Ultraviolet-induced corneal cross-linking (CXL) was established in the beginning of 2000 in Germany and Switzerland. The procedure induces stiffening of the corneal tissue. It was first used for progressive keratoconus.1,2 Later, this technique was adapted to arrest progression in iatrogenic corneal ectatic disorders, bullous keratopathy, and corneal melting.3,4
Infectious keratitis is a potentially vision-threatening condition caused by bacteria, viruses, protozoa, or fungi.5 Therefore, it should be treated promptly. After taking cultures, infectious microbial keratitis is treated with appropriate antimicrobial agents. However, some ulcers do not respond to antimicrobial treatments and the risk for thinning of the cornea and perforation is increased; therefore, alternative treatments are required. In the past, the only treatment that was available for antimicrobial-resistant ulcers was an emergency therapeutic penetrating keratoplasty. However, this procedure has a significant risk for complications and prolonged treatments should be taken.
In 2008, Iseli et al.6 reported the use of CXL for corneal infections for the first time. Since then, CXL has been examined as a adjuvant treatment for infectious keratitis in few studies.7–9 Skaat et al.10 presented a case series of severe infectious keratitis unresponsive to topical therapies that were treated with CXL. They all showed rapid reduction in symptoms and decreased infiltrate size. Hafezi and Randleman11 suggested the use of the acronym PACK, which stands for photoactivated chromophore for keratitis, to differentiate the use of CXL for infectious keratitis from the use of CXL for keratoconus.
The purpose of this study was to evaluate the clinical characteristics, treatments, and the prognosis of all cases of infectious keratitis resistant to conventional medical therapy that were treated by PACK-CXL in our institution between 2012 and 2016.
Patients and Methods
Eighteen consecutive eyes of 18 patients who underwent PACK-CXL for infectious keratitis unresponsive to medical treatment were included in this study. Four patients who did not complete 1 year of follow-up were excluded from our study. The following parameters were documented: patient demographic information (gender and age at diagnosis), ocular history, corrected distance visual acuity (CDVA) before PACK-CXL, eye laterality of infection, ulcer size, ulcer location, presence of hypopyon, antibiotic treatment prior to CXL, culture results, duration of follow-up, CDVA at the end of follow-up, additional surgical procedure such as penetrating keratoplasty, and short- and long-term complications.
Snellen VA at presentation and at the end of follow-up were converted to logarithm of the minimum angle of resolution (logMAR) values.
The study was approved by the local institutional review board of the Sheba Medical Center. The surgical procedure complied with the tenets of the Declaration of Helsinki, and the participants provided informed consent.
Initial Medical Management
All patients underwent corneal scraping for direct smear plated on blood agar plates, chocolate plates, Sabouraud's dextrose agar plates, and Acanthamoeba culture medium at presentation.
In our institution, the initial antimicrobial therapy for ulcers that are larger than 1 mm and central or paracentral consisted of fortified vancomycin eye drops (33 mg/mL) and fortified ceftazidime eye drops (50 mg/mL) hourly for the first 24 hours. All patients in the study received this initial treatment. This regimen was changed later according to culture results, sensitivity, and patients' response. In all cases, the change of the antibiotic regimen was before the PACK-CXL and a few days after presentation.
All patients underwent the same surgical technique. The procedure was performed in operating room conditions. Following the application of topical anesthesia with 0.4% oxybuprocaine hydrochloride eye drops (Localin; Fischer Pharmaceuticals Ltd., Bnei Brak, Israel), mechanical epithelial debridement over the area of the corneal abscess and 2 mm surrounding it was accomplished using a blade. Deepithelialization was followed by instillation of riboflavin 0.1% solution (Lightmed, San Clemente, CA) (10 mg riboflavin-5-phosphate in 10 mL dextran-T-500 20% solution) drops every 2 minutes for 30 minutes, then ultraviolet-A (UV-A) irradiation was applied to the corneal surface for 10 minutes (irradiance of 9 mW/cm2). The UV-A irradiation was performed using the UV-X 2000 illumination system (IROC AG, Zurich, Switzerland). The system was regularly calibrated to the intended 9.0 mW/cm2 of surface irradiance using a UV light meter at a working distance of 10 cm. During the UV-A treatment, hypotonic riboflavin solution was continuously applied every 2 minutes to ensure saturation. Following the procedure, fortified antibiotic treatment was resumed (Table 1).
