Pleasin' Peepers: Sculpting the Equine Eye

The horse’s eye is a complex organ designed by nature for the animal’s survival. Indeed, the horse is a visual species that relies on their eyes a lot to evade predators, identify one another, and navigate the landscape. We’re a visual species, too, and so tend to home in on the eyes immediately as a means to communicate and connect, often on an emotional level. As such, the better we can sculpt our equine eyes, the better the believability of our sculpture and the more successful a connection it can make with someone. Even so, the equine eye can stump many sculptors because of its complexity, intricacies, details, and peculiar angles, making it one of the most tricky body parts to sculpt. Yet if even one of these characteristics is askew, the result can be an unconvincing face. That being the case, let’s discuss some ideas for sculpting equine eyes for more successful results and greater clarity in the sculpting process.

Note: For the purposes of this article, the term “eye” refers to all the features of the eye—the brows, eyelids, eyebrow wrinkles, cranial structure, and fleshy configurations—where as the term “orb” refers only to the eyeball itself.

Basic Biology

The horse has one of the largest orbs of any land mammal, about 2-3” in diameter, about eight times bigger than the human eye. In fact, while some mammals have larger eyes than the horse relative to body size, in absolute dimensions the horse tends to have the largest orbs of any land mammal. (Fun fact: It’s been reported that the circumference of the equine retina is greater than that found in even the bowhead whale!) Equine eyes are set onto the sides of their head, typical of a prey species. However, the equine orb isn’t a perfect ball, but an elongated, egg-shaped sphere that sits on a fat pad. This is why old horses or starving horses can sometimes have sunken eyes as that fat pad has shrunk (old horses can sometimes be underweight because of their spent teeth and improper nutrition). The orb should protrude just the right amount, too, and not too much, otherwise that can indicate hyperthyroidism or ASD (Anterior Segment Dysgenesis). It’s a delicate balance. But the orbs are generally of similar size on all horses and it’s the size of the head and structure of the cranial areas and fleshy parts that make an eye look “larger” or “smaller” between different individuals or breeds. In other words, the actual orbs tend to be of similar size on an Arabian, Quarter horse, Akhal-Teke, Shire, Warmblood and Lusitano, for example. 

The white of the orb is called the sclera which is a tough outer layer that’s covered by a thin membrane called the conjunctiva. You can see the sclera when the horse moves his eye or at rest on some breeds, like the Appaloosa, in particular, and some Tekes and Arabians. The cornea is the clear, liquid-gel filled dome at the front of the orb on top of the iris that protects the inner orb and helps to focus light onto the retina. If you see the equine cornea in certain light from the front, you can see right through it. Then there’s the iris, or that obvious oval, colored portion of the eye which expands or contracts to control the amount of light that enters the pupil. In turn, the pupil is the void in the middle of the eye that opens and closes, controlled by the sphincter muscle of the iris.

The orb is surrounded by the lids, a ring of two layers of muscles that open and close the eye when they relax and contract. There’s also a third eyelid, the nictitating membrane, a pink or brownish membrane that moves over the eye from the inside corner to the outside corner when the eyelids are closed. Tears are essential for the health and function of the eye and are composed of water, mucus, and oil so they evaporate slowly. The lacrimal gland producing the watery portion of tears is located at the top outer edge of each eye. The third eyelid also contributes to watery tears. Likewise, the conjunctiva contains mucus glands (goblet cells) that provide the mucus component while the oily portion is produced by the meibomian glands. Then it’s the nasolacrimal ducts (or lacrimal caruncle or lacrimal puncta) at the front of the eye that drain the tears off to a small opening just inside the nostril, so that’s not snot coming out of the nose, but tears. A unique feature of the equine eye is the corpora nigra, a granular, knobby structure that sits on the iris above the pupil (and sometimes at the bottom of the pupil, too) that is thought to shade the lower portion of the retina from glare, especially while grazing.

