Effect of Conus Eccentricity on Visual Outcomes After Intracorneal Ring Segments Implantation in Keratoconus

Factors predicting the visual outcome of intracorneal ring segment for keratoconus

OBJECTIVES

To identify predictive factors and to construct predictive models using epidemiological and clinical preoperative factors for the visual acuity change after intracorneal ring segment (ICRS) implantation in patients with keratoconus.

METHODS

The medical records of 287 keratoconic eyes of 230 patients implanted with ICRS at Chula Refractive Surgery Center of a tertiary university hospital (Bangkok, Thailand) between January 2012 and March 2022 were retrospectively reviewed for epidemiological and clinical preoperative variables, including those derived from Scheimpflug tomography. After randomly excluding one eye for each bilateral case, the remaining 230 eyes were randomized into two groups: a training group (184 eyes) and a validation group (46 eyes). In the training group, the correlation between the interesting variables and postoperative uncorrected and corrected distance visual acuity change (ΔUDVA and ΔCDVA; logMAR scale) at 6 months was explored, and then the multiple linear regression analysis was used to develop the predictive models. The obtained models were tested using the validation group.

RESULTS

There were 5 and 14 preoperative variables that statistically correlated with ΔUDVA and ΔCDVA respectively. Only the preoperative corrected distance visual acuity (CDVAp) strongly correlated with ΔCDVA (Beta = -0.746). Using multiple regression, the preoperative uncorrected distance visual acuity (UDVAp) and front mean keratometry were selected in the proposed model for ΔUDVA (adjusted R2 = 38.8%), while the CDVAp and index of surface variance (ISV) were selected in the model [Formula: see text] (adjusted R2 = 48.9%). The ΔUDVA and ΔCDVA models were correct in 47.83% and 63.4% of the validation group within 0.20 logMAR, respectively.

CONCLUSIONS

Potential predictive factors and models for ICRS-induced changes in visual acuity are proposed as adjunctive tools for clinicians. Such tools could be used for case selection and during counselling before ICRS implantation to maximize surgical outcomes.

Effect of intracorneal ring segment implantation on high order aberrations comparing patients with eccentric versus central keratoconus

PURPOSE

To assess potential differences between central and eccentric cones in the aberrometric corneal profile and in visual and keratometric outcomes 6 months after intracorneal ring segment (ICRS) implantation for keratoconus.

METHODS

This study compared two groups consisting of 12 patients each, with central or eccentric keratoconus who were treated with femtosecond laser-assisted Keraring implantation. Uncorrected (UDVA) and corrected (CDVA) distance visual acuity, keratometric readings and higher order aberrations (HOAs) including high order aberrations root mean square (HOARMS), coma, spherical aberration and trefoil were measured preoperatively and 6 months after ICRS implantation.

RESULTS

Trefoil and spherical aberration were significantly reduced after ICRS implantation compared to preoperative values in eccentric keratoconus (Trefoil, p = 0.0049; Spherical aberration, p < 0.0001). In central keratoconus spherical aberration was reduced not significantly after ICRS implantation compared to preoperative values (p = 0.087). Coma showed a significant reduction in central (p = 0.0001) and in eccentric keratoconus (p = 0.0001). The reduction of spherical aberration in central keratoconus was significantly positively correlated to improvement in UDVA (Pearson's correlation coefficient, r = -0.66; p = 0.02). In eccentric keratoconus there was a significant positive correlation between reduction of trefoil and improvement in UDVA (Spearmans R, r = -0.69; p = 0.01).

CONCLUSION

Patients both with central and eccentric keratoconus benefit from ICRS implantation. Specifically, our data provide a slightly higher gain in visual performance for eccentric cones 6 month after ICRS implantation, which is accentuated by a greater reduction in spherical aberration and trefoil. Improvements in UDVA are positively correlated with reductions in HOAs.

The number of intracorneal ring segments in asymmetric and central cones

Background

To compare the results of single versus double intracorneal ring segment (ICRS) (KeraRing) implantation in keratoconus with respect to different cone locations.

Methods

Twenty-two eyes of 18 patients with totally asymmetric cones (20–80% or 0–100% distribution along steep axis) were implanted with single ICRS (Group 1), 38 eyes of 32 patients with central or partially asymmetric cones (50–50% or 40–60% distribution along steep axis) were implanted with double ICRS (Group 2), at a depth of 80% of the site of implantation, in channels created with femtosecond laser device. All patients had uncorrected and corrected distance visual acuities (UDVA and CDVA, respectively) of ≤ 0.3 Snellen lines.

Results

In both groups, patients had median UDVA and CDVA gain of 3 Snellen lines (P > 0.05). Postoperative improvement in indices of vertical asymmetry and height decentration in Group 1; simulated keratometry, corneal astigmatism and anterior corneal asphericity values in Group 2 were greater (P < 0.05). A total of 10 eyes (45.5%) in Group 1 were recommended double ring implantation by the manufacturer’s nomogram, but underwent single ICRS implantation and achieved visual, refractive, tomographic outcomes comparable to that in Group 2, although corneal cylindrical correction was less and final topographic astigmatism was greater.

Conclusion

Double ICRS implantation seems to be superior in terms of keratometry, corneal astigmatism and anterior corneal asphericity improvement. Single ICRS implantation in totally asymmetric cones seems to provide satisfactory visual, refractive and tomographic results, similar to double ICRS implantation in central and partially asymmetric cones, by inducing central shift of the cone.

