SPECTACLE LENS STYLES
Single Vision Lenses
Single Vision Lenses as the name implies have only one power which can be set for distance, intermediate or near focus. In a younger patient this lens will actually work for all distances. For anyone requiring a bifocal/ multifocal prescription the lens will be more limited in function as it only has one focus distance. Single Vision lenses can be made from various materials and for a review see our "Spectacle Lens Materials" webpage.
Bifocal Lenses
Bifocal lenses have two distinct powers in the same lens and are used by patients so they do not have to switch between two pair of spectacles. Typically they are used in a condition called presbyopia in which the eye loses the ability to focus from distance to near. In some cases even children though will be fit into a bifocal if they have a condition where the eye has difficulty focusing from far to near. The bifocal lens has two distinct divisions with the top of the lens set for the distance vision and the bottom for near (reading). In some cases the top of the lens can be made for intermediate distance (computer) and the bottom for near. The transition point where the two powers meet results in a clearly visible "line" which is commonly associated with the bifocal. Bifocal lenses can be made from various materials and for a review see our "Spectacle Lens Materials" webpage. Some examples of different bifocal styles are shown below:- Flat Top Bifocal
The flat top bifocal comes in sizes of 25, 28, 35 & 45 millimeters (measured at the widest part of the bifocal). Like all bifocals it has a visible "line" and it's biggest advantage is it offers two very distinct powers. The line is obvious because the change in powers is immediate with the advantage being it gives you the widest reading area without having to look too far down the lens. It is also easy to teach someone how to utilize the bifocal in that you simply use the top for distance and the bottom for reading.
- Curve Top Bifocal
The curve top bifocal comes in sizes of 28, 35 & 45 millimeters (measured at the widest part of the bifocal). It is similair to the Flat Top bifocal except the top line of the bifocal is curved slightly. It still offers two very distinct powers however the curve top is slightly less visible than the traditional flat top design.
- Round Top Bifocal
The round top bifocal comes in sizes of 22, 25 & 28 mm (measured at the widest point of the bifocal). The biggest reason for using the Round Top Bifocal is the bifocal line is not as obvious as in the Flat Top (Note the subtle bifocal in the example on the right). It is not invisible but when worn it tends to be much less noticeable. Functionally, it is the same as the flat top except the patient must look a little further down into the bifocal to get the same width due to the shape of the lens.
- Blended Bifocal
The blended bifocal is a Round Top Bifocal design where the "lines" have been made less visible by blending the transtion zones between the powers. The advantage is cosemetic but the disadvantage is the blended zone creates some visual distortion and one must learn to ignore the distortion. Blended bifocals are not progressive lenses as they only have two powers but that is a common misconception. Please refer to the progressive lenses below.
- Ultex Bifocal
The ultex bifocal is similair to the round bifocal above except much larger and rarely used due to the popularity of the progressive lenses. The advantage is for those that prefer the round bifocal design but need a larger reading area.
- Executive Bifocal
The Executive Bifocal is designed so that the entire top of the lens is one power and the bottom is another. It was traditionally used for those that did alot of deskwork and paperwork. Cosmetically is is the most obvious of all bifocals and these are rarely used anymore due to weight and thickness issues. Also, due to the bottom portion of the lens covering the entire lens it is difficult for many people to walk around in them due to decreased peripheral vision inferiorly.
Trifocal Lenses
Trifocal lenses have three distinct powers and are used for patients that need three working distances in one lens, such as driving, computer and reading. Like the bifocal they are used for patients with presbyopia. The distinction between the two is the trifocal has a middle lens which focuses for intermediate distances. The top of the lens is set for the distance, the middle portion for arms length and the bottom for near (reading). The transition point where the three powers meet result is a visible "line" because the change in powers is immediate. Trifocals are available in the Flat Top and Executive designs as described above and shown above. Trifocal lenses can be made from various materials and for a review see our "Spectacle Lens Materials" webpage.- Flat Top Trifocal
The Flat Top Trifocal is the same design as the flat top bifocal except it has an additional middle lens. This lens is set for intermediate distances such as the computer. The flat top trifocal comes in sizes of 25, 28 & 35 millimeters measured at the widest part of the trifocal.
- Executive Trifocal
The Executive Trifocal is the same design as the executive bifocal except that it has an additional middle section that is for intermediate distances. The advtanges is is offers the widest viewing areas of all trifocals but it is limited mostly for desk / computer work due to its higher weight, thickness. Also, due to the bottom portion of the lens covering the entire lens it is difficult for many people to walk around in them due to decreased peripheral vision inferiorly.
Progressive Lenses- (Invisible Multifocals)
A progressive lens is the most commonly used lens today for patients that require a lens that provides distance, intermediate and near powers at the same time. As with the bifocal and trifocal it is used to correct Presbyopia but unlike the later two it does so with a lens design that has no visible lines. The way this is achieved is that the change in power is progressive rather than abrubt. The advantages to the progressive is that it offers all distances in one lens in a cosemetically appealing way. The disadvantage is that the reading area and intermediate area is smaller than in tradtional flat top designs and there is peripheral distortion in the lens due to the change in powers that the patient must adapt to.
Occupational Lenses
- Computer Lenses- Near Variable Focus
The near variable focus lenses are the most common computer lenses we use today. They are designed so that the top of the lens is for intermediate distance (computer) and the bottom of the lens is for near (reading). The lens does not have any visible lines similair to the progressive above. The near variable focus lenses are soley intended for close work or deskwork and are not to be used for distance viewing. The advantage of this lens design is that the patient can look straight ahead at a desktop computer without having to tilt their head back as they would in a bifocal, trifocal or progressive lens. Typically our near variable lens of choice is the Business Lens by Zeiss (a German Manufacturer) though we use many other lens types.
- Double Bifocal
The double bifocal is a lens design that has two bifocals built into the lens. One is inferior and the other is superior. It is used by patients that require both a distance and near power but also require to read up above their heads, such as an airline pilot reading the gauges overhead.
- Quadrafocal
The quadrafocal lens is similiar to the double bifocal above with the exception that a flat top trifoca is used on the bottom portion of the lens and a flat top bifocal is used on the top. This allows the patient when looking down to have both intermediate and near vision, straight ahead to have distance vision and when looking overhead to have reading vision.
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Dr. Daniel L. Mason, Optometrist
(619)656-1081