searched for articles pertaining to refractive surgery using multiple search terms to identify the top 100 most cited articles in refractive surgery. A publicly available database of more than 100,000 scientists that provides standardized information on multiple variables resulting in a composite indicator (C score) was searched to identify refractive surgery authors. A refractive surgery-specific composite score was created using only the authors' publications that were directly related to refractive surgery. The 100 most cited articles and 40 refractive surgery authors with the highest ranked C score were identified. The article with the most citations by Trokel et al has garnered nearly 800 citations to date. All articles included in the top 100 had 200 or more citations. The peak publication years were 1998 to 2001. Laser in situ keratomileusis (22), photorefractive keratectomy (18), and postoperative corneal ectasia and/or corneal biomechanics (16) were the most represented topics. Emory University generated the most articles (7) and the majority of publications (48%) originated in the United States. Steven E. Wilson, MD, had the highest refractive C score and Jorge L. Alió, MD, PhD, had the most refractive surgery articles and citations. Among all authors listed, the average number of refractive surgery publications was 97, with 35% of the group having more than 100 refractive surgery articles published. All authors on the list had more than 2,000 citations for their refractive surgery articles, whereas 38% had 4,000 or more citations. This list provides a comprehensive assessment of the most cited articles and authors in refractive surgery and demonstrates key focuses and trends in the field over time. [J Refract Surg. 2023;39(2):78-88.].

Clinical Evaluation of Corneal Biomechanics following Laser Refractive Surgery in Myopic Eyes: A Review of the Literature.

The role of corneal biomechanics in laser vision correction (LVC) is currently being raised in the assessment of postoperative corneal ectasia risk. The aim of the paper was to evaluate the changes in corneal biomechanics after LVC procedures based on a systematic review of current studies. The results of a search of the literature in the PubMed, Science Direct, Google Scholar, and Web of Science databases were selected for final consideration according to the PRISMA 2020 flow diagram. Included in our review were 17 prospective clinical studies, with at least 6 months of follow-up time. Corneal biomechanical properties were assessed by Ocular Response Analyzer (ORA), or Corvis ST. The results of the study revealed the highest corneal biomechanics reduction after laser in situ keratomileusis (LASIK) followed by small incision lenticule extraction (SMILE) and surface procedures, such as photorefractive keratectomy (PRK) or laser-assisted sub-epithelial keratectomy (LASEK). In SMILE procedure treatment planning, the use of thicker caps preserves the corneal biomechanics. Similarly, reduction of flap thickness in LASIK surgery maintains the corneal biomechanical strength. Future prospective clinical trials with standardization of the study groups and surgical parameters are needed to confirm the results of the current review.

Laser In Situ Keratomileusis (LASIK) Combined with Prophylactic Corneal Cross-Linking for Correction of Myopia: Regional Analysis of Corneal Morphology.

IntroductionThis study evaluated the outcomes of laser in situ keratomileusis (LASIK) combined with prophylactic corneal collagen cross-linking (CXL) in correcting myopia in cases with increased estimated risk of postoperative corneal ectasia, detected by regional analysis of corneal morphology.MethodsThe retrospective study included 180 eyes of 99 patients. Group 1 (94 eyes of 49 patients) with increased risk of postoperative corneal ectasia, as detected by “Ectasia Risk Factor Score System for LASIK”, underwent femtosecond laser-assisted LASIK (FS-LASIK) combined with prophylactic CXL, using short riboflavin soaking time and low UV energy. Group 2 (86 eyes of 50 patients) with normal corneal topography, who underwent FS-LASIK alone, were used as controls. Refractive and visual outcomes and Scheimpflug topo/tomography were analyzed preoperatively and 1 week, 1 month, and 12 months postoperatively. Mean regional corneal curvature (M) values for three subregions (the central 3.0 mm region, the paracentral 3.0–6.0 mm region, and the peripheral 6.0–9.0 mm region) of both anterior and posterior surfaces were calculated.ResultsAn increase in flattening of the peripheral anterior region and more steepening of the posterior paracentral region were shown at 12 months compared to 1 month postoperatively in group 1. The findings were significantly more pronounced than in group 2 (P < 0.001 and P = 0.035, respectively). The refractive and visual outcomes were comparable in the two groups.ConclusionsProphylactic CXL seems to influence corneal regional reshaping after surgery, while not affecting the 1-year visual and refractive results.

