Spectral‐domain optical coherence tomography evaluation of the cornea, retina, and optic nerve in normal horses

Abstract

The SD-OCT instrument employed in this study may be used on sedated horses and allows the acquisition of high-resolution images, and thickness measurements involving the cornea, retina, and optic nerve.

Evaluation of equine corneal disease using spectral domain optical coherence tomography (SD‐OCT)

“…To the authors’ knowledge, this is the first report on the use of SD‐OCT to evaluate corneal disease in horses, other than our previous publication using SD‐OCT in the characterization of HIK . In this case series, some obvious advantages of the use of SD‐OCT for corneal disease imaging were demonstrated, including the rendering of high‐resolution images (2‐6 µmol/L axial resolution) of cross sections of corneal lesions . The B scan cross‐sectional image provides good anatomic detail for easy interpretation.…”

“…Fixating the OCT was possible, but aligning the fixed OCT and horse eye proved difficult with the current instrument configuration. Therefore, use of the handheld device in a tranquilized horse with its head stabilized was determined to be the most feasible imaging technique, as observed in our previous studies . Improvements in image scan speeds and development of instrument hardware that allows fixation of the hand piece and at the same time allows better access to the equine cornea would decrease image session time and likely improve image quality.…”

“…Corneal imaging with SD‐OCT was selected for this subset of horses to gain a better understanding of the underlying cause, the extent, and depth of the corneal lesion and, in some cases (ie, neoplasia), to determine whether corneal tissue had been invaded. For corneal imaging, SD‐OCT was used as previously described . Briefly, horses were tranquilized with detomidine HCL (0.01‐0.04 mg/kg body weight, IV) and palpebral nerve blocks were performed (1 mL lidocaine HCL).…”

“…Advanced imaging of the equine cornea may assist the clinician to determine the cause, depth, and extent of corneal disease . Modalities such as high‐frequency ultrasound, in vivo confocal imaging, and spectral domain optical coherence tomography (SD‐OCT) provide high‐resolution imaging and show great promise for imaging of the equine cornea . Optical coherence tomography obtains high‐resolution cross‐sectional images of tissue architecture in vivo by interferometry, which correlates the light backscattered from the tissue and the light that has travelled a known distance (reference arm length) to measure the magnitude and echo time delay of backscattered light .…”

“…The advantage of SD‐OCT imaging is that the high resolution and magnification of ocular tissues in vivo approaches the histopathological level (ie, resolution of 2‐6 μm). In horses, the use of SD‐OCT was first reported in 2014 where the technique and feasibility of SD‐OCT use in the standing horse were described along with the normal anatomy of the equine cornea, retina, and optic nerve of the normal horse . The use of SD‐OCT for measurement of equine corneal thickness has also been described; but to date, only a single study exists of the use of this imaging modality in horses with corneal disease .…”