Toric Contact Lenses TODAY

CONTACT LENS SPECTRUM
STAFF REPORT
MAY 1997

Contact Lens Spectrum's consulting editors agree that toric lenses aren't what they used to be -- and astigmats everywhere are grateful for the improvements.

Although they may differ in their approaches to prescribing toric contact lenses, the practitioners we interviewed agree that this modality is a guaranteed practice-builder. Happy astigmats are loyal patients who refer their friends. Ongoing manufacturing improvements, generous return policies, strong corporate support and timely consumer advertising are helping to drive this specialty lens into the mainstream.

TORIC HYDROGELS: A DECADE OF IMPROVEMENTS

The big problem with toric soft lenses is that practitioners tend not to prescribe them, says one practitioner who does. Today's torics are completely different from those of 10 years ago. The lenses of the early '80s were more prism ballasted with more truncation. They were heavy and uncomfortable.

In the past two years in particular, better designs have come to market, reproducibility and accuracy have improved, and the manufacturers' return policies are excellent, an indication that they are confident their products will perform.

Practitioners can now correct moderate and high amounts of cylinder and moderate and high spheres. And specially designed calculators do the math, so you don't have to guesstimate based on the overrefraction or how the lens positions.

MATCHING THE LENS TO THE PATIENT

Available parameters, patient compliance and patient preference all influence your selection of a toric lens. Most manufacturers offer steep and flat base curves, multiple cylinder powers, and numerous plus and minus spherical powers in one or two diameters.

"You have to look at all the factors, including the patient's occupation and social demands," said Glenda Secor, O.D., Huntington Beach, Calif. "Most important, you must learn not only what a patient needs to see, but what she wants to see." (See "Jennifer's Story" on page 28.)

Even astigmatic patients who fall outside the range of standard parameters may be candidates for toric hydrogels manufactured in custom parameters (Fig. 1).

Figure 1

Figure 2

Figure 3

"We're getting a lot of great products from various companies," said Robert Grohe, O.D., Homewood, Ill. "Choosing one 'best' lens over another is becoming more difficult."

ASTIGMATS CAN BENEFIT FROM PLANNED REPLACEMENT TOO

Improved corneal health, patient convenience and the confidence of having spare lenses for emergencies make the planned replacement option just as attractive to toric soft lens wearers as it is to spherical lens wearers. Now that improvements in manufacturing technology have driven costs down and made reproducibility predictable, practitioners are becoming more comfortable prescribing quarterly and monthly replacement.

"I usually first decide which lenses work best for the patient and then choose a replacement schedule," says Barry Kissack, O.D., Honeoye Falls, N.Y. "I like planned replacement. I feel more comfortable about corneal health when I prescribe this modality."

"The younger a patient is, the more frequently I want him to change his lenses because the tears are oily and tend to deposit quicker. I'll prescribe either a monthly or, at the minimum, a quarterly replacement schedule," said Dr. Kissack. "As a patient gets older -- past college age -- I may prescribe quarterly, semiannual or annual replacement. The more responsible a person is (which often doesn't have to do with age), the better able he is to get by with wearing the lenses for longer periods of time."

AVOID THESE COMMON MISTAKES

"Some practitioners tend to change lenses too quickly," says Dr. Kissack. "If the vision is 20/30 or 20/40, they reorder the lenses right away and then find they have to reorder again. Practitioners need to be patient -- and patients need to be patient about their vision. They have to have the lens on their eye for a while before the practitioner can gain an accurate picture of the fit.

"If a patient is seeing 20/40, I usually ask him to come back in a couple of days. I like to schedule the visit for a time when he's been wearing the lenses for at least four hours," said Dr. Kissack. "At the dispensing visit, I explain, 'You may not see your best initially. These are difficult lenses to fit and they're going to take some time.'

MAKING A CASE FOR DIAGNOSTIC FITTING

Although empirical fitting of toric soft contact lenses can be successful for some patients, particularly for the custom torics, practitioners must reserve the right to trial fit when necessary.

This patient's keratometry readings OD were 46.12 @ 100/44.00 @ 10; manifest refraction was: -3.00 -1.75 x 10. Topography is illustrated by the map in Figure 1.

Based on this information, we ordered base curve 8.6mm, diameter 14.0mm, power -3.00 -1.75 x 10. After we dispensed this lens, however, we found that it was too small for this eye. As Figure 2 illustrates, the edge of lens encroached upon the limbus. The lens was not comfortable or stable, and the axis would probably have shifted.

We then placed a diagnostic lens on the eye: base curve 8.4mm, diameter 14.4, -3.00 -1.75 x 10. The manifest refraction over the contact lens was -0.25, yielding visual acuity of 20/20. We ordered 8.4mm, 14.4mm, -3.25 -1.75 x 10. This lens (Fig. 3) provides full coverage and a stable fit.

