The advent of corneal collagen cross-linking (CXL) made it possible to stop or slow keratoconus progression; however, in most patients undergoing CXL, uncorrected visual acuity remains low and often requires rigid gas permeable contact lens fittings or other refractive surgical interventions. Many surgical options, including intracorneal ring segments (ICRS) implantation,1 photorefractive keratectomy (PRK),2,3 and phakic intraocular lens implantation,4–6 are available for visual rehabilitation in keratoconus and all can be combined with CXL. ICRS implantation is a tissue-saving technique that reshapes the cornea and improves topographic abnormalities and visual acuity6,7 and is valuable to patients with poor corrected distance visual acuity or keratoconus with mild to moderate refractive errors.2,8,9 PRK is used for keratoconus with mild refractive error2,3 and a phakic intraocular lens is implanted in patients with moderate to severe ametropia.4–6,10 To our knowledge, there are few published articles addressing the results of PRK after ICRS implantation in keratoconus.11–15
The aim of our study was to evaluate the safety and efficacy of non-topography–guided PRK in treating mild refractive errors after sequential ICRS implantation and CXL in patients with keratoconus.
Patients and Methods
We conducted a retrospective analysis of patients with mild to moderate keratoconus who underwent sequential ICRS implantation and CXL and non-topography–guided PRK from May 2010 to January 2013 at the Beirut Eye Specialist Hospital in Beirut, Lebanon. All patients had a history of progressive keratoconus (ie, an increase in the cone apex keratometry value of 0.75 diopters [D] or an alteration of 0.75 D in the spherical equivalent refraction in the 6 months before surgery) in one or both eyes and were contact lens intolerant (ie, a comfortable wearing time of less than 8 hours per day). All patients met the criteria of the institute and were treated according to Jarade’s protocol for the treatment of keratoconus.6 All surgeries were performed by the same surgeon (EJ).
Preoperative screening consisted of a complete ophthalmic work-up including assessment of uncorrected and corrected distance visual acuity, manifest and cycloplegic refractions, and anterior and posterior segment evaluation with dilated fundus examination. Use of soft and rigid contact lenses was discontinued for 1 week and at least 3 weeks prior to treatment, respectively. Keratoconus diagnosis was based on a combination of computed slit-scanning videokeratography of the anterior and posterior corneal surfaces, keratometric readings, and corneal pachymetry.16–19 Keratoconus was classified in four stages based on the Amsler–Krumeich classification.20,21
Exclusion criteria were a central corneal thickness of less than 400 μm measured by optical pachymetry (Oculus Pentacam; Oculus Optikgeräte GmbH, Wetzlar, Germany), an endothelial cell count of less than 2,000 cells/mm2 measured in the central cornea by specular microscopy, corneal opacification or scars, history of keratitis, peripheral marginal degeneration, previous corneal or intraocular surgeries, and autoimmune or connective tissue disease.
The eye was prepared with a topical anesthetic and iodine solution. All 360° tunnels were created using the IntraLase FS60 (IntraLase Corp., Abbot, IL) at an average depth of 70% of the thinnest area of the mid-peripheral cornea where the tunnel was to be created; we always assumed a minimum corneal tissue depth of 100 μm under the ring. The laser docking ring was centered between the pupillary, visual, and geometric axes. According to our topography-guided nomogram for ICRS implantation,22 the incision was made in the mid-peripheral cornea at an axis that allows insertion of the thickest segment of rings under the steepest area of the cornea. After tunnel creation, the suction was released and the cone and docking ring were removed. The number (one or two) and thickness of the rings to be inserted are largely dependent on the refractive errors to be treated by ICRS implantation. The incision site was sutured with 10-0 nylon after insertion of the rings. Patients were instructed to use tobramycin and dexamethasone sodium phosphate 0.1% eye drops four times daily for 10 days.
