Viscotears carbomer 980

CCM analysis was performed in both eyes using the Heidelberg Retinal Tomograph 3 (HRT‐3) device with the Rostock Cornea Module (RCM) (Heidelberg Engineering GmbH, Heidelberg, Germany). The cornea was locally anesthetized by instilling 1‐drop of 0.4% benoxinate hydrochloride (Chauvin Pharmaceuticals, Chefaro, UK). Viscotears (Carbomer 980, 0.2%, Novartis, UK) was used as the coupling agent between the cornea and TomoCap, and between the TomoCap and objective lens. Patients were instructed to fixate on a target with the eye not being examined. High resolution 400 × 400 μm field of view images are generated using a 670‐nm red wavelength diode laser. Several scans of the sub‐basal nerve plexus in the central cornea were captured. To avoid bias, at a separate time, three high clarity non‐overlapping images per eye were selected based on depth, focus position and contrast as described previously²⁴, ²⁵, ²⁶ by an investigator who was blinded from the diagnosis, cognitive function, and MRI brain volumetry. The central cornea was selected for imaging the sub‐basal nerve plexus. Corneal nerve fiber density (CNFD)‐ main fibers (no./mm²), corneal nerve branch density (CNBD)‐ branches from the main nerve fibers (no./mm²), corneal nerve fiber length (CNFL)‐ length of the main fibers and branches (mm/mm²), and CNBD/CNFD ratio were measured manually using CCMetrics.²⁷

All patients underwent CCM (Heidelberg Retinal Tomograph III Rostock Cornea Module, Heidelberg Engineering GmbH, Heidelberg, Germany). This device uses a 670 nm wavelength helium neon diode laser, which is a class I laser and therefore does not pose any ocular safety hazard. A 63x objective lens with a numerical aperture of 0.9 and a working distance, relative to the applanating cap (TomoCap^©, Heidelberg Engineering GmbH, Heidelberg, Germany) of 0.0 to 3.0 mm is used. The size of each two-dimensional image produced is 384 μm × 384 μm with a 15° × 15° field of view and 10 μm/pixel transverse optical resolution. To perform the CCM examination, local anesthetic (0.4% benoxinate hydrochloride, Chauvin Pharmaceuticals, Chefaro, UK) was used to anaesthetize each eye and Viscotears (Carbomer 980, 0.2%, Novartis, UK) were used as the coupling agent between the cornea and the applanating cap. All patients were asked to fixate on an outer fixation light throughout the CCM scan and a CCD camera was used to correctly position the applanating cap onto the cornea. The examination took approximately 10 minutes for both eyes and was undertaken by experienced examiners (AK, GP, HA and INP), masked from the subject’s clinical status. Images of the endothelial cells and subbasal corneal nerves were captured using the “section” mode.