Continuous Intracorneal Ring Implantation reversibile with low rates of complications in Keratoconus: Study

In the last 20 years, the range of treatment modalities for Keratoconus (KC) has vastly expanded. Novel contact-lens types can significantly improve visual acuity by correcting both lower- and higher-order aberrations. A central problem, however, is that, due to irregularities of the corneal surface, many patients begin to experience CL intolerance (CLI) and surgical measures become necessary. Classical corneal crosslinking (CXL) is an established surgical first step to halt KC by stabilizing the cornea and thereby prevents further ectasia and decreases in visual acuity.

To improve vision in a clinically significant manner, the minimally invasive embedding of intracorneal implants have become increasingly popular. Intracorneal ring segments (ICRS) and 360° intracorneal continuous rings (ICCR) have been developed by different manufacturers and have shown their efficacy in significantly improving visual acuity in eyes with KC and in postponing or completely eliminating the need for keratoplasty. The reported advantages of ICCR compared to ICRS are the more robust improvement of spherical aberrations, increased biomechanical stability and their sustained effectiveness in progressive KC.

To provide further insight into the efficacy of this treatment option and its complications for patients with KC, Thiwa et al retrospectively examined the data collected at three different centers. All treatments were planned in coordination with the manufacturer's reading center, and all patients met the same inclusion and exclusion criteria for ICCR implantation.

This nonrandomized, multi-centric, retrospective cohort study examined visual, keratometric and clinical outcomes evaluated after a minimum follow-up of 2 months. Among the inclusion criteria for the standard treatment group (STG) were corrected distance visual acuity (CDVA) <20/25 Snellen, no central corneal scars, minimum corneal thickness >350µm, and central mean keratometry reading (meanK).

A total of 118 eyes of 118 patients with aged 32 ± 11 years were included in this study. At a median follow-up of 161 days (interquartile range: 111–372 days) ICCR implantation improved the CDVA from a mean of 0.38 to 0.15 logMAR (p<0.0001). Our correlation analysis showed lower preoperative CDVA to be the single best predictor of CDVA improvement, with eyes of a CDVA of 20/80 or lower improving by 4.3 ± 2.0 lines on average. Eyes with a meanK >55 diopters gained 9.04±4.83 lines in UDVA and 2.86±3.09 lines in CDVA.

However, postoperatively these eyes had a CDVA of 0.32±0.21 logMAR which is significantly inferior to the STG outcome (p=0.001372).

Fifteen eyes (12.7%) had to undergo a ring exchange procedure because of refractive under- (9 eyes) or overcorrection (6 eyes). Two eyes (1.7%) experienced medical complications.

In this study, all analyzed visual acuity and topography parameters improved significantly (p < 0.001) with the exception of the thinnest pachymetry value (min. pachy) and topographical astigmatism (topoAsti).

The mean improvement in CDVA, was highly variable, with a standard deviation of 2.1 lines ranging from −2.0 to 10 Lines. This underlines further need for improving selection criteria by performing subgroup analyses.

The subgroup analysis showed eyes with a higher SE were more likely to require reoperation (group 2). Eyes in group 2 had a tendency for inferior compounded CDVA gains compared to group 1 (p=0.13958).

The correlation analysis showed preoperative vision to be the single most useful predictor of postoperative improvement in vision. In other words, high potential for improvement in CDVA was associated with a greater gain in CDVA lines. For instance, the eyes in the upper quartile of preoperative CDVA (as measured in logMAR) were eyes with a CDVA of 20/80 and lower, as measured in Snellen. These eyes gained 4.3 ± 2.0 lines in CDVA on average.

The results of this study further confirm the efficacy of ICCR implantation as a treatment for KC. This promising technique comes with great benefits, particularly for KC patients with reduced preoperative vision (CDVA <20/70) and a low SE. The calculated safety index, low risk of complications and the reversibility of the treatment speak to its safety. The main challenge remains in the low predictability of the magnitude of this improvement in eyes with good spectacle corrected vision (CDVA >20/30).

Source: Thiwa et al; Clinical Ophthalmology 2022:16 3055–3067