Siamese cats have fewer ganglion cells, little stereopsis, less acuity and too much crossing over of optic nerve axons at the optic chiasm. The vertical stenopaic slit pupil of the cat allows for maximum light control and optically decreases astigmatic scatter in the horizontal meridian. The horizontal pupil of the horse would minimize scatter in the vertical meridian. The lens of dogs and cats has weak accommodative ability and therefore they have limited near focus capability. The minimum threshold of light for vision in cats is 6X lower than that of humans.
Central retina is predominantly rods in dogs while it is cones in humans.
The dorsal located tapetum increases vision in dim light. The feline tapetum reflects light 130X more than the human eye. Larger pupil and larger corneas permit more light to enter the eye. The more posterior location of the feline lens makes for a smaller and brighter retinal image. The nasal extension of the retina, the laterality of the eyes, and the horizontal pupil facilitate tremendous peripheral vision for the horse standing with its head up.