Westcon Contact Lens Company

A: When your astigmatic presbyopic patients want soft lenses,be a "can do" practitioner. When you successfully design lenses for these patients, they appreciate it and usually provide future referrals.Soft Bifocals vs. RGP Designs The significant difference between rigid gas permeable and soft presbyopic designs is the technique that provides translation from distance activities to near focusing. RGPs must move in front of the pupillary aperture in order for the patient to see different distances. Soft lenses don't move excessively, so you must design presbyopic lenses with different "zone" sizes to create the same accommodation needs for all distances. Precisely measure the pupils to determine zone size for each eye. Horizon Progressive Toric Westcon Contact Lens Company introduced the first toric soft bifocal seven years ago. The earlier aspheric designs covered the entire optical zone, giving acceptable intermediate and near visual acuity but unpredictable distance vision. To alleviate the problems, Westcon combined aspherical and spherical curves on the anterior surface of their progressive soft lens, while keeping the posterior surface spherical or toric. The aspheric curve is cut only in the center of the front surface to 2.0mm on the dominant eye and 3.0mm on the non-dominant eye. The spherical remainder of the front optical zone provides a large distance power area. The two different center zone sizes enhance each visual range, providing all visual ranges in both eyes a true bifocal design.


Figure 1. Westcon Horizon Bifocal and Progressive are basically the same design with the only exception in the add zone. Dots at 3 and 9 o'clock determine lens orientation on toric.

Horizon Bifocal Spherical Or Toric Design This is a concentric near center add design with a toric posterior curve. Thin zones or double slab- off stabilize the lens axis and provide centration. The basic concentric design has been available for years, but it is well known that the optics are easy to distort in polishing this complex surface. Zones can range from 1.8mm up to 4.0mm. Make the zones smaller on the dominant eye. However, if the patient has a strong need for distance; the zones can be manufactured to compensate for these visual demands. Eye dominance (or controlling eye) tests are equally important in the pre-diagnostic regimen. Designing the Lens Normal-size pupils (3.0mm to 4.5mm) require a near center zone size of 2.5mm for the dominant eye and 3.0mm for the non-dominant eye. On smaller pupils, particularly with hyperopes, start with 2.0mm (dominant) and 2.5mm (non-dominant). For larger pupils, use a 3.0mm for the dominant and 3.5mm for the non-dominant eye. Troubleshooting requires listening to the patient! If the patient complains of diplopia, ghosting or 3-D effect at near, make the near OZ 0.5mm larger on both eyes. If the patient complains of diplopia, ghosting or 3-D effect for distance, then make the near zone OZ 0.5mm smaller on both eyes. If the distance correction is good and the patient requires more plus power at near, increase the add no more than +0.75D. If you need more than +1.00D, increase the near zone size 0.5 mm and do not increase the power.

Take that bold step and prescribe a soft toric bifocal contact lens. As Mikey says, "Try it! You'll like it!"

Q: Describe the design of WESTCON'S HORIZON BI-CON lens.

A: The BI-CON soft lens is a concentric bifocal with a center add zone surrounded by the distant zone. It can be manufactured as a bifocal toric or sphere. The add zone is variable in size and power depending on pupil size and reading power requirement of the patient. The remainder of the anterior optical zone is for distance power. The near and distance zone combined is 8.00mm.

Unlike WESTCON'S HORIZON PROGRESSIVE with aspheric optics, the BI-CON is all spherical optics. On the anterior surface of the BI-CON is the unique dual thin zone, sometimes referred to as the double slab off. This special manufacturing technique results in a thinner flange at the inferior and superior portion of the lens and a thicker flange area on the horizontal part of the lens. The thinner part positions easily under the upper and lower lids while the thicker parts are forced to position between the lids. This dual thin zone serves two purposes. One is to position the lens on axis in the toric design and the other is the ability of the design to aid in keeping the lens centered. There is a small dot at 3 and 9 o'clock when on the eye, close to the edge of the lens for evaluating axis position of the cylinder.

The BI-CON Toric is exactly the same design as the non toric on the anterior of the lens. The difference is the posterior surface where the cylinder is generated in the center of the base curve. There are a total of 3 curves on the back surface of the BI-CON Toric, cylinder, base curve and peripheral curve.

A: The design has a near zone and distant zone in both the right and left lens resulting in all visual ranges both near and far. This modality is not monovision and in fact is an effective step in moving patients from monovision who want to continue wearing contact lenses. We do recommend in most cases to use a slightly smaller near zone in the dominant eye.

A: Generally, a 2.5mm and 3.0mm is a good choice for average-size pupils. Of course a larger or smaller size may be necessary depending on the pupil size. But it must be emphasized that with this bifocal the fitter the ability to really customize the lens to the patient's specific needs because of the availability of different zone sizes and powers in .25 diopter steps.

Suppose, for example, you have a patient who works in somewhat dim light conditions but still needs adequate up-close vision. You may want to use larger zones to accommodate the dilated pupils caused from the dim lights. Another patient may have a strong need for intermediate vision while working at a computer. Simply reduce the add power in the dominant eye keeping full add on the non-dominant eye. Most patients do well with the standard zone sizes, but knowing the patient's specific visual needs and addressing those needs by customizing the zones may be necessary for an optimal fit.

Occasionally the zone size has to be changed due to "shadowing or ghosting" of either the near or distance vision. The rule here is shadowing of distance, go to a smaller zone and shadowing of near, go to a larger zone. Be sure the patient has worn the lens for an adaptation period before making these adjustments.

Q: Why would I choose WESTCON'S HORIZON BI-CON over the other soft bifocals available today?

A: There are several good reasons for considering the BI-CON lenses for your first choice. This was the first soft bifocal with a toric option to enter the market. The concentric design is not a new design to contact lenses, however Westcon took that design, and with the aid of CNC lathes, redeveloped it. The result is much better optical quality. It is a design that has stood the test of time and still considered a very effective option for the presbyopes with astigmatism. No other bifocal, toric, or sphere, has the range of parameters offered in WESTCON'S HORIZON lenses. No fitting set is required and expert consultation is always available.

One more very important reason for fitting the HORIZON lenses is patient loyalty. Because these specialty lenses involve the expertise of a qualified eyecare practitioner for proper fitting and follow up, they are not easily obtained by mail order or internet services. Your patient relies on you for continued care as long as they are using these products, meaning you retain the patient.

Q: How do I determine a good candidate for the WESTCON'S HORIZON BI-CON lenses?

A: There are always exceptions to the rule, however these basic guidelines will help in choosing candidates.

Q: Describe the design of WESTCON'S HORIZON BI-CON lens.