Visual Performance of Center-distance Multifocal Contact Lenses Fit Using a Myopia Control Paradigm

Abstract

Significance.

With multifocal contact lenses (MFCLs) used for myopia control, questions remain regarding visual performance. Information from non-presbyopic patients provides insight on how MFCLs affect visual acuity and reading performance.

Purpose.

To examine the visual performance of center-distance multifocal contact lenses in non-presbyopic adults under different illumination and contrast conditions compared to a single vision contact lens (SVCL).

Methods.

Twenty-five adult subjects were fit with three different lenses (CooperVision Biofinity “D” MFCL +2.50 add, Visioneering Technologies NaturalVue MFCL, CooperVision Biofinity sphere). Acuity and reading performance were evaluated.

Results.

A statistically significant difference in high-contrast distance acuity was observed (Biofinity –0.18 ± 0.06, Biofinity MFCL –0.14 ± 0.08, NaturalVue MFCL –0.15 ± 0.03; RM-ANOVA P = .017). Under mesopic, high-contrast conditions, MFCLs performed worse than SVCLs (Biofinity –0.05 ± 0.091, Biofinity MFCL +0.03 ± 0.09, NaturalVue MFCL: +0.05 ± 0.091; RM-ANOVA P < .0001). Under low-contrast conditions, MFCLs performed one line worse in photopic lighting and two lines worse under mesopic conditions (RM-ANOVA P < .0001). Glare reduced acuity by 0.5 logMAR for all lenses (RM-ANOVA P < .001). A statistically significant difference in near acuity was observed (RM-ANOVA P = .019), but all lenses achieved acuity better than –0.1 logMAR (Biofinity –0.16 ± 0.06, Biofinity MFCL –0.17 ± 0.04, NaturalVue MFCL –0.13 ± 0.08). Reading performance in words per minute (WPM) was worse with MFCLs (Biofinity MFCL 144 ± 22 WPM, NaturalVue MFCL 150 ± 28 WPM) than with SVCLs (156 ±23 WPM; RM-ANOVA P = .019) regardless of letter size (RM-ANOVA P = .13). No difference in acuity between the MFCLs was detected (RM-ANOVA all P > .05).

Conclusions.

MFCLs perform similarly to SVCLs for high-contrast targets and display reduced low-contrast acuity and reading speed. Practitioners should recognize that high-contrast acuity alone does not describe MFCLs visual performance.

Myopia is an increasingly prevalent condition, affecting millions of individuals worldwide. In Asia, prevalence has increased steadily over the last 40 years, with 90% of young people becoming myopic by their college years.^1–4 It is projected that 50% of the world’s population will be myopic by the year 2050, with an estimated 1 billion highly myopic individuals.^5,6

While traditionally, myopia has been considered a relatively benign condition correctable with spectacles and contact lenses, the increasing axial length observed with myopia heightens the risk of developing multiple ocular diseases, such as glaucoma, cataracts, retinal detachment and myopic maculopathy.^7–15 As such, there is increasing pressure on clinicians to provide treatment options that not only correct a patient’s refractive error, but that may also slow the progression of myopia to help prevent future vision loss from comorbidities.

Animal models and clinical trials have shown that the application of myopic retinal defocus can slow the progression of myopia.^16–25 The discovery of the retina’s ability to detect the sign of defocus was key in the development of optical therapies to control myopia progression, culminating with the eventual approval of the first soft contact lens for myopia control in the United States.²⁶ With the exception of the recently approved MiSight contact lens, most soft contact lenses used in the United States to slow myopia progression have been designed for presbyopic patients and are prescribed off-label. In practice, center-distance multifocal contact lenses are utilized to correct distance vision while simultaneously providing the desired myopic retinal defocus, often using the highest available add power to maximize myopic defocus. For example, the Bifocal Lenses in Nearsighted Kids (BLINK) Study group demonstrated that children fit with a +2.50D add center-distance multifocal contact lens achieved acceptable distance vision while providing relative peripheral myopic defocus and reduced myopia progression, whereas the +1.50D add did not provide the desired myopia control effect.^27–29