The statistical analysis was performed using Microsoft Excel 2007 (Microsoft Corporation, Redmond, WA) and JMP Statistical Discovery Software 7.0 (SAS Institute, Cary, NC). The overall significance level was set to an alpha level of 0.05.
Comparison between the CDVA before the procedure and at the end of follow-up was performed by analyzing match pair.
Eighteen eyes of 18 patients underwent PACK-CXL: 61% (11 of 18) were men and 39% (7 of 18) were women. The mean age at the time of the procedure was 58.42 ± 16.3 years (range: 18 to 89 years). The procedure was performed in the right eye in 55% (10 of 18) and in the left eye in 44% (8 of 18). Ocular history included a previous penetrating keratoplasty in 44% (8 of 18), keratouveitis in 16.67% (3 of 18), and glaucoma in 11% (2 of 18).
The mean CDVA at the time of presentation was 1.47 ± 0.72 logMAR (range: 1 to 2.79 logMAR). The average length of the ulcer was 2.75 mm (range: 1 to 5 mm) and width was 3.55 mm (range: 1 to 5 mm); most of the ulcers were central and in most cases a hypopyon was present.
Two representative cases are presented in Figure 1 and Figure A (available in the online version of this article).
A 47-year-old woman who wore daily contact lenses due to myopia presented with a paracentral ulcer. (A) Visual acuity was 20/60. Corneal culture was positive for Pseudomonas aeruginosa and Staphylococcus epidermidis. She was treated with fortified vancomycin and ceftazidime and underwent photoactivated chromophore for keratitis corneal cross-linking (PACK-CXL) on day 14. The ulcer regressed following the procedure, leaving a scar. (B) Six months later her vision was 20/40.
A 79-year-old woman with a history of end-stage glaucoma in the right eye and glaucoma that was treated surgically had cataract extraction surgery followed by a penetrating keratoplasty due to bullous keratopathy in the left eye. (A) She presented with a corneal abscess in the left eye. Her visual acuity on presentation was light perception. She was treated with vancomycin (50 mg/mL) and ceftazidime (33 mg/mL) drops hourly, oral acyclovir 400 mg five times daily, natamycin 5% drops every second hour, and doxycycline 100 mg once daily. Despite treatment, 2 weeks after corneal melting was noted, she underwent corneal cross-linking and the melting area was covered with a glue patch. Four months later, her visual acuity was counting fingers and the glue patch was in place. Penetrating keratoplasty was performed 2 months later.
Microbiology Work-up and Therapy
The cultures from the corneal scrapings were positive in 72% of eyes (13 of 18 patients) and no pathogens were identified in 28% of eyes (5 of 18 patients). The pathogen distribution is summarized in Table 2. All patients were treated by more than one antibiotic. Regarding resistance to antibiotics: 8 patients were sensitive to trimethoprim/sulfamethoxazole, 7 were sensitive to gentamicin, 6 to vancomycin, 5 to ciprofloxacin, 4 to clindamycin and rifampicin, 3 to erythromycin and amikacin, 2 to ceftazidime, oxacillin, and fusidic acid, and 1 to ampicillin and amoxicillin. The distribution of antibiotics, which was given prior to culture results, is summarized in Table 3.
Distribution of Antibiotics
The mean follow-up was 17.23 ± 11.61 months (range: 12 to 36 months). The mean CDVA at the end of follow-up was 1.22 ± 0.89 logMAR (range: 0.00 to 2.07 logMAR). There were no significant changes between CDVA at presentation and the end of follow-up (matched pair, P = .126).
Only 1 patient (6%) underwent emergency penetrating keratoplasty. This patient was 30 years old, had Down syndrome, and underwent penetrating keratoplasty for keratoconus. She was hospitalized with corneal ulcer and the culture grew Moraxella catarrhalis and Streptococcus pneumoniae that were sensitive to vancomycin and ceftazidime. She was treated with fortified antibiotics for 15 days with no improvement and then she underwent PACK-CXL. Ten days later, the cornea perforated. Emergency penetrating keratoplasty was performed. Her visual acuity 6 months later was 20/100. We attribute the fact that only one eye was perforated to the success of CXL in halting the melting process. We would expect more eyes to perforate because all had bad melting ulcers.
