Researchers recently used a new technology called phase-decorrelation optical coherence tomography (PhD-OCT) that corrects for the artifacts introduced by motion in conventional OCT scanning; even tiny movements by patients during scan acquisition introduce errors that could skew results. The finding suggests this new mode may offer a high-resolution, high-speed and noncontact method of determining mechanical properties of the whole cornea.

In their study, published in Investigative Ophthalmology & Visual Science, the researchers note current corneal biomechanical assessment tools are often somewhat invasive, are dependent on intraocular pressure (IOP) and have long acquisition times or limited resolution. PhD-OCT, however, does not. In addition, this potential new tool does not require new equipment. The researchers used M-scans from currently available spectral-domain OCTs.

Using ex vivo porcine eyes and human patients during corneal collagen crosslinking (CXL) treatment, they, in effect, documented motion within the cornea  down to the nanometer level. In both porcine and human eyes, CXL reduced the decorrelation rate, indicating more crosslinks, the study says. The same decorrelation rate reduction was not recorded with sham treatment.

While PhD-OCT was not dependent on IOP variations, it was affected by variations in signal-to-noise ratio, hydration and motion—all of which are correctable, the researchers said in the study.

The study findings show promise for monitoring CXL effects, but the researchers hope it will one day have a broader application. The collagen of a healthy eye is highly confined by the normal microstructural arrangement, while an eye with keratoconus has less confined collagen—which is why CXL is such an effective therapy option. “We hypothesize that PhD-OCT may be able to detect early changes in collagen microstructure associated with keratoconus,” the investigators said in their paper. “This will be investigated in future studies.”

In addition, the authors “expect that PhD-OCT may have several points of impact in the clinic.” First, the technology “may be able to give clinicians real-time feedback on CXL procedures” to help fine-tune results perioperatively; second, it could be used to screen for early-stage keratoconus among groups that are particularly at risk so that “appropriate actions could be taken to correct or stabilize an ectasia before the patient's vision is impaired;” and third, it could help to “characterize the corneal integrity of prospective candidates for LASIK or other refractive surgeries” as a means of preventing postoperative structural instability.

But for now, they conclude that, “PhD-OCT may be a useful and readily translatable tool for investigating biomechanical properties of the cornea and for enhancing the diagnosis and treatment of patients.”

Blackburn BJ, Gu S, Ford MR, et al. Noninvasive assessment of corneal crosslinking with phase-decorrelation optical coherence tomography. Invest Ophthalmol Vis Sci. 2019 January;60:41-51.