Article

CORNEAL GP MULTIFOCAL FITTING AND TROUBLESHOOTING

Corneal GP multifocal lenses provide superior vision quality when the fit is personalized for the right patients.

In 2019, more than one-half of Americans were estimated to be over the age of 38,1 representing a large population of emerging or current presbyopes. Presbyopes of today are facing unprecedented challenges and opportunities. Our ubiquitous digital devices, with their high-contrast screens and small fonts, place increasing demand on the visual system, leading to eye strain and dry eye. Rapid technological advances in lens designs, although providing improvements, can be challenging to review in determining the best option for a patient.

To cater to the more demanding needs of today’s presbyopic population, innovations in progressive spectacle designs and in soft multifocal contact lenses have expanded rapidly over the past decade. However, newer does not always mean better. GP lenses, far from being obsolete, still accounted for 14% of new fits globally in 2019, and GP wearers comprise 17% of the total contact lens population in the United States.2 GP multifocal lenses represent decades of research and innovation and are continuing to improve today.3 There is a definite market for these lenses. When personalized recommendations are presented to the right patients to address their specific needs, we can exceed their expectations.

STEP 1: PATIENT SELECTION

As primary eyecare providers, it is our job to provide the optimum recommendation to our patients based on their lifestyles.4 Correct patient selection is crucial to GP multifocal success.

Determine the Need A careful history of both lifestyle and previous contact lens experience helps practitioners decide whether GP lenses may be the best option for a patient. Ideal patients are those who have a high demand for optical clarity, who do not work or spend a lot of their free time in a dusty environment, and who rarely participate in vigorous activities that require rapid eye movement. Patients’ previous contact lens experience (if any) plays a significant role in their expectations. Those who have had a favorable experience with GP lens wear are obvious candidates, while a history of successful soft lens wear may make it more challenging to adapt to a GP lens design. Alternatively, these smaller lenses are much easier to handle, which makes them a great choice for those who struggle with the application and removal of other lens modalities.

Numbers GP lenses are ideal for patients whose corneal toricity solely contributes to their refractive astigmatism, as the tear lens will stabilize vision regardless of whether the lens rotates (i.e., there will be no residual astigmatism). This can be determined simply by vertexing the spectacle prescription to that of the corneal plane. If the astigmatism at the corneal plane matches the difference in keratometry measurements, a GP lens can be an excellent option. Additionally, bitoric multifocal corneal GP lenses are available for patients who have a high amount of regular corneal astigmatism.5

Anatomy Check While these lenses are highly customizable, a quick anatomy check is also necessary. Palpebral aperture, horizontal visible iris diameter, eyelid anatomy, and pupil size all contribute to the final decision-making. More atypical anterior segment anatomy is well-suited to GP lenses due to their customizability.

Pathology Check Abnormal conjunctival findings, such as filtration blebs and giant papillary conjunctivitis, must be noted. While corneal GP lenses tend to be an excellent choice for avoiding filtration blebs, other lens modalities that have less mechanical interaction with the eyelid may be a better option in cases of giant papillary conjunctivitis. Patients who have pterygia tend to be poor candidates for corneal GP lenses, as the lesion can cause the lens to decenter, while the lens in turn induces mechanical irritation that may lead to progression of the pterygium.6

Patients who have mild dry eye complaints have historically reported less dryness in GP lenses compared to soft lenses.7 Those reporting moderate-to-severe dry eye are better served in a scleral lens design (and, of course, multifocal designs are available for scleral lenses, too).8 Patients who have irregular corneas are usually successful in GP lenses, although multifocal optics may prove to be challenging to their already compromised visual system.

Other Considerations GP lenses, due to the more frequent tear exchange and surface wettability, are less prone to deposits and present a lower risk for eye infections.9 Their durability offers a less expensive option in the long run for patients who have financial concerns, and their reusability may also appeal to an environmentally conscious patient base.

