Here's a brief 2-part summary:

Anti-reflective eyeglass lenses are actually coated with metal oxides that improve vision by reducing glare and reflection. Reflections on the surface of an eyeglass lens can cause ghosting and eye strain. Anti-reflective coatings eliminate these problems and those that are caused by such things as oncoming headlights and fluorescent lighting reflecting off computer screens, two big sources of strain. These coatings also make glasses look better as the surface won't have that noticeable mirror effect.

High index eyeglass lenses eliminate the need for that legendary 'soda bottle look'. The rule of thumb has always been the stronger the eyeglass prescription, the thicker the eyeglass lens in order to accommodate the right amount of light bending. High index lenses changed that and their development enabled eyeglass frame manufacturers to begin creating extremely thin or rimless frames.

High index lenses made out of plastic are very light since less material is used in the construction of the lenses. These lenses can also be made from glass however, because glass is heavier, the end result won't be a lighter feeling lens. There is a range of high index lenses and understanding higher vs. lower index is a bit complicated, so it is best to let your eye doctor explain the differences. In general, higher indexes cost more and should be thinner. These eyeglass lenses also benefit from the addition of an anti-reflective coating which blocks less light.

Photochromatic lenses change from regular clear lenses into dark-colored lenses, similar to that on sunglasses, when they are exposed to sunlight. The convenience of having '2 pair of eyeglasses in 1' is less expensive. Transitions lenses are the most familiar of this type of lens and they are available in practically every prescription and refractive index.

They offer full ultraviolet protection, too. The secret behind the color changing capability is silver halide which is mixed right into the lens when it's being created. In the early days, thicker parts of the lens resulted in darker areas, but this has been virtually eliminated with the introduction of polycarbonate and high-index lenses. Besides Transitions, many other companies offer some variation of the photochromatic lens. Corning, the original developer, has several styles including Thin & Dark and SunSensors, as well as the originals, PhotoGray and PhotoBrown.

Continue to Part 2 for more eyeglass lenses options.