KEY CONCEPTS
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Intrastromal corneal ring segments (ICRSs) reshape the cornea form by modifying its geometry, improving the patient’s corneal surface and leading to a best vision in the majority of treated cases.
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ICRS implantation decreases the keratometric and refractive measures, reduces high order aberrations, and improves visual acuity.
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Success rates after ICRS implantation are high, depending on appropriate patient selection and adherence to suitable nomograms.
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ICRSs can be combined with other procedures, and some complications have been reported; however, it remains a safer surgery when compared with intraocular procedures.
Introduction
Intrastromal corneal ring segment (ICRS) implantation is a surgical technique developed to restore vision and postpone or avoid intraocular invasive procedures or corneal keratoplasty. The rings act as elements that reshape corneal form by modifying its geometry, flattening the central area and decreasing irregular astigmatism, thereby improving the patient’s corneal surface and leading to a best vision in the majority of the cases. Vision rehabilitation is faster than after other corneal surgical procedures, presenting many fewer serious complications, and offering the specific advantages of not removing corneal tissue and minimizing epithelial changes.
It is well documented that ICRS implantation leads to decreases in keratometric readings, spherical equivalent, and cylinder, reduces high order aberrations, and improves uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA) in patients with hereditary or acquired corneal ectasias or irregular astigmatism.
Success rates after ICRS implantation, as described in published articles, are high, depending on appropriate patient selection and adherence to suitable implantation nomograms. Moreover, ICRS implantation can be combined with other procedures such as cross-linking. ,
Outcomes
Corneal changes induced by ICRS implantation are responsible for visual, refractive, and keratometric improvement in patients with ectatic diseases. The procedure has an “orthopedic” function, regularizing the geometry of corneal tissue. In some patients, ring segments act as spacers, interfering with corneal collagen turnover, with consequent increases in the corneal pachymetry and corneal collagen remodeling.
Most of the peer-reviewed scientific literature demonstrates a statistically significant central corneal flattening, improving both uncorrected and corrected visual acuity by reducing spherical equivalent and cylinder and by modifying corneal high order aberrations. A better visual outcome is expected when the alignment of the refractive and keratometric axis angle is <15%. , , All types and brands of ICRSs appear to be safe and effective ( Table 25.1 ). ICRSs are effective even in patients older than 40 years, as demonstrated by Gatzioufas et al. Keraring and Ferrara Ring are more effective in the treatment of keratoconus when compared with Intacs. Piñero et al. demonstrated less astigmatism correction with Intacs and more prevalent symptoms of halos and glare. These findings are related to the nature of the device, with fewer options of shapes and a larger diameter (which induces less corneal central flattening).
TABLE 25.1
Visual/Refractive Outcomes and Complications of ICRS Implantation Reported in Different Studies