STEP 2: LENS SELECTION

A successful fitting starts with choosing the right lens for each patient. Corneal GP multifocals are available in aspheric and translating designs.

Aspheric Corneal GP Designs Aspheric corneal GPs gradually change curvature along the anterior or posterior surface of the lens, resulting in plus power toward the periphery. Due to their center-distance design, these lenses maximize distance and intermediate vision. Patients who primarily function at those distances, such as drivers and computer users, are especially good candidates.

One of the key benefits of aspheric designs is that they work by simultaneous vision, which does not require downward gaze for patients to benefit from the add power and thus allows good intermediate vision for those who work on desktop monitors at eye level. These lenses often provide excellent optical quality. They are especially useful in correcting small amounts of corneal astigmatism that would otherwise be left uncorrected in soft lens designs. These lenses are most successful for patients who have small-to-medium pupil sizes (less than 5mm) due to glare and ghosting of images toward the lens periphery.

Unlike with translating lens designs, aspheric designs require minimal interaction between the lens and the lower eyelid, allowing patients who have loose or low-riding lower eyelids to benefit from the add power. Additionally, these lenses are often very comfortable, as they are typically thinner and do not move as much compared to a conventional tricurve design.

Aspheric corneal GPs can be further broken down into three different categories:

  • Front-Surface Aspheric These lenses are especially great for long-term GP wearers. Often, little-to-no adjustment is needed from their habitual lenses’ back-surface parameters, minimizing the need to refit. This type of multifocal design is extremely customizable. Front-surface asphericity can be incorporated into certain bitoric designs as well as into some specialty lenses for irregular cornea patients.
  • Back-Surface Aspheric A rapidly flattening change in back-surface curvature generates the add effect of these lenses. Traditionally, these lenses were the first go-to aspheric corneal GP designs and were fit 1.00D to 1.50D steeper than K to account for the relatively flatter back-surface geometry. With the radically changing curves needed to incorporate higher adds, these lenses can cause corneal molding and discomfort.
  • Dual-Aspheric Bi-aspheric or dual-surface aspheric lenses have both front-surface and back-surface aspheric optics. As single-surface aspheric lens designs often decrease in the central distance zone with increasing add, distance vision can be compromised in higher-add designs. The lens manufacturers have solved the problem through dual-aspheric designs, placing concentric rings of add surrounding the central distance zone or by incorporating aberration-control optics.

Translating Corneal GPs Translating, or alternating, GP designs have a distance zone and a near add segment, much like a bifocal spectacle lens. The lenses are prism ballasted to rotate the near zone toward the bottom when placed on the cornea. They utilize the lower eyelid to push the lens superiorly during downgaze to place the add zone in front of the pupil. The add segments come in different designs, much like their spectacle counterparts: executive, crescent, and concentric.

What makes these lenses superior is their ability to deliver crisp vision at distance and near. Because the eye is often looking through only one power zone at a time, the ghosting and haloes that are sometimes observed in aspheric lens designs are minimized. Therefore, astigmatic patients who have critical vision demands at either distance or near are great candidates. Additionally, moderate-to-advanced presbyopes who are dissatisfied with aspheric lens vision at near are also ideal candidates, as higher add powers can be incorporated into the lens without concern for deteriorating distance vision.

Combination Designs Some lens companies offer combination designs in which the back-surface aspheric optics are combined with a front-surface translating segment. These lenses are capable of delivering enhanced intermediate vision through the aspheric add and enhanced near vision with the near segment.

Multifocal Corneal GP Alternatives In cases of corneal GP non-adaptation, irregular cornea, poor lens centration, dry eye, or simply of patients who are poor corneal GP candidates, both hybrid and scleral lenses present an alternative option while delivering the crisp vision of a GP lens. While neither lens translates with gaze change, they do offer the option of center-near GP lens optics. Patients who have a history of soft contact lens wear or who failed in soft multifocal fitting are good candidates for these lens designs.

