Visual rehabilitation and outcomes for ectasia after corneal refractive surgery

Anterior, Posterior, and Thickness Cornea Differences after Scleral Lens Wear in Post-LASIK Subjects for One Year

The aim of this study is to analyze the anterior and posterior corneal surface shape and the corneal thickness difference outcomes between before and after scleral lens (ScCL) wear in post-LASIK ectasia subjects for one year. Twenty eyes with post-LASIK ectasia wearing scleral lenses were evaluated in a visit before contact lens and after 1, 6, and 12 months. The study variables analyzed included the apex, nasal, temporal, inferior, and superior corneal thickness; the anterior and posterior surface corneal at corneal diameters of 8, 6, 4, and 2 mm, and high-contrast visual acuity. A statistically significant increment of corneal thickness (p < 0.05) was observed in the inferior area after 6 months and in the superior area in the 12-month follow-up after wearing ScCLs. The anterior corneal curvature presented a flattening and a statistically significant steepening (p < 0.05) in the central and peripheral radii, respectively, after one year. The posterior corneal curvature showed a significant (p < 0.05) steepening, which mainly affected the central region after one year. Despite these changes, high-contrast visual acuity with ScCL correction remained at the same values. The prolonged use of scleral lenses in post-LASIK subjects showed significant changes in the corneal curvature and thickness. These outcomes recommend more detailed and periodic topographic and vision quality checks to monitor the wear in ScCL patients.

Assessment of the specificity of corvis biomechanical index-laser vision correction (CBI-LVC) in stable corneas after phototherapeutic keratectomy

PURPOSE

The Corvis Biomechanical Index-Laser Vision Correction (CBI-LVC) is a biomechanical index to detect ectasia in post-refractive surgery patients (PRK, LASIK, SMILE). This study aims to evaluate the distribution of the CBI-LVC in stable patients who underwent Phototherapeutic Keratectomy (PTK) compared to PRK patients.

METHODS

Patients who underwent PRK and PTK performed between 2000 and 2018 in Humanitas Research Hospital, Rozzano, Milan, Italy and remained stable for at least four years post-surgery were included. All eyes were examined with the Corvis ST (Oculus, Germany), whose output allows the calculation of the CBI-LVC. The distribution and specificity of the CBI-LVC in the two populations were estimated using a Wilcoxon Mann-Whitney test and compared.

RESULTS

175 eyes of 148 patients were included (85 eyes of 50 PTK patients and 90 eyes of 90 PRK patients). The distribution of CBI-LVC in the two groups showed a minor difference, with a median value in PRK patients of 0.000 (95% CI 0.000; 0.002) and 0.008 (95% CI 0.000; 0.037) in PTK patients (Mann-Whitney U test p = 0.023). The statistical analysis showed that the CBI-LVC provided a specificity of 92.22% in the PRK group, while in the PTK group it was 82.35%. Nevertheless, this difference was not statistically significant (Chi-squared test with Yates, p = 0.080).

CONCLUSION

CBI-LVC provided similar specificity in stable PTK patients compared to those who underwent PRK. These results suggest that the CBI-LVC could be a useful tool to aid corneal surgeons in managing PTK patients.

Evidence of Contact Lenses for Vision Rehabilitation in Corneal Diseases: A Review

OBJECTIVES

To evaluate the efficacy and safety of contact lenses (CL) as a therapeutic option for patients affected by a corneal disease and to determinate which is the best lens modality for each disease.

METHODS

A literature review using PubMed was performed. All relevant articles published during the last 15 years have been included.

RESULTS

Various studies point to CL as the best therapeutic option for some corneal diseases and even as an alternative to surgery in some cases. After fitting, patients show an improvement in their functional vision and quality of life, in some cases being able to drive or work again.

CONCLUSIONS

There is a lack of scientific evidence to determine which lens modality is suitable for each corneal pathology. Currently, according to this review, the reason for choosing between the different options depends on the severity of symptoms, and it is worth mentioning that scleral lenses seem to be the best option in advanced stages of disease. However, the expertise of professionals is also an important factor at the time of choosing a particular CL modality. Standardized criteria are still necessary for correct selection of lens modality for a correct management of the disease.

Trends in research on corneal cross linking from 2001 to 2020: a bibliometric analysis

CLINICAL RELEVANCE

The research status and hotspots in the field of corneal cross linking (CXL) can benefit clinicians, researchers and the general public.

BACKGROUND

The purpose of this study was to map the publishing trend on CXL research and explore the research hotspots.

METHODS

A bibliometric analysis was performed using the Web of Science Core Collection to investigate the publishing trend on CXL research. VOSviewer was used to build the knowledge map to visualise the number of annual publications, distribution of countries and institutions, international cooperation, author productivity, source journals and research hotspots in the field of CXL.

RESULTS

A total of 2061 peer-reviewed articles on CXL research were collected from 2001 to 2020, and the annual research production increased over time. The United States was the country with the largest number of published articles, and the University of Zurich was the most active institution. Hafezi F published the largest number of articles on CXL, while Cornea was the journal with the largest number of studies on CXL. The most frequently cited references mainly focus on CXL in the treatment of keratoconus. The keywords were divided in 5 categories: 1) CXL mechanism, 2) ectasia diseases and refractive surgery, 3) corneal biomechanics, 4) efficacy evaluation, 5) treatment of infectious keratitis.

CONCLUSION

The quantity and quality of articles on CXL were evaluated using bibliometric techniques by extracting the data from the Web of Science Core Collection. The research hotspots could provide insights on CXL research, providing valuable information for clinicians to perform research in this field and find potential partners.

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.

Ectasia After Corneal Refractive Surgery: A Systematic Review

INTRODUCTION

The incidence of ectasia following refractive surgery is unclear. This review sought to determine the worldwide rates of ectasia after photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), and small incision lenticule extraction (SMILE) based on reports in the literature.

