Impact of Spherical Aberration Terms on Multifocal Contact Lens Performance

BCLA CLEAR Presbyopia: Management with contact lenses and spectacles

This paper seeks to outline the history, market situation, clinical management and product performance related to the correction of presbyopia with both contact lenses and spectacles. The history of the development of various optical forms of presbyopic correction are reviewed, and an overview is presented of the current market status of contact lenses and spectacles. Clinical considerations in the fitting and aftercare of presbyopic contact lens and spectacle lens wearers are presented, with general recommendations for best practice. Current options for contact lens correction of presbyopia include soft simultaneous, rigid translating and rigid simultaneous designs, in addition to monovision. Spectacle options include single vision lenses, bifocal lenses and a range of progressive addition lenses. The comparative performance of both contact lens and spectacle lens options is presented. With a significant proportion of the global population now being presbyopic, this overview is particularly timely and is designed to act as a guide for researchers, industry and eyecare practitioners alike.

BCLA CLEAR Presbyopia: Evaluation and diagnosis

It is important to be able to measure the range of clear focus in clinical practice to advise on presbyopia correction techniques and to optimise the correction power. Both subjective and objective techniques are necessary: subjective techniques (such as patient reported outcome questionnaires and defocus curves) assess the impact of presbyopia on a patient and how the combination of residual objective accommodation and their natural DoF work for them; objective techniques (such as autorefraction, corneal topography and lens imaging) allow the clinician to understand how well a technique is working optically and whether it is the right choice or how adjustments can be made to optimise performance. Techniques to assess visual performance and adverse effects must be carefully conducted to gain a reliable end-point, considering the target size, contrast and illumination. Objective techniques are generally more reliable, can help to explain unexpected subjective results and imaging can be a powerful communication tool with patients. A clear diagnosis, excluding factors such as binocular vision issues or digital eye strain that can also cause similar symptoms, is critical for the patient to understand and adapt to presbyopia. Some corrective options are more permanent, such as implanted inlays / intraocular lenses or laser refractive surgery, so the optics can be trialled with contact lenses in advance (including differences between the eyes) to better communicate with the patient how the optics will work for them so they can make an informed choice.

Efficacy of Soft Contact Lenses for Myopia Control: A Systematic Review

PURPOSE

To summarize and analyze critically the scientific evidence focused on the effectiveness of the use of hydrophilic contact lenses (HCLs) in myopia control, as well as their impact on visual quality and the involvement on the accommodative and binocular function.

METHODS

This systematic review was developed selecting all original studies which evaluated HCLs for myopia control with follow-up of at least 1 year. Eligible randomized controlled trials (RCTs) were retrieved from PubMed MEDLINE and Scopus. Methodological quality of the studies was assessed using the Critical Appraisal Skills Programme (CASP) for RCTs.

RESULTS

The search provided a total of 276 articles, selecting 13 according to the inclusion and exclusion criteria. The majority of studies evaluating the effectiveness of HCL showed a good efficacy in myopia progression, providing a good quality of vision. The quality of these studies was found to be suitable according to the CASP tool. The accommodative and binocular function with these lenses was evaluated in few studies, reporting a trend to an increase in the accommodative response and exophoria in near vision, while maintaining good level of stereopsis. Aberrometry and pupillometry were only studied in one trial, in which the authors did not find changes in these variables after the use of a myopia control HCL.

CONCLUSIONS

There is a strong evidence about the effectiveness of different HCLs designs for slowing down myopia progression in children, providing all of them good levels of visual quality. However, there is still poor evidence about changes in accommodation and binocular function, as well as in pupil size and aberrometry with myopia control HCLs, being necessary more studies focused on this issue.

Content development for a new item-bank for measuring multifocal contact lens performance

BACKGROUND

Presbyopia is an age-related condition that causes a decreased ability to focus on nearby objects. Multifocal contact lenses are commonly used to address this issue. However, there seems to be a notable dissatisfaction among multifocal contact lens wearers. The absence of a reliable instrument to measure the patient's perspective, despite the widespread use of this method, highlights the need for further research in this area.

OBJECTIVE

The objective of this study is to develop an item-bank integrating all domains necessary to assess the patient's perspective on multifocal contact lens performance, offering a comprehensive measure. The item-bank will ensure a high level of content validity, be self-administered, and will initially be available in Spanish. The aim of this tool is to serve as a valuable resource for research and optometric clinics, facilitating the follow-up of patients with presbyopia who wear multifocal contact lenses or those who are newly starting to use them.

