Question

what will be the vision if power of lens is -3.5D

Answer 1

If you mean, "the defect of vision" (check your question again, tbh it makes no sense), then, the person is suffering from myopia.

How?
Power of the lens is negative. Which means that the focal length of the lens is negative.

We know, a concave lens has a negative focal length. Hence, the lens is a concave one.

A concave lens is used to correct myopia. Hence, the defect of vision is myopia.

Cheers,
NISHTHA.