Features

CLs: Water gradient technology – applied science and future applications

Prof. Michel Guillon and Dr Erich Baumann review the CL material delefilcon A

In-eye wettability has been put forward as one of the main challenges to achieving all-day comfort with contact lenses and may be essential in reducing the high level of contact lens dropout still experienced today. Delefilcon A material was introduced as a unique dual technology combining a low water content silicone hydrogel core, to achieve optimal oxygen supply, with a high water content hydrogel surface to provide a highly lubricious, wettable lens. The objective of this review is to ascertain whether, after several years in use, this technology achieved its intended aim based on review of published literature and completed studies. Material analysis confirmed the water gradient structure of the delefilcon A lens. In vitro analysis of the surface properties demonstrated both a very low coefficient of friction and surface modulus. The clinical literature demonstrated superior on-eye wettability compared to other contact lenses evidenced by a long tear film break-up time, the presence of a continuous tear film during the interblink period, and excellent resistance to dehydration when a break occurs (even in an adverse environment). Minimal tissue interaction was also recorded. Assessments from contact lens users indicated that delefilcon A lenses were preferred over other contact lenses and at least equivalent to spectacles over the course of the day

In the first review (Optician 04.03.22), the in-vitro characteristics of delefilcon A were covered. This second article takes a look at the published literature concerning the in vivo, clinical performance of delefilcon A.


Clinical Performance

Tear film interaction

Contact lens surface on-eye performance is measured by the interaction of the contact lens with the tear film. Non-invasive break up time (NIBUT) measured with a range of techniques has traditionally been the reference parameter (figure 1).

In recent years, with the improvements in high resolution video recording and image analysis, additional parameters have been developed to fully quantify the tear film dynamics over the full inter-blink period.


Figure 2: Interferometry as a measure of tear film surface quality

Figure 2: Interferometry as a measure of tear film surface quality


These techniques have been extensively applied to studying the tear film interaction of delefilcon A compared with other materials in order to ascertain if the unique water gradient surface that produced superior in vitro performance, also produced superior on-eye performance. Key studies include the following:

  • Llorens-Quitana et al,1 using a custom algorithm to analyse videokeratoscopic images, developed a series of parameters describing tear film quality in order to study the pre-lens tear film of delefilcon A and omafilcon A after four hours of wear in a contralateral study design. The results demonstrated that, under the conditions of suppressed blinking, the quality of the tear film pre delefilcon A was superior to that of the tear film pre omafilcon A. The regularity of the tear film during the period, depicted by the Tear Film Quality Index (P = 0.007), was better and the severity of the blink, expressed by the Break Factor Index (P = 0.011) and Analysed Exposed Area (P = 0.033), was less marked for delefilcon A. The data indicate that the superior in vitro surface properties, inherent to the highly hydrophilic water gradient surface previously reported, are associated on-eye with better tear film stability and greater resistance to surface drying during long, opened-eye periods.
  • Szczesna-Iskander et al2 measured delefilcon A and nelfilcon A tear film in the central 4mm by interferometric methods (figure 2) after six hours of wear for an open-eye period of 40 seconds and found results that reinforce the findings of Llorens-Quitana et al.1 They reported that the average tear film surface quality over the period was significantly better for delefilcon A (mean difference 34%; P = 0.012) and that its deterioration during the open-eye period was very different for the two contact lenses with a statistical trend (P = 0.088) to be less for delefilcon A. The data support the claim that the surface properties afforded by the Water Gradient Technology holds the tear film more efficiently, as demonstrated here by a more regular tear film that deteriorates more slowly under a long period of eye opening, such as that often encountered during computer use.