Advance of screening keratoconus before refractive surgery with machine learning

Artificial intelligence (AI) has made important progress in image recognition and disease prognosis prediction in recent years. Along with the development of computer technology, the application scope of AI in the field of ophthalmology is expanding. Keratoconus screening is an important means to determine the indication of refractive surgery and avoid postoperative corneal ectasia, but the accuracy of traditional diagnostic methods is low, especially for subclinical keratoconus. Machine learning, a method to realize artificial intelligence, makes it possible to improve the accuracy of keratoconus screening, and has become a hotspot in the field of refractive surgery recently. The review has clarified the algorithms commonly used in keratoconus screening for refractive surgery, the extraction of corneal features, and the accuracy of model prediction.(Chin J Ophthalmol, 2021, 57: 796-800).

Postoperative corneal biomechanics and influencing factors during femtosecond-assisted laser in situ keratomileusis (FS-LASIK) and laser-assisted subepithelial keratomileusis (LASEK) for high myopia.

The purpose of this study is to compare the postoperative corneal biomechanics and assess the influence factors after femtosecond-assisted laser in situ keratomileusis (FS-LASIK) and laser-assisted subepithelial keratomileusis (LASEK) for high myopia. In this retrospective study, patients who completed 1-year follow-up were included. The corneal biomechanical parameters, including deformation amplitude ratio 2.0 mm (DA ratio 2.0 mm), integrated inverse radius (IntInv Rad), stiffness parameter at first applanation (SP-A1), and Ambrosio relational thickness through the horizontal meridian (ARTh), were measured with Corvis STII. We also investigated the relationship between these biomechanics and preoperative or intraoperative variables. Thirty eyes had FS-LASIK and 30 eyes had LASEK. The changes in DA ratio 2.0 mm, IntInv Rad, and SP-A1 after surgery were significantly smaller in the LASEK group than in the FS-LASIK group, while the change in the ARTh was not significantly different between groups. No significant differences were detected in the mean values of postoperative DA ratio 2.0 mm, IntInv Rad, and SP-A1 between LASEK and FS-LASIK, while significant difference was detected in the mean value of postoperative ARTh. There was a significant correlation between the resident stromal bed thickness and the postoperative DA ratio 2.0 mm, IntInv Rad, or SP-A1. The postoperative ARTh has shown significant correlation with postoperative central corneal thickness and the amount of myopic correction. The effect of LASEK on corneal biomechanics was smaller than FS-LASIK when the same central corneal thickness was consumed. LASEK may be performed with a lower risk of postoperative corneal ectasia than FS-LASIK.

Corneal Ectasia Risk And Percentage Tissue Altered In Myopic Patients Presenting For Refractive Surgery.

PurposeA percentage tissue altered (PTA) score of ≥40% has been advocated as an independent indicator of post-operative ectasia risk following laser in-situ keratomileusis (LASIK). This study was performed to test the hypothesis that refractive procedures, such as laser-assisted sub-epithelial keratectomy (LASEK) or small incision lenticule extraction (SMILE), may alter the range of PTA, within which refractive corneal surgery can be safely performed.SettingRefractive department, tertiary ophthalmic hospital.DesignRetrospective observational study.MethodsReview of case notes was performed for patients who presented for refractive surgeries, other than LASIK. To determine the risk of corneal ectasia for each patient prior to refractive surgery, we estimated what each patient’s PTA would have been if they had undergone LASIK. The Randleman Ectasia Risk Score System (ERSS) was also calculated.Results114 eyes (66 patients) were included. 94 eyes underwent SMILE. 20 eyes underwent LASEK. A significant proportion of eyes had PTA ≥40% – SMILE eyes: up to 31.9%, LASEK eyes: up to 60.0% (at presumed LASIK flap of 120 μm). The maximum calculated PTA was up to 47.9% in the SMILE group and up to 51.5% in the LASEK group. Using ERSS, 12.8–16% of SMILE eyes and 15.0–80.0% of LASEK eyes would have been considered to have moderate-to-high ectasia risk. No post-surgical ectasia was observed at 3 years.ConclusionSMILE and LASEK alter the range of PTA, within which corneal refractive surgery may be performed with a lower risk of developing post-operative corneal ectasia; a safe PTA threshold needs to be determined for these procedures before recommendations for clinical practice can be made.