Despite the rapid adoption of center-distance multifocal contact lenses for myopia control in clinical practice, questions remain on the visual experience for patients. Aspects of visual quality for multifocal contact lenses, such as visual acuity and subjective symptom questionnaires, have been examined in presbyopic and non-presbyopic patients.^30–34 Despite these previous investigations, as new multifocal contact lenses are introduced different visual outcomes may be observed with each unique optical profile. For example, the NaturalVue multifocal contact lens (Visioneering Technologies, Inc.) reports using an extended depth of focus principle to provide a range of clear vision at near, equivalent to a multifocal add power of up to +3.00D. It is unknown whether this design may provide different visual outcomes compared to traditional center-distance multifocal designs. Additionally, there is little information on the effect of glare on acuity with multifocal lenses. While glare is commonly associated with tasks performed by adults, patients fit with multifocal lenses for myopia control may encounter various sources of glare in their environment, such as water, snow, or from electronic devices. These lenses, when fit using a myopia control fitting paradigm of over-refraction adjusted maximum plus power to maximum distance visual acuity, paired with the maximum available bifocal add power to provide myopic retinal defocus,³⁵ may significantly reduce visual acuity under glare conditions. For near performance with multifocal contact lenses, there is information on near visual acuity; however, there is little information on how these lenses affect tasks such as reading in non-presbyopes.^33,36

The purpose of this study was to investigate how two multifocal contact lenses, commonly used off-label indication for myopia control, affect visual performance in non-presbyopic, myopic subjects. We compare the distance visual acuity performance between a traditional center-distance aspheric multifocal, the Biofinity Multifocal “D” Lens with a +2.50 add, and an extended depth of focus design, the NaturalVue Multifocal, with a single vision contact lens (Biofinity Sphere) under different lighting conditions for high- and low-contrast targets. The effect these lenses have on near visual performance, including visual acuity and reading speed, were evaluated with a validated, novel, iPad application.³⁷

METHODS

This study was conducted in accordance with the tenets of the Declaration of Helsinki. Written informed consent was acquired from all subjects prior to study participation and the study was approved by the Institutional Review Board of the University of Houston. Subject demographics are shown in Table 1, including age, sex, refractive error, race, and ethnicity; with race and ethnicity terms used as defined per the 1997 United States Office of Management and Budget guidance on classification of data on race and ethnicity.³⁸

Table 1.

Subject Demographics.

Age (mean ± SD)	24.1 ± 1.5 years
Sex	Male: 7 (28%)
	Female: 18 (72%)
Refraction OD (mean ± SD)	–3.38 ± 1.53 DS. Range –1.00 to –5.00 DS
Refraction OS (mean ± SD)	–3.29 ± 1.66 DS. Range –0.75 to –5.75 DS
Race
White	16 (64%)
Asian	6 (24%)
African American	2 (8%)
Other	1 (4%)
Ethnicity
Hispanic or Latino	18 (72%)
Non-Hispanic	7 (28%)

Overview

This was a single-site, bilateral, single-masked, non-dispensing two visit crossover clinical study. Twenty-five adult subjects, aged 21 to 29 years old, were enrolled and completed the study. Each subject was fit binocularly with three different contact lens designs, 1) Biofinity “D” center-distance multifocal with +2.50 add power (CooperVision, San Ramon, CA), 2) NaturalVue Multifocal contact lens (Visioneering Technologies, Alpharetta, GA), and 3) Biofinity sphere single-vision contact lens (CooperVision). The Biofinity sphere and the Biofinity multifocal contact lens are silicone-hydrogel lenses made of comfilcon A (48% water), have a base curve of 8.6 mm and an overall lens diameter of 14.0 mm. The Biofinity multifocal is a progressive aspheric design, with the “D” lens having a spherical central-distance power, surrounded by a zone of progressively increasing plus power before reaching the maximum amount of plus power at the periphery of the optic zone. The NaturalVue Multifocal is a hydrogel lens made of etafilcon A (58% water), has an 8.3 base curve and an overall lens diameter of 14.5 mm. The NaturalVue Multifocal is described as an extended depth of focus design utilizing a continuous aspheric progression in plus power.³⁹ This design does not specify a labelled bifocal addition power and is indicated for presbyopic correction of up to +3.00D add power. The three contact lens designs were fit binocularly, in random order, over two study visits occurring within a two-week period. Subjects were masked to the contact lens type.

