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Veterinary ophthalmology2026; 29(3); e70174; doi: 10.1111/vop.70174

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

Abstract: To compare equine optic nerve head (ONH) measurements using spectral domain optical coherence tomography (SD-OCT) to detect clinically relevant ONH cupping. Methods: Forty-five eyes from 34 horses were categorized as CONTROL or CUPPED based on indirect ophthalmoscopy and were measured using SD-OCT: Bruch's membrane opening (BMO), optic cup width (OC), anterior laminar depth (ALD), prelaminar thickness (PLT), and cup-to-disk ratio (OC: BMO) at superior (sup.), central (ctr.), and inferior (inf.) ONH locations. Results: The OC:BMO was 0.61 ± 0.09 (sup.), 0.64 ± 0.09 (ctr.), and 0.55 ± 0.10 (inf.) (CONTROL), and 0.60 ± 0.09 (sup.), 0.62 ± 0.08 (ctr.) and 0.54 ± 0.10 (inf.) (CUPPED). The ALD was 0.48 ± 0.20 mm (sup.), 0.50 ± 0.20 mm (ctr.), and 0.42 ± 0.18 mm (inf.) (CONTROL), and 0.49 ± 0.16 mm (sup.), 0.57 ± 0.20 mm (ctr.), and 0.46 ± 0.16 mm (inf.) (CUPPED). The PLT was 0.22 ± 0.08 mm (sup.), 0.17 ± 0.08 mm (ctr.), and 0.17 ± 0.05 mm (inf.) (CONTROL), and 0.21 ± 0.05 mm (sup.), 0.18 ± 0.04 mm (ctr.), and 0.18 ± 0.05 mm (inf.) (CUPPED). The ctr. BMO was significantly increased (mean ± SD of 4.19 ± 0.52 mm) compared to CONTROL (ctr. p = 0.007) eyes. Conclusions: Equine ONHs suggestive of clinical optic nerve head cupping had similar degrees of ONH depression to CONTROL eyes using SD-OCT. Clinical signs such as a prominent lamina cribrosa, ONH pallor, and retinal vascular attenuation may not be reliable predictors of equine ONH cupping. Further research is necessary to determine accurate clinical signs associated with ONH cupping.
© 2026 American College of Veterinary Ophthalmologists.
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Publication Date: 2026-04-04 PubMed ID: 41932856DOI: 10.1111/vop.70174Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study used advanced imaging technology to measure certain structures in the optic nerve head (ONH) of adult horses.
  • The goal was to compare measurements between normal (CONTROL) eyes and those with clinically detected optic nerve head cupping (CUPPED) to see if these signs are reflected in objective measurements.

Background

  • The optic nerve head (ONH) is a key structure in the eye where nerve fibers exit to form the optic nerve; its shape and size can indicate eye health.
  • Optic nerve head cupping refers to an abnormal depression or hollowing of the ONH which can be associated with diseases such as glaucoma in humans and animals.
  • Traditionally, veterinarians use indirect ophthalmoscopy to visually assess the ONH and identify cupping based on clinical signs such as pallor and vessel attenuation.
  • Spectral domain optical coherence tomography (SD-OCT) is a non-invasive imaging technique that produces cross-sectional images of ocular structures with high resolution, allowing precise measurements.

Purpose

  • To utilize SD-OCT to measure specific parameters of the equine ONH.
  • To determine if these measurements correlate with clinical signs of ONH cupping detected by indirect ophthalmoscopy.
  • To assess the reliability of clinical signs in predicting true ONH cupping.

Methods

  • 45 eyes from 34 adult horses were examined and classified into two groups based on clinical evaluation:
    • CONTROL group – eyes without apparent cupping
    • CUPPED group – eyes identified as having ONH cupping
  • SD-OCT was used to measure these parameters at three ONH locations (superior, central, and inferior):
    • Bruch’s membrane opening (BMO) – the anatomical opening where nerve fibers exit
    • Optic cup width (OC) – width of the optic cup or depression
    • Anterior laminar depth (ALD) – depth of the anterior lamina cribrosa
    • Prelaminar thickness (PLT) – thickness of tissue anterior to the lamina cribrosa
    • Cup-to-disk ratio (OC:BMO) – ratio of optic cup width to Bruch’s membrane opening width

Results

  • Measurements for cup-to-disk ratio (OC:BMO) were generally similar between CONTROL and CUPPED groups at all ONH locations, with values roughly around 0.55 to 0.64.
  • Anterior laminar depth (ALD) was slightly higher in CUPPED eyes centrally (0.57mm vs 0.50mm in CONTROL), but differences elsewhere were minor.
  • Prelaminar thickness (PLT) was comparable between groups at all locations.
  • The central Bruch’s membrane opening (BMO) was significantly larger in CUPPED eyes (4.19mm) compared to CONTROL eyes, indicating a measurable difference in ONH anatomy.
  • Other parameters showed no statistically significant differences between groups.

Conclusions

  • Despite the clinical signs suggesting optic nerve head cupping, SD-OCT measurements showed that the degree of ONH depression in CUPPED eyes was similar to CONTROL eyes.
  • Traditional clinical signs such as a prominent lamina cribrosa, pallor of the ONH, and retinal blood vessel attenuation may not be accurate or reliable indicators of true ONH cupping in horses.
  • The significant increase in central BMO size in CUPPED eyes suggests some anatomical alteration but does not necessarily correspond to cupping measurable by OCT.
  • Further studies are needed to identify accurate clinical markers and improve diagnostic techniques for detecting true ONH cupping in equine patients.

Implications

  • This research highlights the importance of using objective imaging tools like SD-OCT for diagnosing optic nerve health in horses.
  • It may lead to changes in how veterinarians assess ocular pathology, moving away from solely clinical examination to incorporating imaging data.
  • Understanding equine ONH anatomy better can help recognize early signs of optic nerve diseases and improve equine ocular care.

Cite This Article

APA
Bostick HN, Keys DA, Bowden AC, McMullen RJ. (2026). Adult Equine Optic Nerve Head Measurements Using Spectral Domain Optical Coherence Tomography. Vet Ophthalmol, 29(3), e70174. https://doi.org/10.1111/vop.70174

Publication

Veterinary ophthalmology
ISSN: 1463-5224
NlmUniqueID: 100887377
Country: England
Language: English
Volume: 29
Issue: 3
Pages: e70174

Researcher Affiliations

Bostick, Hannah N
  • College of Veterinary Medicine, Auburn University, Auburn, Alabama, USA.
Keys, Deborah A
  • Kaleidescope Statistics, Athens, Georgia, USA.
Bowden, Anna Catherine
  • College of Veterinary Medicine, Auburn University, Auburn, Alabama, USA.
McMullen, Richard J
  • College of Veterinary Medicine, Auburn University, Auburn, Alabama, USA.

MeSH Terms

  • Animals
  • Horses / anatomy & histology
  • Tomography, Optical Coherence / veterinary
  • Optic Disk / anatomy & histology
  • Optic Disk / diagnostic imaging
  • Female
  • Male
  • Horse Diseases

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