Soft contact lenses have evolved significantly since their inception in the 1960s. From the first lenses made in Otto Wichterle’s home to today’s modern, mass-produced, molded frequent replacement and disposable lenses, soft lenses continue to be increasingly safer and more comfortable to wear. Modern mass-produced soft contact lenses are available in better materials, more frequent replacement schedules, and expanded parameters, providing a better wearing experience for a greater percentage of those who wear contact lenses. However, there are limitations to what can be cost-effectively provided through molding lenses, and some patients’ needs fall outside of the parameters of these standard lenses. In these cases, lathe-cut, custom soft lenses are the better option.
There are essentially two methods for manufacturing soft lenses: lathe cutting the lenses from a button of material and hydrating them, which is used for custom lenses, or molding the lenses from a liquid polymer, which is used for mass production of frequent replacement and disposable lenses. The process of lathe cutting a lens using a computer software-driven CNC lathe with a diamond cutting tool can produce nearly unlimited lens parameters. This level of sophistication is not needed for the majority of eye shapes and prescriptions, but for those cases when it is, it can create a superior fit or correction for those individuals.
Custom soft lenses can be useful in a wide variety of circumstances. Optically, a custom lens has the ability to correct very high prescriptions, whether for high myopia, high hyperopia, or astigmatic correction beyond the range of mass-produced lenses. In addition, multifocal add powers and zone sizes can be individualized more readily to optimize the presbyopia correction experience or as an off-label use to manage the progression of myopia. Custom soft lenses can also provide a wider range of base curve and diameter options to more optimally fit those eyes that fall outside of the standard shape range that mass-produced lenses can accommodate. Finally, the ability to adjust lens thickness can allow custom soft lenses to better mask corneal irregularity for use in correcting individuals who have irregular corneas.
Using case reports, this article will cover the range of applications for custom soft lenses.
Case 1 A 14-year-old female presented as a new patient for her annual examination and contact lens refitting. Her chief complaint was that she had failed her vision test at school. She was wearing frequent replacement soft toric lenses seven days a week, 13 hours a day, with moderate comfort. She reported that her vision was not great with her lenses. She replaced them every four weeks and used a multipurpose solution for care. Her current lenses have parameters of 8.7mm base curve and 14.5mm diameter, with powers of +2.00D –3.25 x 20 OD and +2.25D –2.25 x 160 OS. Her ocular history was significant for congenital distichiasis OD and OS. Her medical history was normal, and she took no medications.
Her entering acuity with her current lenses (20 days old) was 20/25-2 OD and 20/40-2 OS. The lenses appeared to have excessive coverage, were rotationally stable, and displayed minimal movement. The over-refraction was difficult and variable, with a final over-refraction of –0.50 –1.50 x 45 OD to 20/25 and –1.25 –0.25 x 135 to 20/25 OS.
The lenses were removed, and corneal topography was performed to evaluate the corneal size and shape. The topography demonstrated particularly flat and small corneas OD and OS (Figure 1), with keratometry readings (Ks) of 39.6 x 43.7 @ 100 OD and 39.6 x 43.2 @ 71 OS and horizontal visible iris diameters (HVIDs) of 11.5mm OD and OS. Her 10mm chord corneal sagittal depth (sag) was projected by topography at 1,540 microns OD and OS. Extrapolating her 15mm sag for an 11.5mm cornea (adding approximately 1,875 microns to her 10mm chord) resulted in an estimated 15mm sag of approximately 3,415 microns OD and OS. It is established that the average sag at 15mm measured by anterior segment optical coherence tomography (OCT) is 3,740 microns, with a standard deviation of approximately 190 microns—meaning that her 15mm sagittal depth was nearly two standard deviations shallower than average OD and OS.
An updated refraction resulted in an Rx of OD +2.50 –3.75 x 15 (20/20) and OS +2.75 –3.00 x 165 (20/20). All other examination findings were normal. After evaluating the current lens fit, variable over-refraction that yielded significant minus power, and her poor visual endpoint, it was my impression that mass-produced soft toric lenses were not a good fit for her otherwise shallow corneal sagittal depth—the lens fit was tight, and there was likely some flexing or tenting of the lenses on eye.
