(CNN) When three-year-old thoroughbred Patch takes to the starting gate at this year's Kentucky Derby Saturday, many people -- be it in the stands or watching on TV -- probably won't be aware that this is a very special horse.
At the left-hand side of Patch's head is a dark hole -- about the size of a golf ball -- where his eye used to be.
As a two-year-old, Patch developed an ulcer in his left eye that, despite the best possible medical care, didn't respond to treatment.
Eventually, in June 2016, the colt had his eye removed after trainer Todd Pletcher decided nothing more could be done to save it.
Trevor Breen rode one-eyed showjumper Adventure De Kannan to victory in the 2014 Hickstead Derby and he says the adaption for a horse after losing an eye is more of a mental than a physical one.
"I think the heart, mind and attitude of the horse are big factors in the recovery," Breen told CNN. "The first thing is the obvious one really, they've just got to come to terms with it.
"What they used to be able to see, they now can't. Horses are very good at adapting and I think they sometimes deserve a lot more credit than we give them.
"The key to it all is the mind of the horse. If they have a really good attitude and that they want to do the job that you want them to do, then they'll find a way to do it."
Patch, who was coincidentally given his name before losing an eye, is ranked as an outside -- but not impossible -- 30-1 shot along with three other horses.
Two other runners, Fast and Accurate and Sonneteer are given odds of 50-1.
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Breen is eager to stress that every horse is different and although Adventure De Kannan seamlessly transitioned from two eyes to one, that might not be the case for other horses.
Both Adventure De Kannan and Patch suffered from eye ulcers, meaning the gradual decline of sight in one eye made the post-operation transition more manageable.
Before Adventure De Kannan lost his eye, Breen says he had been trying, unsuccessfully, to win the Hickstead Derby -- considered one of the premier events of the equestrian calendar -- for four years.
Then he and Adventure De Kannan -- less than a year after having the eye removed -- claimed the title for the first time.
"When we took the eye out it was like I rewound the clock about three or four years," Breen recalls. "He got cheeky again, he was like a new person.
"He was such a good-natured horse, he'd never let you know he was depressed. But it must have been affecting him and as soon as we took it out, he was in super form straight away.
"He had a cheekiness and a swagger about him. He was definitely better after the eye went out. You think with yourself, if you have a pain in one place all the time you'd be nearly going through depression."
Though showjumping and flat racing are different disciplines entirely, parallels can be drawn between the recovery procees of both Adventure De Kannan and Patch.
And after overcoming considerable odds to reach America's $2.4 million race, don't bet against Patch doing it again on Saturday.
"It's a credit to him and his professionalism that he was able to adapt so seamlessly to it," his trainer Pletcher told Reuters.
"I was concerned that it might compromise his ability in some way or the way he carried himself. I guess you don't know for sure but it certainly doesn't seem like it has."
"He's a remarkable horse to lose his left eye in the middle of last summer and recover as quickly as he did. It seems to never faze him."