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Accelerated 15 mW pulsed-light crosslinking to treat progressive keratoconus: Two-year clinical results Cosimo Mazzotta, MD, PhD, Stefano Baiocchi, MD, Simone Alex Bagaglia, MD, Mario Fruschelli, MD, Alessandro Meduri, MD, PhD, Miguel Rechichi, MD
Purpose: To assess the clinical and microstructural results of accelerated 15 mW pulsed-light corneal crosslinking (CXL) to treat progressive keratoconus. Setting: Siena Crosslinking Center, Siena, Italy. Design: Prospective case series. Methods: After epithelium removal (with Epi-Clear) and 10 minutes stromal soaking with riboflavin 0.1% hydroxypropyl methylcellulose solution, all eyes had 15 mW/cm2 pulsedlight epithelium-off accelerated CXL for 6 minutes of ultraviolet-A (UVA) irradiation (1 second on/1 second off), maintaining a total UVA exposure of 12 minutes at a fluence of 5.4 J/cm2. The 2-year follow-up examination included uncorrected (UDVA) and corrected (CDVA) distance visual acuities, Scheimpflug tomography, in vivo confocal microscopy (IVCM), and spectraldomain optical coherence tomography (SD-OCT).
C
onventional riboflavin ultraviolet-A (UVA)induced corneal crosslinking (CXL) with epithelium removal is an evidence-based treatment with documented long-term efficacy in stabilizing progressive keratoconus and secondary ectasia in a series of nonrandomized and randomized clinical trials.1–4 It reduces the need for corneal transplantation in patients affected by progressive keratoconus or secondary ectasia.5 The standard irradiance of 3 mW/cm2 for 30 minutes was found to be effective in stiffening the cornea in primary and iatrogenic keratectasia cases.6 However, it also has potential in sterilizing antibiotic-resistant infectious keratitis caused by the cytotoxic effect of the reactive oxygen species generated during the CXL process,7 otherwise known as photoactivated chromophore CXL.8,9
Results: The study comprised 132 eyes of 96 patients (mean age 23.7 years G 4.3 [SD]) with stage II keratoconus. The change in UDVA and CDVA was statistically significant, from 0.51 G 0.106 logarithm of the minimum angle of resolution (logMAR) at baseline to 0.309 G 0.074 logMAR (P Z .0001) and 0.271 G 0.144 logMAR at baseline to 0.135 G 0.100 logMAR (P Z .0023), respectively. Coma values measured by Scheimpflug analysis showed a statistically significant improvement beginning with the first postoperative month (P Z .0004). The IVCM scans documented basal epithelial healing occurring 72 hours after treatment associated with the presence of subepithelial nerves. The SD-OCT scans performed in the central 6.0 mm of corneal diameter documented a demarcation line at a mean depth of 280 G 32 mm. Conclusion: The 15 mW/cm2 pulsed-light epithelium-off accelerated CXL was effective and safe, stabilizing keratoconus progression through 2 years of follow-up. J Cataract Refract Surg 2017; 43:1081–1088 Q 2017 ASCRS and ESCRS
Because the conventional CXL procedure requires a long treatment time (approximately 1 hour),6 accelerated CXL protocols have been proposed to shorten CXL treatment time,10–15 improving the patient’s comfort. According to equal-dose principles stated in the Bunsen-Roscoe Law,16 setting UVA power at 9 mW/cm2 10 minutes, 30 mW/cm2 3 minutes, 18 mW/cm2 5 minutes, and 45 mW/cm2 2 minutes while maintaining a constant energy (fluence) of 5.4 J/cm2 can achieve the same effect as the conventional Dresden protocol of 3 mW/cm2 for 30 minutes.17–19 A recent study20 has shed light on the chain of chemical events occurring during the photochemical activation of riboflavin with UV light, highlighting the importance of corneal oxygenation during treatment. With pulsed or fractionated UVA
Submitted: March 17, 2017 | Final revision submitted: May 1, 2017 | Accepted: May 8, 2017 From the Siena Crosslinking Center (Mazzotta), the Department of Medicine (Mazzotta, Baiocchi, Bagaglia, Fruschelli), Surgery and Neurosciences, Ophthalmology Unit, Siena University, Siena, the Department of Surgical Specialities (Meduri), Ophthalmology Clinic, Messina University, Messina, and the Eye-Center (Rechichi), Catanzaro, Italy. Corresponding author: Cosimo Mazzotta, MD, PhD, Siena Crosslinking Center and Department of Medicine, Surgery and Neurosciences, Ophthalmology Unit, University of Siena, Viale M. Bracci 8, Siena, 53100, Italy. E-mail: [email protected]. Q 2017 ASCRS and ESCRS Published by Elsevier Inc.
0886-3350/$ - see frontmatter http://dx.doi.org/10.1016/j.jcrs.2017.05.030
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Figure 1. The 15 mW/cm2 to 5.4 J/cm2 accelerated CXL surgical technique. A: Removal of corneal epithelial layers by a disposable epi-keratome. B: Corneal epithelium removed from the desired area of 8.0 mm. C: Riboflavin 0.1% dextran-free HPMC stromal soaking. D: Surgical microscope view (10 magnification) of distinct and homogeneous riboflavin 0.1% stromal soaking. E: The UVA pulsed emission under remote control eye tracking. F: Therapeutic soft contact lens application after topical antibiotic medication.
radiation, CXL efficiency might be improved by allowing rediffusion of oxygen during UVA-light-exposure pauses.20 A preclinical laboratory study by Krueger et al.21 found that riboflavin 0.1% with 15 mW/cm2 UVA exposure, using an equivalent total energy exposure of 5.4 J/cm2, was as effective as conventional 3 mW/cm2 CXL and 9 mW/cm2 accelerated CXL in biomechanical strengthening of the cornea. Moreover, when fractionating the UVA exposure with multiple cycles of pulsing light, the corneal extensiometry was equally as effective as without pulsing the light. The study established that in theory, pulsed UVA delivery should improve the degree of CXL, especially with the faster higher irradiance exposures during which oxygen is consumed more quickly.22 In vivo confocal microscopy (IVCM) analysis proved that fractionating UVA exposure by pulsing the light provides better penetration of the treatment, as shown in vivo by Mazzotta et al.23 and recently confirmed by Peyman et al.24 Deeper cell viability is reachable, prolonging exposure time while maintaining the same energy dose delivered into the corneal tissue.23
The present study evaluated the induced corneal microstructural changes (biomicroscopic, corneal spectraldomain optical coherence tomography [SD-OCT], IVCM) and the 2-year functional results (uncorrected [UDVA] and corrected [CDVA] distance visual acuities, tomography) after 15 mW/cm2 pulsed-light accelerated CXL at the standard 5.4 J/cm2 fluence performed in a cohort of patients with progressive stage II keratoconus. The procedure was based on data reported in the aforementioned laboratory study.21 PATIENTS AND METHODS This prospective interventional study evaluated eyes with progressive grade II keratoconus. It followed the tenets of the Declaration of Helsinki, with data collected at the Siena Crosslinking Center, Siena, Italy. After receiving an explanation of the nature and objective of the treatment, all patients provided informed consent. Inclusion criteria were grade II keratoconus (Amsler-Krumeich grading25) with a documented clinical and instrumental progression in the past 6 months of observation, expressed by an increased maximum keratometry value of 1.0 diopter (D) or more, minimum corneal thickness reduction of 10 mm or more, and a worsening of UDVA and CDVA of at least of C1.0 logarithm of the minimum
Figure 2. Postoperative corneal biomicroscopic examination performed on the third day after treatment before and immediately after therapeutic contact lens removal. A: Complete reepithelialization without epithelial defects is shown by riboflavin dye instilled via a riboflavin preservative-free drop (B).
