Learn from Benjamin Franklin's wisdom how all lenses are "specialty" lenses in a sense.
However, what most people do not recognize about Franklin's invention is that it was a compromise, something he did because he found it "more particularly convenient."
What Franklin teaches us through his invention is that all lenses are "specialty" lenses in a sense. In Franklin's case, the specialties were distance vision and near vision, for which he had a dedicated pair of lenses each. From these he created the bifocal-the first specialty multifocal lens. Its purpose was to eliminate the hassle of changing glasses frequently.
Sunwear is the most obvious category of specialty eyewear. I once did some consulting work for a man who owned 15 sunglass kiosks. I was amazed at the vast amount of product knowledge his staff needed to absorb before they could help customers to select the appropriate sunwear.
As tints go from red to violet, the spectrum of colors they absorb and transmit changes dramatically.
All of these colors are also available in Polaroid, a real plus for those who want to remove reflected glare as well.
If you think the specialty sunglass category is not lucrative, think again. I became convinced of its value when I met an optician in Oregon who owned a small chain. He specialized in specialty sunwear and built a fabulous business and reputation on them.