Through-focus performance with multifocal contact lenses: effect of binocularity, pupil diameter and inherent ocular aberrations

Fourier tools for the evaluation of refractive multifocal designs

This paper presents innovative tools and methodologies for the theoretical assessment of optical properties in refractive multifocal designs. Utilizing lens segmentation techniques and classical Fourier optics, these tools can be of help evaluating multifocal contact lenses, intraocular lenses, small aperture designs, and corneal inlays. As an example of their utility, this study presents the through-focus Visual Strehl ratios in the frequency domain of 12 multifocal contact lenses from four companies, derived from the sagittal power profiles obtained with a NIMO equipment (LAMBDA-X) for three base prescriptions (- 6.00 D, - 3.00 D, and + 1.00 D). The contact lenses are also assessed alongside higher-order aberrations obtained from 65 eyes, measured using a Wavefront Sciences Complete Ophthalmic Analysis System (AMO). Diameter variations, corresponding to individual pupil sizes (2.45-6.27 mm), were considered in the evaluation. These novel tools enable the theoretical evaluation of multifocal solutions without the need for prototypes. In the case examples presented, they differentiate between lenses tailored for different presbyopic age groups, offer guidance on optimizing hyperfocal distance in contact lens design, and underscore the relevance of the effective aperture effect. Notably, this paper introduces the pioneering conversion of sagittal powers of multifocal solutions into an equivalent wavefront and optical quality metric, with potential applications in myopia control assessments. The author hopes that readers recognize and utilize these tools to advance the field of refractive multifocality.

Neural binocular summation and the effect of defocus on the pattern electroretinogram and visual evoked potentials for different pupil sizes

PURPOSE

To evaluate the influence of defocus and pupil size on subjective (visual acuity [VA]) and objective (electrophysiology) descriptors of human vision and their effect on binocular visual performance by means of neural binocular summation (BS).

METHODS

Fifteen healthy young subjects were recruited in this crossover study. Pattern electroretinogram (PERG) and visual evoked potentials (VEP) were measured under two levels of positive (+1.5 and +3.0 D) spherical and astigmatic defocus (axis 90°). Pupil size was controlled to reduce the inter-individual variability factor.

RESULTS

Low- and high-contrast VA showed poorer visual performance in the monocular versus the binocular condition. Positive BS (for VA) was higher with greater pupil size and higher levels of defocus. In the visual electrophysiology tests (i.e., VEP and PERG), peak time and amplitude were affected by pupil size and defocus. The increase in peak time was larger and the reduction in amplitude was more significant with greater levels of defocus and smaller pupil sizes. For the VEP, positive BS was found in all conditions, being stronger with larger amounts of defocus and pupil size (for the P100 amplitude). Significant negative correlations were observed between the P100 amplitude and VA BSs.

CONCLUSION

Smaller pupil size and levels of defocus produced greater changes in cortical activity as evidenced by both the PERG and VEP. Considering these changes and the obtained positive BS, the mechanism could be initiated as early as the retinal processing stage, then being modulated and enhanced along the visual pathway and within the visual cortex.

Presbyopia correction with multifocal contact lenses: Evaluation of silent reading performance using eye movements analysis

PURPOSE

Many activities of daily living rely on reading, thus is not surprising that complaints from presbyopes originate in reading difficulties rather in visual acuity. Here, the effectiveness of presbyopia correction with multifocal contact lenses (CLs) is evaluated using an eye-fixation based method of silent reading performance. ΜETHODS: Visual performance of thirty presbyopic volunteers (age: 50 ± 5 yrs) was assessed monocularly and binocularly following 15 days of wear of monthly disposable CLs (AIR OPTIX™ plus HydraGlyde™, Alcon Laboratories) with: (a) single vision (SV) lenses - uncorrected for near (b) aspheric multifocal (MF) CLs. LogMAR acuity was measured with ETDRS charts. Reading performance was evaluated using standard IReST paragraphs displayed on a screen (0.4 logMAR print size at 40 cm distance). Eye movements were monitored with an infrared eyetracker (Eye-Link II, SR Research Ltd). Data analysis included computation of reading speed, fixation duration, fixations per word and percentage of regressions.

RESULTS

Average reading speed was 250 ± 68 and 235 ± 70 wpm, binocularly and monocularly, with SV CLs, improving statistically significantly to 280 ± 67 (p = 0.002) and 260 ± 59 wpm (p = 0.01), respectively, with MF CLs. Moreover, fixation duration, fixations per word and ex-Gaussian parameter of fixation duration, μ, showed a statistically significant improvement when reading with MF CLs, with fixation duration exhibiting the stronger correlation (r = 0.79, p < 0.001) with improvement in reading speed. The correlation between improvement in VA and reading speed was moderate (r = 0.46, p = 0.016), as was the correlation between VA and any eye fixation parameter.

CONCLUSION

Average silent reading speed in a presbyopic population was found improved with MF compared to SV CL correction and was faster with binocular compared to monocular viewing: this was mainly due to the faster average fixation duration and the lower number of fixations. Evaluating reading performance using eye fixation analysis could offer a reliable outcome of functional vision in presbyopia correction.

Multifocal versus modified monovision corrections: A non-dispensing comparison of visual assessment in presbyopic neophytes

Purpose

To compare the visual performance of two simultaneous-vision soft multifocal contact lenses and to compare multifocal contact lens and its modified monovision counterpart in presbyopic neophytes.

Methods

A double-masked, prospective, comparative study was conducted on 19 participants fitted with soft PureVision2 multifocal (PVMF) and clariti multifocal (CMF) lenses in random order. High- and low-contrast distance visual acuity, near visual acuity, stereopsis, contrast sensitivity, and glare acuity were measured. The measurements were conducted using multifocal and modified monovision design with one brand and then repeated with another brand of lens.

Results

High-contrast distance visual acuity showed a significant difference between CMF (0.00 [-0.10-0.04]) and PureVision2 modified monovision (PVMMV; -0.10 [-0.14-0.00]) correction (P = 0.003) and also between CMF and clariti modified monovision (CMMV; -0.10 [-0.20-0.00]) correction (P = 0.002). Both modified monovision lenses outperformed CMF. The current study did not show any statistically significant difference between contact lens corrections for low-contrast visual acuity, near visual acuity, and contrast sensitivity (P > 0.01). Stereopsis at near distance was significantly lower with both modified monovision (PVMMV: 70 [50-85]; P = 0.007, CMMV: 70 [70-100]; P = 0.006) and with CMF (50 [40-70]; P = 0.005) when compared to spectacles (50 [30-70]). Glare acuity was significantly lower with multifocal (PVMF: 0.46 [0.40-0.50]; P = 0.001, CMF: 0.40 [0.40-0.46]; P = 0.007) compared with spectacles (0.40 [0.30-0.40]), but no significant difference was noted between the multifocal contact lenses (P = 0.033).

Conclusion

Modified monovision provided superior high-contrast vision compared to multifocal correction. Multifocal corrections performed better for stereopsis when compared to modified monovision. In parameters like low-contrast visual acuity, near acuity, and contrast sensitivity, both the corrections performed similarly. Both multifocal designs showed comparable visual performances.

Multifocal contact lens vision simulated with a clinical binocular simulator

PURPOSE

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.

Short-term delay in neural response with multifocal contact lens might start at the retinal level

INTRODUCTION

Multifocal simultaneous imaging challenges the visual system to process the multiple overlaps of focused and defocused images. Retinal image processing may be an important step in neuroadaptation to multifocal optical images. Our aims are, firstly to evaluate the short-term effect of different multifocal contact lenses (MF) on retinal activity in young healthy subjects (Experiment#1) and secondly, to evaluate any changes in retinal activity in presbyopic patients fitted with MF over a 15-day period (Experiment#2).