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Figure 3. A: Corneal biomicroscopy performed 1 month after 15 mW/cm2 pulsed light-accelerated CXL treatment shows a distinct demarcation line (yellow arrow). B: The scan performed with SD-OCT confirmed the demarcation line associated with increased reflectivity of the crosslinked stroma (yellow arrow).
angle of resolution (logMAR) (R0.1 decimal equivalent or R0.5 spherical equivalent). Exclusion criteria were corneal opacities or scars, history of herpes simplex virus and other infectious keratitis, autoimmune diseases, and pregnancy. Patients who did not meet the clinical and instrumental keratoconus inclusion criteria were also excluded. Patient Assessment Patients had a full ophthalmologic examination including UDVA, CDVA, slitlamp evaluation, tonometry, and fundoscopy. Keratoconus was evaluated by Scheimpflug corneal tomography (Sirius, Costruzione Strumenti Oftalmici) that provided K values and wavefront analysis measurement, IVCM (Heidelberg Retina Tomograph II, Rostock Cornea Module), anterior segment OCT (iVue, Optovue, Inc.), and endothelial cell count (ECC) (I-Konan Noncon Robo, Konan Medical, Inc.). Surgical Technique Pulsed-light 15 mW/cm2 accelerated CXL protocol at 5.4 J/cm2 standardized fluence was performed under sterile operating
conditions using topical anesthesia oxybuprocaine hydrochloride 0.2% anesthetic drops. Topical pilocarpine 2.0% was administered 20 minutes before treatment. After application of a closed-valve eyelid speculum, the corneal epithelium was removed by an epi-Bowman keratectomy performed with a disposable epi-keratome (Epi-Clear, Orca Surgical) in the central 8.0 mm area (Figure 1, A and B). After epithelium removal, the corneal stroma was soaked for 10 minutes with a riboflavin 0.1% hydroxypropyl methylcellulose (HPMC) dextran-free solution (Vibex Rapid, Avedro, Inc.) (Figure 1, C and D). The riboflavin drops were instilled every minute for 10 minutes, covering the entire corneal surface (both the deepithelialized region and the limbus). Riboflavin stromal saturation was confirmed at the slitlamp before UVAlight irradiation was started. The UVA irradiation was performed with a KXL I UV-A illuminator (Avedro, Inc.) using a 15 mW/cm2 UVA power with pulsed-light emission (1 second on/1 second off) to obtain 12 minutes of UVA irradiation on balance while delivering a standard energy dose of 5.4 J/cm2 (Figure 1, E) over a total treatment time of 22 minutes.
Figure 4. Postoperative IVCM scans 48 to 72 hours after treatment. A: A regular basal epithelial cell mosaic with homogeneous cellularity and well distinct cell borders 30 days after treatment. B: Subepithelial plexus scan showed reduced and damage subepithelial nerve plexus fibers that were not completely lost immediately after treatment. C: Corneal reinnervation was rapid based on the subepithelial nerve plexus nerve fibers. Bright nerve fibers are evident. D: Keratocyte apoptosis in the anterior stroma associated with lacunar corneal edema, hyperreflective trabecular mesh aspect of ECM. E: Keratocytes repopulation with associated lacunar edema reduction and activated keratocytes nuclei 30 days after contact lens removal (F).
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Figure 5. The IVCM analysis showed undamaged cells with slight pleomorphism after the treatment. A: Preoperative image. B: Postoperative image.
After UVA irradiation, the eye was washed with a balanced salt solution, medicated with moxifloxacin and cyclopentolate drops, and dressed with a therapeutic soft contact lens (Figure 1, F). Therapeutic contact lenses were removed 72 hours after the treatment if complete epithelial healing was documented at biomicroscopic examination (Figure 2, A and B). An SD-OCT corneal scan was performed 1 month after treatment to detect demarcation line depth (Figure 3). The IVCM evaluation of the basal corneal epithelium, subepithelial nerve plexus, and corneal stroma keratocytes apoptosis was performed 3 days after treatment with the contact lens on and 30 days after treatment (Figure 4). Statistical Analysis A 2-tailed paired-samples Student t test was used to compare each baseline measurement with the respective follow-up measurement. Differences with a P value less than 0.05 were considered significant. Data were collected and analyzed using Prism software (version 6.0, Graph Pad Software, Inc.).
Postoperative corneal biomicroscopic examination performed on the third day after treatment showed a clear cornea, little edema, and no opacities before and immediately after therapeutic contact lens removal (Figure 2). Seventy-two hours after epithelium removal (Figure 2, A), all patients had complete reepithelialization as shown by the riboflavin dye test instilled via a riboflavin preservative-free drop (Droptest, IROS) (Figure 2, B). Biomicroscopy and Spectral-Domain Optical Coherence Tomography Demarcation Lines
Corneal biomicroscopy performed 1 month after treatment showed a distinct demarcation line (Figure 3, A). Comparative SD-OCT scan confirmed a demarcation line associated with increased reflectivity of the crosslinked stroma that measured at a mean of 280 G 32 mm depth (range 248 to 312 mm) (Figure 3, B). In Vivo Confocal Microscopy
RESULTS The study comprised 132 eyes of 96 patients. The mean age of the 76 men and 20 women was 23.7 years G 4.3 (SD). All patients enrolled in the treatment protocol completed the 24-month follow-up.
Postoperative IVCM scans showed a regular epithelial healing occurring 72 hours after treatment. Native epithelial cells were large with slightly defined cell borders, often oriented in a whorl-like fashion (Figure 4, A). A regular basal epithelial cells mosaic with homogeneous cellularity and
Table 1. Overall study results. 1 Mo Postop Parameter UDVA (logMAR) CDVA (logMAR) K max (D) Coma (mm) CCT (mm)
3 Mo Postop
Preop Mean
Mean ± SD
D
P Value*
Mean ± SD
D2
P Value*
0.51 G 0.106 0.27 G 0.144 48.33 G 2.51 1.01 G 0.02 453.3 G 24.01
0.49 G 0.131 0.22 G 0.152 47.93 G 2.44 0.98 G 0.0195 420.0 G 23.63
0.02 0.05 0.40 0.037 33.3
.743 .0289 .1149 .0004† .0001†
0.38 G 0.094 0.71 G 0.06 47.56 G 1.911 0.955 G 0.015 441.7 G 22.59
0.13 0.10 0.77 0.062 11.6
.0032† .0007† .0835 .0001† .2530
D Z change; CCT Z central corneal thickness; CDVA Z corrected distance visual acuity; K max Z maximum keratometry; logMAR Z logarithm of the minimum angle of resolution; UDVA Z uncorrected distance visual acuity Means G SD *Of change † Statistically significant
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clear distinct cell borders were present 30 days after treatment (Figure 4, B). Subepithelial plexus scans showed rarefaction and damage of subepithelial nerve plexus fibers, although the fibers were not completely lost, 3 days postoperatively (Figure 4, C). The subepithelial nerve plexus nerve fibers showed a rapid tendency to corneal reinnervation 30 days postoperatively, with bright nerve fibers evident (Figure 4, D). The 15 mW/cm2 pulsed-light CXL induced keratocyte apoptosis in the anterior stroma associated with lacunar corneal edema, hyperreflective trabecular meshwork aspect of extracellular matrix (ECM), and apoptotic bodies (Figure 4, E). Gradual keratocyte repopulation with concomitant lacunar edema reduction and presence of activated keratocytes nuclei was recorded 30 days after contact lens removal (Figure 4, F). The corneal endothelium was unaltered after the treatment (Figure 5). The mean preoperative endothelial cell density was 2434 cells/mm2 (range 2182 to 2826 cells/mm2). The mean ECC at 24 months was 2385 cells/mm2 (range 2175 to 2985 cells/mm2).
