440:, giving them superior night vision. This also gives them better vision on slightly cloudy days, relative to bright, sunny days. The large eye of the horse improves achromatic tasks, particularly in dim conditions, which presumably assists in the detection of predators. Laboratory studies show horses are able to distinguish different shapes in low light, including levels mimicking dark, moonless nights in wooded areas. When light decreases to nearly dark, horses can not discriminate between different shapes, but remain able to negotiate around the enclosure and testing equipment in conditions where humans in the same enclosure "stumbled into walls, apparatus, pylons, and even the horse itself."
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jump rails a different color from the footing or the surrounding landscape so that the horse may better judge the obstacle on the approach. Studies have shown that horses are less likely to knock a rail down when the jump is painted with two or more contrasting colors, rather than one single color. It is especially difficult for horses to distinguish between yellows and greens.
307:
350:
perception than a human. The horse uses its binocular vision by looking straight at an object, raising its head when it looks at a distant predator or focuses on an obstacle to jump. To use binocular vision on a closer object near the ground, such as a snake or threat to its feet, the horse drops its nose and looks downward with its neck somewhat arched.
469:
things up close, and horses rarely need to do so. It has been thought that, instead, the horse often tilts its head slightly to focus on things without the benefit of a high degree of accommodation, however more recent evidence shows that the head movements are linked to the horse's use of its binocular field rather than to focus requirements.
86:. The part of the retina covered by light-sensitive cells is therefore termed the pars-optica retinae, and the blind part of the eye is termed the pars-ceaca retinae. The optic disk of the eye, however, does not contain any of these light-sensitive cells, as it is where the optic nerve leaves to the brain, so is a blind spot within the eye.
35:; for example, it is active during both day and night, and it is a prey animal. Both the strengths and weaknesses of the horse's visual abilities should be taken into consideration when training the animal, as an understanding of the horse's eye can help to discover why the animal behaves the way it does in various situations.
353:
A horse will raise or lower its head to increase its range of binocular vision. A horse's visual field is lowered when it is asked to go "on the bit" with the head held perpendicular to the ground. This makes the horse's binocular vision focus less on distant objects and more on the immediate ground
411:
Dichromatic vision is the result of the animal having two types of cones in their eyes: a short-wavelength-sensitive cone (S) that is optimal at 428 nm (blue), and a middle-to-long wavelength sensitive cone (M/L) which sees optimally at 539 nm, more of a yellowish color. This structure may
477:
Any injury to the eye is potentially serious and requires immediate veterinary attention. Clinical signs of injury or disease include swelling, redness, and abnormal discharge. Untreated, even relatively minor eye injuries may develop complications that could lead to blindness. Common injuries and
273:
are made up of three layers of tissue: a thin layer of skin, which is covered in hair, a layer of muscles which allow the lid to open and close, and the palpebral conjunctiva, which lies against the eyeball. The opening between the two lids forms the palpebral tissue. The upper eyelid is larger and
443:
However, horses are less able to adjust to sudden changes of light than are humans, such as when moving from a bright day into a dark barn. This is a consideration during training, as certain tasks, such as loading into a trailer, may frighten a horse simply because it cannot see adequately. It is
371:
The horse has a "visual streak", or an area within the retina, linear in shape, with a high concentration of ganglion cells (up to 6100 cells/mm in the visual streak compared to the 150 and 200 cells/mm in the peripheral area). Horses have better acuity when the objects they are looking at fall in
468:
Horses have relatively poor "accommodation" (change focus, done by changing the shape of the lens, to sharply see objects near and far), as they have weak ciliary muscles. However, this does not usually place them at a disadvantage, as accommodation is often used when focusing with high acuity on
419:
The horse's limited ability to see color is sometimes taken into consideration when designing obstacles for the horse to jump, since the animal will have a harder time distinguishing between the obstacle and the ground if the two are only a few shades different. Therefore, most people paint their
375:
