Snow goggles come with an UVA and UVB protection, these are harmful rays from the sun that are prevalent in snowy areas and shielding the eyes from prolonged exposure is what the goggles are designed for. Therefore, using the same for MX in areas that don’t experience much of the same rays may be too much for the rider.
Snow goggles have a dual lense system and this is not for show. There are two reasons why they are designed that way, the first one is to create a buffer zone between the two lenses filled with air that stop the inner layer from getting cold and transferring that to the face. The second reason is for keeping moisture and fog out. Using this type of goggles for racing in warm areas is ill advised as that design is not made for that kind of an
The ventilation system found in ski goggles is more robust and designed specifically to deal with the cold wind you experience when you move downslope at high speeds. If you were to use these in a warm climate, the ventilation will not be as efficient and you would end up with moisture trapped inside instead.
The lens tint found on the ski goggles is designed to deal with the harsh light reflection that bounces off the snow. The pure white light requires darker tints to counter their glare. Using the same on a motocross trail, there’s a high possibility you’ll not be able to see anything as they’ll be too dark for an environment that doesn’t have any snow.
The ski goggles will not be able to fit into MX helmets if you try to use them both at the same time. Ski goggles are designed to fit into skiing helmets. Trying to sue them with any other kind of helmet will not work as they are totally incompatible, no amount of adjustments will make them work.
The view angles on ski goggles are better and wider as the lens curves towards the temples. Even the peripheral view is covered by the lens. MX goggles on the other hand are designed for dealing with oncoming winds and objects and therefore they only have a directional view that is focused on the way straight ahead.
Most riding goggles have a single lense unlike ski goggles. There’s no need for a double layer of air in between lenses for keeping the cold out since it is assumed that most MX riders use them frequently in warm areas. Therefore, only a single lens is sufficient to keep the wind and the sun from affecting the vision.
In place of anti-fogging, motor goggles are equipped with anti-dust capabilities where both the inside and the outside of the lens are able to repel as much dust as they can to avoid blocking the view once they begin accumulating. Some that are used in cold climates do have anti-fogging abilities but they are not as refined as ski goggles.
MX goggles are smaller in size compared to ski goggles. Their lenses are smaller and don’t have to cover as much space as they only have to deal with harsh light and wind. They don’t have to go all the way to the temples. This means that less materials are used to make them and this reduces their price tags considerably. Optically, they are inferior to ski goggles and even the most expensive MX riding brands will rarely be able to compete with normal ski goggles.
The two types of goggles should not be used interchangeably. There’s no one who is going to stop you from using ski goggles for riding and vice versa, but you’ll be putting yourself in danger as they are not optimised for those kinds of roles.