| Authors a | Eyes Enrolled | ICRS Model | Mean Follow-Up (Months) | Visual Acuity Change | Refractive Change | Complications |
| Abdellah and Ammar | 38 | Keraring | 36 | Mean UCVA improved from 0.93 to 0.63 logMAR and mean BCVA from 0.67 to 0.43 logMAR. | Preoperative MRSE −12.55 D to 9.62 D. Mean sphere measurements from −9.68 D to −7.45 D; mean cylinder from −5.82 D to −4.32 D. K max changed from 53.82 D to 50.47 D; K min from 48.83 D to 47.01 D; and K mean from 51.29 D to 47.51 D. | Corneal neovascularization 14 cases (36.84%), corneal melting 10 cases (26.3%), and ring extrusion 12 cases (31.5%). |
| Alfonso et al. | 56 | Keraring | 6 | BCVA improvement from 0.70 to 0.80 Snellen decimal scale. 15 eyes gained 1 line of BCVA, 9 eyes gained 2 lines, 7 eyes gained 3 lines, and 3 eyes gained 4 lines. | MRSE decreased from −3.10 D to −0.77 D. | 5 eyes lost 1 line of corrected visual acuity; 17 eyes had unchanged BCVA. No other intraoperative or postoperative complications occurred. |
| Alfonso et al. | 219 | Keraring | 6 | In author’s patient classification stage 1, 52.16% of the eyes gained lines in BCVA evaluation, stage 2 65.48%, and stage 3 60%. | A significant decrease in MRSE after surgery was found for stages 1 and 2, but not for stage 3. | 3.20% of the eyes lost 2 or more lines of BCVA. |
| Alió et al. | 13 | Intacs | 48 | BCVA increased from 0.46 logMar (20/50 Snellen) preoperatively to 0.66 logMar (20/30 Snellen) postoperative. | MRSE improved from −5.40 D to −3.95 D; K max decreased from 51.07 D to 47.69 D; and K mean changed 3.13 D. | Extrusion in 7 eyes, excluded from statistical analysis. 4 eyes showed channel deposits, 2 eyes presented superficial vascularization. |
| Alió et al. | 25 | Intacs | 6 | In group A, mean preoperative BCVA was 0.43 logMar (20/50 Snellen) and mean postoperative BCVA 0.82 logMar (20/20 Snellen). In group B, mean preoperative BCVA was 0.36 logMar (20/63 Snellen) and mean postoperative BCVA 0.24 logMar (20/80 Snellen). | Postoperative reduction in spherical dioptric power was 2.11 D and MRSE 2.81 D in group A, only significant in this group. Reduction in K mean was 4.30 D in group A and 6.19 D in group B. | None described. |
| Alió et al. | 26 | Intacs | 12 | BCVA improved from 20/63 to 20/32 Snellen in both groups studied (1 and 2). | MRSE decreased from −5.00 D to −1.73 D in group 1 and −5.50 D to −3.25 D in group 2. | Mild superficial corneal neovascularization observed in 3 eyes. Mild segment migration (1−3 mm) occurred in 7 of 26 eyes. 4 of 26 eyes developed severe segment migration and partial extrusion from the wound. |
| Al-Tuwairqi et al. | 44 | Keraring and MyoRing | 6 | BCVA increased in group A (Keraring) but not in group B (MyoRing); however, 77% of the patients were satisfied in group A and 89% of group B 6 months after surgery. | MSRE decreased by 2.90 D and 3.60 D in groups A and B, respectively; K mean reduced by 4.55 D in group A and 6.51 D in group B. | 3 complications in group A: segment displacement repaired after 1 week, superficial movement of the segment (ring was removed), and infiltrative keratitis (ring was taken off). In group B, 1 eye underwent cross-linking owing to keratoconus progression. |
| Arantes et al. | 25 | Ferrara Ring | 12 | BCVA improved from 0.33 to 0.20 logMAR. | MRSE reduced from −3.67 D to −0.71 D; 3.5 D reduction in K1, 1.53 D in K2, and 2.52 D in K mean . | None described. |
