Evaluating corneal thickness is important in both clinical and research settings. There are a variety of methods to measure corneal thickness in vivo, such as high-resolution ultrasound biomicroscopy and confocal microscopy.1,2 Inadvertent damage to the cornea and imprecise measurements can occur with these modalities because they both require corneal contact.3 In contrast to these methods, optical coherence tomography can be used. This noncontact imaging modality collects high-resolution, cross-sectional images of the cornea by measuring optical reflections.4 The basis of this modality is interferometry, which generates an interference pattern from 2 beams of light, which in turn creates an axial scan. Thousands of these axial scans are collected transversely, which generate a cross-sectional image of the tissue being measured.5 To obtain images of the tissues, SD-OCT devices use a superluminescent diode, a spectrometer, and the Fourier transform algorithm to achieve rapid, high-resolution scans.6,7
The use of SD-OCT devices has been validated as reliable and repeatable for measuring corneal thickness in humans,8–11 dogs,12,13 cats,14 and horses.15,16 Although such devices are becoming more prevalent in veterinary medicine, normative data for corneal thickness measurements by use of this modality are lacking, particularly for farm animal species. The purpose of the study reported here was to measure corneal thickness (specific measurements of the CET, CST, DMT, and TCT) of healthy goats, sheep, and alpacas by use of a portable SD-OCT device. Intraobserver reliability of this device and associated software was evaluated for each corneal layer and for the TCT.
Supported in part by the Cummings School of Veterinary Medicine at Tufts University Companion Animal Fund and by Optovue.
Presented in abstract form at the 46th Annual Conference of the American College of Veterinary Ophthalmologists, Coeur d'Alene, Idaho, October 2015.
The authors thank Dr. Bruce Barton for assistance with the statistical analysis, Kimberly Flink for technical assistance, and Scott Brundage for assistance with the animals.
Corneal epithelial thickness
Corneal stromal thickness
Coefficient of variation
Descemet membrane thickness
Intraclass correlation coefficient
Spectral-domain optical coherence tomography
Total corneal thickness
Akorn Inc, Lake Forest, Ill.
Kowa SL-15 portable slit-lamp biomicroscope, Kowa Co Ltd, Tokyo, Japan.
TonoVet, Icare, Vantaa, Finland.
Welch Allyn binocular indirect ophthalmoscope, Welch Allyn Inc, Skaneateles Falls, NY.
Telazol, Zoetis Inc, Florham Park, NJ.
Putney Inc, Portland, Me.
West-Ward Pharmaceuticals Corp, Eatontown, NJ.
AnaSed LA, MWI Animal Health, Boise, Idaho.
Torbugesic, Pfizer Inc, New York, NY.
Major Pharmaceuticals, Livonia, Mich.
Optovue iVue SD-OCT, provided by Optovue Inc, Freemont, Calif.
Microsoft Excel 2010, Microsoft Corp, Redmond, Wash.
SAS, version 9.2, SAS Institute Inc, Cary, NC.
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