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Institute of Optics, Spanish National Research Council, IO-CSIC, Madrid, SpainWellman Center for Photomedicine, Massachusetts General Hospital. Harvard Medical School, United States
Institute of Optics, Spanish National Research Council, IO-CSIC, Madrid, SpainCenter for Visual Science, The Institute of Optics, Flaum Eye Institute, University of Rochester, NY, United States
The purpose of this study is to compare the binocular visual perception of participants wearing multifocal contact lenses and these same lens designs viewed through a temporal multiplexing visual simulator.
Methods
Visual performance and perceived visual quality at various distances were obtained in 37 participants wearing soft M−CLs and through the SimVis Gekko programmed with the same lenses. In a pilot study (n = 10) visual performance was measured in terms of LogMAR visual acuity (VA) at far (4 m), intermediate (64 cm) and near (40 cm) distances and through-focus VA (TFVA) curves with the simulated M−CLs. In the follow-up study (n = 27), LogMAR VA at far, intermediate and near distances were measured both with the actual and simulated M−CLs. Perceived visual quality was measured in both studies using the Multifocal Acceptance Score (MAS-2EV), and a Participants Reported Outcomes Vision questionnaire. Differences between the metrics obtained with simulated and actual lenses were obtained.
Results
Both actual and simulated M−CLs increased depth-of-focus by a similar amount. Mean LogMAR VA differences with actual and simulated M−CLs ranged between 4 and 6 letters (0.08 ± 0.01, 0.12 ± 0.01 and 0.10 ± 0.01, for far, intermediate and near distances, respectively). MAS-2EV average score differences with actual and simulated M−CLs ranged between −1.00 and + 4.25. Average MAS-2EV scores were not correlated significantly with VA. However, MAS-2EV (average and individual scores) were highly correlated to visual quality questionnaire responses (p < 0.005).
Conclusions
A simultaneous vision simulator accurately represented vision with M−CLs both VA at various distances and perceived visual quality, as measured in a clinical setting. The MAS-2EV metric accurately captured participant reported outcomes of standard vision questionnaires. The combination of SimVis Gekko and MAS-2EV has the potential to largely reduce chair time in M−CLs fitting.
Presbyopia is caused by the age-related stiffening of the crystalline lens preventing it from dynamically changing focus. With the progressive aging of the world’s population in the last decades, the prevalence of presbyopia is estimated to increase from 1.2 billion in 2010 to 1.8 billion in 2050 [
], and it has been reported that the prevalence of presbyopic CL wearers has increased from 16% in 2011 to 25–35% in 2019. Although there are many forms of corrections such as spectacles over CLs, monovision, and multifocal contact lenses (M−CLs), the penetration of M−CLs remains low 8–16% [
], where the far and near images are superimposed on the retina, aiming to provide concurrent clear vision at multiple viewing distances. The superimposition of blurred and focused images causes a compromise, as it decreases the retinal image contrast and increases glare and halos [
]. In general, the interaction of the ocular optics and pupil size with the lens design, as well as the subjects neural processing, all play a role on the perceived visual quality and achieved visual performance with M−CLs [
]. While it has been reported that high patient satisfaction can be achieved with M−CLs (for example, when M−CLs are fitted, they are prescribed 3.6 times more than monovision lenses [
]), fitting M−CLs generally requires a strong time commitment from the doctor and patient. Generally, selection of the distance and addition power is performed over a three-day (or longer) period [
]. Some practitioners do not offer the M−CL option to their patients, discouraged by the presumable compromise of visual quality experienced by patients [
], there is a general consensus that a successful M−CL fit is ultimately highly dependent on the patient’s individual optics and visual tolerance. A device that ultimately enables rapid screening of patients that are suitable for M−CL presbyopic correction and accelerates the selection and optimization process should be highly advantageous in the M−CL clinical practice. A non-invasive binocular visual simulator that provides the patient with a realistic experience of a presbyopic correction without putting lenses on eye would allow evaluating vision with different lens designs (even not physically available), fast comparison between lenses, and quick identification of the needed near add and the optimal binocular combination.
Visual simulators, initially developed in research laboratories, allow vision tests to be performed through manipulated optics, for example, mimicking multifocal lens designs [
]. Most visual simulators are based on adaptive optics (AO) active elements (deformable mirrors or spatial light modulators) where a phase pattern representing a given lens is mapped and projected onto the subject’s pupil. An alternative to AO-based visual simulators are the simultaneous vision simulators based on the principle of temporal multiplexing (Sim + Vis technology™), where the phase profile of a lens is converted into a temporal pattern that drives optical power changes of a tunable lens at high speed [
Simultaneous vision simulators (SimVis) have been evaluated in previous studies. One study incorporated a monocular on-bench SimVis channel into a multi-channel AO visual simulator, and cross-validated for simulation of commercial multifocal IOLs (M−IOLs), against a simulator based on a spatial-light-modulator and the physical lens placed in a cuvette[
], the same monocular on-bench Sim + Vis technology™ was used to represent M−CLs (center-near aspheric designs, of low, medium and high adds) and through-focus quality was measured in subjects with actual and simulated M−CLs. Both, through focus optical (on bench and in vivo) and visual (in vivo) quality measurements captured the expected extended depth of focus with increasing add. Monocular through-focus curves with the monocular on-bench simulated and the actual M−CLs on eye showed significant similarity, demonstrating that monocular on-bench Sim + Vis technology™ captured the through-focus optical and visual performance of the M−CL in most of the subjects.
