SPECIALTY AND CUSTOM SOFT LENSES
SPECIALTY AND CUSTOM SOFT CONTACT LENSES
Many options are available for patients who can’t use "off-the-shelf" soft contact lenses.
JOHN M. LAURENT, OD, PHD, & DANIEL DELIGIO, OD
Eyecare practitioners fitting soft contact lenses today can choose from a wide range of lenses. Standard, “off-the-shelf” lenses are readily available in a variety of hydrogel and silicone hydrogel materials and in spherical powers of +8.00D to –12.00D and cylindrical powers up to –2.25D or –2.75D. Extended range lenses are also available with spherical powers of +15.00D to –20.00D and up to –5.75D in cylindrical powers (Tyler’s Quarterly, 2016). Numerous daily disposable contact lenses are available in similar power ranges as well.
Multifocal (MF) soft contact lenses are available in daily disposable, two-week, and one-month modalities. Most of the MF designs are center-near, although some also offer the option of center-distance. All are usually available in the same variety of materials as other lenses.
In spite of this extensive inventory of “ready-to-wear” soft contact lenses, there are still a significant number of patients who can benefit from specialty and custom soft lenses. Presbyopic patients who have significant astigmatism, aphakic patients, patients who have degenerative myopia or keratoconus, or patients who have unusually steep or flat corneas all may require custom lenses for the best fit and vision.
Regardless of the type of lens design being considered, one limitation common to all custom lenses is the availability of materials that can be lathe-cut or molded in small batches by the laboratories that manufacture these types of lenses. There are a variety of such hydrogel materials with oxygen permeability (Dk) values ranging from 8.4 (polymacon, 38% H2O) to 24 (hioxifilcon A, 59% H2O) (Tyler’s Quarterly, 2016).
Corneal Edema A potential problem with hydrogel materials is corneal edema because the oxygen transmission (Dk/t) values of these lenses will not satisfy the generally accepted criteria for the minimum Dk/t (35 to 50) required to avoid corneal edema in a daily wear contact lens (Harvitt and Bonanno, 1999). The corneal edema problem is exacerbated in higher-powered lenses that must be made thicker than normal. An improvement in Dk is available in one silicone hydrogel material—efrofilcon A, 74% H2O, with a Dk value of 60. Because experience tells us that no single material will be successful for all patients, hopefully there will be additional higher-Dk materials available in the near future.
Cost and Replacement Cycle Two other related considerations with custom and specialty lenses are cost and replacement cycle. Occasionally, the cost of custom soft lenses is so high that patients are expected to wear the same lens for one year. Many custom soft lenses are expected to be replaced every three months. We feel that soft contact lenses can be likened to miniature sponges; i.e., daily removal, cleaning, and disinfection for time periods in excess of one month may create compromised lenses that are a potential problem for some patients.
Another financial factor is the cost associated with trial wear of custom lenses. Some manufacturing laboratories provide free trial lenses, making the initial fitting process a “no-risk” endeavor. In addition, many of the laboratories that do charge for initial lenses offer a 90-day cancellation period in which lenses purchased with a warranty can be returned for credit. However, if the laboratory has a limit on remakes or, in some cases, has a charge for all remakes, the custom soft lens experience can become more expensive.
CUSTOM SOFT MULTIFOCALS
A common current need that is frequently filled by a custom soft contact lens is the need for a soft toric MF lens. There are probably numerous patients currently fit with monovision due to the amount of astigmatism in their correction and the number of readily available, good single-vision soft toric lenses. Many of these patients would be good candidates for soft toric MF lenses if they are not successful with current off-the-shelf soft toric MF lens designs.
Another category of patients who could benefit from these lenses are those who are already wearing soft spherical MF lenses in one or both eyes, but who complain of poor vision and have an over-refraction revealing a significant amount of residual astigmatism. Correcting the cylindrical part of their refractive error could often improve visual acuity by one or more lines. Fortunately, for those patients who can’t succeed with current mass-produced soft toric MF lenses, most custom contact lens laboratories manufacture this type of lens—usually in hydrogel and silicone hydrogel materials.
Custom soft MF lenses are typically simultaneous vision designs with a center-near addition. The near vision with these lenses can be optimized by two adjustments: changing the add power and also by changing the diameter of the near optical zone (OZ). We have often found it difficult to predict the size of the near OZ that will result in the best overall vision for an individual patient. If the near OZ is too small, the patient may not see sufficiently well to read clearly, while a near OZ that is too large will probably interfere with the patient’s distance vision.