Figure 3: Tear meniscus height measurement


  • Wolffsohn et al3 compared the pre-contact lens tear film characteristics of delefilcon A to that of narafilcon A and filcon II-3 over a 16-hour period of wear. The results showed that both the NIBUT (P < 0.001) and the tear meniscus height (figure 3) (P = 0.016) were superior overall for delefilcon A than the other two contact lenses, the difference in NIBUT being clinically significant with a mean increase of 8% and 15% vs. narafilcon A and filcon II-3, respectively. The data confirm the benefits of delefilcon A on-eye due to the superior hydrophilic properties of Water Gradient Technology, as shown by greater tear film stabilisation and more water being held within the interpalpebral region than with other contact lenses.
  • Varikooty et al4 comparing the performance of delefilcon A with somofilcon A and narafilcon A contact lenses over eight hours of wear on a population equally made up of asymptomatic and symptomatic wearers showed that over the period of wear, delefilcon A achieved a longer NIBUT (P < 0.01) than the other two contact lenses, with mean NIBUT differences of approximately 17% for narafilcon A and somofilcon A. Further, subjective lens surface wettability rating revealed a more wettable surface for delefilcon A (P < 0.01) than the other two contact lenses. The data confirmed the beneficial effect of Water Gradient Technology in achieving superior on-eye wettability.
  • Dumbleton et al5 measured the tear film kinetics (TFK) of current delefilcon A and somofilcon A wearers as their habitual contact lenses and with stenfilcon A and narafilcon A contact lenses after six hours of wear of which the last three were in a controlled dry environment (hygrometry of 20%). Three parameters detailing the TFK were reported:
    1. NIBUT
    2. Exposed area at blink (EAbl); this corresponds to the contact lens surface not covered by the tear film at the time of the blink
    3. Dehydration speed (DS); this represents the rate at which the tear film break spreads between the first break and the natural blink.
  • The results showed that, while no or minimal differences in TFK were recorded between somofilcon A and the study materials, TFK were significantly better with delefilcon A than the test contact lenses: delefilcon A mean NIBUT was 32% (P = 0.052) and 45% (P = 0.006) longer than stenfilcon A and narafilcon A, respectively. Delefilcon A mean EAbl of 4.6% was less than a third of stenfilcon A (15.6%, P = 0.024) and narafilcon A (17.6%, P = 0.006). Delefilcon A mean DS of 0.28mm2/s was less than half of the other two materials, stenfilcon A (0.81mm2/s, P = 0.002) and narafilcon A (0.60mm2/s, P = 0.056). The data demonstrate that the Water Gradient Technology maintains superior TFK under adverse environmental conditions. Specifically, here it is shown that slow rate of drying when a break is present leads to a much greater coverage of the contact lens surface by the tear film at the time of the blink and, therefore, better lubrication.
  • Guillon et al6 compared the TFK of current delefilcon A wearers with their habitual contact lenses and with two contact lenses made from senofilcon A (Acuvue Oasys [AO] and Acuvue Oasys 1Day [AO1D]) after the initial three hours of wear. The results showed that NIBUT was longer for delefilcon A, the differences being at the limit of statistical significance with mean differences of -0.68 sec (95% CI -1.68 to +0.31) with AO1D and -0.85 sec (95% CI -2.09 to +0.38) and that EAbl was significantly less for delefilcon A with mean differences of -11.0% (95% CI -17.5 to -4.6) with AO1D and -8.6% (95% CI -14.0 to -3.1) with AO. The data indicate that after the initial three hours of wear, delefilcon A contact lens wettability is superior to that of senofilcon A, this aspect is of high clinical relevance for daily disposable contact lenses as the process of establishing a functional tear film is repeated daily.
  • Guillon et al7 also analysed the lipid layer of the delefilcon A and senofilcon A pre-lens tear film after the initial three hours of wear. This layer is not uniform, with the various lipid components producing a range of visible patterns corresponding to different lipid thicknesses. Their results showed that in the majority of cases the primary pattern recorded (that which corresponds to the pattern occupying the largest area) was in the majority a thick pattern for delefilcon A but not for senofilcon A (P < 0.034). The composition of the lipids produced by the same population over a short period of time is thought to be identical. Hence, it appears counterintuitive that different lipid layers should be present at the surface of the pre-lens tear film for different materials. The material effect is, in fact, an easily explainable indirect effect. As demonstrated by the slower rate of dehydration and the presence of a greater volume of tears, delefilcon A holds a more stable aqueous layer, which makes the spreading of lipids more efficient at forming a continuous layer than over a surface with greater aqueous turbulence.
  • Itokawa et al8 compared the pre-contact lens tear film after 15 minutes of wear of delefilcon A with two hydrogel contact lens materials (etafilcon A and Polymacon) to the cornea before contact lens insertion. Their results showed that delefilcon A tear film characteristics were closest to the cornea than the other two contact lens types. The change in surface temperature for 10 seconds of open eye compared with the change for the cornea was significantly smaller with delefilcon A than with the two contact lenses (P < 0.05). The NIBUT was closer for delefilcon A and etafilcon A than Polymacon (P < 0.05) from the corneal NIBUT. The structure of the aqueous lipid layer combination was more stable for delefilcon A than the other two contact lenses. The data is aligned with Guillon7 in revealing a thicker lipid layer for delefilcon A, here leading to a lower change in surface temperature, indicative of a lower rate of tear film evaporation.
  • Delefilcon A TFK measurements obtained by Guillon et al7 in two different studies carried out approximately a year apart following the same protocol showed that the TFK characterized by a long NIBUT, small EAbl and slow DS were consistent and similarly present in both.