Eligibility

Eligible subjects were required to have a spherical equivalent refraction between -0.75 and -6.00 diopter sphere at the corneal plane, refractive astigmatism of -1.00 diopter cylinder or less, and best-corrected visual acuity of at least 20/30 in each eye. Exclusion criteria included the presence of significant anterior segment disease, history of ocular trauma or surgery, history of refractive surgery, or current rigid gas permeable contact lens wear. Subjects were excluded if they were pregnant or nursing.

Contact Lens Power Selection

Initial refractive error for each subject was measured using an open-field auto-refractor (Grand Seiko WR-5100K; Grand Seiko Co., Hiroshima, Japan), followed by maximum plus power to maximum visual acuity subjective refraction. Initial contact lens power selection for the Biofinity contact lens products was determined using the spherical equivalent spectacle refraction (Sphere + 0.5*Cylinder), vertex corrected for prescriptions beyond - 4.00 diopter sphere. Initial lens selection for the NaturalVue Multifocal lens was determined using the NaturalVue Multifocal QuickStart Calculator (Visioneering Technologies), where the spectacle refraction and the vertex distance to the corneal plane are inputs to determine contact lens power. After initial power selection, the contact lenses were inserted by study personnel and fit was assessed. Once an acceptable fit was achieved, spherical contact lens over-refraction was performed. Distance vision was optimized using the maximum plus to maximum visual acuity approach for each lens type and contact lens power changed if indicated by the over-refraction.

Contact Lens Assessment

Contact lens movement in primary gaze and with push-up test was assessed using a 5-point scale:

• Excessive: Movement with the blink that produces limbal exposure

• Moderate Acceptable: Substantial movement that does not produce limbal exposure, but does not immediately return to the original lens edge position

• Optimal Movement: A freely mobile lens with the blink that immediately returns to the original lens edge position

• Minimal Acceptable: Slight movement with the blink that is less than optimal movement. This movement is less than that observed with a freely mobile lens

• Insufficient: No lens movement or barely detectable movement with the blink. The lens appears adhered to the ocular surface

Contact lens centration was determined via measurement of contact lens corneal overlap from the corneal limbus to contact lens edge measured to the nearest 0.1 mm, using a Haag-Streit slit lamp reticule under 10X magnification. Contact lens decentration was calculated as the difference between temporal and nasal overlap (i.e., temporal overlap – nasal overlap), with positive values representing temporal contact lens decentration and negative values representing nasal contact lens decentration

Visual Acuity and Reading Performance

After a minimum contact lens settling period of 10 minutes, logMAR distance visual acuity was measured monocularly and binocularly using the M&S Technologies Clinical Trial Suite (M&S Technologies; Niles, IL). High- and low-contrast (11% Michelson contrast) logMAR VA was measured at distance with each lens type under photopic lighting (~367.0 Lux), mesopic lighting (<1.0 Lux), and mesopic lighting with a glare source consisting of four lights shining at the patient located at the plane of the acuity monitor (~2.0 Lux). Lighting levels were measured with a Sekonic L-758DR photometer (Sekonic Corporation, Tokyo, Japan) at the eye plane of the subject.

Near high-contrast logMAR visual acuity and mean reading speed were evaluated using an iPad Application developed by Wolffsohn.³⁷ Subjects were seated 40 centimeters from a 9.7 inch 6^th generation iPad (Apple, Cupertino CA) on a reading stand under photopic lighting conditions. With the display brightness of the iPad set to maximum, a measurement of the subject’s interpupillary distance was acquired using the iPad FaceTime camera. Subjects were instructed that they would be presented a series of sentences on the iPad. They were instructed to be as accurate as possible while reading the sentence at a normal cadence. Subjects were instructed that if they made a reading error during the test, they should not go back and correct an error from a previous point in the sentence. Subjects were then presented a series of sentences ranging in letter size from 0.9 to –0.2 logMAR. Beginning at 0.9 logMAR, each subsequent sentence decreased in size by 0.1 logMAR. Subjects read the sentence aloud and immediately pressed a “Read” button after completion of the sentence. Once the text became too small to read, the subject pressed a “Can’t Read” button. Upon completion of the test, the examiner identified words that the subject read incorrectly with the option to play back the recorded audio, noted the incorrect words and the iPad software calculated near logMAR acuity and mean reading speed in words per minute (WPM) from the automatically timed audio trace (Figure 1).

