Does the Level of Available Oxygen Impact Comfort in Contact Lens Wear?: A Review of the Literature

The Impact of Comfort Eluting Agents and Replacement Frequency on Enhancing Contact Lens Performance

This review explores the development and clinical implications of soft contact lenses designed to elute comfort agents, emphasizing their role in enhancing user experience and ocular health. As discomfort remains one of the primary reasons for discontinuation of lens wear, this concept aims to address this challenge by gradually releasing these agents over their period of use. This review also explores the effectiveness, safety, and user satisfaction associated with frequent replacement schedules of these lenses. Clinical trials demonstrate that lenses with eluting comfort agents significantly reduce dryness and irritation, leading to improved wear-time and overall comfort. The findings suggest that frequent replacement not only enhances lens hygiene but also maximizes the therapeutic benefits of the eluted agents, promoting a healthier ocular environment. The implications for practice highlight a shift towards more patient-centered approaches in contact lens design and management, aiming to improve adherence and satisfaction among users. This research paves the way for future innovations in contact lens technology, focusing on personalized solutions that cater to individual comfort needs.

Optimization of the Oxygen Permeability of Non-Silicone Hydrogel Contact Lenses Through Crosslinking Modifications

The main weakness of non-silicone hydrogel contact lenses is their low oxygen permeability (Dk). Hence, we have tried to optimize their Dk using various concentrations and lengths of the poly (ethylene glycol) dimethacrylate crosslinker in a mixture of N,N-Dimethylacrylamide and Cyclohexyl methacrylate monomers. After synthesizing the different contact lenses, we evaluated their chemical, optical, and mechanical properties. The resultant non-silicone hydrogel contact lenses presented similar high water contents (75.69-80.60%) and adequate optical (e.g., a transmittance ranging from 85.91% to 99.91% and a refractive index between 1.3630 and 1.3740) and elongation at break (178.95-356.05%) characteristics for clinical applications. Conversely, they presented high contact angles (81.00-100.00°) and a low Young's modulus (0.066-0.167 MPa). Regarding the impact of the crosslinking modifications, the water content, contact angle, refractive index, transmittance, and Young's modulus of the synthesized lenses were slightly affected by crosslinker conditions. In contrast, the elongation at break (178.95-356.05%) and, more importantly, the oxygen permeability, which reached values of up to 73.90 Fatt units, were considerably impacted by the crosslinker conditions. To our knowledge, this study demonstrates for the first time that, in addition to water, other usual hydrogel components, like crosslinkers, can modulate the Dk of non-silicone contact lenses. It also provides a simple and scalable method to fabricate more permeable non-silicone lenses.

Silicone hydrogel versus hydrogel soft contact lenses for differences in patient-reported eye comfort and safety: A Cochrane systematic review summary

SIGNIFICANCE

This work is significant because it is the first Cochrane systemic review that compares the comfort and safety of hydrogel and silicone hydrogel soft contact lenses (SCL).

PURPOSE

This study aimed to conduct a systemic review of randomized trials comparing the comfort and safety of silicone hydrogel and hydrogel SCLs.

METHODS

CENTRAL, MEDLINE Ovid, EMBASE.com , PubMed, LILACS, ClinicalTrials.gov , and World Health Organization International Clinical Trials Registry Platform were searched on or before June 24, 2022, to identify randomized clinical trials that compared silicone hydrogel and hydrogel SCLs.

RESULTS

Seven trials were identified and evaluated. One trial reported Ocular Surface Disease Index results, with the evidence being very uncertain about the effects of SCL material on Ocular Surface Disease Index scores (mean difference, -1.20; 95% confidence interval, -10.49 to 8.09). Three trials reported visual analog scale comfort score results, with no clear difference in comfort between materials, although results were of low certainty; trial results could not be combined because the three trials reported results at different time points. None of the included trials reported Contact Lens Dry Eye Questionnaire 8 or Standard Patient Evaluation of Eye Dryness scores. There was no evidence of a clinically meaningful difference (>0.5 unit) between daily disposable silicone hydrogel and hydrogel SCLs in corneal staining, conjunctival staining, or conjunctival redness (very low certainty evidence).