We discussed her options for better vision, including bitoric corneal GP, hybrid, or scleral lenses, but she preferred staying with soft toric lenses if possible. We decided to proceed with trying to design a better fit and better correction for her with custom soft lenses.
We ordered for her a pair of C-Vue Advanced toric lenses (Unilens/Bausch + Lomb [B+L]), with a base curve radius of 8.9mm and an overall diameter of 14.0mm OD and OS. We also ordered the lenses with more correction for astigmatism, as there were no limitations on the cylinder or axis. The powers of her new lenses were +2.50 –3.75 x 15 OD and +2.75 –2.75 x 165 OS. The lenses were dispensed upon arrival. Her immediate impression was that the lenses were comfortable and that the vision OS was improved over her prior lenses. The lens fit demonstrated good coverage and centration, with minimal rotation OD and OS (Figure 2).
An over-refraction suggested adjusting the axis OD to 20º rather than 15º. At the follow-up evaluation, this adjustment to the axis was confirmed, and the lens OD was reordered with all parameters the same other than the axis change. At the final follow-up evaluation, the patient reported good comfort and fit, improved vision (20/20-2 OD and OS), and better visual stability than with her mass-produced soft toric lenses.
Case 2 A 42-year-old male presented for a contact lens fitting upon referral from a laser vision center. His history was significant for moderate-to-high myopia and astigmatism. He was deemed to be a non-candidate for laser-assisted in situ keratomileusis (LASIK) because his corneal thickness was too thin for his Rx. He reported that one of the reasons why he had sought LASIK was because he was never comfortable in contact lenses. His ocular and medical history were unremarkable otherwise.
His visual acuity with his glasses was 20/20 in each eye. All entrance tests were normal. A refraction revealed a prescription of –7.00 –2.50 x 12 OD and –7.75 –1.75 x 169 OS. Slit lamp examination was unremarkable. Corneal topography revealed Ks of 45.00 x 47.25 @ 10 OD and 45.25 x 46.75 @ 80 OS. In addition, his corneal diameter measured 12.5mm OD and OS. Following this evaluation, it was clear that he would be best fit in custom soft lenses, primarily because the steep Ks combined with his large corneas created a significant sagittal depth.
We ordered him a pair of SpecialEyes Toric lenses with the following parameters: OD 8.1mm base curve, 15.2mm diameter, –6.25 –2.25 x 12, hioxifilcon 54%-water material and OS 8.1mm base curve, 15.2mm diameter, –6.75 –1.50 x 169, hioxifilcon 54%-water material. At dispensing, the patient remarked that these were the first contact lenses that he had ever tried that he couldn’t feel on his eyes. The lenses demonstrated good coverage and centration, with minimal rotation (Figure 3). His vision measured 20/20-2 OD and 20/20-2 OS. An over-refraction revealed that an extra –0.25D sphere in each eye would improve acuity to 20/20. The lenses were dispensed, and the patient was scheduled for a follow-up evaluation in two weeks.
At his appointment two weeks later, he reported that he was very happy with the comfort and fit of the lenses and was satisfied with the vision as well. We demonstrated the change in vision with the extra –0.25D with loose lenses, and he did appreciate the improved distance vision. Another set of lenses was ordered with the same base curve and diameter but an extra 0.25D of minus in each eye. After wearing this updated Rx for another two weeks, he ordered three more pairs to complete his annual supply replaced on a quarterly basis.
Keys to Improving Fit Using custom soft lenses to more optimally fit a particularly shallow or deep cornea can provide better comfort, centration, and stability of vision. One component of the soft lens fitting process that is often neglected is corneal diameter and its impact on the overall depth of the eye at 14mm to 15mm, where a mass-produced soft lens would land. The impact of corneal diameter on total sagittal depth at 15mm is significant. For a 12.5mm cornea, the average sagittal depth of an eye at the 15mm chord is 400 microns deeper compared to a cornea that has similar central keratometric values but a corneal diameter of 11.5mm.
When considering soft lens fitting, as these two cases demonstrate, any combination of smaller HVID with flatter Ks or larger HVID with steeper Ks needs to be considered an outlier and would benefit from a custom soft lens fit. However, to know this, measurement (or at least educated estimation) of HVID must become part of the fitting process.
