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Treatment of visual problems after intracorneal ring implantation

Purpose To report the effect of wavefront-guided photorefractive keratectomy and corneal collagen cross-linking (CXL) on visual problems after Ferrara ring segment placement. Materials and methods A 32-year-old male patient was treated with a Ferrara ring segment for keratoconus. One year later, the ring was removed due to severe glare complaints. After 6 months, wavefront-guided photorefractive keratectomy and CXL were applied simultaneously to correct high order aberration and refractive error. Results Six months after the wavefront-guided photorefractive keratectomy and CXL, the uncorrected distance visual acuity was 20/25, and there was a 30% decrease in coma aberrations. The glare complaint regressed. Conclusion Wavefront-guided surface ablation and CXL may reduce high order aberrations and glare complaints after intrastromal corneal ring implantation.


Introduction
Intrastromal corneal ring segments (ICRS), which were initially designed to correct mild to moderate myopia, have been demonstrated as a surgical option to manage keratoconus. [1][2][3] Its therapeutic effects are based on the induction of remodeling of the corneal anterior and posterior surface's topography, which improves the optical quality of the cornea and reduces the optical aberrations, with consequent improvement in visual acuity. 4,5 Currently there are many types of commercially available ICRSs, such as Intacs ® (Addition Technologies, Des Plaines, IL, USA), Keraring (Mediphacos, Belo Horizonte, Brazil), and Ferrara ring (Ferrara Ophthalmics, Belo Horizonte, Brazil). The Ferrara intrastromal ring segment used in this study has a small radius of curvature and a triangular anterior surface. 6 The unique triangular shape with a flat posterior surface is purported to induce a prismatic effect on the cornea which reduces glare and halo. 7 However these complaints were reported in 10% of the Ferrara cases followed over a 5-year period. 8 Although these symptoms may disappear over time, pilocarpine or brimonidine tartrate drops are recommended for persistent cases. In addition, increase in high order aberrations (HOAs) after ICRS implantation is another problem that may affect visual quality. 9,10 The photorefractive keratectomy (PRK) plus corneal collagen cross-linking (CXL) procedure is an effective treatment option for progressive keratoconus. This procedure was found to be associated with stable refractive and topographic outcomes and with a  11 Herein, we describe a case of visual complaint after Ferrara ring segment placement, which was treated successfully with wavefront-guided PRK and CXL procedures after the ring was extracted.

Case report
A 32-year-old male patient was referred to our department from an ophthalmology clinic, with bilateral keratoconus. He worked with heavy metals and could not use contact lenses or eyeglasses on the job. His uncorrected distance visual acuity was 20/200 and corrected distance visual acuity was 20/100 with −5.00 −2.50 × 30° in the right eye. The uncorrected distance visual acuity was 20/70 and corrected distance visual acuity was 20/40 with −2.50 −2.00 × 175° in the left eye. The slitlamp examination and intraocular pressure and examination were normal for both eyes. Corneal topographi- In an attempt to improve vision, Ferrara ICRS implantation was planned for the correction of the corneal steepening and irregularity. Two Ferrara ring segments with 250 µm thickness and 160° arch-length were to be placed temporally and nasally using a 30 kHz femtosecond laser (IntraLase™ FS Laser, Abbott Medical Optics,) in compliance with the Ferrara nomogram in the right eye. The Purkinje reflex was chosen as the central point. The patient rejected treatment of the left eye. After Ferrara ring segment implantation, the corrected distance visual acuity was 20/40 with optimal centralization of the ring segments (Figure 2A and B). However the patient had severe light glare complaints under photopic conditions in his right eye. Corneal topography revealed diminishing keratometric values (Figure 2C), and the Zernike analysis with Pentacam (Oculus Opticgerate GmbH) showed an increase in vertical coma and trefoil ( Figure 2D). Twelve months use of brimonidine drops did not eliminate this complaint. After 1 year, the rings were removed but the glare persisted. The aberrometric measurements taken from the right eye by Wav-eScan demonstrated that HOA root mean square error was 0.75 µm and coma domination was 0.404 µm ( Figure 3A). Based on these results, wavefront-guided PRK along with CXL was planned to correct refractive errors and aberrations of the right eye.
The wavefront-guided ablation pattern was prepared using a WaveScan aberrometer and transferred to a VISX S4 IR device (Abbott Medical Optics, Santa Ana, California, USA).
Estimated ablation depth was 50 µm. Mitomycin-c (Onko Ecza Sanayi ve Tic. Ltd., Sti., Istanbul, Turkey) at 0.02% was applied for 20 seconds to impede haze and regression. Following PRK, CXL was applied in compliance with the Dresden protocol. 12 A 6.5 mm optical zone was used with a transition zone of 8.5 mm. Six months after Wavefront-guided PRK and CXL procedures, the uncorrected distance visual acuity was 20/25. The high order root mean square score was drawn back to 0.39 µm, and coma aberration was reduced to 0.277 µm ( Figure 3B). The patient's glare complaints ceased, and no haze was seen. At the 12 month visit, refractive status, visual acuity, wavefront analyses, and topograpgical measurements were unchanged ( Figure 3C and D).

Discussion
Visual problems such as glare and halo are two of the expected complications after ICRS implantation, and it may adversely affect daily activities. Although no comprehensive studies have been conducted on glare and halo after ICRS implantation, one study showed that 10% of the Ferrara cases had halo complaint after surgery, and it has been associated with pupil size. 8 In our case, glare complaint could not be explained by pupil size, which was 6 mm. We hypothesized that the cause of glare might be HOAs, and studies have shown increases in HOAs after ICRS implantation. 9,10 HOAs can also have a significant impact on one's quality of vision and are often linked to visual glare and halos.
Glare symptom tends to get better over time. In severe cases, nighttime application of pilocarpine or brimonidine tartrate drops may be prescribed in order to constrict the pupil and alleviate undesired reflexes. Also Torquetti et al developed segments with a yellow filter in the matrix to avoid blue light at night, which can significantly decrease the incidence of glare and halos. 8 In our study, after ICRS had been extracted, a combination treatment including wave-front guided PRK and CXL was applied to the patient. We achieved a reduction in HOAs and an improvement in glare symptom.
A few studies have reported the use of CXL along with topography-guided PRK in order to provide better visual rehabilitation in patients with keratoconus. [13][14][15][16][17] Moreover, only one study, carried out by Kremer et al, has reported the use of wavefront-guided PRK along with CXL in keratoconic eyes. 18 As we considered that our patient's glare symptom was associated with HOAs, we performed wavefront-guided PRK.
In summary, this report contributes new information to the literature. First, a severe glare complaint that is resistant to medical therapy may present after ICRS implantation. Second, symptoms of glare and HOAs may persist after the removal of ICRS. Lastly, wavefront guided PRK and CXL treatment may yield a reduction in HOA and an improvement of glare symptom in a keratoconic eye that has undergone ICRS extraction.

Disclosure
No financial support was provided for this study. This manuscript has been read and approved by all the authors. The authors report no conflicts of interest in this work.