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

Area of Science:

• Ophthalmology
• Veterinary Medicine
• Imaging Technology

Background:

• Optic nerve head (ONH) cupping is a key indicator of glaucoma in humans.
• Accurate assessment of ONH cupping in horses is crucial for diagnosing and managing potential vision-threatening conditions.
• Spectral domain optical coherence tomography (SD-OCT) offers high-resolution imaging for detailed ONH structural analysis.

Purpose of the Study:

• To evaluate the efficacy of SD-OCT in quantifying equine ONH parameters.
• To compare ONH measurements between horses with and without clinical signs of ONH cupping.
• To determine if SD-OCT can detect clinically relevant ONH cupping in horses.

Main Methods:

• Forty-five equine eyes were classified as CONTROL or CUPPED based on indirect ophthalmoscopy.
• SD-OCT was employed to measure Bruch's membrane opening (BMO), optic cup width (OC), anterior laminar depth (ALD), and prelaminar thickness (PLT).
• Measurements were taken at superior, central, and inferior ONH locations, and the cup-to-disk ratio (OC:BMO) was calculated.

Main Results:

• No significant differences in OC:BMO ratios were observed between CONTROL and CUPPED groups across all locations.
• Anterior laminar depth (ALD) showed some variation but lacked consistent differences between groups.
• Central BMO was significantly increased in CUPPED eyes compared to CONTROL eyes (p=0.007).

Conclusions:

• Equine ONHs with clinical signs of cupping exhibited similar ONH depression to control eyes when assessed by SD-OCT.
• Traditional clinical signs like lamina cribrosa prominence, ONH pallor, and vascular attenuation may not be reliable indicators of ONH cupping in horses.
• Further research is needed to identify accurate clinical signs associated with equine ONH cupping.