Ocular manifestations of equine motor neuron disease.

The research article is investigating the ocular characteristics found in horses affected by equine motor neuron disease (EMND). Often overlooked, these visual signs aid in diagnosing this neurodegenerative disease, contributing to swift and accurate treatments.

Subjects and Methodology

• The researchers used 42 horses who exhibited classic signs of EMND, as confirmed by their clinical history and necropsy results.
• An eye examination of each of these horses was performed, noting changes such as pigmentation patterns and hyperreflectivity in certain areas.
• Electroretinography (ERG) was carried out to measure the electrical response of the horse’s retina. Reduced or extinguished amplitudes were recorded in most cases.
• A histopathological study was conducted on the horses’ retinas, targeting the retinal pigment epithelial (RPE) and neural retina.
• Vitamin E levels were also measured in all horses as they were not on any supplementation.

Findings

• Most of the horses exhibited peculiar retinal changes, including a pigmented reticulated pattern that varied in color from yellow-brown to black.
• Hyperreflectivity forming mosaic patterns were another significant find in the tapetal fundus.
• ERG results demonstrated a significant drop (or complete extinction) in B-wave amplitudes, indicating a likely dysfunction in cone or rod photoreceptors in the retina.
• No apparent visual impairment was noticed in any of the horses.
• Post examination, the RPE showed congestion with ceroid-lipofuscin, which is a marker of cellular damage and aging.
• Retinal degeneration was variable even within the same eye.
• Unique green and orange fluorescence were detected using thin layer chromatography (TLC) on the RPE and neural retina, notable as this differs from the norm in healthy horses.
• All horses had vitamin E levels below 1.0 µg/ml, raising the question of a potential role of vitamin E deficiency in EMND.

Significance

• This research is important because ocular manifestations are not commonly associated with EMND, a disease that primarily affects muscle coordination.
• The discovery of distinctive eye-related signs could help veterinarians diagnose this disease more quickly, leading to improved management and treatment.
• The contribution of vitamin E deficiency to EMND might provide a new avenue for preventing or treating the disease.