Ahzidal's Helm of Vision is a unique Ancient Nord Helmet and part of Ahzidal's Armor set found in The Elder Scrolls V: Dragonborn.
It can be obtained in Kolbjorn Barrow on a pedestal behind a puzzle gate during the fourth investment stage of the quest "Unearthed".
Your Conjuration and Rune spells cost 25% more, but can be cast at greater range.
The enchantment on this helmet is quite self-explanatory; choosing to equip this piece of headgear would be useful for players who constantly cast runes or conjure allies from Oblivion.
It can be upgraded with a steel ingot at a workbench and also benefits from the Advanced Armors perk, which doubles the improvement.