Figure 1.

Example of the Wolffsohn iPad application for evaluating near visual acuity and reading speed. (A) shows a representative reading task at 0.9 LogMAR. The subject reads the randomized passage aloud and presses READ upon completion of the task or CAN’T READ if the presented text size is too small to discern. (B) shows the grading interface. The investigator reviews the subject’s recording of the passage (Play) and selects the words misread by the subject (red) versus correctly read words (black).

Pupil Size

Pupil size was measured at both study visits under photopic and mesopic lighting conditions with the NeurOptics VIP-300 Pupillometer (NeurOptics, Laguna Hills, CA). Subjects fixated on a distance target with the left eye and pupil size was measured for the right eye under photopic and mesopic conditions. Pupil size was measured to the nearest 0.1mm.

Statistical Analyses

A sample size of 24 subjects was determined to adequately to detect a 0.1 logMAR (one line) difference in low-contrast visual acuity between lens designs with 90% power at an alpha level of 0.05, assuming a standard deviation for the change in visual acuity of 0.15 logMAR. As the data were not significantly different from a normal distribution, statistical analyses were conducted using repeated-measures analyses of variance (RM-ANOVA), with adjusted post-hoc t-tests, when appropriate. For distance visual acuity, the RM-ANOVA included three repeated factors—lens type (Biofinity Sphere, Biofinity Multifocal, NaturalVue Multifocal), letter contrast (high contrast and low contrast), and lighting condition (photopic, mesopic, mesopic with glare). Near visual acuity was analyzed using RM-ANOVA with one repeated factor (lens type). RM-ANOVA for reading speed included two factors—lens type and letter size (logMAR).

RESULTS

Contact Lens Fitting Characteristics

All lenses fit were determined to have acceptable movement in primary gaze. Spherical over-refraction was performed in a phoropter using a maximum plus to maximum visual acuity approach with binocular blur balance under photopic conditions. Out of 50 total eyes, three eyes in the single vision lens required a power modification, with a mean ± standard deviation over-refraction of +0.33 ± 0.12 diopter sphere. Twenty-nine (29) of 50 eyes wearing the Biofinity MF required over-refraction, with an average over-refraction of –0.37 ± 0.13 diopter sphere. Only one eye wearing the NaturalVue MF required an over-refraction, of power –0.50 diopter sphere to optimize distance visual acuity.

Slight temporal contact lens decentration was observed throughout the study. For the right eye, the mean contact lens decentration was +0.28 ± 0.23 mm temporal for the Biofinity sphere contact lens, +0.28 ± 0.28 mm temporal for the Biofinity Multifocal and +0.28 ± 0.21 mm temporal for the NaturalVue Multifocal. There was no significant difference in contact lens centration between the three contact lenses (P = .99). All lenses evaluated in the study had adequate paralimbal coverage, and no lens in the study was evaluated as having excessive contact lens decentration that would warrant lens discontinuation.

Visual Acuity

LogMAR visual acuity under high- and low-contrast conditions depended on the lighting condition (photopic, mesopic, mesopic with glare) and the lens type (lens*contrast*lighting interaction; P = .015).

High-Contrast Visual Acuity

High-contrast visual acuity is shown in Figure 2. Regardless of contact lens type, high-contrast distance visual acuity was always better than low-contrast acuity (all P < .05). All three contact lens designs provided mean (± standard deviation) photopic distance acuity better than –0.1 logMAR (Biofinity sphere –0.18 ± 0.06, Biofinity Multifocal –0.14 ± 0.08, NaturalVue Multifocal: –0.15 ± 0.03). A statistically significant, but clinically insignificant, difference in visual acuity between the single vision lens and the multifocal contact lenses was observed (P = .017), with each multifocal contact lens performing approximately 1.5 to 2 letters worse than the single vision lens. Under mesopic conditions, a statistically significant and clinically meaningful difference in high-contrast visual acuity was observed (P < .0001) with both multifocal contact lens designs performing approximately one line worse than the single vision contact lens (Biofinity sphere –0.05 ± 0.09, Biofinity Multifocal 0.03 ± 0.09, NaturalVue Multifocal: 0.05 ± 0.09). With the addition of a glare source under mesopic conditions, there was no difference in mean visual acuity, and multifocal contact lens designs continued to perform approximately 1 line worse than the single vision contact lens (Biofinity sphere –0.05 ± 0.081, Biofinity Multifocal 0.05 ± 0.08, NaturalVue Multifocal: 0.06 ± 0.08).

