Manuscript Review by Kathy Dumbleton

Seven-day Extended Wear and 30-day Continuous Wear of High Oxygen Transmissibility Soft Silicone Hydrogel Contact Lenses: A Randomized 1-year Study of 504 Patients.

Sven Erik G. Nilsson. CLAO 2001 July;27(3): 125-136.

Many patients desire the convenience of wearing their contact lenses on a continuous basis, only having to remove the lenses when they need replacing, therefore avoiding daily handling and the regular use of care regimens. With conventional lens materials extended periods of lens wear have been associated with higher complication rates, in particular microbial keratitis^1,2,and in 1989 the maximum recommended period for extended wear was reduced to 7 days. The complications historically associated with extended wear have resulted in practitioners and patients becoming concerned about the potential safety issues associated with this modality.

High Dk silicone hydrogel lenses have been shown to supply sufficient oxygen to effectively eliminate hypoxia³and have overcome many of the complications associated with acute^4,5and chronic^6-9oxygen deprivation. Despite the elimination of hypoxia, several clinical complications have been reported to occur as a result of silicone hydrogel lens wear^10-14and there is particular interest in whether the incidence of these complications increases with the number of nights that the lenses are worn consecutively without removal.

The paper published by Sven Erik Nilsson in the July 2002 issue of the CLAO journal reports the results from a multicentre clinical trial in which the clinical performance and complication rate were compared when silicone hydrogel lenses were worn for up to 7 consecutive days or 30 consecutive days without removal. 504 adapted soft contact lens wearers at 23 contact lens practices in Sweden were randomly assigned to either 7 day/6 night or 30 day/29 night wearing schedules. All patients were fitted with PureVision (Bausch & Lomb Inc.) silicone hydrogel (balafilcon A) contact lenses with a Dk/t of 110. All lenses were replaced monthly and the study lasted for a period of one year.

Subjective symptoms and complaints (in most cases dryness, discomfort and burning / itching) were mild. There were no significant differences in the reporting rates for the two wearing schedule groups. Lens wettability was very good or excellent for the majority of lenses and deposition rates were very low and there were no differences between the two groups.

No significant differences were found between the wearing schedule groups for the reported rates of corneal staining or superior epithelial arcuate lesions (SEAL). There were also no differences in the annual incidence of inflammatory reactions including corneal infiltrates, contact lens acute red eye (CLARE) or contact lens papillary conjunctivitis (CLPC). No cases of microbial keratitis occurred in either group in this study.

Traditional signs of hypoxia, epithelial edema, microcysts and corneal striae, were observed infrequently and the annualized incidence rates were unaffected by wearing schedule. Interestingly, although bulbar and limbal hyperemia decreased significantly within a month of commencing PureVision lens wear in both wearing schedule groups, the 7 day/6 night lens group showed significantly more bulbar/limbal injection (p=0.03) and vascularization (p=0.001) than the 30 day/29 night group.

The overall success rate for patients remaining in the study for the full 12 months was slightly better for the 30-day group (84.4%) than the 7-day group (79.5%). These rates increased to 92.4% and 86.8% respectively when patients who discontinued from the study for non lens related reasons were discounted.

The author concludes that the complication rates for both groups were low and that high oxygen transmissibility silicone hydrogel lenses are as safe when worn for 30 consecutive days as when they are worn for 7 consecutive days. In summary practitioners can be confident in prescribing these lenses to suitable patients for periods of wear of up to 30 consecutive days without removal.

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2. Cheng KH, Leung SL, et al.: Incidence of contact-lens-associated microbial keratitis and its related morbidity. Lancet 1999; 354;9174: 181-5.

3. Fonn D, du Toit R, et al.: Sympathetic swelling response of the control eye to soft lenses in the other eye. Invest Ophthalmol Vis Sci 1999; 40;13: 3116-21.

4. Papas E, Vajdic C, et al.: High oxygen-transmissibility soft contact lenses do not induce limbal hyperaemia. Curr Eye Res 1997; 16;9: 942-948.

5. du Toit R, Simpson TL, et al.: Recovery from hyperemia after overnight wear of low and high transmissibility hydrogel lenses. Curr Eye Res 2001; 22;1: 68-73.

6. Dumbleton KA, Chalmers RL, et al.: Vascular response to extended wear of hydrogel lenses with high and low oxygen permeability. Optom Vis Sci 2001; 78;3: 147-51.

7. Fonn D, MacDonald KE, et al.: The ocular response to extended wear of a high Dk silicone hydrogel contact lens. Clin Exp Optom 2002; 85;3: 176-82.

8. Covey M, Sweeney DF, et al.: Hypoxic effects on the anterior eye of high-Dk soft contact lens wearers are negligible. Optom Vis Sci 2001; 78;2: 95-9.

9. Keay L, Sweeney DF, et al.: Microcyst response to high Dk/t silicone hydrogel contact lenses. Optom Vis Sci 2000; 77;11: 582-5.

10. Dumbleton K. Adverse events with silicone hydrogel continuous wear. Contact Lens & Anterior Eye 2002; 25;3: 137-146.

11. Holden BA, Stephenson A, et al.: Superior epithelial arcuate lesions with soft contact lens wear. Optom Vis Sci 2001; 78;1: 9-12.

12. O'Hare N, Naduvilath T, et al.: A Clinical Comparison of Limbal and Paralimbal Superior Epithelial Arcuate Lesions (SEALs) in High Dk EW. Invest Ophthalmol Vis Sci 2001; 42;4: s595.

13. Stern J, Skotnitsky C, et al.: Comparison of the incidence of contact lens papillary conjunctivitis (CLPC) between six and thirty night high Dk soft extended wear schedules. Invest Ophthalmol Vis Sci 2001; 42;4: s597.

14. Lim L, Loughnan MS, et al.: Microbial keratitis associated with extended wear of silicone hydrogel contact lenses. Br J Ophthalmol 2002; 86;3: 355-7.