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

Abstract

OBJECTIVE To compare image quality and acquisition time of corneal and retinal spectral domain optical coherence tomography (SD-OCT) under 3 different sedation-anesthesia conditions in horses. ANIMALS 6 middle-aged geldings free of ocular disease. PROCEDURES 1 randomly selected eye of each horse was evaluated via SD-OCT under the following 3 conditions: standing sedation without retrobulbar anesthetic block (RB), standing sedation with RB, and general anesthesia with RB. Five regions of interest were evaluated in the cornea (axial and 12, 3, 6, and 9 o’clock positions) and fundus (optic nerve head). Three diagnostic scans of predetermined quality were obtained per anatomical region. Image acquisition times and total scans per site were recorded. Corneal and retinal SD-OCT image quality was graded on a subjective scale from 0 (nondiagnostic) to 4 (excellent). RESULTS Mean values for the standing sedation without RB, standing sedation with RB, and general anesthesia conditions were 24, 23, and 17, respectively, for total cornea scan attempts; 23, 19, and 19 for total retina-scan attempts; 14.6, 13.2, and 9.2 minutes for total cornea scan time; 19.1, 9.2, and 13.0 for total retina scan time; 2.0, 2.3, and 2.5 for cornea grade; and 2.7, 2.9, and 2.5 for retina grade. CONCLUSIONS AND CLINICAL RELEVANCE The RB facilitated globe akinesia and improved the percentage of scans in frame and region of interest accuracy for retinal imaging via OCT in horses. Retrobulbar blocks improved clinical image acquisition while minimizing motion artifact.

Retrobulbar lidocaine injection via the supraorbital fossa is safe in adult horses but produces regionally variable periocular anaesthesia

“…This was verified in a pilot cadaveric assessment using computed tomography (CT), demonstrating deposition of contrast medium lateral and caudal to the retrobulbar cone (Figure ). This problem was also described in a recent in vivo abstract of horses undergoing direct retrobulbar injection to facilitate akinesia of the globe 10 . Thus, modification to the direct injection may be required for some horses wherein the needle is angled slightly medially (Figure 1) as previously described by Berge and Lichenstern 11 .…”

“…This problem was also described in a recent in vivo abstract of horses undergoing direct retrobulbar injection to facilitate akinesia of the globe. 10 Thus, modification to the direct injection may be required for some horses wherein the needle is angled slightly medially (Figure 1) as previously described by Berge and Lichenstern. 11 In our cadaveric assessment, this technique more often resulted in intraconal deposition of the contrast medium (Figure S1).…”