Figure 2.

High-Contrast Visual Acuity (logMAR) with a single vision contact lens (SVCL) and multifocal (MF) contact lenses under various lighting conditions. A statistically significant difference in visual acuity between the single vision lens and the multifocal contact lenses was observed under photopic (*, P = .017) and mesopic (#, P < .001) conditions. No difference in visual acuity was observed for mesopic versus mesopic + glare conditions for any lens type. Error bars represent SEM.

Low-Contrast Visual Acuity

Low-contrast visual acuity is shown in Figure 3. Low-contrast distance visual acuity under photopic conditions was better than under mesopic conditions for all lenses (all P < .001). Mean photopic, low-contrast visual acuity with the multifocal contact lens designs performed 5–6 letters worse than with the single vision lens (Biofinity sphere –0.02 ± 0.09, Biofinity Multifocal: 0.08 ± 0.09, NaturalVue Multifocal: 0.10 ± 0.09). Under mesopic, low-contrast conditions without glare, acuity was reduced approximately 2 lines with the multifocal contact lenses compared to the single vision lens (Biofinity sphere 0.18 ± 0.096, Biofinity Multifocal 0.40 ± 0.09, NaturalVue Multifocal: 0.42 ± 0.09). Lighting change from photopic to mesopic conditions led to an approximate 2 line reduction in visual acuity with the single vision lens (P < .001) and an approximate 3 line reduction with multifocal contact lenses (P < .001). The addition of a glare source resulted in additional reduction in visual acuity of approximately 0.5 line LogMAR for all lens types (Biofinity sphere: 0.24 ± 0.06, Biofinity Multifocal: 0.45 ± 0.14, NaturalVue Multifocal: 0.51 ± 0.11, P < .001). There was no significant difference in visual acuity between the two different multifocal contact lenses, regardless of testing condition (all P > .05).

Figure 3.

Low-contrast visual acuity with single vision contact lenses (SVCL) and multifocal (MF) contact lenses under various lighting conditions. Photopic low contrast acuity was worse with multifocal lenses (*; P < .001) compared to SVCL. Comparing mesopic to photopic conditions, a two-line reduction in visual acuity was observed for the SVCL lens and a three-line reduction was observed for each MF contact lens (#; P < .001). Glare further reduced acuity by 0.5 logMAR for all lenses compared to photopic conditions (^; P < .001) There was no significant difference in visual acuity between the two multifocal contact lenses for any lighting condition (P > .05). Error bars represent SEM.

Near Visual Acuity and Reading Performance

Mean near reading visual acuity was better than –0.10 logMAR for all three lenses (Figure 4A). A statistically significant, but not clinically meaningful difference was observed in acuity between the lens types (single vision lens: –0.16 ± 0.06, Biofinity Multifocal: –0.17 ± 0.04, Biofinity Multifocal: –0.13 ± 0.08, P = .019).

Figure 4.

Near binocular reading acuity (A), Radner reading speed (B) and mean reading speed by letter size (C) with single vision and multifocal contact lenses. Radner reading speed was significantly reduced with multifocal contact lenses compared to the single vision contact lens; however, no difference was observed between the Biofinity D multifocal and the NaturalVue multifocal (P = .95; Panel B). Multifocal contact lenses displayed a reduced reading speed for all letter sizes compared to single vision lenses (P < .05; (C) Sample size reduces as subjects reach threshold acuity. Error bars represent SEM.

Letter size (P < .0001) and contact lens type (P = .038) each had an effect on words read per minute under binocular viewing conditions; however, the effect of letter size on reading speed did not differ by lens type (lens*letter size interaction, P = .178). Mean reading speed at each letter size for each lens is presented in Figure 4C. Average reading speed across all letter sizes was better with the Biofinity single vision contact lens (156 ± 23 WPM) compared to the Biofinity multifocal contact lens (144 ± 22 WPM) and the NaturalVue multifocal contact lens (150 ± 28 WPM) (both P < .05, Tukey’s WSD Adjusted). There was no difference in reading speed between the two multifocal contact lenses (P = .95; Figure 4B).