The eye was anesthetized by proparacaine hydrochloride 0.5% drops three times at 5-minute intervals. After positioning the patient under the operating microscope, an eyelid speculum was inserted and the central 9-mm corneal epithelium was removed with a blunt spatula. A mixed riboflavin 0.1% dextran solution was instilled every 2 minutes until it penetrated the cornea after approximately 30 minutes. The UV-X illumination system (version 1000; IROC AG, Zurich, Switzerland) was then focused on the cornea apex at a distance of 5 cm for 30 minutes, providing a radiant energy of 3.0 ± 0.3 mW/cm2. The required irradiance of 3.0 mW/cm2 was calibrated prior to each treatment using the LaserMate-Q (LASER 2000, Wessling, Germany). During ultraviolet-A administration, riboflavin drops were applied to the cornea every 2 minutes. Thinnest and central corneal thickness were monitored to ensure that neither parameter dropped below 400 μm. The eye was washed with balanced salt solution and two drops of gatifloxacin 0.3% were instilled before a bandage soft contact lens was fitted. Patients received 500 mg acetaminophen twice daily for 3 days, one drop of 0.3% gatifloxacin six times daily for 7 days, one drop of 0.1% tobramycin–dexamethasone four times daily for 10 days, and one drop of 0.5% loteprednol five times daily and tapered for a period of 5 weeks postoperatively. The bandage soft contact lens was removed on postoperative day 4 and the eye was examined by slit-lamp microscopy to confirm complete corneal epithelialization. Complete assessment was performed at 1 and 6 months postoperatively and included visual acuity, refraction, and anterior and posterior topography. Keratoconus stabilization was assessed only after the 6-month follow-up after CXL. Keratoconus was considered stabilized if the measured refraction was similar for at least 3 months and all treated eyes were considered stable at the time of PRK.
Patients were eligible for PRK at least 6 months after CXL and after maintaining stable refraction for 3 months. Manifest refraction was performed by the same optometrist. The Allegretto Wave excimer laser (Wave-Light Laser Technologie AG, Erlangen, Germany) was used to perform standard, non-topography–guided PRK with a 5.5- to 6-mm optical zone and a transition zone of less than 1 mm was performed with a maximum ablation depth set at 50 μm because of the presence of ICRS. In cases with moderate myopic refractive errors, the optical zone or treated myopic errors were decreased to exceed 50 μm of ablation depth. Three drops of 0.4% oxybuprocaine hydrochloride and ofloxacin were instilled. The central 8-mm corneal epithelium was first mechanically removed using a blunt spatula and then PRK was performed. Mitomycin C was not used. The corneal surface was then irrigated with balanced salt solution and a bandage soft contact lens was fitted and kept in place until the epithelium fully healed. Postoperatively, patients received 500 mg acetaminophen twice daily for 3 days, one drop of 0.3% gatifloxacin six times daily for 7 days with one drop of 0.1% tobramycin–dexamethasone four times daily for 10 days, and one drop of 0.5% loteprednol five times daily and slowly tapered for a period of 5 weeks. The bandage soft contact lens was removed on postoperative day 4 and the eye was examined with slit-lamp microscopy to confirm complete corneal epithelialization. Complete assessment included visual acuity, refraction, and anterior and posterior topography and was performed at 1 and 6 months postoperatively. Uncorrected and corrected distance visual acuity, manifest refraction spherical equivalent, flat and steep topographic keratometry values, and thinnest corneal thickness were recorded for patients at baseline, the last follow-up after ICRS implantation and CXL, and 6 months after PRK.
Statistical analysis was performed using SPSS for Windows (version 16.0; SPSS, Inc., Chicago, IL). The Wilcoxon signed rank test was used to compare parameters. A two-tailed P value of .05 or less was considered statistically significant.
Seventeen eyes of 14 patients (8 men and 6 women) with a mean age of 32.3 ± 6.4 years at the time of ICRS implantation were included in this study. Time between CXL and PRK ranged from 6 to 10 months with stable refraction for at least 3 months and was recorded for all patients. Bilateral surgery was performed in 3 patients. The mean spherical and cylindrical powers at baseline (before ICRS implantation) were −5.45 ± 1.64 and 3.86 ± 1.15 D, respectively. According to the Amsler–Krumeich classification, 8 eyes had stage I keratoconus, 8 eyes had stage II keratoconus, and only 1 eye had stage III keratoconus. All patients had an endothelial cell count greater than 2,200 cells/mm2 at baseline. The mean central corneal thickness was 463 ± 49.5 μm. Intacs SK segments (Addition Technology, Inc., Des Plaines, IL) were inserted in 8 eyes and Keraring SI6 segments (Mediphacos Ltda., Belo Horizonte, Brazil) were inserted in 8 eyes. One eye concomitantly received both segments.
Visual Acuity Outcomes
Individual preoperative and postoperative visual acuity and refractive data for the 17 eyes are reported in Table A (available in the online version of this article). Mean visual acuity, refraction, and keratometry values at baseline and 6 months postoperatively are presented in Table 1. Uncorrected distance visual acuity significantly improved at 6 months after ICRS implantation and CXL and further improved 6 months after PRK. Corrected distance visual acuity significantly improved 6 months after ICRS implantation and CXL. However, corrected distance visual acuity remained stable after PRK. Overall, 94% of eyes had an uncorrected distance visual acuity of 20/30 or better on Snellen chart by 6 months postoperatively.
