-their night vision is quite good but not good enough for jumping in darkness or without enough light

-Horses refuses to jump, spooks or weave between fences are sometimes because we assume that they see what we see.

-horses that don’t have their necks set high on the withers and head position slightly higher. Their heads will lift in the last few strides before the jump. As they then have a brief view of the jump
-Their visual is their most weak sense, that is why they rely more on sense of smell and hearing. That is why they might spook at something that isn’t moving or scary. But, it might be a smell or sound that is near by.
-Older horses with healthy eyes take in less sunlight. Therefore they see things bit gloomier and darker. That will also affect in their performance as well
https://equusmagazine.com/riding/visual-discrepancies-31223