Pupil Diameter

A statistically significant, but clinically insignificant, difference in pupil size under photopic conditions of 0.18 mm was observed between visits 1 and 2 (4.25 ± 0.57 mm vs. 4.07 ± 0.50 mm; P = .02). There was no difference in pupil size under mesopic conditions between visits (5.82 ± 0.73 mm vs. 5.78 ± 0.62 mm; P = .68).

DISCUSSION

With increasing use of multifocal contact lenses for myopia control, eye care practitioners will be asked how this technology may affect the vision of their patients. In our study, multifocal contact lenses displayed slight, but clinically acceptable, reductions in visual acuity compared to single vision contact lenses under most conditions. Letter contrast had the greatest impact on visual performance. When letter contrast was reduced, an expected reduction in performance was observed, and this effect was more pronounced for multifocal lenses. While this reduction in vision with reduced target contrast may not be a significant concern for young children, this could become significant when patients wearing these contact lenses become older. There is no consensus best practice for when to discontinue multifocal contact lens wear in myopia control patients. As such, eye care practitioners are likely to encounter teenage myopia control patients who report visual difficulty with multifocal lenses in low light conditions as they assume more tasks that occur under these conditions, such as night driving.

While the addition of a glare source was expected to negatively affect visual performance,³² we only observed small reductions in visual acuity and the magnitudes of these reductions were consistent across lens designs. For high-contrast optotypes, glare resulted in no significant clinical reduction in binocular visual acuity for any lens design. When letter contrast was reduced, the addition of glare did not precipitously drop acuity, with only an approximate 0.5 line logMAR reduction for all lens types. The similar magnitude of reduction with the glare source for all designs suggests that the multifocal optical profiles assessed in our study did not result in a significant increase in intraocular stray light compared to single vision optics. While no significant objective reduction in performance was observed, patients may report subjective symptoms of glare, ghosting or halos when wearing these lenses.^30,31,33

When considering near vision performance, all of the lenses in this study provided similar binocular reading acuity, and the bifocal addition in multifocal contact lenses did not provide additional near vision resolution. This most likely represents a floor effect, where the vision achieved with all three lenses approached the limit of visual resolution for the retina, which is approximately 20/13 Snellen equivalent in young adults.⁴⁰ Despite achieving good acuity with all three lens designs, reading speed with multifocal contact lenses was reduced compared to single vision lenses. This reduction in reading speed occurred regardless of text size, suggesting that the multifocal lens optical profiles assessed did have an effect on the identification of text during reading. When considering the use of multifocal contact lenses for myopia control, near visual acuity may only provide a partial picture of what these patients encounter in a real-world environment. The impact of multifocal contact lenses on critical near vision tasks, such as reading, should be investigated further.

An interesting finding of the study was that similar distance visual acuity, near visual acuity, and reading performance was achieved with both multifocal contact lens designs, despite the reported difference in optical profiles. While the optical profiles of the two multifocal contact lenses may not result in differing performance, these profiles do affect how eye care practitioners fit the respective lenses. When fitting multifocal contact lenses for myopia control, eye care practitioners are balancing the distance vision requirements of their patients with the need to maximize the peripheral myopic defocus. Eye care practitioners should fit lenses using maximum plus power to best distance acuity to prevent over-minusing the patient and potentially negating the desired peripheral myopic defocus. When selecting the initial contact lens power for the Biofinity +2.50D add multifocal, the vertex corrected spherical equivalent contact lens power did not achieve acceptable distance for 58 percent of eyes (29/50). On average, these eyes required additional minus power to achieve acceptable distance vision, consistent with a previous report. ²⁷ Despite this additional minus power, these lenses have been shown to reduce myopia progression while providing acceptable distance vision when fit using this approach.²⁸ An alternative approach to achieve acceptable distance vision with the Biofinity multifocal could be to reduce the bifocal add power. In this situation, you could achieve acceptable distance vision without additional minus added to the distance prescription; however, this could lead to a reduction in myopia control treatment efficacy, as was observed when subjects wearing a +1.50D bifocal add displayed more myopic progression than subjects fit with a +2.50D add.²⁸

