Like #53 response above, the critical factor is seeing the front sight crisp & clear. Cataract surgery, Lasik, PRK, apertures, tape w/pinholes etc. aside.
(I shot at some considerable distance where fog/rain/mist almost obscured the B & W target. Coach said hold on the darkest part of the blur ... I did, and others also, scores were admirable. That taught me a lesson!)
So if I shoot NMLRA musket, for example, want the front sight blade crisp, OK that the target & rear sight fuzzy. Yes, rules allows a small hole in the rear sight leaf, but it is too far away to help me much.
Keep tinkering with reading spectacles of various strengths (diopters), they are an inexpensive alternative. But be certain to see an ophthalmologist to catch glaucoma, cataracts, mac deg, that no spectacles can ever fix.