Yep!... well I'll take your word for it on them being called "horse eyes"... I know them as "lucky beans" or "beach beans"...
...they grow on shrubs or trees and fall into the ocean and end up on beaches near and far...I found them both on beaches...
... one on Grand Island Louisiana 35+ years ago, where I was told they only found them there after tropical storms or hurricanes
 ... and one in the Yucatan Peninsula, Mexico 25+ years ago, where I was told they were fairly common
I used to have a couple of others, but I'm not sure what happened to them.
I think the ones I have are actually different species, one is a called a "hamburger bean" (
Mucuna sloanei) and the other a "sea purse" ( 
Dioclea reflexa )... but i could be mistaken on the exact species...
edit, just found these links:
http://www.seabean.com/guide/Mucuna_sloanei/
http://www.seabean.com/guide/Dioclea_reflexa/