DISCUSSION At present, CXL might be the de facto first choice therapy to halt the progression of the early stages of corneal ectasia, showing good long-term visual results and few complications. Regarding the therapeutic benefit of CXL in stabilizing corneal ectasia progression,1–3 the early diagnosis of keratoconus and secondary corneal ectasia are mandatory. The physical concept stated in Bunsen-Roscoe’s law of reciprocity16 allowed us to study high-irradiance CXL protocols according to the so-called equal-dose principle.17–19 In our recent studies of different accelerated CXL protocols with continuous and fractionated (pulsed) high-irradiance UVA light exposure,20,23,26 IVCM analysis showed significant differences in keratocyte apoptosis (ie, treatment penetration) that might have significant biomechanical and clinical implications in terms of long-term ectasia stabilization and functional outcomes of treatment. The IVCM and corneal OCT data verifying the postoperative cells apoptosis, nerve disappearance, and the demarcation lines induced by accelerated CXL, showed a mean treatment penetration of 150 mm (range 140 to 200 mm measured from epithelial surface) after 30 mW/cm2 continuous light-accelerated CXL and of 220 mm (range 200 to 250 mm measured from the epithelial surface) after fractionated- or pulsed-light accelerated CXL.23 As per biomechanical studies by Shumacher et al.,27 CXL treatment should cover at least 200 mm of the corneal stroma. Contradictory results are reported in the literature28 after accelerated CXL protocols using UVA power of 9 mW,10–15 18 mW,29 and 30 mW.30 Accelerated CXL with irradiance of 9 mW/cm2 for 10 minutes was shown to be effective in stabilizing topographic parameters after a 12-month follow-up in corneas with mild to moderate keratoconus.10–15 After treatment, the UDVA improved and all tested corneal parameters stabilized. Moreover, 9 mW/cm2 accelerated CXL was safe for the corneal endothelium, stabilizing the progression of keratoconus and iatrogenic ectasia with a significant reduction in topographic K values and a significant increase in CDVA, which is comparable to results with conventional 3 mW/cm2 CXL over a midterm (2 year) follow-up.12 In a recent study,13 accelerated CXL with 18 mW/cm2 UVA power yielded less topographic flattening than conventional CXL. Refractive and visual results of accelerated CXL using continuous-light and pulsed-light
Functional Outcomes
Table 1 shows the overall study results. The mean UDVA showed a clinical improvement from baseline to the 24-month follow-up (P Z .0001). The difference became statistically significant by the third month (P Z .0032) (Figure 6). The mean CDVA showed a clinical improvement that became statistically significant by the first postoperative month (P Z .0289). The difference between baseline and the 24-month follow-up was statistically significant (P Z .0023) (Figure 6). The change in the mean maximum K values from baseline to the 24-month follow-up was not statistically significant (P Z .66) (Figure 7). The reduction in the mean coma values was statistically significant from the first postoperative month (P Z .0004). The difference between baseline and the 24-month follow-up was statistically significant as well (P ! .0001) (Figure 7). The reduction in the mean minimum corneal thickness from baseline to the first postoperative month (P ! .0001) was statistically significant. However, the difference became statistically insignificant by the third postoperative month (P Z .25) and remained so at the 24-month follow-up (P Z .50) (Figure 7). Table 1. (Cont.) 6 Mo Postop
12 Mo Postop
24 Mo Postop
Mean ± SD
D3
P Value*
Mean ± SD
D4
P Value*
Mean ± SD
0.32 G 0.08 0.10 G 0.11 47.08 G 1.60 0.956 G 0.014 444.4 G 11.88
0.15 0.105 1.25 0.061 5.3
!.0001† .0012† .0254† !.0001† .138
0.33 G 0.05 0.07 G 0.096 47.21 G 1.707 0.95 G 0.193 452.0 G 14.55
0.18 0.12 1.12 0.067 0.8
!.0001† .0005† .0372† !.0001† .925
0.309 G 0.074 0.135 G 0.144 47.91 G 1.56 0.94 G 0.014 458.6 G 12.83
D5
P Value*
0.21 0.136 0.42 0.082 5.03
!.0001† .0023† .1795 !.0001† .503
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Figure 6. The UDVA and CDVA (CDVA Z corrected distance visual acuity; LogMAR Z logarithm of the minimum angle of resolution; UDVA Z uncorrected distance visual acuity).
Figure 7. Mean maximum K values, coma values, minimum CCT (CCT Z central corneal thickness; Kmax Z maximum keratometry).
treatment at 30 mW/cm2 were similar to those of conventional 3 mW/cm2 CXL after 12-months of follow-up.30 Although the method provided faster recovery and better patient comfort, the depth of the demarcation line after 30 mW/cm2 was less than 200 mm of corneal stroma, which might be the limit with this accelerated protocol.23–26 In a recent study, Sadoughi et al.31 compared conventional 3 mW CXL and 9 mW accelerated CXL in patients with bilateral progressive keratoconus. Fellow eyes were randomly assigned to conventional CXL or accelerated CXL. After 12 months of follow-up, the refractive, visual, keratometric, and aberrometric outcomes were similar between the 2 treatments. In our opinion, to ensure long-lasting stability of keratoconus and secondary ectasia, the UVA power setting and exposure time should be targeted to allow a treatment penetration of at least at 250 mm, overcoming the anterior portion of the corneal stroma because the anterior 40% of the central corneal stroma represents the strongest region of the cornea (stiff cornea), whereas the posterior 60% of the stroma is at least 50% weaker.31–33 Moreover, according to Kohlhaas et al.,34 the CXL treatment significantly stiffened the cornea in the anterior 200 mm only. The depth-dependent stiffening effect was
explained by the absorption behavior of UVA in the riboflavin-treated cornea, and approximately 70% of the UVA irradiation was absorbed within the anterior 200 mm and only 20% in the next 200 mm. This might affect long-term stabilization of ectasia based on different crosslinking penetration rates. To achieve this goal, while maintaining a standard 5.4 J/cm2 dose delivery, the UVA power can be calibrated between 9 mW/cm2 and 15 mW/cm2 with continuous or pulsed light.34 A laboratory study by Krueger et al.21 found that effective CXL required the presence of oxygen in addition to sufficient penetration of riboflavin and UVA exposure. It was determined that accelerated CXL was as efficacious as the conventional protocol and a better strain (elongation) test was achieved with 15 mW/cm2 at 5.4 J/cm2 fluence with continuous-light (6 minutes) or pulsed-light (12 minutes; 1 second on/1 second off) UVA exposure. Microstructural analysis after the first clinical application of this protocol found a mean demarcation line of 280 G 32 mm with no endothelial damage or other side effects. The 2-year functional outcomes were similar and comparable with those of conventional 3 mW/5.4 J/cm2 CXL and 9 mW/5.4 J/cm2 accelerated CXL. However, some differences emerged in pulsed-light versus continuous-light use.22,23,25 With the
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15 mW/5.4 J/cm2 accelerated CXL protocol, the treatment time is short and the pulsed light maintained, achieving a treatment penetration that is almost comparable with that of conventional 3 mW CXL and 9 mW/cm2 continuous-light accelerated CXL.10,11 In addition, the 15 mW/5.4 J/cm2 accelerated CXL protocol caused less subepithelial plexus nerve damage, as documented by the incomplete loss of nerve fibers on early postoperative IVCM scans. Furthermore, in conventional CXL the UDVA and CDVA are often worse in the first 1 to 3 months postoperatively because of variable glare disability related to stromal edema, keratocytes loss, and thin epithelium.35 In contrast, the 15 mW pulsed-light accelerated CXL protocol at a 5.4 J/cm2 energy dose resulted in less glare disability with no statistically significant visual acuity decay in the first 3 postoperative months, perhaps because postoperative edema was less. Based on our study results, 15 mW/cm2 pulsed-light accelerated CXL is a safe and effective option to stabilize keratoconus progression. Over the 2-year follow-up, there was a statistically significant improvement in UDVA and CDVA with a distinct tendency toward a general improvement in all clinical and instrumental parameters and without adverse events or complications. As a practical consideration, we have no hesitation accepting the opinion of Krueger et al.21 regarding the advantages in clinical applications of accelerated CXL, not only because of the reduction in treatment time and increased patient’s comfort, but also because of the reduced postoperative glare disability, reduced subepithelial nerve plexus nerves damage, less postoperative haze36,37 on slitlamp examination compared with the Dresden protocol,1,4 and lack of endothelial damage with substantial keratoconus stabilization. The present study confirms the clinical safety of 15 mW accelerated CXL pulsed-light treatment with epithelium removal and its efficacy based on the stabilization of keratoconus progression with no complications during a 24-month follow-up.
