What is a wall-eyed horse?
A wall-eyed horse is one with an excessively pale eye, or with two eyes of different colours.

A wall-eyed horse is one with an excessively pale eye, or with two eyes of different colours. It’s a description of colour rather than a diagnosis, and the word is old enough to sit in the regional dictionaries: the Yorkshire Historical Dictionary, compiled at the University of York, defines it as “used generally of a horse with both eyes excessively light-coloured, or with different-coloured eyes”.
It’s an old word, and the dictionary dates it: a West Stonesdale record of 1618 lists “a mare, wall-eyed with a starr, value 30s” — a description doing the job a passport silhouette does now, identifying one animal by its eye and its face marking.
It describes appearance, not a defect. A pale or blue eye is a pigment matter, and sight is not affected by the colour itself. Why some horses have blue eyes covers what produces it.
The word belongs to a family of British colour terms rather than to veterinary language; what makes a horse coloured covers the rest of them.
It’s also the first thing an owner looks for in a picture. Our portraits are made from your own photograph.