METHODS

In Experiment-#1, 10 emmetropic healthy young subjects were included to evaluate the short-term effect of different MFs designs. In Experiment #2, 4 presbyopic subjects were included to wear MF for 15 days. Following the ISCEV Standards, multifocal electroretinograms (mfERGs) were recorded to evaluate different retinal regions under different conditions: with single vision contact lens (SVCL) and with center-distance and center-near MF.

RESULTS

In Exp#1 the peak time of N1, P1 and N2 were found to be delayed with the MF (p ≤ 0.040). There was a significant reduction for N1 amplitude in all retinal regions (p < 0.001), while for P1 and N2 amplitudes this reduction was more significant in the peripheral regions (p < 0.005, ring 5 to 6). With center-near MF the mean response density (nV/deg²) showed a significant decrease in all wave components of the mfERGs response, particularly from Ring 3 to Ring 6 (p < 0.001, all Rings). In Exp#2, the mean mfERG response is similar between SVCL and center-distance MF, while center-near MF showed an increase in implicit time N1 and P1 on day 1 that tends to recover to baseline values after 15 days of MF wear.

CONCLUSIONS

significant changes in the mfERGs responses were found with the MF lens, being most noticeable with the center-near MF lens design. The present results suggest that the observed delay in cortical response described during the adaptation to multifocality may partially begin at the retina level.

The efficacy of multifocal soft contact lenses for the alleviation of asthenopic symptoms in myopes with accommodative lag

PURPOSE

To evaluate the efficacy of multifocal soft contact lenses to reduce asthenopic symptoms in myopes with accommodative lag.

METHODS

Twenty-four myopic participants, aged 18-35 years, with mean spherical equivalent (MSE) of ≤ -0.75D, were recruited in a randomised, double-blind crossover study. All participants were existing contact lens wearer with near orthophoria or esophoria, presenting with subjective asthenopic symptoms at baseline [Convergence Insufficiency Symptom Survey (CISS) score ≥ 21] and a lag of accommodation ≥ +0.75 D. All participants were initially fitted with single vision contact lenses for a one month period. Participants were then randomly assigned 1:1 to wear low add or high add multifocal soft contact lenses for a further month. After this period, the groups were reversed. Data were collected at baseline and following one month's wear of each lens. Change in CISS score was evaluated as the primary outcome measure, while secondary outcome measures were changes in accommodative lag and heterophoria status.

RESULTS

Baseline CISS score was (mean ± SD) 25.04 ± 4.58. Post-intervention scores were as follows: single vision: 24.46 ± 4.59, low add: 12.17 ± 6.89, high add: 13.71 ± 7.23. Both low add and high add multifocal soft contact lens wear was associated with an improvement in CISS score compared to baseline CISS and single vision (all p < 0.01). No significant difference was found between the CISS score for the baseline CISS and single vision (p = 1.00). No significant difference was found in lag of accommodation between lens conditions (all p > 0.05), however, there was an exophoric shift in near heterophoria between single vision and both multifocal contact lenses (low add: (mean difference 1.33 Δ, p = 0.02; high add: mean difference 1.23 Δ, p = 0.02) but not between habitual spectacle or any other modality (all p > 0.05).

CONCLUSIONS

The use of multifocal soft contact lenses for a one-month period was associated with reduced severity of asthenopic symptoms in pre-presbyopic myopes with accommodative lag. Whilst improvement of symptoms does not appear to be mediated by a significant reduction in accommodative lag, changes in heterophoria may play a role in reducing asthenopic symptoms.

Vision with spatial light modulator simulating multifocal contact lenses in an adaptive optics system

Visual simulators are useful tools to provide patients experience of multifocal vision prior to treatment. In this study, commercially available center-near aspheric multifocal contact lenses (MCLs) of low, medium, and high additions were mapped on a spatial light modulator (SLM) and validated on a bench. Through focus visual acuity (TFVA) was measured in subjects through the SLM and real MCLs on the eye. A correlation metric revealed statistically significant shape similarity between TFVA curves with real and simulated MCLs. A Bland-Altman analysis showed differences within confidence intervals of ±0.01 logMAR for LowAdd/MediumAdd and ±0.06 logMAR for HighAdd. Visual performance with simulated MCLs outperformed real MCLs by ∼20%. In conclusion, SLM captures the profile of center-near MCLs and reproduces vision with real MCLs, revealing that the MCL profile and its interactions with the eye's optics (and not fitting aspects) account for the majority of the contributions to visual performance with MCLs.

Impact of the pupil size - central optical zone diameter relationship on visual performance in aspheric multifocal contact lenses

PURPOSE

To determine the impact of different central optical zone diameters (COZDs), obtained from pupil size, on the visual performance of presbyopic subjects fitted with centre-distance simultaneous-image multifocal contact lenses (SIMCLs).

METHODS

Thirty-two presbyopic volunteers, between 45-58 years of age, participated in this prospective, controlled, double-blind study. Subjects were fitted with 5 centre-distance SIMCLs of variable COZD, determined from the measurement of pupil size under photopic light conditions and corresponding to 60, 70, 80, 90 and 100 % of pupil diameter. Subjects visual performance was evaluated through the measurement of distance, intermediate and near visual acuity (VA), "visual functional range" (VFR) obtained from the VA Defocus Curve (VADC) and Contrast Sensitivity Function (CSF), using a third-generation retina display iPad.

RESULTS

Statistically significant differences were obtained for both distance (p = 0.01) and intermediate (p = 0.001) VA amongst designs. Best results were obtained with 80 % and 90 % COZDs compared to 60 %. No significant differences in VFR (p > 0.05) were obtained amongst the different COZDs. 90 and 100 % COZDs offered statistically significant better results at 6 and 18 cycles per degree (cpd) in the CSF, compared to the 60 and 70 % designs.

CONCLUSIONS

SIMCLs with COZDs of 80-90 % and of 90-100% of photopic pupil diameter offered better distance and intermediate VA, without a decline in near performance, and superior contrast sensitivity at medium and high spatial frequencies respectively, compared to lower COZD designs.

Optical and Visual Quality With Physical and Visually Simulated Presbyopic Multifocal Contact Lenses

Purpose

As multifocal contact lenses (MCLs) expand as a solution for presbyopia correction, a better understanding of their optical and visual performance becomes essential. Also, providing subjects with the experience of multifocal vision before contact lens fitting becomes critical, both to systematically test different multifocal designs and to optimize selection in the clinic. In this study, we evaluated the ability of a simultaneous vision visual simulator (SimVis) to represent MCLs.

Methods

Through focus (TF) optical and visual quality with a center-near aspheric MCL (low, medium and high near adds) were measured using a multichannel polychromatic Adaptive Optics visual simulator equipped with double-pass, SimVis (temporal multiplexing), and psychophysical channels to allow measurements on-bench and in vivo. On bench TF optical quality of SimVis-simulated MCLs was obtained from double-pass (DP) images and images of an E-stimulus using artificial eyes. Ten presbyopic subjects were fitted with the MCL. Visual acuity (VA) and DP retinal images were measured TF in a 4.00 D range with the MCL on eye, and through SimVis simulations of the same MCLs on the same subjects.

