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Sammanfattning: Skiascopy is used to objectively determine the refractive power of the eye. Except for a Swedish study in 2007, where 93 horses of different breeds and ages were examined with respect to their refractive status, most studies on equine refraction were published about one century ago or more. The objective of this study is to examine the refractive status of healthy warm-blooded trotting horses. Skiascopy was performed in 117 horses in total, aged 3 days to approximately 22 years old. In a pilot study, it was determined whether young horses were able to accommodate or not during skiascopy. The horses in the pilot study were all younger than 14 months. In foals younger than 1,5 months we saw a significant difference in the skiascopy result in the right eyes before and after topical atropine was instilled, but not in the left eye. In horses between 9 and 14 months old, there was no significant difference before and after atropine instillation. Cykloplegia is accordingly not necessary in horses older than 9 months. The study shows that foals are born predominantly hyperopic. The refraction of the young horse rapidly progresses toward emmetropia. In the elderly horse, the progression is not as fast, but refraction is still changing and slowly progressing toward myopia. A non-linear, mathematical model was developed to show the development of the refractive status based on the data obtained in our study.