At the end of follow-up, 4 more eyes underwent a therapeutic penetrating keratoplasty due to a central corneal scar that limited vision. The average time from diagnosis of corneal abscess to CXL was 10 days.
CXL for ulcers that are resistant to antibiotics has become a common practice.12 In the current study, CXL was done for corneal ulcers that were large, central, and resistant to antibiotics. During the follow-up period after PACK-CXL, only 1 eye had perforated. More than 70% of eyes did not undergo penetrating keratoplasty at the end of follow-up.
The use of PACK-CXL as a first-line or sole treatment is still under investigation. Tal et al.13 examined the efficacy of PACK-CXL as primary therapy for Staphylococcus aureus–induced corneal ulcers in a rabbit model and found a beneficial effect with a trend toward a shorter healing time and a significantly smaller final scar size. In humans, Makdoumi et al.14 proposed a prospective non-randomized clinical trial to investigate the efficiency of CXL as first-line therapy in bacterial keratitis. They recruited 16 patients clinically diagnosed as having infectious bacterial keratitis who had not received any previous antibiotic (topical or systemic) treatment. Of 16 patients, 15 showed complete epithelial closure and all showed signs of improvement and reduction of inflammatory response to the bacteria. Nevertheless, 2 patients needed additional antibiotic therapy to treat their disease. However, they uncovered the microbicidal effect of CXL in early bacterial keratitis as a first-line treatment in this trial.14 No other large randomized control trial has been done to determine the best protocol of treatment in PACK-CXL.
In our institute, CXL was performed as an adjuvant treatment to antibiotics an average 10 days after treatment was initiated in cases that were clinically unresponsive to treatment, the ulcer increased in size, and the cornea was thinning or melting despite treatment. All cases were severe ulcers; the mean CDVA at presentation was worse than 20/200. Most of the infections were central and more than 2 cm in size. There is no consensus in the literature on whether CXL is effective for fungal ulcers.15–17 In our case series, all of the infections were bacterial; this is due to the fact that fungal ulcers are not treated by CXL in our institution.
There is no consensus in the literature as to when CXL should be done. Different reports described different timing for PACK-CXL, ranging between 2 and 45 days from infection presentation.18–20 The presented cases above were treated a few years ago and the CXL was performed after more than 10 days on average from the presenting infection. In our institution, CXL is currently performed earlier if there is no improvement under antibiotic treatment. The best timing to perform the procedure should be examined in a larger prospective, randomized trial. Moreover, the only case with emergency penetrating keratoplasty underwent CXL 25 days after diagnosis of corneal abscess, whereas other cases that had late penetrating keratoplasty underwent CXL 10 days later. Those that did not have penetrating keratoplasty at all underwent CXL 7 days after diagnosis of PACK-CXL. Therefore, we assume that it is better to perform CXL as early as possible.
Price and Price12 found that hypopyon is associated with a lower success rate. We did not find an association between hypopyon presentation and CDVA and penetrating keratoplasty. Larger studies should examine this assumption.
Makdoumi and Backman21 reported that the bactericidal efficacy of CXL differed between different microorganisms from 60% mean extermination of Enterococcus faecalis strains to 92% mean extermination Pseudomonas strains. Moreover, they found that methicillin-resistant S. aureus was eradicated to a greater extent than the non-resistant strain. Staphylococcus epidermidis, the most common pathogen in our study, had 81% elimination. The antibiotics that we used in the current study varied.
The question of whether CDVA improves after PACK-CXL was examined in the past and no consensus was found. An improvement was found in some studies,22,23 but not in others.24,25 Mattila et al.23 described 7 cases of combined CXL and amniotic membrane transplantation in the treatment of severe or conventional treatment-resistant P. aeruginosa keratitis. Their results were promising. All eyes were spared and all of them had improved CDVA.23 Said et al.24 compared 21 eyes that underwent PACK-CXL treatment in addition to antimicrobial therapy to 19 eyes that received only antimicrobial therapy. They found no differences in the average time until healing and no differences in CDVA between groups. However, the corneal ulceration's width and length was significantly greater in the PACK-CXL group.24 In our group, we did not find differences between CDVA before CXL to the end of follow-up. This is due to the fact that most of the ulcers were central and large. All patients presented with poor CDVA and after the infection subsided were left with significant corneal scars that limited vision.