The horse is very sensitive to motion, as motion is usually the first alert that a predator is approaching. Such motion is usually first detected in their periphery, where they have poor visual acuity, and horses will usually act defensive and run if something suddenly moves into their peripheral
349:
The wide range of monocular vision has a trade-off: The placement of the horse's eyes decreases the possible range of binocular vision to around 65° on a horizontal plane, occurring in a triangular shape primarily in front of the horse's face. Therefore, the horse has a smaller field of depth
345:
This provides a horse with the best chance to spot predators. The horse's wide range of monocular vision has two "blind spots," or areas where the animal cannot see: in front of the face, making a cone that comes to a point at about 90–120 cm (3–4 ft) in front of the horse, and right
285:
produces tears, providing nutrition and moisture to the eye, as well as helping to remove any debris that may have entered. The apparatus includes the lacrimal gland and the accessory lacrimal gland, which produce the tears. Blinking spreads the fluid over the eye, before it drains via the
160:
of the eye lies posterior to the iris, and is held suspended by the ciliary suspensory ligament and the ciliary muscle, which allows for "accommodation" of the eye: it allows the lens to change shape to focus on different objects. The lens is made up of onion-like layers of
117:
of the eye, causing the yellowish-green eye shine when light is directed into the animal's eyes at night. The tapetum lucidum reflects light back onto the retina, allowing for greater absorption in dark conditions. The iris lies between the cornea and the
78:, which are more light-sensitive, providing night vision, but only seeing light and dark differences. Since only two-thirds of the eye can receive light, the receptor cells do not need to cover the entire interior of the eye, and line only the area from
404:) of most humans. In other words, horses naturally see the blue and green colors of the spectrum and the color variations based upon them, but cannot distinguish red. Research indicates that their color vision is somewhat like
346:
behind its head, which extends over the back and behind the tail when standing with the head facing straight forward. Therefore, as a horse jumps an obstacle, it briefly disappears from sight right before the horse takes off.
362:
take their horses' use of distance vision into consideration, allowing their horses to raise their heads a few strides before a jump, so the animals are able to assess the jumps and the proper take-off spots.
153:. The cornea (clear covering on the front of the eye) is made up of connective tissue and bathed in lacrimal fluid and aqueous humor, which provides it nutrition, as it does not have access to blood vessels.
55:
The eyeball of the horse is not perfectly spherical, but rather is flattened anterior to posterior. However, research has found the horse does not have a ramped retina, as was once thought.
706:
Locke, MM; LS Ruth; LV Millon; MCT Penedo; JC Murray; AT Bowling (2001). "The cream dilution gene, responsible for the palomino and buckskin coat colors, maps to horse chromosome 21".
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in front of the horse, suitable for arena distances, but less adaptive to a cross-country setting. Riders who ride with their horses "deep", "behind the vertical", or in a
846:
Harman AM, Moore S, Hoskins R, Keller P. Horse vision and the explanation of visual behaviour originally explained by the ‘ramp retina’. Equine Vet J 1999; 31(5):384–390.
178:
Although usually dark brown, the iris may be a variety of colors, including blue, hazel, amber, and green. Blue eyes are not uncommon and are associated with
174:
Homozygous cream dilutes ("double-dilutes") have pale blue eyes, while the blue eyes associated with white markings (bottom) are a clearer, deeper color.
388:
A representation of how a horse possibly sees a red or a green apple (bottom) compared to how red and green apples are usually seen by most humans (top)
1089:
Harman AM, Moore S, Hoskins R, Keller P (1999). "Horse vision and an explanation for the visual behaviour originally explained by the 'ramp retina'".
1079:
Prince JH, Diesem CD, Eglitis I, Ruskell GL. "Anatomy and histology of the eye and orbit in domestic animals." Springfield, IL: CC Thomas; 1960.
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70:) is made up of cells which are extensions of the brain, coming off the optic nerve. These receptors are light-sensitive, and include
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frame decrease the range of the horse's distance vision even more, focusing only a few feet ahead of the front feet. Riders of
330:
Horse eyes are among the largest of any land mammal, and are positioned on the sides of the head (that is, they are positioned
690:
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this region. They therefore will tilt or raise their heads, to help place the objects within the area of the visual streak.