Figure 4 Staining underneath the lens is likely to be mechanical in origin


Figure 5 Limbal redness, as shown here, is an indicator of oxygen supply


Figure 6 Staining in the exposed conjunctival and eyelid margin are related to lens wettability and lubricity


Ocular tissue interaction

The interaction between the ocular tissue and a contact lens are multifactorial. With reference to the ocular surface, any corneal staining or conjunctival staining under the contact lens is considered of mechanical origin and linked to the contact lens rigidity (figure 4). Corneal swelling and limbal redness are indicators of oxygen supply to the cornea and, hence, linked to the contact lens transmissibility (figure 5). Finally, staining in the exposed conjunctival area and eyelid margin are related to the contact lens surface wettability and lubricity, respectively (figure 6).

A number of studies have reported the effect of wearing delefilcon A vs other materials on ocular tissue:

  • Wolffsohn et al3,9 in the 16 hours of wear study using the Efron scale recorded less corneal staining with delefilcon A than with narafilcon A (P = 0.031) or filcon II-3 (P < 0.001) at the end of the wearing period. The data would indicate that the very low surface rigidity of delefilcon A uniquely cushions any mechanical interaction related to the lens bulk.
  • Lafosse et al10 measured the effect of eight hours of wear of delefilcon A on the ocular tissue of 40 neophyte presbyopic patients. Rating staining using the Efron scale, they found that post wear staining was unchanged from pre-wear baseline (cornea P = 0.727; conjunctiva P = 0.092) confirming the good interaction of delefilcon A with ocular tissue in a population more susceptible to ocular surface defects. The data add supporting evidence that the very low surface modulus and friction coefficient of delefilcon A is beneficial in optimising the interaction between the contact lens and the ocular surface.
  • Varikooty et al4 also compared the effect of the eight hours of wear of delefilcon A, somofilcon A and narafilcon A on ocular tissue. Their study showed that all three contact lens types produced little tissue disturbance, but whenever they reported statistically significant differences, the lower effect was associated with delefilcon A. Further, bulbar redness remained unchanged with delefilcon A over the eight-hour period of wear, but significantly increased (P < 0.01) with somofilcon A and narafilcon A. Bulbar redness is considered a clinical marker of inflammation in this region, hence it is of interest to note that delefilcon A, which has the most stable tear film, is also the only one that does not produce any change in this clinical marker of the inflammatory status of the exposed conjunctival area.
  • Michaud et al11 in a crossover study, refitted symptomatic monthly contact lens wearers with both delefilcon A and nelfilcon A and reported that the odds ratio of developing light to moderate conjunctival staining with nelfilcon A vs delefilcon A was 14.3 (95% CI: 3.1 to 66.2). Further, corneal staining was significantly more marked with nelfilcon A (P < 0.001) than with delefilcon A, the odds ratio of greater staining for the former being 8.8 (95% CI: 2.2 to 35.1).


Subjective acceptance

Review of the literature has shown the interaction between delefilcon A, the tear film and ocular tissue to be excellent. The key question from a contact lens wearer viewpoint: does this translate into significantly superior comfort and reduced rates/degrees of dryness, discomfort and irritation? From a clinical perspective, has any association between superior clinical acceptance and improved tear film or tissue interaction been demonstrated?