An advantage of the Sim + Vis technology™ simulations over other approaches are their see-through nature, which has allowed the development of a compact binocular instrument, suitable for tests in the clinic. The SimVis Gekko™ (2EyesVision, Madrid) is a see-through, wearable and programmable binocular simultaneous vision simulator, with a wide field of view (>20 deg) [
]. The SimVis Gekko has been evaluated in patients prior to intraocular lens surgery with diffractive M−IOL, comparing their pre-operative simulated through-focus visual acuity to their post-operative through-focus acuity with the implanted IOLs [
]. CLs simulation follows similar processes to an IOL simulation. An advantage of studies involving CLs is the possibility for the same patient to test different designs both through the simulator and with the CL on eye, while with M−IOLs a direct comparison with the simulator pre-operatively and the corresponding implanted IOL post-operatively can be done only for one design. Besides, with CLs other factors beyond optical design that may affect performance may involve CL decentration and conformity.
A visual quality metric recently introduced and validated, the Multifocal Acceptance Score to Evaluate Vision (MAS-2EV) [
], assesses perceived quality of natural scenes at day, night, near and far (as well as near stereovision) through multifocal optics. In an earlier publication, the MAS-2EV was utilized to compare perceived visual quality, and the visual benefit across different presbyopic corrections (binocular bifocal lenses, monovision and modified monovision) administered with CLs or with the SimVis Gekko [
In this paper, SimVis Gekko is used to simulate binocular presbyopic correction with M−CLs. Visual performance and perceived visual quality were assessed with M−CLs placed on eye. Both sets of measurements were performed in a clinical environment. M−CLs were fitted in participants according to the manufacturer fitting guidelines. Conversely, the M−CLs were programed in SimVis Gekko, following prior validations on bench and in participants in an AO system, presented earlier [
]. Comparisons of actual and simulated lenses were performed using visual acuity (high-contrast), the MAS-2EV metric, and participant reported visual quality questionnaires.
2. Methods
Through-focus visual acuity curves (TFVA), visual acuity (VA) at different distances, perceived visual quality (MAS-2EV metric[
]) were performed on participants with the SimVis Gekko simulating commercial M−CLs (1-Day ACUVUE® Moist Brand Multifocal, Johnson & Johnson Vision Care, Jacksonville, FL, USA) and the actual lenses on eye.
In a pilot study, TFVA curves were measured with simulated lenses in SimVis Gekko. The purpose of this study was to characterize the full TFVA curves with the M−CLs and evaluate the agreement between MAS-2EV and ProVision questionnaire. In a follow-up study, VA at far (4 m), intermediate (64 cm) and near distance (40 cm), MAS-2EV scores and ProVision Questionnaire responses were obtained with the actual M−CLs and the M−CLs represented in the SimVis Gekko. The measurements were obtained in two different sessions on different days, in a random order (SimVis Gekko or M−CLs in the first session). Unless otherwise noted, the tests were done binocularly.
2.1 Participants
Ten participants participated in the pilot study (age: 53 ± 4 years; spherical error: −0.19 ± 2.15 D; astigmatism ≤ 0.75 D) using SimVis Gekko only and 27 additional participants participated in the follow-up study (age: 52 ± 7 years; spherical error: −0.74 ± 2.49 D; astigmatism < 0.75 D), in two different visits separated by a week (7 ± 1 days) randomly assigned (in one visit the participant was measured with the SimVis Gekko, and in another visit with the M−CLs on eye). None of the participants participated in both studies. All participants had good ocular health, except for their refractive errors. Inclusion criteria for the study were: age ranging between 40 and 70 years old; distance spherical equivalent refraction in the range of + 4.00 D to −6.00 D in each eye; cylinder ≤ 0.75 D; required add power between + 0.75 D to + 2.50 D; and best corrected visual acuity of 20/20-3 or better in each eye. Natural binocular vision was tested using a 4-dot Worth test to discard fusion dysfunction, which was an exclusion criterion. Eye dominance was determined by the + 1.00 D blur test.
Table 1. shows the demographic and refractive profiles of the participants, along with the tested lenses in each participant. The optical power for the M−CLs and SimVis Gekko was selected based upon initial selection recommended by the 1-Day Acuvue Moist Multifocal fitting guide [
Table 1Sample’s profile, with their participant ID, age (years old), gender (F: female, M: male), spherical equivalent (Sph. Equiv.) for the right (OD) and left (OS) eye, the addition (add) needed for 1-Day Acuvue Moist Multifocal lenses and the ocular dominance.
The measurements in the pilot study were performed at the Visual Optics and Biophotonics Lab (Consejo Superior de Investigaciones Cientificas, CSIC). The measurements of the follow-up study were performed in Centro Boston de Optometría (Madrid), by two experienced optometrists. The protocol and experiments of both studies conformed to the tenets of the Declaration of Helsinki, with protocols approved by CSIC Ethics Committee. The participants signed an informed consent after receiving an explanation of the nature and implications of the study.
