Clinical Outcomes of an Asymmetric Model of Intrastromal Corneal Ring Segments for the Correction of Keratoconus

Abstract

Purpose: To evaluate the clinical outcomes of a new model of intrastromal corneal ring segments (ICRSs) (Keraring AS) in patients with keratoconus and quantify subsequent changes in refraction and corneal topography. Methods: This nonrandomized, single-center, retrospective observational study explores the effect of progressive thickness ICRS implantation in patients with keratoconus with a 3-month follow-up. After creating an intrastromal tunnel using a femtosecond laser, 1 or 2 ICRSs of progressive thicknesses (150/250 μm or 200/300 μm) and 160-degree arc length were implanted. Changes in uncorrected distance visual acuity, best-corrected distance visual acuity, refractive outcomes, corneal astigmatism, and maximum keratometry readings were recorded before and after surgery. Results: The study cohort consisted of 82 patients (104 eyes) with a mean age of 31.2 ± 10 years. At 3 months, ICRS implantation significantly improved uncorrected and corrected visual acuities from 0.82 to 0.46 (logarithm of the minimum angle of resolution [LogMAR]) and from 0.31 to 0.21 (LogMAR), respectively (P < 0.001). The mean spherical error reduced from −1.74 diopters (D) to −0.90 D (P < 0.001), and the mean cylindrical error reduced from −4.22 D to −2.01 D (P < 0.001). The manifest refraction spherical equivalent reduced from −3.85 D to −1.91 D (P < 0.001). All topographic parameters were reduced, including maximum keratometry (53.6 D vs. 50.3 D) and keratometric astigmatism (−4.6 D vs. −2.2 D) (P < 0.001). Conclusions: The Keraring AS provides a new, apparently safe, and effective means of improving visual acuity and reducing the refractive error and mean keratometry in eyes with asymmetric keratoconus.

<p>Asymmetric Thickness Intracorneal Ring Segments for Keratoconus</p>

“…All this is in line with the reported by Prisant et al, 12 although they have implanted only 1 segment in all Type 2 cases, and can be explained by the desirable cone re-centering effect made possible by the ICRS in these more decentered and aberrated cones. The same study 12 found a greater effect both in subjective refractive and tomographic measurements in the Type 3 cases and explained that with the supposed greatest flattening effect of the 2 segments implanted in all of these more centered and myopic cones. The present study, despite a greater effect on spherical equivalent in the Type 3 group, showed a higher topographic flattening effect in the Type 2 group.…”

“…Only one eye showed an increase in Kmax, yet with an improvement of one line in CDVA. These results have the same pattern but with slightly smaller decreases than the reported by Prisant et al 12 The Visumring ® implantation 14 showed a higher decrease in sphere and both K1 and K2, yet with an increase in topographic astigmatism and this can be explained as those were probably implantations of a large arc length ICRS in more myopic and central cones. Comparing with the large series from Vega et al 13 of symmetrical ICRS implants in paracentral cones, this study found similar spherical equivalent decrease but higher decrease in keratometry readings.…”

“…In relation to the complications, no rings have been explanted until the end of follow-up, similar to the reported by Prisant et al, 12 and different than the 5 explants due to corneal melting reported with the larger Visumring ®14 The ICRS broken during implantation was immediately replaced without associated consequences. Regarding manual tunnelization, no differences in the difficulty of ring insertion due to the progressive thickness throughout the ring body, were found.…”

“…16 The present study showed a clinically relevant decrease both in RMS and in HOA, but without significant statistical differences. While another study 12 with AS did not perform aberrometric analysis, the Visumring ®14 showed a higher decrease in total RMS but probably due to the effect on myopic spherical aberration, as the decrease in HOA was similar to the present study for a 6mm pupil. Two eyes showed a substantial increase both in the total RMS and the HOA, but without decrease in visual acuity (one maintained and another increase 1 Snellen line in CDVA).…”

“…Limitations of the present study are the retrospective non-randomized design, the limited number of cases and the manual implantation technique. As the final ICRS result in corneal regularization may only be achieved at six months in some cases, the authors consider follow-up time a relative strength when compared with other work 12 that studied the same type of ICRS as it had only three months follow-up and without possibility of stretching it, because crosslinking and topo-guided photorefractive keratectomy were performed thereafter in all patients.…”