There are many optical effects of filters

Although claims of effects of filters have not been fully trialled there are massive levels of anecdotal evidence to suggest that they are of help to large numbers of people. We see effects in

1 acuity (can affect lens performance and amblyopia - lazy eye)

2 refractive error (particularly important in night driving)

3 visual fields

4 binocular vision including squints

5 accommodation

6 convergence

7 stereoscopic vision and more