947:
Wouters L, De Moor A (1979). "Ultrastructure of the pigment epithelium and the photoreceptors in the retina of the horse".
822:
58:
The wall of the eye is made up of three layers: the internal or nervous tunic, the vascular tunic, and the fibrous tunic.
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220:
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587:
1417:
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578:
Hartley, C; Grundon, RA (2016). "Chapter 5: Diseases and surgery of the globe and orbit". In Gilger, BC (ed.).
400:. This means they distinguish colors in two wavelength regions of visible light, compared to the three-color (
671:
405:
732:
The eyes and skin of palominos and buckskins are often slightly lighter than their non-dilute equivalents.
1279:
44:
1475:
1153:
686:"Cream dilution (CrD." Australian Equine Genetics Research Centre, web page accessed July 20, 2007 at
523:
920:
Stachurska A, Pieta M, Nesteruk E (2002). "Which obstacles are most problematic for jumping horses?".
109:. The choroid has a great deal of pigment, and is almost entirely made of blood vessels. It forms the
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508:
384:
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Horses have more rods than humans, a high proportion of rods to cones (about 20:1), as well as a
278:) to protect the cornea. It lies on the inside corner of the eye, and closes diagonally over it.
334:). This means horses have a range of vision of about 350°, with approximately 65° of this being
74:, which are less light-sensitive, but allow the eye to see color and provide visual acuity, and
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460:(near-sightedness), with few being far-sighted. Wild horses, however, are usually far-sighted.
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275:
43:
The equine eye includes the eyeball and the surrounding muscles and structures, termed the
31:
is one of the largest of any land mammal. Its visual abilities are directly related to the
408:
in humans, in which certain colors, especially red and related colors, appear more green.
8:
326:
A horse with the head held vertically will have binocular focus on objects near its feet.
1001:
Roth, LS; Balkenius, A; Kelber, A (2008). Roth, L.S.; Balkenius, A.; Kelber, A. (eds.).
800:
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Illustrated Atlas of
Clinical Equine Anatomy and Common Disorders of the Horse Vol. II
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743:"Genetics of Champagne Coloring." The Horse online edition, accessed May 31, 2007 at
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will temporarily make it difficult for the animal to judge what is in front of it.
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687:
670:"Choosing an American Paint Horse" PetPlace.com web site accessed July 20, 2007 at
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339:
335:
228:
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American Paint Horse is a breed wherein most representatives are of pinto coloring
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can move more than the lower lid. Unlike humans, horses also have a third eyelid (
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1200:
1019:
694:
437:
393:
318:
A horse can use binocular vision to focus on distant objects by raising its head.
110:
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are typically greenish shades: aqua at birth, darkening to hazel with maturity.
126:) but also allows varying amounts of light to pass through its center hole, the
1397:
1313:
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606:
Sivak JG, Allen D (1975). "An evaluation of the ramp retina on the horse eye".
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198:. In the case of horses with white markings, one or both eyes may be blue, or
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have arisen because horses are most active at dawn and dusk, a time when the
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The adnexa of the eye, including the third eyelid (seen in the left corner)
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672:
http://www.petplace.com/horses/choosing-an-american-paint-horse/page1.aspx
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breed having an eightfold higher risk than the general horse population.
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The range of a horse's monocular vision, blind spots are in shaded areas
215:, always have light blue eyes to match their pale, cream-colored coats.
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1382:
397:
208:
205:
83:
1500:
1333:
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Saslow C (1999). "Factors affecting stimulus visibility for horses".
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Horses are capable of having dichromatic (differently-colored) eyes.
75:
71:
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Swelling of the upper eyelid caused by a physical impact to the area
170:
1367:
859:, Online edition, June 1, 2007. Web site accessed July 27, 2007 at
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246:
242:
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150:
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also important in riding, as quickly moving from light to dark or
322:
290:, which carries the lacrimal fluid into the nostril of the horse.