The equine pupil is shaped like a rectangular oval to extend the scope of the field of vision. Depending on the light intensity, this pupil can close to be more of a slit in bright light or open to become rounder in low light. Currently, it’s believed that horses have about 20/30 to 20/60 vision. Cones cells are suited for bright light (day) vision whereas rods are designed for low light (night) vision. In the horse, that rods to cone ratio is about 20:1 as compared to humans who have a 9:1 ratio. As such, the horse’s retina is more designed to detect motion in low light conditions, exactly when a predator is most likely to be active and when the horse is most likely to be grazing (while the horse grazes throughout the day and night, it peaks just before dusk and after dawn). However, the study results determining color detection in horses are conflicting though scientists do suspect that they can at least see in dichromatic vision, maximally sensitive to medium-long wavelengths and short wavelengths. It’s also thought that the horse’s visual acuity changes with color. For example, it’s been found in one study that their acuity goes down when blue is involved. But put it all together and it’s currently thought that horses can see greens, blues, and in some cases oranges and yellows, but the jury is still out for reds. More study is definitely needed here. However, it should be mentioned that while trichromatic color vision (such as we have) allows us to see a greater range of colors, dichromacy has definite advantages. For example, trichromacy can obscure features between objects based on other features like texture whereas this isn’t believed to be the case with dichromats. In this case, certain objects may simply be more visible to horses than to people in some instances. (Incidentally, a study found that horses loaded into trailers much more readily when the traditional black mats were replaced with green mats.) What’s more, due to the large orb size and large retinal surface, it’s believed that the image magnification in the equine eye is 50% greater than that of the human eye, making things, like a potential predator or any small movement, really stand out to them by appearing larger.

The horse’s eye also has a tapetum lucidum to improve night vision even more which you can see at night if light is shown into their eyes, making them glow. However, this membrane makes the low light images a bit fuzzier. Curiously, the equine eye isn’t well adapted to making the transition between bright to dark lighting situations which is why they can be reluctant to enter dark places right away like a trailer, stall, or building. On the other hand, it’s also likely that the horse can be more easily blinded by sudden bright light as well, perhaps making them hesitate when pulled out of a dark stall into bright sunshine. Give them a moment for their eyes to adjust though and they’ll be fine.

The exact visual acuity of the equine eye is still unknown for certain, with many studies providing conflicting evidence. So at this time, it’s generally believed that equine vision, at least in bright light, is poorer in comparison to people, however, it’s thought the horse has the visual advantage in low light conditions. But seeing in great detail isn’t so helpful for the horse, evolutionarily speaking, in lieu of motion detection and general awareness of their surroundings. Not surprisingly then, it’s thought that the equine eye is well-designed for peripheral vision, able to detect peripheral motion really well which makes sense for a prey animal vulnerable to ambush attack. Horses also have two kinds of vision, binocular and monocular. Monocular vision means that the horse can see both sides of their body independently for two totally different views, seeing in an arc of about 200-210˚ which is why it’s nearly impossible to sneak up on a horse. But it’s also believed the horse’s brain processes both views independently which may be why they need to see the same object with both sides to familiarize themselves. Or conversely, if an object passes from the vision of one eye to the other, it will seem to surprisingly appear to the other eye, causing the horse to startle. However, it’s also been reported that horses have interocular transfer in which stimuli perceived by one eye is also recognized by the other eye, so more study is still necessary here. Created together by the cornea’s size and curvature, the pupil’s shape and size, and the retina’s angular extent, this monocular vision overlaps in front of their face just below their noses, creating a binocular field of vision of about 65-80˚ for depth perception. However, this monocular vision doesn’t overlap behind the horse’s head or body, creating a blindspot of about 20˚. It also creates a blind spot in front of their forehead and just below the nose where the whiskers take over for sensory detection. As such, a horse literally can’t see what they’re eating, your hand on their muzzle, or the treats you feed them. But all this is why it’s smart to feed treats with a flat hand and to always make the horse aware you’re in their blindspots so they don’t become triggered into flight or kicking. Nonetheless, all the horse has to do is change their head position to see in these blindspots which is why fixing their heads can make some horses nervous. For instance, to see distance, the horse usually raises their head or to see a full 360˚ view, they just have to move their head side to side a bit. Curiously, there may be a stallion/gelding to mare difference in visuospatial ability (depth perception and the interpretation of three-dimensional perspective) with males being more adept than females, which tends to hold true for many mammalian species. It’s unclear why this is or if it’s even present in the horse so the jury is still out on that, too.

