EYEGLASSES
Only one distance is clear, whether it's far away (distance), computer length (intermediate), or reading length (near). One pair will only work for one distance.
Bifocal has two distances stacked on the lens that are clear, and can be any combination of the single visions but is typically distance on top and reading on bottom. There is a visible line separating the two and no other distance is clear, but the distances have wide views. Trifocals have all three distances stacked with the same pro's and con's.
Progressives are gradual trifocals but without the lines. All distances are clear, but the periphery is blurry. How much periphery is blurry depends on the design of the progressive.
These lenses are designed for people who work at a computer for more than half the day. They're like normal progressives except the main difference is that the computer zone is the largest and centered on the eye, and there's almost no blur in the periphery. The main disadvantage is the distance zone is cut off, so you can't walk or drive with these on.
A blue light filter has been shown to help with regulating circadian rhythms, and can potentially help with eye strain and Computer Vision Syndrome (CVS). They have a subtle warm tint to them that relaxes the eyes, but isn't recommended for people who need accurate color perception for their jobs or hobbies.
An anti-reflective coating significantly reduces glare from lights and screens in both daytime and especially nighttime. It also helps sharpen vision and has built in scratch resistance. Some AR coatings even help repel water and oil.
Transitions turn the lenses dark when outdoors. They can come in a variety of colors, darknesses, and can even work in the car or be polarized. Typical time to fully darken is less than 30 seconds and fully clear up is less than 2 minutes.
Polarized sunglasses aren't just darkly tinted lenses like most sunglasses. Think of polarized as anti-reflective to the extreme - they cut down on significantly more glare than just a tint, and have crisp, clear vision.
Lenses come in many materials, ranging from CR-39 plastic (the heaviest and thickest), to polycarbonate (thin, lightweight, impact-resistant, UV resistant), to hi-index (ultra-thin and lightweight).
Frames come in almost every variation, both for form and function. There are metal frames, plastic frames, rimless, semi-rimless, hybrid, with nosepads or without nosepads, or a combination. Whatever the frame, it should fit snugly, not be too large or too small, and be geared towards your prescription.