Cross-linking and intracorneal ring segments--review of the literature

Results of Follow-up in Pediatric Keratoconus Treated With Intracorneal Ring Segments Implantation Alone or in Combination With Corneal Cross-linking

PURPOSE

To report visual and topographic outcomes of pediatric keratoconus with intracorneal ring segments (ICRS) implantation alone or in combination with accelerated corneal cross-linking (A-CXL).

METHODS

A descriptive, retrospective observational study was performed. Medical records of patients younger than 18 years at Fundación Oftalmológica Nacional in Bogotá, Colombia, were reviewed. Demographic data, follow-up time, preoperative and postoperative uncorrected (UCVA) and best corrected (BCVA) visual acuity, manifest refraction, and tomography were evaluated. SPSS software (version 22.0; SPSS, Inc) was used for analysis.

RESULTS

Twenty-six eyes of 19 patients with a mean age of 16.5 ± 1.8 years were analyzed, and 16 were boys (84.2%). Median follow-up time was 39.6 months (inter-quartile range [IQR] = 30). Fifteen patients (78.9%) had a history of allergic conjunctivitis. Sixteen eyes (61.5%) received ICRS implantation with A-CXL and 10 eyes (38.4%) received ICRS implantation only. Global results (including ICRS implantation with A-CXL and ICRS implantation only) were: (1) median UCVA of 0.90 logarithm of the minimum angle of resolution (logMAR) (IQR = 0.85) preoperatively improved to 0.54 logMAR (IQR = 0.70) postoperatively; (2) median BCVA of 0.43 logMAR (IQR = 0.39) preoperatively improved to 0.30 logMAR (IQR = 0.26) postoperatively; and (3) median spherical equivalent of -5.37 diopters (D) (IQR = -5.28) preoperatively improved to -4.12 D (IQR = -3.57) postoperatively. There was a reduction in half of the sphere and cylinder. The median maximum keratometry was 54.40 D (IQR = 7.4) preoperatively and 49.80 D (IQR = 5.3) postoperatively. The median asphericity was -1.18 (IQR = 0.70) preoperatively and changed to -0.75 (IQR = 0.68) postoperatively. No patient presented with complications before or after surgery.

CONCLUSIONS

ICRS implantation only or in combination with A-CXL induced visual and topographic improvement in patients with keratoconus, which was maintained throughout the follow-up time. It seems to be a safe procedure to delay or avoid corneal transplantation in the pediatric population. [J Pediatr Ophthalmol Strabismus. 2022;59(2):118-127.].

Two-Year Follow-up of Intracorneal Ring Segments Implantation in Adolescent Patients With Keratoconus

PURPOSE

To evaluate the visual, refractive, topographic, and aberrometric outcomes after intracorneal ring segments (ICRS) implantation in adolescent patients with keratoconus.

METHODS

A retrospective longitudinal study was undertaken with a total of 61 eyes from 47 patients with keratoconus, aged between 13 and 18 years, implanted with a Ferrara-type ICRS. Topography (flattest keratometry, steepest keratometry, and asphericity), uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refractive error (sphere and cylinder), and aberrometric measurements (spherical aberration and vertical coma) were evaluated before surgery and at 1 month, 6 months, 1 year, and 2 years after surgery.

RESULTS

UDVA exhibited a statistically significant increase at all times from 1 month to 2 years postoperatively (P < .001), whereas CDVA showed a statistically significant improvement at 1 month, 6 months, and 2 years (P < .002), but dropped in significance at 1 year postoperatively (P = .097). The refractive error analysis showed no variation in statistical significance in the sphere (P = .712) after 2 years. The cylinder presented a statistically significant decrease in diopters at all times from preoperatively to 2 years postoperatively (P < .007). Steepest keratometry manifested a statistically significant decrease in steepness at all times after surgery (P < .001), whereas flattest keratometry lost significance at 1 year (P = .298) and 2 years (P = .053) postoperatively. There was no statistically significant change in the spherical aberration at any of the measured times. The vertical coma was only significantly different at 2 years postoperatively (P = .001).

CONCLUSIONS

ICRS implantation is a safe and effective treatment for improving visual and corneal morphological parameters as shown at 2 years of follow-up in adolescent patients with keratoconus. It is a good option to flatten and regularize the cornea and to temporarily improve the quality of life of young patients and delay the need for keratoplasty. [J Refract Surg. 2021;37(2):91-97.].

Intrastromal Corneal Ring Segments for Astigmatism Correction after Deep Anterior Lamellar Keratoplasty

Background. To evaluate the change in corneal astigmatism after intrastromal corneal ring segment (ICRS) implantation in keratoconus patients with previous deep anterior lamellar keratoplasty (DALK). Design was a longitudinal, retrospective, interventional study. The study included 25 eyes of 24 patients with keratoconus who had DALK performed at least two years prior to ICRS implantation. All patients had a clear corneal graft with up to 8.00 D of corneal astigmatism and intolerance to contact lenses. The studied parameters were age, sex, corrected distance visual acuity (CDVA), maximum keratometry (K1), minimum keratometry (K2), spherical equivalent, and astigmatism. There was a statistically significant decrease in the postintervention analysis as follows: 3.5 D reduction in K1 (p < 0.001); 1.53 D in K2 (p = 0.005); and 2.52 D (p < 0.001) in the average K. The spherical equivalent reduced from -3.67 D (±2.74) to -0.71 D (±2.35) (p < 0.001). The topographic astigmatism reduced from 3.87 D preoperatively to 1.90 D postoperatively (p < 0.001). The CDVA improved from 0.33 (±0.10) to 0.20 (±0.09, p < 0.001). ICRS implantation is a useful option for the correction of astigmatism after DALK as it yields significant visual, topographic, and refractive results.

