Introduction
Fungal diseases affect over a billion people and
kill more than 1.5 million people worldwide (1). Many pathogens become resistant to
broad-spectrum antibiotic and antifungal therapy, due to various
resistant strains of pathogens. The World Health Organization (WHO)
has recently published a list of resistant pathogens involved in
infectious keratitis: Methicillin-resistant Staphylococcus
aureus (MRSA), vancomycin-intermediate and resistant
Staphylococcus aureus, carbapenem-resistant Pseudomonas
aeruginosa (PA), and vancomycin-resistant Enterococcus
faecium (VRE) (2). Diabetes
mellitus, low socioeconomic status, contact lens usage and topical
corticosteroids are the main risk factors for fungal keratitis
(2).
Infectious keratitis represents a serious concern
for ophthalmologists, with a progressively growing incidence in the
last few years (3), A recent
article published in The Lancet estimates an annual number of 1.4
million cases (4). All of these
concerns force us to elaborate on new techniques for better
management of these infections Other medical specialties are using
alternate treatments for infections management, for example a
recent study proves the efficiency of boric acid in vaginal
candidosis (5).
Collagen cross-linking (CXL) is a treatment option
for corneal ectasia and its application has been recently extended
to corneal melting and infectious keratitis. CXL could be a
treatment perspective for infectious keratitis resistant to
antimicrobial therapy or associated with corneal melting as
ultraviolet light and riboflavin have direct antimicrobial effect
and increase the mechanical strength of the cornea (6-8).
Panda et al (9), Bettis
et al (10) and Spoerl et
al (11) published important
results concerning the possible promising action of CXL for the
treatment of infectious keratitis. CXL is thought to have multiple
mechanisms of action on the corneal tissue, strengthening the
mechanical properties of the cornea, increasing tissue resistance
to enzymatic digestion, promoting healing and reducing
inflammation, relieving pain and restoring the corneal architecture
(7-12).
Many recent studies have confirmed the efficacy of the Dresden
protocol when using CXL, not only for stopping the progression of
keratoconus but also for the treatment of corneal melting and
infectious keratitis (12-17).
As this protocol is time-consuming, important efforts have been
made to decrease the total procedure time. Thus, the so-called
‘accelerated protocols’ (A-CXL) were developed. Currently,
high-intensity UVA lamps, associated with a decrease in irradiation
time, allow the same photochemical effect to be obtained. At the
9th International Congress of corneal cross-linking held in 2013 in
Dublin, Ireland, the concept of photoactivated chromophore for
infectious keratitis (PACK-CXL) was created in order to better
distinguish the use of CXL for the treatment of infectious
keratitis from CXL for the treatment of progressive keratoconus
(18-20).
In order to investigate the clinical efficacy and
safety of accelerated corneal collagen CXL (PACKA-CXL) vs.
conventional corneal collagen CXL (PACK-CXL) in the management of
infectious keratitis associated with corneal melting, we conducted
a prospective comparative study to observe the differences in final
visual acuities and healing time between the 2 groups.
Patients and methods
This prospective, comparative study was approved by
the Ethics Committee of Emergency Eye Hospital Bucharest and
informed consent was obtained from each patient. Inclusion criteria
consisted of adult patients with chronic corneal ulcer with
microbial or fungal etiology, hospitalized at the Bucharest
Emergency Eye Hospital and Clinic between January 2014 and October
2018. All patients had undergone local and systemic antibiotic and
antifungal treatment without any improvement.
Patients were divided into two groups. Group A
underwent conventional corneal Collagen CXL (PACK-CXL), using
Dresden protocol and group B underwent accelerated corneal collagen
CXL (PACKA-CXL). A complete ophthalmological evaluation including
visual acuity, anterior segment slit-lamp evaluation and optical
coherence tomography of the cornea was performed at baseline, on
first day, postoperatively and at 3 days, 1 week, 2 weeks, 1 month,
2 months, 3 months, 6 months and 12 months, postoperatively.
Direct samplings of the infected corneal ulcer and
lower conjunctival fornix were submitted to the central laboratory
for culture and antibiogram. The systemic treatment consisted of
broad-spectrum new-generation antibiotics and antifungal drugs. The
local treatment included fortified antibiotic and antifungal drops
and also atropine. Patients with a poor response to medication were
included in the study to perform a session of corneal crosslinking.
After CXL procedure, the antimicrobial treatment was continued
until the healing was complete.
Statistical analysis
The results are presented as the mean and standard
deviation for continuous variables, after the previous testing of
normal distribution and as absolute and percentage frequencies for
the nominal variable. We studied the differences between the 2
groups, comparing on one side the mean of quantitative variables
using the t-test and on the other side the frequencies of
qualitative variables using the Fisher exact test. We used a
statistical significance threshold of 0.05. The statistical
analysis of data was conducted using SPSS 23.0 software (IBM
Corp.).
Results
A total number of 16 eyes from 16 patients were
included in the study, 8 eyes randomized for each group. The
demographic and clinical parameters of the patients assigned in
each group before CXL were similar and are summarized in Table I.
 | Table IDemographic and clinical parameters of
groups A and B. |
Table I
Demographic and clinical parameters of
groups A and B.