METHODS

A systematic review was conducted according to modified Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Publications were identified by a search of eight electronic databases for relevant terms between 1984 and 2021. Patient characteristics and preoperative values including manifest refractive spherical refractive equivalent (MRSE), central corneal thickness (CCT), anterior keratometry, postoperative residual stromal bed (RSB), and percent tissue altered (PTA) were summarized. In addition, annual rates of each refractive surgery were determined, and incidence of post-refractive ectasia for each type was calculated using the number of ectatic eyes identified in the literature.

RESULTS

In total, 57 eyes (70 eyes including those with preoperative risk factors for ectasia) were identified to have post-PRK ectasia, while 1453 eyes (1681 eyes including risk factors) had post-LASIK ectasia, and 11 eyes (19 eyes including risk factors) had post-SMILE ectasia. Cases of refractive surgery performed annually were estimated as 283,920 for PRK, 1,608,880 for LASIK, and 96,750 for SMILE. Reported post-refractive ectasia in eyes without preoperative identifiable risk factors occurred with the following incidences: 20 per 100,000 eyes in PRK, 90 per 100,000 eyes in LASIK, and 11 per 100,000 eyes in SMILE. The rate of ectasia in LASIK was found to be 4.5 times higher than that of PRK.

CONCLUSION

Post-refractive ectasia occurs at lower rates in eyes undergoing PRK than LASIK. Although SMILE appears to have the lowest rate of ectasia, the number of cases already reported since its recent approval suggests that post-SMILE ectasia may become a concern. Considering that keratoconus is a spectrum of disease, pre-existing keratoconus may play a larger role in postoperative ectasia than previously accounted for in the literature.

Simultaneous photorefractive keratectomy and accelerated collagen cross-linking in high-risk refractive surgery (Tehran protocol): 3-year outcomes

PURPOSE

To evaluate safety and efficacy of performing simultaneous photorefractive keratectomy (PRK) and collagen cross-linking (CXL) in myopic patients with preoperative risk factors for developing keratectasia.

METHODS

Seventeen eyes of 15 patients with at least one of the following risk factors were recruited: central keratometry (K_max) between 48 and 50, difference between inferior, superior corneal power (I-S value) between 1.4 and 1.9 and corneal thickness between 450 and 480 µm. Upon final stage of standard PRK, 0.02% mitomycin was applied for 30-50 s, and then, accelerated CXL was performed for 5 min. Pre- and postoperative Oculus Pentacam^® imaging for keratometry values, measurement of uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) were done for all patients.

RESULTS

Mean follow-up time was 32.08 ± 7.79 months (range 25-49 months). Mean age of patients was 28.78 ± 3.80 years. Mean postoperative spherical equivalent was + 0.19 ± 0.42 (- 0.5 to + 1.0 [D]). Mean UDVA and CDVA improved from 0.9062 ± 0.485 log MAR and 0.0148 ± 0.043 log MAR to 0.0173 ± 0.040 log MAR and 0.0057 ± 0.023 log MAR, respectively (P = 0.011, P = 0.735). Mild degree of early postoperative stromal haze was seen which did not persist more than 6 months. There was no late stromal haze, corneal ectasia or other major postoperative complication in the follow-up period.

CONCLUSION

Combined PRK and accelerated CXL is an efficient and safe procedure for high-risk refractive surgery candidates, with no increased risk of persistent corneal haze.

Comparison of clinical results between trans-PRK and femtosecond LASIK for correction of high myopia

Background

To compare the clinical outcomes of transepithelial photorefractive keratectomy (TPRK) with femtosecond laser-assisted in situ keratomileusis (FS-LASIK) for correction of high myopia.

Methods

In this prospective, non-randomised, cohort study, 85 eyes of 46 patients treated with TPRK and 80 eyes of 42 patients treated with FS-LASIK were included. All eyes were highly myopic (spherical equivalent refraction <− 6.00 diopters). Both TPRK and FS-LASIK were performed by Schwind Amaris 750S excimer laser. Visual acuity, refraction, corneal high order aberration (HOA) and other variables were analyzed before and at 1, 3, 6, 12 months after surgery.

Results

At 12 months after surgery, uncorrected logMAR distance visual acuity (UDVA) in the TPRK and FS-LASIK groups was − 0.04 ± 0.04 and − 0.01 ± 0.08, respectively (P = 0.039). Corrected logMAR distance visual acuity (CDVA) was − 0.06 ± 0.05 and − 0.04 ± 0.05 in both groups (P = 0.621). For UDVA, 86% of eyes in the TPRK group and 80% in the FS-LASIK group remained unchanged or improved one or more logMAR lines (P = 0.314), compared to preoperative CDVA. For CDVA, 97% of eyes in the TPRK group and 90% in the FS-LASIK group remained unchanged or improved one or more lines (P = 0.096), compared to preoperative CDVA. Spherical equivalent refraction was − 0.05 ± 0.39 and − 0.26 ± 0.47 in both groups (P = 0.030). 87% of eyes in the TPRK group and 73% in the FS-LASIK group achieved ±0.50 D target refraction (P = 0.019). All 85 eyes (100%) in the TPRK group and 75 eyes (92%) in the FS-LASIK group were within ±1.00 D of target (P = 0.003). Root mean square (RMS) of corneal total HOA and vertical coma in the TPRK group were lower compared with the FS-LASIK group (P < 0.001 for both variables).

Conclusions

TPRK and FS-LASIK showed good safety, efficacy and predictability for correction of high myopia. Clinical outcomes of TPRK were slightly better than FS-LASIK.

Ectasia after keratorefractive surgery: Analysis of risk factors and treatment outcomes in the Indian population

Purpose:

To analyze the risk factors in eyes developing ectasia following keratorefractive procedures. In addition, the study assessed visual outcomes following various treatment modalities for ectasia.

