HANDHELD SD-OCT

Experience using a handheld high-resolution spectral domain OCT (SD-OCT) platform (Envisu, Bioptigen) for intraoperative imaging indicates it has a range of applications that should make it a helpful tool in clinical research and daily practice, reported Soumya Nanaiah MS, at the 26th Asia-Pacific Association of Cataract & Refractive Surgeons Annual Meeting. Speaking in a free paper session on refractive surgery, Dr Nanaiah reviewed findings from evaluations performed with the imaging system in cases of LASIK, corneal collagen crosslinking (CXL), intracorneal ring segment (ICRS) implantation and cataract refractive surgery.

“This SD-OCT machine comes with a handheld probe that enables intraoperative measurements with patients in the supine position,” said Dr Nanaiah, a cataract and refractive surgery fellow at the Narayana Nethralaya Eye Hospital, Bangalore, India. She noted that the instrument is useful in assessing treatment depths in various refractive procedures as well as to determine anatomic changes and responses of ocular tissues to treatments.

During LASIK, the device was used to evaluate stromal bed characteristics and flap thickness in groups of 50 eyes each where either a mechanical microkeratome or a femtosecond laser was used for flap creation. The intraoperative images clearly showed differences in edge architecture and stromal bed smoothness between the two techniques. In addition, analysis of data collected using the calipers available with the device to measure flap thickness demonstrated significantly better predictability was achieved using the femtosecond laser. Images from eyes that underwent ICRS placement into femtosecond laser-created channels were analysed to determine placement depth. The investigators found no tendency for any part of the segments to be more superficial than another, and there was no statistically significant difference comparing the planned segment depth and that achieved postoperatively.

In CXL, the handheld SD-OCT device was used to evaluate depth of riboflavin penetration in eyes that underwent complete or only partial (grid pattern) removal of the epithelium. In serial imaging of eyes in which the epithelium was completely removed, a homogenous hyperreflective band denoting soakage was observed after 30 and 60 minutes at mean depths of 54.2 μm and 72.4 μm, respectively. Similar depths of riboflavin penetration were measured after 30 and 60 minutes in the partial removal group in areas where the epithelium was off (56.9 and 74.2 microns, respectively), but the depth of penetration at both time points was significantly less at sites corresponding to areas where the epithelium was still intact (18.9 and 24.7 microns, respectively).

“In patients who had LASIK with CXL, we observed a pseudo-Bowman’s membrane at the interface between the flap and the bed,” Dr Nanaiah reported. Most recently, the investigators are applying the imaging tool to compare the features of cataract surgery clear corneal and sideport incisions created using a manual technique versus with a femtosecond laser and to confirm whether or not free-floating caps were achieved after femtosecond laser capsulotomy.