CONCLUSIONS

The overall evidence for a difference between all included silicone hydrogel and hydrogel SCL trials was of very low certainty, with most trials judged as having a high overall risk of bias. There was insufficient evidence to support recommending one SCL material over the other. Future well-designed trials are needed to generate high certainty evidence to further clarify differences in SCL material comfort and safety.

Silicone hydrogel versus hydrogel soft contact lenses for differences in patient-reported eye comfort and safety

BACKGROUND

Ocular discomfort is the leading cause of permanent discontinuation of soft contact lens (SCL) wear. Silicone hydrogel and hydrogel materials are the two major categories of SCLs, with silicone hydrogel materials being newer and more breathable than hydrogel materials. Whether comfort is associated with SCL material is controversial despite numerous studies. Similarly, the difference between these materials in terms of safety outcomes (e.g. frequency of microbial keratitis) is unclear.

OBJECTIVES

To evaluate the comparative effectiveness and safety of silicone hydrogel compared with hydrogel SCLs on self-reported comfort, dry eye test results, and adverse events in SCL-wearing adults 18 years of age or older.

SEARCH METHODS

The Cochrane Eyes and Vision Information Specialist searched the electronic databases for randomized controlled trials (RCTs). There were no restrictions on language or date of publication. We searched the Cochrane Central Register of Controlled Trials (CENTRAL, including the Cochrane Eyes and Vision Trials Register; 2022, Issue 6), MEDLINE Ovid, Embase.com, PubMed, LILACS (Latin American and Caribbean Health Science Information database), ClinicalTrials.gov, and World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP). We also searched the reference lists of identified studies, review articles, and guidelines for information about relevant studies that may not have been identified by our search strategy. Furthermore, we contacted investigators regarding ongoing trials. The most recent database search was conducted on 24 June 2022.

SELECTION CRITERIA

Our search selection criteria included RCTs, quasi-RCTs, and cross-over RCTs.

DATA COLLECTION AND ANALYSIS

We applied standard Cochrane methodology.

MAIN RESULTS

We included seven parallel-group RCTs conducted in the USA, the UK, Australia, Germany, India, and Turkey. A total of 1371 participants were randomized. The duration of SCL wear ranged from one to 52 weeks. Study characteristics and risk of bias The median number of participants per trial was 120 (interquartile range: 51 to 314), and the average age ranged from 20.7 to 33.0 years. Women represented the majority of participants (range 55% to 74.9%; 5 RCTs). Collectively, the included trials compared eight different silicone hydrogel SCLs with three different hydrogel SCLs. Five trials compared daily disposable SCLs, and two compared extended wear SCLs (worn for seven days and six nights). New SCL wearers were enrolled in three trials. Two trials included both new and established SCL wearers, and two trials did not report participants' history of SCL use. Five trials were sponsored by industry. We judged the overall risk of bias to be 'high' or 'some concerns' for the safety and efficacy outcomes. Findings One trial reported Ocular Surface Disease Index (OSDI) results, with the evidence being very uncertain about the effects of SCL material on OSDI scores (mean difference -1.20, 95% confidence interval [CI] -10.49 to 8.09; 1 RCT, 47 participants; very low certainty evidence). Three trials reported visual analog scale comfort score results, with no clear difference in comfort between materials, but the evidence was of very low certainty; trial results could not be combined because the three trials reported results at different time points. The evidence is very uncertain about the effect of SCL material on discontinuation of contact lens wear (risk ratio [RR] 0.64, 95% CI 0.11 to 3.74; 1 RCT, 248 participants). None of the included trials reported Contact Lens Dry Eye Questionnaire (CLDEQ-8) or Standard Patient Evaluation of Eye Dryness (SPEED) scores. There was no evidence of a clinically meaningful difference (> 0.5 unit) between daily disposable silicone hydrogel and hydrogel SCLs in corneal staining, conjunctival staining, or conjunctival redness (very low certainty evidence). Adverse events Very low certainty evidence from two trials comparing daily disposable SCLs suggested no evidence of a difference between lens materials in the risk of vision-threatening adverse events at one to four weeks (RR 0.68, 95% CI 0.08 to 5.51; 2 RCTs, 368 participants). Two trials comparing extended wear SCLs indicated that hydrogel SCLs may have a 2.03 times lower risk of adverse events at 52 weeks compared with silicone hydrogel SCLs (RR 2.03, 95% CI 1.38 to 2.99; 815 participants), but the certainty of evidence was very low.

