Sep. 09, 2024
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Frequent replacement and daily disposable contact lenses are generally produced in a one-size-fits-all design. But, as we know, patients&#; eyes come in a variety of shapes and sizes, and the one-size-fits-all concept does not work as well with contact lenses as it does with spectacle lenses. Patients have differing horizontal visible iris diameters (HVIDs), corneal eccentricities, and aberrations&#;as well as a variety of prescription and material requirements&#;that are not available in mass-produced contact lenses. Custom soft contact lenses will satisfy the total range of patients&#; anatomical and prescription needs to achieve a successful outcome.
Spherical, toric, and multifocal prescriptions that fall outside of the stock lens range are the easiest to prescribe in a custom soft lens. Mass-produced lenses are limited in terms of power and axis availability as well as multifocal zone sizes. Practitioners must evaluate corneal curvature and HVID combinations to select a design that will be comfortable and that will fit properly. When patients are not happy with the comfort or vision with their current lenses, troubleshooting may reveal the need for custom soft lenses. These personalized designs can deliver accurate prescriptions and precise fitting parameters, resulting in improved comfort, lens stability, and reduced total optical aberrations.
We sent a survey to members of the American Academy of Optometry&#;s Cornea, Contact Lenses and Refractive Technologies (CCLRT) Section asking them to describe their utilization of custom soft lenses. Of the 124 respondents, 78% reported that they prescribe custom soft lenses to manage astigmatism, presbyopia, ametropia, and anisometropia as well as for myopia management and to retain contact lens prescriptions.
When frequent replacement or daily disposable lenses fail to deliver acceptable vision or comfort, 78% of the respondents select custom soft lenses over other contact lens modalities to attempt to resolve these issues. These practitioners indicated that they initially choose mass-produced lenses over custom soft lenses for the following reasons: convenience (59% of respondents), improved comfort (11%), convenience of immediate dispensing (11%), ease of prescribing (10%), cost (6%), and reduced chair time (4%).
When the survey respondents initially selected custom soft lenses, it was to take advantage of expanded parameters to improve the lens fit, enhance comfort, and provide precise vision. To improve outcomes, 80% of these practitioners changed the lens power; 79% adjusted base curve; 66% modified diameter; 41% changed the material; and 19% adjusted lens thickness. When asked to identify which parameters are most important to guarantee a successful custom soft lens fit, respondents cited the following:
When asked to identify the most important characteristic to define custom soft lens success, 21% selected stability of vision, 38% chose comfort, and 21% selected visual acuity.
Resolve Soft Toric Rotation Toric lens stability cannot typically be enhanced with a one-size-fits-all contact lens design. Custom soft toric lenses often will solve the fitting and lens stability problems that occur when patients wear mass-produced lenses.
When troubleshooting soft toric lens rotation, the survey respondents improved the fit by:
HVID, or cornea size, is an important parameter to consider when fitting soft contact lenses, as it is the controlling factor for sagittal height. An average HVID is approximately 11.8mm.1 When HVIDs are larger or smaller than average, base curve adjustments are required for properly fitted lenses. For every 0.2mm larger than 12.0mm, add 1.00D to the flat keratometry value, resulting in a steeper-fitting lens; for every 0.2mm smaller than 11.6mm, subtract 1.00D from the flat keratometry value, resulting in a flatter-fitting lens.2
Selecting the appropriate lens diameter ensures corneal coverage, good centration, lack of limbal compression, absence of edge standoff, and sufficient lens movement, all of which contribute to stable vision. A soft lens should overlap the limbal region by at least 0.5mm in every direction. As a general rule, adding 2.0mm to the HVID is a good approximation when determining an initial lens diameter that will fit an eye and provide sufficient coverage around the cornea without putting stress on the limbal stem cells.3 An eye that has a large HVID, whether from a congenital anomaly such as megalocornea or is simply larger than normal, requires a steeper lens design. The deeper sagittal height would cause a normal frequent replacement or daily disposable lens to fit loosely and move on the eye with the blink. A smaller HVID with a shallower sagittal height requires a flatter base curve. A mass-produced lens would fit too tightly, causing limbal compression and possibly red eye. Eyes that have either larger or smaller HVIDs will benefit from custom soft lenses.
Case 1: Troubleshooting HVID Problems A 31-year-old patient stopped wearing contact lenses because of poor vision and comfort, but he is highly motivated to resume wearing them. The patient stated that his previous lenses caused his vision to go in and out of focus.
