Sterile Excimer Laser Shaped Allograft Corneal Inlay for Hyperopia: One-year Clinical Results in 28 Eyes

BCLA CLEAR Presbyopia: Management with corneal techniques

Corneal techniques for enhancing near and intermediate vision to correct presbyopia include surgical and contact lens treatment modalities. Broad approaches used independently or in combination include correcting one eye for distant and the other for near or intermediate vision, (termed monovision or mini-monovision depending on the degree of anisometropia) and/or extending the eye's depth of focus [1]. This report reviews the evidence for the treatment profile, safety, and efficacy of the current range of corneal techniques for managing presbyopia. The visual needs and expectations of the patient, their ocular characteristics, and prior history of surgery are critical considerations for patient selection and preoperative evaluation. Contraindications to refractive surgery include unstable refraction, corneal abnormalities, inadequate corneal thickness for the proposed ablation depth, ocular and systemic co-morbidities, uncontrolled mental health issues and unrealistic patient expectations. Laser refractive options for monovision include surface/stromal ablation techniques and keratorefractive lenticule extraction. Alteration of spherical aberration and multifocal ablation profiles are the primary means for increasing ocular depth of focus, using surface and non-surface laser refractive techniques. Corneal inlays use either small aperture optics to increase depth of field or modify the anterior corneal curvature to induce corneal multifocality. In presbyopia correction by conductive keratoplasty, radiofrequency energy is applied to the mid-peripheral corneal stroma, leading to mid-peripheral corneal shrinkage and central corneal steepening. Hyperopic orthokeratology lens fitting can induce spherical aberration and correct some level of presbyopia. Postoperative management, and consideration of potential complications, varies according to technique applied and the time to restore corneal stability, but a minimum of 3 months of follow-up is recommended after corneal refractive procedures. Ongoing follow-up is important in orthokeratology and longer-term follow-up may be required in the event of late complications following corneal inlay surgery.

Increasing depth of focus with allogeneic presbyopic inlays: 3-year results

PURPOSE

To demonstrate the safety and efficacy of allogenic corneal inlays designed to increase the depth of focus (DoF) in treated eyes.

SETTINGS

Medipol University Hospital, Istanbul, Turkey.

DESIGN

Prospective case series.

METHODS

This study includes 50 eyes of 25 patients with a follow-up of 3 years. Emmetropic patients with presbyopia had implantation of allogenic corneal inlays in the nondominant eye. The uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and uncorrected near visual acuity (UNVA) were evaluated in all eyes. A subjective visual acuity test system (Multifocal Lens Analyzer 3.0 application) was used to analyze the DoF by measuring the defocus curves.

RESULTS

No significant difference between the treated and fellow eyes in UDVA and CDVA was found, whereas UNVA was significantly better in the treated eyes ( P = .20, P = .07, P < .01, respectively). Comparing to the preoperative CDVA, there was a 1-line decrease in CDVA in 6 (%24) patients. The mean defocus curves reveal a DoF of 1.1 diopters (D) for the untreated eye at the logMAR = 0.2 threshold. By contrast, the mean DoF of the treated eye and binocularly was 2.8 D. The areas under the curve were significantly better in the near, intermediate, and total distances in the treated eyes, whereas it was better for the far distances in the untreated eyes. All values were significant ( P = .023 total, P < .01 others).

CONCLUSIONS

Allogenic presbyopic inlay implantation may be safe and provided a clinically and statistically significant increase in the DoF leading to good far, intermediate, and near-visual acuity in emmetropic presbyopic patients.

Electron beam-irradiated donor cornea for on-demand lenticule implantation to treat corneal diseases and refractive error

The cornea is the major contributor to the refractive power of the eye, and corneal diseases are a leading cause of reversible blindness. The main treatment for advanced corneal disease is keratoplasty: allograft transplantation of the cornea. Examples include lenticule implantation to treat corneal disorders (e.g. keratoconus) or correct refractive errors. These procedures are limited by the shelf-life of the corneal tissue, which must be discarded within 2-4 weeks. Electron-beam irradiation is an emerging sterilisation technique, which extends this shelf life to 2 years. Here, we produced lenticules from fresh and electron-beam (E-beam) irradiated corneas to establish a new source of tissue for lenticule implantation. In vitro, in vivo, and ex vivo experiments were conducted to compare fresh and E-beam-irradiated lenticules. Results were similar in terms of cutting accuracy, ultrastructure, optical transparency, ease of extraction and transplantation, resilience to mechanical handling, biocompatibility, and post-transplant wound healing process. Two main differences were noted. First, ∼59% reduction of glycosaminoglycans resulted in greater compression of E-beam-irradiated lenticules post-transplant, likely due to reduced corneal hydration-this appeared to affect keratometry after implantation. Cutting a thicker lenticule would be required to ameliorate the difference in refraction. Second, E-beam-sterilised lenticules exhibited lower Young's modulus which may indicate greater care with handling, although no damage or perforation was caused in our procedures. In summary, E-beam-irradiated corneas are a viable source of tissue for stromal lenticules, and may facilitate on-demand lenticule implantation to treat a wide range of corneal diseases. Our study suggested that its applications in human patients are warranted. STATEMENT OF SIGNIFICANCE: Corneal blindness affects over six million patients worldwide. For patients requiring corneal transplantation, current cadaver-based procedures are limited by the short shelf-life of donor tissue. Electron-beam (E-beam) sterilisation extends this shelf-life from weeks to years but there are few published studies of its use. We demonstrated that E-beam-irradiated corneas are a viable source of lenticules for implantation. We conducted in vitro, in vivo, and ex vivo comparisons of E-beam and fresh corneal lenticules. The only differences exhibited by E-beam-treated lenticules were reduced expression of glycosaminoglycans, resulting in greater tissue compression and lower refraction suggesting that a thicker cut is required to achieve the same optical and refractive outcome; and lower Young's modulus indicating extra care with handling.