Mean Visual Acuity, Refractive, and Keratometry Data at Baseline After ICRS, CXL, and PRK
Refraction significantly improved after the three procedures (Table 1). The spherical component of refraction measured by manifest refraction significantly improved 6 months after ICRS implantation and CXL and PRK. The cylindrical component also significantly improved 6 months after ICRS implantation and CXL and PRK.
Keratometric readings measured by topography significantly improved after ICRS implantation and CXL (Table 1). Mean flat keratometry values decreased 6 months after ICRS implantation and CXL and further changed after PRK. Mean steep keratometry values decreased 6 months after ICRS implantation and CXL and changed after PRK.
Safety, Efficacy, and Complications
The safety index was calculated as the mean postoperative corrected distance visual acuity divided by the mean preoperative corrected distance visual acuity. The safety index of the three procedures and PRK 6 months postoperatively was 1.95 and 1.06, respectively.
The efficacy index was similarly calculated (mean postoperative uncorrected distance visual acuity divided by the mean preoperative corrected distance visual acuity). The efficacy index of the three procedures and PRK 6 months postoperatively was 1.78 and 0.97, respectively.
There were no serious complications after ICRS implantation. All epithelial defects healed within 4 days after CXL. Epithelial healing after PRK was within the expected range of 3 to 5 days; there were no signs of ectasia deterioration during the follow-up period after PRK. Infectious keratitis or clinically significant haze did not occur during the follow-up period.
Combined ICRS implantation and CXL has been suggested as a synergistic technique that acts on both the cornea shape and its biomechanical strength to improve visual acuity, refraction, and keratometry for patients with keratoconus.1 PRK is an alternative treatment for patients intolerant to rigid gas permeable contact lenses in selected cases of mild keratoconus. In these cases, PRK is combined with CXL to stabilize the remaining stromal bed and avoid progression of ectatic disease. This combined approach is a safe alternative for correcting minor refractive error in keratoconus and offers patients functional vision and stabilization of the ectatic disorder.3,23–25 Corrected mild refractive errors that enhance visual acuity are commonly encountered after combined ICRS implantation and CXL, mainly in mild to moderate keratoconus. There are limited reports on the safety and efficacy of PRK for visual rehabilitation of patients with keratoconus with mild refractive errors after ICRS implantation and CXL.11–15 The results of these reports are summarized in Table 2.
Reports on the Safety and Efficacy of PRK for Visual Rehabilitation of Patients With Keratoconus With Mild Refractive Errors After ICRS and CXL
In the current study, sequential ICRS implantation, CXL, and non-topography–guided PRK (performed 6 months after the other two procedures) resulted in a significant and stable improvement in visual acuity and refractive data 6 months postoperatively. Furthermore, progressive cornea flattening was observed with a significant reduction of the flat and steep keratometry values.
The treatment sequence in our case series is different from most of the aforementioned reports in which ICRS implantation was performed first and followed by combined PRK and CXL. Only Coskunseven et al.15 used the same sequence, but with different time intervals (6 months between two consecutive procedures) and using transepithelial topography-guided PRK versus the standard PRK used in our study. In our study, ICRS implantation was performed first and CXL was performed 4 weeks later. The maximum effect of ICRS implantation was observed 4 to 8 weeks after insertion, which justifies the wait for CXL. We consider it important to not perform CXL prior to 1 month after ICRS implantation to allow sufficient time for the ICRS to affect the corneal architecture. CXL without ICRS implantation had a limited effect on corneal flattening and only a mild, nonclinically significant effect was observed in keratometry reading flattening according to our previous clinical observation.6 However, CXL after ICRS implantation had a clinically significant flattening effect that was demonstrated by a significant hyperopic shift of refraction 6 months after CXL. Therefore, PRK was not performed until 6 months after CXL to allow the flattening effect to occur.
