I want to supply soft progressive contact lenses to my patients. How do they work?
I will focus here on progressive contact lenses and not bifocal contact lenses. Soft progressive contact lenses have a smooth and gradual transition between the power for near vision, the power for distance vision, and sometimes intermediate vision, very much like progressive spectacle lenses. Bifocals have an abrupt difference in the line between the near and normal vision prescription areas of the contact lens. Depending on the object being viewed, the wearer’s eye uses the region(s) of the contact lens that provide the sharpest vision.
There are two types of simultaneous vision designs: concentric and aspheric.
Concentric soft progressive contact lenses typically contain the lens power for seeing distant objects in the centre of the lens, which is surrounded by concentric rings of near and distance powers.
Typically, at least two concentric power rings are within the pupil area in normal lighting, but this varies as the pupil dilates and constricts due to varying light conditions.
The locations of the powers in a concentric design can vary:
Some have the near power in the centre of the lens, known as centre-near.
Some have a centre-distance design for the dominant eye and a centre-near design for the non-dominant eye.
Aspheric soft progressive contact lenses have a gradual change in power from far to near, with no visible lines in the lenses. They also make use of simultaneous vision, so the patient must learn to select the proper contact lens power for the moment.
A number of aspheric multifocal contacts are now available as daily disposable lenses.
I have previously written about setting patient expectations at the correct level. Some patients find these lenses difficult to use. I will shortly write about how to determine the dominant eye.