Learn English – Why does “not a one” sound incorrect, but “not a single one” sounds okay

The simplest explanation, which does not really delve into linguistics at all, is that "ten" is not a unit that you use in multiples. That is, "20" is not spoken of as "two-tens", "50" is not spoken of as "five-tens". Thus there is no need for the disambiguation of specifying "one ten". (French seems to have decided that if you don't specify a count, "one" is assumed, as you don't say "un cent", "un mille", "un milliard", etc.)

In this case, the eye is standing for the whole system of visual perception.

This is an example of synecdoche - a figure of speech in which a part of something stands for the whole of the thing (or vice versa)*.

Chambers Dictionary : figure of speech in which a part of something is used to refer to or denote the whole thing, or the whole to refer to or denote a part