2.2 Multifocal contact lenses (M−CLs)
The M−CLs used in this work were 1-Day ACUVUE® Moist Brand Multifocal (Johnson & Johnson Vision Care, Jacksonville, FL, USA). The lenses are Etafilcon A, center-near aspheric with a hybrid back curve design with standard geometry parameters (Base Curve: 8.4 mm, Total diameter: 14.3 mm) and are daily disposable. Distance power ranged from −6.00 to + 4.00 diopters, in 0.25 D steps, with three different add powers: low, +1.25 D; medium, +1.75 D and high, +2.50 D. Further details on the theoretical and real lenses profiles can be found in a previous publication [
]. The baseline far refraction was performed following the standard optometric practice, with a fogging technique, obtaining the maximum monocular plus acceptable to achieve the best VA. Then, the near addition was measured at near distance (40 cm). The optical power of the multifocal lenses was based on the spherical equivalent refraction (vertex corrected if over −4.00D) and add power was chosen for both eyes. If the add was between + 0.75 to + 1.25, the selected lenses were low add in both eyes; in the add was + 1.50 or + 1.75 medium add lenses were selected for both eyes; however, if the patient had an addition between + 2.00 to + 2.50, a high addition lens was selected for the non-dominant eye while the dominant eye was fitted with a medium addition lens. No refraction enhancement over the selected base power was performed. Participants were examined under the slit-lamp before and after measurements, to check for their eligibility and to confirm no effect of lens wear during the study. A lens settling time of 10 min was allowed before measurements. Evaluation of the lens centration on the cornea, primary gaze movement, up-gaze movement, and tightness was carried out following routine standard practice [
] was used in this study to simulate non-invasively the corresponding M−CLs (1-Day Moist; Low, Medium and High add) for a 4-mm pupil diameter. Multifocality is simulated by the principle of temporal multiplexing, whereby a tunable lens driven at high speed through a custom electronic driver, reproduces the power profile of the multifocal lens, providing a static appearance of the multifocal images on the retina. Previous publications [
] describe in detail the principle of operation, calibration and compensation of dynamic effects of the tunable lenses to accurately reproduce the through-focus performance of a lens. Also, in a previous publication [
] it is showed the temporal profile for the simulated 1-Day Moist M−CLs in the Sim + Vis Technology, it was validated it on bench as well as reported measurements of VA in presbyopic participants using the Sim + Vis technology incorporated in a channel in an AO System.
A high-speed focimeter is used to calibrate the SimVis Gekko device, measuring the optical power ranging, at least, from –1 D to 4 D. The dynamic response of the tunable lenses was also characterized in that the dioptric range to produce an optimal simulation of the M−CLs [
]. The calibration of the optical power was checked weekly by measuring the position of the distance and near foci of the high add M−CL, which showed variations of 0.14 D on average (and never higher than 0.25 D). No recalibration of the SimVis Gekko was performed during the study.
The SimVis Gekko is provided with dedicated mounts for trial lenses, which are used to compensate for the participant’s refraction (therefore the SimVis Gekko was only used to simulate the multifocal component of the M−CL) and to obtain TFVA curves. Also, the system is provided with LEDs (which can be switched on from the controlling iPad) to assist in the alignment of the optical modules with the participant’s eyes. The SimVis Gekko is operated wirelessly from an iPad (Apple Inc.), which allows selection of the pre-programmed M−CLs for each eye.
2.4 Visual acuity (VA) measurements
ETDRS 2000 series high contrast retro-illuminated charts at a distance of 4 m from the participants were used to measure the baseline VA of participants (to check their inclusion criteria), VA in TFVA curves measurements (pilot study) and to measure VA at far in both studies.
LogMAR VA was measured in the pilot study for different vergences, changed by placing with trial lenses in a dedicated slot in the SimVis Gekko. Vergences ranged from −4.50 D to + 2.00 D in 0.50 D steps [
]. Measurements were performed binocularly. Three different charts were interchanged during measurements to avoid learning effects. LogMAR VA corresponding to the minimum legible letter was recorded for far, intermediate and near distance with the multifocal lenses (both actual and simulated).
Chart luminance and room illumination were controlled and checked before each measurement using a L-858D-U Light Meter (Sekonic Corporation, Japan). Far ETDRS chart luminance was kept between 181 – 208 cd/m2 and near charts luminance was kept between 222 to 275 cd/m2 and the room illuminance between 394 and 597 lx.
2.5 mAS-2EVTM
The Multifocal Acceptance Score to Evaluate Vision (MAS-2EVTM) is a metric that was recently presented and validated to evaluate global quality of vision [
]. The metric comprises five perceptual scores (PS) of multi-stimuli images of day and night scenes, at far (4 m) and near (40 cm) distance, and a stereovision target at near. The participant gives perceptual scores [
] represent four different daily-life visual activity areas (Fig. 1.B): far-day, far-night, near-day, and near-night. The far-day scenes stimuli include a face, a street scene and a poster; the far-night set, representing urban scenes at night, including a car with the lights on (a pair of bright white LEDs is superimposed to the image to more closely mimic a glaring source), and a readable license plate, a ballet show and a night street. The near images include reading text, cell phone screens in day and night modes, and a car dashboard. The stimuli of MAS-2EV were displayed on a standard monitor screen of 42″ for far distance (4 m), and on standard iPad screen of 9.8″ at near distance (40 cm). For far distance, the brightness of the displays was not changed between day and night conditions. For near distance, the brightness of the iPad was changed, for day condition it was at the maximum level (218.07 ± 0.62 cd/m2) and for night condition was at the minimum (1.99 ± 0.006 cd/m2).