Results

TF optical (on bench and in vivo) and visual (in vivo) quality measurements captured the expected broadening of the curves with increasing add. Root mean square difference between real and SimVis-simulated lens was 0.031/0.025 (low add), 0.025/0.015 (medium add), 0.019/0.011 (high add), for TF DP and TF LogMAR VA, respectively. A shape similarity metric shows high statistical values (lag κ = 0), rho = 0.811/0.895 (low add), 0.792/0.944 (medium add), and 0.861/0.915 (high add) for TF DP/LogMAR VA, respectively.

Conclusions

MCLs theoretically and effectively expand the depth of focus. A novel simulator, SimVis, captured the through-focus optical and visual performance of the MCL in most of the subjects. Visual simulators allow subjects to experience vision with multifocal lenses prior to testing them on-eye.

Translational Relevance

Simultaneous visual simulators allow subjects to experience multifocal vision non-invasively. We demonstrated equivalency between real multifocal contact lenses and SimVis-simulated lenses. The results suggest that SimVis is a suitable technique to aid selection of presbyopic corrections in the contactology practice.

Bifocal and Multifocal Contact Lenses for Presbyopia and Myopia Control

Bifocal and multifocal optical devices are intended to get images into focus from objects placed at different distances from the observer. Spectacles, contact lenses, and intraocular lenses can meet the requirements to provide such a solution. Contact lenses provide unique characteristics as a platform for implementing bifocality and multifocality. Compared to spectacles, they are closer to the eye, providing a wider field of view, less distortion, and their use is more consistent as they are not so easily removed along the day. In addition, contact lenses are also minimally invasive, can be easily exchangeable, and, therefore, suitable for conditions in which surgical procedures are not indicated. Contact lenses can remain centered with the eye despite eye movements, providing the possibility for simultaneous imaging from different object distances. The main current indications for bifocal and multifocal contact lenses include presbyopia correction in adult population and myopia control in children. Considering the large numbers of potential candidates for optical correction of presbyopia and the demographic trends in myopia, the potential impact of contact lenses for presbyopia and myopia applications is undoubtedly tremendous. However, the ocular characteristics and expectations vary significantly between young and older candidates and impose different challenges in fitting bifocal and multifocal contact lenses for the correction of presbyopia and myopia control. This review presents the recent developments in material platforms, optical designs, simulated visual performance, and the clinical performance assessment of bifocal and multifocal contact lenses for presbyopia correction and/or myopia progression control.

Optimization of the Light Sword Lens for Presbyopia Correction

Purpose

We propose and evaluate the modifications of a light sword lens (LSL) to obtain better performance for distance vision while maintaining good operation for near and intermediate vision.

Methods

The modifications consisted of assigning angular or circular windows for distance vision while rescaling the LSL profile in the remaining area of the element. The objective performance of the redesigned LSLs was verified numerically by the Strehl ratio and experimentally using correlation coefficients and Michelson contrast. Subjective assessments were provided by monocular visual acuity (VA) and contrast sensitivity (CS) through-focus curves for six patients with paralyzed accommodation. The tested object vergence range was [-4.0, 0.0] diopters (D). All experiments were conducted in a custom-made monocular visual simulator.

Results

Computational simulations and objective experiments confirmed the better performance of the modified LSL for the imaging of distant objects. The proposed angular and radial modulations resulted in flat VA and CS through-focus curves, indicating more uniform quality of vision with clearly improved distance vision. The VA provided by the modified LSL profiles showed a maximal improvement of 1.5 lines of acuity with respect to the VA provided by the conventional LSL at distance vision.

Conclusions

Optimized LSLs provide better imaging of distant objects while maintaining a large depth of focus. This results in comparable and acceptable quality for distance, intermediate, and near vision. Therefore, the modified LSLs appear to be promising presbyopia correctors.

Translational Relevance

The new design of LSL reveals an improved performance for all ranges of vision and becomes a promissory element for a real presbyopia correction in clinical applications.

Contrast sensitivity and visual acuity in subjects wearing multifocal contact lenses with high additions designed for myopia progression control

OBJECTIVES

To assess the visual performance of multifocal contact lenses (MFCLs) with high addition powers designed for myopia control.

METHODS

Twenty-four non-presbyopic adults (mean age 24 years, range 18-36 years) were fitted with soft MFCLs with add powers of +2.0 D (Add2) and +4.0 D (Add4) (RELAX, SwissLens) and single vision lenses (SVCL; Add0) in a counterbalanced order. In this double-masked study, half of the participants were randomly fitted with 3 mm-distance central zone MFCLs while the other half received 4.5 mm-distance central zone MFCLs. Visual acuity was measured at distance (3.0 m) and at near (0.4 m). Central and peripheral contrast sensitivity was evaluated at distance using the Gabor patch test. The area under the logarithmic contrast sensitivity function curve (ALCSF) was calculated and compared between the groups (i.e. different additions powers used).

RESULTS

Near and distance visual acuities were not affected by the lenses, neither Add2 nor Add4, when compared to Add0, however, CZ3 significantly reduced distance visual acuity with Add4 when compared to CZ4.5 (-0.08 logMAR vs. for CZ3 and -0.18 logMAR for CZ4.5, p = 0.013). MFCLs impaired central ALCSF only when Add2 was used (15.99 logCS for Add2 and 16.36 logCS for SVCLs, p = 0.021). Peripheral ALCSF was statistically lower for both addition powers of the MFCLs when compared to SVCLs (12.70 for Add2 and Add4, 13.73 for SVCLs, p = 0.009). The above effects were the same for both central zones used.

CONCLUSIONS

MFCLs with CZ3 diameter and high add power (Add4) slightly reduced distance visual acuity when compared to CZ4.5 but no reduction in this parameter was found with medium add power (Add2). Central contrast sensitivity was impaired only by MFCLs with the lower add power (Add2). Both add powers in the MFCLs reduced peripheral contrast sensitivity to a similar extent.

Presbyopia Correction Using Multifocal Soft Contact Lenses in Patients With Monofocal Intraocular Lenses

OBJECTIVES

To investigate the effectiveness of presbyopia correction using multifocal soft contact lenses (MF SCLs) for pseudophakic subjects with monofocal intraocular lenses (IOLs).

METHODS

In 11 subjects, after monofocal IOL implantation, disposable MF SCLs (Dailies Total 1 Multifocal, Alcon) were daily used for 3 months. Binocular visual acuity between 0.3 and 5 m was measured using an all-distance vision tester (AS-15, Kowa) at 1 and 3 months and compared before and during MF SCL wear. Binocular contrast sensitivity testing was conducted under mesopic and photopic illuminations at 1 month.

RESULTS

The mean manifest refraction spherical equivalent before MF SCL wear was -0.36 D. The add powers of used MF SCLs were +1.25, +2.00, and +2.50 D in 1, 16, and 5 eyes, respectively. The mean binocular visual acuities during MF SCL wear were 20/20 or better between 0.5 and 5 m and significantly improved at 0.7 m or less (P<0.025). There was no change in the mesopic contrast sensitivity, whereas the photopic contrast sensitivity at 18 cycles per degree was degraded during MF SCL wear.

CONCLUSIONS

The use of MF SCL was effective for presbyopia correction in pseudophakic subjects with monofocal IOL, and favorable binocular vision would be obtained in a range from distance to intermediate.