STEP 3: LENS FITTING AND TROUBLESHOOTING

For new fitters, reviewing the fitting guide prior to fitting a particular lens design is paramount to success. While most lenses in a fitting set work similarly, knowing how each trial lens differs within a fitting set will reduce chair time and minimize refits. Your laboratory consultants are an extremely valuable resource for adjusting parameters specific to their lens designs. When in doubt, sending a photo or video to the consultants can be beneficial for troubleshooting.

Aspheric Corneal GPs An ideal fitting of these lenses is typically with a central or slightly superior position, with limited (less than 1mm) lens movement with the blink. Moderate translation in downward gaze, although not necessary, allows patients to benefit from the slightly increased add in the periphery of the lens.

These lenses can be fit diagnostically or empirically using keratometry values, refractive error, and pupil size. Empirical fitting is preferred when available for patients who are new to GPs to provide them with an initial “wow” in vision quality that facilitates lens adaptation. By fitting empirically, the first lens that a patient wears is very close to the correct power. A –5.00D myope wearing a –3.00D multifocal diagnostic lens will have blurry vision until the over-refraction is performed, and patients often do not understand what is occurring during the over-refraction. As a result, they may have an underwhelming initial impression with diagnostic fitting.

Initial assessment after lens placement is similar to that of a traditional tricurve GP. Instill sodium fluorescein; a numbing eye drop is also recommended to reduce reflex tearing in new GP wearers. With slit lamp biomicroscopy, the relationship to the upper eyelid (lid attachment or interpalpebral), lens centration, and fluorescein pattern should be observed. Mild variations in fluorescein patterns are expected for the different designs.

  • Front-Surface Aspherics Fitting these lenses approximately on-K minimizes corneal molding and resulting distortion. Look for a fairly even alignment relationship, similar to that of a standard spherical GP. These designs tend to have a slightly lid-attached fit, which can enhance initial patient comfort. If a patient is already wearing a spherical GP design, attempt to achieve a similar alignment relationship to that which the patient is already comfortable.
  • Back-Surface Aspherics As a result of the rapid flattening of the back surface toward the periphery, an adjustment to the base curve radius is needed (compared to front-surface aspherics). Base curve radii for back-surface aspheric designs are typically steeper compared to base curve radii for spherical designs to prevent a loose-fitting lens. Each design will differ in how the base curve radius is chosen, so refer to the fitting guide for base curve radius selection and desired fluorescein pattern. Typically, these lenses will have a slightly steep pattern. The steeper back surface, combined with the aspheric shape, generally results in a more central lens position than that observed with front-surface aspherics.

For both aspheric corneal GP lens types, lens position in primary gaze is the most important factor for patients to utilize the simultaneous vision optics. As such, lens centration needs to be optimized before any power changes are determined:

  • For inferior decentration and excessive movement, steepen the base curve radius.
  • For lateral decentration (Figure 1), increase lens diameter if the corneal apex is centered. For patients who have a decentered corneal apex, another lens design is recommended.

    Figure 1. Temporally decentered aspheric lens showing alignment fitting pattern. Centration can be achieved by steepening the base curve and/or increasing the diameter.
    All images courtesy of Kevan Smith, OD

  • For superior decentration, use a back-surface aspheric design.

Perform over-refraction outside of the phoropter to simulate a real-world environment as much as possible. This should be done for all multifocal designs. The starting point will depend on whether a patient is wearing a diagnostic lens or an ordered lens.

For diagnostic lenses, first occlude the nondominant eye. Use loose lenses until the best distance acuity is achieved. Be sure to push plus power as much as the patient can tolerate; by not over-minusing the distance correction, near vision will be optimized. Repeat for the second eye, occluding the dominant eye. If you have a short refracting lane, after you have noted a patient’s best distance visual acuity (VA), consider confirming the endpoint by having the patient look down a hallway or out into the parking lot, again making the situation as real-world as possible.