Combined corneal cross-linking and 320° intrastromal corneal ring segments in progressive keratoconus: one-year results

BACKGROUND

Intrastromal corneal ring segments (ICRS) attain regularization of corneal surface in keratoconus (KC), while collagen cross-linking (CXL) halts or slows its progression. The long-arc 320° rings combined with CXL may have a dual-benefit synergistic effect of surface regularity and progression halt.

METHODS

This was a prospective case series study including eyes with progressive KC. Femto-assisted 320° ICRS implantation and epi-off CXL 8 weeks later were carried out in all cases. Uncorrected (UCVA) and corrected distance visual acuity (CDVA) were assessed using Snellen's chart, while corneal tomography was evaluated using Scheimpflug imaging. Follow-up was carried out 3, 6, and 12 months after the CXL.

RESULTS

Thirty-two eyes of 32 patients with progressive KC were included, 18 males and 14 females, and the mean age was 23.1 years. According to the Amsler-Krumeich classification, four eyes had stage 1 KC, 20 had stage 2 KC, and eight had stage 3 KC, and UCVA and CDVA improved from 0.1 ± 0.15 and 0.2 ± 0.19 to 0.4 ± 0.2 (P>  0.01) and 0.5 ± 0.2 (P>  0.01) respectively at 12 months. Manifest refraction spherical equivalent was reduced from - 5.6 ± 2.3 to - 1.1 ± 1.3 D at 12 months after the procedure (P>  0.01). In addition, maximum keratometry was significantly reduced from 54.8 to 49.3 diopters (P>  0.01), while the asphericity index (Q value) has changed from - 1.4 to - 0.25 (P>  0.01) after 12 months. No significant differences were detected between central (n = 12) and eccentric (n = 20) KC in all outcomes.

CONCLUSION

The 320° ICRS-CXL protocol has improved the visual and the tomographic outcomes at 1 year in our patients with progressive KC. No differences were detected between central and eccentric cases. Further larger studies could ensure the safety profile of the combined protocol.

Evaluation of a Tangential Map-Based Nomogram for Intrastromal Corneal Ring Segments' Implantation in Keratoconus: One Year Results

Purpose

To evaluate a new tangential map-based nomogram versus the axial map-based nomogram for ICRS in keratoconus.

Methods

A prospective case series study including 64 eyes of 64 patients who underwent ICRS implantation. Cone location was determined for each eye with two maps: the axial and the tangential. Appropriate ring selection was determined using two surgical nomograms: axial map-based and tangential map-based. Visual, refractive, and topographic outcomes were assessed before, as well as at 3, 6, and 12 months after ICRS implantation.

Results

The cone location, and consequently the ring selection, was significantly different in the two nomograms with a “centralization tendency” in the tangential map. In the axial group, UDVA and CDVA improved from 0.12 ± 0.04 and 0.24 ± 0.08 to 0.28 ± 0.08 and 0.4 ± 0.1, respectively. Similarly, MRSE substantially decreased from −6.7 ± 3.3 to −1.2 ± 1.1D at 12 months after the procedure. In the tangential group, UDVA and CDVA improved from 0.09 ± 0.06 and 0.2 ± 0.1 to 0.5 ± 0.2 and 0.7 ± 0.2, respectively. MRSE substantially decreased from −4.9 ± 1D at 12 months after the procedure. In the tangential group, UDVA and CDVA improved from 0.09 ± 0.06 and 0.2 ± 0.1 to 0.5 ± 0.2 and 0.7 ± 0.2, respectively. MRSE substantially decreased from −4.9 ± 1D at 12 months after the procedure. In the tangential group, UDVA and CDVA improved from 0.09 ± 0.06 and 0.2 ± 0.1 to 0.5 ± 0.2 and 0.7 ± 0.2, respectively. MRSE substantially decreased from −4.9 ± 1P=0.01^∗. Similarly, the gain in the CDVA was 0.4 and 0.15 in the tangential and axial groups, respectively, at 12 months, P=0.01^∗. Similarly, the gain in the CDVA was 0.4 and 0.15 in the tangential and axial groups, respectively, at 12 months,

Conclusion

The tangential map-based nomogram attained better visual and refractive outcomes at 1 year. In addition, the cone location was significantly different between both maps with a centralization tendency in the tangential one.

Intracorneal Ring Segment Implantation in the Management of Keratoconus: An Evidence-Based Approach

Intracorneal ring segment (ICRS) implantation represents a modern, minimally invasive, surgical option for visual improvement in patients with keratoconus. ICRS modify the corneal geometry in a manner that enhances its refractive properties and thereby, they improve visual acuity. It is well-documented that implantation of ICRS decreases the keratometric readings, spherical equivalent and cylinder, reduces high-order aberrations and improves uncorrected distance visual acuity (UDVA) and best-corrected distance visual acuity (BCDVA) in patients with keratoconus. Success rate after ICRS implantation is high, depending on appropriate patient selection and adherence to suitable implantation nomograms, and most important, the overall complication rate is very low. This review is summarizing current indications/contra-indications for ICRS implantation, implantation techniques, clinical outcomes and potential complications, shedding light on myths and realities related to this innovative surgical option.