Horses without ocular disease maintain similar electroretinographic responses and peripapillary retinal thicknesses across age groups.

Overview

• This study examined whether aging affects retinal function and retinal thickness in healthy horses.
• The researchers found that both electroretinography (ERG) responses and retinal thickness remain stable across different age groups in horses without ocular disease.

Objective of the Study

• To determine the impact of age on equine retinal function measured by electroretinography (ERG) and peripapillary retinal thickness measured by optical coherence tomography (OCT).
• Hypotheses tested: (1) ERG b-wave amplitudes would decrease with age, (2) total retinal thickness (TRT) would not vary significantly across age groups.

Methodology

• Subjects: 15 clinically healthy horses divided into three age groups: ≤ 10 years, 11 to 20 years, and ≥ 21 years (5 horses per group).
• Procedures included:
  • Electroretinography (ERG) to evaluate retinal function under scotopic (dark-adapted) and photopic (light-adapted) conditions using RETevet equipment.
  • Measurement of implicit times and amplitudes of a- and b-waves during ERG tests.
  • High-resolution fundus photography to visualize the retina.
  • Spectral-domain optical coherence tomography (OCT) to assess total retinal thickness (TRT) in the nasal, dorsal, and temporal peripapillary regions (around the optic nerve head).
• Comparison of these parameters among the three age groups.

Key Findings

• No statistically significant differences in ERG implicit times or amplitudes were found between the age groups, indicating stable retinal electrophysiological function with aging in healthy horses.
• Similarly, peripapillary retinal thickness in nasal, dorsal, and temporal regions did not differ significantly across age groups, showing no age-related thinning in healthy equine retinas.

Interpretation and Significance

• The study suggests that normal aging in horses without ocular disease does not lead to decreased retinal function or retinal thinning as measured by ERG and OCT.
• Stable ERG parameters suggest retinal cells maintain functional integrity with age, at least up to 21 years and beyond in horses.
• Peripapillary retinal thickness remaining constant implies no structural degeneration or atrophy associated purely with aging.
• Clinically, if a horse presents with reduced ERG amplitudes or retinal thinning, it should not be attributed to normal aging but should prompt investigation for underlying pathology.
• This provides valuable baseline data for veterinarians to differentiate between disease and age-related changes in equine ophthalmology.

Limitations and Considerations

• Sample size was small (15 horses), which may limit generalizability; however, the study balanced groups by age category.
• Only horses with clinically normal eyes were included, so findings apply to healthy eyes specifically.
• Other factors such as breed, sex, and environmental influences were not mentioned and could potentially affect retinal parameters.
• Future studies could explore a larger and more diverse population or examine specific ocular diseases in relation to age.

Summary

• This research demonstrates that in horses without ocular disease:
  • Retinal function measured by ERG remains consistent across young, middle-aged, and older horses.
  • Peripapillary retinal thickness measured by OCT also remains stable across age groups.
  • Hence, retinal changes seen in clinical settings are more likely due to disease rather than normal aging.