So compared to people, horses have a far bigger field of vision with a panoramic view, seeing longer distances and both the horizon and ground better. However, horses aren’t so well adapted to see detail or contrasting colors and are more adapted for low light conditions. Motion detection is a big component to equine vision for obvious reasons whereas human eyes are more adapted to detect detail and depth perception (stereoacuity) which is about 72 greater than that of a horse. The equine eye is also very good at seeing patterns (and they’re very good at remembering them) which may be why they may spook at items that are recently “out of place” such as a new planter, bucket, bench, blanket, etc. Remember that new items could be a crouching predator because there’s absolutely nothing in the equine evolutionary past that prepares them for “bucket” or  “chair" that moves around. Quite literally, to a horse, anything new in their familiar surroundings could be dangerous to them. Interestingly, science has also made a correlation not just between body mass and eye size, but also the maximum running speed of an animal and eye size. In this, it’s believed that those animals that run fast tend to have larger eyes because they require good vision to avoid running into things which may be another explanation for the horse’s large eyes. Overall though, it seems the horse’s eyes are designed to keep “half an eye on everything” rather than humans who tend to intently focus on specific targets.

The canthi are angled onto the cranium in a more or less consistent way. Generally speaking, most horses have their canthi angled about 40° - 42° to the Ear-Eye-Nostril Alignment (EENA). However, this is a guide, not gospel! So life study and references can provide a good mental library and handy guidance. But getting this angle is important because if the canthi are angled improperly, the eye can look odd. (Note: Some breeds' eye angles deviate away from the EENA a bit such as Iberians, Kladrubers, or Campolinas so take a little bit more care measuring the canthi of such individuals to make sure they're correct.)

The horse is remarkably expressive with their eyes and those corresponding muscles can be quite finessed in their motion and expression, even those that move the orb itself. In this, the orbs can move up and down, for and aft, and can move symmetrically and even side-to-side like a “cat clock.” A frightened horse can even draw his orb in a little bit, creating a more sunken eye (which can also happen in a tetanus seizure). Also note that the pupil tends to stay more or less parallel to the ground regardless of head position as the orb muscles keep that pupil oriented to the horizon (called cyclovergence), so pay attention to that in your references. Also note their eyelids and eyebrow movements and wrinkles, which reveal a great deal about their mood and focus. Eyes can also be shaped differently between breeds. For instance, Arabians tend to have a rounder eye while Iberians usually have a more almond-shaped eye, and some Drafters can have a rather triangular eye with pronounced brows, and then some Tekes have their cool hooded eyes. So pay attention to breed differences when sculpting the eyes in this regard. 

The equine eye is set high and far up towards the crown on the skull. This is because as evolution developed the huge battery of long crowned teeth, the head was stretched forwards below the eye to make room in the jaw for the long tooth roots. So make sure your sculpted eyes aren’t placed too far down on the head to interfere with those tooth roots. Generally speaking then, the horse’s eyes are set on the upper third of the head, as measured from the bottom "v" of the ears to the front canthi, then one more time to about mid-cheek then to the end of the muzzle. There are individual and breed variations, or course, but that one-third rule is a handy place to start your adjustments.

The zygomatic arches are obvious landmarks behind the eye sockets, flowing up towards the ears, making them important to sculpt correctly. The “salt cellar” or that obvious “U” is formed by the zygomatic arch (Arcus zycomaticus), the orbital arch and the external frontal crest (Os frontale) of the skull and is oriented towards the crown, through which the coronoid process of the mandible pokes in-and-out while chewing (which you can observe on the living animal when they’re eating). Then below the zygomatic arches is the condyle process of the mandible, which articulates at the joint of the jaw, behind the eye. In other words, the zygomatic arches and the mandible should align correctly with the back of the jaw, the ears, and the eye, otherwise the sculpture will have inaccurate cranial structure. 