Methods:

In this retrospective study, data of patients who underwent keratorefractive procedures, presenting to the refractive services of a tertiary eye care hospital in South India between January 2016 and May 2019 was analyzed. Of these, the eyes that developed ectasia were noted and the possible risk factors were determined. Visual outcomes following treatment with corneal collagen crosslinking (CXL) with or without intracorneal ring segment implantation (ICRS) or topography-guided corneal ablation (T-PRK) were analyzed.

Results:

Forty eyes of 26 patients developed ectasia following keratorefractive procedures, with a mean interval of 73.1± 45.4 months between primary procedure and ectasia development. Of these, 14 patients had bilateral presentation. Identifiable risk factors included ablation depth >75 μm (59.25%), percentage of tissue altered (PTA) >40% (48.14%), residual stromal bed <300 μm (22.22%), mean refractive spherical equivalent >8 D (25.92%), inferior–superior (I–S) asymmetry >1.4D (7.40%), central corneal thickness (CCT) <500 μm (7.40%), Belin Ambrosio Display (BAD) >2.5 (7.40%), posterior float elevation maximum ≥18 μm (3.70%), and pellucid marginal degeneration (PMD; 3.70%).

Conclusion:

Our study shows that only 70% of the eyes demonstrated an identifiable risk factor for the development of ectasia. Ablation depth of >75 μm and the PTA >40% were the most common risk factors. Treatment following CXL with ICRS or T-PRK demonstrated significantly better visual outcomes in comparison with CXL alone.

Evaluation of new Corvis ST parameters in normal, Post-LASIK, Post-LASIK keratectasia and keratoconus eyes

The aim of this study was to evaluate the distribution of new Corneal Visualisation Scheimpflug Technology (Corvis ST) parameters in normal, Post-laser in situ keratomileusis (LASIK), Post-LASIK keratectasia (KE) and keratoconus (KC) eyes, and explore the diagnostic ability of these parameters in distinguishing KE from LASIK eyes. Twenty-three normal eyes, 23 LASIK eyes, 23 KE eyes and 23 KC eyes were recruited in this study. The following new Corvis ST parameters were measured: Max Inverse Radius, deformation amplitude (DA) Ratio Max [2 mm], Pachy Slope, DA Ratio Max [1 mm], Ambrosio’s relational thickness horizontal (ARTh), Integrated Radius, stiffness parameter at first applanation (SP-A1) and Corvis biomechanical index (CBI). The general linear model, linear regression model, relation analysis and receiver operating characteristic (ROC) curve were performed. The Max Inverse Radius, DA Ratio Max [2 mm], Pachy Slope, DA Ratio Max [1 mm], Integrated Radius and CBI in LASIK eyes, KE eyes and KC eyes were higher than in normal eyes, while the ARTh and SP-A1 parameters were lower than in normal eyes. The KE eyes had higher Max Inverse Radius, DA Ratio Max [2 mm], Pachy Slope, DA Ratio Max [1 mm], Integrated Radius, and lower SP-A1 value than LASIK eyes (all P < 0.05). The central corneal thickness was related to the Pachy Slope (r = −0.485), ARTh (r = −0.766), SP-A1 (r = 0.618) in KE eyes (all P < 0.05). The area under the ROC curve of Integrated Radius, Max Inverse Radius, DA Ratio Max [2 mm] and SP-A1 were above 0.800 in identifying KE from LASIK eyes. Thus, the new Corvis ST parameters were different between LASIK and KE eyes, suggesting that they might be helpful in distinguishing KE eyes from LASIK eyes. However, a further multi-center and large sample study is necessary to confirm these findings.

Mechanical outcome of accelerated corneal crosslinking evaluated by Brillouin microscopy

PURPOSE

To quantify corneal mechanical changes induced by corneal crosslinking (CXL) procedures of different ultraviolet-A (UVA) intensity and exposure time using Brillouin microscopy.

SETTINGS

University of Maryland, College Park, Maryland, USA.

DESIGN

Experimental study.

METHODS

Porcine cornea samples were debrided of epithelia and soaked with riboflavin 0.1% solution. Samples were exposed to a standard 5.4 J/cm² of UVA radiation with varying intensity and exposure time as follows: 3 mW/cm² for 30.0 minutes, 9 mW/cm² for 10.0 minutes, 34 mW/cm² for 2.65 minutes, and 50 mW/cm² for 1.80 minutes. Using Brillouin microscopy, the Brillouin modulus for each sample was computed as a function of radiation intensity/exposure time. For validation, the Young's modulus was found with the stress-strain test and compared at each irradiation condition.

RESULTS

The standard 3 mW/cm² irradiance condition produced a significantly larger increase in corneal Brillouin modulus than the 9 mW/cm² (P ≤ .05), 34 mW/cm² (P ≤ .01), and 50 mW/cm² (P ≤ .01) conditions. Depth analysis showed similar anterior sections of the standard and 9 mW/cm² conditions but significantly less stiffening in the central and posterior of the 9 mW/cm² condition. The stiffening of the standard protocol was significantly larger in all sections of the 34 mW/cm² and 50 mW/cm² conditions (P ≤ .01). The overall change in Brillouin-derived Brillouin modulus correlated with the increase in Young's modulus (R² = 0.98).

CONCLUSIONS

At a constant UVA light dose, accelerating the irradiation process decreased CXL stiffening. Brillouin analysis showed that accelerated protocols were especially ineffective in the deeper portions of the cornea.

Corneal refractive surgery combined with simultaneous corneal cross-linking: Indications, protocols and clinical outcomes-A review

Corneal refractive surgery is one of the most common approaches for correction of refractive errors. Combined corneal refractive surgery and corneal cross-linking (CXL) has been proposed as a method to achieve better refractive stability and to prevent iatrogenic corneal ectasia. However, there are concerns regarding its indications, surgical safety, standardization of protocols and long-term effect on corneal tissue. This review article aims to discuss the current knowledge and recent updates on combination of CXL and refractive surgery.