Once the two distance over-refracting lenses are determined, use a trial frame to test near vision with real print (a font-size calibrated near acuity card with actual text is better compared to a Snellen chart). If distance acuity was the same for both eyes, over-refract at near with both eyes open and loose lenses over both eyes. Be a little stingy with adding more plus power, but recognize that a diagnostic lens will not likely have the correct add power for that patient. As an example, let’s say that the initial diagnostic lens had a –3.00D sphere power with a +1.50D add. If the distance over-refraction was –2.00D, and near over-refraction through this was +0.50D, the final lens power is –5.00D/+2.00D add.

For ordered lenses, the over-refraction process is similar but should take less time, as the distance and near powers should be close to correct. Over-refraction in this case will depend on the quality of vision. If distance vision is acceptable, you should still over-refract at distance to make sure that the lenses are not over-minused. Again, in a free-space setting, attempt to determine whether the patient will accept any more plus power in the distance. If so, you can consider adding that to the next order, if needed. If they can accept more plus power at distance, recheck with and without those same lenses at near to determine whether any change at near is needed.

If distance VA was acceptable but near vision was not after pushing plus power in the distance, an additional over-refraction at near is needed. It may be necessary to either increase the add power in both eyes or consider incorporating modified monovision (in the nondominant eye, either add some plus power over the distance or switch to a higher add power). Patients who have difficulty tolerating distance aberration with increased add power should be refit into a dual-surface design, which better controls higher-order aberration by providing a larger distance zone. Another consideration is that if a patient who has good distance vision complains of poor near vision without taking more near power during over-refraction, make sure that the lens is positioning adequately and is translating slightly in downgaze.

Translating Corneal GPs These lenses are traditionally fit slightly flatter than K to allow the lower lid to interact with the lens during downward gaze. However, many new designs are now available in a larger diameter that are fit with either an alignment relationship or with slight apical clearance to improve initial comfort.3 While some of these lenses can be designed empirically,10 less experienced fitters would likely achieve more success with a diagnostic fitting set due to large variations in anatomy and lid tension. Desirable anatomical traits for translating corneal GP lenses include a superior lid that slightly covers the upper cornea, a lower eyelid within 1mm below and 1.5mm above the lower limbus, and tight lower lid tension. Patients who have any pupil size or a decentered corneal apex can be fitted in these lenses.

As with aspheric corneal GP lenses, the initial evaluation of translating lenses is similar to that of spherical GP designs, with attention to eyelid interaction, lens centration, and fluorescein pattern. Makes sure to review the fitting guide to see the ideal fluorescein pattern for the specific lens design, and first fit the back surface to the cornea. Once an initial lens is determined, carefully note the location and stability of the segment (seg) in the primary gaze (Figure 2). The ideal seg height is at the lower pupil margin for most designs in most patients. Evaluate lens translation by having patients look slightly down while holding up the upper eyelid (Figure 3). The add zone during downgaze should cover approximately one-half of the pupil (as you would see it when looking through the slit lamp) to minimize distortion from the segment line.

Figure 2. Translating GP viewed with white light and cobalt blue filter. The lens shows a slight lid-attached alignment fitting, with the segment line slightly encroaching into the pupil. Mild temporal decentration is tolerated in a translating design. However, this patient complained of fluctuating vision and monocular diplopia with the blink. The segment height was lowered on adjustment.

Figure 3. Evaluation of the add zone during downgaze. Not enough translation was observed in this case. The patient complained of fluctuating vision at near. The lens edge was flattened to allow increased translation on downgaze.

Depending on the position of the lower lid, the segment zone can be adjusted by changing the overall lens diameter or by adjusting the seg height. Finally, perform an over-refraction at both distance and near while making sure that the patient is looking through the correct seg at each distance. Use a similar approach as when over-refracting aspheric designs, as described above.

The amount of prism is often determined by the laboratory. It is often desirable to have the lower lens edge align with the lower lid; if the lens is picked up excessively with the blink, reordering the lens with a greater amount of prism should help solve this problem. Your laboratory consultant can advise you on the best management option when troubleshooting these designs.

