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New hybrid multifocal contacts offer effective correction, comfort
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SynergEyes (Carlsbad, Calif.) has introduced a new design in its portfolio of hybrid contact lenses that not only offers gas-permeable lens acuity with soft lens comfort and centration, but also a viable alternative to spectacles for the patient with presbyopia.
Prescribing contact lenses for the astigmatic presbyope is a significant challenge. This recent addition to the market, the SynergEyes Multifocal, specifically addresses the optical needs of those patients and at the same time does not require a sacrifice in initial comfort.
Case report
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JC came to our clinic wearing soft toric lenses with over-the-counter reading glasses. She is an active individual who works in marketing for a local athletic footwear manufacturer and her visual demands are broad. She had become frustrated with constantly having to take her reading glasses on and off and was seeking an alternative correction for her presbyopia.
Her manifest refraction is: –5.00 – 1.75 x 10 OD and -4.25 – 2.00 x 170 OS with a +2.00 D add OU. Topographical maps indicated symmetrical with-the-rule astigmatism limbus-to-limbus. She was ultimately prescribed the SynergEyes Multifocal, a simultaneous vision, target-style, bifocal with a concentric spherical center add.
This multifocal’s spherical distance optics surrounding the central near zone provide excellent visual acuity at every distance and a comfortable all-day wear schedule. The key to success with this new technology is appropriate parameter selection and communicating with patients to determine the best balance for distance, intermediate and near vision.
Based on A lens platform
The multifocal is based on the SynergEyes-A platform. This hybrid lens incorporates an 8.4-mm Paragon HDS 100 (Dk/t 100) GP lens center that is bonded to a 27% water, nonionic (Group 1) hydrogel skirt. The optical zone of the GP lens is 7.8 mm, and the overall lens diameter is 14.5 mm. Unlike standard hydrogel lenses, the skirt thickness is consistent across all power ranges.
The manufacturer will provide a 20-lens trial set that includes 10 base curve radii (8.0 mm to 7.1 mm in 0.10-mm steps). A flat skirt curve (radii of 1.3 mm) is provided for the 7.1-mm and 7.2-mm base curves and a steep skirt curve (radii of 1.0 mm) is provided for base curves 7.3 mm to 8.0 mm. All lenses are plano sphere power with the +1.75 D power. Both the 1.9-mm and 2.2-mm segment sizes are provided in each base curve.
Diagnostic evaluation
The first goal of the diagnostic evaluation is to focus on the base curve-to-cornea fitting relationship. All of the SynergEyes hybrid lens designs are most successful when significant apical clearance is achieved between the back surface of the contact lens and the front surface of the cornea.
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Images: Smythe JL | |
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| Apical clearance options: This staining shows minimal apical clearance (left) and preferred apical clearance for the SynergEyes Multifocal. | |
An effective starting point is to choose a base curve radius 1.25 D steeper than flat K and to round up to the next steepest base curve if the exact lens falls between two available radii. A handheld slide rule is provided by SynergEyes as well as an electronic fitting calculator, available at www.synergeyes.com, for quick guidance with base curve selection. The electronic calculator will also calculate predicted residual astigmatism after the lacrimal lens masks corneal toricity. Initially, select the steeper skirt curve first; however, smaller-than-average corneas – those less than 11.5 mm – will typically require the flatter skirt.
Once the initial lens is selected, place two drops of liquid high-molecular weight NaFl into the lens bowl. Fluoresoft-0.35% (Holles Laboratories, Cohasset, Mass.) is available as a preservative-free liquid with approximately five drops in each ampule. Insertion is easiest when the lens is balanced between the index and middle fingers and the patient leans forward slightly.
Observe the central NaFl pattern with cobalt blue light at the highest illumination, using a yellow Wratten 12 barrier filter in front of the microscope system. The ideal lens will have significant apical clearance without a central bubble and a skirt radius that provides centration, 0.10 mm to 0.20 mm of movement post-blink, free to move with the “push-up” test and no edge standoff. This sagittal depth and central clearance prevents late-onset lens tightening and corneal staining.
In our case, JC’s approximate simulated keratometric values are: 44.00 D/46.00 D at 090 OU. During the diagnostic evaluation, lenses were inserted with base curve radii 0.50 D different between OD and OS for comparison. The first lens on the right eye was 1.00 D steeper than K and displayed minimal apical clearance. The second lens was 1.50 D steeper than K and displayed the perfect fitting relationship.
Both the slide rule and lens calculator determine the ideal distance power required based on keratometric readings, the vertex-corrected manifest refraction and the lacrimal lens effects (remember SAMFAP – steeper add minus; flatter add plus – meaning steeper-than-K base curves require more minus power to compensate). With this information, it is easy to predict the expected over-refraction, which should be performed in normal room illumination with handheld loose lenses. With the trial lens set used for diagnostic evaluations, the ideal distance power required can be accurately determined. The next step is to determine the add power.