Simultaneous Accelerated Corneal Crosslinking and Laser In situ Keratomileusis for the Treatment of High Myopia in Asian Eyes

Background:

LASIK Xtra is a recently described technique which combines LASIK and accelerated corneal cross-linking(CXL) in the same setting. Its long-term outcome in Asians with high myopia is not well described.

Objectives:

To compare the efficacy, predictability and safety of LASIK Xtra with LASIK in patients with high myopia.

Method:

This is a retrospective study comparing 50 consecutive eyes undergoing LASIK Xtra for the correction of high myopia and/or myopic astigmatism (-6.63 to -15.50 D manifest spherical equivalent) with a matched control group of 50 eyes undergoing LASIK alone for correction of high myopia (-6.00 to -12.25 D manifest spherical equivalent). Mean follow-up was 5.7 months (range, 1.5-13.3 months) for LASIK Xtra and 3.6 months (range, 1.7-4.2 months) for LASIK only. Outcome measures included Uncorrected Distance Visual Acuity (UDVA), Corrected Distance Visual Acuity (CDVA), refraction and intraoperative and postoperative complications.

Results:

At post-operative 3 months, all eyes achieved UDVA of 20/40 or better, and 80.0% of LASIK Xtra eyes achieved UDVA of 20/20 or better, compared to 66.0% of LASIK only eyes (p = 0.115). Efficacy indices were 0.99±0.17 for LASIK Xtra and 0.94±0.17 for LASIK only (p = 0.164). The proportion of eyes within ±0.50 D of attempted correction was 84% in the LASIK only group and 72% in the LASIK Xtra group at post-operative 3 months (p = 0.148). Safety indices were 1.11±0.19 and 1.11±0.18 in the LASIK Xtra and LASIK only groups, respectively (p = 0.735).

Conclusion:

LASIK Xtra achieved comparable safety, predictability and efficacy as LASIK in patients with high myopia. Good refractive stability was attained at 6-12 months. Further long term studies are required to determine whether simultaneous CXL is able to reduce postoperative LASIK keratectasia in high-risk individuals.

In vivo confocal laser microscopy of morphologic changes after small incision lenticule extraction with accelerated cross-linking (SMILE Xtra) in patients with thin corneas and high myopia

PURPOSE

To evaluate the microstructural modifications and safety of small incision lenticule extraction combined with accelerated cross-linking (SMILE Xtra) in high myopia and thin corneas by means of in vivo confocal microscopy (IVCM) and 3D-OCT after a 6-month follow-up.

METHODS

Forty-three eyes with high myopia and thin corneas were enrolled. All eyes underwent SMILE procedure. After the lenticule was extracted, 0.25% riboflavin was injected into the interface and allowed to diffuse for 60 s. The eye was irradiated with UVA radiation of 30 mW/cm² for 90 s through the cap. The total energy delivered was 2.7 J/cm². Morphologic modifications of corneal architecture were evaluated prior to SMILE Xtra and 7 days, 1, 3, and 6 months after SMILE by in vivo confocal microscopy (IVCM) and 3D-OCT.

RESULTS

The corneal epithelial cells showed slight damage until 3 months postoperatively. The subepithelial nerve plexus decreased but no absence within the treatment zone at the first week after treatment, recolonized at 3 months postoperatively, and had mostly recovered at the 6 months postoperative but remained less than its normal baseline state. Keratocytes were absent in the surgical interface area, and the presence of strong reflective particles and cicatricial reaction in the anterior stroma were observed during the entire 6-month examination period. Increased hyperreflectivity was observed from the cap side at a depth of 60 µm to stroma bed at a depth of 388 µm through 6 months. The depth of the demarcation line in 40 eyes (93.0%) was at a mean depth of 296.12 ± 47.86 μm (range, 211-388 μm). No particular change between preoperative and postoperative corneal endothelium was observed.

CONCLUSIONS

Confocal microscopy showed increased hyperreflectivity in the SMILE Xtra eyes, and no changes in corneal endothelium. We confirmed the safety of the SMILE Xtra but recognize that larger and longer-term studies of SMILE Xtra are necessary.

Risk Assessment for Corneal Ectasia following Photorefractive Keratectomy

PURPOSE

To analyze the risk factors associated with a series of ectasia cases following photorefractive keratectomy (PRK) and all published cases.

METHODS

In a retrospective study on post-PRK ectasia patients, 9 eyes of 7 patients were included, in addition to 20 eyes of 13 patients from the literature. Risk of post-PRK ectasia was calculated using the ectasia risk score system (ERSS) for laser in situ keratomileusis (LASIK) patients. The percent tissue altered (PTA) was also evaluated.

RESULTS

ERSS scoring of zero for age, RSB, and spherical equivalent was found in 66%, 86%, and 86% of the eyes, respectively. Pachymetry risk score was 2 in 60% of the eyes and 3 or 4 in 16% of the eyes. Topography risk score was 3 in 41% of the eyes and 4 in 21% of the eyes. Cumulative ectasia risk score was ≥4 (high risk) in 77% of the eyes and ≥3 (medium and high risk) in 86% of the eyes. Average PTA was 23.2 ± 7.0%. All eyes but one had a PTA < 40%.

CONCLUSIONS

Preoperative corneal topographic abnormalities and thin corneas may be significant risk factors for developing ectasia following PRK. Post-LASIK ectasia risk scoring also has relevance in the risk for developing post-PRK ectasia.

