Snow blindness is temporary blindness caused by reflected bright light in the snow field. As snow field has a high rate reflection of sunlight, staring at the snow field is just like staring at the sunlight. It usually occurs at high altitudes on highly reflective snow fields. So mountain climbers should wear sunglasses to protect their eyes.
Snow blindness will make your vision decrease temporarily, but it won't cause permanent vision loss. It is usually caused by exposure of your eyes to bright sunlight that is reflected from snow. In most cases, snow blindness will disappear if you get indoors and have your eyes rest.