Fig. 1ProVision questions (A) with the positive (green) and negative questions (black) and MAS-2EV images (B) from top to bottom: Far-Day; Far-Night; Near-Day and Near-Night.
Additionally, near stereo-acuity was measured at 40 cm. Random-dot anaglyphs (observed through cyan/red glasses) with seven in-depth Snellen-E letters were presented with different orientations and different crossed disparities, ranging from 400 to 50 arcsec. Stereo-acuity was converted to a 0 (disparities above or equal to 400 arcsec) to 10 (disparity of 50 arcsec) scale.
The sequence of MAS-2EV measurements were near stereopsis, far and near daylight scoring, 4 min of dark adaptation, far and near night scoring.
MAS-2EV was measured after measuring the VA with the actual and simulated-MCLs, while the patient was seeing through the multifocal correction.
2.6 ProVision questionnaire
The CLUE™ questionnaire, also referred as Patient Reported Outcomes Vision (ProVision) questionnaire, is a validated questionnaire developed by Johnson & Johnson [
] to assess patient satisfaction with contact lenses. In this study, we used a subset of twenty-two questions of the CLUETM questionnaire addressing quality of vision (and not other domains of CLUETM such as comfort and handling. Participants completed the questionnaire after removal of M−CLs fitting or SimVis Gekko, at the end of each session.
Figure 1.A shows the 22 questions (left column), where questions in green were classified for this study as positive (scored between 1 and 5) and questions in black are classified as negative (scored from −1 to −5). There are five different possible answers: Strongly Disagree; Disagree; Neither agree nor disagree; Agree; Strongly Agree. Questions that were answered as “Not applicable” were not quantified. For this study, the overall ProVision questionnaire response (from weighted individual responses) can range from + 50 (if all positive questions were scored as + 5 and negative questions as −1) to −38 (if all positive questions were scored as + 1 and negative questions as −5).
The ProVision questionnaire was completed after removal of M−CLs/SimVis Gekko, as per protocols described above.
2.7 Data analysis
The pilot study involved measurements of TFVA, and the depth of focus (DOF) was defined as the dioptric range of the TFVA curve for which participant’s VA was 0.2 logMAR [
LogMAR VA at far (4 m), intermediate (64 cm) and near (40 cm) was measured both with SimVisGekko and with the actual M−CLs. Comparisons between simulated and actual M−CLs were performed in terms of logMAR differences (95% confidence intervals and 2-way ANOVA).
MAS-2EV is graphically represented as a polygon, with the Perceptual Scores (PS) in each vertex: the measured stereopsis (upper vertex) and the four PS measured for far-day, far-night, near-day, and near-night. The geometrical center of the polygon corresponds to score 0 and the maximum separation of the vertex to score 10. A metric of the overall visual quality with a specific correction is given by the unweighted average (MAS-2EV Modulus) of the five vertices.
MAS-2EV modulus was calculated from scores obtained with the actual and SimVis Gekko-simulated M−CLs. The ProVision questionnaire mean scores were also calculated for responses obtained with the actual and SimVis Gekko-simulated M−CLs. Differences between scores obtained with simulated and M−CLs were calculated, and the statistical significance of the differences were obtained using paired-sample-ttest (p < 0.05 significance level).
Spearman correlations were analyzed between VA at far and near distance and MAS-2EV mean PS for far and near (averaged for day and night), both for CLs and SimVis Gekko. Spearman correlations between MAS-2EV and ProVision questionnaires were analyzed for average scores, as well as for far, near, night and day specific questions. The statistical significance of the linear correlation was tested using the Spearman correlation coefficient (p < 0.05 significancy level).
3. Results
3.1 TFVA curves with SimVis Gekko-simulated M−CLs
Fig. 2 shows the TFVA and VA results for all ten participants, for patients with low medium and medium + high add contact lenses in upper, middle and bottom row, respectively. The DOF is indicated by the area under the curve above the dotted line and the isolated gray symbols. The graphs also logMAR VA measured at intermediate and near measured placing the target at different physical distances: far (4 m = 0D, diamond), intermediate (64 cm = -1.50 D, square) and near (40 cm = -2.50 D, triangle). On average across participants, the VA difference measured with the targets at a given distance or by vergence change (TFVA measurement) was −0.03 ± 0.04, 0.03 ± 0.01, 0.00 ± 0.00 logMAR at far distance, 0.04 ± 0.14, 0.03 ± 0.10, 0.02 ± 0.00 logMAR for intermediate and −0.08 ± 0.16, −0.01 ± 0.14, −0.05 ± 0.05 logMAR for near distance, for low, medium and medium + high add lenses simulation respectively. A 2-way ANOVA analysis indicated that the differences were not statistical influenced by the lens type (p = 0.60) nor the distance (p = 0.22).