Unaided visual acuity was OD 20/200&#;, OS 20/200&#;, OU 20/100&#;. Refraction was OD &#;2.00 &#;2.25 x 025, 20/20 and OS &#;1.25 &#;3.75 x 175, 20/30. The patient&#;s HVIDs measured 12.31mm OD and OS. Simulated keratometry (Sim K) readings were OD 45.67/43.27 @ 018 and OS 46.42/42.51 @ 167 (Figure 1).
Figure 1. This patient&#;s larger-than-normal HVIDs required custom soft lenses with larger diameters to improve comfort as well as the stability and quality of the visual acuity.The contact lens parameters ordered were as follows: OD base curve radius (BCR) 8.2mm, overall diameter (OAD) 15.0mm; power &#;2.00 &#;2.00 x 025; OS BCR 8.3mm, OAD 15.1mm, power &#;1.25 &#;3.50 x 175. Visual acuity with these lenses was OD 20/20, OS 20/25+, OU 20/20+2 (stable with exceptional comfort).
The patient&#;s large HVIDs were fit with a steep base curve and a large diameter, increasing the sagittal height of the toric lens to fit comfortably on these larger-than-normal corneas and reducing lens rotation to improve quality of vision.
Being able to tailor multifocal design parameters based on a patient&#;s unique anatomical features and visual needs will improve contact lens success. When asked why they choose custom soft multifocal lenses, the CCLRT members who responded to our survey cited the following benefits:
With custom soft contact lenses, practitioners can offer patients who have unique prescriptions multifocal lenses with near-center or distance-center optics as well as offer off-label myopia management for young progressing myopes. These lenses can be fabricated in spherical and/or toric configurations with powers available in 0.10D increments, cylinder axes in 1º increments, and unlimited base curve options to better match the cornea. Other customization options include:
Most frequent replacement and daily disposable contact lenses designed to manage presbyopia have one-dimensional near and distance zones that must be properly balanced to improve outcomes. These lenses typically do not center perfectly on the eye, causing the near and distance optics to be offset. Because the nasal sclera tends to be steeper compared to the temporal sclera, the lenses tend to decenter nasally. The decentered optics can induce spherical aberration and coma, further distorting clarity.
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In addition to the greater range of parameter and design availability, custom soft lenses can be fabricated with decentered optics to align the line of sight with the correct optics of the lens, thus improving multifocal success. Practitioners have the freedom to design these lenses with unique power profiles and fitting characteristics that produce optically superior outcomes.
Case 2: Custom Soft Multifocals for a Competitive Edge A 60-year-old professional archer reported poor vision while competing. He had previously worn soft mass-produced contact lenses. Refraction was OD &#;3.50 &#;0.25 x 123, 20/20 and OS &#;3.75 &#;0.50 x 066, 20/20, with a +2.50D add OD and OS. Sim K readings were OD 44.00/44.50 @ 072 and OS 44.50/45.00 @ 119.
Contact lens parameters were ordered as follows: OD BCR 7.90mm, OAD 14.10mm, power &#;3.62D; OS BCR 7.90mm, OAD 14.10mm, power &#;3.25 &#;0.50 x 066. The add was +1.00D in a near-center design, with a 2.4mm central zone diameter and a 3.7mm intermediate zone diameter.
This national leaderboard contender competes indoors and outdoors under various lighting conditions. His lenses were ordered with customized tints to enhance his vision for specific conditions (Figure 2). His best-corrected visual acuities were OD 20/15, OS 20/15, and OU 20/10-2.
Figure 2. A custom soft lens fabricated using a 3.5mm central amber tint to increase contrast sensitivity.With custom soft contact lenses, zone size can be tailored to improve multifocal fitting when difficulties arise from distance or near vision inadequacies. Custom lenses also can solve many fitting challenges relating to out-of-range corneal shapes and sizes. The effect of pupil diameter on optical zone size is an important consideration when fitting multifocal contact lenses. The center and its surrounding zone size should be chosen based on a patient&#;s mesopic pupil size. A 2.5mm pupil requires a different zone size compared to a 4.0mm pupil. This is no different from aligning the segment height of a progressive spectacle lens. Standard frequent replacement and daily disposable multifocal lenses in most cases do not allow for pupil size variability. With custom soft multifocal designs, however, practitioners can specify a wide range of zone diameters. For example, some custom soft multifocal designs incorporate multiple zones, and practitioners can control the width of the intermediate and peripheral zones in addition to the central zone. Modifying the zone sizes of multifocal lenses, particularly when considering pupil size, will improve success with presbyopia-correcting contact lenses.
