Daily Disposable vs Continuous Wear with High-Dk Silicone Hydrogels

Ulrike Stahl

Ulrike Stahl is currently working as a Research associate at the Vision Cooperative Research Center in Sydney, Australia, where she is responsible for coordinating clinical research studies on contact lenses. In fulfillment of her Optometry study at the University of Applied Sciences in Berlin, Germany she wrote her Diploma thesis at the VisionCRC and the School of Optometry and Vision Science, University of New South Wales. She recently has been awarded a very competitive International Postgraduate Research Scholarship from UNSW, to conduct her PhD. Ulrike's main interests include the effects of contact lenses on the tear film and dry eye problems with contact lenses.

A 6-month follow-up of successful refits from daily disposable soft contact lenses to continuous wear of high-Dk silicone-hydrogel lenses (Ophthal Physiol Opt 2004 24:130-141)

BM Aakre, AE Ystenaes, MJ Doughty, Ø Austrheim, B Westerfjell, MT Lie
Department of Optometry and Visual Science, Buskerud University College, Norway
Department of Vision Sciences, Glasgow-Caledonian University, UK

Surveys have shown that up to 97% of ametropes would like to wear their lenses on an extended or continuous wear schedule so that they are "permanently" corrected and do not need to insert and remove lenses every day (1,2). Yet, the penetration of this modality of wear remains very low in certain countries (3). This may be due partially to delay in release of silicone hydrogel lenses to some markets and/or practitioner reluctance to endorse the continuous wear modality. Aakre and colleagues therefore investigated the potential for success of silicone hydrogel continuous wear shortly after their release to the Norwegian marketplace and compared this to what can perhaps be considered the most convenient daily wear modality, daily disposable lens wear.

In order to critically review this paper, it is useful to first clearly define the notion of ‘success’ in contact lens wear. From the patient’s point of view, this will consist of a lens that provides clear comfortable vision in a convenient system. Practitioners will also require that the lens induces minimal changes to the ocular physiology and a low complication rate (4). Aakre and colleagues refitted 30 successful daily disposable lens wearers with silicone hydrogel lenses and compared the results to the findings of 19 subjects that were maintained in daily disposable lens wear. Participants were examined over six months and the range of variables assessed covered the complete spectrum of success including visual acuity (high and low contrast), objective and subjective refraction, central corneal thickness, corneal neovascularisation, bulbar and limbal hyperaemia, contact lens induced papillary conjunctivitis, epithelial staining, presence of tear debris, mucin balls, microcysts, and infiltrates, and finally endothelial density, polymegethism and pleomorphism. Subjective ratings for overall vision, comfort and any experienced symptoms were also obtained.

Overall, the daily disposable hydrogel and continuous wear silicone hydrogel lenses performed equally well. There were no differences in subjective and objective vision, corneal thickness, tear debris, mucin balls, microcysts, endothelial characteristics or subjective vision and comfort between the two lens types. At the end of the study, silicone hydrogel lens wearers had less corneal staining, bulbar hyperemia, and limbal neovascularisation compared to the daily disposable lens wearers which is in accordance with previous reports (5,6). These differences were likely due to the lower oxygen transmissibility of the hydrogel lenses compared to the silicone hydrogel lenses. Interestingly, the authors reported that nine of the 16 daily disposable lens wearers developed more lid changes than the silicone hydrogel lens wearers.

The reasons for discontinuation in the silicone hydrogel lens group included discomfort (n = 4), allergy-related effects (n =1), contact lens peripheral ulcers (CLPU) (n = 3) and reasons unrelated to lens wear (n = 3) whereas daily disposable wearers left the study because of poor health unrelated to their contact lenses (n = 2).

Overall Aakre and colleagues’ study demonstrate that silicone hydrogel lenses adequately fulfill the desire of ametropes for convenient and easy lens wear, preferably on a continuous wear schedule. However as for all lens types, practitioners need to adopt strategies to monitor their patients for any potential complications or adverse reactions. These strategies may include, for example, increased frequency of follow-up visits and 24-hour access to emergency care.

References

1. Sweeney D, du Toit R, Keay L, et al. Clinical performance of silicone hydrogel lenses. In: Sweeney D, ed. Silicone Hydrogels Continuous-wear contact lenses; 2004.
2. Holden B. The Glenn A.Fry Award Lecture 1988: The ocular response to contact lens wear. Optom Vis Sci. 1989;66(11):717-733.
3. Morgan P, Efron N, Woods C, et al. International contact lens prescribing in 2004. Contact Lens Spectrum. 2005;Januar.
4. Terry R, Schnider C, Holden B, et al. CCLRU standards for success of daily and extended wear contact lenses. Optom Vis Sci. 1993;70(3):234-243.
5. Dumbleton K, Chalmers R, Richter D, Fonn D. Changes in myopic refractive error with nine moths' extended wear of hydrogel lenses with high and low oxygen permeability. Optom Vis Sci. 1999;76(12):845-849.
6. Papas E, Vajdic C, Austen R, Holden B. High-oxygen-transmissibility soft contact lenses do not induce limbal hyperaemia. Curr Eye Res. 1997;16(9):942-948.