Fig. 2TFVA and VA measurements obtained with the SimVis Gekko simulating M−CLs: upper row, low add in both eyes; middle row, medium add in both eyes; bottom row, medium add in dominant eye and high add in non-dominant eye. The solid lines (and same-colored circles) represent logMAR measurements performed with vergence induced with trial lenses. The isolated diamonds represent the VA measured at far (4 m), intermediate 64 cm) and near (40 cm) distances. The dashed horizontal black lines represent logMAR VA = 0.2. Depth of focus (DOF), defined as the dioptric range for which VA is above this line, is indicated by the value on the right above the line (in D).
The TFVA curves for low add lenses show a single peak centered between + 0.50 D and −0.50 D, while the medium add and medium + high add lenses generally produce two differentiated peaks, with the far focus centered between −0.50D and 0.00D, and the intermediate/near peak icentered between −1.50 and −2.00 for medium add, and between −2.00 and −2.50 D in medium add + high add lenses. VA at the best focus was above 0.00 logMAR VA in all cases, except for S#6 and S#8 with medium add lenses.
DOF was on average 2.33 ± 0.29 D for the low add, 2.00 ± 0.00 D for the medium add and 2.83 ± 0.29 D for the medium + high add. Participant S008 was excluded from the average, as the entire range was below 0.2 logMAR VA.
3.2 VA with actual M−CLs vs. SimVis Gekko-simulated M−CLs
Fig. 3 shows some representative examples and the mean across participants of binocular VA at far, intermediate and near distance, with SimVis Gekko simulated lenses (orange asterisks) and actual M−CLs (blue circles). In general, there is a similar variation of VA with distance with simulated and actual M−CLs, with some participants showing a very close match in absolute values (i.e. S#14, S#21 and S#34).
Fig. 3Some participant’s examples and mean across participants for the binocular logMAR VA measurements with SimVis Gekko (orange asterisks) and M−CLs (blue circles) at far, intermediate and near distance.
On average, the VA achieved with the simulated-CLs were −0.08 ± 0.10 at far distance, 0.06 ± 0.06 at intermediate distance and 0.12 ± 0.06 at near distance. The VA values obtained with the fitted CLs were −0.13 ± 0.07 at far distance, −0.06 ± 0.08 at intermediate distance and 0.03 ± 0.07 at near distance. The average logMAR VA difference between the simulated and the actual MCLs was: for far distance, 0.07 ± 0.01, 0.07 ± 0.01 and 0.04 ± 0.08 for the low, medium and medium + high add respectively; for intermediate distance, 0.15 ± 0.03, 0.08 ± 0.01 and 0.10 ± 0.01 for the low, medium and medium + high add respectively; for near distance, 0.09 ± 0.00, 0.09 ± 0.03 and 0.07 ± 0.00 for the low, medium and medium + high add lenses, respectively.
Mean logMAR VA difference between M−CLs and SimVis Gekko was estimated with the 95% confidence intervals (Table 2) for all participants. Mean VA difference (simulated - actual) was 0.08 ± 0.01 logMAR VA for far, 0.12 ± 0.01 logMAR VA for intermediate and 0.1 ± 0.01 logMAR VA for near distance, averaged across participants. Although these VA differences were not statistically significant (2-way ANOVA) influenced by the lens design (p = 0.37) nor the distance (p = 0.11), performance with simulated lenses tended to mimic the salient features of performance measured with M−CLs. Namely, VA was better at distance than at intermediate and acuity was better at intermediate than at near.
Table 2Mean Estimates and 95% Confidence Intervals for Binocular, High Luminance, High Contrast - logMAR Visual Acuity, StdError: standard error, Conf.Li.: confidence limits.
3.3 MAS-2EV and ProVision questionnaire with SimVis Gekko-simulated M−CLs (Pilot Study)
Overall ProVision questionnaire scores were 22.67 ± 8.62 with the low add lenses, 14.74 ± 4.99 with the medium add lenses, and 14.33 ± 17.56 with medium + high add lenses (ProVision questionnaire scale from + 50 to −38).
Fig. 4 shows the MAS-2EV polygons for all participants. Simulated low add M−CLs show relatively higher scores at distance (8.67 ± 0.82 PS, averaged across participants), and lower scores at near (2.07 ± 2.07 PS), consistent with an almost monofocal performance. Conversely, scores at near increase with medium (6.63 ± 1.60 PS) and medium + high add (5.83 ± 1.47 PS) simulated M−CLs, at the expense of reducing the score at far (8.38 ± 1.19 PS and 6.67 ± 1.75 PS, respectively).
Fig. 4MAS-2EV metric responses for all participants with the with the SimVis Gekko-simulated M−CLs: participants with low add lenses (4A, in black), with medium add lenses (4B, in green) and with medium and high add lenses (4C, in pink).
3.4 MAS-2EV with actual M−CLs vs SimVis Gekko-simulated M−CLs
Fig. 5 shows some examples of the MAS-2EV polygons both with actual M−CLs (in blue) and SimVis Gekko-simulated M−CLs (in orange). In some participants MAS-2EV polygons with simulated lenses differed from those with actual lenses (S020, S021; S022 or S035, with a maximum intra-participant MAS-2EV Modulus difference of 3.40 ± 2.19), while in other participants there was a close match (S016, S017 or S031, with a minimum MAS-2EV Modulus difference of 0.00 ± 1.00). S013 and S024 showed the same polygon shape with actual and simulated lenses, but different size.
