If you are anything like me you will have google at the ready when learning about optics. As soon as I read the term 'eye relief' I googled 'What is eye relief?' and a whole bunch more. After learning about it more and listening to some other folks who know far more than I do I learned this.

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Eye relief is also an important factor to consider when using optics on firearms, such as scopes or red dot sights. Eye relief is the distance between the eyepiece of the optic and the user's eye, and it determines how comfortable and accurate the user will be when aiming through the optic. Long eye relief allows the user to comfortably view the reticle from a distance, while short eye relief can cause discomfort or even strain on the user's eye. It is important to choose an optic with appropriate eye relief for the intended use and user, as well as the recoil of the firearm. Too short of an eye relief can result in the user getting "scope bite," where the eyepiece of the scope hits the user's eyebrow or cheek during recoil. Too long of an eye relief can make it difficult for the user to get a proper sight picture and may affect accuracy.