The teardrop bone (or facial crest) runs down from the zygomatic arches, from behind the eye, to about midway down the head and more or less follows the EENA. Also observe that the area below the lower rim of the eye isn’t always flat, but can often have a little bulge of flesh. Eyelashes grow out of the upper lid and whisker bumps are often present on the lower bulge of flesh. The skin of the eye area is thin and delicate and so many little wrinkles and fleshy details can be present, especially around the front canthi so look for those in study.

Sculpting Sequence

Note: The process described here refers to a “traditional” size sculpture. Adjustments in clay amounts will be necessary for larger or smaller size sculptures.

• Have a clean slate. This means that if you’re customizing, remove a goodly portion of the eye and zygomatic arches and sand the area a bit with medium sandpaper to remove harsh dremeling tracks that could interfere with your sculpting. If you’re sculpting from scratch, have this area relatively clear and flat.
• Look at the piece and decide where to put the eye. Take measurements if you have to and mark in any reference points with a pencil or divots. You can even draw the eye in if you wish with a pencil or tool.
• Take a blob of sculpting material about the size of a pea and smoosh it on where the actual eye is supposed to be.
• For the zygomatic arches, make a short snake, about the thickness of a thin pipe cleaner, and a small ball. Place the snake above the eye blob and arched upwards and towards the ear and ball below it, aligned more or less with the base of the ear.  
• Then add a smaller clay snake veering towards the crown, leaving a middle hollow to create the “salt cellar.” 
• Plane and blend the material into the surface, removing or adding material as needed to create a proportioned, well-placed and correctly planed idea of the eye. (Another method is to make a ball for the orb, of appropriate size, and lay in the upper brow and the lower rim independently with short snakes of clay then blend and refine. Find the method that works for you.)
• With measurements, find and mark the canthi with a blade tool, making sure their angulations are correct to the EENA. These will be the front and back corners of the eye, so be sure they’re correct for a proper orb size and placement. Then with a blade tool, gently draw in and outline the orb. I recommend tapping in the epoxy to mark it rather than making a drawing motion which can tear or pull the epoxy to create distortions (oil and ceramic clays aren't prone to this effect, thankfully, and polymer clays are a little bit, but not as much as epoxy clays). When you're done with that, be sure to check it again to confirm the eye is correctly placed and sized and angled and make adjustments as needed. Work quickly if you're working in epoxy clay.
• When you’re satisfied with this step, use your preferred sculpting tool to block in the features, adding dimension and form. Round out the orb and refine it. Block in the eye lids and lower rim. At this point though, refrain from fiddling with delicate details and instead concentrate on the big ideas. And work as fast as you can because that epoxy will cure faster than you think. Then gently smooth with rubbing alcohol and brushes (or Goo Gone or turpenol* for oil clays or clean water for ceramic clays; the rubbing alcohol also works with polymer clays). (Tip: If you’re working in epoxy clay, dip your sculpting tools in 91% rubbing alcohol to add lubrication, helping to avoid tearing or distorting things while you work. Don’t soak though, just coat the tool.)
• Now you can begin to focus on the details, such as eyebrows, wrinkles, the lower rim, etc. Crispify and clean them up, also cleaning up the definition of your orb, too. Just always be watchful for distortions that happen with fiddling so you don’t go off track; check your work often. (Tip: Small filbert brushes, like size 2 and 4, are great for smoothing eye areas.)
• Be sure to continually check the alignments and structure of your eye to stay on track, and continue to add and clean up detail. You can even detail in the third eyelid and the lacrimal caruncle in the front canthi if you wish (or you can paint those in later). Just keep scale in mind if you do sculpt them in.
• When done, allow the epoxy to stiffen up then you can add eyelashes if you wish. To do this, roll out a tiny snake of sculpting material and pop it lengthwise along the top eyelid. Then gently blend this into the eyelid, making sure its shape and qualities relay the idea of delicate eyelashes. When blocked in, allow it to rest until the epoxy is slightly stiffer, then delicately sculpt in the hairs with a blade tool, gently sculpting from the ends of the eyelashes to the eyelid and delicately visa versa. Use your finger as a support if you need to (you can lightly coat your finger in rubbing alcohol to provide a release so you won’t tear those eyelashes off when you move your finger). Smooth with rubbing alcohol and brush, do further refinements and re-smooth…then finito!

