Single Vision Lenses
These are lenses with one working distance only. For kids and adults 40 and under it can be used for all ranges. But for those who need a specific working distance it can be used just for reading, computer, or anything that works with the prescription required.
Bifocal and Tri-Focal Lenses
The lenses of bifocals have two different optical powers that work with two distance ranges. It can be for distance and near, intermediate and near, or any ranges you would like to specify. Bifocals can be for people with “presbyopia” – the inability to focus on near objects. It can also be used for people who have specific needs like a pilot or auto mechanic who needs help in focusing at two different distances. These lenses one distinctive line on the lens to separate the prescriptions.
Trifocals are lenses with three different focusing distances. Usually for distance, intermediate and near. These lenses have two lines that are visible on the lenses. It can be used as an option to people who do not adapt to the progressive lenses.
Progressive lenses are multifocal lenses that change gradually in corrective power from the top half of the lens to the bottom, and thus contain more than two lens powers. Many people prefer progressive lenses for cosmetic reasons – since they don’t have an obvious line going across the lens where the corrective power changes.
Progressive lenses are mostly used for distance zone and reading zone. For long term computer users it is recommended that they be fitted into a computer office lens to maximize visual comfort.
There are five basic eyeglass lens materials:
- CR-39 (normal plastic)
- Polycarbonate (extremely durable)
- Mid-index plastic (1.56) (thinner than normal plastic – better for tinted lenses)
- High-index plastic (1.6, 1.67, 1.7) (ultra-thin and light-weight)
- Glass (outdated – not as safe as plastic lenses, also more expensive)
The five primary types of coatings for lenses are:
- Scratch Resistant: for extra durability
- UV Protective: for greater UV protection (helps prevent cataracts and retinal damage)
- Anti-Reflective: reduces reflections, halos around lights, and glare
- Tinted: for cosmetic reasons, or to produce greater visual contrast
- Photochromic (such as Transition lenses): This coating may improve vision for some people, and helps protect from UV light