A number of studies have addressed these aspects of clinical performance:

  • Two initial multisite evaluations, one in Australia/New Zealand12 and one in Europe13,14 compared delefilcon A acceptance and preference to the participants’ own contact lenses. The results clearly indicate that delefilcon A achieved very good comfort with 86% to 93% of participants agreeing or strongly agreeing that delefilcon A was comfortable all day long and that delefilcon A was preferred to the habitual contact lenses in 82% to 90% of cases.
  • Marx et al15 in Europe and Michaud et al11 in Canada each carried out a multi-site study producing conclusive evidence that delefilcon A achieved a high level of subjective acceptance. Marx et al (n = 92) took the ultimate challenge of fitting neophytes with delefilcon A contact lenses and comparing their subjective response with the contact lenses to their subjective response with their habitual spectacles. The results after two weeks of wear showed superior physical acceptance and superior vision:
    • Comfort: 59% reported overall comfort was better with delefilcon A (P = 0.01); comfort rating on 0 to 10-point scales (higher is better) was superior for delefilcon A for daytime (delefilcon A 8.9, spectacles 8.3; P ≤ 0.001), at the end of the day (delefilcon A 8.3, spectacles 7.5; P ≤ 0.001) and overall (delefilcon A 8.8, spectacles 8.1; P ≤ 0.001).
    • Vision: 67% and 92%, respectively, reported that they agreed or strongly agreed that for overall vision and peripheral vision, delefilcon A was better than spectacles (P < 0.001); quality of vision for daytime and at the end of the day was also superior for delefilcon A (P ≤ 0.001).
  • Michaud et al11 (n = 76) followed a crossover study design that involved symptomatic monthly contact lens wearers refitted with both delefilcon A and nelfilcon A in a random order. At the completion of one month of wear there was a significant increase in comfortable wearing time from a mean baseline of 7.6 hours with delefilcon A (mean 10.7 hours; P = 0.031) but not with nelfilcon A (mean 8.5 hours; P = 0.394). Similarly, an improvement in subjective symptoms measured through contact lens dry eye questionnaire-8 (CLDEQ8) scores (baseline 17.2) was achieved with delefilcon A (8.3; P < 0.001) but not with nelfilcon A (16.1; P = 0.397).
  • Nick et al16 refitted 121 symptomatic contact lens wearers with delefilcon A and narafilcon A (Acuvue TruEye) in a two-week crossover study. They reported better end of day comfort, better quality of vision and lower end of day dryness with delefilcon A than for narafilcon A (P < 0.001) along with more than two additional hours of comfortable wearing time with delefilcon A (11.6 vs. 9.3 hours; P < 0.001). Surface wettability rated on a 10-point scale was also shown to be significantly better with delefilcon A (9.3 vs. 7.4; P < 0.001).
  • Kern et al17 carried out a crossover study of two-week duration (N = 166 multifocal wearers) that compared the subjective acceptance of their habitual multifocal contact lenses with delefilcon A multifocal. The results showed that delefilcon A achieved better results in longer comfortable wearing time (12.8 vs. 9.4 hours/day), end of day comfort, end of day dryness and dryness during device usage.
  • Dumbleton et al18 tracked the end of day comfort in a crossover study that showed that delefilcon A achieved superior on eye wettability than stenfilcon A and narafilcon A over the first three hours of wear. The results showed that delefilcon A achieved over two hours of additional comfortable wearing time than the two other contact lenses (13.2 hours vs. 11.1 hours for both stenfilcon A and narafilcon A) and that significantly more wearers strongly agreed that the lens was comfortable at the end of the day for delefilcon A (50%) than with stenfilcon A (28%) or narafilcon A (24%). A hypothesis put forward for further testing was that on-eye wettability, in particular initial wettability, may have some impact later in the day on both end of day wettability and comfort.
  • Guillon et al19 tracked the end of day comfort in a crossover study which showed that delefilcon A achieved superior on-eye wettability than senofilcon A over the first three hours of wear. Two versions of senofilcon A contact lenses were used (Acuvue Oasys and Acuvue Oasys 1Day). Delefilcon A produced significantly greater comfort than Acuvue Oasys (P < 0.001) and trended towards higher comfort against the Acuvue Oasys 1Day (P = 0.112). The data in this study confirmed the data reported by Dumbleton et al5, reinforcing the potential hypothesis of an association between wettability during initial wear and comfort at the end of the day.

