Get to the Point

Frame and lens pointers for high Rx's

Karlen McLean, ABOC, NCLC

Knowing how to handle high-powered Rx's when they cross your dispensary door is a key component to offering expert service to your patients along with a pleasing product outcome. Most high myopes and presbyopes today are aware that there are options other than "Coke bottle" lenses; however, the choices they face may overwhelm them, and the "education" they pick up online may or may not apply to their lifestyle and Rx specifics.

A high Rx generally begins at +/− 3.00D to +/+ 5.00D and up. However, experts cite +/− 2.50D as the best starting point to recommend high index lenses. Other factors to consider are high cylinder and high add powers (usually anything above +2.50D). To best equip yourself to work with high Rx's, use EB's pointers whenever you work with a high-powered Rx.

HIGH RX FRAME POINTERS

1 Rule of thumb: When fitting frames for highpowered Rx's, select small, roundish frames that center the pupil symmetrically for the best visual acuity and cosmetic appearance. Try to keep decentration under 3mm.

2 Plastic or substantial metal frames are the best choices to hide lens thickness.

3 Pre-adjust frames, including face form, pantoscopic tilt, and bridge and temple alignment, before taking measurements. Pantoscopic tilt on most frames should be 6 to 10 degrees. Proper pantoscopic tilt is especially important when fitting multifocals/ PALs to achieve the widest possible field of vision.

4 When making the eye exam appointment and in subsequent follow-ups to the appointment, patients should be instructed to bring in their previous eyewear on the day of their visit. This allows opticians to check the previous eyewear for lens material and design, measurements, base curves, and other �landmarks� that are significant to fitting new high index lenses successfully. It also helps to assess what frames the patient has previously worn in order to make new frame recommendations that improve product appearance and performance.

5 Minus-power lenses are thicker temporally, while plus-power lenses are thicker centrally/nasally. Keep this in mind when selecting frames that will best disguise the thickness of the fabricated Rx.

6 Supply the same type of high index lens for both lenses in a pair of eyewear. Finished lenses may use flatter curves in plus powers and semi-finished lenses may have steeper front curves; mixing the two could cause �ocular confusion� and an unacceptable appearance.

If patients wear high index lenses in one frame, they should be encouraged to have high index lenses in all their frames, as they will notice visual and comfort differences between high index and other lens materials. To achieve this, some ECPs offer price breaks on multiple pair purchases.

HIGH Rx Sunlenses

As with everyday lenses in a high-powered Rx, the best frame to choose for sunlenses is roundish, especially at the corners, and definitely small. Center the pupil, minimize decentration, and consider patient demographics and lifestyle when recommending lens material.

WRAPS: Wrap frames' primary feature is an extreme curve to create a face-forming fit. Generally, wrap styles won't accommodate thinner, flatter high index lenses from a function standpoint, as high index lenses are more likely to physically pop out of wrap frames, and, due to typically large wrap lens sizes, be too thick to look well or wear effectively. If wraps are worn for sports or safety reasons or by active adults and kids, a high-impact lens material should be recommended instead of high index.

RX: Generally, wraps are Rx-able in powers ranging from +4.00 to −6.00. Angle and vertex distance will likely cause object viewing differences when compared to nonwrap eyewear, especially in higher powers. Since wrap frames fit close to the face, adding a high-powered lens may cause lashes to brush against the lens or the lens/frame to rest against brows or cheeks due to lens thickness.

HIGH RX LENS POINTERS

1 Rule of thumb: Don't go high index on an Rx that's less than +/− 2.50. Lower Rx patients may benefit from aspheric optics combined with AR, but high index lens' thinner appearance and lighter weight typically won't be demonstrable in a small frame in powers less than +/− 2.50D. Some practices automatically recommend high index for Rx's over +/− 5.00, and usually high index is considered with Rx's over +/− 3.00.

2 AR is a necessity with high index to avoid aberrations, especially in the periphery, and for the best visual acuity. AR eliminates reflections, meaning enhanced visual performance and comfort for wearers. Most high index lenses automatically come with AR from manufacturers or labs due to this reason.

3 Aspheric/atoric designs ramp up high index features, including increased thinness and flatness, lighter weight, and less magnification/ minification for a more pleasing cosmetic appearance and better visual clarity. Aspheric lenses help reduce pincushion effect (plus lenses) and barrel distortion (minus lenses).

4 Rimless high index lenses are a matter of discretion from both an aesthetic and professional standpoint. Some ECPs dispense high index rimless and semi-rimless eyewear, particularly in 1.67 material, while others take a Duty to Warn stance and choose to dispense rimless in only poly, Trivex, or other high-impact materials.

5 Match base curves as closely as possible to what the patient is currently wearing. Explain to those who have not previously worn high index that they may initially experience �more natural� vision when they pick up their lenses, since the size change in magnification (plus Rx) or minification (minus Rx) may appear different when viewed through high index lenses.

6 Bevels should be as knifeedged as possible on high index lenses to sturdily fit plastic and metal frames.

That said, plus-power lenses are often naturally thin-edged, so care must be taken not to chip or flake lenses when fitting/adjusting pluspowered eyewear. EB

PROTOCOL Pointers

Always…

■ Call to verify the Rx with the prescribing doctor.

■ Trial lens the patient whenever possible.

■ Demonstrate thickness/lens material and type options.

■ Check previous eyewear base curves, OCs, PDs, and Rx (actually do this, don't go by records alone). Try not to deviate from the previous lens measurements unless: 1. They are wildly incorrect, or 2. There are visual performance issues that can only be settled through updating these measurements.

■ Pre-adjust the frame, then measure monocular PD with a pupilometer, and determine OCs by having the patient hold their head normally as you mark the demo lens at the center of each pupil.

■ Use manufacturer cut-out charts to ensure that the lenses will lay out properly.

■ Supply the lab with the proper PD and decentration. Don't give modified measurements to try to get an even thinner lens.

■ Verify Rx and quality (i.e., bevel firmness, lens appearance, etc.) during final inspection. When checking the high index lens Rx, be sure the lensometer wavelength is calibrated to the U.S. standard Helium D-Line setting.

■ Use your lab as a resource; check with the lab before finalizing a high index sale to make sure the final product will be optically and cosmetically pleasing.