Undersökning av ögats brytningsförmåga i ett svenskt hästmaterial

Sammanfattning: Skiascopy, also called retinoscopy, is a method for determining the refractive power of the eye. There are only a few, old studies made on equine refraction. The aim of this study was to investigate the refractive power in a population of Swedish horses. The study consists of a review of relevant studies done on animals and an experimental part where the refractive power of 93 horses of different age, breed and usage was examined. A pilot study of 12 horses was performed regarding the importance of cycloplegia when doing skiascopy on horses. The results of the pilot study show no significant difference in the skiascopy results between the group before and after cycloplegia were induced. Consequently, there is no need of inducing cycloplegia before doing skiascopy in adult horses. The study shows that horses usually were emmetropic (normally sighted) with minor deviations toward myopia or hyperopia. There was a clear relation between age and refractive error. With increasing age, the horses became more nearsighted, myopic. Furthermore, the results suggested that refractive power was different in different breeds. Icelandic horses were more farsighted, hyperopic, and thoroughbreds were more myopic. Horses used for dressage were more myopic than horses used for other purposes. Given that this study includes a relatively small number of horses, it would be interesting to study a larger population with respect to age, breed and usage. Furthermore, it would also be interesting to study the refractive power of foals and young horses.