Toric Contact Lenses
Reviewed by Henry Rosenthal, OD
Spherical contact lenses correct nearsightedness or farsightedness and are indicated by a minus or plus in your prescription. Toric contact lenses correct astigmatism, which can accompany either nearsightedness or farsightedness. These two are often compared to one another, and though they are made up of the same materials, it's the design of the lens that separates them completely.
Unlike spherical lenses, toric lenses have two different powers in the lens. By having this characteristic the toric lens must remain in one position for the best visual acuity, too much movement of the lens can significantly reduce visibility. Some of them are made heavier at the bottom to prevent them from too much movement or rotation.
New advancements in technology over the past 30 years has allowed scientists and doctors to create new toric lenses with specific customizations like color, material, disposability, multifocal and bitoric. But to this day, scientists' biggest dilemma when creating new toric lenses is sustaining lens stability.
Who Are Toric Lenses For?
Toric lenses can be worn by anyone with a corneal astigmatism, lenticular astigmatism, or combinations of both. Patients who have tried spherical lenses first but continued to have poor vision, patients with large degrees of astigmatism ranging from 3-5D, patients with residual astigmatism, and patients who find discomfort, or corneal swelling with Rigid Lenses are all good candidates for toric lenses.
Toric Lens Costs
There are two things you'll have to pay for when wearing toric lenses; doctor visits and the lenses. Everything that involves toric lenses, such as fittings, exams and the lenses themselves will be more expensive than regular lenses, depending on your health coverage. Toric lenses are also more expensive than ordinary contacts, most products averaging $50-$75 for a supply of six.
Daily Care and Usage
This would depend on which type of toric lens you wear. Daily disposables are said to be the most convenient when it comes to caring for your contacts. They don't require any extra care products like solutions and cases. Extended wearers or 30-day wearers should properly clean and disinfect lenses daily and try not to expose themselves to too much smoke, chemicals, etc. Overnight wearers don't necessarily need to clean or disinfect their lenses daily, however nothing is wrong with this practice.Whether or not your lenses have customizations done to them like color or multifocal functions, your doctor should have specific care instructions for you to take home. Usually you would soak your lenses in a specific solution for cleaning and disinfecting, followed by a rinse and an allowed time for drying before placing them back into your eyes. For a quicker dry time, you can pat your lenses with a paper towel.
Toric Lens Materials
Depending on which type of toric lens you wear or intend to wear it can be made up of one of the following materials; Silicone Hydrogel (most common), Omafilcon A, Methafilcon A, Polymacon, Hilafilcon A, Hilafilcon B, or Balafilcon A.
Customized Options for Toric Lenses
More than 40% of the vision-corrected population requires astigmatic corrections for levels of 0.75D or more. This is one of the many reasons why scientists have been able to develop toric lens with multiple options like disposability, color, and multifocal capabilities. Disposable toric contact lenses can be either daily disposables or 30-day silicone hydrogel wear, and can also be available in many colors to either change or enhance your natural eye color. Some colors are available as disposables, but most colored toric lenses are non-disposable. Multifocal are also non-disposable, but are great for correcting Presbyopia. Some brands have developed soft toric multifocal lenses, but doctors often prescribe an RGP lens for correcting Presbyopia.
Different Types of Toric Lenses Available
Rigid gas permeable lenses are made of stiff material that retains its shape when you blink and comes in numerous bifocal and multifocal designs like back toric (bitoric), front toric and bitoric lenses with prism ballast. RGP lenses are made of permeable materials that allow oxygen to reach the eye easily. They're durable lenses but can still break or tear. They incorporate silicone for flexibility but require you to adapt to the texture and shape of the lens before comfort sets in.
Patients rarely request RGP lenses over soft toric lenses since they give instant comfort to users. Soft hydrogel toric lenses must be able to stay in place as your eye moves. This is done by thick-thin zones (removing material at the apex), lens truncation (cutting off the bottom of the lens, leaving it flat) and prism ballasting (which makes it thicker and heavier)
Bitoric lenses allow corrections to be made on either side of the lens.They are usually introduced to patients whose corneal astigmatisms exceed 2.00D. Bitoric lenses are available for high astigmatic prescriptions and come in soft, rigid gas permeable or disposable materials.
The high oxygen permeability of Balafilcon A, a silicone hydrogel material found in hydrogel lenses, allows 300% to 500% more oxygen transmission and the material also has a high percentage of bound water, so it does not dehydrate as quickly.There are two designs for soft hydrogel toric lenses; prism ballast and aspheric. The prism ballast design prevents the lens from rotating and helps it to stabilize quickly in the eye. An aspheric design removes visual distortion in low-light situations when pupil sizes are larger, also known as "fine tuning".
Problems with Soft Toric Lenses
Unfortunately some patients will reject toric lenses for a variety of reasons. Discomfort is the main reason why patients stop using toric lenses. It can be caused by movement of the lens, a foreign body sensation of the lens, or a constant awareness of the lens due to the pressure of the lens on the lower lid. Another problem patients have with using these lenses is the constant movement of the axis in the lens. The axis is similar to the earth's axis, its in the middle of the lens and keeps your line of vision clear. If the axis is constantly moving, a decrease of vision will occur. An improper fitting of the lens can also pose a nuisance for the patient.
Problems with RGP Toric Lenses
Patients report problems with vision like blurriness and fuzziness after a few hours of wear with RGP lenses. Some also experience excessive dryness of the eye after only a few hours of wear. Fogginess due to edema (swelling) is usually a bigger problem for patients who suffer from photophobia, or light sensitivity.
Options for Mild Astigmatism
If you have a small amount of astigmatism, between zero and 1.00D, a toric lens might not even be necessary. Talk to your doctor, but you may be able to wear a regular spherical RGP or even a spherical soft lens instead. RPG's can cover up the need for a correction of astigmatism and doctors can give you a higher powered spherical soft lens to mask a small astigmatic correction.
[Page updated 12/2010]
