Cycling glasses aren't a fashion statement, they are essential. Not only do they need to be lightweight, strong and fit well they also have to protect your eyes from strong or even moderate sunlight. More high-end models will have Photochromatic lenses that actually adapt to changing light conditions. Also consider the type of riding you will be doing. For time trialists and triathletes a rimless frame might be a better option. All weather riders might prefer something with interchangeable lenses.