Normal lens size should be OD / R = 0, OS / L = 0, in neutral size and does not interfere with your vision. Cheap glasses are not measured in the level of lens neutrality, a smooth lens surface, and alignment of the central point. This can cause eye pain, blurred vision, headaches, multiple views, and can cause cataracts and brain tumors. Therefore, you should only buy the recommended and licensed best sunglasses for trail running for your own health and safety.
Paint Materials On Frame
Cheap glasses maker certainly will not pay attention to the level of security. So most cheap glasses will use paint that is not in accordance with existing standards and there are hazardous materials in it. The use of glasses with such hazardous paint can cause your skin itching, irritation, and cancer.
Be wise in choosing glasses before buying them, the way is to try the glasses you want to buy for about 2 to 3 minutes, to match the position, robustness, and size that should fit your eyes. If it does not match, then feel free to cancel the intention of buying those glasses.