By DEEPAK GUPTA, OD
Stamford, Conn.
In recent years we have seen a dramatic improvement in the technology and growth of the planned replacement soft toric lens market. The emergence of these lenses means that patients who experienced problems with conventional soft torics can now enjoy the same comfort, visual acuity and ease of care as spherical lens wearers.
Toric lenses are available for a two-week, one month and three-month disposal schedule (see Planned Replacement Soft Toric Lenses below). Unlike RGPs, which many patients cannot tolerate, soft lenses require considerably less adaptation time, are more comfortable and may be worn intermittently for sports or recreational use.
Matching the patient with the lens
With the vast selection of lenses available, which one do you fit? As with anything else, there is no right answer. We all have our own favorites. I have found that there is no one lens that works for every patient. Even the most successful of toric lenses offer a 80- to 85-percent success rate, which means that you must have a back up lens or two available. Here are some of the criteria I use in determining which soft toric lens to use:
Patients with dry eyes. I tend to use the Proclear Compatible Toric (CooperVision, nee Biocompatibles). This lens is made of the same omafilcon A material as the spherical product, which is wonderful for dry eye patients. The only problem with this lens is that the fit tends to be loose, resulting in poor stability and excessive rotation. If I cant get a good fit with this lens, the Biomedics Toric (Ocular Sciences) is an excellent choice as well.
Patients who wear the lens for long hours or even sleep in them. I avoid lenses with exceptionally low DK values such as the Preference Toric (Cooper Vision) or Optima Toric (B&L). An Acuvue Toric (Vistakon) or a Soflens 66 Toric (B&L) are sometimes better alternatives because of their higher DK values.
Patients who are heavy protein depositors. Any of the two-week lenses are good for these patients. In severe cases, I also prescribe a product such as Clerz Plus or SupraClens (Alcon), both of which contain protein removers to control this problem.
Patients with high astigmatism. I used to fit a specialty, quarterly replacement lens such as the Hydrasoft Toric (CooperVision) or the Sunsoft Toric (Ocular Science). But with the recent release of the Frequency 55 Toric XR (CooperVision), patients with astigmatism of up to 4.25 D can still enjoy the benefits of a monthly replacement lens.
Keeping cylinder axis aligned Ill Never Understand Practitioners who tell their astigmatic patients that they can only wear RGPs or conventional (yearly) toric lenses. With the quality of toric lenses on the market today, not fully correcting for astigmatism is ridiculous. Most doctors would not consider excluding the refractive cylinder in an eyeglass prescription, so why should it be acceptable in contact lenses? DEEPAK GUPTA, OD
Regardless of modality, soft toric lenses require some means of keeping their cylinder axis properly aligned with that of the patients refractive error. Most employ one of three methods:
Prism ballasting. This common method of stabilization entails adding more lens material mass to the inferior portion of the lens, making that part of the lens thicker. Doing this helps prevent the lens from rotating. This is one of the more common methods of lens stabilization, as it offers a good compromise between patient comfort and good stability.
Mild astigmats who are unhappy with their vision, yet continue to wear spherical lenses. Some of this undoubtedly stems from that fact that many of us were taught in school to fit a patient with .75 D of astigmatism with spherical lenses. Patients with mild astigmatism used to do well with spherical soft lenses because conventional soft lenses were relatively thick and able to mask corneal astigmatism of less than 1.00 D. However, since most doctors now prefer to fit disposable or planned replacement lenses which are thinner, they mask very little astigmatism leaving these patients with less than optimal visual acuity.
Lens truncation. This design involves cutting off the bottom portion of the lens, leaving it flat or truncated. The flat edge of the lens usually aligns with the lower lid, and the bottom corners help hold the lens in place. Lens truncation is an effective stabilization system, but it tends to make the lens less comfortable.
Thin zones. This design is also called dynamic stabilization and double slab-off. It involves removing lens material at both the apex (superior portion) and base (inferior portion) of the lens creating thin zones at the top and bottom. These thin zones allow the eyelids to exert pressure on the lens and hinder its rotation. This design offers the greatest comfort of the three stabilization methods, but it also provides the least resistance to rotation.
A better alternative
Todays planned replacement soft toric contact lenses are a much better alternative than conventional soft toric lenses and even RGPs. Theyre more economical, more reproducible and more widely available. These lenses are great for patients who are heavy protein depositors, patients who frequently tear or lose their lenses, or those with active lifestyles who prefer to have multiple spare lenses.
And with the wide array of excellent quality planned replacement soft toric lenses on the market, every practitioner should see a high rate of fitting success.
Dr. Gupta (deegup4919@hotmail.com) practices full-scope optometry at Stamford Ophthalmology in Stamford, Conn.
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