AUTHORS' CONCLUSIONS

The overall evidence for a difference between all included silicone hydrogel and hydrogel SCLs was of very low certainty, with most trials at high overall risk of bias. The majority of studies did not assess comfort using a validated instrument. There was insufficient evidence to support recommending one SCL material over the other. For extended wear, hydrogel SCL may have a lower risk of adverse events at 52 weeks compared to silicon hydrogel. Future well-designed trials are needed to generate high certainty evidence to further clarify differences in SCL material comfort and safety.

TFOS Lifestyle: Impact of contact lenses on the ocular surface

Several lifestyle choices made by contact lens wearers can have adverse consequences on ocular health. These include being non-adherent to contact lens care, sleeping in lenses, ill-advised purchasing options, not seeing an eyecare professional for regular aftercare visits, wearing lenses when feeling unwell, wearing lenses too soon after various forms of ophthalmic surgery, and wearing lenses when engaged in risky behaviors (e.g., when using tobacco, alcohol or recreational drugs). Those with a pre-existing compromised ocular surface may find that contact lens wear exacerbates ocular disease morbidity. Conversely, contact lenses may have various therapeutic benefits. The coronavirus disease-2019 (COVID-19) pandemic impinged upon the lifestyle of contact lens wearers, introducing challenges such as mask-associated dry eye, contact lens discomfort with increased use of digital devices, inadvertent exposure to hand sanitizers, and reduced use of lenses. Wearing contact lenses in challenging environments, such as in the presence of dust and noxious chemicals, or where there is the possibility of ocular trauma (e.g., sport or working with tools) can be problematic, although in some instances lenses can be protective. Contact lenses can be worn for sport, theatre, at high altitude, driving at night, in the military and in space, and special considerations are required when prescribing in such situations to ensure successful outcomes. A systematic review and meta-analysis, incorporated within the review, identified that the influence of lifestyle factors on soft contact lens dropout remains poorly understood, and is an area in need of further research. Overall, this report investigated lifestyle-related choices made by clinicians and contact lens wearers and discovered that when appropriate lifestyle choices are made, contact lens wear can enhance the quality of life of wearers.

Exploring the factors which impact overall satisfaction with single vision contact lenses

PURPOSE

To explore the impact of subjective factors (lens handling, comfort and vision) on overall single vision contact lens satisfaction.

METHODS

Correlation analysis of a prospective, randomised, double-masked, bilateral crossover study involving 55 adapted lens wearers fitted with somofilcon A (SiHy) (clariti® 1 day, CooperVision) and etafilcon A (Hy) (1 DAY ACUVUE® MOIST, Johnson & Johnson Vision) was conducted. Subjective ratings of lens handling, comfort and vision collected after 1 week of lens wear for each lens type were correlated with overall satisfaction. Data were analysed by combining data for both lens types and also for each lens separately.

RESULTS

For the combined analysis, significant correlations (p < 0.01) were found between subjective ratings of overall satisfaction and ratings of handing for application (r = 0.64), handling for removal (r = 0.50), comfort upon application (r = 0.59), comfort at end of day (r = 0.61), overall satisfaction with comfort (r = 0.88) and overall satisfaction with vision (r = 0.64). Correlation analysis of the per lens data showed that lens specific correlations of overall satisfaction with handling for lens application varied greatly with lens material (SiHy: r = 0.26, p = 0.05 vs Hy: r = 0.72, p < 0.01). Correlation strength of comfort upon application/at end of day with overall satisfaction also varied with lens material (Application: SiHy: r = 0.40 vs Hy: r = 0.61; End of day: SiHy: r = 0.76 vs Hy: r = 0.58; all p ≤ 0.01).

CONCLUSION

Overall satisfaction was significantly correlated with the specific subjective evaluations of handling, vision and comfort. Correlations of overall satisfaction and ease of handling for each lens type suggest that, for habitual contact lens wearers, dissatisfaction with handling at the time of lens application can play a major role in overall dissatisfaction with a lens. Handling for application had a similar correlation (r) value as vision, suggesting that handling for application should not be underestimated when considering overall patient satisfaction.