Alternate method: You can roll snakes to form the upper brow and lower lid with the eyeball in between then blend that all together, if that's easier. Try it and see which approach works better for you. Some artists even use BBs for the orbs, giving them a hard surface to sculpt the lids and brows on.

Things To Keep in Mind

• Avoid creating orbs that are too protruding or bulbous since this can indicate hypothyroidism or ASD (Anterior Segment Dysgenesis), both rather serious pathologies. But also avoid creating orbs that are too flat or deflated since this is unnatural and may indicate a puncture injury. It’s a delicate balance to get right so do a lot of study and use good reference photos.
• Avoid creating eyes oriented too forwards on their axis, like a person or predator. The equine eye should sit more on the side of the head because the horse is a prey animal.
• Be careful to maintain that slight outward angle at the top of the eye so the eyes aren’t flat on the sides of the head.
• Be sure the eyes aren’t so far down on the head as to interfere with the roots of the teeth. Make sure they’re located in that upper third portion of the head.
• Make sure both eyes protrude from the skull symmetrically. However, avoid creating eyes that sit too far out on the cranium like frog’s eyes. So be mindful of the equine cranial structure supporting and protecting the orbs.
• Small or shrunken eyes can indicate dehydration, a puncture wound, or several severe eye diseases such as Equine Recurrent Uveitis (ERU). Indeed, a shrunken eye is usually blind. The third eyelid tends to cover these eyes, too. So overall, avoid accidentally sculpting this kind of eye.
• Keep your eye in proportion, don’t let it grow to an unnatural size. Horse eyes are often a lot smaller than our penchant for neonatus characteristics.
• Make sure the canthi are angled correctly and consistent with both eyes.
• Be sure that both eyes are as symmetrical as possible and placed symmetrically from the centerline of the head.
• Breed differences exist in surrounding eye structure such as among Tekes, Exmoors, Drafts, mules, donkeys, etc., so pay attention to those features.
• Avoid creating brow ridges that extend beyond realistic parameters, becoming too heavy or overly protruding.
• Make sure the zygomatic arches are aligned properly with the mandible. Also make sure they're oriented correctly, not tipped down towards the jaw or tipped up too far towards the forelock. They should veer right towards the ear, aligning with the top of the ear root and the base of the ear.
• The planes of the eye are important so be careful to get them correct in the formative stages and avoid distorting them as you work. They’re sorta planed outward at the upper lid and inward at the front canthi. 
• Avoid a caricatured structure of the eye. While the eyes of horses in many old paintings are dramatic, their stylized treatment doesn’t look authentic on a realistic sculpture. Keep in mind, too, that a strong “triangle eye,” or a strongly lifted brow can indicate pain according to the pain index or grimace scale so keep context in mind with the whole design of your piece.
• Keep the eyelids looking fleshy, flexible and soft, avoiding a harsh or cut-in treatment with their sculpting. This is where gentle smoothing with solvent and brushes can shine.
• Don’t forget to sculpt in the lower rim of the eye; it adds definition and interest. You may wish to sculpt in the lower bulge too, though it’s not present on all horses.
• Be mindful of detail from delicate wrinkles, textures, and whisker bumps to the subtle play of the eyelids and the structures at and around the front canthi.
• Use tools that are in scale for what you’re sculpting because tools that are too big will leave grooves that are too large. Think of it this way, if your piece was scaled up to life-size, how big would all those eyelid grooves actually be?