Although the ulcers were large and melting, only one eye underwent emergency penetrating keratoplasty. One may think that more severe cases would undergo emergency penetrating keratoplasty.26,27 We believe that this low rate may be attributed to good response to the CXL treatment, which stopped the melting procedure. We excluded patients with less than 1 year of follow-up.
The limitations of our study are the small number of patients and that the patients who had CXL were those with the most complicated ulcers. Patients with small and peripheral ulcers were not included. Further studies are needed.
In our study, patients with large, central corneal ulcers and poor CDVA underwent CXL. The pathogens and treatments varied. At the end of follow-up, there was no significant change in CDVA. In those complicated cases, only 1 patient underwent emergency penetrating keratoplasty. We believe that CXL prevented further melting. Larger studies should be done to examine those findings.
- Ehlers N, Hjortdal J, Nielsen K, Søndergaard A. Riboflavin-UVA treatment in the management of edema and nonhealing ulcers of the cornea. J Refractive Surg. 2009;5:S803–S806. doi:10.3928/1081597X-20090813-08 [CrossRef]
- Hafezi F, Kanellopoulos AJ, Wiltfang R, Seiler T. Corneal collagen crosslinking with riboflavin and ultraviolet A to treat induced keratectasia after laser in situ keratomileusis. J Cataract Refract Surg. 2007;33:2035–2040. doi:10.1016/j.jcrs.2007.07.028 [CrossRef]
- Wollensak G, Spoerl E, Seiler T. Riboflavin/ultraviolet-a-induced collagen crosslinking for the treatment of keratoconus. Am J Ophthalmol. 2003;135:620–627. doi:10.1016/S0002-9394(02)02220-1 [CrossRef]
- Wollensak G, Spoerl E, Seiler T. Stress-strain measurements of human and porcine corneas after riboflavin-ultraviolet-A-induced cross-linking. J Cataract Refract Surg. 2003;29:1780–1785. doi:10.1016/S0886-3350(03)00407-3 [CrossRef]
- Green M, Apel A, Stapleton F. Risk factors and causative organisms in microbial keratitis. Cornea. 2008;27:22–27. doi:10.1097/ICO.0b013e318156caf2 [CrossRef]
- 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. doi:10.1097/ICO.0b013e318169d698 [CrossRef]
- Koppen C, Vryghem JC, Gobin L, Tassignon MJ. Keratitis and corneal scarring after UVA/riboflavin cross-linking for keratoconus. J Refract Surg. 2009;25:S819–S823. doi:10.3928/1081597X-20090813-11 [CrossRef]
- Micelli Ferrari T, Leozappa M, Lorusso M, Epifani E, Micelli Ferrari L. Escherichia coli keratitis treated with ultraviolet A/riboflavin corneal cross-linking: a case report. Eur J Ophthalmol. 2009;19:295–297. doi:10.1177/112067210901900221 [CrossRef]
- Makdoumi K, Mortensen J, Crafoord S. Infectious keratitis treated with corneal crosslinking. Cornea. 2010;29:1353–1358. doi:10.1097/ICO.0b013e3181d2de91 [CrossRef]
- Skaat A, Zadok D, Goldrich Y, et al. Riboflavin/UVA photochemical therapy for severe infectious keratitis. Eur J Ophthalmol. 2014;24:21–28. doi:10.5301/ejo.5000330 [CrossRef]
- Hafezi F, Randleman JB. PACK-CXL: defining CXL for infectious keratitis. J Refract Surg. 2014;30:438–439. doi:10.3928/1081597X-20140609-01 [CrossRef]
- Price MO, Price FW Jr, . Corneal cross-linking in the treatment of corneal ulcers. Curr Opin Ophthalmol. 2016;27:250–255. doi:10.1097/ICU.0000000000000248 [CrossRef]
- Tal K, Gal-Or O, Pillar S, Zahavi A, Rock O, Bahar I. Efficacy of primary collagen cross-linking with photoactivated chromophore (PACK-CXL) for the treatment of Staphylococcus aureus-induced corneal ulcers. Cornea. 2015;34:1281–1286. doi:10.1097/ICO.0000000000000550 [CrossRef]
- Makdoumi K, Mortensen J, Sorkhabi O, Malmvall BE, Crafoord S. UVA-riboflavin photochemical therapy of bacterial keratitis: a pilot study. Graefes Arch Clin Exp Ophthalmol. 2012;250:95–102. doi:10.1007/s00417-011-1754-1 [CrossRef]
- Uddaraju M, Mascarenhas J, Das MR, et al. Corneal cross-linking as an adjuvant therapy in the management of recalcitrant deep stromal fungal keratitis: a randomized trial. Am J Ophthalmol. 2015;160:131–134. doi:10.1016/j.ajo.2015.03.024 [CrossRef]
- Alshehri JM, Caballero-Lima D, Hillarby MC, et al. Evaluation of corneal cross-linking for treatment of fungal keratitis: using confocal laser scanning microscopy on an ex vivo human corneal model. Invest Ophthalmol Visual Sci. 2016;57:6367–6373. doi:10.1167/iovs.16-20110 [CrossRef]
- Hao ZQ, Song JX, Pan SY, et al. Corneal collagen cross-linking and liposomal amphotericin B combination therapy for fungal keratitis in rabbits. Int J Ophthalmol. 2016;9:1549–1554.