Addressing common myths and misconceptions in soft contact lens practice

Advances in contact lens technology over the past 50 years since the commercialisation of the first soft lenses in 1971 have been incredible, with significant changes in contact lens materials, frequency of replacement, care systems and lens designs occurring. However, despite the widespread availability of contact lenses, penetration rates for those who need vision correction remain in the low single digits and many practitioners seem to hold on to concepts around the potential value of contact lenses that appear based in the dim and distant past and are certainly no longer valid today. This review addresses 10 common 'myths and misconceptions' around soft contact lenses using an evidence-based approach that can hopefully dispel some of these incorrect assumptions.

Compressive behaviour of soft contact lenses and its effect on refractive power on the eye and handling off the eye

PURPOSE

To investigate the stress-strain behaviour of 9 soft contact lens materials, that are commonly used in the market, under uniaxial compression loading.

METHODS

Seven types of hydrogel and two types of silicone-hydrogel soft contact lens materials were hydrated in phosphate-buffered saline (PBS) solution then subjected to uniaxial compression loads. The load rate was set to 16.0 N/min starting with two consecutive initial 5.0 N loading cycles followed by three relaxation periods of 4.0 min within which there were two more 5.0 N loading cycles and eventually, a full loading cycle that stopped at a load of 49.0 N. The load and contraction data obtained experimentally were analysed to derive the stress-strain behaviour. Finite Element (FE) analysis was then utilised to evaluate the performance of soft contact lenses on the human eye and handling lenses off the eye.

RESULTS

Unlike tensile tests, all tested materials showed nonlinear behaviour when tested under compression. When fitted to first-order Ogden hyperelastic model, parameter μ was found to be varying in the range 0.12 to 0.74 MPa and material parameter α was found to be varying in the range 8.2 to 20.326 among the nine tested materials. Compression modulus of elasticity was 2.2 times higher than the tensile modulus of elasticity on average. FE simulation with nonlinear Ogden constitutive model showed a limited change (8%~12%) in the optical performance when compared to other material models, however, it predicted higher stress when the lens was simulated under bending during off-eye handling.

CONCLUSIONS

Compression tests revealed slightly nonlinear behaviour when materials were strained under compression stress down to 15% ~ 30% of their nominal heights. Considering the physiological compression loading range of 8 mmHg, secant moduli of elasticity were 1.5% to 6.9% higher than the tension moduli of elasticity depending on the material. Tensile-based moduli of elasticity could be used in FE analysis as a step towards simulating the optical performance of soft contact lenses on-eye. However, nonlinear compression-based material models are recommended for FE analysis of soft contact lenses when lens-handling is investigated off-eye.

Impact of Contact Lens Material, Design, and Fitting on Discomfort

OBJECTIVE

To review the effect of contact lens (CL) material, design, and fitting characteristics on CL discomfort.

METHODS

A PubMed search identified publications describing subjective comfort and CL material, fitting, and design parameters. The review included clinical signs associated with discomfort that may be a consequence of these parameters.

RESULTS

Reduced lens movement or more CL tightness were associated with improved comfort. Increased lens-induced paralimbal conjunctival staining and indentation, considered as quasi-indicators of CL fitting or edge design, were also associated with better comfort. No recent studies have evaluated varying CL design parameters and subjective comfort. Silicone hydrogel CLs are no different in comfort compared with hydrogel CLs. Lower equilibrium water content is associated with improved comfort in hydrogel CL wear. Coefficient of friction shows promise as a material factor potentially associated with comfort. Lid wiper epitheliopathy and lid-parallel conjunctival folds have been linked with comfort in established wearers.

CONCLUSIONS

Recent studies have confirmed the association between more mobile CLs and more discomfort, whereas closer conformity of the CL to the bulbar conjunctiva improved subjective comfort. There is no evidence to support the perceived comfort difference between silicone hydrogel and hydrogel CL. There has been limited progress in understanding the impact of varying specific CL design parameters. Although specific clinical signs may be predictive of discomfort, their role in the natural history of discomfort remains unclear. A better understanding of the relationship between coefficient of friction and comfort and strategies to improve lubricity may hold promise for limiting CL discomfort.