WHAT WAS KNOWN Preclinical laboratory data show that riboflavin 0.1% with 15 mW/cm2 UVA exposure, using an equivalent total energy exposure of 5.4 J/cm2 is as effective as conventional 3 mW/cm2 CXL and 9 mW/cm2 accelerated CXL in the biomechanical strengthening of the cornea.
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WHAT THIS PAPER ADDS The study confirmed the clinical safety and efficacy of 15 mW/cm2 pulsed light-accelerated CXL protocol in stabilizing keratoconus progression during a 24-month follow-up. There were no complications.
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REFERENCES 1. Raiskup F, Theuring A, Pillunat LE, Spoerl E. Corneal collagen crosslinking with riboflavin and ultraviolet-A light in progressive keratoconus: ten-year results. J Cataract Refract Surg 2015; 41:41–46 2. O’Brart DPS, Patel P, Lascaratos G, Wagh VK, Tam C, Lee J, O’Brart NA. Corneal Cross-linking to halt the progression of
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keratoconus and corneal ectasia: seven-year follow-up. Am J Ophthalmol 2015; 160:1154–1163 Caporossi A, Mazzotta C, Baiocchi S, Caporossi T. Long-term results of riboflavin ultraviolet A corneal collagen cross-linking for keratoconus in Italy: the Siena Eye Cross Study. Am J Ophthalmol 2010; 149:585–593 Wittig-Silva C, Chan E, Islam FMA, Wu T, Whiting M, Snibson GR. A randomized, controlled trial of corneal collagen cross-linking in progressive keratoconus; three-year results. Ophthalmology 2014; 121:812–821. Available at: http://www.aaojournal.org/article/S0161-6420(13)01004-X/pdf. Accessed June 6, 2017 Godefrooij DA, Gans R, Imhof SM, Wisse RPL. Nationwide reduction in the number of corneal transplantations for keratoconus following the implementation of cross-linking. Acta Ophthalmol 2016; 94:675–678 Spoerl E, Mrochen M, Sliney D, Trokel S, Seiler T. Safety of UVA–riboflavin cross-linking of the cornea. Cornea 2007; 26:385–389 Iseli HP, Thiel MA, Hafezi F, Kampmeier J, Seiler T. Ultraviolet A/riboflavin corneal cross-linking for infectious keratitis associated with corneal melts. Cornea 2008; 27:590–594 Tabibian D, Richoz O, Riat A, Schrenzel J, Hafezi F. Accelerated photoactivated chromophore for keratitis–corneal collagen cross-linking as a firstline and sole treatment in early fungal keratitis. J Refract Surg 2014; 30:855–857 Tabibian D, Mazzotta C, Hafezi F. PACK-CXL: corneal cross-linking in infectious keratitis. Eye Vis 2016; 3:11. Available at: https://www.ncbi.nlm.nih .gov/pmc/articles/PMC4836155/pdf/40662_2016_Article_42.pdf. Accessed June 6, 2017 Elbaz U, Shen C, Lichtinger A, Zauberman NA, Goldich Y, Chan CC, Slomovic AR, Rootman DS. Accelerated (9-mW/cm2) corneal collagen crosslinking for keratoconusda 1-year follow-up. Cornea 2014; 33:769–773 € o €ktas¸ E, Duru N, Ozk €se A, Atas¸ M, Yuvacı _I, Arifog lu HB, Ulusoy DM, Go Zararsız G. Accelerated corneal crosslinking for treatment of progressive keratoconus in pediatric patients. Eur J Ophthalmol 2017; 27:319–325 Marino GK, Torricelli AAM, Giacomin N, Santhiago MR, Espindola R, Netto MV. Accelerated corneal collagen cross-linking for postoperative LASIK ectasia: two-year outcomes. J Refract Surg 2015; 31:380–384 Chow VWS, Chan TCY, Yu M, Wong VWY, Jhanji V. One-year outcomes of conventional and accelerated collagen crosslinking in progressive keratoconus. Sci Rep 2015; 5:14425. Available at: http://www.ncbi.nlm.nih.gov/pmc /articles/PMC4585888/pdf/srep14425.pdf. Accessed June 6, 2017 Hashemian H, Jabbarvand M, Khodaparast M, Ameli K. Evaluation of corneal changes after conventional versus accelerated corneal crosslinking: a randomized controlled trial. J Refract Surg 2014; 30:837–842 Shetty R, Pahuja NK, Nuijts RMMA, Ajani A, Jayadev C, Sharma C, Nagaraja H. Current protocols of corneal collagen cross-linking: visual, refractive, and tomographic outcomes. Am J Ophthalmol 2015; 160:243–249 Brindley GS. The Bunsen-Roscoe law for the human eye at very short durations. J Physiol 1952; 118:135–139. Available at: http://onlinelibrary. wiley.com/doi/10.1113/jphysiol.1952.sp004779/epdf. Accessed June 6, 2017 Wernli J, Schumacher S, Spoerl E, Mrochen M. The efficacy of corneal crosslinking shows a sudden decrease with very high intensity UV light and short treatment time. Invest Ophthalmol Vis Sci 2013; 54:1176–1180. Available at: http://iovs.arvojournals.org/article.aspx?articleidZ2127751. Accessed June 6, 2017 Schumacher S, Oeftiger L, Mrochen M. Equivalence of biomechanical changes induced by rapid and standard corneal cross-linking, using riboflavin and ultraviolet radiation. Invest Ophthalmol Vis Sci 2011; 52:9048–9052. Available at: http://iovs.arvojournals.org/article.aspx?articleidZ2187529. Accessed June 6, 2017 Kamaev P, Friedman MD, Sherr E, Muller D. Photochemical kinetics of corneal cross-linking with riboflavin. Invest Ophthalmol Vis Sci 2012; 53:2360–2367. Available at: http://iovs.arvojournals.org/article.aspx? articleidZ2188913. Accessed June 6, 2017 Mazzotta C, Moramarco A, Traversi C, Baiocchi S, Iovieno A, Fontana L. Accelerated corneal collagen cross-linking using topography-guided UV-A energy emission: preliminary clinical and morphological outcomes. J Ophthalmol 2016:2031031. Available at: http://downloads.hindawi.com /journals/joph/2016/2031031.pdf. Accessed June 6, 2017 Krueger RR, Herekar S, Spoerl E. First proposed efficacy study of high versus standard irradiance and fractionated riboflavin/ultraviolet A cross-linking with equivalent energy exposure. Eye Contact Lens 2014; 40:353–357 Kling S, Richoz O, Hammer A, Tabibian D, Jacob S, Agarwal A, Hafezi F. Increased biomechanical efficacy of corneal cross-linking in thin corneas due to higher oxygen availability. J Refract Surg 2015; 31:840–846