Problems with translating corneal GPs, beyond over-refraction adjustments, are broadly classified into three categories: poor distance vision, fluctuating vision, and poor near vision.

  • Poor Distance Vision This usually results when a lens is positioned too inferiorly and does not cover the pupil during primary gaze or when the add zone is covering the pupil due to a high seg height or a superiorly fitted lens. Overall diameter can be increased in cases of inadequate lens coverage. When a lens is decentered superiorly, it can be steepened to reduce lid attachment (Figure 4) or the lens index/prism can be adjusted. Furthermore, the seg height can be lowered if the lens is otherwise positioning properly.

    Figure 4. (Left) Initial flat-fitting lens showing temporal decentration. (Right) Centration was achieved by steepening the base curve radius for improved fitting on the cornea.

  • Fluctuating Vision This is often a result of excessive lens rotation or lens movement with the blink, causing the near segment to move into the visual axis. Steepening the lens minimizes upper eyelid interaction, and lowering the segment helps to shift the add zone toward the lens periphery. As mentioned previously, increasing the prism will decrease lens movement with the blink. In patients who have an upswept lower eyelid contour that causes excessive lens rotation with the blink, the prism axis can be adjusted to counter the rotation caused with each blink.
  • Poor Near Vision This can occur when patients are not viewing through the near zone. If the seg height is too low, raising the segment line should solve the problem. The overall diameter and base curve radius can also be adjusted to improve the fitting characteristics. Much like with bifocal spectacle lenses, patients also need to look down for full translation of the lens and to access the reading segment. Flattening the edge of a poorly translating lens—using a flatter base curve radius or a flatter peripheral curve radius—will help the lower eyelid catch the lens and push it up.

CONCLUSION

Multifocal corneal GP lenses are a tried-and-true technology, and they are still improving in their capabilities and design. These lenses are easy to care for and handle due to their small size. When fitted well, they are capable of delivering great vision at all distances, meeting the visual demands of our patients while catering to their modern, fast-paced lifestyle. Be sure to include them in your presbyopic lens toolbox! CLS

REFERENCES

  1. Tanzi A, Hagan S. Half of Americans Are Now Over the Age of 38. Bloomberg. 2019 June.
  2. Morgan PB, Woods CA, Tranoudis IG, et al. International Contact Lens Prescribing in 2019. Contact Lens Spectrum. 2020 Jan;35:26-32.
  3. Potter RT. New Designs in GP Translating Bifocals and Multifocals. Contact Lens Spectrum. 2016 Dec;31:30, 32-35.
  4. Quinn TG. Matchmaking: Presbyopic Patient with Contact Lenses. Contact Lens Spectrum. 2020 Jan;35:13.
  5. Lampa M. Presbyopia and Astigmatism. Contact Lens Spectrum. 2018 Feb;33:14.
  6. Alipour F, Khaheshi S, Soleimanzadeh M, Heidarzadeh S, Heydarzadeh S. Contact Lens-related Complications: A Review. J Ophthalmic Vis Res. 2017 Apr-Jun;12:193-204.
  7. Bennett, ES. RGPs for Borderline Dry Eye. Contact Lens Spectrum. 1996 Aug. Available at https://www.clspectrum.com/issues/1996/august-1996/rgps-for-borderline-dry-eye .
  8. Pucker AD. Treating Dry Eye with Scleral Lenses. Contact Lens Spectrum. 2019 July;34:11,13.
  9. Stapleton F, Keay L, Edwards K, et al. The Incidence of Contact Lens-Related Microbial Keratitis in Australia. Ophthalmology. 2008;115:1655-1662.
  10. Bennett ES, Henry VA, Richdale K, Benoit DP. Multifocal contact lenses. In Clinical Manual of Contact Lenses, 5th ed. 2019 Oct:440-491.