Introduction:
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:
The majority of eyes tested were emmetropic (83.63%), with 68.5% of horses having refractive errors of ≤ -0.50D or ≥ +0.50D. Refractive errors of greater than 1.50D (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 2 Thoroughbred crosses having a tendency towards myopia and Warmbloods / Shires towards hyperopia.
Discussion / Conclusion:
The retinoscopic survey found emmetropia to be the predominant refractive state of the equine eye with no evidence of an overall trend towards 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 behavioural problems
