Progressive lenses are by far one of the most complex lenses on the market. This often leaves the patient begging to know what the difference is between brands and designs.
What all progressive lenses have in common is a distance section towards the top of the lens, a reading section towards the bottom nasal area of the lens, and connecting these two is an intermediate corridor. On either side of the corridor are blending zones.
Some lenses have larger reading or larger intermediate zones others have a much softer blending zone resulting in less peripheral distortion. Each designer has their trade mark ‘design’. Lets take a look at what makes some of these lenses so different.
HARD vs SOFT
There are two main categories for progressive lens design. These are hard and soft designs. This refers to the amount of blur that is located in the peripheral blending zones. The front of a progressive lens consists of a complex series of curves. These curves are blended at the least used section of the lens, the peripheral and nasal.
Hard lenses have a much higher concentration of blending in these zones. This allows for a much clearer distance and reading but can give the wearer an intense ‘swimming’ feeling.
Later lens designers reduced the harshness of hard lens designs by creating the soft lens. These lenses increase the blending zones. This spreads them out into the distance and reading portion of the lens. People who tend to be very active in their lenses can appreciate the reduced swimming feeling.
Today lens designers are taking into consideration that neither hard nor soft design is ideal. Myopes and Hyperopes have different needs.
For instance, a myopic person (near sighted) does not need a large reading area however the wearer is more sensitive to distortion in the distance. So a design with a softer distance and a harder near design would be ideal.
A hyperopic person (far sighted) has the opposite needs. Hyperope’s are not as sensitive to distortion in the distance but needs a larger reading zone. In this case a harder design is used for distance with softer for the reading area.
In addition to the above designs is something called variable inset. This refers to how far the reading segment is placed nasally. The minifying nature of a minus or diverging lens used for the correction of Myopia means that the wearer does not need to converge their eyes as much. Wear as the magnifying nature of a plus or converging lens used for the correction of Hyperopia means that additional convergence is needed so the reading segment is placed more nasally than for a myope.
It used to be that larger eye sizes were all the rage but times have changed. The older progressive lenses just did not fit in the smaller modern styles. To remedy this American Optical introduced the first ‘short corridor’ progressive lens called the AO Compact.
The idea was to shorten the distance between the distance and reading sections of the lens. This would allow the lens to be fit in many of today’s smaller styles. The one draw back is that the power change is much more immediate due to the shortened corridor.
You may be wondering ‘So how do I know what lens is right for me?’ Well, your Optician will often employ a technique called Life Style Dispensing. This is where the Optician will ask you questions about your work, hobbies etc. to try and determine your visual needs.
From this he or she will determine which lens would be best based on what they have available. You may also wonder ‘How does my doctor’s office determine which lenses they use?’
All lens manufacturers have same basic designs; a short corridor, basic design, premium design etc., but like anything it’s a business and offices choose a company that will give them the best deal and the best warranty.