Clinical Efficacy of Pinhole Soft Contact Lenses for the Correction of Presbyopia

We investigated the clinical efficacy of pinhole soft contact lenses for presbyopia correction. Twenty participants with presbyopia wore pinhole soft contact lenses in the non-dominant eye for 2 weeks. Manifest refraction, Goldmann binocular visual field tests, contrast sensitivity tests, and biomicroscopic examinations were performed along with evaluations of questionnaire responses and the binocular corrected distance visual acuity (CDVA), distance-corrected near visual acuity (DCNVA), distance-corrected intermediate visual acuity (DCIVA), and depth of focus, both before and after 2 weeks of lens wear. DCNVA at 33 and 40 cm and DCIVA at 50 and 70 cm showed significant improvements after pinhole lens wear (P-value: <0.001, <0.001, <0.001, and 0.046, respectively), with no changes in the binocular visual field and binocular CDVA. Contrast sensitivities under photopic and mesopic conditions decreased at some frequencies; however, visual function questionnaire scores significantly improved (all P-values <0.001). These findings suggest that pinhole contact lenses effectively correct presbyopia.

Multifocal contact lenses: towards customisation?

PURPOSE

Firstly, to determine if eyes with spherical aberration (SA) that deviates significantly from the average level underperform when fitted with a simultaneous-imaging contact lens (CL) with a power profile calculated for an 'average eye'. Secondly, to determine if CL customisation can improve image quality in these eyes after fitting with a bifocal CL.

METHODS

A statistical model of the wavefront aberration function of normal eyes was used to generate a vector of Zernike fourth-order SA coefficients from 100 synthetic eyes. Four bifocal power profiles were modelled: centre-near (CN) or centre-distance (CD), and two-zone or four-zone. All designs had 0.1-mm-wide transition zones. Different levels of distance and add powers were modelled, using well-established computational wave-optics methods. Zone widths were optimised to obtain maximal multifocal efficiency (MFE), a metric based on the visual Strehl that synthesises the through-focus curve in one number. The MFE was calculated for each synthetic eye coupled with each bifocal power profile.

RESULTS

For an 'average eye', the mean MFE values were 0.33 vs 0.25 and 0.32 vs 0.29, for CN vs CD and two vs four zone designs, respectively. When the four power profiles were assessed in eyes with non-average levels of ocular SA, the MFE decreased with higher levels of SA (eye and CL combined) for all designs. Some of this reduction in MFE could be prevented by adjusting the nominal distance and add power of the bifocal profiles to compensate for the increased or decreased level of combined SA. The four-zone CN profile showed better tolerance for different levels of ocular SA than the two-zone designs, but this was not true for the four-zone CD design.

CONCLUSION

Eyes with SA levels differing significantly from the average level underperform when fitted with simultaneous-imaging CLs with power profiles calculated for average eyes. Our findings suggest that visual performance at distance and near when wearing bifocal CLs can be improved by using a semi-customised approach.

Combined Effect of Ocular and Multifocal Contact Lens Induced Aberrations on Visual Performance: Center-Distance Versus Center-Near Design

PURPOSE

To evaluate the combined effects of inherent ocular aberrations and induced aberrations with a multifocal soft contact lens (MFCL) after 15 days of lens wear in presbyopic participants and their influence on visual performance at distance and near under high and low contrast conditions.

METHODS

Forty presbyopic participants (mean age, 48.7±3.4) presenting a mean addition of 1.53±0.58 D were fitted with Biofinity Multifocal (CooperVision) and included in the study. Measurements comprised distance and near monocular high (100%) and low contrast (10%) logMAR visual acuity (VA). Ocular aberrations were obtained with Hartmann-Shack aberrometer (IRX3, Imagine Eyes) and analyzed for 2 mm and maximum round natural pupil.

RESULTS

Distance VA was significantly higher in dominant eye, whereas near VA was significantly better in the non-dominant eye (P<0.05 in all conditions). For a 2-mm pupil in the dominant eye fitted with MFCL, spherical-like aberration significantly increased (P=0.027) so as higher-order aberrations (HOA) (P=0.002). A significant increase was also observed in spherical-like aberrations (P=0.001), coma-like aberrations (P=0.006) and HOA (P=0.004) in non-dominant eye. For the maximum round natural pupil size, a significant decrease in vertical coma was observed (P=0.018) in dominant eye, whereas a significant increase in spherical-like (P<0.001) and coma-like aberrations (P=0.007) was observed in non-dominant eye. A negative significant correlation was found between vertical coma and high contrast VA (Rho=-0.405, P=0.011) in dominant eye; whereas in non-dominant eye, a significant correlation was found between induced secondary astigmatism and distance VA under high (Rho=0.556, P<0.001) and low contrast (Rho=0.448, P=0.005).

CONCLUSIONS

On-eye visual performance of MFSCL is dependent on the high-order aberrations induced by dominant and non-dominant design coupled with the wearer's inherent aberrations.

Presbyopia: Effectiveness of correction strategies

Presbyopia is a global problem affecting over a billion people worldwide. The prevalence of unmanaged presbyopia is as high as 50% of those over 50 years of age in developing world populations, due to a lack of awareness and accessibility to affordable treatment, and is even as high as 34% in developed countries. Definitions of presbyopia are inconsistent and varied, so we propose a redefinition that states "presbyopia occurs when the physiologically normal age-related reduction in the eye's focusing range reaches a point, when optimally corrected for distance vision, that the clarity of vision at near is insufficient to satisfy an individual's requirements". Strategies for correcting presbyopia include separate optical devices located in front of the visual system (reading glasses) or a change in the direction of gaze to view through optical zones of different optical powers (bifocal, trifocal or progressive addition spectacle lenses), monovision (with contact lenses, intraocular lenses, laser refractive surgery and corneal collagen shrinkage), simultaneous images (with contact lenses, intraocular lenses and corneal inlays), pinhole depth of focus expansion (with intraocular lenses, corneal inlays and pharmaceuticals), crystalline lens softening (with lasers or pharmaceuticals) or restored dynamics (with 'accommodating' intraocular lenses, scleral expansion techniques and ciliary muscle electrostimulation); these strategies may be applied differently to the two eyes to optimise the range of clear focus for an individual's task requirements and minimise adverse visual effects. However, none fully overcome presbyopia in all patients. While the restoration of natural accommodation or an equivalent remains elusive, guidance is given on presbyopic correction evaluation techniques.

Light disturbance with multifocal contact lens and monovision for presbyopia

Dysphotopsia affects a significant number of patients, particularly after visual correction with multifocal optical designs.

PURPOSE

Evaluate light distortion (LD) in two modalities of contact lens (CL) wear: multifocal (MF) and monofocal (MV).

METHODS

This was a randomized, double-masked, crossover study involving 20 presbyopic patients. Patients were randomized first into either MF or MV for 15 days of use with a 1 week wash-out period between each lens type. The LD was evaluated with the Light Distortion Analyzer (LDA, University of Minho) under monocular and binocular conditions. The light distortion index (LDI, %), among other parameters were analyzed. Subjective quality of vision was assessed with the Quality of Vision (QoV).

RESULTS

The LD showed an increase in all parameters in both CL modalities being significant for MV in the non-dominant eye (p < 0.030, for all LD parameters). For the MF, there was also a significant increase in LDI (p = 0.016) and in BFCrad (p = 0.022) in the non-dominant eye. After 15 days of MF lens wear, there was a significant decrease in all LD parameters (p < 0.002) in the dominant eye. Binocularly, a significant improvement from 1 to 15 days was observed for LDI (p = 0.009) and BFCrad (p = 0.0013) with MF. The QoV questionnaire showed no significant changes with neither CL.

CONCLUSIONS

Adaptation to light disturbances induced by MF CL is more effective compared to MV. Practitioners will have greater success if they prepare their patients for the adaptation required as their vision will get better and have less of an issue with light disturbance.

