Ophthalmic examination in the horse is generally limited to crude assessment of vision and screening for ocular lesions. The refractive state of equine eyes and the potential impact on vision and performance requires further investigation.Objective
To assess the refractive state of a large, mixed-breed sample of horses and ponies in the United Kingdom (UK).Procedure
The refractive state of both eyes of 333 horses and ponies was determined by streak retinoscopy, and the effect of age, height, gender, breed and management regime on the refractive state assessed.Results
Emmetropia was found in 557 of 666 (83.63%) of eyes; 228/333 (68.5%) of the horses/ponies were emmetropic in both eyes. Refractive errors of greater than 1.50 D (in either direction) were found in 2.7% of the eyes tested. Ametropic eyes included hyperopia (54%) and myopia (46%). Anisometropia was found in 30.3% of horses and ponies. Breed of horse/pony was the only factor that affected refractive state (in the left eye only, P < 0.05) with Thoroughbred crosses having a tendency toward myopia and Warmbloods/Shires toward hyperopia.Discussion and Conclusion
The retinoscopic survey found emmetropia to be the predominant refractive state of the equine eye with no evidence of an overall trend toward myopia or hyperopia. However, individual and breed-related differences were found. Such factors should be considered in the selection of horses for sport and leisure, and when evaluating their performance potential. More comprehensive visual testing would be valuable in identifying underlying causes of behavioral problems.