- Khalili MR, Jahadi HR, Karimi M, Yasemi M. Corneal collagen cross-linking for treatment of bacterial and herpetic keratitis. J Clin Diagn Res. 2017;11:NC12–NC16.
- Abbouda A, Abicca I, Alió JL. Current and future applications of photoactivated chromophore for keratitis-corneal collagen cross-linking (PACK-CXL): an overview of the different treatments proposed. Semin Ophthalmol. 2018;33:293–299. doi:10.3109/08820538.2015.1123731 [CrossRef]
- Garg P, Das S, Roy A. Collagen cross-linking for microbial keratitis. Middle East Afr J Ophthalmol. 2017;24:18–23.
- Makdoumi K, Backman A. Photodynamic UVA-riboflavin bacterial elimination in antibiotic-resistant bacteria. Clin Exp Ophthalmol. 2016;44:582–586. doi:10.1111/ceo.12723 [CrossRef]
- Tabibian D, Mazzotta C, Hafezi F. PACK-CXL: Corneal cross-linking in infectious keratitis. Eye Vis. 2016;3:11. doi:10.1186/s40662-016-0042-x [CrossRef]
- Mattila JS, Korsback A, Krootila K, Holopainen JM. Treatment of Pseudomonas aeruginosa keratitis with combined corneal cross-linking and human amniotic membrane transplantation. Acta Ophthalmol. 2013;91:e410–e411. doi:10.1111/aos.12115 [CrossRef]
- Said DG, Elalfy MS, Gatzioufas Z, et al. Collagen cross-linking with photoactivated riboflavin (PACK-CXL) for the treatment of advanced infectious keratitis with corneal melting. Ophthalmology. 2014;121:1377–1382. doi:10.1016/j.ophtha.2014.01.011 [CrossRef]
- Vajpayee RB, Shafi SN, Maharana PK, Sharma N, Jhanji V. Evaluation of corneal collagen cross-linking as an additional therapy in mycotic keratitis. Clin Exp Ophthalmol. 2015;43:103–107. doi:10.1111/ceo.12399 [CrossRef]
- Tangpagasit W, Reanpinyawat T. Outcome of urgent penetrating keratoplasty for corneal ulcer at Thammasat University Hospital. J Med Assoc Thailand. 2016;99:71–76.
- Wang JY, Xie LX, Song XS, Zhao J. Trends in the indications for penetrating keratoplasty in Shandong, 2005–2010. Int J Ophthalmol. 2011;4:492–497.
|Treatment target||Infectious keratitis|
|Soak time and interval (minutes)||30(q2)|
|Treatment time (minutes)||30|
|Average size of the ulcer (mm)||Width 2.75, Height 3.5|
| Central||55.55% (10/18)|
| Paracentral||16.67% (3/18)|
| Inferior-temporal||11.11% (2/18)|
| Superior-temporal||11.11% (2/18)|
| Inferior||5.56% (1/18)|
|Hypopyon, yes/no (%)||14:4 (77.78: 22.22)|
Distribution of Antibiotics
|Antibiotics||No. of Paitents|