-- Michael Ward, B.S., C.O.T.

 

"Another common mistake is not changing the base curve of a lens when the vision just doesn't make sense," said Dr. Kissack. "If the overrefraction and the power of the lens don't give the expected result, then usually the optical system is not correct and the practitioner needs to change the base curve. Physically, the lens will look the same on the eye, but because of the different curve of the back of the lens, it will create a different optical system. You need to be very sure that the final lens power is close to the spectacle correction. Some practitioners continue to order the same base curve and change the power.

"Based on the size of the eye, you'll tend to select a particular diameter lens, but if the optical system isn't working, you may have to change the diameter," Dr. Kissack noted.

FITTING PEARLS

• Remember, the orientation mark on a toric lens is just that, not the location of the cylinder axis.
• Usually a patient will not accept as much cylinder power in a contact lens as is recorded in his manifest refraction. Be sure to correct for vertex distance in each meridian in high powers.
• The amount of rotation is related to the level of power. For high powers, the patient won't tolerate as much shift. Usually 10 degrees of rotation or less is acceptable.
• Remember, one clock hour of rotation is 30 degrees.
• Always inform the patient that a few refittings may be needed before the final Rx is determined.

 

 

GUARANTEED FIT PROGRAMS ENSURE SUCCESS

"I don't hesitate to reorder a lens, even for a small change like an axis shift or a power change," says Dr. Secor. "Most companies offer a 100 percent credit so you're never left with a lens you can't use. The only cost is staff time to reorder the lens. I don't keep a large inventory of toric soft lenses. Empirical fitting adds an extra week to the process, but patients accept this."

TORIC RGPS: MIXED REVIEWS

Although some practitioners feel prescribing a toric RGP is a daunting task, others believe this modality has a lot to offer -- crisp vision, ease of handling and care, durability and a multitude of parameters. Those who believe RGPs slow the progression of myopia say they usually prescribe toric RGPs for their young myopes with astigmatism. "Even if RGPs have only a small potential to retard myopia progression, I'll try them first," says Dr. Secor.

"We do use some toric RGPs in our practice, and they do require extra chair time for trial fittings and lens refinement," said Dr. Grohe, "but when indicated, they do a great job."

Patients who might benefit from this modality include previous rigid lens wearers with moderate to significant amounts of corneal cylinder or patients who may have worn hard or rigid lenses then switched to soft lenses but decided to return to RGPs because they weren't satisfied with the vision.

LET THE FEES FIT THE TIME

There are practitioners who still avoid fitting toric lenses because they know it's going to take some time, but those who do, agree that the rewards can be worth the effort.

 

A WELL-FITTING TORIC HYDROGEL LENS.

"Astigmatism does take more time, but most patients who have astigmatism realize they have a more complicated prescription," said Dr. Secor. "They know they need specialty care and are willing to pay for it. They are incredibly loyal and they refer their friends.

"Practitioners should have refund policies because, regardless of your best efforts, occasionally you will fail," Dr. Secor said. "You must have a time limit -- a bailout point -- when you're still able to walk away and part as friends. That needs to be clearly spelled out in the beginning."

"The key is to spend the extra time with patients to explain the mechanism of prescribing toric lenses -- that it will take one or two or three pairs of lenses to achieve optimum vision and fit," says Dr. Kissack."

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Characteristics of a Well-Fitted toric Hydrogel Lens

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• Full corneal coverage and good centration (no limbal-edge contact).
• Sufficient movement to allow tear exchange under the lens during blink in primary or up-gaze or when the lens is pushed with the lower lid.
• Good comfort.
• Acceptable visual acuity with overrefraction.

A steep lens will exhibit:

1. Good centration.

2. Insufficient or no movement during a blink in primary or up-gaze.

3. Good comfort.

4. Blurred vision between blinks.

5. Possibly stable axis mislocation.

6. Possibly excessive lens rotation.

A flat lens will exhibit:

1. Decentration.

2. Excessive movement during a blink in primary or up-gaze.

3. Reduced comfort.

4. Lens edge standoff.

5. Blurred vision immediately after the blink.

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THE ADVANTAGES OF CORPORATE SUPPORT

"Some companies tend to be more consumer friendly to both the practitioner and the patient in terms of promoting their products. They advertise extensively, offer convenient shipping programs and are generous with sample lenses," says Dr. Grohe.

"Today practitioners are bombarded by threats from managed care and refractive surgery," he said. "Companies that back up their lenses with significant media exposure help drive patients to the practice. This type of support goes a long way to keep my patient base intact."

JUST DO IT

"There's no question that fitting toric contact lenses is a time-consuming task. I had to trial-and-error for a while before gaining skill and confidence. I would tell practitioners, determine you're going to do it and just learn it," said Dr. Kissack. CLS