Measuring the patient’s pupil size does not appear to be a very good predictor of the optimal size of the near OZ. One good strategy is to simply order the standard near OZ diameter recommended by the manufacturer and increase or decrease the size dependent on the patient’s visual acuity (VA). To know which lens in which eye requires adjustment, it is helpful to test a patient’s distance and near VA in each eye separately.
When a patient has decreased distance or near vision, usually one eye will be seeing worse compared to the other; in such cases, the fitter can concentrate on improving the vision in that eye. Occasionally, improving the near vision will result in decreased distance vision or vice versa, and it may not be possible to satisfy all of the visual needs of that particular patient, even with a custom lens.
Aside from the ability to customize a lens for a patient’s astigmatic or MF needs, most custom soft MF lenses also have a wide range of available base curves and diameters, allowing an eyecare practitioner to optimize overall lens movement, centration, and corneal coverage.
CUSTOM POWER RANGE
Sometimes there are patients who simply need lens powers beyond the normal range of the standard soft lenses. Among these are the occasional patients who have degenerative or pathological myopia. Custom soft lenses can be routinely manufactured with +20.00D to –20.00D and, in some cases, +50.00D to –50.00D of spherical correction (Tyler’s Quarterly, 2016).
In these cases, it is often helpful to try a standard trial contact lens on the patient even if the power is not correct, just to evaluate the fit or the amount and direction of rotation in the case of a toric lens. This information can be used to help choose the parameters of a custom contact lens.
Additionally, refracting patients who have very high plus or minus corrections can be challenging. A good way to double-check the power you need to order is to find a standard soft trial lens with the highest plus power (+10.00D or higher) or the highest minus power (–12.00D or higher) available that fits the patient. Then perform an over-refraction and add the vertex-adjusted result to the power of the trial contact lens. For example, if a highly myopic patient is refracted with a –12.00D trial contact lens on the eye, and the over-refraction is –6.00 –3.00 x 090, then the over-refraction adjusted for a vertex distance of 14mm is –5.50 –2.50 x 090, and the final contact lens power needed is –17.50 –2.50 x 090.
Aphakia, most commonly associated with congenital cataract and the need for early extracapsular cataract extraction, often requires contact lenses with plus powers in excess of +15.00D. These lenses can be manufactured in a variety of hydrogel materials (Dk ranges from 8.4 to 28), a silicone hydrogel material (Dk 60), or, in limited parameters, from a silicone elastomer (elastofilcon A) with a Dk of 340. Several laboratories offer these lenses in powers up to +30.00D spherical and up to –10.00D cylindrical (Tyler’s Quarterly, 2016).
Keratoconus and other cases of irregular cornea are most commonly fit with corneal GP or scleral lenses. However, in many of these cases, patients have found corneal GP lenses to be uncomfortable or prone to decentration. If these patients also decline to be fit with scleral lenses, soft lenses may be the only remaining option to improve vision beyond that available with spectacles. Most soft lenses for keratoconus are relatively thick (0.35mm to 0.65mm center thickness) to maintain surface shape and to cover the underlying corneal irregularity (Tyler’s Quarterly, 2016).
An exception is a lens made to vault the central part of the cornea, providing an underlying lacrimal lens, similar in principle to a scleral lens. The fitting of these specialized lenses is very brand-specific and requires you to become familiar with the fitting guide provided by the manufacturing laboratory. Although some of these lenses are available in a variety of materials, due to the thickness of the lenses and the decreased Dk/t value, we would currently recommend using lenses made with the silicone hydrogel material, efrofilcon A (Dk 60).
We usually reserve keratoconus soft lens fittings for cases in which the corneal irregularity is not too extreme, but contact lens practitioners should be encouraged to try these lenses on any patient who has an irregular cornea and is unable or unwilling to wear GP lenses. One patient, a 36-year-old male with longstanding keratoconus, had best-corrected spectacle VA of 20/40 OD and 20/200 OS, whereas best-corrected visual acuity (BCVA) with specialty soft lenses was 20/25 OD and 20/50 OS. In this case, the patient was GP-intolerant and very happy with the vision and comfort of his soft lenses. Another patient who had relatively mild keratoconus complained of halos and ghost images with his spectacle Rx even though VA was 20/20-2 OD and 20/25-1 OS. His VA was basically the same with specialty soft lenses, but the halos and ghost images were greatly reduced. Therefore, he felt his vision was much better with the contact lenses.