Find balance, not compromise
Patients are often told that success with a multifocal or bifocal contact lens requires a “compromise.” The downside of this strategy is that compromise has a negative connotation. No one really wants to compromise in life, especially with his or her vision. A better strategy is to find balance.
When it comes to contact lens correction of presybopia, a reasonable goal is to find an appropriate prescription that provides the best balance of distance, intermediate and near vision, and at the same time works for approximately 75% of the patient’s visual demands. The selection of the add power is an important step in achieving balance.
Break away from spectacle lens prescribing habits by thinking in terms of minimum add possible and even consider unequal add powers. The hybrid multifocal is available in three add powers: +1.25 D, +1.75 D and +2.25 D, with two segment sizes: 1.9 mm and 2.2 mm. If a patient’s specific add requirement falls between the available parameters, initially order the lower add power. The smaller 1.9 mm center near segment size should also be selected first.
The goal of this strategy is to optimize distance visual acuity, which aids in initial adaptation. The add power or segment size can always be increased after the patient has the opportunity to wear the lenses in his or her daily environments during a trial period.
In our case, JC’s lenses were ordered as follows:
OD BC 7.50 mm/SC 8.8 mm/-6.25 D/+1.75 D add/1.9 mm seg
OS BC 7.50 mm/SC 8.8 mm /-5.50 D/+1.75 D add /1.9 mm seg
Patient communication is critical when problem solving any aspect of contact lens wear, but especially during the refinement process with specialty lens designs that have sophisticated optics. Adaptation is similar to prescribing progressive-addition spectacles, therefore, limit changes on the first day. If the fit and binocular visual acuity are acceptable, wait to refine the prescription until after a 1-week trial.
Patient follow-up
Follow-up assessment should be done after the lenses have been on the eye for several hours. Remind the patient to wear their lenses into all appointments and ideally insert them at least 4 hours prior to their visit.
Many strategies can be used to solve common complaints, and often it is most effective to approach changes in one lens only initially. After each significant change, give the patient the opportunity to “test-drive” the new parameters in his or her own environment. Engage the patient in the decision making on which combination of lens powers, base curves and segment zones provides the most comfortable balance for his or her lifestyle.
Ghosting, blurring
“Ghosting or blurring” around images is common during adaptation to simultaneous vision. If the symptom persists or is particularly bothersome with reading in low light, try increasing the near segment size to 2.2 mm initially on the preferred sighting, or non-dominant eye.
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Image: Adams G |
Another tip is to confirm that the segment is centered over the pupil. This can best be seen indirectly by shining a direct ophthalmoscope through the pupil (it is not readily visible with the slit-lamp). Another technique is to perform corneal topography over the lens. A decentered segment could cause image doubling or insufficient near visual acuity.
When the patient complains about blurred vision, follow up with appropriate questions to determine if it is at all distances, specific to distance, intermediate or near vision and if it primarily occurs in low vs. high illumination conditions. Over-refractions should be done with handheld loose lenses with both eyes viewing binocularly.
If a patient requires more than 0.50 D change to improve visual acuity, consider appropriately increasing or decreasing the add power rather than significantly altering the distance prescription. The near segment zone size can be increased to improve near visual acuity, and the add power could be decreased in one eye to improve intermediate distance vision.
In our case, JC enjoyed 20/20 visual acuity in both eyes at distance and near, but found it was challenging to see her computer comfortably during her workday. The +2.00 D swinging lens test was used to determine that her right eye is her preferred sighting eye, and she now has a lower add power of +1.25 on that eye only.
To determine which eye is preferred, have the patient view the distance Snellen chart through their full distance correction binocularly. Hold a +2.00 D loose trial lens in front of the right eye and then the left. The eye that experiences the most visual disturbance with the fogging lens in front of it is the sighting eye.
Appropriate fitting relationship
Finally, remember that the optics of all multifocal contact lenses work best with the appropriate fitting relationship. In the event that lens tightening occurs during the wear schedule, increase the base curve or the skirt curve as the next step. Flatten the curves only if a central bubble is observed or significant mid-peripheral bubbles appear under the skirt.
Contact lens correction of presbyopia has long been a coveted golden egg. With the new hybrid lens design, not only is this achievable, but even the astigmatic presbyope can enjoy the excellent visual acuity of a GP with soft lens comfort.
For more information:
- Jennifer L. Smythe, OD, MS, FAAO, a member of the Editorial Board of Primary Care Optometry News, is the associate dean for academic programs and a professor of optometry at Pacific University College of Optometry. She can be reached at Pacific University College of Optometry, 2043 College Way, Forest Grove, OR 97116; (503) 352-2770; fax: (503) 352-2929; e-mail: smythej@pacificu.edu. Dr. Smythe has no direct financial interest in the products mentioned in this article, nor is she a paid consultant for any companies mentioned.
- The SynergEyes Multifocal is available from SynergEyes, 2232 Rutherford Rd., Carlsbad, CA 92008; (877) SEE-2012; www.synergeyes.com.