METHODOLOGY

The MCL-PRO item bank, followed a systematic and step-wise inductive approach to gather information, following the recommendations outlined in the COSMIN guidelines and similar studies. The process involved the following steps: (1) Literature review and relevant existing items identification (2) Social media review, (3) Semi-structured focus groups, (4) performing qualitative analysis, (5) refining and revising the items, and (6) generating the content of the item bank.

RESULTS

A total of 575 items were included in the item-bank hosted under 8 different domains that were found to be important for presbyopic population: visual symptoms (213), activity limitation (111), ocular symptoms (135), convenience (36), emotional well-being (33), general symptoms (16), cognitive issues (21) and economic issues (10).

CONCLUSION

The item-bank created has followed standardised methodology for its development and encloses all the aspects for MCL performance evaluation from patients perspective.

Visual Performance and Higher Order Aberrations Obtained With Omafilcon A Dual-Focus and Single-Vision Contact Lens Designs

OBJECTIVE

The purpose of this study was to assess the visual performance and monochromatic higher-order aberrations (HOAs) obtained while wearing a MiSight dual-focus (DF) contact lenses (CL) in comparison with a single-vision contact lens (SVCL).

METHODS

A randomized, double-masked, cross-over study was performed. Participants were fitted with a DFCL and a SVCL composed of the same material (omafilcon A) and parameters. Logarithm of the Minimum Angle of Resolution high-contrast (100%) and low-contrast (10%) visual acuity (VA) and contrast sensitivity (CS) for 3, 6, 12, and 18 cycles per degree were measured. Higher-order aberrations were also evaluated using a Hartmann-Shack aberrometer with the CLs on.

RESULTS

Twenty-four subjects (21 females and 3 males) with a mean age of 21.9±1.9 years (range: 18-27) were included. Low-contrast VA was significantly lower with the DFCL regarding the SVCL design (0.39±0.23 vs 0.25±0.18, P=0.002). However, there were no differences in high-contrast VA between both CLs (-0.03±0.10 vs -0.09±0.14, P=0.187). Contrast sensitivity was lower with the DFCL under all spatial frequencies (P≤0.048). Second-, third-, fourth-, and fifth-order aberrations were significantly (P<0.001) higher for the DFCL. There were also significant differences between DFCL and SVCL in defocus (0.87±0.28 vs 0.16±0.35, P<0.001), oblique trefoil (-0.16±0.27 vs -0.01±0.08, P=0.005), vertical coma (0.13±0.17 vs 0.00±0.08, P=0.002), and spherical aberration (0.09±0.11 vs -0.02±0.05, P=0.002).

CONCLUSION

Visual performance for detecting low-contrast targets is reduced when wearing MiSight DFCL compared with a SVCL with the same material. The main reason might be the induction of second-order and HOAs by the DFCL design.

Comparison of visual performance and image quality between a myopia-control contact lens and a single-vision contact lens

OBJECTIVE

This study aimed to evaluate the visual performance and image quality of concentric dual-focus-designed contact lenses (CLs) compared with single-vision CLs in myopic Chinese people.

METHODS

Twenty myopic volunteers aged between 18 and 26 years were recruited at a university eye hospital to wear both defocus-incorporated soft contact (DISC) lenses and single-vision CLs for 1 week in random order. High- and low-contrast visual acuity (VA), contrast sensitivity (CS), ocular higher-order aberrations (HOA), Strehl ratio and the Quality of Vision (QoV) questionnaire were assessed with each type of CL at weekly follow-up.

RESULTS

Distance VA was not affected by DISC lenses compared to single-vision CLs in either high (p = 0.414) or low contrast (p = 0.431). However, there was a significant reduction in low-contrast near VA with DISC lenses compared with single-vision CLs (p = 0.011). The differences of CS between DISC lenses and single-vision CLs were significantly associated with lighting conditions and spatial frequencies (F = 128.81, P < 0.001). Compared with single-vision CLs, wavefront aberrations of DISC lenses were significantly increased in total HOA, trefoil, and spherical aberrations for either 3.0 mm or 6.0 mm pupil size. The Strehl ratio wearing DISC lenses reduced significantly compared to the single-vision CLs (p < 0.001) at a pupil diameter of 6.0 mm. QoV scores were higher overall (p = 0.026) and frequency (p = 0.019) with DISC lenses than with single-vision CLs, indicating poorer visual performance.