Oral omega-3 fatty acid treatment for dry eye in contact lens wearers

PURPOSE

The aim of this study was to evaluate the effect of dietary omega-3 fatty acid (O3FA) supplementation on dry eye symptoms, tear film tests, and conjunctival impression cytology in patients with contact lens wear-associated dry eye.

METHODS

In this randomized, double-blind, multicentric trial, contact lens wearers (n = 496) were randomized to receive either O3FAs or placebo capsules (corn oil) twice daily for 6 months. Subjects underwent examinations at baseline, 3 months, and 6 months. At each visit, a questionnaire of dry eye symptoms and lens wear comfort was administered. Subjects further underwent measurement of tear film break-up time (TBUT) and a Schirmer test. Conjunctival impression cytology was performed by the transfer method. Improvement in symptoms and lens wear comfort were primary outcome measures. Changes from baseline in TBUT, Schirmer, and Nelson grade at 6 months were secondary outcome measures.

RESULTS

The mean improvement in symptom score in the O3FA group was 4.7 ± 2 (2.0) as compared with 0.5 ± 2 (0.9) in the placebo group (P < 0.0001). Lens wear comfort levels improved significantly (P < 0.0001) from baseline. There was a significant increase in TBUT [3.3 ± 2 (1.5)] and Nelson grade [0.7 ± 2 (0.6)] in the O3FA group (P < 0.0001) as compared with 0.3 ± 2 (0.6) and 0.1 ± 2 (0.4) in the placebo group (P = 0.164 and 0.094, respectively). However, the magnitude of increase in Schirmer score [2.0 ± 2 (1.5)] was relatively small (P = 0.08).

CONCLUSIONS

The results of this study point toward benefits of orally administered O3FAs in alleviating dry eye symptoms, improving lens wear comfort, and cytological changes in contact lens wearers.

Prevention and removal of lipid deposits by lens care solutions and rubbing

PURPOSE

Despite the prevalence of silicone hydrogel (SiHy) contact lenses, there are relatively few studies that evaluate the efficacy of multipurpose lens care solutions (MPSs) in reducing lipid deposition on these lenses and the effect of rubbing on the removal. Therefore, we used an in vitro soaking and rubbing model to compare the effectiveness of borate buffered saline (BBS) and two commercial MPSs, PureMoist and Biotrue, in preventing sorption of representative polar and nonpolar lipids.

METHODS

Radiolabeled cholesterol (CH) and dipalmitoylphosphatidylcholine (DPPC) were sorbed on two SiHy lenses (senofilcon A and balafilcon A) from an artificial tear fluid. Deposition and removal were evaluated by quantitative solvent extraction and scintillation counting.

RESULTS

The efficiencies of the MPSs in reducing lipid deposition are somewhat dependent on lens material. Both DPPC and CH sorption on senofilcon A are greater when lenses are preconditioned in BBS compared with preconditioning in either MPS (p < 0.05). However, neither MPS affects lipid sorption on balafilcon A lenses (p > 0.05). As for removal of presorbed lipids, neither PureMoist, Biotrue, nor BBS removed CH in the absence of rubbing. When a simulated rubbing protocol was used, minimal but detectible CH was removed (p < 0.05) from senofilcon A and balafilcon A lenses (likely only from the lens surface). These commercial solutions were not substantially better than BBS in removing DPPC, with or without rubbing (p > 0.05).

CONCLUSIONS

These data suggest that MPSs do not appreciably alter lipid sorption. Rubbing lenses removes a small amount of sorbed lipids. Yet, we recommend that MPSs be used as they may disinfect SiHy lenses and may clean their surfaces of large particles.

Comparison Between Bandage Contact Lenses and Pressure Patching on the Erosion Area and Pain Scale in Patients With Corneal Erosion

PURPOSE

Corneal erosion is common in eye emergency cases. Extensive corneal erosions result in severe pain and prolonged healing time. This study aimed to compare bandage contact lenses with pressure patching in terms of reducing the size of the erosion area, pain scale in patients with corneal erosion and its complications.