| Boxer Wachler et al. | 74 | Intacs | 1 | 45% of the patients gained ≥2 lines in BCVA, 51% of 74 eyes had no change of BCVA, and 4% of 74 lost ≥2 lines. | MRSE decreased from −3.89 D to −1.46 D. | 1 eye experienced a superficial channel dissection with anterior Bowman layer perforation. Segment migration and externalization was found in 1 eye. |
| Colin et al. | 10 | Intacs | 12 | Gain of 2 lines in BCVA; improvement from 0.38 logMAR (20/50 Snellen scale) to 0.22 logMAR (20/32 Snellen scale). | MRSE changed 2.12 D and K max decreased 4.60 D. | None described. |
| Colin | 57 | Intacs | 12 | BCVA of 20/40 Snellen or better improved from 53% of patients preoperatively to 74% of patients. | MRSE improved to 3.1 D; K mean changed in 3.70 D. | At the 6-month examination, 9 patients reported “moderate” or “severe” visual symptoms consisting of discomfort ( n = 1), itching ( n = 1), burning ( n = 1), photophobia ( n = 1), difficulty with night vision ( n = 1), glare ( n = 3), and fluctuating vision ( n = 1). Dissatisfaction with visual symptoms was the reason for removal of the inserts in 7 eyes (12%). |
| Coskunseven et al. | 50 | Keraring | 12 | BCVA was a gain of 1.3 lines (range, loss of 2 lines to a gain of 4 lines). | MRSE decreased from −5.62 D to −2.49 D. | Segment migration to the incision site was seen in 3 eyes (6%) at the first postoperative day. |
| Ertan et al. | 118 | Intacs | 12 | 73.7% of eyes gained lines in BCVA evaluation. | MRSE decreased from −7.57 D to −3.72 D; K mean decreased from 51.56 D to 47.66 D. | Epithelial plugs at the incision site occurred in 15.2% of the eyes. 8.5% of the eyes presented granulomatous particles around the ring in the first 6 months, resolved using steroids drops. |
| Ertan et al. | 306 | Intacs | 4 | 15% and 10.7% gained lines of UCVA and BCVA, respectively. | MRSE decreased from −7.81 D to −4.72 D; K mean decreased from 50.70 D to 47.91 D. | Segment extrusion occurred in 3 eyes 6 months after ICRS implantation. |
| Fahd et al. | 30 | Intacs | 6 | BCVA improved from 20/42 to 20/27Snellen. | MRSE decreased from −2.24 D to −1.02 D; central K decreased from 49.14 D to 47.43 D. | Deposits in 7 eyes and 1 patient with transient foreign-body sensation and glare. |
| Cueto et al. | 58 | Ferrara Ring | 60 | BCVA improved from 0.16 to 0.11 logMAR. | MRSE declined from −2.74 D to −1.42 D. | Loss of 2 lines in BCVA during first 6 months in 4 eyes. No intra- or postoperative complications. |
| Fernandez-Vega Cueto et al. | 409 | Ferrara Ring | 6 | BCVA changed from 0.69 to 0.77 Snellen decimal scale. | MRSE declined from −4.16 D to −2.81 D; K max decreased from 48.23 D to 46.31 D. | None described. |
| Ferrara et al. | 1073 | Ferrara Ring | 12 | For group 1 of patients, UCVA increased to 20/80 Snellen and BCVA increased to 20/40 Snellen. For group 2 of patients, UCVA increased to 20/13 Snellen and BCVA increased to 20/60 Snellen. | For group 1 of patients, asphericity decreased to −0.35, MRSE decreased to −2.26 D, and K mean decreased to 45.72 D. For group 2 of patients, asphericity decreased to −0.56, MRSE decreased to −4.14 D, and K mean decreased to 48.10 D. | Undercorrection (needing implantation of additional segment) 16 eyes (1.49%), overcorrection (needing segment removal and reimplantation) 11 eyes (1.02%), extrusion 6 eyes (0.56%), malposition 4 eyes (0.37%), progressive corneal steepening 2 eyes (0.18%), and ring neovascularization 2 eyes (0.18%). |
| Heikal et al. | 30 | Keraring | 6 | BCVA improved from 0.85 to 0.14 logMAR. | MRSE reduced from −5.43 D to −2.43 D; K max decreased from 55.85 D to 44.05 D. | None described. |
