TDK conference 2019

In this study we used streak retinoscopy or skiascopy, a well-known procedure in human medicine, to asses the refractive state of equines’ eye. Our aim was to measure and compare the refractive error of both eyes in horses, ponies and donkeys, and to determine its correlation with gender and age.

In this study, 30 horses, 30 ponies and 30 donkeys with healty eyes were examined using a streak retinoscope and positive or negative skiascope bars in both vertical and horizontal meridians. The retinoscopy was done by the same examiner. From the measurements the spherical equivalent (meridian value that is closer to zero, SE), cylinder (difference of the two meridians, which can be + or -), and the mean refractive error (mean of the two eyes' spherical equivalent, MRE) and the value of anisometropia (difference of the two eyes' MRE) were calculated. For statistical analysis Student's t-test, Kruskal–Wallis one-way analysis of variance, Spearman's rank correlation coefficient and Wilcoxon signed-rank test were used. SE of the horses' eyes were -0.26±0.21 D, ponies' +0.08±0.18 D and donkeys' -0.09±0.17 D, MRE was -0.26±0.29 D, +0.08±0.25 D and -0.09±0.22 D, respectively. This shows that the horses and donkeys were rather myopic and ponies hyperopic. The ratio of hyperopic, emmetropic and myopic animals in horses was 0%-90%-10%, in ponies 6.67%-83.33%-10%, in donkeys 3.33-86.67-10%. Emmetropia was found in the biggest proportion in horses, and there were no hyperopic horse. Emmetropic ponies and donkeys were fewer than horses, and there were more myopic than hyperopic animals.

The greatest refractive error was measured in ponies (+2.5 D), while the lowest in horses and donkeys (-4.5 D). The rate of astigmia was relatively high in the 3 groups (40, 50 and 45%), and the number of bilateral astigmia also (13.33%, 33.33%, 26.6%), so there's a greater chance in a pony that the refractive error of the two meridians are not equal. Greater ratio of anisometropia (36.67%, 23.33%, 43.30%) was found in donkeys.

The correlation between SE, CYL, MRE, anisometropia and age or gender was not significant in horses and ponies, however donkeys' SE and MRE correlated with both gender and age: mares were more hyperopic than stallions, and the SE, MRE increases with age. The difference between the horizontal and vertical meridians’ refractive error was significant in ponies.

In conclusion most of the examined equidae were emmetrop, significant ametropia is rare among them. If we widen the group, and do more research, we will be able to discover more defects, diseases, that manifest only in the change of the behavior or in poor performance.