DESIGN

A randomized open-label clinical trial was conducted.

METHODS

Subjects with mechanical corneal erosion were selected to use either bandage contact lenses or pressure patching. All subjects received antibiotic eye drops and 0.5% tropicamide eye drops. Evaluations were done 24 and 72 hours after treatment. The size of the corneal erosion area, pain scale, and complications were assessed.

RESULTS

A total of 32 eyes (16 eyes in each group) were studied. The change in the size of the corneal erosion area was greater in the bandage contact lens group than in the pressure patching group, although there was no significant difference. In the bandage contact lens group, 56.25% of the eyes were healed at 24 hours and 43.75% were healed at 72 hours. In the pressure patching group, 62.50% were healed at 24 hours and 12.50% were healed at 72 hours. The change in pain scale was significantly greater in the bandage contact lens group than in the pressure patching group. No complications were found in both groups.

CONCLUSIONS

Bandage contact lenses are an effective alternative to treating mechanical corneal erosion because of their effect in reducing pain without causing any complications.

[Correct contact lens hygiene]

Although contact lenses have long been established in ophthalmology, practical aspects of handling contact lenses is becoming increasingly less important in the clinical training as specialist for ophthalmology. Simultaneously, for many reasons injuries due to wearing contact lenses are increasing. In order to correct this discrepancy, information on contact lenses and practical experience with them must be substantially increased from a medical perspective. This review article deals with the most important aspects for prevention of complications, i.e. contact lens hygiene.

Are silicone hydrogel contact lenses more comfortable than hydrogel contact lenses?

The current literature review was intended to investigate whether the use of silicone hydrogel contact lenses has resulted in improved comfort compared with that of hydrogel contact lenses when both are used for daily wear. The conclusion reached is that silicone hydrogel contact lenses, which were initially developed to eliminate hypoxia during overnight wear, have not significantly improved comfort compared with the comfort achieved with hydrogel contact lenses when worn on a daily wear basis, even though a body of the published literature would suggest to the contrary. A careful review and consideration of the literature demonstrates that the relative comfort achieved with the two types of contact lenses is in fact highly dependent on the study methodology: Although refitting studies have concluded enhanced comfort with silicone hydrogels, the more robust study designs involving concurrent controls and masking were not able to show a difference, and some even concluded an inferior performance. Evidence-based review has however clearly demonstrated that comfort cannot be considered in isolation but is contact lens specific and depends on the material surface and bulk properties, lens design characteristics, and modality of use of the contact lens, and may also be significantly influenced by the replacement frequency and interaction with any lens care system that may be used.

Comfort and vision with silicone hydrogel lenses: effect of compliance

PURPOSE

Silicone hydrogel (SH) lenses are usually replaced after 2 weeks (2W) or 1 month (1M); however, many patients do not comply with the manufacturers' recommended replacement frequency (MRRF). The purpose of this analysis was to investigate the effect of compliance with MRRF on comfort and vision in SH wearers.

METHODS

As a part of a larger study investigating compliance with MRRF, patients were asked to rate their subjective comfort and vision from 0 (very poor) to 10 (excellent) in the morning, at the end of the day (EVE), when lenses were new, and needed replacing (NR).

RESULTS

One thousand three hundred forty-four patients wore 2W replacement modality (2WR) (n = 717) or 1M replacement modality (1MR) (n = 617) SH lenses. Comfort and vision in the morning and when lenses are new were significantly higher than for EVE and NR (p < 0.001). Twenty-nine percent (95% confidence interval 25.3-32.4) of 1MR and 59% (95% confidence interval 55.5-62.7) of 2WR wearers were non-compliant with the MRRF. Compliance had a significant effect on EVE (p = 0.002, p = 0.008) and NR (p < 0.001, p < 0.001) comfort and vision. After accounting for compliance, EVE and NR comfort and EVE vision were higher for 1MR than 2WR (p = 0.015, p = 0.044, p = 0.019).

CONCLUSIONS

Compliant patients had better EVE and NR comfort and vision than non-compliant patients, regardless of replacement modality. Optimal subjective performance with SH lenses seems to be facilitated by replacing lenses as recommended.