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I've never heard anyone say, "Perfect Vision" I've only ever heard, 20/20, or terrible vision... perfect is so loosely used, the word's effectiveness is pointless anymore. No one has any idea of what "perfect" actually is. For a human, that's normal vision, not perfect. For a hawk, it would be terrible vision. kthnxbai.

For example, 20/20 is considered normal. 20/40 indicates that the line you correctly read at 20 feet away can be read by a person with normal vision from 40 feet away.

20/20 or 6/6 vision can be considered nominal performance for human distance vision; 20/40 or 6/12 vision can be considered half that acuity for distance vision and 20/10 or 6/3 vision would be twice normal acuity. [2] The 20/x number does not directly relate to the eyeglass prescription required to correct vision, because it does not specify the nature of the problem corrected by the lens, only the resulting performance. Instead an eye exam seeks to find the prescription that will provide at least 20/20 or 6/6 vision.[citation needed] However, some attempt has been made to provide an approximate conversion between an eyeglass prescription and the 20/x system.[3]

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A visual acuity of 20/20 is frequently described as meaning that a person can see detail from 20 feet away the same as a person with normal eyesight would see from 20 feet. If a person has a visual acuity of 20/40, he is said to see detail from 20 feet away the same as a person with normal eyesight would see it from 40 feet away. It is possible to have vision superior to 20/20: the maximum acuity of the human eye without visual aids (such as binoculars) is generally thought to be around 20/10 (6/3) however, recent test subjects have exceeded 20/8 vision.[7] Some birds of prey, such as hawks, are believed to have an acuity of around 20/2;[8] in this respect, their vision is much better than human eyesight.