Laser Vision Correction in Treating Myopia

Myopia is a generally benign refractive error with an increasing prevalence worldwide. It can be corrected temporarily with glasses and contact lenses and permanently with laser vision correction. The 2 main procedures currently being performed for myopia correction are photorefractive keratectomy and laser-assisted in situ keratomileusis. Each technique has its advantages, but they appear to yield similar visual outcomes 1 year after surgery. Laser vision correction for myopia was considered a paradigm shift because healthy eyes could now undergo a surgical procedure to permanently and safely correct the error by altering the center of the cornea, which was previously off limits because of the potential for loss of transparency. Customized ablation using wavefront aberrometry and its optimized profiles were created to correct higher-order aberrations and give more vision quality to patients. Topography-guided ablation, initially used for complex retreatments, shows potential to make vision even better than glasses and contact lenses in a recent study on previously untreated eyes. One major concern is to identify corneas that are at risk of developing ectasia after the procedure. Topographic and tomographic screening indices have been implemented clinically, but there is still much to learn about corneal biomechanics. A more recently developed procedure for myopia correction is small-incision lenticule extraction, in which a lenticule is created in the cornea's stroma with a femtosecond laser and extracted through a small corneal incision. Long-term outcomes and new complication risks need to be better understood as this procedure develops.

Estimation of the hybrid lens parameters through rigid gas permeable lens fitting

PURPOSE

To estimate the fitting parameters of the hybrid contact lens in patients with corneal ectasia using the rigid gas permeable (RGP) lens.

METHODS

Thirty-four eyes with corneal ectasia were evaluated in this study. The patients were examined once with the RGP lens and once with the hybrid contact lens. The relationship between the base curvature of the RGP and the vault of the hybrid lens and the correlation between their powers were analyzed.

RESULTS

We found a linear relationship between the base curvature of the RGP lens and the vault of the hybrid lens (P < 0.001) (R(2) = 0.45). Moreover, we found a correlation between the power of the RGP and hybrid lens (P < 0.001) (R(2) = 0.4). However, a 0.5 mm decrease in the base curvature radius of the RGP lens increased the vault of the hybrid lens by 72 μ.

CONCLUSION

The results of this study could be used for better and faster selection of the first hybrid contact lens.

Measurement of corneal tangent modulus using ultrasound indentation

Biomechanical properties are potential information for the diagnosis of corneal pathologies. An ultrasound indentation probe consisting of a load cell and a miniature ultrasound transducer as indenter was developed to detect the force-indentation relationship of the cornea. The key idea was to utilize the ultrasound transducer to compress the cornea and to ultrasonically measure the corneal deformation with the eyeball overall displacement compensated. Twelve corneal silicone phantoms were fabricated with different stiffness for the validation of measurement with reference to an extension test. In addition, fifteen fresh porcine eyes were measured by the developed system in vitro. The tangent moduli of the corneal phantoms calculated using the ultrasound indentation data agreed well with the results from the tensile test of the corresponding phantom strips (R(2)=0.96). The mean tangent moduli of the porcine corneas measured by the proposed method were 0.089±0.026MPa at intraocular pressure (IOP) of 15mmHg and 0.220±0.053MPa at IOP of 30mmHg, respectively. The coefficient of variation (CV) and intraclass correlation coefficient (ICC) of tangent modulus were 14.4% and 0.765 at 15mmHg, and 8.6% and 0.870 at 30mmHg, respectively. The preliminary study showed that ultrasound indentation could be applied to the measurement of corneal tangent modulus with good repeatability and improved measurement accuracy compared to conventional surface displacement-based measurement method. The ultrasound indentation can be a potential tool for the corneal biomechanical properties measurement in vivo.

Corneal Changes After Collagen Crosslinking for Keratoconus Using Dual Scheimpflug Imaging

Purpose:

To evaluate corneal changes after collagen crosslinking (CXL) therapy for keratoconus (KCN) using the Galilei dual Scheimpflug analyzer.

Methods:

This prospective, nonrandomized clinical study included 35 eyes of 32 keratoconus patients who had undergone CXL. The eyes were saturated with riboflavin solution and were subjected for 30 minutes to ultraviolet-A (UV-A) light with irradiance of 3 mW/cm². Effectiveness of the treatment was assessed by measuring uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), manifest cylinder/sphere, keratometry, pachymetry, posterior and anterior elevations by the Galilei dual Scheimpflug analyzer. Prior to treatment and 8 months after therapy, Scheimpflug analysis was performed using the Galilei system. The four sets of data including keratometry values, pachymetry, elevation parameters and surface indices were statistically analyzed and compared.

Results:

Mean patient age was 22.3 ± 3.8 years and mean postoperative follow-up was 8.1 ± 3.2 months. There was a significant increase in UCVA (0.54 ± 0.35 Log MAR preoperatively to 0.49 ± 0.34 LogMAR postoperatively, P = 0.01) and BCVA (0.21 ± 0.19 Log MAR preoperatively to 0.16 ± 0.17 LogMAR postoperatively, P = 0.01). Mean cycloplegic spherical equivalent refractive error was −4.13 ± 2.65 Diopter (D) preoperatively and − 4.67 ± 2.96 D postoperatively (P < 0.001). During the follow-up period, no significant difference was observed in pachymetric and elevation data postoperatively.

Conclusion:

Corneal stabilization could be achieved by collagen crosslinking therapy for keratoconus in terms of corneal thickness, keratometry values, elevation parameters and surface indices.

Femtosecond Laser-Assisted Corneal Small Incision Allogenic Intrastromal Lenticule Implantation in Monkeys: A Pilot Study

PURPOSE

Lenticule implantation can be used to correct vision problems. However, it is significantly restrained by the sources of autologous lenticules. The aim of the present study was to investigate the feasibility and effects of femtosecond laser-assisted corneal small incision allogenic intrastromal lenticule implantation (AILI) in monkeys.

METHODS

Six healthy adult monkeys were included in this study. Femtosecond lenticule extraction (-4.0 diopter [D] correction, 5.0-mm optical zone) was performed in one eye of two monkeys and both eyes of one monkey. Each extracted refractive lenticule was allogenically transplanted into a femtosecond laser-created corneal stromal pocket in one eye of the other two monkeys and one monkey's both eyes. Pre- and postoperative (1 or 3 days, 1 month, and 6 months) slit lamp microscopy, corneal topography, anterior segment optical coherence tomography, and in vivo confocal microscopy were performed.

