Whether you are nearsighted or farsighted, have astigmatism, or need a bifocal prescription because of presbyopia, there’s a soft contact lens design specially suited to correct your vision. During your contact lens evaluation and fitting, your eye doctor will recommend the best soft contact lens design for your specific needs.
Soft Contact Lenses for Nearsightedness and Farsightedness
Soft contact lenses that correct nearsightedness or farsightedness are called spherical single vision lenses. These lenses are the most popular type of soft contact lens sold.
Spherical single vision soft lenses have the same power and curvature in all meridians. (Think of the lens as a bicycle wheel lying on its side. The hub of the wheel is the center of the lens, and each spoke is a meridian.)
Since spherical lenses have the same power in all meridians, only one number is required to describe lens power. Contact lens power is expressed in units called diopters (D). Soft contact lenses are manufactured in power increments of 0.25 D. (If your contact lens power is -2.50 D, the next stronger lens power available is -2.75 D.)
Contact lenses that correct nearsightedness have a minus (-) lens power. Lenses that correct farsightedness have a plus (+) power.
Example: A soft contact lens with a power of -2.50 D (sometimes written “-2.50 sph” or simply “-2.50”) corrects 2.50 diopters of nearsightedness.
Popular brands of spherical single vision soft contact lenses include ACUVUE(R) Advance(TM) and ACUVUE(R) 2 (Vistakon/Johnson & Johnson), Focus(R) Dailies and Night & Day(R) (Ciba Vision), SofLens(R)38 (Bausch & Lomb), and Frequency(R)55 Sphere (CooperVision).
Soft Contact Lenses for Astigmatism
Soft contact lenses that correct astigmatism (in combination with nearsightedness and/or farsightedness) are called toric single vision lenses. These lenses have different powers in different lens meridians to correct the irregularly – shaped cornea of an eye with astigmatism.
Toric soft lenses also have a special weighting system and different thicknesses in different lens meridians to keep the lens from rotating on the eye. Stable positioning of toric lenses is essential: For consistently clear vision, the meridional lens powers must remain in front of their intended meridians of the astigmatic eye.
Toric soft lenses have two numbers to describe lens power: a sphere power (sph) and a cylinder power (cyl). Sphere powers can be plus (+) or minus (-); cylinder powers are always minus. The sphere power always comes first in the prescription; the cylinder power is always second.
The sphere power is the contact lens power prescribed for the flattest meridian of the eye. The cylinder power, when added to the sphere power, indicates the total contact lens power prescribed for the steepest meridian of the eye.
Toric soft lens prescriptions include a third number, called the cylinder axis. The axis always comes last in the prescription, preceded by an “x”. The axis indicates the location (measured in angle degrees) of the flattest meridian of the eye (i.e. the meridian that requires only the sphere power.) The meridian of the eye that requires the sphere power plus the added cylinder power is located 90 degrees from the axis.
Meridian locations are determined by superimposing an imaginary protractor scale in front of the eye. The protractor scale measures radial positions in 1-degree increments, starting from the right side. The 90-degree meridian is a vertical line; the 180-degree meridian is a horizontal line.
Example: A toric soft contact lens has a power of -2.00 -1.00 x 180. (The sphere power is -2.00, the cylinder power is -1.00 and the cylinder axis is 180.) This lens corrects 2.00 diopters of nearsightedness in the horizontal (180-degree) meridian of the eye and 3.00 diopters of nearsightedness (2.00 + 1.00) in the vertical (90-degree) meridian of the eye. The difference (1.00 D) is the amount of astigmatism, which is equal to the cylinder power of the prescription.
Popular brands of toric single vision soft lenses include Focus(R) Toric (Ciba Vision), SofLens(R) 66 Toric (Bausch & Lomb), Frequency(R)55 Toric (CooperVision), and ACUVUE(R) Toric (Vistakon/Johnson & Johnson).
Soft Contact Lenses for Presbyopia
Presbyopia is the normal age-related loss of near focusing ability that affects adults over age 40. Soft contact lenses designed to correct presbyopia (in combination with nearsightedness and/or farsightedness) are called bifocal or multifocal lenses.
Bifocal and multifocal soft lenses have a spherical (distance) power to correct nearsightedness or farsightedness and one or more magnifying powers in a portion of the lens for close-up vision. This additional magnifying power to correct presbyopia is called the add power.
Like sphere and cylinder powers in contact lens prescriptions, add powers are measured in diopters (D). Add powers are always preceded by a plus sign (+) and typically range from +1.00 to +3.00 D.
The performance of bifocal and multifocal soft contact lenses depends on a number of factors, including the fit of the lenses and the size of the wearer’s pupils. Frequently, people who wear bifocal or multifocal soft lenses have slightly less clear vision compared to their visual acuity when wearing single vision contact lenses for distance vision and reading glasses (over their contact lenses) for near vision. But most bifocal and multifocal soft contact lens wearers are willing to make this trade-off for the ability to be able to see adequately well up close without having to rely on reading glasses.
Popular brands of bifocal and multifocal soft contact lenses include Acuvue(R) Bifocal (Vistakon/Johnson & Johnson), SofLens(R) Multi-Focal (Bausch & Lomb), Focus(R) Progressive (Ciba Vision), and Proclear Compatibles(R) Multifocal (CooperVision).
Monovision Contact Lenses for Presbyopia
Another way to correct presbyopia with soft contact lenses is to use single vision lenses (either spherical or toric), prescribed in a way so one eye is optimized for distance vision and the other eye is optimized for near vision. This technique is called monovision.
Many contact lens wearers who are unsuccessful with bifocal or multifocal lenses feel they see more clearly and comfortably with monovision single vision lenses. This is especially true for people with astigmatism, since most bifocal and multifocal contact lenses don’t correct astigmatism.
An added benefit of monovision is affordability. The cost of replacing single vision lenses is usually significantly lower than the cost of replacing multifocal or bifocal lenses.
If you are over age 40 and presbyopic, ask your eye doctor to demonstrate the option of monovision during your contact lens evaluation and fitting.