CONCLUSION

DISC lenses provide satisfactory distance VA. However, the higher scores of the QoV questionnaire with DISC lenses may be related to decreased CS at medium or high spatial frequencies and increased higher-order aberrations.

The effect of concentric and aspheric multifocal soft contact lenses on binocular vision in young adult myopes

PURPOSE

Multifocal soft contact lenses (MFCLs) are prescribed to inhibit myopia progression; these include aspheric and concentric designs. The effects of MFCLs on visual quality, accommodation and vergence in young-adult myopes were evaluated.

METHODS

Participants were twenty-six myopes (19-25 years, spherical equivalent -0.50 to -5.75D), with normal binocular vision and no past myopia control. Pupil sizes were 4.4 ± 0.9 mm during distance viewing and 3.7 ± 0.8 mm at near. In random order, participants wore four MFCLs: Proclear single vision distance, MiSight concentric dual focus (+2.00D), distance center aspheric (Biofinity, +2.50D) (CooperVision lenses), and NaturalVue aspheric (Visioneering Technologies). Testing included visual acuity, contrast sensitivity (Pelli-Robson), stereoacuity, accommodation response, negative and positive relative accommodation, horizontal phorias, horizontal fusional vergence and AC/A ratio, and a visual quality questionnaire.

RESULTS

The four lenses differed in distance (p = 0.001) and near visual acuity (p = 0.011), and contrast sensitivity (p = 0.001). Compared with the single vision lens, the Biofinity aspheric had the greatest visual impact: 0.19 ± 0.14 logMAR distance acuity reduction, 0.22 ± 0.15 log contrast sensitivity reduction. Near acuity was affected less than distance acuity; the reduction was greatest with the NaturalVue (0.05 ± 0.07 logMAR reduction). The MFCLs altered the autorefraction measure at distance and near (p = 0.001); the accommodation response was less with aspheric lenses. Negative relative accommodation reduced with the aspheric lenses (p = 0.001): by 0.9 ± 0.5D with Biofinity and 0.5 ± 0.7D with NaturalVue. Exophoric shifts were greater with aspheric lenses (1.8 ± 2.4Δ Biofinity, 1.7 ± 1.7Δ NaturalVue) than with the concentric MiSight (0.5 ± 1.3Δ).

CONCLUSIONS

MFCLs alter visual performance, refraction and vergence; two aspheric lenses had greater effect than a concentric lens.

Short-term tear film stability, optical quality and visual performance in two dual-focus contact lenses for myopia control with different optical designs

Purpose

To assess and compare short‐term visual and optical quality and tear film stability between two dual‐focus (DF) prototype myopia control contact lenses (CLs) having different inner zone diameters.

Methods

Twenty‐eight myopic subjects were included in this randomised, double‐masked crossover study. Refraction, best‐corrected visual acuity (VA) and tear film stability were measured at baseline (i.e., when uncorrected). Subjects were then binocularly fitted with the DF CLs, with only the sensorial dominant eye being assessed. Lenses were of the same material and had inner zone diameters of either 2.1 mm (S design) or 4.0 mm (M design). Visual and physical short‐term lens comfort, over‐refraction, best‐corrected VA, stereopsis at 40 cm, best‐corrected photopic and mesopic contrast sensitivity (CS), size and shape of light disturbance (LD), wavefront aberrations, subjective quality of vision (QoV Questionnaire) and tear film stability were measured for each lens.

Results

Both CL designs decreased tear film stability compared with baseline (p < 0.05). VA and photopic CS were within normal values for the subjects' age with each CL. When comparing lenses, the M design promoted better photopic CS for the 18 cycles per degree spatial frequency (p < 0.001) and better LD (p < 0.02). However, higher‐order aberrations were improved with the S design (p = 0.02). No significant difference between the two CLs was found for QoV scores and tear film stability.

Conclusions

Both DF CLs provided acceptable visual performance under photopic conditions. The 4.0 mm inner zone gave better contrast sensitivity at high frequencies and lower light disturbance, while the 2.1 mm central diameter induced fewer higher‐order aberrations for a 5 mm pupil diameter. Both CLs produced the same subjective visual short‐term lens comfort.