Fig. 5Some examples for the binocular MAS-2EV polygons measured with SimVis Gekko (orange) and M−CLs (blue) for the low add lenses (low), medium add lenses (mid), and the combination of the medium and high add lenses (mid + high).
Fig. 6 shows the MAS-2EV Modulus (excluding stereovision) for all measured participants, with the actual (blue) and the simulated M−CLs (orange) grouped by lens add. Standard deviations across day/night/near/far scores are represented.
Fig. 6Average perceptual score (all scores from MAS-2EV excluding stereovision) in all participants, with M−CLs (blue) and simulated lenses (orange). Standard deviations are represented as black lines. Across subject average ± std for each of the three lens types: 8.25 ± 0.99 for actual M−CLs and 8.29 ± 1.01 for simulated M−CLs, for the low add; 7.37 ± 1.18 for actual M−CLs and 5.77 ± 1.37 for simulated M−CLs, for the medium add; and 7.38 ± 1.62 for actual M−CLs and 6.31 ± 1.05 for simulated M−CLs, for the medium + high add.
The average PS for MAS-2EV with actual and simulated low add M−CLs were not statistically significantly different (8.25 ± 0.99 and 8.29 ± 1.01, respectively; p = 0.91; paired-sample t-test). Higher add lenses produced lower average PS, with PS scores higher for actual M−CLs than for the simulated M−CLs: avg PS 8.25 ± 0.99 for actual M−CLs and 8.29 ± 1.01 for simulated M−CLs, for the low add, avg PS 7.37 ± 1.18 for actual M−CLs and 5.77 ± 1.37 for simulated M−CLs, for the medium add (statistically significantly different, p < 0.001), and avg PS 7.38 ± 1.62 for actual M−CLs and 6.31 ± 1.05 for simulated M−CLs, for the medium + high add (not statistically different, p = 0.1). PSs are consistently lower for night than for day for all lens designs, both for actual M−CLs (10.50% lower) and simulated M−CLs (4.60% lower). However, the discrepancy between actual and simulated M−CLs is highest for day conditions (PS scores are 8.13 ± 0.96 PS for actual M−CLs and 6.69 ± 1.66 PS for simulated M−CLs).
There was a significant positive correlation of the metric between the actual M−CL and the SimVis Gekko simulator across all conditions and participants (p = 0.03; r = 0.43, Spearman) within confidence intervals of ± 2.80PS out of a 0–10 scale (Bland-Altman). An 81.48% of participants report a MAS-2EV score with the simulated M−CLs that is within 2 PS of the MAS-2EV score1 with actual M−CLs and a 62.96% within 1 PS.
3.5 ProVision questionnaire with actual M−CLs vs SimVis Gekko-simulated M−CLs
ProVision questionnaire (ranged from + 50 to −38) average scores are represented in Fig. 7 for all participants (organized by lens type) comparing actual M−CLs (blue bars) with simulated M−CLs (orange bars). Except for a few exceptions (i.e., S20, S32, S33, S15, S22) there was a very good correspondence between the ProVision scores with actual M−CLs and with simulated M−CLs (2–17 minimum to maximum points of difference). When discrepancies occur, in the ProVision questionnaire there was no bias towards actual or simulated M−CLs.
Fig. 7ProVision questionnaire responses for all participants, organized by lens simulation, wearing M−CLs (blue) and SimVis Gekko (orange).
On average, both actual and simulated M−CLs showed the same trends. There was a better ProVision overall perception with the low add lens (25.67 ± 10.42 PS for M−CLs, 22.83 ± 13.56 PS for simulated M−CLs), than with the medium lens (16.92 ± 16.04 PS for M−CLs, 10.46 ± 10.60 PS for simulated M−CLs) or with the medium + high add lenses (8.63 ± 16.95 PS for the actual M−CLs, 15.00 ± 15.74 PS for simulated M−CLs).
For the vision questionnaire responses, there was no statistically significant differences between actual and simulated lenses for neither add (p = 0.33 for low add; p = 0.19, for medium add; p = 0.44, medium + high add). 81.48% of participants report ProVision score with simulated M−CLs that is within 17.6 PS (equivalent to 2 PS in the MAS-2EV scale) of the ProVision score with actual M−CLs, the same percentage of participants as in the MAS-2EV metric. 51.85% of participants report a difference within an 8.8 PS (equivalent to 1 PS in the MAS-2EV scale).
3.6 Correlations between VA and MAS-2EV
The standard method to assess vision with M−CLs is the measurement of high contrast VA, even if VA is a limited descriptor of the quality of vision. In contrast, MAS-2EV is a subjective metric to measure participant’s perceived visual quality. Fig. 8 shows the measured logMAR VA versus the subjective scores obtained with MAS-2EV, for far (spots) and near distance (triangles), both with the actual M−CLs (blue) and simulated M−CLs (orange), including all measured participants (pilot and full studies). LogMAR VA and MAS-2EV scores were not correlated at far vision for neither actual M−CLs (p = 0.47 r = -0.15; Spearman) or simulated M−CLs (p = 0.84 r = -0.03; Spearman), nor at near vision with M−CLs (p = 0.06 r = -0.36; Spearman) but it was significantly correlated at near vision with simulated M−CLs (p = 0.04 r = -0.34; Spearman).