Sculpting Tips

• If using epoxy clay, soft artificial brushes dipped in rubbing alcohol can be used to smooth sculpted details. If using oil clays, Goo Gone or turpenol works the same way. If using ceramic clays, clean water is best (just be careful with water use and grog-filled clays otherwise you risk a bumpy, grainy finish).
• Eyes are easiest to sculpt if you have tools to fit the shapes needed. I recommend a pointed spoon-like tool, a pointed tool, a ball end tool and a curved blade tool. Tools can be actual sculpting tools, sharpened pencils, dental tools, the ends of paint brushes, or burnishing tools. Really, whatever works for you!
• Use a pair of calipers to make sure things are proportionally correct. These are of particular usefulness with sculpting the other eye for symmetry. I recommend the Prospek calipers.
• A handy trick is to draw a straight line down the front of the face with a pencil; it should run perfectly down the nasal bone and bisect the entire head into equal halves. Then use a T-square along this centerline to draw a 90° line to mark the eyebrows and the front canthi, giving you two references for sculpting the other eye. This bisecting line is also useful to make sure your brows are of equal dimensions, too, because you can use the line as a landmark for your calipers to judge how much each one protrudes as compared to the other.

Wrap Up

Make no mistake...sculpting eyes is tricky! What media you use...epoxy, oil, polymer, or ceramic...can make a huge difference in how easy you find it to be, too, so experiment. Indeed, epoxy clays can move around a lot as you sculpt them, making them more prone to distortions plus you have to contend with the cure time. On the other hand, the open time of polymer, ceramic, and oil clays could be a big boon for you and they don't move around so much. Likewise, the tools you use can make a huge difference so play around with many to find those that suit your approach best.

But the happy news is that with practice and study, sculpting eyes becomes easier and easier with each sculpture. And really, the only really tricky part is creating a second eye to match the first (uffdah). Bilateral symmetry! Ack! Keep working at it though and you’ll get the hang of sculpting eyes rather quickly. A handy practice method is to have a junker model with the eye area removed and using something like Sculpey to keep sculpting eyes over and over again. You’ll get the hang of it pretty quickly! The point being that you probably won't hit your target right off the bat if you're a beginner so be patient with your piece and especially with yourself. Don't beat yourself up! It takes experience to sculpt good eyes and that just takes repetition. Just keep at it.

It's also important to realize that eyes are pretty much wholly anatomically based, meaning that there's really very little fudge factor when it comes to their structure and angles as compared to, say, big muscle groups which can have a lot of goo-induced morphing and momentary distortions. The only such things really applicable to eyes are individually based variations, breed differences, and expression so really work to maintain those anatomical points best you can as you work.

It's said that the eyes are the "windows to the soul" and this is certainly true for both people and horses. Truly, you can learn a lot about a horse's character, mood, and focus by simply watching their eyes. You can learn a lot about their discomfort levels as well. All this means then that you should consider the whole context of your piece when you design the eyes so everything marries together or you aren't portraying something counter to your intentions. For instance, putting strongly activated brows to create a "triangle eye" on your performance piece could indicate pain, stress, or fear. Truly, horses express themselves all the time and the eye is a big feature of that communication, something we always have to be mindful of as we compose our pieces.

Any which way though, do a lot of field study and pore over reference photos, practice and be bold, and you can be sculpting great eyes in no time at all! And most of all, have fun doing it because equine eyes are truly one of the most enjoyable features to sculpt that really brings a sculpture to life! They give the viewer a great and meaningful focal point to connect to as well. And boy...when they're painted or patina-ed...wow! So have at it...all eyes are on you!

*Turpenol is a 70% 91% rubbing alcohol/30% turpenoid mix. It’s far less aggressive in its melting abilities than Goo Gone so it’s great for final smoothing or if you simply want something gentler.

You can't depend on your eyes when your imagination is out of focus.

~ Mark Twain