Letters: Material matters
Author: Dr Noel Brennan, David Ruston and John Meyler
We refer to the article entitled ‘Why are 1 day SiH lenses a good choice for my patients?’ published in Optician on November 6, 2020.
This is based on a publication that appeared in Contact Lens and Anterior Eye in June 2020.1 We are pleased to see it has been revised to some degree following our letter to the editor of that journal2 setting out our concerns, including that the conclusion of the paper was not supported by the selective body of evidence in the publication.
We still have significant concerns with this revised article. Fundamentally, we still fail to be convinced that the conclusion ‘for the vast majority of patients SiH 1 day CLs are most likely to result in long term successful wear’ is in any way justified by the evidence base cited. Perhaps a more apt title would have been ‘Why are 1 day lenses a good choice for my patients?’
We feel it is regrettable that a major overview entitled ‘30 years of “quiet eye” with etafilcon A’3 was not referred to in the article. This was a review of 1643peer-reviewed publications concerning the performance of the world’s most popular daily disposable (DD) material, a hydrogel, led by Professor Nathan Efron and co-authored by eight globally renowned researchers.
To quote from this publication: ‘Although the prescribing of silicone hydrogel lenses is increasing, millions of lens wearers globally have been wearing hydrogel lenses for many years and exhibit a physiologically stable “quiet eye”, with a low profile of adverse events. Hydrogel lenses are demonstrated to maintain a low inflammatory response and infection risk profile during daily wear, which in the case of etafilcon A, may be related to its low modulus, and the naturally-protective, anti-microbial, non-denatured lysozyme absorbed into the lens from the tear fluid.’
Additionally, and specifically, we would draw attention to the following:
- The article refers extensively to a survey of eye care professionals’ (ECP) perceptions,4 but the authors do not call out the limitations of the survey, even though they do in the peer reviewed original article. The authors of this work acknowledged the survey questions were phrased with an emphasis on SiHy materials and their possible benefits over hydrogels and included the results for ‘slight agreement’ with the statement, so potentially increasing the percentages significantly as there was no neutral response in the questionnaire.
- The authors use the survey results to support the notion that ECPs believe SiHy DDs are mostly better for their patients but then also present evidence that ECPs are wrong to think more oxygen equals more comfort. We would propose that what matters most in supporting clinical judgement is the scientific evidence base and not a survey of opinions.
- The authors remind us that (hydrogel) DDs launched 25 years ago and cite four studies which show ‘some hydrogel 1 day lenses provide sufficient oxygen to prevent corneal oedema, neovascularisation and limbal and bulbar hyperaemia for daily wear.’ They then critique two of them on the basis the patients wore the lenses for between five and six hours, yet do not acknowledge the benchmark work of Holden et al5 that shows that when subjects are exposed to the levels of oxygen present (as under the contact lenses evaluated) corneal swelling peaks after two hours and plateaus thereafter.
- On the subject of napping while wearing DD CLs, the authors remind us that no DD lens has regulatory approval for closed eye wear, whether napping or otherwise. ECPs should be wary of recommending a specific material for napping as this would be ‘off label’ and, in any event, there is no evidence of any difference in long-term complications when napping in hydrogels or SiHy lenses.
- As ECPs we all seek to avoid the only sight threatening complication of CL wear, microbial keratitis (MK). The authors refer to an editorial6 that highlighted one study reporting a lower severity (but not lower incidence) in extended wear of SiHy and hydrogel contact lenses. To date no study on the severity of MK in DD Daily wear or any other study on reusable lens wear shows any difference in severity or incidence between SiHy and hydrogel lenses. One study that did include DD hydrogel wearers showed etafilcon A wearers to have the lowest rate of MK compared to other brands.7
- Table 1 in the publication shows modulus values that have presumably been gleaned from manufacturers’ data. This is despite there being no internationally recognised methodology for modulus measurement, making such comparisons potentially misleading. In fact, one of the authors of the paper conducted a recent study that used a standardised methodology to compare between different materials8 and found that, for example, stenfilcon A (MyDay) had a modulus of 0.67, and was thus almost identical to the 0.68 measured for senofilcon A (Acuvue Oasys), which is not reflected in table 1.