PRECISION MULTIFOCAL DESIGN
Case 3 A 12-year-old male presented for a contact lens examination. He had been a patient in the clinic for several years, initially fitted in glasses, then in orthokeratology lenses, and then finally in a mass-produced center-distance soft multifocal lens, all in an attempt to slow the progression of his myopia. He had failed in orthokeratology lenses, as his Rx had already become significant and he was unable to achieve a good outcome. His chief complaint at this visit was decreased distance vision with his current lenses. He had no other ocular or systemic history worth noting. His current lenses had parameters of 8.6mm base curve, 14.0mm diameter, –5.50D OD and OS, with +2.50D add.
His entering acuity was 20/50 OD and 20/50-1 OS at distance. An over-refraction of –1.00D in each eye yielded acuity of 20/25-1 in each eye. The lens fit looked acceptable, and all ocular health findings were normal. His manifest refraction was measured at –7.00 OD and –7.25 OS.
After discussing the findings with his parents, they expressed concerned about the continued progression of myopia and the lack of sharp acuity with the mass-produced soft multifocal lenses. Considering all options—including re-attempting orthokeratology albeit with reservation regarding the likelihood of success, continuing in the same lenses with a higher distance Rx, or moving to a custom soft lens that might have a better chance of retarding the progression of his myopia—his parents opted for custom soft multifocal lenses. The custom lenses had the potential to work better on all fronts, including the ability to create a more pronounced ring of plus in the midperiphery of the cornea as well as providing better distance acuity by creating a more optimal distance zone diameter.
After measuring his Ks and HVIDs, and knowing that his current lenses provided an acceptable fit at 14.0mm, we ordered him a pair of SpecialEyes Multifocal lenses manufactured with hioxifilcon D 54%-water material in parameters of 8.3mm base curve, 14.0mm diameter, and powers of –6.25D OD and –6.50D OS, with a +5.00D add and a 4.0mm distance zone. The lenses were dispensed and evaluated. Visual acuity measured 20/20-2 in each eye, and the patient reported good comfort with the new lenses. An over-refraction did not improve his visual acuity. The lenses were dispensed, and he was scheduled for a follow-up evaluation.
One week later, he reported no significant issues with the lenses. His vision was 20/25+1 OD, 20/20-2 OS, and 20/20 OU. The fit looked acceptable. An over-refraction did not improve his vision. Corneal topography was performed over the lenses to verify good placement of the add zone and significant plus power (Figure 4).
Custom Soft Multifocal Benefits Custom soft multifocal lenses have nearly unlimited ability to achieve optimum add power and zone size, either in a center-distance or a center-near design, and some designs are even available with decentered add zones to compensate for a lens that is decentered. Unlike mass-produced lenses, in which the add zones are all typically the same within a lens design and the add powers are available in only a few options, custom soft lenses can be individualized to the unique visual needs and attributes of each patient. Useful for managing presbyopia, visual stress from digital device use, or myopia progression, custom soft multifocal lenses have a variety of applications.
Case 4 A 29-year-old male presented for a contact lens fitting. He is on active duty in the military and had returned from a tour in Afghanistan several months prior. During his time there, he noted his vision changing radically; when he returned to the United States, he had his eyes checked and was diagnosed with keratoconus. At the time, he was about to be reassigned and was not fitted in lenses. He presented for a contact lens fitting with the hope of improving his vision.
His entering acuity unaided was 20/80 OD and 20/100 OS. All entrance tests were normal. Manifest refraction was OD +1.00 –3.25 x 153, with an acuity of 20/30-1 and OS +1.75 –5.25 x 15 to achieve 20/40-2. Slit-lamp examination revealed clear corneas with no scarring and vertical striae in each eye. Corneal topography revealed definite keratoconus in each eye (Figure 5). Fundus examination revealed no pathology OD and OS.
After discussing options for correcting vision, including spectacle correction (which he felt was not adequate), corneal GP lenses, hybrid lenses, scleral lenses, or soft keratoconus lenses, we decided to proceed with scleral lenses. We achieved an acceptable lens fit OD and OS, but over-refraction did not yield a good visual outcome. We then proceeded to try corneal GP lenses, which also did not yield good visual results. Finally, we opted to try custom soft keratoconus lenses to see whether we could obtain a better visual outcome.
