The bottom half of bifocal lenses reduce the efforts needed to focus so as to see nearby objects more clearly. Research also suggests that wearing bifocals as well as other multifocals may help reduce focusing demands in children with myopia (nearsightedness) while they read or do near work.
Your round-top lenses are typically fitted so that the line between the upper and lower portions rest at the same level as your lower eyelid. As you drop your eyes to read downward, your eyes will naturally use the segment for near-vision.
Photochromic lenses are available in nearly all lens materials and designs, including hi index, bifocal and progressive lenses . An added benefit of photochromic lenses is that they shield your eyes from 100 percent of the sun's harmful UVA and UVB rays.
Because a person's lifetime exposure to sunlight and UV radiation has been associated with cayarcts later in life, it's a good idea to consider photochromic lenses for children's eyewear as well as for eyeglasses for adults.
Adding anti-reflective to photochromic lenses enhances their performance even further. AR coating allows more light to pass through photochromic lenses for sharper vision in low-light conditions (such as driving at night), and eliminates bothersome reflections of sunlight and other light from the backside of the lenses in bright conditions.