| Hellstedt et al. | 50 | Intacs | 12 | Gain of lines of BCVA 76.70% in 6 months and both BCVA and UCVA improved throughout follow-up. Visual functioning index improved from 61.6 to 80.8, and the percentage of satisfaction with vision improved from 24.3% to 87.5% at 12 months. | Mean change in spherical error of 2.67 D. Vector analysis of astigmatism correction showed that mean change in corneal astigmatism was 2.9 D at 6 months postoperatively. | In 8% of eyes, both Intacs segments were removed. In addition, 7 refractive adjustments in 7 eyes were performed successfully to improve visual and surgical outcome. |
| Israel et al. | 29 | KERATACx Plus | 6 | BCVA improvement from 0.17 to 0.50 Snellen decimal scale. | K1 decreased from 49.42 D to 45.05 D, K2 from 54.23 D to 48.93 D, and K mean from 51.71 D to 46.88 D. | None described. |
| Jabbarvand et al. | 21 | MyoRing | 12 | BCVA improved in group 1 from 0.26 to 0.24 logMar and in group 2 from 0.35 to 0.23 logMar. | K max improved in group 1 from 49.59 D to 44.16 D and in group 2 from 49.73 D to 44.77 D. | Transient sensation of foreign body in 4 patients in group 1 and 3 patients in group 2. |
| Jadidi et al. | 32 | MyoRing | 3 | BCVA improvement from 0.47 to 0.22 logMAR. | MRSE improvement from −10.51 D to −1.32 D; reduction of 3.55 D in K mean . | None described. |
| Kanellopoulos et al. | 20 | Intacs | 12 | BCVA improved from 20/37 to 20/22 Snellen. | MRSE improved from −5.33D to −1.87 D; K mean decreased from 49.50 D to 46.35 D. | 1 case of anterior chamber perforation, 6 eyes had ring exposure secondary to corneal thinning over the implants postoperatively, and a dense corneal infiltrate developed in 1 patient at 7th month after surgery. |
| Kwitko and Severo | 51 | Ferrara Ring | 39 | BCVA improved in 86.4% of eyes, was unchanged in 1.9%, and worsened in 11.7%. UCVA improved in 86.4% of eyes, was unchanged in 7.8%, and worsened in 5.8%. | MSRE was reduced from −6.08 D to −4.55 D and mean refractive astigmatism from −3.82 D to −2.16 D. K mean reduced from 48.76 D to 43.17 D. | Intracorneal ring segment decentration occurred in 2 eyes (3.9%), segment extrusion in 10 eyes (19.6%), bacterial keratitis in 1 eye (1.9%) with segment extrusion, and disciform keratitis in 1 eye (1.9%). |
| Kymionis et al. | 36 | Intacs | 60 | Preoperative UCVA was 20/50 Snellen or worse in all eyes; at the last follow-up examination, 10 (59%) of 17 eyes had UCVA of 20/50 Snellen or better. 6 eyes (35%) maintained preoperative BCVA, whereas the remaining 10 eyes (59%) experienced a gain of 1 up to 8 lines. | MSRE reduced from −5.54 D to −3.02 D. Mean change in keratometry 1.57 D. | 1 eye lost 3 lines of BCVA. |
| Lisa et al. | 32 | Keraring | 6 | BCVA improved from 0.67 to 0.80 Snellen decimal scale. Postoperatively, BCVA was better than 20/40 Snellen in 96.9% of eyes and 20/25 or better in 56.2% of eyes. | MRSE decreased from −1.93 D to −0.26 D; K max decreased from 48.63 D to 44.98 D. | 4 eyes lost 1 line in vision. |
| Lisa et al. | 43 | Ferrara Ring | 33 | BCVA improved from 0.36 to 0.17 logMAR. The percentages of eyes with BCVA of 0.3 logMAR or better increased from 51.2% to 95.3%. | MRSE declined from −3.19 D to −1.88 D; K max declined from 53.89 D to 51.27 D. | None described. |
| Miraftab et al. | 30 | Intacs | 27.8 after surgery | BCVA improved from 20/40 to 20/32 Snellen. | K mean decreased from 47.23 D to 45.66 D. | None described. |
