Understanding Artificial Lens Implant Technologies
Our eye is like a camera and must continually shift its focus from far to near and to various distances in between. Young people have the best system, a flexible human lens that is constantly and automatically adjusting its shape to change focus. This is like having an “auto-focus” camera where you just point the camera (or eye) at something, and the focus is automatically and instantly adjusted.
With age, we all lose this convenience and end up with a “manual” focus camera — we must manually change the focus by switching between different pairs of eyeglasses for each distance that we need to see.
Bifocals and trifocals are like having 2-3 different pairs of glasses combined into one frame. Progressive (“no line”) eyeglasses allow us to see all four zones by looking through different parts of our eyeglasses as though we had 4 different pairs of glasses stacked one above the other. There are four primary zones or distances at which we need to be able to see details.
Primary Vision Zones
- Zone 1
- Far distance – street signs, golf balls, distant animals, theater stage
- Zone 2
- Indoor distance – pictures on the kitchen wall, faces across the table, TV 8 feet away
- Zone 3
- Intermediate – dashboard, store shelves, stove, desktop computer, piano, bathroom mirror
- Zone 4:
- Near-reading, cell phone, tablet device, medicine bottle label
Artificial Lens Choices
There are 4 categories of artificial lenses for cataract patients to choose from: Basic lenses, Toric lenses, Extended focus lenses, and Trifocal lenses.
Basic IOL
With the basic, single focus artificial lens implant, you select which 1 of the 4 zones you want to see optimally without any eyeglasses on. People who select a basic lens implant should expect to wear glasses most of the time after cataract surgery. People with astigmatism who select a basic lens implant should expect to wear glasses all the time after cataract surgery to correct the astigmatism and provide for clear vision at all 4 zones.
Extended Focus IOL
Extended focus lens implants provide greater focusing range due to increased “depth-of-focus”. Compared to the basic lens implant set for distance (zone 1), patients with the extended focus lens can expect good vision without glasses in zones 1, 2, & 3 but still require reading glasses (zone 4).
Because there is less range of vision without glasses there is also less loss of contrast sensitivity and less nighttime halo and glare compared to a multifocal or trifocal implant. Extended focus lenses are often a good option for people who want more range of vision than a basic lens but fewer side effects than what would occur with a multifocal or trifocal implant.
Trifocal IOL
The trifocal lens implant can provide continuous focus across all 4 zones. This occurs naturally and automatically without having to look through different parts of the artificial lens, so the mechanism is completely different than with wearing trifocal or progressive eyeglasses. People who select the trifocal implant wear glasses the least often, but you must have a healthy eye to do well with this sophisticated technology. In addition, all trifocal implants have decreased contrast sensitivity and associated nighttime glare and/or halos that can be bothersome to some people. These nighttime symptoms do not disappear with glasses or contact lenses as they are part of the lens implant technology within the eye, however most people adapt and do well with this technology.
Lens for Astigmatism
Astigmatism is a natural blur or misfocus caused by an imperfect shape of the cornea at the front of the eye. Instead of placing the astigmatism correction into one’s glasses or contact lenses, it can be incorporated into the artificial lens implant instead. The name of this built-in feature is toric, and it can be incorporated into any of the 3 lens implant types (single focus, extended focus, or trifocal).