Allograft corneal ring segment for keratoconus management: Istanbul nomogram clinical results

PURPOSE

To evaluate the clinical feasibility and visual outcomes of allograft corneal ring segment implantation for the treatment of keratoconus.

METHODS

This case series, included forty-four eyes of 32 patients with a 6-month follow-up. All cases were treated according to the Istanbul nomogram. In the Istanbul Nomogram, corneal tunnels of 4 × 7.5 mm diameters are created at depth of 200 μm and implanted with sterile allograft corneal rings (KeraNaturalTM, Lions VisionGift, Portland, OR, USA) at the cone location. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), spherical equivalent (SE) and keratometric values were compared preoperatively versus postoperatively.

RESULTS

There was significant improvement in UDVA, CDVA, SE and topographic keratometric values. The mean preoperative CDVA (Snellen, decimal) increased from 0.29 ± 0.20, to 0.56 ± 0.26 (P < 0.001), at the last visit. There was no statistically significant difference between preoperative and postoperative thinnest pachymetry values (P = 0.509). No major complications or adverse event were observed during and after the operation.

CONCLUSIONS

The results of this pilot study show that sterile allograft corneal ring segments may be safe, effective and enhance the visual performance of keratoconus patients. Larger clinical studies are needed to demonstrate the effectiveness and safety with long term follow-up.

Review of Presbyopia Treatment with Corneal Inlays and New Developments

Presbyopia may represent the largest segment of refractive errors that is without an established and effective refractive surgery treatment. Corneal Inlays are materials (synthetic or allogenic) implanted in the stroma of patients’ corneas to improve presbyopia. These inlays, introduced into the United States in 2015 via the small-aperture corneal inlay (KAMRA^TM, SightLife Surgical/CorneaGen, Seattle, Washington, United States), were met with an initial wave of enthusiasm. Subsequent models like the shape-changing corneal inlay (RAINDROP^TM, Revision Optics, Lake Forest, California, United States) offered excellent results for patients, but longer-term research raised questions about patient safety. At the time of this article, no synthetic corneal inlays are available in the United States for the correction of presbyopia. Other options for presbyopia correction include allograft corneal inlays, trifocal synthetic corneal inlays, pharmacologic therapies, scleral incisions or additive techniques and PresbyLASIK. Presently, allograft inlays consist of corneal lenticules removed from patients undergoing Small Incision Lenticule Extraction (SMILE). We will review corneal inlays and other alternative procedures that may provide effective and predictable treatments for patients with presbyopia.

Excimer Laser Corneal Refractive Surgery in the Clinic: A Systematic Review and Meta-analysis

Objective

To systematically evaluate the efficacy, safety, recovery speed, and long-term visual quality of excimer laser corneal refractive surgery and to provide evidence-based medicine for the promotion and use of excimer laser corneal refractive surgery.

Methods

Randomized controls on excimer laser refractive surgery in Web of science, PubMed, EMBASE, ScienceDirect, Cochrane Library, China Knowledge Network (CNKI), China VIP Database, Wan Fang Database, and China Biomedical Literature Database (CBM) were searched by the computer. Randomized controlled trial (RCT) data were extracted independently by two researchers, and the risk of bias of each included RCT was assessed according to the Cochrane Handbook 5.1.0 criteria. Meta-analysis of the collected data was performed using RevMan5.4 statistical software.

Results

In the end, 9 high-quality literatures were included, with a total of 4366 samples, and meta-analysis was used. There was no significant difference in uncorrected visual acuity WMD after excimer laser keratorefractive surgery, but there was a statistically significant difference in WMD in the safety of excimer laser keratorefractive surgery. The results of uncorrected visual acuity (close) indicated the following: Chi2 = 13.56, DF = 5, P = 0.02, and I2 = 100%; the results of uncorrected visual acuity (distance) indicated the following: Chi2 = 34.44, DF =5 (P < 00000), and I2 = 85%; the results of best corrected visual acuity (myopia) indicated the following: Chi2 = 0.65, DF = 3, P = 088 > 0.05, and I2 = 0%; the results of best corrected visual acuity (hyperopia) indicated the following: Chi2 = 1.80, DF = 3, P = 0.61 > 0.05, and I2 = 0%.

Conclusion

Excimer laser corneal refractive surgery is safe and effective, with faster recovery and better long-term visual acuity treatment effect. However, more studies and follow-up with higher methodological quality and longer intervention time are needed for further validation.