Comprehensive design method of a soft multifocal contact lens with NURBS

This study presents a comprehensive method for designing a multifocal contact lens (MCL) with Snell's law and non-uniform rational B-spline (NURBS) curves. Instead of using thin lens approximation, general mathematical formulas have been developed to achieve the accurate coordinates of points on the anterior lens surface profile of the MCL to meet various given optical power distributions. Then the NURBS curve is adjusted to fit these data points to obtain the smooth front lens surface profile. This method not only improves the accuracy of the optical power profiles of MCLs but also reduces the spherical aberration in near/distance optical zones. The experimental results show that the power profiles of soft MCLs agree with those of the simulation results and original design requirements. The proposed method has been proven for the MCL design, and it can be feasibly applied in complex optical lens designs.

Multifocal contact lenses: A bibliometric study

PURPOSE

To analyze the state of scientific publications in multifocal contact lenses field through a bibliometric study.

METHODS

The database used to carry out the study was SCOPUS and contained the descriptors "multifocal contact lens", "bifocal contact lenses", "progressive contact lenses" and "presbyopia contact lenses", limited to the fields of title, keywords and abstract. The indicators applied in this research were: doubling time and annual growth rate, Price's transience index, Lotka's law of scientific productivity, and Bradford's zones.

RESULTS

A total of 346 articles were published between 1960 and 2019. The growth in the number of publications matches the exponential adjustment slightly better (R = 0.53). The duplication time was 13.2 years. The productivity level is focused on articles with an average number of authors of just 2.06 per article. The Bradford core was formed by two journals, Optometry and Vision Science and Eye and Contact Lens.

CONCLUSIONS

Research on multifocal contact lenses has exponential growth, without evidence of having reached a saturation point. The main countries in scientific production in this field are the United States and Australia.

Multifocal contact lens design, not addition power, affects accommodation responses in young adult myopes

PURPOSE

Prolonged nearwork has been implicated in myopia progression. Accommodation responses of young-adult myopes wearing different multifocal contact lenses were compared.

METHODS

Twenty adults, 18-25 years, with myopia (spherical equivalent refraction -0.50 to -5.50 D, mean -2.1 ± 1.6 D) wore five lens types in random order: Proclear single vision distance (SV), MiSight concentric dual-focus +2.00 D Add (MS), Biofinity aspheric centre distance +1.50 D Add (CD1) and +2.50 D Add (CD2) (all Coopervision), and NaturalVue aspheric (Visioneering Technologies) (NVue). Using a Grand-Seiko WAN-5500 autorefractor with binocular correction and viewing right eye accommodative responses were measured after a 10 min adaptation period at 4.0, 1.0, 0.5, 0.33 and 0.25 m distances. Dynamic measurements were taken for 4 s at 6 Hz. Accommodative stimuli and responses were referenced to 4 m (i.e., refraction differences between 4 m and nearer distances). Accommodation lags and refraction instabilities (standard deviations of dynamic responses) were determined. For comparison, results were obtained for an absolute presbyopic eye, where trial lenses counteracted the accommodation stimulus.

RESULTS

For SV and MS, accommodation responses were similar to the stimulus values. For aspheric lenses CD1, CD2 and NVue, accommodation responses were approximately 1.0 D lower across the stimulus range than with SV and MS, and rates of change were approximately 0.84 D per 1 D stimulus change. MS produced greater refraction instabilities than other lenses. For the presbyope, changes in refraction matched the trial lenses, indicating that corrections due to measurement through the different lenses were not needed.

CONCLUSION

Reductions in accommodation response occurred in young myopes wearing aspheric multifocal contact lenses independent of the labelled 'add' power. The concentric dual-focus MS lens produced minimal lags but had greater instability than the other lenses. The results indicate that the mechanism of multifocal contact lenses slowing myopia progression is unlikely to be through relaxing accommodation, at least in young adults.

Correcting Presbyopia With Autofocusing Liquid-Lens Eyeglasses

OBJECTIVE

Presbyopia, an age-related ocular disorder, is characterized by the loss in the accommodative abilities of the human eye. Conventional methods of correcting presbyopia divide the field of view, thereby resulting in significant vision impairment. We demonstrate the design, assembly and evaluation of autofocusing eyeglasses for restoration of accommodation without dividing the field of view.

METHODS

The adaptive optics eyeglasses comprise of two variable-focus liquid lenses, a time-of-flight range sensor and low-power, dual microprocessor control electronics, housed within an ergonomic frame. Subject-specific accommodation deficiency models were utilized to demonstrate high-fidelity accommodative correction. The abilities of this system to reduce accommodation deficiency, its power consumption, response time, optical performance and MTF were evaluated.