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23. Mazzotta C, Hafezi F, Kymionis G, Caragiuli S, Jacob S, Traversi C, Barabino S, Randleman JB. In vivo confocal microscopy after corneal collagen crosslinking. Ocul Surf 2015; 13:298–314 24. Peyman A, Nouralishahi A, Hafezi F, Kling S, Peyman M. Stromal demarcation line in pulsed versus continuous light accelerated corneal cross-linking for keratoconus. J Refract Surg 2016; 32:206–208 €re Kera25. Krumeich JH, Daniel J. Lebend-Epikeratophakie und Tiefe Lamella toplastik zur Stadiengerechten chirurgischen Behandlung des Keratokonus (KK) I-III [Live-epikeratophakia and deep lamellar keratoplasty for stagerelated treatment of keratoconus]. Klin Monatsbl Augenheilkd 1997; 211:94–100 26. Mazzotta C, Traversi C, Caragiuli S, Rechichi M. Pulsed vs continuous light accelerated corneal collagen crosslinking: In vivo qualitative investigation by confocal microscopy and corneal OCT. Eye 2014; 28:1179–1183. Available at: http://www.nature.com/eye/journal/v28/n10/pdf/eye2014163a.pdf. Accessed June 6, 2017 27. Schumacher S, Mrochen M, Wernli J, Bueeler M, Seiler T. Optimization model for UV-riboflavin corneal cross-linking. Invest Ophthalmol Vis Sci 2012; 53:762–769. Available at: http://iovs.arvojournals.org/article.aspx ?articleidZ2188118. Accessed June 6, 2017 28. Chan TCY, Chow VWS, Jhanji V, Wong VWY. Different topographic response between mild to moderate and advanced keratoconus after accelerated collagen cross-linking. Cornea 2015; 34:922–927 29. Hashemi H, Miraftab M, Seyedian MA, Hafezi F, Bahrmandy H, Heidarian S, Amanzadeh K, Nikbin H, Fotouhi A, Asgari S. Longterm results of an accelerated corneal cross-linking protocol (18 mW/cm2) for the treatment of progressive keratoconus. Am J Ophthalmol 2015; 160:1164–1170 30. Mazzotta C, Traversi C, Paradiso AL, Latronico ME, Rechichi M. Pulsed light accelerated crosslinking versus continuous light accelerated crosslinking: one-year results. J Ophthalmol 2014:604731. Available at: http://downloads .hindawi.com/journals/joph/2014/604731.pdf. Accessed June 6, 2017 31. Sadoughi MM, Einollahi B, Baradaran-Rafii A, Roshandel D, Hasani H, Nazeri M. Accelerated versus conventional corneal collagen cross-linking in patients with keratoconus: an intrapatient comparative study. Int Ophthalmol 2016 Dec 29 [Epub ahead of print] 32. Randleman JB, Dawson DG, Grossniklaus HE, McCarey BE, Edelhauser HF. Depth-dependent cohesive tensile strength in human
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34.
35.
36.
37.
donor corneas: implications for refractive surgery. J Refract Surg 2008; 24:S85–S89 Smolek MK, McCarey BE. Interlamellar adhesive strength in human eyebank corneas. Invest Ophthalmol Vis Sci 1990; 31:1087–1095. Available at: http://iovs.arvojournals.org/article.aspx?articleidZ2160455. Accessed June 6, 2017 Kohlhaas M, Spoerl E, Schilde T, Unger G, Wittig C, Pillunat LE. Biomechanical evidence of the distribution of cross-links in corneas treated with riboflavin and ultraviolet A light. J Cataract Refract Surg 2006; 32:279–283 Mazzotta C, Caporossi T, Denaro R, Bovone C, Sparano C, Paradiso A, Baiocchi S, Caporossi A. Morphological and functional correlations in riboflavin UV A corneal collagen cross-linking for keratoconus. Acta Ophthalmol 2012; 90:259–265. Available at: http://onlinelibrary.wiley.com/doi/10.1111 /j.1755-3768.2010.01890.x/pdf. Accessed June 6, 2017 Greenstein SA, Fry KL, Bhatt J, Hersh PS. Natural history of corneal haze after collagen crosslinking for keratoconus and corneal ectasia: Scheimpflug and biomicroscopic analysis. J Cataract Refract Surg 2010; 36:2105–2114. Available at: http://www.vision-institute.com/UserFiles/File/CXL%20Haze %20Published.pdf. Accessed June 6, 2017 Kim BZ, Jordan CA, McGhee CNJ, Patel DV. Natural history of corneal haze after corneal collagen crosslinking in keratoconus using Scheimpflug analysis. J Cataract Refract Surg 2016; 42:1053–1059
Disclosure: None of the authors has a financial or proprietary interest in any material or method mentioned.
First author: Cosimo Mazzotta, MD, PhD Siena Crosslinking Center and Department of Medicine, Surgery and Neurosciences, Ophthalmology Unit, University of Siena, Siena, Italy
ARTICLE
Accelerated 15 mW pulsed-light crosslinking to treat progressive keratoconus: Two-year clinical results Cosimo Mazzotta, MD, PhD, Stefano Baiocchi, MD, Simone Alex Bagaglia, MD, Mario Fruschelli, MD, Alessandro Meduri, MD, PhD, Miguel Rechichi, MD
Purpose: To assess the clinical and microstructural results of accelerated 15 mW pulsed-light corneal crosslinking (CXL) to treat progressive keratoconus. Setting: Siena Crosslinking Center, Siena, Italy. Design: Prospective case series. Methods: After epithelium removal (with Epi-Clear) and 10 minutes stromal soaking with riboflavin 0.1% hydroxypropyl methylcellulose solution, all eyes had 15 mW/cm2 pulsedlight epithelium-off accelerated CXL for 6 minutes of ultraviolet-A (UVA) irradiation (1 second on/1 second off), maintaining a total UVA exposure of 12 minutes at a fluence of 5.4 J/cm2. The 2-year follow-up examination included uncorrected (UDVA) and corrected (CDVA) distance visual acuities, Scheimpflug tomography, in vivo confocal microscopy (IVCM), and spectraldomain optical coherence tomography (SD-OCT).
