The advent of corneal collagen crosslinking (CXL) using ultraviolet A (UV-A) redefined the progressive keratoconus (KC) treatment paradigm from one of management to one of active, non-invasive intervention. Accelerated CXL, one variation of the Dresden protocol, uses higher levels of UV light over shorter durations of time, in effect administering the same UV dosage as conventional CXL treatments while providing for reduced procedure time.
Although duration and level of irradiance are important aspects of CXL, follow-up time in prospective CXL studies are integral to proving the efficacy and safety of accelerated CXL protocols.
A new study in the journal Cornea looked at the impact of accelerated CXL, mediated by exposure to a UV-A irradiance of 18 (mW/cm2) for a period of five minutes, on progressive keratoconus.1 The study examined the effects of the CXL protocol through follow-up visits over the course of up to 21.7 months.
According to researchers at the University of Muenster Medical Center, the indexes of surface variance and height decentration, which are the most sensitive and specific criteria by which efficacy of CXL is determined, were shown to match those of standard CXL. Importantly, corneal complications did not occur in any subjects of the study.
The new accelerated CXL protocol matched the efficacy and safety of standard CXL protocols, as demonstrated by looking at keratoconus and corneal health indices over acceptable follow-up times.
Early detection of keratoconus before laser-based surgery, in which subclinical KC may lead to full ectasia post-surgery, is a major priority. Researchers used a new in vivo, noncontact corneal biomechanical analysis device called the Corvis ST (Oculus) in addition to new indicators of early KC called applanation length level and deflection length level, to improve subclinical KC detection. Currently, subclinical keratoconus is difficult to detect because distinguishing a normal eye from a keratoconic eye has not been device-independent; by using the keratoconus percentage index (KISA%) and commonly used topographic patterns, the study was able to better define KC, which may be used in the future to detect early KC more often.
Also, a new form of OCT called swept-source Fourier-domain optical coherence tomography (SS-OCT) uses a special mathematical analysis to detect subclinical KC, which puts prospective laser-based surgical patients at high risk for post-surgical ectasia. Using the KISA% along with SS-OCT, researchers were able to detect subclinical KC to a high degree of accuracy. All new early KC detection technologies become more accurate when using device-independent indices to differentiae between normal and keratoconic eyes.
1. Alnawaiseh M, Rosentreter A, Bohm MRR ,et al. Accelerate (18mWcm2) corneal collagen cross-linking for progressive keratoconus. Cornea epub ahead of print.
2. Steinberg J, Katz T, Lucke K. Screening for keratoconus with new dynamic biomechanical in vivie Scheimpflug analyses. Cornea epub ahead of print.
3. Steinberg J, Casagrande MK, Fings A, et al. Screening for subclinical keratoconus using swept-source Fourier domain anterior segment optical coherence tomography. Cornea epub ahead of print.