RESULTS

Average corrected accommodation deficiencies for 5 subjects ranged from -0.021 D to 0.016 D. Each accommodation correction calculation was performed in ∼67 ms which consumed 4.86 mJ of energy. The optical resolution of the system was 10.5 cycles/degree, and featured a restorative accommodative range of 4.3 D. This system was capable of running for up to 19 hours between charge cycles and weighed ∼132 g.

CONCLUSION

The design, assembly and performance of an autofocusing eyeglasses system to restore accommodation in presbyopes has been demonstrated.

SIGNIFICANCE

The new autofocusing eyeglasses system presented in this article has the potential to restore pre-presbyopic levels of accommodation in subjects diagnosed with presbyopia.

Clinical performance of presbyopia correction with a multifocal corneoscleral lens

AIM

To assess the clinical performance of a multifocal corneoscleral lens for the presbyopia correction.

METHODS

A prospective clinical trial of the Onefit™ A multifocal corneoscleral lens was conducted with 40 participants with presbyopia. At 4wk of continuous wear of the corneoscleral lens, changes in the distance, intermediate, and near visual acuity (VA) were evaluated. The safety of the corneoscleral lens, central corneal thickness (CCT), corneal endothelial cell count, binocular stereopsis, tear film break-up time (BUT), corneal staining, corneal edema, corneal neovascularization (NV), and conjunctival hyperemia were examined. In addition, a subjective questionnaire addressing satisfaction (rated from 1 to 5 points) and discomfort (rated from 1 to 5 points) was administered.

RESULTS

Forty participants were enrolled in this study. Six participants were excluded because of poor compliance with lens fitting (n=2) and loss to follow-up (n=4). The mean age of the participants was 53.0±4.9y. At 4wk of continuous wear of the corneoscleral lens, the best corrected far, intermediate, and near VA was 0.08±0.11, 0.10±0.12, and 0.10±0.12 logMAR, respectively. These results were significant improvements over the baseline uncorrected VA (far: P=0.004; intermediate: P=0.004; near: P=0.002). CCT, corneal endothelial cell count, binocular stereopsis, BUT, corneal staining, corneal edema, corneal NV, and conjunctival hyperemia were not significantly different between baseline and after corneoscleral lens use. The average satisfaction scores for fit sensation; corrected far, intermediate, and near VA; and ease of handling were 4.1, 3.4, 3.6, 3.5, and 3.4, respectively. The average discomfort scores for dryness, irritation, foreign body sensation, redness, fogging, and halo were 1.7, 1.8, 1.5, 1.7, 1.7, and 1.3, respectively.

CONCLUSION

Far, intermediate, and near VA are improved in presbyopic patients with the multifocal corneoscleral lens compared to uncorrected baseline VA, without adverse ocular effects. This evidence supports the safety and effectiveness of presbyopia correction with multifocal corneoscleral lenses.

Subjective Evaluation of Defocus and Astigmatism Combinations Using Image Simulation in Presbyopes

SIGNIFICANCE

Image simulation is a useful and efficient tool to explore the impact of defocus and astigmatism combinations on visual acuity and image quality score when accommodation is taken into account.

PURPOSE

The goal of this experiment was to determine if a simulation is able to predict visual acuity and image quality score (IQS) with defocus and astigmatism combinations in presbyopes.

METHODS

We measured visual acuity and IQS in five defocus and astigmatism combinations in either real or simulated conditions. In real conditions, the subjects viewed a stimulus through an ophthalmic lens or a deformable mirror. In simulated conditions, subjects viewed images of the same stimulus with simulated blur. The amounts of defocus and astigmatism combinations of a progressive addition lens in near vision were generated through a static correction of the subject's aberrations. We simulated three levels of accommodation: subject could not accommodate (FOC0), subject could accommodate to the less hyperopic focal point (FOC1), or subject could accommodate to the circle of least confusion (FOC2).

RESULTS

Visual acuity or IQS did not differ between mirror and progressive addition lens conditions. Visual acuity measured in real blur conditions differed significantly from that in FOC0 simulated blur condition but were similar to that in FOC1 and FOC2 simulated blur conditions. Image quality score obtained in real conditions were between scores measured with the FOC0 and FOC1 simulated conditions, suggesting that the subjects were able to produce a low level of accommodation.