One limitation to this approach is that we used PRK ablation profiles and parameters initially designed for virgin corneas. Biophysical and chemical properties of the corneas are altered after CXL and it is unclear whether ablation outcomes identified in this study are reproducible in other cross-linked corneas. According to our nomogram, corneal irregularities associated with poor corrected distance visual acuity are always treated by ICRS implantation that, contrary to topography-guided PRK, is an additive procedure and does not impose additional risks to further weaken the cornea in keratoconus.6
In our study, corneal irregularity was treated by ICRS implantation to regularize the corneal surface and all patients achieved satisfactory corrected distance visual acuity postoperatively. Residual mild refractive errors after ICRS implantation were treated by non-topography–guided PRK because it has a better tissue-saving and predictable ablation profile than topography-guided PRK and the high degree of corneal distortion induced by ICRS implantation renders corneal aberration measurement unreliable. In addition, the high amount of corneal distortion induced by the ICRS insertion made it difficult to obtain the total wavefront measurement. In cases for which total wavefront measurement was achievable, it was considered incorrect and unreliable. Therefore, we limited treatment after ICRS implantation to non-topography–guided, nonwavefront PRK.
We found that non-topography–guided PRK allows for correction of residual refractive error that persists after combined ICRS implantation and CXL with a smaller excessive ablation risk. We set an upper limit for maximum ablation of approximately 50 μm to avoid causing additional weakening of the cornea and to maintain a sufficient residual stromal bed. Uncorrected distance visual acuity significantly improved postoperatively. The PRK safety and efficacy indices were 1.06 and 0.97 at 6 months postoperatively, respectively. The refraction parameters were entered using the same nomogram used for PRK in virgin corneas. Because of the presence of ICRS, the effective optical zone is considered to be inside the rings and the PRK optical zone was set to be 6 mm or less. The PRK transition zone was also limited to less than 1 mm because we believe that it does not significantly affect the outcomes due to the presence of the ring. Topical mitomycin C was not used to avoid unpredictable behavior in CXL and because the magnitude of refractive errors treated by PRK was considered to be mild in all cases. No corneal haze or scars were observed postoperatively.
Primary limitations of the current study were the retrospective design and relatively small number of eyes included. However, because mean outcomes were significant with this small number, it is likely that a larger sample size would further corroborate these findings. Nonetheless, it would be valuable to perform a similar study with a larger sample to more exactly characterize outcomes. Another limitation of this study is the relatively short follow-up period (6 months after PRK). Because the most cross-linked, superficial stromal tissue is removed, it is unclear whether visual acuity, refraction, and keratometry outcomes would have shown continued improvement, stabilization, or decline beyond 6 months postoperatively. Future studies including a longer follow-up period would allow for elucidation of these long-term effects. Finally, the endothelial cell count was not assessed after the combined procedures and that could be considered a safety limitation.
Our retrospective case series found that sequential ICRS implantation followed 1 month later by CXL and at least 6 months later by non-topography–guided PRK is a safe and effective therapy for improving visual acuity, refraction, and keratometry outcomes in patients with moderate keratoconus.
- Chan CC, Sharma M, Wachler BS. Effect of inferior-segment Intacs with and without C3-R on keratoconus. J Cataract Refract Surg. 2007;33:75–80. doi:10.1016/j.jcrs.2006.09.012 [CrossRef]
- Kymionis GD, Portaliou DM, Kounis GA, Limnopoulou AN, Kontadakis GA, Grentzelos MA. Simultaneous topography-guided photorefractive keratectomy followed by corneal collagen cross-linking for keratoconus. Am J Ophthalmol. 2011;152:748–755. doi:10.1016/j.ajo.2011.04.033 [CrossRef]
- Krueger RR, Kanellopoulos AJ. Stability of simultaneous topography-guided photorefractive keratectomy and riboflavin/UVA cross-linking for progressive keratoconus: case reports. J Refract Surg. 2010;26:S827–S832. doi:10.3928/1081597X-20100921-11 [CrossRef]
- Kymionis GD, Grentzelos MA, Karavitaki AE, Zotta P, Yoo SH, Pallikaris IG. Combined corneal collagen cross-linking and posterior chamber toric implantable collamer lens implantation for keratoconus. Ophthalmic Surg Lasers Imaging. 2011;42:e22–e25.
- Güell JL, Morral M, Malecaze F, Gris O, Elies D, Manero F. Collagen crosslinking and toric iris-claw phakic intraocular lens for myopic astigmatism in progressive mild to moderate keratoconus. J Cataract Refract Surg. 2012;38:475–484. doi:10.1016/j.jcrs.2011.10.031 [CrossRef]
- Fadlallah A, Dirani A, El Rami H, Cherfane G, Jarade E. Safety and visual outcome of Visian toric ICL implantation after corneal collagen cross-linking in keratoconus. J Refract Surg. 2013;29:84–89. doi:10.3928/1081597X-20130117-01 [CrossRef]
- Rabinowitz YS. Intacs for keratoconus. Curr Opin Ophthalmol. 2007;18:279–283. doi:10.1097/ICU.0b013e3281fc94a5 [CrossRef]
- Miranda D, Sartori M, Francesconi C, Allemann N, Ferrara P, Campos M. Ferrara intrastromal corneal ring segments for severe keratoconus. J Refract Surg. 2003;19:645–653.
