Many pet owners ask veterinary ophthalmologists if their pets see well enough. The act of seeing is a blend of multiple factors like the perception of depth, field of view, perception of motion, color differentiation, and acuity. The brain integrates all these to generate a useful vision. Even though it is impossible to instruct our pets to go through an eye-chart, it is quite possible to make informed assumptions regarding their vision.
Dogs can see color
It was earlier believed that dogs could see the world as black and white, but this theory is now debunked. Modern research has shown that your dog could see some semblance of color. The retina enclosed cone photoreceptors determine the color perception. Such cone cells function excellently in bright light conditions. They comprise about 20 percent of the central retina photoreceptors in your dog. In contrast, the macula or central retina has only cones. A number of behavioral tests done in dogs have suggested that these animals could distinguish between blue color and red color but frequently confuse between red and green.
Visual field and acuity
The location of the eyes determines the peripheral vision and the visual field amount which can be observed at the same time with both an animal's eyes. Such binocular vision is a must for making the proper judgment concerning distances. Your dog has eyes positioned on sides of its head, leading to a 240 degrees visual field. In contrast, a human field is 200 degrees. Your dog's binocular field of vision approximates half of you, a human. Your dog's eye, however, is modified for night-time hunting. The function of the pupil is similar to a camera aperture. It has the capability to dilate for the maximum capture of light. It also helps that tapetum is present in the eyes. This is a reflective layer that functions to intensify the animal's vision when the animal finds itself in dim light. The tapetum provides the mirror effect when your dog looks directly into the headlights of any approaching vehicle. Although the tapetum organ enhances the dim light vision, the reflected light scatter could lead to reduced acuity.
Visual acuity is defined as the ability to focus in such a way that two objects seem to be distinct entities. In humans, the eye chart is used to measure visual acuity. Retinoscopy could be used to measure the same in animals and also human infants. The visual acuity of any normal dog is calculated to be anywhere between 20 percent and 40 percent of humans'. It implies that a dog could distinguish an object when the latter is 20 feet away compared to a human who can see 90 feet. Acuity refers to the functional clarity of eye structures like vitreous, cornea, lens, and aqueous humor.