In conclusion, the extensive clinical evidence gathered in a range of studies, including refitting studies and crossover studies, on representative populations involving neophytes, symptomatic and asymptomatic wearers, pre-presbyopic and presbyopic populations indicated that delefilcon A attained a high level of comfort throughout the day that is superior to other contact lens materials.


Discussion & Conclusion

The premise for this literature review was to ascertain whether the manufacturer assertion that the Water Gradient Technology that combines a high Dk, low water content silicone hydrogel core with a high water content hydrogel surface provides superior on-eye performance and wearer acceptance.

The first part of the review (Optician 04.03.22), that covered the in vitro studies, established the unique water gradient structure and associated properties of the delefilcon A lens. This second part of the review dealt with the clinical literature showing that delefilcon A surface structure achieved superior on-eye wettability over other contact lens materials. This was demonstrated by a long tear film break-up time, the presence of a continuous tear film during the interblink period and excellent resistance to dehydration when a break occurs even in an adverse environment. There is also minimal interaction with ocular tissue. Subjective acceptance was overall superior to other contact lenses and equal to spectacles over the wearing day.

In conclusion, this review supports the hypothesis that the unique Water Gradient Technology of the delefilcon A lens results in superior clinical performance and greater wearer acceptance. Now it is time to explore the potential of adapting Water Gradient Technology to modalities beyond daily disposable. There is a great opportunity to support better patient outcomes in the replacement schedule they prefer. Should the challenge be met in adapting this technology to other replacement modalities, it would represent another landmark in the continuing evolution of contact lens materials.


  • Professor Michel Guillon is the Clinical director of Ocular Technology Group – International in London and visiting professor in the School of Life and Health Sciences at Aston University. He is consultant and advisor to a number of ophthalmic pharmaceutical and medical device companies in the area of dry eye, contact lenses, vision measurement and clinical study design and regulatory.
  • Dr Erich Bauman is Senior Director, Project Leadership for Alcon’s Vision Care R&D unit in Atlanta and a Fellow of the American Academy of Optometry.

This article is based on a publication in Contact Lens Spectrum and is supported by Alcon.

References

  1. Llorens-Quintana C, Mousavi M, Szczesna-Iskander D, et al. Non-inva- sive pre-lens tear film assessment with high-speed videokeratoscopy. Contact Lens & Anterior Eye. 2018;41:18-22.
  2. Szczesna-Iskander DH. Comparison of tear film surface quality measured in vivo on water gradient silicone hydrogel and hydrogel contact lenses. Eye & Contact Lens. 2014;40:23-27.
  3. Wolffsohn JS, Mroczkowska S, Hunt OA, et al. Crossover evaluation of silicone hydrogel daily disposable contact lenses. Optometry & Vision Science, 2015;92:1063-1068.
  4. Varikooty J, Schulze MM, Dumbleton K, et al. Clinical performance of three silicone hydrogel daily disposable lenses. Optometry & Vision Science, 2015;92:301-311.
  5. Dumbleton K, Guillon M, Patel K, et al. Quantification of contact lens wettability after prolonged visual device use under low-humidity conditions. Poster presented at: Annual Meeting of the Association for Research in Vision and Ophthalmology; Seattle, Washington, USA; May 1-5, 2016.
  6. Guillon M, Patel K, Gupta R, et al. Daily disposable contact lenses initial on-eye wettability. Poster presented at: Annual Meeting of the British Contact Lens Association; Liverpool, UK; June 9-11, 2017.
  7. Guillon M, Patel K, Gupta R, et al. Pre-contact lens tear film kinetic measurement repeatability under normal and adverse environmental conditions. Abstract presented at: Annual Meeting of the Association for Research in Vision and Ophthalmology; Baltimore, Maryland, USA; May 7-11, 2017.
  8. Itokawa T, Okajima Y, Suzuki T, et al. Association between ocular surface temperature and tear film stability in soft contact lens wearers. Investigative Ophthalmology & Vision Science. 2018;59:771-775.