Case 3: Pupil Diameter Is Key to Multifocal Success A 46-year-old patient had reduced vision at distance and near with frequent replacement multifocal soft contact lenses. The refraction was OD &#;13.50 &#;0.75 x 085, 20/20 and OS &#;13.00 &#;1.00 x 100, 20/20, with +1.75D add. The mesopic pupil diameter was 3.50mm OD and OS. Sim K readings were OD 42.50/42.50 @ 090 and OS 42.00/42.25 @ 167.
Contact lenses were ordered in the following parameters: OD BCR 8.30mm, OAD 15.00mm, power &#;10.75 &#;0.75 x 083, +1.50D add, near-center diameter 2.0mm, intermediate zone diameter 3.0mm; OS BCR 8.40mm, OAD 15.00mm; power &#;10.50 &#;1.00 x 100; +1.50D add, near-center diameter 2.0mm, intermediate zone diameter 3.0mm. The visual acuity with these lenses was 20/20 OD and OS (stable), near J1. This case illustrates the importance of incorporating pupil diameter measurements into the contact lens evaluation.
Research is proving that smaller, distance-center optical zones affect orthokeratology and custom soft lens designs for myopia management and axial elongation.4,5 Results from these studies suggest that pupillary diameter and plus power ring diameter in orthokeratology and soft lens designs will slow axial length elongation better than standard distance-center designs would. For example, Pauné and colleagues found that decreasing the size of the central distance zone resulted in 76% less axial length growth.4 Further research suggests that pupil size, coma, and spherical aberration can further enhance myopia management techniques.5,6
Case 4: Successful Fitting for Myopia Management A 12-year-old child has experienced myopia progression for three years. Each year, her prescription has increased an average of 0.62D.
Her refraction was OD &#;5.50 &#;1.25 x 180, 20/20 and OS &#;6.00 &#;1.25 x 180, 20/20. Mesopic pupil diameter was 4.50mm OD and OS. Sim K readings were OD 44.25/45.75 @ 180 and OS 44.25/45.75 @ 180.
Hybrid lenses were ordered with the following parameters: OD BCR 7.50mm, medium skirt radius, OAD 14.5mm, power &#;5.75D, add +2.50D, distance-center diameter 2.8mm, near-surround diameter 3.8mm; OS BCR 7.50mm, medium skirt radius, OAD 14.5mm, power &#;6.25D, add +2.50D, distance-center diameter 2.8mm, near-surround diameter 3.8mm. Visual acuity with these lenses measured 20/20 OD and OS (stable); near J1.
The patient has worn these lenses for two years. At the most recent evaluation, no change in prescription was required. The patient has enjoyed clear, comfortable vision.
Being able to customize soft contact lenses empowers practitioners to solve uncommon vision and comfort challenges, such as red/green color deficiencies, vertical imbalances, and corneal irregularities. In some cases, custom designs may be your only option to successfully fit a patient. For example, adjusting the thickness of a lens or prescribing prosthetic lenses can address problems related to irregular or disfigured corneas. Custom-tinted lenses can improve contrast sensitivity not only for sports-related activities but also for patients who have retina problems.
Case 5: Customized Toric Lenses for a National Football League Player A 22-year-old professional football player had reduced visual acuity with his frequent replacement soft contact lenses prescribed for myopia. His visual acuity with these soft spherical lenses was OD 20/50 and OS 20/60. Refraction was OD +5.00 &#;0.75 x 175, 20/20 and OS +5.50 &#;1.00 x 032, 20/20. Sim K readings were OD 39.50/41.00 @ 081 and OS 39.75/41.00 @ 107. HVID measured 12.2mm OD and OS.
Contact lenses were ordered in the following parameters: OD BCR 8.50mm, OAD 15.4mm, power +5.75 &#;0.75 x 175; OS BCR 8.50mm, OAD 15.4mm, power +6.00 &#;1.25 x 032. Visual acuity with these lenses was 20/20 OD and OS (stable).
Because of the patient&#;s larger-than-average HVID, the lens diameter was increased to 15.4mm to achieve optimum lens stability. In addition, the lenses were fabricated with a light amber tint (Figure 3) to improve contrast sensitivity.