Corneal Collagen Cross-Linking

To review outcomes of corneal collagen cross-linking (CXL) for keratoconus (KC) or ectasia in a cornea subspecialty practice. Results from controlled clinical trials at a single site cornea subspecialty practice, including 104 eyes (66 KC and 38 ectasia). Outcomes and the natural course of changes in postoperative parameters including maximum keratometry (KMax), uncorrected visual acuity (UCVA), and best-corrected visual acuity (BCVA) over 12 months are reviewed. In addition, corneal topography indices, wavefront higher-order aberrations, and the natural history of wound healing after CXL are discussed. Characteristics associated with CXL outcomes are reviewed as well. In predicting treatment outcomes for KMax and BCVA, the preoperative patient characteristics examined were gender, age, disease group, cone location, thinnest pachymetry, UCVA, BCVA, and KMax. At 1 year, an average of 1.7 diopter (D) flattening in KMax was found. Mean BCVA improved slightly more than 1 line (from 0.35±0.24 to 0.23±0.21 logMAR). All postoperative parameters similarly follow a trend of worsening between baseline and 1 month, and improvement thereafter. More specifically, quantitative improvements are typically seen at 3 months and may continue between 3 and 12 months. A review of baseline patient characteristics indicated that (1) eyes with preoperative KMax of 55 D or steeper were 5.4 times more likely to gain 2 D or more of KMax flattening at 1 year after CXL, and (2) eyes with preoperative BCVA of 20/40 or worse were 5.9 times more likely to gain 2 or more Snellen lines at 1 year after CXL. Conversely, no baseline characteristic was found to correlate with treatment complications of continual topographic steepening or loss of vision. Corneal collagen cross-linking seems to be effective in decreasing progression of KC, with improvements in optical measures in many patients. Postoperative parameters discussed within this review followed a seemingly reproducible trend in their natural course over 12 months. Generally, the trend observed was immediate worsening between baseline and 1 month, resolution at approximately 3 months, and improvement thereafter. In predicting outcomes after CXL, no patient characteristics showed correlations with negative treatment outcomes such as loss of vision or continual topographic steepening. However, steeper KMax (≥55 D) and poorer BCVA (≤20/40) at the time of treatment correlated with better postoperative KMax and BCVA outcomes at 1 year, respectively. These outcome predictors should be considered when offering CXL to patients with KC or postoperative corneal ectasia.

SD-OCT Analysis of Regional Epithelial Thickness Profiles in Keratoconus, Postoperative Corneal Ectasia, and Normal Eyes

To assess corneal microarchitecture and regional epithelial thickness profile in eyes with keratoconus, postoperative corneal ectasia (ectasia), and normal unoperated eyes (controls) using spectral-domain optical coherence tomography (SD-OCT). Regional corneal epithelial thickness profiles were measured with anterior segment SD-OCT (Optovue RTVue-100, Optovue Inc., Fremont, CA). Epithelial thickness was assessed at 21 points, 0.5 mm apart, across the central 6-mm of the corneal apex in the horizontal and vertical meridians. One hundred twenty eyes were evaluated, including 49 eyes from 29 patients with keratoconus, 32 eyes from 16 patients with ectasia, and 39 eyes from 21 control patients. Average epithelial thickness at the corneal apex was 41.18 ± 6.47 μm (range: 30 to 51 μm) for keratoconus, 46.5 ± 6.72 μm for ectasia (range: 34 to 60 μm), and 50.45 ± 3.92 μm for controls (range: 42 to 55 μm). Apical epithelial thickness was significantly thinner in eyes with keratoconus (P < .0001) and ectasia (P = .0007) than in controls. Epithelial thickness ranges in all other areas varied widely for keratoconus (range: 21 to 101 μm) and ectasia (range: 30 to 82 μm) compared to controls (range: 43 to 64) (P = .0063). SD-OCT demonstrated significant central and regional epithelial thickness profile differences between keratoconus, ectasia, and control eyes, with significant variability and unpredictability in ectatic eyes. This regional irregularity may necessitate direct epithelial thickness measurement for treatments where underlying stromal variations may be clinically relevant, including corneal collagen cross-linking or topography-guided ablations.

