Eyes of Arabian horses found to be more sensitive than other breeds tested in study

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The five regions of the cornea evaluated. D = Dorsal, T = Temporal, V = Ventral, N = Nasal and C = Central. The central region was the most sensitive, followed by the nasal, temporal, ventral and dorsal regions, the latter being the least sensitive. Image: Pontes Oriá et al. http://dx.doi.org/10.1590/0103-8478cr20160995
The five regions of the cornea evaluated. D = Dorsal, T = Temporal, V = Ventral, N = Nasal and C = Central. The central region was the most sensitive, followed by the nasal, temporal, ventral and dorsal regions, the latter being the least sensitive. Image: Pontes Oriá et al. http://dx.doi.org/10.1590/0103-8478cr20160995

The surface of the eye in Arabian horses was found to be more sensitive than those of other breeds tested in a study in Brazil.

Researchers from the Federal University of Bahia and other institutions set about testing the corneal sensitivity of five horses breeds – the Arabian, Mangalarga Marchador, Pure Blood Lusitano, Quarter Horse, and Brazilian Sport Horse.

In all, 145 healthy horses had their sensitivity values measured in five different regions of the cornea using a Cochet-Bonnet esthesiometer.

The procedure was performed by gently touching the cornea with a nylon filament just 0.12mm in diameter. It was 6cm long in the initial test, during which the eye surface was touched three times in a bid to get a blink reflex.

If no reflex was observed, the filament length was reduced by 0.5cm at a time, and the test repeated until blinks were achieved for all three contacts, or until the shortest length of 0.5cm was reached.

The researchers, whose findings have been reported online in Ciência Rural, found that the corneal touch threshold differed for different regions of the cornea, and that there were significant differences among the horse breeds tested.

Median values ± semi-interquartile range of corneal touch threshold for the different eye regions. The results, with the numbers representing the length of the nylon filament in centimetres that achieved the blink response three times to the touch. The higher values correspond to greater corneal sensitivity. PSA - Arabian horse, MM - Mangalarga Marchador, PSL - Pure Blood Lusitano, QM - Quarter Horse, BH - Brazilian Sport Horse. Different superscript letters indicate significant differences between corneal regions. Table: Pontes Oriá et al. http://dx.doi.org/10.1590/0 103-8478cr20160995
Median values ± semi-interquartile range of corneal touch threshold for the different eye regions. The numbers represent the length of the nylon filament in centimetres that achieved the blink response three times to the touch. Higher values correspond to greater corneal sensitivity. PSA – Arabian horse, MM – Mangalarga Marchador, PSL – Pure Blood Lusitano, QM – Quarter Horse, BH – Brazilian Sport Horse. Different superscript letters indicate significant differences between corneal regions. Table: Pontes Oriá et al. http://dx.doi.org/10.1590/0103-8478cr20160995

For all the breeds tested, the central region (the quadrant above the pupil) was the most sensitive.

The nasal quadrant (closest to the nose) was the second-most-sensitive region, followed by the temporal (outer) quadrant, then the ventral (lower) quadrant, with the dorsal (upper) region being the least sensitive.

Arabian horses presented higher sensitivity values, proving to be the most sensitive in all of the corneal regions. The researchers wondered if this was a result of the breed’s unique cranial shape and prominent eyes.

The study team comprised Eunice Santos de Andrade, João Victor Romano Vieira, Deusdete Conceição Gomes Júnior, Ana Claúdia Santos Raposo, Paula Diniz Galera and Arianne Pontes Oriá.

Corneal sensitivity in five horse breeds
Eunice Santos de Andrade, João Victor Romano Vieira, Deusdete Conceição Gomes Júnior, Ana Claúdia Santos Raposo, Paula Diniz Galera and Arianne Pontes Oriá.
Cienc. Rural vol.47 no.6 Santa Maria 2017 Epub May 18, 2017 http://dx.doi.org/10.1590/0103-8478cr20160995

The full study, published under a Creative Commons License, can be read here

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