RESULTS

Corneal edema occurred in the early postoperative days with a large number of hyperreflective particles around the borders. Corneal tissue edema gradually decreased. Nerve fiber regeneration could be detected in the lenticule layer at 6 months. Overall, 3.27 ± 1.2 D corneal power was increased at 6 months, accounting for 82% of the intended correction. At the same time point, corneal stroma was 69 ± 11 μm thicker than preoperative ones and was roughly equal to the maximum thickness of implanted lenticules. No significant complications were observed.

CONCLUSIONS

The AILI technique seems to be feasible and safe for increasing corneal stromal thickness and changing corneal refractive power, which may provide a useful method for treatment of keratoectasia, presbyopia, and hyperopia.

Clinical evaluation of rigid gas permeable contact lenses and visual outcome after repaired corneal laceration

OBJECTIVE

To evaluate the clinical value of rigid gas permeable contact lenses (RGPCLs) in patients with traumatic corneal scarring and address implications of primary corneal repair.

METHODS

Eighteen subjects with a history of corneal laceration were fit with RGPCLs. Scar locations were divided into two zones; each patient was examined using Pentacam. Entering data included uncorrected visual acuity (UCVA), spectacle-corrected visual acuity (SVA), time between injury and RGPCL fitting, location and size of scar, and amount of corneal astigmatism. Follow-up data included RGPCL visual acuity (RGPCLVA), RGPCL-related complications, and dropout characteristics. Visual acuity values were converted to logMAR for analysis.

RESULTS

No serious complications occurred. The average time between suture removal and RGPCL fitting was 5.7±5.5 months. Average corneal astigmatism was -3.44±2.09 diopters. One subject had developed corneal ectasia. RGPCLVA was more than 0.1 in three subjects: one experienced primary corneal repair complications, and two subjects (<10 years) developed amblyopia. In both zones, the difference in RGPCLVA outcome between zone I and zone II was not statistically significant (F=0.060, P=0.809). The difference between SVA in zones I and II was found to be statistically significant (F=6.131, P=0.026), as were the differences between SVA and RGPCLVA (F=8.598, P=0.010). The scar size had no significant influence on RGPCLVA, SVA, or UCVA. Four participants (22.2%) were successfully fit. Dropout characteristics included ocular discomfort, inconvenience, parental apprehension, and low motivation.

CONCLUSIONS

Rigid gas permeable contact lens is an ideal method for evaluating visual potential in patients with traumatic corneal astigmatism. Pentacam examinations of those patients with poor RGPCLVA can help an ophthalmologist find and understand existing problems in suture techniques.

Accelerated Corneal Collagen Cross-linking for Postoperative LASIK Ectasia: Two-Year Outcomes

PURPOSE

To evaluate the effectiveness and safety of accelerated corneal collagen cross-linking for postoperative LASIK ectasia after 2 years.

METHODS

A prospective, single-center case series was performed with patients treated for postoperative LASIK ectasia. All eyes underwent accelerated corneal collagen cross-linking (CCL-Vario Crosslinking; Peschke Meditrade GmbH, Zurich, Switzerland) at 9 mW/cm(2) for 10 minutes. The main outcome measures were changes in uncorrected distance visual acuity, corrected distance visual acuity, central corneal thickness, corneal topography, and endothelial cell density. These parameters were assessed at baseline and at the 6-month and 1- and 2-year follow-up visit.

RESULTS

The study enrolled 40 eyes of 24 patients (15 male and 9 female) with a mean age of 33.8 ± 7.5 years (range: 24 to 52 years) that attained at least 2 years of follow-up. The surgical procedure was uneventful in all cases. All eyes stabilized after treatment without any further signs of progression and no statistically significant changes in the mean uncorrected distance visual acuity (P = .649), corrected distance visual acuity (P = .616), mean keratometry (P =.837), steep keratometry (P = .956), ultrasonic pachymetry (P = .135), slit-scanning pachymetry (P = .276), and endothelial cell density (P = .523). In addition, 72.5% of the patients presented stable or gains of Snellen lines over time.

CONCLUSIONS

Accelerated corneal collagen cross-linking seems to be safe and effective in halting postoperative LASIK ectasia progression after 2 years of follow-up. However, a longer follow-up period with a larger cohort is needed to validate these findings.

[Long-term results of lasik refractive error correction after penetrating keratoplasty in patients with keratoconus]

OBJECTIVE

To evaluate the long term results of Lasik for residual refractive errors (RE) after penetrating keratoplasty (PKP) for keratoconus (KC).

DESIGN

Retrospective cohort.

METHOD

Records of 14 consecutive patients (19 eyes) who had Lasik after PKP for KC were retrospectively reviewed. In all eyes with refractive stability and suture removed before Lasik, far distance Visual Acuity with (AVCC) and without correction (AVSC), spherical equivalent (EE), refractive (Ast) and keratometric (dK) astigmatism were analyzed pre- and post-operatively before and after one year of follow up. Data were analyzed using Shapiro-Wilk normality test, Student t test and Mann-Whitney test. A P-value of <0,05 was considered statistically significant.

RESULTS

The mean follow-up time was 3.16 months for the follow-up before one year postoperative and 5.8 years for the follow-up after one year postoperative. The best spectacle corrected visual acuity of 0,11 LogMAR (DE 0,07) before Lasik remained stable throughout the study. The SE decreased from -2.6 (DE 3.53) to -0,36 D (DE 1.33) (P<.05) for the follow-up before one year postoperative and -1.28 D (DE 1.63) (P=.07) for the follow-up after one year postop. The refractive cylinder was reduced from -3.43 (DE 1.35) preoperative to -1.37 D (DE 1.24) (P<.05) and -3.21 D (DE 2.29) (P=.36) in the long term after one year of follow-up.