| Miranda et al. | 36 | Ferrara Ring | 12 | BCVA improved in 29 eyes (80.56%). | MRSE decreased from −7.29 D to −4.80 D. | Segment decentration in 1 eye (2.7%), asymmetric positioning in 2 eyes (5%), migration of the segments in 2 eyes (5%), segment extrusion in 5 eyes (13.8%), and bacterial keratitis in 1 eye (2.7%). |
| Moreira et al. | 10 | Ferrara Ring | 3 | BCVA improved from 0.7 to 0.4 logMAR. | 50% of eyes improved BCVA ≥0.5 logMAR. | In 2 patients, corneal perforation was observed. Segment externalization was found in 1 eye and 3 patients had segment migration. |
| Mounir et al. | 623 | Keraring | 48 | BCVA improved from 0.79 to 0.72 logMAR in 18-month postoperative evaluation. | MRSE decreased from −10.86 D to −7.52 D in 18-month postoperative evaluation; K1 from 49.13 D to 46.88 D; K2 from 53.50 D to 49.83 D; and K mean 51.31 D to 48.35 D. | Intraoperative complications occurred in 44 eyes (7.1%), and were represented by vacuum loss, incomplete or decentered tunnel creation, misdirection of the ring, perforation to anterior chamber, broken body, or orifice of the ring. Postoperative complications occurred in 35 eyes (5.6%): segment migration or extrusion, incision opacification, infectious keratitis, corneal melting, sterile keratitis, and steroid-induced glaucoma. |
| Muftuoglu et al. | 89 | Keraring | 6 | BCVA improved from 0.35 to 0.07 logMAR. | MRSE changed from −4.54 D to −0.98 D; K mean improved from 46.39 D to 42.64 D. | None described. |
| Nobari et al. | 15 | MyoRing | 10 | BCVA improved from 0.39 to 0.19 logMAR. | MRSE decreased from −6.00 D to −0.70 D; K values decreased significantly (K max 5.00 D, K min 1.10 D, and K mean 4.00 D). | Halo and glare in night vision in 1 patient. |
| Peña-García et al. | 127 | Keraring | 6 | Studied patients were divided into grade 1 and 2 groups. Patients with grade 1 gained at least 1 line of BCVA in 30.77% of cases. BCVA remained unchanged in 46.15% of cases. In the best group, BCVA increased from 0.16 to 0.06 logMAR, but did not improve in the remaining cases. | Keratometry improved significantly in the best group; mean K2 power decreased by almost 3.00 D from preoperatively to 6 months postoperatively; K mean also decreased by almost 3.00 D. | None described. |
| Rabinowitz et al. | 30 | Intacs | 12 mechanical group 6 femto-group | Improvement in BCVA (3.92 laser vs 1.63 mechanical group). | MRSE changed 2.96 D in mechanical group and 3.98 D in femto-group; K mean change in mechanical group 2.52 D and 2.91 D in the other group. | No data. |
| Rocha et al. | 34 | Ferrara Ring | 6 | BCVA improved from 0.51 to 0.18 logMAR. | MRSE decreased from −7.52 D to −3.61 D; K mean decreased from 51.36 D to 47.19 D, K1 from 48.79 D to 45.69 D, and K2 from 54.25 D to 48.82 D. | None described. |
| Sadoughi et al. | 18 | Keraring | 4 | BCVA improved from 0.39 to 0.26 logMAR. | MRSE decreased from −8.03 D to −3.01 D, K mean decreased from 51.43 D to 47.42 D. | Ring deposits in 4 eyes, without visual impairments. |
| Sandes et al. | 58 | Ferrara Ring | 16 | BCVA improved from 0.5 to 0.3 logMAR (20/60 to 20/40 Snellen). | Reduction in K mean from 49.87 D to 47.34 D. | None described. |
| Shabayek and Alió | 21 | Keraring | 6 | Improvements in BCVA from 0.54 to 0.71 Snellen decimal scale. | MRSE decreased by 2.28 D, K mean decreased 2.24 D. | Localized infectious keratitis occurred in 1 eye (4.8%); incision opacification occurred in 8 eyes (38%). |
