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

Abstract

Purpose:The purpose of this case series is to evaluate the use of spectral domain optical coherence tomography (SD-OCT) imaging in equine corneal disease to demonstrate the feasibility, diagnostic effectiveness, and limitations of this imaging modality. Methods: Retrospective study: Handheld SD-OCT (Envisu, Bioptigen Inc, Morrisville, NC) was used for high-resolution imaging of horses with corneal disease presenting to the North Carolina State University Equine Ophthalmology Service from 2013 to 2018. Results: Fourteen horses were included in this study, including six horses with corneal ulceration, three with stromal abscesses (SA), three with immune-mediated keratitis (IMMK), and two with ocular neoplasms. High-resolution images of the cornea were obtained using handheld SD-OCT in standing horses; however, acquiring images was time-consuming due to the inherent movement of the examiner and horse. Despite this, in horses with corneal ulcers, SA, and IMMK, SD-OCT assisted with determining location of disease in the cornea (eg, superficial, mid-stromal, endothelial) and if disruption of Descemet's membrane was present. In horses with neoplasia, the SD-OCT helped to determine whether the cornea had neoplastic invasion from anterior chamber masses. Conclusions: Results from this retrospective study suggest that handheld SD-OCT for imaging the cornea of horses is feasible and may be helpful in determining depth and extent of lesions in the cornea.

Corneal thickness and anterior chamber depth of the normal adult horse as measured by ultrasound biomicroscopy

“…The normative data included in the present report provide an important reference that can be used as a comparison for clinical cases of both corneal and anterior segment disease. While UBM is inferior to SD-OCT in terms of image resolution, UBM has wider applicability for anterior segment imaging in that UBM can image nontransparent tissues including conjunctiva, sclera, and uvea as well as through dense corneal opacities that create significant artifact with OCT. 34 Limitations of UBM include the requirement of globe contact for image acquisition, which precludes use of UBM in fragile globes. Additionally, depth of penetration is limited to the anterior segment.…”

Comparison of image quality of corneal and retinal optical coherence tomography using sedation and general anesthesia protocols with or without retrobulbar anesthesia in horses

“…3,4 This imaging technique has also been used to describe clinical cases of corneal and uveal diseases. [5][6][7][8][9][10][11]28 No scales have been established to grade the quality of OCT images for the cornea and retina, but scales used to grade aqueous humor flare using time domain OCT have been reported. 28 Diagnostic image quality should distinguish layers of the cornea including the epithelium, stroma, and Descemet membrane/endothelial complex as well as the layers of the retina.…”

“…2 Several other veterinary species have since been evaluated, including 2 studies 3,4 documenting the use of handheld spectral domain OCT (SD-OCT) to evaluate the normal cornea, retina, and optic nerve of horses. OCT has also been utilized to evaluate heterochromic iridocyclitis with secondary keratitis and Descemet membrane detachments and separations, 9,10 and a case series 11 describes a variety of ocular lesions in horses. To minimize motion artifacts, OCT is often performed in veterinary species while they are under general anesthesia (GA), whereas all published reports of OCT in horses involved standing sedation with local eyelid anesthetic blocks.…”

Evaluation of equine corneal disease using ultrasound biomicroscopy

“…Unlike SD-OCT, UBM can image through dense corneal opacities. 16 However, UBM does not provide nearly the same level of resolution, particularly when compared to confocal microscopy. 13 Therefore, each imaging modality has different benefits and limitations.…”