Is it possible to have vision loss from allergic reaction in eye?

Rarely. Most reactions to airborne allergens, while uncomfortable and annoying, primarily affect your conjunctiva, the thin membrane that covers the white part of the eye and lines the inner eyelids. The most common symptoms are itching & watering though blurry vision sometimes occurs. Rare reactions associated with eczema or other conditions can cause severe inflammation that may affect your eyesight.
Depends. Most eye allergies occur on the surface and mostly cause itching, watery eyes. Allergic reactions to systemic medications can potentially affect the eye to a greater extent, causing scarring and vision loss. Allergic reactions inside the eye itself are extremely rare, but could cause significant vision loss if they occurred.