Custom soft prosthetic lenses fill a need for which there are often very few alternative options other than the patient living with the condition—whatever it is—or wearing a patch. Only a limited number of manufacturing laboratories work with these types of lenses, and the material selection is also limited due to tinting requirements. So far, there are no silicone hydrogel materials available for custom, prosthetic tinting.
There are two separate aspects to fitting these lenses: 1) Selecting the correct diameter and base curve to properly fit the eye along with any needed power; and 2) the appearance of the lens, in which you need to choose a color/tint, pupil size, and sometimes an iris location on the lens. The color is usually meant to match the other eye; there is sometimes an option to send the laboratory a photograph of the eye to be matched.
One of the authors took close-up photographs of the good eye of a patient who wanted a prosthetic lens for the other eye. Photographs were taken in outdoor lighting and also in the clinic with overhead fluorescent lighting, and both were sent to the laboratory. The lens subsequently made by the laboratory, which attempted to match the photograph, was a very poor match when actually worn by the patient. The same laboratory then sent a trial lens set that resulted in a much better match. Figure 1A shows the patient without a contact lens, while Figure 1B shows the patient with the prosthetic right lens ordered after the trial lens fitting. Figure 2A shows a strabismic patient. Figure 2B shows the same patient wearing a prosthetic lens with a decentered iris and pupil on the deviating eye.
Figure 1. A patient without a contact lens (A), and the same patient with a prosthetic lens on the right eye (B).
Figure 2. A strabismus patient (A), and the same patient in which the deviating eye has a prosthetic lens with a decentered iris and pupil (B).
Courtesy of Dr. Mitch Cassel of Custom Color Contacts.
A somewhat more frivolous variation of the colored soft lens is the theatrical or “Halloween” lenses, examples of which are readily available online. Because contact lenses are medical devices that must be cleared by the U.S. Food and Drug Administration (FDA), a prescription is required for these lenses, even for those in plano power. Figure 3 shows a volunteer model wearing some lenses from a discontinued fitting set.
Figure 3. Examples of theatrical contact lenses.
These types of lenses typically come in a median base curve and a diameter meant to fit most eyes. Due to the material properties required for tinting, these lenses are currently made from polymacon, a previously mentioned material that has a 38% water content and a Dk value of 8.4 (Tyler’s Quarterly, 2016). Practitioners should keep in mind the low oxygen permeability of this material and caution their patients against sleeping in these lenses. Aside from this caution, theatrical lenses can add much enjoyment to a contact lens practice.
OTHER USES FOR CUSTOM SOFT LENSES
Some patients have limitations that are beyond a practitioner’s control, such as sensitivity/lens awareness issues, problems with dexterity, or simply the inability to properly remove a GP lens. Patients who have not been able to adapt to the lid awareness of a GP lens, or whose GP lenses are frequently decentered or lost, may be prime candidates for a custom soft lens when their required lens parameters fall outside of the standard range.
Soft lenses usually result in much less lid awareness compared to GP lenses and are rarely lost or decentered on the eye. Patients who have Parkinson’s disease, rheumatoid arthritis, or the absence of a hand or fingers may not be able to safely apply and remove GP corneal or scleral lenses and yet find it possible to handle a custom soft contact lens, which offers a little more flexibility regarding application and removal and does not need to be filled with solution.
Some specialty and custom soft lenses require additional knowledge or experience for successful fitting. However, for most of us, adding specialty and custom soft contact lenses to our practices simply involves knowing what types of lenses are available and developing a relationship with the labs that manufacture them.
These lenses offer us an opportunity to serve many patients who have ocular conditions that are not correctable with off-the-shelf contact lenses. Fitting specialty and custom soft lenses may allow us to make a significant difference in someone’s life while also helping to establish our reputation for fitting unique or difficult cases.
Custom soft lenses provide a very important option for those patients who, when successfully corrected with these lenses, can help build your specialty lens practice. With the new advancements in lens design and manufacturing technology, look for the use and applications of these lenses to increase in the years ahead. If you are not already fitting theses lenses, spread your wings a little and plan on ordering some trial lenses for your next patient who could benefit from contact lenses outside of the usual and customary range. CLS
For references, please visit www.clspectrum.com/references and click on document #253.
Dr. Laurent is an associate professor at the University of Alabama School of Optometry.
Dr. Deligio is an assistant professor at Midwestern University-Chicago College of Optometry.