| Shetty et al. | 14 | Intacs | 12 | At 6 months, UCVA improved from 0.05 to 0.16 Snellen decimal scale, and BCVA improved from 0.50 to 0.67 Snellen decimal scale. | Spherical refractive error improved from −6.68 D to −3.11 D, whereas cylindrical refractive error improved from −4.89 D to −3.64 D. MRSE reduced from −9.13 D to −4.93 D, and K mean decreased from 53.01 D to 49.42 D. | 1 eye (7.14%) developed superficial corneal vascularization 3 weeks postoperatively, directed toward the incision site. Vascularization resolved after suture removal and topical fluorometholone therapy. |
| Siganos et al. | 26 | Ferrara Ring | 6 | BCVA improved from 0.37 to 0.60 Snellen decimal scale. | MRSE decreased from −6.91 D to −1.11 D. | In 2 eyes, the rings had to be removed early in the postoperative period, owing to superficial implantation of the rings and asymmetrical placement. |
| Stival et al. | 41 | CornealRing | 32 | BCVA improved in group A (post-PRK ectasia) from 0.30 to 0.11 logMAR and in group B (post-LASIK ectasia) from 0.43 to 0.17 logMAR. | MRSE decreased from −2.97 D to −2.05 D in group A and −3.31 D to −2.42 D in group B; K max decreased from 45.34 D to 43.74 D in group A and from 49.96 D to 47.55 D in group B. | None described. |
| Tognon et al. | 1222 | Keraring | 3 | BCVA improved in all satisfied patients after surgery; in the majority of dissatisfied patients mean BCVA did not improve. Before the procedure, the distribution of patients according to visual impairment was not homogeneous, and the majority of the patients were in moderate visual impairment group (World Health Organization Classification for Visual Impairment). After the procedure, a larger number of the patients ascended to normal or mild visual impairment groups. | Not detailed. | 67 surgical complications (external environment or anterior chamber perforation, late or early infection, late or early segment extrusion, and malposition/movement of the ICRS after procedure). 164 patients dissatisfied after ICRS implantation. |
| Torquetti et al. | 36 | Ferrara Ring | 120 | BCVA improved from 0.45 to 0.29 logMAR; 66.7% of patients gained 2 or more lines of BCVA at 10 years. | K max decreased from 54.99 D to 50.65 D. | Ring segment exchange required in 2 eyes and keratoplasty in 2 eyes. |
| Torquetti et al. | 37 | Ferrara Ring | 30 | BCVA improved from 20/160 to 20/50 Snellen. | MRSE decreased from −4.64 D to −3.04 D; K mean reduced from 49.33 D to 46.16 D. | None described. |
| Torquetti et al. | 138 | Ferrara Ring | 6 | BCVA improved from 20/100 to 20/40 Snellen; 2 or more lines of BCVA gained in 87% of eyes. | MRSE reduced from −7.02 D to −3.29 D; K1 reduced from 50.5 D to 46.0 D, K2 55.2 D to 49.0 D, and K mean reduced from 53.3 D to 47.8 D. | 4 cases of migration and 2 cases of intraoperative perforation; all cases were excluded from statistical analysis. |
| Vega-Estrada et al. | 18 | Intacs and Keraring | 69 | Decimal BCVA changed from 0.59 to 0.68 in 6 months and to 0.63 in 5 years. | MRSE changed from −4.35 D to −2.10 D in 6 months and −4.79 D in 5 years. | None described. |
| Yildirim et al. | 8 | Keraring | 67 | Improved BCVA from 0.69 to 0.29 logMAR. | MRSE decreased 5.7 D; K mean decreased 2.1 D. | None described. |
| Zare et al. | 30 | Intacs | 6 | Mean UCVA improved from 0.60 to 0.29 logMAR and mean BCVA from 0.25 to 0.13 logMAR. | MRSE improved from −6.93 D to −3.23 D and mean refractive cylinder from −4.65 D to −3.90 D. K mean decreased from 49.84 D to 47.90 D. | 3 eyes had ring exposure and 1 eye had bacterial keratitis and ring exposure. |
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