Extended depth of focus contact lenses vs. two commercial multifocals: Part 1. Optical performance evaluation via computed through-focus retinal image quality metrics

PURPOSE

To compare the computed optical performance of prototype lenses designed using deliberate manipulation of higher-order spherical aberrations to extend depth-of-focus (EDOF) with two commercial multifocals.

METHODS

Emmetropic, presbyopic, schematic eyes were coupled with prototype EDOF and commercial multifocal lenses (Acuvue Oasys for presbyopia, AOP, Johnson & Johnson & Air Optix Aqua multifocal, AOMF, Alcon). For each test configuration, the through-focus retinal image quality (TFRIQ) values were computed over 21 vergences, ranging from -0.50 to 2.00D, in 0.125D steps. Analysis was performed considering eyes with three different inherent aberration profiles: five different pupils and five different lens decentration levels.

RESULTS

Except the LOW design, the AOP lenses offered 'bifocal' like TFRIQ performance. Lens performance was relatively independent to pupil and aberrations but not centration. Contrastingly, AOMF demonstrated distance centric performance, most dominant in LOW followed by MED and HIGH designs. AOMF lenses were the most sensitive to pupil, aberrations and centration. The prototypes demonstrated a 'lift-off' in the TFRIQ performance, particularly at intermediate and near, without trading performance at distance. When compared with AOP and AOMF, EDOF lenses demonstrated reduced sensitivity to pupil, aberrations and centration.

CONCLUSION

With the through focus retinal image quality as the gauge of optical performance, we demonstrated that the prototype EDOF designs were less susceptible to variations in pupil, inherent ocular aberrations and decentration, compared to the commercial designs. To ascertain whether these incremental improvements translate to a clinically palpable outcome requires investigation through human trials.

Extended depth of focus contact lenses vs. two commercial multifocals: Part 2. Visual performance after 1 week of lens wear

PURPOSE

To compare the visual performance of prototype contact lenses designed via deliberate manipulation of higher-order spherical aberrations to extend-depth-of-focus with two commercial multifocals, after 1 week of lens wear.

METHODS

In a prospective, participant-masked, cross-over, randomized, 1-week dispensing clinical-trial, 43 presbyopes [age: 42-63 years] each wore AIROPTIX Aqua multifocal (AOMF), ACUVUE OASYS for presbyopia (AOP) and extended-depth-of-focus prototypes (EDOF) appropriate to their add requirements. Measurements comprised high-contrast-visual-acuity (HCVA) at 6m, 70cm, 50cm and 40cm; low-contrast-visual-acuity (LCVA) and contrast-sensitivity (CS) at 6m and stereopsis at 40cm. A self-administered questionnaire on a numeric-rating-scale (1-10) assessed subjective visual performance comprising clarity-of-vision and lack-of-ghosting at various distances during day/night-viewing conditions and overall-vision-satisfaction.

RESULTS

EDOF was significantly better than AOMF and AOP for HCVA averaged across distances (p≤0.038); significantly worse than AOMF for LCVA (p=0.021) and significantly worse than AOMF for CS in medium and high add-groups (p=0.006). None of these differences were clinically significant (≤2 letters). EDOF was significantly better than AOMF and AOP for mean stereoacuity (36 and 13 seconds-of-arc, respectively: p≤0.05). For clarity-of-vision, EDOF was significantly better than AOP at all distances and AOMF at intermediate and near (p≤0.028). For lack-of-ghosting averaged across distances, EDOF was significantly better than AOP (p<0.001) but not AOMF (p=0.186). EDOF was significantly better than AOMF and AOP for overall-vision-satisfaction (p≤0.024).

CONCLUSIONS

EDOF provides better intermediate and near vision performance than either AOMF or AOP with no difference for distance vision after 1 week of lens wear.

Reducing starbursts in highly aberrated eyes with pupil miosis

PURPOSE

To test the hypothesis that marginal ray deviations determine perceived starburst sizes, and to explore different strategies for decreasing starburst size in highly aberrated eyes.

METHODS

Perceived size of starburst images and visual acuities were measured psychophysically for eyes with varying levels of spherical aberration, pupil sizes, and defocus. Computationally, we use a polychromatic eye model including the typical levels of higher order aberrations (HOAs) for keratoconic and post-LASIK eyes to quantify the image quality (the visually weighted Strehl ratio derived from the optical transfer function, VSOTF) with different pupil sizes at both photopic and mesopic light levels.

RESULTS

For distance corrected post-LASIK and keratoconic eyes with a night-time pupil (e.g., 7 mm), the starburst diameter is about 1.5 degrees (1 degree for normal presbyopic eyes), which can be reduced to ≤0.25 degrees with pupil sizes ≤3 mm. Starburst size is predicted from the magnitude of the longitudinal spherical aberration. Refracting the eye to focus the pupil margin also removed starbursts, but, unlike small pupils, significantly degraded visual acuity. Reducing pupil diameter to 3 mm improved image quality for these highly aberrated eyes by about 2.7 ×  to 1.7 ×  relative to the natural pupils when light levels were varied from 0.1 to 1000 cd m^-2 , respectively.

CONCLUSION

Subjects with highly aberrated eyes observed larger starbursts around bright lights at night predictable by the deviated marginal rays. These were effectively attenuated by reducing pupil diameters to ≤3 mm, which did not cause a drop in visual acuity or modelled image quality even at mesopic light levels.

Fitting success for three multifocal designs: Multicentre randomised trial

PURPOSE

To determine if the discontinuation of commercially-available simultaneous vision Multifocal Soft Contact Lenses is independent from the multifocal design. To determine causes for discontinuation and psychosocial factors involved.

METHODS

Multicentre single-blinded randomised controlled trial with external blinded evaluation for a three months follow-up period for three intervention groups. 150 single-vision soft wearers were randomly assigned a spherical near centred lens (S-CN), distance centred lens (CD) or aspherical near centred lens (A-CN). Cases of discontinuation, anxiety and quality of life were measured at one week and one month.

RESULTS

120 females and 30 males were included with an age range of 40-62 (48.79 ± 5.23). At one month, the S-CN design had a statistically significant higher risk of discontinuation than the other two OR: 6.12 (95%CI 2.5-14.9). Twenty-eight subjects discontinued wearing S-CN at first week (56%), while discontinuation of CD and A-CD were 15 (30%) and 11 (22%), with a statistically significant difference between S-CN design and the other two (p = 0.001). There were not statistically significant differences when direct comparison between discontinuation of CD and A-CN was made (p = 0.36). Thirty-two percent discontinued the use because of poor distance vision and 28% because of both poor distance and near vision. Psychosocial factors were not statistically significant.

CONCLUSIONS

Discontinuation of Multifocal Soft Contact Lenses is dependent on the design. Most common cause for discontinuation is poor distance vision. Psychosocial factors do not impact on discontinuation rates.

Impact of Spherical Aberration Terms on Multifocal Contact Lens Performance

PURPOSE

To investigate the impact of the primary (PSA) and secondary (SSA) spherical aberration terms on visual performance (VP) in presbyopes, as measured using multifocal (MFCL) soft contact lenses on eye.

METHODS

Seventeen presbyopes (age: 55.1 ± 6.9 years) wore seven commercial lenses (four center-near (MFCL N), one center-distance (MFCL D), one bifocal, and one single vision control). Unaided and with each lens on eye, the PSA and SSA terms were obtained with an aberrometer, the BHVI-EyeMapper (low illumination, natural and 4 mm pupil diameter). High- and low-contrast distance visual acuity, contrast sensitivity, high-contrast visual acuities at near, and range of clear vision were measured. In addition, subjective VP variables included clarity of vision at distance and near, ghosting, and overall vision satisfaction. Pearson's correlation was used to determine the association between the PSA and SSA terms and the VP variables.