To conclude, we totally agree with the authors that DD CLs offer significant benefits in convenience and performance over reusable lenses. We do not agree that there is any significant evidence that for daily wear SiHy materials, as a group, offer any patient benefits over hydrogel DD CLs, except for one brand that was shown to be as comfortable, while another significantly less so.9
The authors present no significant evidence of potential long-term health benefits in the wear of SiHy DDs, particularly in view of the 30-year review paper previously referred to. They do, however, highlight that DD hydrogel CL wear resulted in no significant adverse events when fitted in younger patients for myopia management over a three-year period, so rather seem to contradict themselves. Indeed one of the authors concluded from a previous peer-reviewed article that ‘Although SiH contact lenses have been shown to provide superior oxygen transmissibility as compared to HEMA lenses, there is currently no clear evidence in the literature to support SiH 1 day lenses being superior to hydrogel 1 day lenses with respect to adverse events, wettability or comfort.’4
The role of the ECP remains critical at selecting the lens material, design and modality that best meets individual patient needs. Comfort performance can vary significantly across SiHy DD and hydrogel DD brands so grouping and comparing performance results across material types can be misleading. Lens choice should, of course, also consider oxygen delivery, especially in thicker lens designs, but balancing this with the knowledge that the three main reasons for contact lens wear discontinuation (comfort, vision and handling10,11) are not improved by increasing Dk/t. Hydrogel DD CLs continue to form an important part of the DD portfolio from which ECPs can select to drive patient satisfaction and successful long-term contact lens wear.
Dr Noel Brennana MScOptom, PhD FAAO, David Rustonb BSc FCOptom DipCL FAAO FIACLE and John Meylerc BSc FCOptom DipCL
a Clinical Research Fellow Myopia Control Platform Johnson & Johnson Vision Care, Inc.
b Director Global Professional Education & Development Johnson & Johnson Medical Ltd.
c Global Head, Professional Education & Development Johnson & Johnson Medical Ltd.
- Sulley A, Dumbleton K. Silicone hydrogel daily disposable benefits: The evidence. Cont Lens Anterior Eye. 2020 Jun;43(3):298-307.
- Brennan N, Ruston D, Meyler J. Letter to the Editor: "Silicone hydrogel daily disposable benefits: The evidence". Cont Lens Anterior Eye. 2020 Jun;43(3):308-309.
- Efron N, Brennan NA, Chalmers RL, Jones L, Lau C, Morgan PB, Nichols JJ, Szczotka-Flynn LB, Willcox MD. Thirty years of 'quiet eye' with etafilcon A contact lenses. Cont Lens Anterior Eye. 2020 Jun;43(3):285-297.
- Orsborn G, Dumbleton K. Eye care professionals' perceptions of the benefits of daily disposable silicone hydrogel contact lenses. Contact Lens & Anterior Eye 2019; 42: 373-9.
- Holden BA, Sweeney DF, Sanderson G. The minimum precorneal oxygen tension to avoid corneal edema. Investigative Ophthalmology & Visual Science 1984;25:476-80.
- Efron N. Twenty years of silicone hydrogel contact lenses: a personal perspective. Clin Exp Optom. 2020 May;103(3):251-253.
- Stapleton F, Naduvilath T, Keay L, et al. Risk factors and causative organisms in microbial keratitis in daily disposable contact lens wear. PloS one 2017;12:e0181343.
- Sulley A, Arnold K, Mundorf M. Daily disposable and reusable contact lens moduli – are they really different? Contact Lens & Anterior Eye 2018; 41(S54).
- Lazon de la Jara P, Diec J, Naduvilath T, et al. Measuring Daily Disposable Contact Lenses against Nonwearer Benchmarks. Optometry and Vision Science 2018;95:1088-95.
- Sulley A, Young G, Hunt C, McCready S, Targett MT, Craven R. Retention rates in new contact lens wearers. Eye Contact Lens 2018; 44: S273–s82.
- Dumbleton K, Woods CA, Jones LW, Fonn D. The impact of contemporary contact lenses on contact lens discontinuation, Eye Contact Lens 2013; 39: 93–99.