As a world leader of toric contact lenses, CooperVision has the products and the expertise to help you successfully fit toric lenses. The links on this page are designed to give you easy access to a variety of helpful toric fitting information, including procedures for diagnostic and empirical fitting.
TORIC HISTORY
Today, practitioners have many lenses to choose from, complete with wide parameter ranges and excellent reproducibility.
Unsatisfactory vision with soft toric contact lenses should no longer be expected. Patients with high cylinders ranging up to 10.00D are successfully wearing soft toric lenses. In one study, Christopher Snyder, OD showed VA to be equal between RGP and soft toric lenses. (Snyder C., Daum KM, Wiggins NP. Visual performance in the correction of astigmatism with contact lenses: spherical RGPs vs. toric hydrogels. ICLC 1994;21(4):127-131)
A study by Holden (Holden BA. The principles and practice of correcting astigmatism with soft contact lenses. Aust J Optom. 1975;58:279) found that 45% of the spectacle lens market are potential soft toric candidates with 0.75D or better. Based on these results, there is a large segment of the population that can benefit from superior vision a toric soft lens affords. Practitioners have found that fitting specialty contact lens products offers opportunities for practice growth.
Large amounts of astigmatism can be effectively corrected with a soft toric contact lens. Custom soft toric contact lenses have been readily available and used for the past decade.
The diagram below shows the most current silicone hydrogel soft contact lens available in the market today. The Biofinity Toric soft contact lens utilizes several proven toric technologies. It combines a naturally wetting, low modulus material with the highest oxygen permeability, Dk = 128, of any toric soft contact lens today. These material characteristics also support the approval for six night / seven day extended wear.
The optimized ballast design as shown below captures the best of toric technologies.
- Horizontal ISO thickness which improves stability by reducing lens rotation.
- Wide ballast band which increases the area devoted to stability.
- Smooth continuous surface which reduces lid interaction, improves comfort and further adds to stability.
By utilizing Aquaform Technology in combination with the these proven design features, CooperVision is able to provide the practitioner with a toric soft contact lens that can be fit successfully either empirically or with a diagnostic fitting set of lenses.
CANDIDATE
In general, good candidates for toric soft contact lenses must possess the same qualities as good candidates for soft spherical contact lenses. Problems seen with soft contact lens wearers in general (such as poor compliance and deposits) can also plague the toric soft patient. Also, poor tear film and dry eyes can prevent patients from successful wear. Some practitioners suggest a lower water material, for patients with dryness problems.
To simplify toric soft contact lens fitting, we can ask ourselves several logical questions:
- Is this patient a candidate for toric soft contact lenses?
- What material best meets the patients needs?
- Which lens is available for the parameters that are necessary to fit the patient?
SELECTION
How is the toric lens (brand) design selected?
The first step is a good case history. Successful practitioners attribute their success with contact lenses to their communication or listening skills. Patient expectations should be discussed and product selection must be based on the patient's individual needs. Through your interview with the patient, you should be able to set criteria for this specific patient's needs, which will help you select the best possible product for this patient. Does the patient want to wear the lenses overnight? Does the patient want to wear contact lenses part time or full time? Would the patient be a good candidate for single use contact lenses? Once you establish the patient as a candidate for toric soft contact lenses, you must select a fitting method or philosophy. The choices are empirical or diagnostic fitting.
How is the toric soft contact lens design selected (empirical)?
Toric soft contact lenses that are fit empirically are fit off the patient’s spectacle prescription vertexed to the corneal plane. CooperVision's Toric Calculator is an excellent tool for converting a spectacle prescription to the contact lens prescription.
How is the toric soft contact lens design selected (diagnostic)?
Diagnostic fitting
Diagnostic fitting requires more chair-time to fit the patient, although the extra time involved may increase the likelihood of first fit success. The parameters are selected from a diagnostic set, and the lens is placed on the patient's eye and evaluated after the lens has equilibrated.
Combination of fitting philosophies
Many practitioners use a combination of the two fitting philosophies. If there is a diagnostic set of contact lenses handy, the first lens is chosen according to the empirical fitting guidelines. Lens performance is evaluated and if it appears acceptable, the patient is dispensed the diagnostic lenses. The patient is given an opportunity to evaluate the lenses under everyday wearing conditions. Upon return for follow-up, the lenses can be changed if they are not performing properly. It is possible for the rotation or the over-refraction to change over a week's period of time. A large inventory of diagnostic contact lenses is extremely helpful to insure success when fitting toric soft contact lenses. If diagnostic contact lenses are not available, many fitters will use the empirical fitting method.
FIT TEST
Supplemental testing: Push-up test
The push-up test entails moving the lens up and down manually; the amount of movement and change in lens positioning can be observed. Tight or steep-fitting soft contact lenses will either be difficult to move or will not move at all. Loose or flat-fitting soft contact lenses will move an excessive amount. Stability of rotation can be judged with the push-up test. If the rotation changes more than 5 to 10 degrees on push-up, you may want to consider a lens change. This would largely depend on the patient's sensitivity to rotational changes.
Once the physical fitting characteristics of the lens are judged to be acceptable, a complete sphero- cylindrical over-refraction (SCOR) can be used to determine the final power. With the advent of handheld programmable calculators and Web-based programs (i.e. CooperVision's Toric Calculator), some practitioners exclusively use SCOR instead of LARS.