Mild Topographic Abnormalities that Become More Suspicious on Scheimpflug Imaging

Although several screening methods exist, postoperative corneal ectasia after refractive surgery is a severe complication. One possibility for this might be the fact that screening methods may fail in detection of preoperative risk factors such as forme fruste keratoconus (FFKC). Retrospective evaluation of four cases that showed only mild changes of FFKC on placido-based topography but revealed indicative findings on Scheimpflug imaging (Pentacam). While in placido-based topography evaluation of corneal topography did not show a clear FFKC, the evaluation of corneal topography on Scheimpflug imaging together with the data of spatial corneal thickness revealed distinctive FFKC in all cases presented. Although both methods bear the risk of not detecting pre-existing FFKC, Scheimpflug imaging seems superior to placido-based corneal topography alone.

Visual rehabilitation and outcomes for ectasia after corneal refractive surgery

To analyze the visual outcomes and method of final visual correction in eyes with corneal ectasia after laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK). Emory University Department of Ophthalmology and Emory Vision, Atlanta, Georgia, USA. This retrospective review comprised 74 eyes of 45 patients with corneal ectasia after LASIK (72 eyes) or PRK (2 eyes). Outcomes included postoperative uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), best corrected visual acuity (BCVA), and refraction; method of final visual correction; and time to rigid gas-permeable (RGP) contact lens failure. Corneal ectasia developed a mean of 19.2 months after surgery. Postoperatively, the mean UCVA was 20/400 and the mean BSCVA before ectasia management was 20/108. After ectasia management, the mean BCVA was 20/37 and the final BCVA was 20/40 or better in 78% of eyes. Final visual correction was achieved with RGP lenses in 77% of eyes, spectacles in 9%, collagen crosslinking in 3%, intracorneal ring segments in 1%, and penetrating keratoplasty (PKP) in 8%. Two eyes with intracorneal ring segments required segment explantation and subsequent PKP. One eye that had PKP had a graft-rejection episode; there were no graft failures. Two eyes (3%) did not require a visual device to improve visual acuity. The mean time for successful RGP lens wear was 24.8 months; 80% of cases initially managed with RGP lenses were successful with this form of treatment. The majority of eyes developing postoperative corneal ectasia achieved functional visual acuity with RGP lens wear and did not require further intervention. Penetrating keratoplasty can usually be postponed or avoided by alternative methods of visual rehabilitation; however, PKP, when necessary, can provide good visual outcomes.

Mathematics of laser in situ keratomileusis for high myopia

Purpose: To determine the maximal ablation that can be safely performed with laser in situ keratomileusis (LASIK) to maintain long-term corneal integrity.Setting: TLC The Windsor Laser Center, Windsor, Canada.Methods: The pretreatment protocols for the VISX Star, Summit Omnimed, and Chiron Technolas 116 excimer lasers generally apply 1 to 2 pm per diopter (D) at an optical zone of 3.0 mm or less to avoid the postoperative central islands that can occur with broad-beam excimer lasers. The ablation depth per diopter for the VISX Star, Summit Omnimed, Chiron Technolas 116, and Chiron Technolas 217 excimer lasers ranges from 10 to 24 pm per diopter depending on the size and number of ablation zones and the excimer laser used.Results: Previous experience with lamellar surgery suggests that at least 250 pm of central posterior stromal tissue should be preserved to maintain long-term corneal integrity and avoid postoperative corneal ectasia. If a 160 μm flap is created for LASIK, the average 550 pm cornea will have 140 pm of corneal stroma available for ablation. Depending on the excimer laser and ablation nomogram used, the maximal LASIK correction for the average cornea ranges from 9.8 to 15.0 D.Conclusion: The preoperative corneal thickness and the depth of the excimer laser ablation must be evaluated before LASIK to ensure that adequate posterior corneal stroma is preserved.