CONCLUSIONS

Lasik refractive results regress one year after the operation; therefore it is not an effective long-term surgical refractive procedure for residual refractive errors after PKP for KC.

Deep anterior lamellar keratoplasty for keratectasia after laser in situ keratomileusis

PURPOSE

To assess the efficacy of deep anterior lamellar keratoplasty (DALK) for treating post-LASIK keratectasia.

SETTING

Poostchi Eye Research Center, Shiraz University of Medical Sciences, Shiraz, Iran.

DESIGN

Retrospective interventional cases series.

METHODS

The same surgeon performed all DALK procedures using the Melles manual technique. The preoperative and postoperative corrected distance visual acuity (CDVA), spherical equivalent (SE) refraction, keratometry (K) readings, and endothelial cell profiles were compared.

RESULTS

The cohort comprised 20 eyes of 18 patients (72% women) with a mean age of 29 years ± 4 (SD). The mean follow-up was 31.8 ± 17.0 months (range 6 to 60 months). The mean Snellen CDVA improved significantly from 20/191 before DALK to 20/23 after DALK (P < .001). The mean of the modulus of SE refraction was 11.9 ± 6.6 diopters (D) and 11.4 ± 4.3 D, respectively (P = .446). The mean K value was 52.2 ± 7.0 D before DALK and 46.0 ± 1.9 D after DALK (P = .001); the mean apical K value, 59.5 ± 5.1 D and 49.9 ± 2.8 D, respectively (P < .001); and the mean keratometric astigmatism, 4.3 ± 2.4 D and 1.9 ± 1.2 D, respectively (P = .003). The endothelial cell profile did not change significantly, and no major complications related to DALK occurred. Twelve eyes had additional refractive procedures to correct residual ametropia.

CONCLUSION

Deep anterior lamellar keratoplasty using the Melles manual technique was effective and safe in restoring CDVA in patients with post-LASIK keratectasia; however, high residual ametropia was a common finding.

Same-day intrastromal corneal ring segment and collagen cross-linking for ectasia after laser in situ keratomileusis: long-term results

PURPOSE

To report the long-term results of combined same-day intrastromal corneal ring segment placement and corneal collagen cross-linking (CXL) for postoperative laser in situ keratomileusis (LASIK) ectasia.

DESIGN

Retrospective, interventional case series.

METHOD

This retrospective, interventional cases series was performed in Turkiye Hospital Eye Clinic and the Department of Ophthalmology, Fatih University Medical Faculty Hospital, Istanbul, Turkey. Sixteen eyes of 14 patients with postoperative ectasia after LASIK were enrolled. All consecutive patients were treated with femtosecond laser-assisted intrastromal corneal ring segment implantation and followed by same-day corneal collagen cross-linking for ectasia occurring after LASIK. Main outcome measures included uncorrected distance visual acuity, corrected distance visual acuity, spherical and cylindrical refraction, and simulated keratometry values.

RESULTS

The mean age ± standard deviation of the 10 women and 4 men was 33.0 ± 6.5 years (range, 23 to 44 years), and the mean follow-up was 43 months (range, 36 to 62 months). The uncorrected distance visual acuity improved significantly from 1.18 ± 0.42 logarithm of the minimal angle of resolution (logMAR) units to 0.44 ± 0.22 logMAR (P < .001), and the corrected distance visual acuity improved significantly from 0.46 ± 0.26 logMAR to 0.21 ± 0.14 logMAR (P < .001). The mean spherical and cylindrical refraction decreased significantly (P < .001 for both). The maximum keratometry value decreased from baseline by 49.3 ± 4.9 diopters (D) to 43.9 ± 2.8 D at the last visit, and the minimum keratometry value decreased from 44.3 ± 4.7 D to 41.5 ± 3.5 D (P < .001 for both). No serious complications were shown during follow-up.

CONCLUSIONS

Implantation of intrastromal corneal ring segment implantation combined with same-day corneal collagen cross-linking was a safe and effective treatment for ectasia occurring after LASIK. It also significantly improved the visual acuity, refraction, and keratometry values.

Clinical utility of combined Placido-scanning-slit midperipheral and thinnest point pachymetry after corneal ablation for myopia

PURPOSE

The aim of this study was to assess the random error of the thinnest point and midperipheral pachymetry with a combined Placido-scanning-slit system (Orbscan II) in the intermediate-term follow-up of excimer laser keratorefractive surgery for treating myopia.

METHODS

Sixty-five patients who had undergone aspheric surface ablation for treating myopia with a minimum follow-up of 6 months, and showed no biomicroscopically detectable corneal haze, were subjected to 5 consecutive topographic examinations. All eyes underwent a complete ophthalmic examination before the surgery. The within-subject SD (Sw), repeatability (2.77 × Sw), coefficient of repeatability (2.77 × Sw/mean), and intraclass correlation coefficients of pachymetry at the thinnest point and in each 4 quadrants at a 6-mm diameter were calculated.

RESULTS

The patients had a mean age of 31.9 ± 6.2 years, and the average follow-up was for 7.5 ± 2.6 months. The mean ablation depth for myopia was 63.6 ± 23.6 μm. The average pachymetry for the thinnest point and midperipheral superior, inferior, nasal, and temporal locations was 456.9, 602.0, 595.5, 609.7, and 566.1 μm, respectively. The repeatability (and coefficient of repeatability) for the thinnest point and midperipheral superior, inferior, nasal, and temporal locations was 26.5 (5.8%), 37.9 (6.3%), 31.0 (5.2%), 30.5 (5.0%), and 35.4 μm (6.2%), respectively. The intraclass correlation coefficients were 0.96, 0.88, 0.89, 0.97, and 0.91 for each location, respectively.