When fitting the NaturalVue multifocal, the add power cannot be changed and the only option to achieve acceptable distance vision is to change the distance prescription. There is little published literature regarding use of the NaturalVue multifocal for myopia control. A retrospective case series on the use of the NaturalVue multifocal for myopia control did not detail how contact lens power was selected, except for stating that the lenses were prescribed “within their indicated use for the correction of myopia”.⁴¹ In our study, we used the company published fitting application to determine the initial lens power, as recommend for the correction of myopia. This application calculates the vertex corrected spherical equivalent refraction and tells the eye care practitioner which lens to select. In our study, the initial contact lens power selected by the application subsequently became the final power for 49 of 50 eyes. During over-refraction, these eyes did not accept additional plus power without a reduction in distance acuity, while one eye required additional minus power to achieve acceptable distance acuity. The difference in the required over-refractions for the two lens designs suggests that the optical profiles between the two multifocal are indeed different; however, this difference did not affect objective visual performance.

Other studies have examined aspects of visual performance with multifocal contact lens use in non-presbyopes. Kollbaum et al. evaluated the visual performance of the center-distance concentric ring multifocal MiSight contact lens (CooperVision) and the Proclear D progressive aspheric design with a +2.00 diopter bifocal addition (CooperVision). They found no difference in high-illumination, high-contrast vision with multifocal contact lenses compared to spectacle correction; however, patient-reported measures of lens performance were lower with multifocal contact lenses.³⁶ Kang and Wildsoet reported that the Proclear D multifocal with bifocal additions of +1.50 and +3.00 diopters did little to reduce visual acuity in young adult myopes.⁴³ The DIMENZ study reported that children wearing a center-distance, concentric-ring multifocal contact lens design with a +2.00 diopter bifocal addition had no difference in distance visual acuity or contrast sensitivity.²¹

Compared to other reports, our findings were consistent with the vision obtained with the Biofinity D multifocal. The BLINK Study found no difference in best-corrected, high-contrast acuity after contact lens over-refraction with the Biofinity D +2.50D add lens compared to spectacles; however, their average over-refraction was higher (average –0.50 to –0.75D) than that observed in our study. ²⁹ Gong et al. found that the +2.50 diopter add Biofinity D multifocal caused an approximate 1-line reduction in acuity under high- and low-illumination conditions compared to single vision contact lenses.⁴² Our findings with the NaturalVue multifocal suggest that the extended depth of focus design provides vision comparable with reported vision for center-distance aspheric and center-distance concentric ring designs. This is consistent with a meeting abstract reporting that a prototype myopia control lens similar to the NaturalVue multifocal provided subjective vision similar to that provided by spherical optics (Miller J, et al. Optom Vis Sci 2011;88:E-Abstract 115896.).

Potential limitations of the study include that the age of the patient population, 21 to 29 years old, does not reflect the age patients will be fit for myopia control in clinical practice. Additionally, the study was a non-dispensing assessment of vision, and visual quality at the fitting visit may over, or underestimate final visual performance with multifocal lenses.^30,31,34 One other potential limitation of the study is that accommodation and phoria status were not evaluated during the reading performance task. While there are reports that multifocal contact lenses affect accommodation and phoria status in non-presbyopes, others have indicated that dual focus lenses do not prevent children from accommodating for near tasks.^21,42 It remains unclear how these changes may affect reading speed. Because reading speed in our study was reduced regardless of font size, the observed reduction may not be due to a change in the binocular status of the subjects and could represent the impact of multifocal optical profiles on functional near performance.

The use of multifocal contact lenses for myopia control is projected to increase as health care providers recognize the potential health implications of unchecked myopia. We found that multifocal contact lenses achieved vision that is slightly reduced compared to single vision contact lenses; however, the different optical profiles of the two multifocal lenses provide similar vision across test conditions. Multifocal contact lenses may impact reading performance in non-presbyopic patients, and this reduction does not appear to be font size dependent. Based on our observations, it is important that practitioners fitting these lenses recognize that high-contrast acuity alone does not fully describe the effect of multifocal contact lenses on visual performance. When discussing the risks and benefit of multifocal contact lenses for myopia control, eye care practitioners should educate parents and patients on the potential visual impact of these lenses to ensure informed decision making before initiating treatment.