Fig. 8Measured logMAR VA, represented in Y axis, versus the score recorded with the MAS-2EV metric, in the X axis, for all participants (pilot and follow-up study) at far distance (spots) and near distance (triangles) measured with the actual M−CLs (blue) and its simulation (orange) with their correlation.
3.7 MAS-2EV and ProVision questionnaire correlations
Fig. 9 shows correspondences between MAS-2EV scores and ProVision questionnaire scores including all measured participants (pilot and full studies). MAS-2EV Modulus and ProVision questionnaire average score for all participants was highly correlated (p = 0.0023 r = 0.5625, Spearman, for actual M−CLs in blue; p = 0.0135 r = 0.4079, Spearman, for simulated M−CLs in orange).
Fig. 9ProVision questionnaire scores and MAS-2EV metric perceptual scores for all participants, with actual M−CLs (blue) and simulated M−CLs (orange).
ProVision questionnaire scores related with far distance vision (Fig. 10.A) were highly correlated with the mean MAS-2EV scores for far distance for day and night conditions (M−CL p = 0.0074 r = 0.5124; simulated M−CLs p = 0.0001 r = 0.6137). ProVision questionnaire scores related with near distance vision (Fig. 10.B) were highly correlated with the mean MAS-2EV scores for near distance (M−CL p = 0.0063 r = 0.5211; simulated M−CLs p = 0.0025 r = 0.4879) for far distance for day and night conditions. ProVision questionnaire scores related with night vision (Fig. 10.C) were highly correlated with the mean MAS-2EV scores for night vision at near and far (M−CL p = 0.0005 r = 0.6336; simulated M−CLs p = 0.0077 r = 0.4367).
Fig. 10ProVision questions correlated with the perceptual score of the MAS-2EV metric for far distance (A), near distance (B) and nighttime condition (C), both with actual M−CLs (blue) and simulated M−CLs (orange); **p < 0.005; ***p < 0.0005.
Multifocal contact lenses (M−CLs) are increasingly used for presbyopia correction. Selecting the optimal correction can be a challenging procedure and may entail long chair time and trial and error. Simultaneous visual simulators that allow patients to experience vision with different multifocal designs without the need for lens insertion could reduce the number of lenses tested on eye and therefore facilitate M−CL prescription.
This study investigated the accuracy of representation of M−CL designs in a binocular simultaneous vision simulator (SimVis Gekko, 2EyesVision) comparing visual perception and performance in patients with the simulated and the actual M−CLs on. VA measurements at different distances, MAS-2EV metric and a standard questionnaire were performed, and the differences in these metrics measured with the simulated or the real lens were analyzed.
4.1 Performance of actual M−CLs
Previous studies have investigated the same rotationally symmetric center near M−CLs used in the current study (1-day Acuvue Moist, Johnson & Johnson). A study measuring visual performance of the lens on eye after one week of wear in 57 presbyopic patients [
] analyzed the visual performance on 275 patients after ten days of wearing the M−CLs and reported logMAR VA values of − 0.09 ± 0.1, −0.07 ± 0.08 and 0.04 ± 0.10 for far, intermediate and near distance respectively. The VA results obtained in this study (-0.13 ± 0.07 at far, −0.06 ± 0.08 at intermediate and 0.03 ± 0.07 at near distance) compare well with the VA range of previous literature.
As in previous studies, it was found the highest DOF with the higher add. This effect of the M−CLs depth-of-focus (DOF) expansion with increasing near addition was observed in previous studies with presbyopic and young subjects with paralyzed accommodation. However, DOF values (Fig. 2) were slightly higher than those reported in previous studies. Potential reasons for the higher DOF could be the presence of some residual accommodation (as the participants with low add lenses, i.e., the younger group, presented a higher-than-expected DOF at baseline), and the effect of higher order aberrations. Unlike Vedhakrishnan et al [
] studies, the current study was performed binocularly. Binocular measurements could, on the one hand, stimulate residual accommodation as the system allowed for convergence and pupil constriction [
]. The pupil diameter was not measured in this study, and it could play and important role both in the relative effect of the eye’s native aberration on the performance of the M−CLs and on convergence.
4.2 mAS-2EV
Quality of vision is multifactorial. Observers experience and must operate under a wide range of visual conditions (luminance, pupil diameter, etc…) and visual scenes [
]. It is recognized that high contrast VA is a limited descriptor of the quality of vision. Besides, the complexity and unfamiliarity of multifocal vision [
] require more comprehensive evaluation methods. Traditionally quality of vision is clinically assessed through questionnaires given to the patient to report his/her comfort and performance in different situations, relying on the patient’s memory and subjective reporting. There is an ample range of visual quality questionnaires, generally adapted to specific eye conditions or treatments. The questions of the ProVision questionnaire, extracted from the CLUETM questionnaire developed by Johnson & Johnson, were selected specifically to assess vision with multifocal corrections [
] represent a range of visual situations (faces, street scenes, theater, driving, navigating a map, reading, halos at night, and stereo tasks) compatible with the ProVision questionnaire, so that the participants could respond to the questionnaire in the experimental session.