CONCLUSIONS

This study provides the repeatability of the thinnest and midperipheral pachymetry using the combined Placido-scanning-slit system in transparent corneas after laser keratorefractive surgery for treatment of myopia. The test-retest reliability provided here will help differentiate real corneal thickness change from measurement noise. For this, only pachymetric changes >6% are likely to be real and therefore useful when evaluating postoperative keratectasia suspects.

SD-OCT analysis of regional epithelial thickness profiles in keratoconus, postoperative corneal ectasia, and normal eyes

PURPOSE

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).

METHODS

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.

RESULTS

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).

CONCLUSION

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.

Deep anterior lamellar keratoplasty: indications, surgical techniques and complications

The concept of lamellar keratoplasty (LK) is not new. However, it had been abandoned and largely replaced by the time-honored technique of penetrating keratoplasty (PK) because LK is technically demanding, time consuming and gives suboptimal visual outcomes due to interface irregularity arising from manual lamellar dissection. Recent improvements in surgical instruments and introduction of new techniques of maximum depth of corneal dissection as well as inherent advantages such as preservation of globe integrity and elimination of endothelial graft rejection have resulted in a re-introduction of LK as an acceptable alternative to conventional PK. This review article describes the indications, different techniques, clinical outcomes and complications of deep anterior LK.

Treatment strategies for corneal ectasia

PURPOSE OF REVIEW

To review the most recent management strategies for corneal ectasia after keratorefractive surgery.

RECENT FINDINGS

Management options for postoperative ectasia include conservative management with various types of contact lenses such as rigid gas permeable lenses, custom wave front-guided soft contact lenses, hybrid lenses and tandem soft contact lens-rigid gas permeable lenses. Minimally invasive surgical options including corneal ring segment implantation with Intacs, KeraRings or Ferrara rings have shown to have good results in the initial period after insertion. However, there appears to be some evidence that this initial effect may regress with time. Collagen cross-linking is also minimally invasive and has been documented to stop the progression of ectasia and in some cases may cause regression. Recently, techniques combining collagen cross-linking with intracorneal ring segments or with topography-guided excimer laser treatments have shown to have promising results.

SUMMARY

Early management of ectasia is essential to prevent its progression and to preserve visual potential. There are several management options that are available that may be used to reduce the need for corneal transplantation for these patients.

Refractive surgery after corneal transplant

PURPOSE OF REVIEW

Ametropia and astigmatism following successful penetrating keratoplasty can seriously impact a patient's quality of vision. Similar limitations can result following anterior lamellar keratoplasty (ALK) and Descemet's stripping endothelial keratoplasty (DSEK). These patients often suffer from aniseikonia and can be intolerant of spectacles and contact lenses. Refractive surgery can correct both ametropia and astigmatism following corneal transplantation and improve a patient's final visual outcome. The same methods used to correct naturally occurring refractive errors are being used with increasing success in patients who have undergone corneal transplants.

RECENT FINDINGS

Many refractive options are available to treat ametropia following penetrating keratoplasty. Incisional keratotomies have been employed to treat high amounts of astigmatism. Photorefractive keratectomy (PRK) and laser in-situ keratomileusis (LASIK) are also used to treat myopia, hyperopia and astigmatism. LASIK has been shown to have an overall better outcome compared to PRK; however, the use of mitomycin-C with PRK has improved results. Phakic and pseudophakic piggyback intraocular lenses are also being used to treat high degrees of ametropia and astigmatism; however, the long-term results are somewhat limited.

SUMMARY

Refractive surgery can improve the final visual outcome of patients who have undergone successful corneal transplantation. Currently available modalities provide many options for patients who are intolerant of spectacles and contact lenses. Continued advances and research will enable surgeons to optimize visual quality in postkeratoplasty patients.

Comparative study of riboflavin-UVA cross-linking and "flash-linking" using surface wave elastometry

PURPOSE

To investigate comparative stiffness values in porcine corneas after standard cross-linking and a new, rapid method of cross-linking (flash-linking) using surface wave elastometry.

METHODS

Ten porcine eyes were treated using an ultraviolet A (UVA) double diode light source with a wavelength of 370 nm and delivering an irradiance of 4.2 mW/cm2 at a distance of 1.2 cm while applying 0.1% riboflavin-5-phosphate drops to the central cornea every 5 minutes as a photosensitizer for 30 minutes (riboflavin-UVA group). The next 10 porcine corneas were treated with a single application of a customized photoactive crosslinking agent and 30 seconds of UVA light at the same power and wavelength (flash-linking group). Following treatment, the Sonic Eye system (PriaVision Inc) was used to measure ultrasound surface wave propagation time between two fixed-distance transducers applied to the cornea along central horizontal and vertical positions. Intraocular pressure was continuously monitored.

RESULTS

Mean surface wave velocity was determined from the last 5 of 10 sequential measurements for each eye, and was 90.87 +/- 15.26 m/s for all eyes with a mean standard deviation (SD) of 2.34 m/s among each eye in the riboflavin-UVA group versus 83.66 +/- 12.30 m/s with a mean SD of 2.69 m/s among each eye in the flash-linking group before treatment and 109.2 +/- 21.76 m/s with a mean SD of 2.15 m/s among each eye (riboflavin-UVA group) versus 109.2 +/- 18.42 m/s with a mean SD of 2.26 m/s among each eye (flash-linking group) after cross-linking. The mean surface wave velocity increased by 18.3 units from 90.87 to 109.2 m/s (P = .003) after cross-linking with riboflavin-UVA, and by 25.5 m/s from 83.66 to 109.2 m/s (P = .0001) after flash-linking. Surface wave velocity was noted to increase after both cross-linking techniques, but the differences observed did not reach statistical significance (P = .74).

CONCLUSIONS

A new, rapid method of cross-linking (flash-linking) is introduced by the use of a customized photoactive cross-linking agent. The method demonstrates similar efficacy in stiffening the cornea (when measured with surface wave elastometry) in comparison to standard cross-linking, but requires only 30 seconds of UVA exposure.