Podcast 5: Corneal Collagen Cross-Linking and Keratoconus

Podcast 5:  Corneal Collagen Cross-Linking and Keratoconus


Podcast 5 Corneal Collagen Cross-Linking and Keratoconus This series of podcasts is hosted by the Vision
Center of Excellence, a joint program of the Department of Defense and Department of Veterans
Affairs. The podcast series provides concise summaries
of issues and reports targeted to Department of
Defense and Veterans Affairs vision providers overseeing care for our Service members and
Veterans. This podcast summarizes and comments on two
articles published in Ophthalmology. The first is
titled “Corneal Collagen Cross Linking with Riboflavin and Ultraviolet-A Irradiation for
Keratoconus”, and is co-authored by Dr. Hassan Hashemi and colleagues and published in August
2013. The second article, co-authored by Dr. Christine Wittig-Silva and colleagues, is
titled “A Randomized, Controlled Trial of Corneal Collagen
Cross-Linking in Progressive Keratoconus” and
was published in January 2014. Keratoconus is a bilateral, asymmetric and
progressive disease in which the normally round,
dome-like cornea becomes thin and develops a cone-like bulge. Once the cornea becomes
distorted, it does not return to its normal shape. Unlike other eye diseases or vision
problems that occur later in life, this disorder has a much
earlier onset seen in the teens, twenties and thirties. The
early prevalence of this disease affects a population that is comparable to the active
duty US military force. Management of keratoconus
is dependent on the severity of the disease, which
makes timing of diagnosis critically important. In more severe cases of keratoconus, where
other interventions such as contact lenses are not
effective, a corneal transplant may be required. Historic and existing treatments focus on
improving quality of vision and halting progressive vision
loss; however, the search continues for more effective treatments that address long-term
degeneration and halt its progression. One of these newer treatments is called Corneal
Collagen Cross Linking or CXL. The two reports by Hashemi
and colleagues and Wittig-Silva and colleagues both examine CXL and its efficacy
in treating keratoconus. The results of each of these
studies show positive long-term outcomes that support this novel treatment. The study by Hashemi and colleagues includes
data on the five-year stability of keratoconic eyes
treated with CXL. The authors point out that there are few long-term studies that evaluate
this method. In this study, 40 eyes of 32 patients
with progressive keratoconus were treated with CXL
no later than one month after baseline eye exams. All eyes were monitored for any signs
of disease progression. Patients ranged in age
from 15 – 35 years and 65 percent were male, a
patient sample similar to the US military active duty force. Patients were tested for
various measures, including both best and uncorrected
visual acuity as well as maximum keratometry levels. Eyes were tested at one, three and
six months as well as one, two, four and five years
after the initial CXL treatment. The authors report that at the five-year mark, there was
significant improvement in best corrected visual acuity
compared to baseline. Corneal thickness, uncorrected visual acuity and maximum keratometry showed
no significant change over the same time period. Based on findings across measures, the authors
concluded that CXL may stop disease progress. The study done by the Witting-Silva group
evaluated 46 CXL-treated eyes and 48 non-treated control keratoconic eyes. The patients examined
in this study were between 16 – 50 years of age, similar to the US active duty population.
The patients’ eyes and progression of the disease
were followed for three years. After analyzing the data, the treated group demonstrated
stabilization of the disease, with substantial improvement in both best- and un-corrected
visual acuity as well as maximum simulated keratometry
values at one, two and three years. In comparison, third-year data from the untreated
group displayed a progressive worsening of their
keratoconus, with significant decreased uncorrected visual acuity and increased maximum
simulated keratometry values. The results of this study show the ability of CXL to halt
disease progression. This study was unique because
most studies to date did not utilize a control group
when studying the effects of CXL. Results in both studies showed that there
was stabilization of the disease process and in some
cases, an improvement in overall visual acuity. Variation in results may be attributed to
differences in amount of eyes evaluated as well as the devices used to calculate curvature.
Both groups of researchers agree that there are
some limitations to the CXL treatment. Not every
patient with keratoconus or other corneal disorders can have the procedure. In the study
by Hashemi and colleagues, the researchers limited
their patients to those with more than 400 microns of corneal tissue. It is suspected
that without ample corneal tissue, the UV-A light from the
CXL device could damage corneal endothelial cells. Other similar exclusion criteria in
the studies revolved around previous eye surgery and evidence
of corneal scarring prior to surgery. While CXL complications are rare, the Witting-Silva
group did report three adverse events over the
three year period. However, all events were temporary and were resolved. The two studies discussed here are among several
that highlight the safety and benefits of CXL in
treating keratoconus. While the FDA has reviewed applications for approval of this treatment,
CXL is not yet officially recognized among most health systems in the US, including the
military. The anticipation is that in the long-term,
CXL may become available to military personnel as an
alternative to traditional treatment options, such as contact lenses and corneal surgery.
Because this disease has direct implications for force
readiness and is a potentially career-changing diagnosis for Service members, the Department
of Defense continues to monitor CXL as a treatment for keratoconus. Active duty personnel
should discuss this diagnosis and available treatment options with their medical provider
and commanding officer for further guidance. This production was brought to you by the
Vision Center of Excellence. Our mission is to lead and
advocate for programs and initiatives to improve vision health, optimize readiness and enhance
quality of life for Service members and Veterans. Working with TRICARE, the Military Health
System, other Centers of Excellence and the Veterans Health Administration, the Vision
Center of Excellence works to enhance collaboration
between Department of Defense and Department of
Veterans Affairs vision care providers, provide guidance for clinical practice and facilitate
patient-centered support. For more information, visit us online at vce.health.mil or on Facebook.

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