Figure 3. A light amber tint was added to these custom lenses to improve contrast sensitivity during a professional sport. The diameter was also increased to accommodate larger-than-normal HVIDs.Case 6: Incorporating Prism in Soft Toric Contact Lenses A 39-year-old woman reported reduced visual acuity and asthenopia while wearing frequent replacement soft contact lenses to correct her myopia. Refraction was OD &#;6.25 &#;1.00 x 085, 20/20 and OS &#;5.75 &#;0.75 x 070, 20/20. Sim K readings were OD 45.50/47.75 @ 118 and OS 45.25/45.75 @ 165. HVID measured OD 11.20mm and OS 11.30mm. Binocular testing indicated a 3.5D base-down prism OD.
Contact lenses were ordered in the following parameters: OD BCR 7.80mm, OAD 14.4mm, power &#;5.25 &#;0.75 x 105, 3.00D base-down prism; OS 7.90mm, OAD 14.50mm, &#;5.25 &#;0.75 x 070, 1.50D base-down prism. Visual acuity with these lenses was 20/20+2 OU (stable).
Soft custom toric contact lenses can, to some extent, mask corneal irregularities and provide acceptable vision in certain situations. Soft custom contact lenses are able to provide practitioners with the flexibility to manipulate multiple parameters to create the optimal lens-to-cornea relationship. In this case, controlling lens diameter and back-surface prism was crucial to enhance centration and stability. (Note: when adding prism to a contact lens, the base curve must be steepened to stabilize the increased weight from rotation.) Increasing the central thickness of the lenses reduced some of the corneal toricity by reducing lens flexure and masking the effects of cornea irregularity.
Case 7: Improving Cosmesis and Quality of Life A 34-year-old woman who was self-conscious about her disfigured eye whenever she was out in public was seeking a contact lens to mask the anomaly. The HVID measured 11.9mm. The mesopic pupil diameter was 3.2mm. The intensity of the discoloration required a black pupil with a surrounding brown iris (Figure 4).
Figure 4. The eye before (left) and after (right) prosthetic lens application.Custom soft prosthetic lenses can improve quality of life for patients who limit their public interactions because they are self-conscious about their appearance. In these cases, remember that the HVID will help determine the lens diameter and base curve along with the power, if needed. To help match the two eyes, measure the pupil diameter of the non-affected eye. To guarantee an accurate color match, send a photograph of the non-affected eye to the laboratory.
Adding a tint to a custom soft lens will enhance cosmesis by masking anomalies and will improve contrast sensitivity and enhance vision for patients who have retinal disease.
The mass-produced soft contact lens market has a tool chest filled with similar products that fit alike with comparable power availability and nearly universal diameters. When this tool chest of lenses is not successful, custom lenses can fill the void created by today&#;s stock lens products. Custom lenses can be fabricated in any power, cylinder, or multifocal configuration including distance-center, near-center, annular, or aspheric designs. Custom soft multifocals can be fit for myopia management as well as for presbyopia. Custom soft lenses can be manufactured with prism for vertical imbalance, with thicker lens profiles to correct irregular astigmatism, or as tinted or opaque colored lenses that can improve cosmesis and contrast sensitivity as well as problems with glare. Patients who have severe light sensitivity will benefit from filtered custom contact lenses for conditions including cataracts, macular degeneration, glaucoma, diabetic retinopathy, and retinitis pigmentosa. Specialty lens practitioners have a tool chest reserved specifically for custom soft lens products including hybrid designs.
Soft custom lenses offer practitioners the opportunity to recommend lens wear to patients who were previously told that they could not wear contact lenses and to enhance their quality of life. This contact lens modality can enhance patients&#; cosmetic appearance and visual abilities in a way not provided by any other lens type, and it offers freedom from glasses and improved contact lens comfort for non-average eyes. Custom soft contact lenses solve the problems inherent in a &#;one-lens-fits-all&#; fitting philosophy. CLS
Dr. Davis is the medical director at the Contact Lens Clinic at Davis EyeCare. He is also co-founder of EyeVis, Eye and Vision Research Institute developing novel contact lens designs. He has proprietary interest in BostonSight and has received remuneration from Humana, EyeMed, and SynergEyes.
Dr. Schwartz, a CCLRT Diplomate, has a specialty contact lens practice in Owings Mills, MD. He reports no conflicts of interest. Contact him at .
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