RESULTS

PSA (natural pupil) was more negative (P < .05) with the MFCL N (mean PSA = -0.053 ± 0.080 μm) and bifocal (PSA = +0.005 ± 0.067 μm) lenses and more positive with the MFCL D lens (PSA = +0.208 ± 0.160 μm) than the control (+0.067 ± 0.072 μm). SSA (natural pupil) was significantly more positive for the MFCL N lenses (mean SSA = +0.025 ± 0.029 μm) compared to the control (SSA = -0.001 ± 0.017 μm). PSA and SSA terms were significantly (P < .05) correlated with 78% and 56% of VP variables, respectively, but the correlation coefficients were weak, ranging between |0.210| and |0.334|. Although distance variables showed improved VP with more positive PSA or negative SSA, most near variables showed improved VP with more negative PSA. Range of clear focus was greater for more negative PSA terms.

CONCLUSIONS

The amount and direction of PSA and SSA terms, as measured with different MFCLs on eye, can affect VP at different distances. Results of this study may provide useful information when designing new or optimize existing MFCLs for improved VP at specific distances.

Power Profiles of Commercial Multifocal Soft Contact Lenses

Purpose

To evaluate the optical power profiles of commercially available soft multifocal contact lenses and compare their optical designs.

Methods

The power profiles of 38 types of multifocal contact lenses—three lenses each—were measured in powers +6D, +3D, +1D, −1D, −3D, and −6D using NIMO TR1504 (Lambda-X, Belgium). All lenses were measured in phosphate buffered saline across 8 mm optic zone diameter. Refractive index of each lens material was measured using CLR 12-70 (Index Instruments, UK), which was used for converting measured power in the medium to in-air radial power profiles.

Results

Three basic types of power profiles were identified: center-near, center-distance, and concentric-zone ring-type designs. For most of the lens types, the relative plus with respect to prescription power was lower than the corresponding spectacle add. For some lens types, the measured power profiles were shifted by up to 1D across the power range relative to their labeled power. Most of the lenses were designed with noticeable amounts of spherical aberration. The sign and magnitude of spherical aberration can either be power dependent or consistent across the power range.

Conclusions

Power profiles can vary widely between the different lens types; however, certain similarities were also observed between some of the center-near designs. For the more recently released lens types, there seems to be a trend emerging to reduce the relative plus with respect to prescription power, include negative spherical aberration, and keep the power profiles consistent across the power range.

Objective assessment of the effect of pupil size upon the power distribution of multifocal contact lenses

AIM

To analytically assess the effect of pupil size upon the refractive power distributions of different designs of multifocal contact lenses.

METHODS

Two multifocal contact lenses of center-near design and one multifocal contact lens of center-distance design were used in this study. Their power profiles were measured using the NIMO TR1504 device (LAMBDA-X, Belgium). Based on their power profiles, the power distribution was assessed as a function of pupil size. For the high addition lenses, the resulting refractive power as a function of viewing distance (far, intermediate, and near) and pupil size was also analyzed.

RESULTS

The power distribution of the lenses was affected by pupil size differently. One of the lenses showed a significant spread in refractive power distribution, from about -3 D to 0 D. Generally, the power distribution of the lenses expanded as the pupil diameter became greater. The surface of the lens dedicated for each distance varied substantially with the design of the lens.

CONCLUSION

In an experimental basis, our results show how the lenses power distribution is affected by the pupil size and underlined the necessity of careful evaluation of the patient's visual needs and the optical properties of a multifocal contact lens for achieving the optimal visual outcome.

Short-term comparison between extended depth-of-focus prototype contact lenses and a commercially-available center-near multifocal

PURPOSE

To compare the visual performance of prototype contact lenses which extend depth-of-focus (EDOF) by deliberate manipulation of multiple higher-order spherical aberration terms and a commercially-available center-near lens (AIR OPTIX Aqua Multifocal, AOMF).

METHODS

This was a prospective, cross-over, randomized, single-masked (participant), short-term clinical trial where 52 participants (age 45-70 years) were stratified as low, medium or high presbyopes and wore EDOF and AOMF on different days. Objective measures comprised high and low contrast visual acuity (HCVA/LCVA, logMAR), and contrast sensitivity (log units) at 6m; HCVA at 70cm, 50cm and 40cm and stereopsis (seconds of arc) at 40cm. HCVA at 70cm, 50cm and 40cm were measured as "comfortable acuity" rather than conventional resolution acuity. Subjective measures comprised clarity-of-vision and ghosting at distance, intermediate and near, overall vision satisfaction and ocular comfort (1-10 numeric rating scale) and lens purchase (yes/no response). Statistical analysis included repeated measures ANOVA, paired t-tests and McNemar's test.

RESULTS

Significant differences between lens types were independent of strata (p≥0.119). EDOF was significantly better than AOMF for HCVA at 40cm (0.42±0.18 vs. 0.48±0.22, p=0.024), stereopsis (98±88 vs. 141±114, p<0.001), clarity-of-vision at intermediate (8.5±1.6 vs. 7.7±1.9, p=0.006) and near (7.3±2.5 vs. 6.2±2.5, p=0.005), lack-of-ghosting (p=0.012), overall vision satisfaction (7.5±1.7 vs. 6.4±2.2, p<0.001) and ocular comfort (9.0±1.0 vs. 8.3±1.7, p=0.002). Significantly more participants chose to only-purchase EDOF (33% vs. 6%, p=0.003).). There were no significant differences between lens types for any objective measure at 6m or clarity-of-vision at distance (p≥0.356).

CONCLUSIONS

EDOF provides better intermediate and near vision performance in presbyopes than AOMF with no difference for distance vision during short-term wear.

Soft multifocal simultaneous image contact lenses: a review

Soft multifocal simultaneous image contact lenses have boomed in recent years due to the growing number of presbyopic patients demanding visual solutions, allowing them to maintain their current standard of living. The concept of 'simultaneous image' is based on blur interpretation and/or blur tolerance of superimposed multiple images on the retina formed by various powers of a contact lens. This is the basis for a specific type of multifocal contact lens developed for the compensation of presbyopia. Manufacturers have released a great variety of soft simultaneous image lens designs to meet different patient needs but their fitting is still unsatisfactory in some cases. Some presbyopes discontinue wearing contact lenses due to some limitations in visual quality and comfort that can be overcome with an appropriate contact lens selection based on a comprehensive pre-fitting evaluation. This paper aims to review the different types of soft multifocal contact lenses that are currently available for presbyopic correction and to define the steps and factors crucial for their fitting, such as pupil, aberrations, accommodation and centring. A discussion about useful tools to achieve a customised fitting leading to a successful outcome, such as the defocus curve, power profile and questionnaires, is performed.

Short-Term Visual Performance of Novel Extended Depth-of-Focus Contact Lenses

PURPOSE

To compare the objective and subjective visual performance of a novel contact lens which extends depth of focus by deliberate manipulation of higher-order spherical aberrations and a commercially available zonal-refractive multifocal lens.