C
onventional riboflavin ultraviolet-A (UVA)induced corneal crosslinking (CXL) with epithelium removal is an evidence-based treatment with documented long-term efficacy in stabilizing progressive keratoconus and secondary ectasia in a series of nonrandomized and randomized clinical trials.1–4 It reduces the need for corneal transplantation in patients affected by progressive keratoconus or secondary ectasia.5 The standard irradiance of 3 mW/cm2 for 30 minutes was found to be effective in stiffening the cornea in primary and iatrogenic keratectasia cases.6 However, it also has potential in sterilizing antibiotic-resistant infectious keratitis caused by the cytotoxic effect of the reactive oxygen species generated during the CXL process,7 otherwise known as photoactivated chromophore CXL.8,9
Results: The study comprised 132 eyes of 96 patients (mean age 23.7 years G 4.3 [SD]) with stage II keratoconus. The change in UDVA and CDVA was statistically significant, from 0.51 G 0.106 logarithm of the minimum angle of resolution (logMAR) at baseline to 0.309 G 0.074 logMAR (P Z .0001) and 0.271 G 0.144 logMAR at baseline to 0.135 G 0.100 logMAR (P Z .0023), respectively. Coma values measured by Scheimpflug analysis showed a statistically significant improvement beginning with the first postoperative month (P Z .0004). The IVCM scans documented basal epithelial healing occurring 72 hours after treatment associated with the presence of subepithelial nerves. The SD-OCT scans performed in the central 6.0 mm of corneal diameter documented a demarcation line at a mean depth of 280 G 32 mm. Conclusion: The 15 mW/cm2 pulsed-light epithelium-off accelerated CXL was effective and safe, stabilizing keratoconus progression through 2 years of follow-up. J Cataract Refract Surg 2017; 43:1081–1088 Q 2017 ASCRS and ESCRS
Because the conventional CXL procedure requires a long treatment time (approximately 1 hour),6 accelerated CXL protocols have been proposed to shorten CXL treatment time,10–15 improving the patient’s comfort. According to equal-dose principles stated in the Bunsen-Roscoe Law,16 setting UVA power at 9 mW/cm2 10 minutes, 30 mW/cm2 3 minutes, 18 mW/cm2 5 minutes, and 45 mW/cm2 2 minutes while maintaining a constant energy (fluence) of 5.4 J/cm2 can achieve the same effect as the conventional Dresden protocol of 3 mW/cm2 for 30 minutes.17–19 A recent study20 has shed light on the chain of chemical events occurring during the photochemical activation of riboflavin with UV light, highlighting the importance of corneal oxygenation during treatment. With pulsed or fractionated UVA
Submitted: March 17, 2017 | Final revision submitted: May 1, 2017 | Accepted: May 8, 2017 From the Siena Crosslinking Center (Mazzotta), the Department of Medicine (Mazzotta, Baiocchi, Bagaglia, Fruschelli), Surgery and Neurosciences, Ophthalmology Unit, Siena University, Siena, the Department of Surgical Specialities (Meduri), Ophthalmology Clinic, Messina University, Messina, and the Eye-Center (Rechichi), Catanzaro, Italy. Corresponding author: Cosimo Mazzotta, MD, PhD, Siena Crosslinking Center and Department of Medicine, Surgery and Neurosciences, Ophthalmology Unit, University of Siena, Viale M. Bracci 8, Siena, 53100, Italy. E-mail: [email protected]. Q 2017 ASCRS and ESCRS Published by Elsevier Inc.
0886-3350/$ - see frontmatter http://dx.doi.org/10.1016/j.jcrs.2017.05.030
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Figure 1. The 15 mW/cm2 to 5.4 J/cm2 accelerated CXL surgical technique. A: Removal of corneal epithelial layers by a disposable epi-keratome. B: Corneal epithelium removed from the desired area of 8.0 mm. C: Riboflavin 0.1% dextran-free HPMC stromal soaking. D: Surgical microscope view (10 magnification) of distinct and homogeneous riboflavin 0.1% stromal soaking. E: The UVA pulsed emission under remote control eye tracking. F: Therapeutic soft contact lens application after topical antibiotic medication.
radiation, CXL efficiency might be improved by allowing rediffusion of oxygen during UVA-light-exposure pauses.20 A preclinical laboratory study by Krueger et al.21 found that riboflavin 0.1% with 15 mW/cm2 UVA exposure, using an equivalent total energy exposure of 5.4 J/cm2, was as effective as conventional 3 mW/cm2 CXL and 9 mW/cm2 accelerated CXL in biomechanical strengthening of the cornea. Moreover, when fractionating the UVA exposure with multiple cycles of pulsing light, the corneal extensiometry was equally as effective as without pulsing the light. The study established that in theory, pulsed UVA delivery should improve the degree of CXL, especially with the faster higher irradiance exposures during which oxygen is consumed more quickly.22 In vivo confocal microscopy (IVCM) analysis proved that fractionating UVA exposure by pulsing the light provides better penetration of the treatment, as shown in vivo by Mazzotta et al.23 and recently confirmed by Peyman et al.24 Deeper cell viability is reachable, prolonging exposure time while maintaining the same energy dose delivered into the corneal tissue.23
The present study evaluated the induced corneal microstructural changes (biomicroscopic, corneal spectraldomain optical coherence tomography [SD-OCT], IVCM) and the 2-year functional results (uncorrected [UDVA] and corrected [CDVA] distance visual acuities, tomography) after 15 mW/cm2 pulsed-light accelerated CXL at the standard 5.4 J/cm2 fluence performed in a cohort of patients with progressive stage II keratoconus. The procedure was based on data reported in the aforementioned laboratory study.21 PATIENTS AND METHODS This prospective interventional study evaluated eyes with progressive grade II keratoconus. It followed the tenets of the Declaration of Helsinki, with data collected at the Siena Crosslinking Center, Siena, Italy. After receiving an explanation of the nature and objective of the treatment, all patients provided informed consent. Inclusion criteria were grade II keratoconus (Amsler-Krumeich grading25) with a documented clinical and instrumental progression in the past 6 months of observation, expressed by an increased maximum keratometry value of 1.0 diopter (D) or more, minimum corneal thickness reduction of 10 mm or more, and a worsening of UDVA and CDVA of at least of C1.0 logarithm of the minimum
Figure 2. Postoperative corneal biomicroscopic examination performed on the third day after treatment before and immediately after therapeutic contact lens removal. A: Complete reepithelialization without epithelial defects is shown by riboflavin dye instilled via a riboflavin preservative-free drop (B).
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Figure 3. A: Corneal biomicroscopy performed 1 month after 15 mW/cm2 pulsed light-accelerated CXL treatment shows a distinct demarcation line (yellow arrow). B: The scan performed with SD-OCT confirmed the demarcation line associated with increased reflectivity of the crosslinked stroma (yellow arrow).
angle of resolution (logMAR) (R0.1 decimal equivalent or R0.5 spherical equivalent). Exclusion criteria were corneal opacities or scars, history of herpes simplex virus and other infectious keratitis, autoimmune diseases, and pregnancy. Patients who did not meet the clinical and instrumental keratoconus inclusion criteria were also excluded. Patient Assessment Patients had a full ophthalmologic examination including UDVA, CDVA, slitlamp evaluation, tonometry, and fundoscopy. Keratoconus was evaluated by Scheimpflug corneal tomography (Sirius, Costruzione Strumenti Oftalmici) that provided K values and wavefront analysis measurement, IVCM (Heidelberg Retina Tomograph II, Rostock Cornea Module), anterior segment OCT (iVue, Optovue, Inc.), and endothelial cell count (ECC) (I-Konan Noncon Robo, Konan Medical, Inc.). Surgical Technique Pulsed-light 15 mW/cm2 accelerated CXL protocol at 5.4 J/cm2 standardized fluence was performed under sterile operating
conditions using topical anesthesia oxybuprocaine hydrochloride 0.2% anesthetic drops. Topical pilocarpine 2.0% was administered 20 minutes before treatment. After application of a closed-valve eyelid speculum, the corneal epithelium was removed by an epi-Bowman keratectomy performed with a disposable epi-keratome (Epi-Clear, Orca Surgical) in the central 8.0 mm area (Figure 1, A and B). After epithelium removal, the corneal stroma was soaked for 10 minutes with a riboflavin 0.1% hydroxypropyl methylcellulose (HPMC) dextran-free solution (Vibex Rapid, Avedro, Inc.) (Figure 1, C and D). The riboflavin drops were instilled every minute for 10 minutes, covering the entire corneal surface (both the deepithelialized region and the limbus). Riboflavin stromal saturation was confirmed at the slitlamp before UVAlight irradiation was started. The UVA irradiation was performed with a KXL I UV-A illuminator (Avedro, Inc.) using a 15 mW/cm2 UVA power with pulsed-light emission (1 second on/1 second off) to obtain 12 minutes of UVA irradiation on balance while delivering a standard energy dose of 5.4 J/cm2 (Figure 1, E) over a total treatment time of 22 minutes.
