Refractive errors

Refractive states were assessed to determine the prevalence and severity of refractive errors. Streak retinoscopy was performed using a retinoscope (Welch Allyn®, New York) and a set of skiascopic lenses (Sunwin®, China) after pharmacologic mydriasis, 10 minutes after tropicamide instillation. The retinoscope was placed in front of the evaluator’s eye with a distance of approximately 65 cm from the dog. A correction of –1.5 diopters was made due to the distance between the retinoscope and the eye. All the measurements were performed by the same veterinary ophthalmologist (FMF) and required only physical restraint of the animals. Emmetropia was considered when the streak retinoscopy values were between or equal to –0.5 and +0.5 diopters after correction was accounted (Kubai et al., 2008). Ametropia was considered when an eye had myopia (refractive errors were below –0.5 diopters) or hyperopia (when the value was higher than +0.5 diopters). Furthermore, anisometropia was considered when a difference of refractive errors between the eyes of the same dog was ≥1.0 diopters.