In this study we found that neither the ProVision questionnaire nor the MAS-2EV metric were statistically correlated (p > 0.05; Fig. 8) with the high contrast VA. This supports the notion that high contrast VA is a poor predictor of overall subjective image quality, as the world is rich with spatial frequency content, and many tasks are well supported by mid-range spatial frequencies, but good VA is more heavily dependent on high spatial frequencies. However, the correlation between the Provision questionnaire and the MAS-2EV metric was highly statistically significant (p < 0.05–0.0005; Fig. 1) both for actual and simulated M−CLs. This finding suggests that the MAS-2EV metric can be used as a fast and quantitative alternative to vision questionnaires, well suited for use in the clinic. Furthermore, visual questionnaires are used to collect the patient reported outcome to a certain treatment. However, when the MAS-2EV is applied in combination with the SimVis Gekko it is conceivable to anticipate the prospective performance of various possible lenses before fitting them in eye, with the potential to improve and largely reduce chair time in M−CLs fitting [
The pilot study showed that there was no systematic bias in the through-focus curves measured with defocus induced with trial lenses with respect to those measured using proximity targets. In the follow-up study M−CLs VA, MAS-2EV scores and ProVision questionnaire simulations were directly measured (with actual and simulated M−CLs) at far, intermediate and near distances. On average, the differences in VA between the simulated and the actual M−CLs were between 4 and 6 logMAR VA letters. The differences were lower for far distance (0.08 ± 0.01) than for intermediate and near (0.12 ± 0.01 and 0.10 ± 0.01, respectively).
In a previous study, M−CLs were simulated as a spatial phase pattern in an SLM, the average differences in VA between actual and simulated M−CLs were −0.01, −0.03 and −0.1, for far, intermediate and near, respectively, for a 5-mm pupil diameter [
]. The differences were negligible with a small bias towards a better performance with the SLM. Participants’ pupils were dilated, and participants performed all the measurements through an artificial 5-mm pupil. A potential reason for the lower discrepancy is the constant pupil for actual and simulated CLs. Vinas et al using SimVis in an Adaptive Optics system reported differences of 0.02, 0.04, 0.08. In that study the Sim + Vis M−CLs were programmed for 4-mm, and an artificial pupil of 4-mm allowed measurements with both actual M−CLs and Sim + Vis-simulated M−CLs to be performed with the same pupil diameter. However, the improved VA values with simulated-MCLs in this study (-0.08 at far distance, 0.06 at intermediate and 0.12 at near distance) compared to those found by Vinas et al [
] (0.14 logMAR VA at far, 0.18 at intermediate and 0.17 at near distance) could be due to binocular summation, as this measurements were done binocularly [
The observed trend of slightly better VA with M−CLs than with SimVis Gekko may be due to a range of known differences between the two. First, it should be noted that the SimVis Gekko lenses are programmed based on the theoretical M−CL power profile. There are several factors that may cause deviations from the theoretical phase/temporal pattern representation of the lenses, including CLs conformity to the cornea, contributions of the tear lens, and CL decentrations. In a center-near M−CL design, CL decentration may improve distance performance at the cost of reduced near performance.
Second, an anticipated source of difference between actual and simulated M−CL is pupil diameter. While the study was performed with natural pupils to represent a natural condition, the pupil diameter as well as its variation between light conditions, and convergence [
] is expected to vary across individuals, potentially exposing the participants with an ample range of pupil diameters in the actual CLs condition. However, the M−CLs were programmed for a fixed pupil diameter of 4 mm in all conditions. Future developments may incorporate adjusting the pupil in the SimVis Gekko or matching the programmed lens with the natural pupil diameter of the participant, in each condition.
On the other hand, participants reported a more stable vision with the simulator than with the CLs. Variability in visual performance with M−CL has been typically associated with on-eye CL movements (average range around 0.40–0.60 mm) [
]. Given the design of M−CL, on-eye CL movement alters the effective lens area for far and near, with fluctuations affecting either positively or negatively visual performance during the visual task [
], the methodology used in the current study with clinical eyecharts does not limit the time allowed to perform the task. Shifts in CL centration during the letter reading task may allow participants to improve measured VA.
In conclusion, SimVis Gekko can be used to guide the selection of presbyopic corrections, allowing the patient to experience the world with those corrections before fitting (CLs) or surgery (IOLs or presbylasik). The use of the MAS-2EV metric in combination with SimVis Gekko helps to reduce chair time in CL fitting as well as to reduce uncertainties in IOL or presbyopic surgeries.
Funding
This research has received funding from the European Research Council under the IMCUSTOMEYE Ref. 779,960 H2020 - EU.2.1.1. Industrial Leadership to SM; SILK-EYE Ref. 833,106 Excellent Science – ERC to SM; and the H2020-MSCA-IF-GF-2019-MYOMICRO-893557 to MV. National Eye Institute P30 Core Grant EY001319-46 (Center for Visual Science) and Unrestricted grant Research to Prevent Blindness (Flaum Eye Institute) to SM. This research was supported also from the Spanish Government under the Spanish Government Grant FIS2017-84753-R to SM, and ISCIII DTS16/00127 to CD; Madrid Regional Government IND2017/BMD7670 to XB; and Master Clinical Research Agreement between Johnson and Johnson Vision Care (USA), 2EyesVision, Centro Boston de Optometría and IO-CISC.
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