CONCLUSIONS

Accommodation may play a role when comparing optical and simulated defocus and astigmatism combinations. Presbyopic subjects are able to produce a low level of accommodation that may counterbalance a part of the deleterious effect of the astigmatism on image quality. Simulation remains a useful tool if the correct accommodation state is taken into account.

Visual quality of juvenile myopes wearing multifocal soft contact lenses

Background

It is unclear whether multifocal soft contact lenses (MFSCLs) affect visual quality when they are used for myopia control in juvenile myopes. The aim of this study was, therefore, to investigate the effect of MFSCLs on visual quality among juvenile myopia subjects.

Methods

In a prospective, intervention study, thirty-three juvenile myopes were enrolled. Visual perception was assessed by a quality of vision (QoV) questionnaire with spectacles at baseline and after 1 month of MFSCL wear. At the one-month visit, the high (96%) contrast distance visual acuity (distance HCVA) and low (10%) contrast distance visual acuity (distance LCVA) were measured with single vision spectacle lenses, single vision soft contact lenses (SVSCLs) and MFSCLs in a random order. Wavefront aberrations were measured with SVSCLs, with MFSCLs, and without any correction.

Results

Neither distance HCVA (p > 0.05) nor distance LCVA (p > 0.05) revealed any significant difference between MFSCLs, SVSCLs and single vision spectacle lenses. The overall score (the sum of ten symptoms) of the QoV questionnaire did not show a statistically significant difference between spectacles at baseline and after 1 month of MFSCL wear (p = 0.357). The results showed that the frequency (p < 0.001), severity (p = 0.001) and bothersome degree (p = 0.016) of halos were significantly worse when wearing MFSCLs than when wearing single vision spectacle lenses. In contrast, the bothersome degree caused by focusing difficulty (p = 0.046) and the frequency of difficulty in judging distance or depth perception (p = 0.046) were better when wearing MFSCLs than when wearing single vision spectacle lenses. Compared with the naked eye, MFSCLs increased the total aberrations (p < 0.001), higher-order aberrations (p < 0.001), trefoil (p = 0.023), coma aberrations (p < 0.001) and spherical aberrations (SA) (p < 0.001). Compared with the SVSCLs, MFSCLs increased the total aberrations (p < 0.001), higher-order aberrations (p < 0.001), coma aberrations (p < 0.001) and SA (p < 0.001). The direction of SA was more positive (p < 0.001) with the MFSCLs and more negative (p = 0.001) with the SVSCLs compared with the naked eye.

Conclusions

Wearing MFSCLs can provide satisfactory corrected visual acuity (both distance HCVA and distance LCVA). Although the lenses increased the aberrations, such as total aberrations and higher-order aberrations, there were few adverse effects on the distance HCVA, distance LCVA and visual perception after 1 month of MFSCL use.

Trial registration

Chinese Clinical Trial Registry: ChiCTR-OOC-17012103. Registered 23 July 2017, http://www.chictr.org.cn/usercenter.aspx

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.

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.

Disability glare in soft multifocal contact lenses

PURPOSE

The study investigated the effect of the design of multifocal contact lenses on the sensitivity to contrast and disability glare.

METHODS

Contrast sensitivity was measured in 16 young adults (mean age: 25.5±2.5years) at a distance of 2m under two conditions: no-glare and glare. Two designs (Center Near and Center Distance) of the Biofinity soft contact lens were used to simulate correction for presbyopes, while a correction with single vision trial lenses and contact lenses acted as controls.

RESULTS

The design of the used multifocal contact lenses had a significant influence on the log area under the curve of the contrast sensitivity function (AUC-CSF). Compared to the spectacle lens correction, the AUC-CSF was significantly reduced, in case CS was measured with the Center Near design lens, under the no-glare (p<0.001) and the glare condition (p: p<0.001). In case of the Center Distance design contact lens, the AUC-CSF was significantly smaller in case CS was tested under glare (p=0.001). Disability glare (DG) was depending on the spatial frequency and the design of the multifocal lens, while the Center Distance design produced higher amounts of DG (p<0.001), compared to the other used corrections.

CONCLUSION

The optical design of a multifocal contact lenses has a significant impact on the contrast sensitivity as well as the disability glare. In order to dispense the best correction in terms of contact lenses, the sensitivity to contrast under no-glare and glare conditions should be tested a medium spatial frequencies.