Contact Lens Design & Materials
Two New SiHy Lens Options
By Neil Pence, OD, FAAO
Two silicone hydrogel contact lenses have entered the market in recent months. Let's take a look at the details of these new contact lens options for your patients.
A New Option for Astigmatism
Bausch + Lomb introduced Pure-Vision2 HD for Astigmatism last month. It is produced in the same material as the company's Pure-Vision Toric (balafilcon A) lens, but in a significantly altered design. Changes in the ballasting as well as an increase in the overall lens diameter and the size of the optic zone are intended to enhance lens stability.
The basic prism-ballasted design has been altered, making the lens thinner at the 6 o'clock position. Its “Auto Align Design” consists of the inferior nasal and inferior temporal areas being the thickest portions of the lens, creating a peri-ballast type effect. The diameter has been increased to 14.5mm (compared to 14.0mm for PureVision Toric), and the optic zone is 8.0mm.
PureVision2 HD for Astigmatism also features correction for spherical aberration in both the sphere and cylinder meridians, which should improve vision for patients. The new design has a thinner edge profile to enhance comfort, and a wetting agent (poloxamine) has been added to the blister package.
PureVision2 HD for Astigmatism is recommended for daily wear and monthly replacement. It has a single orientation line at 6 o'clock. Initial launch parameters include sphere powers from plano to −6.00D (0.25D steps) and cylinder powers of −0.75D, −1.25D, and −1.75D in axes of 10 degrees to 180 degrees (10-degree steps), with expansions in sphere and cylinder powers expected in 2012.
A New Multifocal Option
CooperVision's Biofinity Multi-focal is manufactured in the Biofinity comfilcon A material. It is recommended for monthly replacement and is approved for daily wear and up to six nights of extended wear.
The new lens features a slight modification of the basic “Balanced Progressive” design used for CooperVision's Proclear and Frequency 55 Multifocals. There continues to be “D” (center-distance) and “N” (center-near) lens designs. The aspheric intermediate zone that surrounds each center zone now transitions into a spherical power zone, whereas the previous design presumably continued to be aspheric. Thus, the D lens center-distance zone now transitions into an aspheric intermediate power surrounded by a spherical near power annulus in the peripheral optic zone. Likewise, the N lens has a spherical distance power ring in its periphery. The goal is to slightly enhance near vision in the D lens and perhaps allow improved distance vision in the N lens as compared to the Proclear Multifocal.
Biofinity Multifocal also has a new recommended fitting technique. For spectacle adds in which the +1.00D or +1.50D add power contact lenses are appropriate, the initial approach is to fit two D lenses. If better near vision is needed, an N lens in one eye might be tried at a later follow-up visit. When using the +2.00D and +2.50D add power lenses, the standard approach is to use one D and one N lens in the respective eyes. If spectacle add powers fall between available contact lens parameters (+2.25D, for example), it is suggested to round the add power down when selecting the first diagnostic lenses (i.e. use +2.00D add power lenses, one D/one N in this case).
It is recommended that equal adds be selected for the initial fitting of Biofinity Multifocal, and experience suggests that slightly altering the sphere power in one eye may be a better next step than going to unequal adds. Biofinity Multifocal parameters include sphere powers of +6.00D to −8.00D (0.50 steps over −6.00D) and add powers of +1.00D, +1.50D, +2.00D, +2.50D. D lens and N lens designs are each available in all parameters. CLS
Dr. Pence is the associate dean for Clinical and Patient Care Services, Indiana University School of Optometry in Bloomington, Indiana. He is a consultant or advisor to B+L, Ciba Vision, and Vistakon and has received research funding from AMO. You can reach him at firstname.lastname@example.org.