Soft Toric Lenses: Contacts for those with Astigmatism
Introduction and Overview
Astigmatism is a common vision condition affecting a large portion of the population. In an eye without astigmatism, the cornea, the clear dome-shaped “window” over the iris, is shaped like a sphere, similar to a basketball. In astigmatism, the cornea has different curvatures, much like that of an American football.
As this illustration shows, a football has more curve to it when measured horizontal, parallel to the line of stitches than it does running around its middle. Optically, an eye that is shaped like that will have different refractive errors (nearsightedness or farsightedness) in the vertical orientation than in the horizontal. In effect, the different curvatures require different prescription lenses to provide clear vision to an eye with astigmatic curvature. In spectacle lenses, the curvatures are ground into the lens to provide good vision, and the lenses are held in position by the frames, so lens cannot rotate into incorrect alignment.
Correcting mild to moderate astigmatism with RGPs (rigid gas-permeable lenses) is not usually a problem, because the tears fill in the space behind the contact lens and this provides the right correction along with the power in the contact. Soft lenses, however, don’t work the same way.
In soft contact lenses, rotation of the lens on the eye must be stabilized in a similar way to spectacle lenses, to keep the correction lined up properly.
The alignment of the astigmatic correction, referred to as the axis of rotation, is usually done in one of two ways: either a small amount of prism is added to the bottom of the contact lens, making it heavier and thus using gravity to hold it in alignment, or the lens is made with thin zones in the upper and lower areas which allows the eyelids to hold the thicker area through the center in place. A soft toric lens that is working well will usually only rotate about 5 degrees in either direction as the person wearing it blinks and goes through the usual day.
There are currently about two dozen brands of popular toric soft lenses available for the eyecare practitioner to choose from for the best comfort and vision of the wearer. The right choice for each individual will include evaluation of the anatomy of the eyelids, the space between the top and bottom lids, how tightly the eyelids hug the eye, the water content of the lens (all soft contact lenses contain some percentage of water, usually ranging from about 40% to 60% of the total volume of the lens on the eye. The water in the lens allows oxygen to flow through it so the cornea can breathe) and the method of stabilizing the lens against axis rotation.
Another factor to consider is the amount of correction needed to provide good vision. Soft toric lenses have the correction built into them when they are made, so the practitioner must match the powers available to the prescription needed.
The eyecare practitioner will also consider whether the soft toric lens is available in multi-packs for planned replacement, daily wear or extended wear use, the visual demands of the patient’s lifestyle and the environment in which they will be used.
Most patients using toric soft contact lenses will have clear, comfortable vision all day long.
Care of Toric Soft Contact Lenses
The necessary care of soft toric lenses is the same as that for any other soft lens. They will need to be cleaned whenever they are removed and disinfected with fresh solution for several hours in the lens case before being worn again. Most people who are successful soft lens wearers get into a routine of removing their lenses, cleaning them and then soaking them overnight in the disinfection solution. In addition, there may be a separate rinsing solution to use before inserting the lenses into the eye.
Patients in toric soft lenses will need to follow instructions provided for the care of their lenses, and use the proper solutions.
Some helpful hints for successful toric soft lenses include:
- Always clean and rinse your hands before handling the lenses.
- Do not use lenses or solutions that have passed their expiration date.
- Avoid mixing up your lenses. (Tip: Do the care routine for one eye at a time, from removing the lens and cleaning it and storing it in its lens case; don’t remove the lens from the other eye until the first one is already in its compartment in the lens case.)
- Discard any lens that has been dried out or damaged.
- Hot and windy conditions or particularly low humidity may make the lenses feel dry; use an approved contact lens rewetting solution if necessary.
- Indoor tasks that require visual concentration such as working at a computer or reading sometimes causes people to blink less often. This can also cause the lenses to feel dry, so take frequent breaks to look around the room and blink often. Rewetting drops will help here as well.
- Avoid getting foreign contaminates on the lenses, including soap, hand lotion, hair spray, deodorant, perfume or other aerosol products. (Tip: If you use sprays, close your eyes until the spray settles.)
For more information about the use and care of soft contact lenses, please see the article titled Contact Lenses: [A Great Way to See! (Section Two)].
Don’t wear any lens in the following situations:
- It the lens causes a foreign body sensation in the eye, or even if it just doesn’t “feel right, don’t ignore it. (Tip: remove the lens, check to be sure it is right side out and rinse it, then replace it in the eye. If it still doesn’t feel right, don’t wear it.)
- If there is excessive watering or eye secretions during your wear time, redness, burning, stinging, itching, light sensitivity or visual disturbances like rainbows or halos around objects, check with your eyecare practitioner right away.
- If you experience unusual dryness or reduced comfort during your wear time, or blurred vision, check with your practitioner.
Cost of Toric Soft Lenses
The fitting and dispensing appointments for toric soft lenses are slightly longer than those necessary for regular spherical lenses (not for astigmatism). The lenses themselves are also somewhat more expensive, due to the complexity and sophisticated technology needed to make them.
The follow-up visits and the solutions needed for their care will be about the same as for spherical lenses.
In general, toric soft lenses will cost about twice as much as spherical soft lenses.
Toric soft lenses have become a useful and functional solution for patients with astigmatism. They are available in just about any prescription and provide clear, comfortable vision all day. Their care and handling are the same as for any other soft lens.
Ask your eyecare practitioner about toric soft lenses to find out if they are right for you.