145:
and protects the eye. The sclera (white of the eye) is made up of
1429:
1402:
797:"Animal Eye Care. "About animal vision." Accessed March 11, 2010"
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428:
355:
186:. The white spotting patterns most often linked to blue eyes are
146:
98:
661:. Equistar Publication, Limited. Marysville, OH. Copyright 2000.
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142:
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67:
874:"Photopigment basis for dichromatic color vision in the horse"
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Carroll J, Murphy CJ, Neitz M, Ver Hoeve JN, Neitz J (2001).
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127:
79:
19:
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511:(ERU) occurs in 10-15% of the equine population, with the
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The ocular muscles allow the eye to move within the skull.
231:, often have light brown eyes. The eyes of horses with the
94:
366:
1251:
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651:
649:
647:
645:
1003:"The absolute threshold of colour vision in the horse"
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includes recurrent uveitis and periodic ophthalmia ("
642:
582:(3rd ed.). John Wiley & Sons. p. 151.
432:
Mare and foal with eyeshine from the tapetum lucidum
1000:
1070:. Howell Book House. New York, NY. Copyright 1998.
823:"Horsewyse: How horses see. Date Accessed 7/11/07"
456:Many domestic horses (about a third) tend to have
1068:Horse Owner's Veterinary Handbook, Second Edition
789:
1523:
861:http://www.thehorse.com/viewarticle.aspx?ID=9670
745:http://www.thehorse.com/viewarticle.aspx?ID=9686
688:http://www.aegrc.uq.edu.au/index.html?page=30056
657:Riegal, Ronald J. DMV, and Susan E. Hakola DMV.
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1125:"Current Research, from Blindappaloosas.org"
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122:, and not only gives the eye its color, (
1052:"Shedding Light on Equine Night Vision"
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427:
383:
321:
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260:
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18:
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367:Visual acuity and sensitivity to motion
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541:A horse with solar keratosis carcinoma
1352:Evolution of color vision in primates
1175:
1149:
994:
855:McDonnell, Sue. "In Living Color."
757:Western Horse Behavior and Training.
13:
1103:10.1111/j.2042-3306.1999.tb03837.x
416:of the eye are especially useful.
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14:
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1056:online edition, October 12, 2009
720:10.1046/j.1365-2052.2001.00806.x
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16:Eyesight capabilities of horses
1066:Giffin, James M and Tom Gore.
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253:are not yet fully understood.
1:
988:10.1016/S0168-1591(98)00205-6
934:10.1016/S0168-1591(02)00042-4
561:
478:diseases of the eye include:
1020:10.1371/journal.pone.0003711
620:10.1016/0042-6989(75)90189-3
472:
165:
7:
1280:Simple eye in invertebrates
10:
1553:
1476:Infrared sensing in snakes
524:Keratoconjunctivitis sicca
396:, they have two-color, or
241:As in humans, much of the
50:
38:
1448:
1360:
1347:Evolution of color vision
1332:
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1239:
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1091:Equine Veterinary Journal
759:Main Street Books, 1975.
452:Near- and far-sightedness
406:red-green color blindness
256:
113:when it crosses over the
509:equine recurrent uveitis
338:and the remaining 285°
433:
389:
327:
319:
311:
266:
175:
124:see "eye color," below
24:
1481:Monocular deprivation
1440:Underwater camouflage
1435:Structural coloration
1413:Disruptive coloration
431:
387:
325:
317:
309:
264:
173:
22:
1461:Blindness in animals
1393:Counter-illumination
1342:Evolution of the eye
580:Equine Ophthalmology
424:Sensitivity to light
276:nictitating membrane
221:single-dilute creams
97:) is made up of the
976:Appl Anim Behav Sci
922:Appl Anim Behav Sci
211:, sometimes called
1408:Deimatic behaviour
755:Miller, Robert W.