- Kamburoglu G, Ertan A. Intacs implantation with sequential collagen cross-linking treatment in postoperative LASIK ectasia. J Refract Surg. 2008;24:S726–S729.
- Jarade E, Dirani A, Fadlallah A, Khoueir Z, Antoun J, Cherfan G. Visian toric ICL implantation for residual refractive errors after ICRS implantation and corneal collagen cross-linking in keratoconus. J Refract Surg. 2013;29:444. doi:10.3928/1081597X-20130617-01 [CrossRef]
- Kymionis GD, Grentzelos MA, Portaliou DM, et al. Photorefractive keratectomy followed by same-day corneal collagen cross-linking after intrastromal corneal ring segment implantation for pellucid marginal degeneration. J Cataract Refract Surg. 2010;36:1783–1785. doi:10.1016/j.jcrs.2010.06.044 [CrossRef]
- Iovieno A, Légaré ME, Rootman DB, Yeung SN, Kim P, Rootman DS. Intracorneal ring segments implantation followed by same-day photorefractive keratectomy and corneal collagen cross-linking in keratoconus. J Refract Surg. 2011;27:915–918. doi:10.3928/1081597X-20111103-03 [CrossRef]
- Kremer I, Aizenman I, Lichter H, Shayer S, Levinger S. Simultaneous wavefront-guided photorefractive keratectomy and corneal collagen crosslinking after intrastromal corneal ring segment implantation for keratoconus. J Cataract Refract Surg. 2012;38:1802–1807. doi:10.1016/j.jcrs.2012.05.033 [CrossRef]
- Al-Tuwairqi W, Sinjab MM. Intracorneal ring segments implantation followed by same-day topography-guided PRK and corneal collagen CXL in low to moderate keratoconus. J Refract Surg. 2013;29:59–63. doi:10.3928/1081597X-20121228-04 [CrossRef]
- Coskunseven E, Jankov MR II, Grentzelos MA, Plaka AD, Limnopoulou AN, Kymionis GD. Topography-guided transepithelial PRK after intracorneal ring segments implantation and corneal collagen CXL in a three-step procedure for keratoconus. J Refract Surg. 2013;29:54–58. doi:10.3928/1081597X-20121217-01 [CrossRef]
- Maeda N, Klyce SD, Smolek MK. Comparison of methods for detecting keratoconus using videokeratography. Arch Ophthalmol. 1995;113:870–874. doi:10.1001/archopht.1995.01100070044023 [CrossRef]
- Rabinowitz YS, Rasheed K, Yang H, Elashoff J. Accuracy of ultrasonic pachymetry and videokeratography in detecting keratoconus. J Cataract Refract Surg. 1998;24:196–201. doi:10.1016/S0886-3350(98)80200-9 [CrossRef]
- Fam HB, Lim KL. Corneal elevation indices in normal and keratoconic eyes. J Cataract Refract Surg. 2006;32:1281–1287. doi:10.1016/j.jcrs.2006.02.060 [CrossRef]
- Quisling S, Sjoberg S, Zimmerman B, Goins K, Sutphin J. Comparison of Pentacam and Orbscan IIz on posterior curvature topography measurements in keratoconus eyes. Ophthalmology. 2006;113:1629–1632. doi:10.1016/j.ophtha.2006.03.046 [CrossRef]
- Krumeich JH, Daniel J, Knülle A. Live-epikeratophakia for keratoconus. J Cataract Refract Surg. 1998;24:456–463. doi:10.1016/S0886-3350(98)80284-8 [CrossRef]
- Alió JL, Shabayek MH. Corneal higher order aberrations: a method to grade keratoconus. J Refract Surg. 2006;22:539–545.
- Jarade E. Mathematical model of corneal remodeling after intracorneal ring surgery in keratoconus. Paper presented at: Annual Meeting of the American Society of Cataract and Refractive Surgery. ; April 11, 2010. ; Boston, MA. .
