Ind. Code § 22-3-3-12
If an employee has sustained a permanent injury either in another employment, or from other cause or causes than the employment in which he received a subsequent permanent injury by accident, such as specified in section 31, he shall be entitled to compensation for the subsequent permanent injury in the same amount as if the previous injury had not occurred: Provided, however, That if the permanent injury for which compensation is claimed, results only in the aggravation or increase of a previously sustained permanent injury or physical condition, regardless of the source or cause of such previously sustained injury or physical condition, the board shall determine the extent of the previously sustained permanent injury or physical condition, as well as the extent of the aggravation or increase resulting from the subsequent permanent injury, and shall award compensation only for that part of such injury, or physical condition resulting from the subsequent permanent injury. Provided further, however, That amputation of any part of the body or loss of any or all of the vision of one or both eyes shall be considered as a permanent injury or physical condition.
IC 22-3-3-12