Figure 4. Postoperative IVCM scans 48 to 72 hours after treatment. A: A regular basal epithelial cell mosaic with homogeneous cellularity and well distinct cell borders 30 days after treatment. B: Subepithelial plexus scan showed reduced and damage subepithelial nerve plexus fibers that were not completely lost immediately after treatment. C: Corneal reinnervation was rapid based on the subepithelial nerve plexus nerve fibers. Bright nerve fibers are evident. D: Keratocyte apoptosis in the anterior stroma associated with lacunar corneal edema, hyperreflective trabecular mesh aspect of ECM. E: Keratocytes repopulation with associated lacunar edema reduction and activated keratocytes nuclei 30 days after contact lens removal (F).
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Figure 5. The IVCM analysis showed undamaged cells with slight pleomorphism after the treatment. A: Preoperative image. B: Postoperative image.
After UVA irradiation, the eye was washed with a balanced salt solution, medicated with moxifloxacin and cyclopentolate drops, and dressed with a therapeutic soft contact lens (Figure 1, F). Therapeutic contact lenses were removed 72 hours after the treatment if complete epithelial healing was documented at biomicroscopic examination (Figure 2, A and B). An SD-OCT corneal scan was performed 1 month after treatment to detect demarcation line depth (Figure 3). The IVCM evaluation of the basal corneal epithelium, subepithelial nerve plexus, and corneal stroma keratocytes apoptosis was performed 3 days after treatment with the contact lens on and 30 days after treatment (Figure 4). Statistical Analysis A 2-tailed paired-samples Student t test was used to compare each baseline measurement with the respective follow-up measurement. Differences with a P value less than 0.05 were considered significant. Data were collected and analyzed using Prism software (version 6.0, Graph Pad Software, Inc.).
Postoperative corneal biomicroscopic examination performed on the third day after treatment showed a clear cornea, little edema, and no opacities before and immediately after therapeutic contact lens removal (Figure 2). Seventy-two hours after epithelium removal (Figure 2, A), all patients had complete reepithelialization as shown by the riboflavin dye test instilled via a riboflavin preservative-free drop (Droptest, IROS) (Figure 2, B). Biomicroscopy and Spectral-Domain Optical Coherence Tomography Demarcation Lines
Corneal biomicroscopy performed 1 month after treatment showed a distinct demarcation line (Figure 3, A). Comparative SD-OCT scan confirmed a demarcation line associated with increased reflectivity of the crosslinked stroma that measured at a mean of 280 G 32 mm depth (range 248 to 312 mm) (Figure 3, B). In Vivo Confocal Microscopy
RESULTS The study comprised 132 eyes of 96 patients. The mean age of the 76 men and 20 women was 23.7 years G 4.3 (SD). All patients enrolled in the treatment protocol completed the 24-month follow-up.
Postoperative IVCM scans showed a regular epithelial healing occurring 72 hours after treatment. Native epithelial cells were large with slightly defined cell borders, often oriented in a whorl-like fashion (Figure 4, A). A regular basal epithelial cells mosaic with homogeneous cellularity and
Table 1. Overall study results. 1 Mo Postop Parameter UDVA (logMAR) CDVA (logMAR) K max (D) Coma (mm) CCT (mm)
3 Mo Postop
Preop Mean
Mean ± SD
D
P Value*
Mean ± SD
D2
P Value*
0.51 G 0.106 0.27 G 0.144 48.33 G 2.51 1.01 G 0.02 453.3 G 24.01
0.49 G 0.131 0.22 G 0.152 47.93 G 2.44 0.98 G 0.0195 420.0 G 23.63
0.02 0.05 0.40 0.037 33.3
.743 .0289 .1149 .0004† .0001†
0.38 G 0.094 0.71 G 0.06 47.56 G 1.911 0.955 G 0.015 441.7 G 22.59
0.13 0.10 0.77 0.062 11.6
.0032† .0007† .0835 .0001† .2530
D Z change; CCT Z central corneal thickness; CDVA Z corrected distance visual acuity; K max Z maximum keratometry; logMAR Z logarithm of the minimum angle of resolution; UDVA Z uncorrected distance visual acuity Means G SD *Of change † Statistically significant
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clear distinct cell borders were present 30 days after treatment (Figure 4, B). Subepithelial plexus scans showed rarefaction and damage of subepithelial nerve plexus fibers, although the fibers were not completely lost, 3 days postoperatively (Figure 4, C). The subepithelial nerve plexus nerve fibers showed a rapid tendency to corneal reinnervation 30 days postoperatively, with bright nerve fibers evident (Figure 4, D). The 15 mW/cm2 pulsed-light CXL induced keratocyte apoptosis in the anterior stroma associated with lacunar corneal edema, hyperreflective trabecular meshwork aspect of extracellular matrix (ECM), and apoptotic bodies (Figure 4, E). Gradual keratocyte repopulation with concomitant lacunar edema reduction and presence of activated keratocytes nuclei was recorded 30 days after contact lens removal (Figure 4, F). The corneal endothelium was unaltered after the treatment (Figure 5). The mean preoperative endothelial cell density was 2434 cells/mm2 (range 2182 to 2826 cells/mm2). The mean ECC at 24 months was 2385 cells/mm2 (range 2175 to 2985 cells/mm2).
DISCUSSION At present, CXL might be the de facto first choice therapy to halt the progression of the early stages of corneal ectasia, showing good long-term visual results and few complications. Regarding the therapeutic benefit of CXL in stabilizing corneal ectasia progression,1–3 the early diagnosis of keratoconus and secondary corneal ectasia are mandatory. The physical concept stated in Bunsen-Roscoe’s law of reciprocity16 allowed us to study high-irradiance CXL protocols according to the so-called equal-dose principle.17–19 In our recent studies of different accelerated CXL protocols with continuous and fractionated (pulsed) high-irradiance UVA light exposure,20,23,26 IVCM analysis showed significant differences in keratocyte apoptosis (ie, treatment penetration) that might have significant biomechanical and clinical implications in terms of long-term ectasia stabilization and functional outcomes of treatment. The IVCM and corneal OCT data verifying the postoperative cells apoptosis, nerve disappearance, and the demarcation lines induced by accelerated CXL, showed a mean treatment penetration of 150 mm (range 140 to 200 mm measured from epithelial surface) after 30 mW/cm2 continuous light-accelerated CXL and of 220 mm (range 200 to 250 mm measured from the epithelial surface) after fractionated- or pulsed-light accelerated CXL.23 As per biomechanical studies by Shumacher et al.,27 CXL treatment should cover at least 200 mm of the corneal stroma. Contradictory results are reported in the literature28 after accelerated CXL protocols using UVA power of 9 mW,10–15 18 mW,29 and 30 mW.30 Accelerated CXL with irradiance of 9 mW/cm2 for 10 minutes was shown to be effective in stabilizing topographic parameters after a 12-month follow-up in corneas with mild to moderate keratoconus.10–15 After treatment, the UDVA improved and all tested corneal parameters stabilized. Moreover, 9 mW/cm2 accelerated CXL was safe for the corneal endothelium, stabilizing the progression of keratoconus and iatrogenic ectasia with a significant reduction in topographic K values and a significant increase in CDVA, which is comparable to results with conventional 3 mW/cm2 CXL over a midterm (2 year) follow-up.12 In a recent study,13 accelerated CXL with 18 mW/cm2 UVA power yielded less topographic flattening than conventional CXL. Refractive and visual results of accelerated CXL using continuous-light and pulsed-light
Functional Outcomes
Table 1 shows the overall study results. The mean UDVA showed a clinical improvement from baseline to the 24-month follow-up (P Z .0001). The difference became statistically significant by the third month (P Z .0032) (Figure 6). The mean CDVA showed a clinical improvement that became statistically significant by the first postoperative month (P Z .0289). The difference between baseline and the 24-month follow-up was statistically significant (P Z .0023) (Figure 6). The change in the mean maximum K values from baseline to the 24-month follow-up was not statistically significant (P Z .66) (Figure 7). The reduction in the mean coma values was statistically significant from the first postoperative month (P Z .0004). The difference between baseline and the 24-month follow-up was statistically significant as well (P ! .0001) (Figure 7). The reduction in the mean minimum corneal thickness from baseline to the first postoperative month (P ! .0001) was statistically significant. However, the difference became statistically insignificant by the third postoperative month (P Z .25) and remained so at the 24-month follow-up (P Z .50) (Figure 7). Table 1. (Cont.) 6 Mo Postop
12 Mo Postop
24 Mo Postop
Mean ± SD
D3
P Value*
Mean ± SD
D4
P Value*
Mean ± SD
0.32 G 0.08 0.10 G 0.11 47.08 G 1.60 0.956 G 0.014 444.4 G 11.88
0.15 0.105 1.25 0.061 5.3
!.0001† .0012† .0254† !.0001† .138
0.33 G 0.05 0.07 G 0.096 47.21 G 1.707 0.95 G 0.193 452.0 G 14.55
0.18 0.12 1.12 0.067 0.8
!.0001† .0005† .0372† !.0001† .925
0.309 G 0.074 0.135 G 0.144 47.91 G 1.56 0.94 G 0.014 458.6 G 12.83
D5
P Value*
0.21 0.136 0.42 0.082 5.03
!.0001† .0023† .1795 !.0001† .503
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Figure 6. The UDVA and CDVA (CDVA Z corrected distance visual acuity; LogMAR Z logarithm of the minimum angle of resolution; UDVA Z uncorrected distance visual acuity).
