Have you installed the latest
patch?
Most re-release versions of the game should already be updated to the latest 1.0034A version, as shown in the bottom right corner of the main menu, so would not need to be patched. The DVD version is already updated, and the patch (designed for the CD version) should not be installed.
This fairly rare, but IIRC can be associated with equipping and unequipping items with an Elven Sight or Ranger Sight skill bonus, while also knowing the skill at a particular level (so the combined skill level adds up to more than 5). If installing the patch doesn't help, or if you already have the latest version, there are several ways to fix your sight.
The sight range can be modified directly, if you are comfortable using a hex editor.
see
Some more hex offsets..., and perhaps
Teleporting Anywhere, via hex editor as a reference.
Alternately, you can use
iZakaroN's SaveEditor (or from
Kiya's site, with description) to unlearn any levels of the sight skills that you have, then load the save and learn/re-learn Elven Sight, save and use the editor again to unlearn Elven Sight. The sight range is added to your base value when you learn the skill, so by using the editor to repeatedly re-learn it, you can increase the sight range as much as you wish. Since you are not completely blind, it should not take much to get back to a normal sight range (test it by entering new areas and seeing how the fog of war clears around your character).
In any case, you may wish to use the editor to unlearn the sight skills, to make sure they don't cause a problem with the associated equipment bonuses.
You could use
DAD's item editor to give a ring a sight bonus, but then if you took it off (visiting the dwarven king, or the bar fight) you would be blind again. IIRC you can remove skill bonuses using the item editor, so that could help eliminate future problems mixing with the character's passive sight skills.