METHODS

A prospective, cross-over, randomized, single-masked, short-term clinical trial comprising 41 presbyopes (age 45 to 70 years) wearing novel Extended Depth of Focus lenses (EDOF) and ACUVUE OAYS for Presbyopia (AOP). Each design was assessed on different days with a minimum overnight wash-out. Objective measures comprised high-contrast visual acuity (HCVA, logMAR) at 6 m, 70 cm, 50 cm, and 40 cm; low-contrast visual acuity (LCVA, logMAR) and contrast sensitivity (log units) at 6 m; and stereopsis (seconds of arc) at 40 cm. HCVA at 70 cm, 50 cm, and 40 cm were measured as "comfortable acuity" rather than conventional resolution acuity. Subjective performance was assessed on a 1-10 numeric rating scale for clarity of vision and ghosting at distance, intermediate and near, overall vision satisfaction, ocular comfort, and lens purchase. Statistical analysis included repeated measures ANOVA and paired t tests.

RESULTS

HCVA, clarity of vision, and ghosting with EDOF were significantly better than AOP (p < 0.01); however, differences were dependent on testing distances and add groups. Post hoc analysis showed EDOF was significantly better than AOP for HCVA at 70 cm (0.11 ± 0.11 vs. 0.21 ± 0.16, p < 0.001), 50 cm (0.26 ± 0.17 vs. 0.36 ± 0.18, p = 0.003), 40 cm (0.42 ± 0.17 vs. 0.52 ± 0.21, p = 0.001), and LCVA at 6 m (0.22 ± 0.08 vs. 0.27 ± 0.12, p = 0.024). EDOF was significantly better than AOP for clarity of vision at distance (7.7 ± 1.6 vs. 6.8 ± 2.3, p = 0.029), intermediate (8.8 ± 1.4 vs. 7.0 ± 2.2, p < 0.001), and near (7.4 ± 2.4 vs. 5.2 ± 2.7, p < 0.001), ghosting at distance (9.1 ± 1.2 vs. 8.1 ± 2.5, p = 0.005), and overall vision satisfaction (7.6 ± 1.6 vs. 6.0 ± 2.6, p < 0.001). More participants chose to purchase EDOF compared to AOP (61 vs. 39%) and significantly more chose to only-purchase EDOF compared to only-purchase AOP (27 vs. 5%, p = 0.022).

CONCLUSIONS

When compared with AOP, EDOF lenses provide better intermediate and near vision performance in presbyopic participants without compromising distance vision.

Randomized Crossover Trial of Silicone Hydrogel Presbyopic Contact Lenses

PURPOSE

To assess the performance of four commercially available silicone hydrogel multifocal monthly contact lens designs against monovision.

METHODS

A double-masked randomized crossover trial of Air Optix Aqua multifocal, PureVision 2 for Presbyopia, Acuvue OASYS for Presbyopia, Biofinity multifocal, and monovision with Biofinity contact lenses was conducted on 35 presbyopes (54.3 ± 6.2 years). After 4 weeks of wear, visual performance was quantified by high- and low-contrast visual acuity under photopic and mesopic conditions, reading speed, defocus curves, stereopsis, halometry, aberrometry, Near Activity Visual Questionnaire rating, and subjective quality of vision scoring. Bulbar, limbal, and palpebral hyperemia and corneal staining were graded to monitor the impact of each contact lens on ocular physiology.

RESULTS

High-contrast photopic visual acuity (p = 0.102), reading speed (F = 1.082, p = 0.368), and aberrometry (F = 0.855, p = 0.493) were not significantly different between presbyopic lens options. Defocus curve profiles (p < 0.001), stereopsis (p < 0.001), halometry (F = 4.101, p = 0.004), Near Activity Visual Questionnaire (F = 3.730, p = 0.007), quality of vision (p = 0.002), bulbar hyperemia (p = 0.020), and palpebral hyperemia (p = 0.012) differed significantly between lens types, with the Biofinity multifocal lens design principal (center-distance lens was fitted to the dominant eye and a center-near lens to the nondominant eye) typically outperforming the other lenses.

CONCLUSIONS

Although ocular aberration variation between individuals largely masks the differences in optics between current multifocal contact lens designs, certain design strategies can outperform monovision, even in early presbyopes.

Pupil diameter, working distance and illumination during habitual tasks. Implications for simultaneous vision contact lenses for presbyopia

PURPOSE

To determine working distance, pupil diameter and illumination in real life conditions in a sample of presbyopic participants performing habitual tasks.

METHODS

A total of 59 presbyopic subjects (aged between 45 and 63 years) with different occupational backgrounds participated in the study. Participants were first interviewed regarding their habitual tasks with the aid of an ad hoc questionnaire, following which in-office photopic and mesopic pupil diameter was determined. Pupil diameter was also evaluated while participants conducted each of the self-reported habitual tasks by taking a photograph, which was later submitted to image analysis. In addition, working distance was determined with a measuring tape and the illumination that reached the pupil during each of the different tasks was measured, in lux, with a light meter.

RESULTS

The four most common habitual tasks were computer use, reading, sewing and sports. A high intersubject variability was found in pupil diameter, working distance and illumination conditions while conducting the same task. Statistically significant differences were found between the in-office measured photopic and mesopic pupil diameters and those obtained while participants were conducting their habitual tasks in real life conditions (all p<0.001).

CONCLUSIONS

Potential multifocal contact lens users may present with different ages, different jobs or hobbies and different preferences regarding lighting conditions and working distances. This results in different pupil size, even within the same task. This information may be critical when selecting a particular lens design and add power. Eye care practitioners are therefore advised to assess pupil diameter in real life conditions.

Visual Performance of a Multifocal Contact Lens versus Monovision in Established Presbyopes

PURPOSE

To compare subjective and objective visual performance of the Air Optix Aqua Multifocal lens to monovision in a group of subjects requiring a medium level of reading-addition power.

METHODS

Fifty participants with reading additions between 1.25 and 2.00 diopters (inclusive) were randomized into a prospective, crossover clinical trial. They wore monovision and multifocals for 2 weeks in a randomized order. High- and low-contrast logMAR (logarithm of the minimum angle of resolution) acuity and stereopsis were measured at the beginning and end of each period. During each phase, participants performed specific tasks followed by subjective rating surveys and also completed satisfaction rating surveys on days 3, 7, and 12; all were transferred in real time using BlackBerry smartphones. A general rating survey was completed at the dispensing and 2-week visits.

RESULTS

Forty-nine participants completed the study (mean age, 52 years). Distance and near high- and low-contrast acuities were significantly better (p < 0.05) with monovision at all visits. High-contrast intermediate acuity was only better (p < 0.05) with multifocals after 2 weeks. Stereopsis was equivalent after 2 weeks, but better (p < 0.05) with multifocals at dispensing. Subjective ratings were generally equivalent between modalities although there was a trend for multifocals to be rated higher for focus changing and driving, whereas monovision tended to be rated higher for near tasks. For both corrections, the satisfaction survey showed no significant change between days 3, 7, and 12, and the general survey showed that comfort was maintained but subjective vision ratings decreased significantly over the 2 weeks. Twenty-five participants (51%) preferred multifocals, 18 (37%) preferred monovision, and the remaining 6 (12%) declared both unacceptable.

CONCLUSIONS

In this cohort, distance and near acuities were better with monovision, whereas the subjective ratings tended to favor the Air Optix Aqua Multifocal, with the exception of near performance. Preference was statistically similar between both corrections, with a trend toward preferring the multifocal.

Optical power distribution of refractive and aspheric multifocal contact lenses: Effect of pupil size

PURPOSE

To evaluate the power profile within the optic zone of different designs of multifocal contact lenses (CLs) and to analyze how the effect of pupil size could impact on their optical performance.