Based upon the fitting guide recommendations, using average K readings of 46.4 OD and 50.9 OS, we initially fitted him in an 8.2mm base curve, 8.6mm fitting curve, 15.0mm diameter lens with an Index of Thickness (IT) of 0 OD, while the left eye was fitted with a 7.4mm base curve, 8.4mm fitting curve, 15.0mm diameter lens with an IT of 1. The right lens appeared slightly flat, with excessive movement; the 8.2mm base curve lens was subsequently replaced with the 7.8mm base curve, 8.4mm fitting curve lens. The lenses as this point demonstrated good centration, coverage, and rotational stability. An over-refraction of the right eye revealed a visual acuity of 20/20-1 with +4.25D sphere. The left eye over-refracted to 20/30-2 with a +4.75D sphere. Sphero-cylindrical over-refraction of the left eye of +6.00 –3.25 x 13 improved the visual acuity to 20/25+1.
We decided to try an IT 2 lens next on the left eye to see whether we could improve the visual acuity and reduce the cylinder needed in the Rx. With the same base curve, fitting curve, and diameter and with an IT of 2, the left eye achieved 20/20-2 with an over-refraction of +5.00 –1.50 x 15. The lens was rotationally stable. We proceeded to order an initial pair of lenses in the following parameters: OD Novakone (Alden Optical/B+L) 7.8mm base curve, 8.4mm fitting curve, 15.0mm diameter, –1.50D, IT 0, hioxifilcon D material and OS Novakone 7.4mm base curve, 8.4mm fitting curve, 15.0mm diameter –1.50 –1.50 x 15, IT 2, hioxifilcon D material.
At dispensing, the patient reported that initial comfort was quite good with the lenses. After 10 minutes of settling time, his visual acuity was measured at 20/25 OD and 20/25 OS. The fit of the lenses appeared to be as desired, with good movement, coverage, and centration OD and OS (Figure 6) and no rotation of the toric lens OS (Figure 7). An over-refraction of +1.00 –0.50 x 160 in the right eye yielded a slight improvement in acuity. The left eye improved slightly with an over-refraction of +1.00 –0.75 x 20. The lenses were dispensed after training on application, removal, and care, and he was given Biotrue multipurpose solution (B+L) for cleaning and disinfection.
At the follow-up evaluation 12 days later, The patient reported good comfort and generally good vision with the lenses. He felt that the vision was noticeably better, but he was having more issues with near vision and eye strain than with distance vision. His visual acuity was 20/25 OD and 20/25-2 OS. The lens fit looked stable, and the corneas appeared to be tolerating lens wear well. An over-refraction yielded essentially the same outcome as at the dispensing appointment. The lenses were reordered with the adjusted Rx (–0.75 OD and –0.50 –2.00 x 15 OS) and dispensed a week later. With the new power containing less minus, he felt that the vision was improved, particularly at near. We ordered his remaining lenses for an annual supply and scheduled him for a follow-up evaluation in six months, as this was his first time in lenses.
When the Unexpected Happens Some patients who have corneal irregularity cannot achieve acceptable vision and/or an acceptable fit with GP lens options. In addition, some of these patients do not wish to wear GP lenses, particularly if they historically have been soft lens wearers. For such patients, consider special design custom soft lenses to meet their needs.
As these four cases demonstrate, soft lenses can be customized to accomplish a wide variety of fitting outcomes, including improving comfort and fit, helping to better correct presbyopia or manage myopia, and even to correct some forms of irregular astigmatism, among other uses. Recognizing the instances in which corneal sagittal depth is either shallow or deep (as a factor of keratometric readings and corneal diameter) can help you determine those cases for which a custom soft lens can better fit an eye. Understanding how to customize add zone sizes and powers in custom soft multifocal designs can bring success to a higher percentage of presbyopes or progressing myopes. Finally, irregular cornea patients who do not achieve the visual success that you would expect from corneal GP or scleral lenses are possible candidates for custom soft lenses for keratoconus or other unusual corneal conditions. Knowing when to forgo the mass-produced soft lens options for something more personalized can surprise your patients and enhance your practice profile. CLS