Figure 7. Mean maximum K values, coma values, minimum CCT (CCT Z central corneal thickness; Kmax Z maximum keratometry).
treatment at 30 mW/cm2 were similar to those of conventional 3 mW/cm2 CXL after 12-months of follow-up.30 Although the method provided faster recovery and better patient comfort, the depth of the demarcation line after 30 mW/cm2 was less than 200 mm of corneal stroma, which might be the limit with this accelerated protocol.23–26 In a recent study, Sadoughi et al.31 compared conventional 3 mW CXL and 9 mW accelerated CXL in patients with bilateral progressive keratoconus. Fellow eyes were randomly assigned to conventional CXL or accelerated CXL. After 12 months of follow-up, the refractive, visual, keratometric, and aberrometric outcomes were similar between the 2 treatments. In our opinion, to ensure long-lasting stability of keratoconus and secondary ectasia, the UVA power setting and exposure time should be targeted to allow a treatment penetration of at least at 250 mm, overcoming the anterior portion of the corneal stroma because the anterior 40% of the central corneal stroma represents the strongest region of the cornea (stiff cornea), whereas the posterior 60% of the stroma is at least 50% weaker.31–33 Moreover, according to Kohlhaas et al.,34 the CXL treatment significantly stiffened the cornea in the anterior 200 mm only. The depth-dependent stiffening effect was
explained by the absorption behavior of UVA in the riboflavin-treated cornea, and approximately 70% of the UVA irradiation was absorbed within the anterior 200 mm and only 20% in the next 200 mm. This might affect long-term stabilization of ectasia based on different crosslinking penetration rates. To achieve this goal, while maintaining a standard 5.4 J/cm2 dose delivery, the UVA power can be calibrated between 9 mW/cm2 and 15 mW/cm2 with continuous or pulsed light.34 A laboratory study by Krueger et al.21 found that effective CXL required the presence of oxygen in addition to sufficient penetration of riboflavin and UVA exposure. It was determined that accelerated CXL was as efficacious as the conventional protocol and a better strain (elongation) test was achieved with 15 mW/cm2 at 5.4 J/cm2 fluence with continuous-light (6 minutes) or pulsed-light (12 minutes; 1 second on/1 second off) UVA exposure. Microstructural analysis after the first clinical application of this protocol found a mean demarcation line of 280 G 32 mm with no endothelial damage or other side effects. The 2-year functional outcomes were similar and comparable with those of conventional 3 mW/5.4 J/cm2 CXL and 9 mW/5.4 J/cm2 accelerated CXL. However, some differences emerged in pulsed-light versus continuous-light use.22,23,25 With the
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15 mW/5.4 J/cm2 accelerated CXL protocol, the treatment time is short and the pulsed light maintained, achieving a treatment penetration that is almost comparable with that of conventional 3 mW CXL and 9 mW/cm2 continuous-light accelerated CXL.10,11 In addition, the 15 mW/5.4 J/cm2 accelerated CXL protocol caused less subepithelial plexus nerve damage, as documented by the incomplete loss of nerve fibers on early postoperative IVCM scans. Furthermore, in conventional CXL the UDVA and CDVA are often worse in the first 1 to 3 months postoperatively because of variable glare disability related to stromal edema, keratocytes loss, and thin epithelium.35 In contrast, the 15 mW pulsed-light accelerated CXL protocol at a 5.4 J/cm2 energy dose resulted in less glare disability with no statistically significant visual acuity decay in the first 3 postoperative months, perhaps because postoperative edema was less. Based on our study results, 15 mW/cm2 pulsed-light accelerated CXL is a safe and effective option to stabilize keratoconus progression. Over the 2-year follow-up, there was a statistically significant improvement in UDVA and CDVA with a distinct tendency toward a general improvement in all clinical and instrumental parameters and without adverse events or complications. As a practical consideration, we have no hesitation accepting the opinion of Krueger et al.21 regarding the advantages in clinical applications of accelerated CXL, not only because of the reduction in treatment time and increased patient’s comfort, but also because of the reduced postoperative glare disability, reduced subepithelial nerve plexus nerves damage, less postoperative haze36,37 on slitlamp examination compared with the Dresden protocol,1,4 and lack of endothelial damage with substantial keratoconus stabilization. The present study confirms the clinical safety of 15 mW accelerated CXL pulsed-light treatment with epithelium removal and its efficacy based on the stabilization of keratoconus progression with no complications during a 24-month follow-up.
WHAT WAS KNOWN Preclinical laboratory data show that riboflavin 0.1% with 15 mW/cm2 UVA exposure, using an equivalent total energy exposure of 5.4 J/cm2 is as effective as conventional 3 mW/cm2 CXL and 9 mW/cm2 accelerated CXL in the biomechanical strengthening of the cornea.
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WHAT THIS PAPER ADDS The study confirmed the clinical safety and efficacy of 15 mW/cm2 pulsed light-accelerated CXL protocol in stabilizing keratoconus progression during a 24-month follow-up. There were no complications.
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REFERENCES 1. Raiskup F, Theuring A, Pillunat LE, Spoerl E. Corneal collagen crosslinking with riboflavin and ultraviolet-A light in progressive keratoconus: ten-year results. J Cataract Refract Surg 2015; 41:41–46 2. O’Brart DPS, Patel P, Lascaratos G, Wagh VK, Tam C, Lee J, O’Brart NA. Corneal Cross-linking to halt the progression of
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Disclosure: None of the authors has a financial or proprietary interest in any material or method mentioned.
First author: Cosimo Mazzotta, MD, PhD Siena Crosslinking Center and Department of Medicine, Surgery and Neurosciences, Ophthalmology Unit, University of Siena, Siena, Italy