New Technique of Femtosecond Laser-Assisted Intracorneal Ring Segment Implantation

PURPOSE

To describe a new technique of femtosecond laser-assisted intracorneal ring segment implantation.

METHODS

The study included 6 eyes of 5 patients. Software of the LDV Z6 femtosecond laser was modified to create a 110-degree reverse side cut between the corneal surface and incision instead of the conventional 90 degree angle (which changed the angle between the incision and tunnel from conventional 90-70 degrees) and 2 disjointed tunnels separated by 10 degrees arc length at the proximal and distal ends.

RESULTS

One-year postoperatively, there were no cases of segment extrusion or touch/overlap. Anterior segment optical coherence tomography showed appropriate position of the rings in all eyes postoperatively. Improvement was also found in visual, refractive, keratometric, and asphericity parameters.

CONCLUSIONS

The results of this pilot study are promising. A comparative prospective study with more eyes and longer follow-up may confirm whether this technique is better than the conventional femtosecond laser-assisted one.

Corneal thickening and central flattening induced by femtosecond laser hyperopic-shaped intrastromal lenticule implantation

PURPOSE

To investigate the feasibility of the procedure and the modifications of the corneal curvature and profile obtained with a novel technique of stromal-lentoid implantation in ex vivo human corneas.

DESIGN

Experimental ex vivo study in human corneas.

MATERIALS AND METHODS

Twelve stromal lentoids were produced by means of hyperopic femtosecond lenticule extraction (FLEx) with the VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany) with a refractive power of +8.00 D and optical zone of 6.0 (six lenticules) and 5.0 mm (six lenticules), respectively. The posterior surface of these stromal lentoids presented a higher curvature with respect to the anterior surface and, therefore, the thinnest point is located at the center of the lenticule, gradually thickening towards the periphery. Another 12 corneas underwent femtosecond laser intrastromal pocket creation at a depth of 115 microns, for lenticule insertion. After intrastromal lenticule implantation the changes of corneal profiles were evaluated by means of corneal topography and anterior segment optical coherence tomography (OCT).

RESULTS

The implantations of intrastromal lenticules were successful in all cases with proper distention and centration. A mid-peripheral forward shift of the anterior corneal surface along with a thickening (greater in periphery) was induced. There was a significant flattening of anterior corneal central areas of 7.31 ± 1.52 D (p = 0.002). Diameters of the flattening area were found to be consistently correlated with the optical zone diameter of the implanted lenticules (p = 0.006). Central flattening was similar in both groups. OCT pachymetry maps showed an increase of corneal thickness consistently correlated with implanted lentoid thickness and diameter.

CONCLUSION

The implantation of modified hyperopic-shaped intra-corneal stromal lentoid is a feasible and reproducible technique for achieving central corneal flattening while increasing thickness. Whether this procedure may be beneficial in the treatment of refractive errors or ectatic corneal disorders such as keratoconus merits further study.

Assessment of a Novel Corneal-Shaping Device With Simultaneous Corneal Collagen Cross-Linking Using a Porcine Eye Model

PURPOSE

Corneal collagen cross-linking (CXL) alone cannot substantially improve refractive errors. We designed a novel corneal-shaping device, showing that a prototype applied during CXL can alter corneal curvature to a greater extent than CXL alone in a porcine eye model.

METHODS

The device prototype was made with flat, UV-transmissible material. Enucleated porcine eyes were deepithelialized and perfused. Preexperimental and postexperimental corneal curvature (K) measurements and Anterior Segment Optical Coherence Tomography imaging were performed. A conventional CXL protocol was followed. Six experiments of 6 treatment groups in duplicate were performed (n = 12/group): (A) no CXL + no device, (B) no CXL + 30 minutes device, (C) 10 minutes, CXL + no device, (D) 10 minutes, CXL + device, (E) 30 minutes, CXL + no device, and (F) 30 minutes, CXL + device.

RESULTS

There was a significant decrease (P < 0.001) in corneal curvature after 30 minutes. CXL between group F (-1.54 ± 0.90 D) and groups E (+0.34 ± 0.53 D), B (+0.69 ± 1.02 D), or A (+0.22 ± 1.24 D). The demarcation line depth was greater in group F (34% ± 4%) than group D (30% ± 4%, P < 0.05). Groups D (-2.3% ± 21%) and F (0.24% ± 15%) had less change in corneal thickness than in control groups A (15% ± 12%, P < 0.05) and E (12% ± 11%, P < 0.05).

CONCLUSIONS

Application of our corneal-shaping device during CXL significantly decreased corneal curvature compared with controls. Anterior Segment Optical Coherence Tomography imaging showed comparable extent of cross-linking in eyes treated ± device. This demonstrates that our novel device used during CXL may further promote corneal strengthening and refractive correction in patients.

Keratoconus and Other Corneal Diseases: Pharmacologic Cross-Linking and Future Therapy

The ability to cross-link collagen fibers and use this technique to strengthen the cornea has become of great interest to ophthalmologists in the last decade. For progressive diseases such as keratoconus, collagen cross-linking confers the possibility of halting progression and stabilizing the cornea, a benefit that is not observed with any other current treatment. Collagen cross-linking uses riboflavin combined with ultraviolet A light to induce the formation of bonds between collagen fibrils that strengthen the cornea. This chapter will discuss the theory, technique, indications, and complications of corneal cross-linking. Much of what will be discussed is in areas of active research that will likely be further clarified as more experience is gained with this procedure.