| Characteristics | Group A (PACK-CXL)
(n=8) | Group B (PACKA-CXL)
(n=8) | P-value |
|---|
| Age, years (mean ±
SD) | 39.9±19.8 | 40.2±15.0 | 0.967 |
| Sex, n (%) | | | 0.614 |
|
Male | 5 (62.5) | 4 (50.0) | |
|
Female | 3 (37.5) | 4 (50.0) | |
| Site | | | 0.317 |
|
Central | 5 (62.5) | 3 (37.5) | |
|
Paracentral | 3 (37.5) | 5 (62.5) | |
| Treatment length
before presentation (weeks) | 5.2±2.6 | 5.9±4.4 | 0.738 |
| Microbiologic
culture | | | |
|
Positive | 7 (87.5) | 6 (75.0) | 0.522 |
| Ulcer size
(mm2) | 17.6±13.5 | 17.4±15.7 | 0.973 |
| Infiltrate area
(mm2) | 29.0±21.3 | 28.0±20.1 | 0.924 |
| Time to healing
(days) | 34.9±11.4 | 32.9±9.4 | 0.708 |
| Superficial
vascularization | | | 0.202 |
|
0 | 5 (62.5) | 2 (25.0) | |
|
1 | 1 (12.5) | 3 (37.5) | |
|
2 | 2 (25.0) | 1 (12.5) | |
|
3 | 0 (0.0) | 2 (25.0) | |
| Deep
vascularization | | | 0.289 |
|
0 | 5 (62.5) | 2 (25.0) | |
|
1 | 2 (25.0) | 3 (37.5) | |
|
2 | 1 (12.5) | 3 (37.5) | |
The mean age of the patients from Group A was
39.9±19.8 years, not significantly different (P=0.967) from the
mean age of Group B (40.2±15.0 years). Five patients from Group A
and 4 patients from Group B were males, with no significant gender
differences between groups (P=0.614). Five patients from Group A
had a central lesion and 3 patients had a paracentral lesion; in
Group B the situation was exactly opposite (P=0.317).
The patients from Group A had previous treatment for
5.2±2.6 weeks, not significantly different (P=0.738) from Group B
(5.9±4.4). Seven patients from Group A and 6 from B had a positive
culture, with no significant differences between groups
(P=0.522).
The ulcer size (mm2) and infiltrative
area (mm2) were not significantly different, but greater
in Group A vs. Group B (17.6±13.5 and 29.0±21.3 vs. 17.4±15.7 and
28.0±20.1, respectively). The distribution based on superficial and
deep vascularization was not significantly different between the
groups (P=0.202 and P=0.289, respectively).
The mean time to healing in patients from Group A
(34.9±11.4 days) was 2 days longer than in Group B (32.9±9.4 days),
but the difference did not reach statistical significance
(P=0.708).
Discussion
Corneal crosslinking represents an intensely studied
method of treatment and many authors have published their results
on this subject. Richoz et al conducted a significant and
valuable study (16). They
inoculated ex vivo porcine corneas with a suspension of
Gram-negative (Pseudomonas aeruginosa) and Gram-positive
(Staphylococcus aureus) bacterial strains. After incubation,
PACK-CXL was performed, at two irradiation settings: 5 min at 18
mW/cm2 and 2.5 min at 36 mW/cm2. There were
significant differences (P<0.001) between control corneas and
cross-linked corneas. The results revealed similar killing rates
for both bacterial strains (approximately 93%), whether they
undertook the accelerated or long protocol. The authors concluded
that PACK-CXL, when used for treating infectious keratitis, seems
to preserve its antimicrobial efficacy, even with shorter time of
exposure. After clinical validation, the results can be transferred
to routine practice, allowing a shortened treatment time. Tabibian
et al reported the case of a 24-year-old man with fungal
keratitis related to contact lens wearing. Accelerated PACK-CXL as
a single treatment was performed and evolution of the infiltrate
was favorable within 24 h (17).
Makdoumi et al published promising results in 16 patients
who underwent PACK-CXL as first-line treatment for infectious
keratitis (18). In a prospective
study involving 40 patients, 21 treated with PACK-CXL and 19
treated with antimicrobial therapy, Said et al found that
the average healing time was shorter in the PACK-CXL group,
although not statistically significant (19). In addition, the number of related
complications was lower in the PACK-CXL group, supporting the
efficacy and safety of PACK-CXL in treating microbial keratitis.
Rapuano et al recently described the implications of sodium
hydroxymethylglycinate (SMG) in pharmacologic cross-linking of the
cornea in the treatment of keratitis (21). The modified crosslinking (M-CXL)
performed by Kasparova et al consisted of associating the
crosslinking procedure with frequent instillations of antimicrobial
drops. In a group of 24 treated patients, they reported a reduction
in treatment time by 42%, as compared to the control group treated
with conservative treatment (22).
Ting et al (20) performed a
comprehensive meta-analysis comprising 46 articles and 435
patients. This meta-analysis compared the standard antimicrobial
treatment alone for infectious keratitis with PACK-CXL as adjuvant
therapy. The authors concluded that the average healing time was
less than 7 days for patients treated with adjuvant PACK-CXL when
compared to 10 days for standard antimicrobial treatment alone.
In conclusion, our study suggests that the
accelerated photoactivated chromophore collagen cross-linking
procedure is as safe and efficient as the conventional procedure in
infectious keratitis treatment. While having comparable costs, the
time required for the accelerated procedure is 3 times shorter thus
offering significant advantages for patient comfort.
Acknowledgements
Not applicable.
Funding
No funding was received.
Availability of data and materials
The datasets used and/or analyzed during the current
study are available from the corresponding author on reasonable
request.
Authors' contributions
IRB and FB contributed to the study design,
participated in the entire review process and prepared the
manuscript. GB, LB, CM and DAB contributed to collecting the
relevant literature, data analysis and critical interpretation.
DCB, MZ and MB conceived the review concept and modified the
manuscript. All authors read and approved the final version of the
manuscript.
Ethics approval and consent to
participate
The study was approved by the Ethics Committee of
the Emergency Eye Hospital Bucharest (document no. 7/06.01.2020)
and informed consent was obtained from each patient.
Patient consent for publication
Not applicable.
Competing interests
All the authors declare that they have no competing
interests.
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