Horse vision and an explanation for the visual behaviour originally explained by the ‘ramp retina’.
Abstract: Here we provide confirmation that the 'ramp retina' of the horse, once thought to result in head rotating visual behaviour, does not exist. We found a 9% variation in axial length of the eye between the streak region and the dorsal periphery. However, the difference was in the opposite direction to that proposed for the 'ramp retina'. Furthermore, acuity in the narrow, intense visual streak in the inferior retina is 16.5 cycles per degree compared with 2.7 cycles per degree in the periphery. Therefore, it is improbable that the horse rotates its head to focus onto the peripheral retina. Rather, the horse rotates the nose up high to observe distant objects because binocular overlap is oriented down the nose, with a blind area directly in front of the forehead.
Publication Date: 1999-10-03 PubMed ID: 10505953DOI: 10.1111/j.2042-3306.1999.tb03837.xGoogle Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research debunks the ‘ramp retina’ theory, suggesting that horses do not rotate their heads to focus on the peripheral retina, but lift their noses high to see distant objects due to the downwardly oriented binocular overlap and a blind area in front of the forehead.
Overview of the Study
- This research aims to disprove the theory of the ‘ramp retina’ in horses, which was previously thought to cause their head rotation behavior when trying to visualize their surroundings. The ‘ramp retina’ theory suggested that the eyes of horses had varying axial lengths at different points (from the streak region to the dorsal periphery) with the belief that this variety led to the horse’s unique visual behavior.
- The researchers in this study found only a 9% variation in the eye’s axial length between these two areas, and this variation was in the opposite direction to what the ‘ramp retina’ theory proposed.
Key Findings
- The study found that instead of the ‘ramp retina’, the acuity in the inferior retina’s visual streak was significantly higher (16.5 cycles per degree) than in the peripheral area (2.7 cycles per degree).
- This finding suggests that it is unlikely that horses rotate their head to focus onto the peripheral retina, as suggested by the ‘ramp retina’ theory.
Alternative Explanation for Head Rotation
- The researchers provide a new theory to explain the horse’s head rotation. They propose that horses lift their noses higher in the air to visually inspect distant objects. The rationale provided is that the binocular overlap (the area that both eyes can see simultaneously) in horses is oriented down their noses.
- Significantly, there is a blind area directly in front of the forehead. Hence, horses need to lift their noses high to circumvent this blind area and maintain a panoramic view of their surroundings.
Conclusion
- This new understanding of horse vision, provided by the study, could be crucial in the training of horses, where understanding their perspectives is essential. It could also benefit veterinary ophthalmologists who work with horse vision impairments.
Cite This Article
APA
Harman AM, Moore S, Hoskins R, Keller P.
(1999).
Horse vision and an explanation for the visual behaviour originally explained by the ‘ramp retina’.
Equine Vet J, 31(5), 384-390.
https://doi.org/10.1111/j.2042-3306.1999.tb03837.x Publication
Researcher Affiliations
- Department of Psychology, University of Western Australia, Nedlands, Australia.
MeSH Terms
- Animals
- Behavior, Animal
- Cell Count
- Eye / anatomy & histology
- Ganglia, Sensory / cytology
- Horses / physiology
- Refractive Errors / veterinary
- Retina / cytology
- Retina / physiology
- Vision, Ocular / physiology
- Visual Acuity
- Visual Fields
Citations
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