METHODS

The optical power distribution within the optic zones of multifocal CLs was measured by the Nimo TR1504 (LAMBDA-X, Belgium). The multifocal CLs under study were the Acuvue Bifocal, the Acuvue Oasys for Presbyopia, the PureVision Multifocal and the PureVision 2 for Presbyopia. Each design was considered in all their available addition powers. All lenses had a nominal power of -3.0D. At the same time, three lenses of each model were considered and five consecutive readings of each lens were performed.

RESULTS

The results show that the PureVision Multifocal and the PureVision 2 for Presbyopia have aspheric power profiles. Both designs showed aspheric center-near designs with a smoother progression of the optical power in the PureVision 2 for Presbyopia. The Acuvue Bifocal and the Acuvue Oasys for Presbyopia are shown to have concentric alternating near and far zones. Apart from the refractive rings, the Acuvue Oasys for Presbyopia showed an increase in negative (or less positive) values toward the periphery of the lens.

CONCLUSIONS

Besides the refraction, the knowledge of the power profiles of multifocal CLs and the effect of pupil size on the optical distribution of these lenses could be crucial to understand the performance of these designs when they are fitted.

Impact of contact lens zone geometry and ocular optics on bifocal retinal image quality

PURPOSE

To examine the separate and combined influences of zone geometry, pupil size, diffraction, apodisation and spherical aberration on the optical performance of concentric zonal bifocals.

METHODS

Zonal bifocal pupil functions representing eye + ophthalmic correction were defined by interleaving wavefronts from separate optical zones of the bifocal. A two-zone design (a central circular inner zone surrounded by an annular outer-zone which is bounded by the pupil) and a five-zone design (a central small circular zone surrounded by four concentric annuli) were configured with programmable zone geometry, wavefront phase and pupil transmission characteristics. Using computational methods, we examined the effects of diffraction, Stiles Crawford apodisation, pupil size and spherical aberration on optical transfer functions for different target distances.

RESULTS

Apodisation alters the relative weighting of each zone, and thus the balance of near and distance optical quality. When spherical aberration is included, the effective distance correction, add power and image quality depend on zone-geometry and Stiles Crawford Effect apodisation. When the outer zone width is narrow, diffraction limits the available image contrast when focused, but as pupil dilates and outer zone width increases, aberrations will limit the best achievable image quality. With two-zone designs, balancing near and distance image quality is not achieved with equal area inner and outer zones. With significant levels of spherical aberration, multi-zone designs effectively become multifocals.

CONCLUSION

Wave optics and pupil varying ocular optics significantly affect the imaging capabilities of different optical zones of concentric bifocals. With two-zone bifocal designs, diffraction, pupil apodisation spherical aberration, and zone size influence both the effective add power and the pupil size required to balance near and distance image quality. Five-zone bifocal designs achieve a high degree of pupil size independence, and thus will provide more consistent performance as pupil size varies with light level and convergence amplitude.

Influence of spherical aberration, stimulus spatial frequency, and pupil apodisation on subjective refractions

PURPOSE

To test competing hypotheses (Stiles Crawford pupil apodising or superior imaging of high spatial frequencies by the central pupil) for the pupil size independence of subjective refractions in the presence of primary spherical aberration.

METHODS

Subjective refractions were obtained with a variety of test stimuli (high contrast letters, urban cityscape, high and low spatial frequency gratings) while modulating pupil diameter, levels of primary spherical aberration and pupil apodisation. Subjective refractions were also obtained with low-pass and high-pass stimuli and using 'darker' and 'sharper' subjective criteria.

RESULTS

Subjective refractions for stimuli containing high spatial frequencies focus a near paraxial region of the pupil and are affected only slightly by level of Seidel spherical aberration, degree of pupil apodisation and pupil diameter, and generally focused a radius of about 1-1.5 mm from the pupil centre. Low spatial frequency refractions focus a marginal region of the pupil, and are significantly affected by level of spherical aberration, amount of pupil apodisation, and pupil size. Clinical refractions that employ the 'darker' or 'sharper' subjective criteria bias the patient to use lower or higher spatial frequencies, respectively.

CONCLUSIONS

In the presence of significant levels of spherical aberration, the pupil size independence of subjective refractions occurs with or without Stiles Crawford apodisation for refractions that optimise high spatial frequency content in the image. If low spatial frequencies are optimised by a subjective refraction, spherical refractive error varies with spherical aberration, pupil size, and level of apodisation. As light levels drop from photopic to scotopic, therefore, we expect a shift from pupil size independent to pupil size dependent subjective refractions. Emphasising a 'sharper' criterion during subjective refractions will improve image quality for high spatial frequencies and generate pupil size independent refractions.

Developments in the correction of presbyopia I: spectacle and contact lenses

PURPOSE

To outline the refractive problems associated with presbyopia and to review the basis and relative merits of currently-available methods for their correction, with detailed consideration of spectacle and contact lens approaches.

CONTENTS

In the developed world, most of the present population will spend roughly half their lives as presbyopes. The well-known presbyopic changes with age in amplitude of accommodation and required near addition are briefly reviewed, together with the less widely acknowledged slow drifts that occur in distance refraction. The desirability of restoring to presbyopes clear vision for objects at any distance, ideally corresponding to vergences within the range of at least 0 to -5 D, in any viewing direction, is stressed. A general outline is given of possible corrective methods. Methods which satisfy the needs of a 50 year-old may not be suitable for the 80 year-old. Corrections may involve both fixed- and variable-focus lens systems, and surgical methods which modify the optics of the cornea, replace the crystalline lens with different fixed optics, or attempt to at least partially restore active accommodation. Some more recent methods of spectacle and contact lens correction are described in more detail. Particular attention is given to recent commercially-developed spectacles in which the corrective power can be varied actively by either mechanical (liquid-filled deformable lenses or Alvarez lenses) or electrical (liquid crystal lenses) means to allow objects at different distances to be seen clearly. Contact lens corrections show less progress and are still preferred only by a minority of older patients, most of whom are early presbyopes.

SUMMARY

The rising proportion of presbyopes in the population, covering an age span of around 40 years, represents both a problem for those concerned with giving their patients the best vision possible at both far and near viewing distances and a commercial opportunity. Traditional single-vision distance and near, bifocal, and progressive spectacle lens solutions, together with contact lens modalities for presbyopic correction, are being challenged by a variety of new approaches. It remains to be seen whether the latter will receive wide acceptance in practice.

In vitro power profiles of multifocal simultaneous vision contact lenses

PURPOSE

To evaluate the power profile of multifocal contact lenses (CLs) using a new technology based on quantitative deflectometry.

METHODS

The Nimo TR1504 was used to analyze the power distribution of multifocal CLs. The CLs under study were: Air Optix Aqua Multifocal Low, Medium and High Addition and Focus Progressives. Three lenses of each model were considered.

RESULTS

All multifocal CLs showed a power profile characterized by a change toward more positive power values when aperture sizes become smaller. The near refractive addition of the lenses under study was +2.61 D, +1.44 D, +1.30 D and +0.30 D for the Focus Progressives, the Air Optix Aqua Multifocal High, Medium Add and Low Add, respectively. The refractive power of the Focus Progressives did not reach the value of the nominal distance power until a radial distance of 0.9 mm from the center of the lens. For the Air Optix Aqua Multifocal Low Add the distance nominal power was reached at a radial distance of 1.5mm from the center of the lens, whereas this occurred at a distance of 1.8mm for the Air Optix Aqua Multifocal Medium and High Add.

CONCLUSION

The relation between the pupil diameter of the patients and the power profile of these CLs has a crucial implication on the final distance correction and near addition that these lenses provide to patients. Practitioners should know the power profile of these CLs and measure the pupil diameter of each patient in different situations in order to carry out a customized fitting.