693:2007-08-29 at the
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398:dichromatic vision
390:
328:
320:
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283:lacrimal apparatus
267:
176:
25:
23:The eye of a horse
1519:
1518:
1511:Visual perception
1506:Underwater vision
1471:Feature detection
1466:Eyespot apparatus
1425:Eyespot (mimicry)
1373:Animal coloration
1176:Vision in animals
878:Journal of Vision
803:on April 28, 2015
772:978-0-385-08181-8
614:(12): 1353–1356.
507:"). Spontaneous
402:trichromic vision
376:field of vision.
288:nasolacrimal duct
33:animal's behavior
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1491:Palpebral (bone)
1324:Schizochroal eye
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1127:. Archived from
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955:(8): 1066–1071.
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482:Corneal abrasion
340:monocular vision
336:binocular vision
194:, and sometimes
137:consists of the
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438:tapetum lucidum
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392:Horses are not
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297:Visual capacity
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111:tapetum lucidum
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1449:Related topics
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180:white markings
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1285:Mammalian eye
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1260:Arthropod eye
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1131:on 2016-09-09
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1097:(5): 384–90.
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829:on 2016-10-27
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486:Corneal ulcer
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464:Accommodation
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135:fibrous tunic
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64:nervous tunic
61:
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21:
1319:Parietal eye
1265:Compound eye
1220:
1133:. Retrieved
1129:the original
1119:
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949:Am J Vet Res
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903:. Retrieved
884:(2): 80–87.
881:
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867:
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831:. Retrieved
827:the original
817:
805:. Retrieved
801:the original
791:
784:Happy Trails
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380:Color vision
374:
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329:
302:Visual field
292:
280:
268:
240:
237:
217:Heterozygous
204:
177:
134:
123:
103:ciliary body
90:
63:
57:
54:
42:
28:
26:
1496:Pseudopupil
1378:Aposematism
1297:Mollusc eye
394:color blind
192:frame overo
1526:Categories
1486:Ommatidium
1418:coincident
1383:Camouflage
1361:Coloration
1302:cephalopod
1196:Chameleons
1135:2007-11-21
833:2007-07-11
608:Vision Res
562:References
446:vice versa
223:, such as
206:Homozygous
105:, and the
84:optic disk
29:equine eye
1501:Rhopalium
1334:Evolution
1307:gastropod
1275:Eye shine
1270:Eagle eye
1201:Dinosaurs
1054:The Horse
857:The Horse
782:Sellnow,
519:Habronema
513:Appaloosa
491:Keratitis
473:Disorders
332:laterally
251:eye color
229:buckskins
225:palominos
200:part-blue
166:Eye color
76:rod cells
1368:Albinism
1111:10505953
1039:19002261
1007:PLOS ONE
905:July 27,
900:12678603
807:July 11,
728:11736803
691:Archived
636:31898878
247:etiology
243:genetics
184:patterns
151:collagen
1430:Mimicry
1403:Crypsis
1216:Mammals
1030:2577923
786:, p. 46
628:1210017
501:Uveitis
360:jumpers
356:rollkur
271:eyelids
249:behind
161:tissue.
147:elastin
99:choroid
82:to the
51:Eyeball
39:Anatomy
1221:horses
1183:Vision
1109:
1037:
1027:
961:525910
959:
898:
770:
763:
726:
634:
626:
586:
458:myopia
257:Adnexa
196:sabino
143:cornea
139:sclera
115:fundus
101:, the
68:retina
45:adnexa
1290:human
1211:Toads
1191:Birds
632:S2CID
128:pupil
80:pupil
72:cones
1252:Eyes
1231:cats
1226:dogs
1206:Fish
1107:PMID
1035:PMID
957:PMID
907:2007
896:PMID
809:2007
768:ISBN
761:ISBN
724:PMID
675:Note
624:PMID
584:ISBN
414:rods
281:The
269:The
245:and
227:and
158:lens
156:The
149:and
141:and
133:The
120:lens
107:iris
95:uvea
93:(or
89:The
66:(or
62:The
27:The
1099:doi
1025:PMC
1015:doi
984:doi
930:doi
886:doi
716:doi
616:doi
219:or
182:or
1528::
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