Lens-Maker's Glasses

When an attack critically strikes, it will make a sharp noise, and the damage text will be emboldened with a red outline.

Explanation about Stacking & Crit Chance
Each stack of linearly increases your critical chance by 7%. Normally, having at most 14 stacks of this item will guarantee you 100% critical chance:
 * Every character starts with 1% crit chance at the beginning.
 * All crit chance increasing items, including (+5%),  (+5%),  (+6%), and  (+7%), additively contribute to the crit chance together.
 * Although the value of crit chance is not capped, crit chance has no effect beyond 100%.


 * If no other crit chance increasing item has been picked already, picking up a will raise crit chance by 10% (as what the in-game item description says) instead of 7%. Otherwise, picking up the first  will only give you 7%.

All of this translates into:
 * If is the only crit-enhancing item that has been collected in the run, the crit chance on 14 stacks would be: 1% + (10% × 1) + (7% × 13) = 102% ➙ 100%.
 * If at least one of the other crit-enhancing items has been collected before the 1st pair of glasses, the minimum crit chance on 14 stacks would be: 1% + >5% + (7% × 14) = 104% ➙ 100%.

Item Synergies

 * Harvester's Scythe: Heals you each time you crit, as well as boosting your crit a small amount.
 * Predatory Instincts: Gives you bonus attack speed each time you crit, as well as boosting your crit by a small amount.
 * Wicked Ring: Reduces your cooldowns by one second each time you crit as well as boosting your crit chance.
 * Frost Relic: The icicles that spawn after you kill an enemy from Frost Relic can crit.
 * Brilliant Behemoth: The explosions can crit.
 * AtG Missile Mk. 1: The damage that this item bases on is the actual final damage dealt, so the crit damage will be the basis for the damage output of each missile. (AtG Missile Mk. 2 works differently.)
 * Ukulele, Mortar Tube: Same reasoning as AtG Missile Mk. 1.

Trivia

 * The mailing location, Grievenkamp, is a reference to John E. Grievenkamp, an optical scientist.
 * The old crit chance stacking was: (1 - (0.9)^x)*100, while x is the number of stacks. This formula worked in an unknown old patch, and has been since changed, there is no information if this was a bug or if it was a untold test.
 * Getting this item makes a red star shape appear above the player character.