It is not difficult to recognize an Asian face from a Caucasian face due to their distinctive facial profile. When it comes to eyeglasses, the height of the nose bridge and the cheekbone have an effect on the positioning of the glasses on the face. In general, an Asian face is characterized by a low nose bridge and prominent cheekbone while Caucasian face has a high nose bridge and receding cheekbone. Since glasses are designed to sit on the nose bridge and its rim extending down to the cheeks, it is important the glasses are designed to match the facial profile for optimum comfort.
The most distinctive difference between an Asian fit and a Caucasian fit is the depth of the nose pad. For glasses to fit comfortably, the lens should not be seated too close to the eyes or the eyelashes would brush against them. When the nose bridge is shallow, the nose pad needs to be deeper such that the lens is further when the edge of the nose pads is resting against the nose bridge. This also reduces the incidence of the cheeks touching the bottom of the glasses rim when you smile which causes your glasses to slip down.
Your glasses are supported on your face by your ears and your nose bridge. If your cheeks touch the bottom of your glasses rim when you smile or talk, it will lift the nose pad off your nose bridge. This removes the support from your nose bridge and if your glasses temple does not provide adequate support, your glasses will slip down your nose. Therefore, a deep seating nose pad will ensure that it is in constant contact with your nose bridge as you talk and smile.
Asian fit glasses is just a general term for glasses with deeper seating nose pad. The human facial profile is more varied than this generalization. That is why eyewear from Oakley and Swiss Flex have come out with a variety of nose pad designs such that the user may find a closer match than existing eyewears.
Asian fit glasses are not restricted for Asian face. Anybody with lower nose bridge will benefit from Asian fit eyeglasses especially children and teens. The important point here is that the glasses are designed with a deeper seating nosepad to fit a particular facial profile instead of an ethnic group.