As you may expect, flat lenses are shaped flat. They do not possess any spherical shape, and are typically found on less expensive, basic model goggles. While low in price, flat lenses have a more limited viewing window than spherical lenses, putting the concentration on what is visibly in front of you. The amount of peripheral vision is limited with flat lenses and the viewing window also tends to be slightly distorted. The distorted viewing angle occurs because the flat shape allows light to come through the lens at a different angle on the top and bottom than in the middle. The end result is that your viewing window can appear magnified or misshapen.
Additionally, flat lenses can often catch sunlight at odd angles, resulting in intense glare on occasion. This is important to keep in mind when purchasing or using flat lens goggles. If you are using them and this occurs, your goggles are not broken or malfunctioning on you, it’s simply the shape of the lens. If you’re on a budget or simply want something basic, a flat lens goggle is likely to be the best option for you.