Adult Equine Optic Nerve Head Measurements Using Spectral Domain Optical Coherence Tomography.

Clinical signs may not reliably predict equine optic nerve head cupping; SD-OCT needed for accurate assessment.

This study evaluated optic nerve head (ONH) measurements in 45 equine eyes using spectral domain optical coherence tomography (SD-OCT) to assess the reliability of clinical signs in detecting ONH cupping. Eyes were categorized as either CONTROL or CUPPED based on indirect ophthalmoscopy findings. Multiple ONH parameters were measured including Bruch's membrane opening (BMO), optic cup width, anterior laminar depth (ALD), prelaminar thickness (PLT), and cup-to-disk ratio at superior, central, and inferior locations. Results demonstrated that clinically cupped equine ONHs exhibited similar degrees of ONH depression compared to control eyes on SD-OCT imaging. The only statistically significant difference identified was increased central BMO in the cupped group (p=0.007). The study concludes that clinical signs traditionally associated with ONH cupping in horses—such as prominent lamina cribrosa, ONH pallor, and retinal vascular attenuation—may not reliably indicate actual ONH cupping. The findings suggest that current clinical assessment methods may be inadequate for detecting equine ONH pathology and that further research is needed to establish accurate diagnostic criteria.

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