Degenerative optic neuropathy in a horse.

The research article discusses a case of blindness in a horse due to degeneration of the optic nerves and tracts and explores potential causes for the condition.

Case Presentation and History

• The subject of the investigation was a four-year-old Australian Stud Book pony mare. This horse was the only one from her birth stud to develop blindness.
• At one and a half years old, the horse was sold and relocated to Wagga Wagga in southern New South Wales. Shortly after this move, she was treated with trichlorphon followed by a half-yearly treatment with mebendazole.
• The mare grazed on pasture composed of a mix of subterranean clover and rye grass, which was complemented with clover and lucerne hay, wheaten chaff, and a mineral-vitamin premix. The horse also had limited exposure to cape weed and Paterson’s Curse.
• A significant history event was the use of 2,4-dichlorophenoxyacetic acid ester*, a compound sprayed on the paddock where the mare was kept a month before the onset of blindness symptoms.

Observations and Findings

• The early indication of blindness was the mare’s tendency to collide with objects in unfamiliar surroundings. She didn’t exhibit this behavior in her own yard.
• Clinical examination revealed cloudiness in her left cornea, and in both eyes, there was notable dilation of the pupil along with a weak pupillary light reflex.
• Despite these symptoms, ophthalmoscopic inspection only revealed minor abnormalities—both optic discs showed pallor, and there was slightly reduced vascularity.
• After two months of these symptoms, the mare was euthanized as per the owner’s request.

Pathological Findings

• Post-mortem examinations of the mare revealed that beyond the diffuse opacity of the left cornea, there were no significant gross pathological findings.

Implications and Interpretations

• In this case, the etiology of the degenerative optic neuropathy—the cause of the mare’s blindness—remains unclear. Still, the authors seek to investigate potential causes, encompassing the possibilities of nutritional deficiencies, exposure to toxins, or the effects of the specific treatments mentioned in the case history.