The horse's eye is an extremely complex structure with intricate anatomy and is often overlooked when being drawn. It's incredible to think that both the eye and all the muscles surrounding it all fit within the socket. I've deliberately not drawn in the eyelashes as it's the structure of the eye I'm wanting to see. 

The horse is a prey animal so has monocular vision. This vision is the result of having one eye located on each side of the skull instead of both eyes in the front. This means that the horse has far greater peripheral vision. Horses eyes are also among the largest of any land mammal. 

Here are some more interesting facts about horse's eyes thanks to Horse and Hound Magazine:

1) Horses may, in fact, have an ability to judge distance at high speed. They can certainly assess ground conditions quickly for a hasty escape from danger.

2) Equine eyes have excellent visual acuity (focus) for distant objects but may find it difficult to focus on objects less than a metre away. They cope better in low light than we do, however.

3) Most humans are trichromats, having perception of the three primary colours. Horses appear to have dichromatic capability only, much like the red-green deficiency that we call colour blindness.

4) Horses tend to keep “half an eye on everything”, rather than focusing on specific targets.

When you really begin to study and draw the horse's eye in more detail it dawns on you just how complicated it actually is. The muscles around the eye, the folds of skin which create the eyelids, the inner areas of the eye. There are so many different levels to it. When drawing in a more expressive way there is a tendency to cut out some of these finer details because you're aiming to give an impression of a horse's eye rather than a detailed representation. However, I do think it's important for me to understand my subject thoroughly so that it becomes easier for me to infuse my own perception and perspective into my personal practice.