- Kymionis GD, Kontadakis GA, Kounis GA, et al. Simultaneous topography-guided PRK followed by corneal collagen cross-linking for keratoconus. J Refract Surg. 2009;25:S807–S811. doi:10.3928/1081597X-20090813-09 [CrossRef]
- Kanellopoulos AJ. Comparison of sequential vs same-day simultaneous collagen cross-linking and topography-guided PRK for treatment of keratoconus. J Refract Surg. 2009;25:S812–S818. doi:10.3928/1081597X-20090813-10 [CrossRef]
- Stojanovic A, Zhang J, Chen X, Nitter TA, Chen S, Wang Q. Topography-guided transepithelial surface ablation followed by corneal collagen cross-linking performed in a single combined procedure for the treatment of keratoconus and pellucid marginal degeneration. J Refract Surg. 2010;26:145–152. doi:10.3928/1081597X-20100121-10 [CrossRef]
Mean Visual Acuity, Refractive, and Keratometry Data at Baseline After ICRS, CXL, and PRK
||6 Months After ICRS-CXL
||6 Months After PRK
|Mean ± SD
||Mean ± SD
||Mean ± SD
||1.17 ± 0.38
||0.45 ± 0.11
||0.18 ± 0.06
||0.44 ± 0.09
||0.17 ± 0.08
||0.15 ± 0.05
||−5.45 ± 1.64
||−2.57 ± 1.15
||−1.1 ± 0.41
||3.86 ± 1.15
||2.13 ± 1.11
||0.98 ± 0.37
|K flat (D)
||46.51 ± 2.12
||44.33 ± 2.29
||43.01 ± 1.75
|K steep (D)
||50.76 ± 2.19
||47.41 ± 2.91
||46.61 ± 2.17
|Thinnest corneal thickness (μm)
||463 ± 49.50
||476 ± 50.80
||457 ± 53.20
Reports on the Safety and Efficacy of PRK for Visual Rehabilitation of Patients With Keratoconus With Mild Refractive Errors After ICRS and CXL
||Results at last F/U visits
|Kymionis et al.16
||Combined PRK/CXL after ICRS implantation (time interval = 12 m)
||Standard PRK procedure (Allegretto 400-Hz laser platform)
||F/U = 9 months; UDVA improved from counting fingers to 20/25; CDVA improved from 20/40 to 20/25; keratometry values (steep/flat) improved from 46.73/38.67 to 44.92/39.01
|Iovieno et al.17
||Combined PRK/CXL after ICRS implantation (time interval = 21 ± 8.6 m)
||Standard PRK procedure (VISX Star S4 IR laser platform)
||F/U = 6 months; standard PRK procedure; mean UDVA improved to −0.4 ± 0.2 logMAR; mean SE refraction decreased to 0.10 ± 1.30; keratometry and total aberrations also improved
|Kremer et al.18
||Combined PRK/CXL after ICRS implantation (time interval ≥ 6 m)
||Wavefront-guided PRK (VISX Star S4 IR laser platform)
||F/U = 12 months; mean decimal UDVA improved from 0.20 ± 0.12 to 0.55 ± 0.15; mean decimal CDVA improved from 0.58 ± 0.13 to 0.77 ± 0.17; mean cylinder decreased from −3.60 ± 1.70 to −1.30 ± 1.10 D
|Al-Tuwairqi & Sinjab19
||Combined PRK/CXL after ICRS implantation (mean time interval = 6 m [3 to 11 m])
||Topography-guided PRK (Schwind Amaris laser platform)
||F/U = 6 months; UDVA improved from 0.7 ± 0.32 to 0.08 ± 0.08 logMAR; CDVA improved from 0.16 ± 0.19 to 0.02 ± 0.04 logMAR; mean spherical component decreased from −3.65 ± 3.08 to 0.06 ± 1.6 D; mean astigmatism component decreased from −3.31 ± 1.5 to −0.98 ± 0.75 D; mean average keratometry values decreased from 47.28 ± 1.99 to 41.42 ± 3.22 D
|Coskunseven et al.20
||3 steps: ICRS then CXL then PRK (time interval = 6 m between consecutive steps)
||Topography-guided transepithelial PRK (Allegretto 400-Hz laser platform)
||F/U = 6 months; UDVA improved from 1.14 ± 0.36 to 0.25 ± 0.13 logMAR; CDVA improved from 0.75 ± 0.24 to 0.13 ± 0.06 logMAR; mean spherical equivalent refraction decreased from −5.66 ± 5.63 to −0.98 ± 2.21 D; mean steep/flat keratometry values decreased from 54.65 ± 5.80/47.80 ± 3.97 to 45.99 ± 3.12/44.69 ± 3.19 D