Daily Wear: Silicone Hydrogels and Adverse Responses

Background

In the first of this series of three editorials, Kathy Dumbleton described the typical behavior of silicone hydrogel lenses when they are prescribed on a daily basis. For practitioners, the availability and popularity of silicone hydrogel materials means that the likelihood of having to diagnose, treat and/or manage complications associated with their use is increasing. Whilst much has been published on the rates and characteristics of adverse reactions to silicone hydrogels during continuous or extended wear, practitioners may find it more difficult to obtain advice on how to manage complications arising during daily wear of these materials.

Toxic Staining

There have been frequent reports of asymptomatic corneal staining in subjects wearing silicone hydrogel lenses on a daily wear basis, most particularly when PHMB lens care systems are used [1-3]. A large prospective parallel cell clinical trial involving 335 subjects and daily wear (DW) of the four silicone hydrogel lenses currently available in Australia (PureVision, Focus Night & Day, Acuvue Advance, O₂Optix) was conducted at our research centre. The properties of these lenses are provided in Table 1. A range of PHMB (Aquify), Alexidine (ReNu MoistureLoc), Polyquad (Opti-Free Express) or hydrogen peroxide (AOSept Plus) lens care systems were prescribed with these lenses.

* Ross et al. Silicone Hydrogels: Trends in Products and Properties. Presented at BCLA 29^th Clinical Conference & Exhibition, Brighton, UK; 3-5 June, 2005.

Results largely confirmed those previously reported by others i.e. toxic staining was present in approximately 7% of eyes overall, but of course this proportion may be higher with specific lens type – solution combinations. Typically staining was not associated with the presence of any subjective symptoms, was scattered across the whole cornea but tended to be denser in the corneal periphery and often involved the surrounding conjunctival epithelium. Incompatibilities were specific to particular lens-care system combinations and could not be generally attributed to a particular lens type or a single care system ingredient. Staining, however, remained rarest overall with the use of hydrogen peroxide systems. Practitioners would therefore be wise to adopt the following general management strategies:

1. Stain all subjects routinely at all follow-up visits
2. Change lens care product and/or lens type if significant staining is noted and review
3. Consider preferential use of hydrogen peroxide systems in atopic subjects

Contact Lens Papillary Conjunctivitis (CLPC)

CLPC is traditionally classified as a hypersensitivity reaction to contact lens deposits. The increased risk for CLPC in silicone hydrogel extended wear [4,5] suggests that mechanical factors play a larger role than previously suspected, at least in this particular modality of wear. One would also predict that silicone hydrogels of lower modulus may also pose less of a challenge to the palpebral conjunctiva and hence lead to a lower complication rate. Overall low rates of CLPC were found for all silicone hydrogel lenses when worn on a daily wear schedule. In the large scale 6-month study described above, one of 88 subjects wearing O₂Optix lenses and two of 61 subjects wearing Acuvue Advance nevertheless developed the condition. Practitioners should therefore not become complacent and should continue to routinely examine the upper palpebra of all contact lens wearers. The recommended management for CLPC need not change. It should include classic strategies such as temporarily discontinuing contact lens wear, reducing wear time, increasing lens replacement frequency and modifying lens type (see Feature Review).

SEALs and corneal erosions

It is thought that corneal erosions and superior arcuate epithelial lesions (SEALs) are caused by mechanical interactions between the contact lens and the cornea [6,7]. Definitive rates are difficult to assess but it’s been suggested that these may occur more readily with the stiffer silicone hydrogel materials. As stated above, it could then be expected that the lower modulus silicone hydrogels may lead to a lower complication rate. In the study described before, no cases of erosions were observed. SEALs were observed more frequently in wearers of Focus Night & Day and PureVision compared to those wearing O₂Optix and Acuvue Advance. It remains unclear whether this apparent low rate can be attributed to the daily wear schedule or to the properties of the lens materials. The management of erosions or SEALs includes temporary discontinuation of lens wear, prophylactic antibiotic treatment, and refitting with a different base curve or material.

Corneal infiltrates

There have been suggestions that silicone hydrogel lenses, when worn on an extended wear basis, constitute a risk factor for the development of infiltrative keratitis [8]; however, a recent meta analysis contradicts this [4]. Morgan et al. report a low (~0.6%) annual incidence of non-severe keratitis with silicone hydrogel DW [9]. This appears to be lower than the rate for silicone hydrogel extended wear (EW) [10]. In our experience, the rate during silicone hydrogel DW will approach that of hydrogel DW, which is approximately 1 to 2% [11]. Again, management strategies should include temporary discontinuation of lens wear for significant events.

Microbial Keratitis

Microbial keratitis remains the single most serious complication that concerns the wider ophthalmic community because of its associated risk for significant morbidity. It has been well established that the incidence of corneal ulcer is approximately five times lower in DW than EW [12,13] but until recently it had been impossible to predict whether silicone hydrogel lenses with their higher oxygen transmissibility would prove to be safer during overnight wear.

A one-year study from Australia and New Zealand designed to determine the relative risk and incidence of microbial keratitis with all modes of lens wear and all lens types is nearing completion. Most recent results indicate that silicone hydrogels have had little impact on the risk of infection with EW [14,15]. There is a greater risk of infection with overnight wear compared to DW with silicone hydrogels, and the rate of infection with silicone hydrogel DW at 4.5 per 10,000 wearers is not different to that of 3.1 per 10,000 in hydrogel daily wear [15].

Summary

Practitioners intending to prescribe silicone hydrogels on a daily wear basis should remember that with the added benefits of increased oxygen availability comes the usual risks involved with the wear of any contact lens. Because of this, they need to maintain their usual monitoring practices and manage any adverse reaction according to the standard protocol. In addition, they should remain alert to the possibility of solution incompatibilities when prescribing first or second generation silicone hydrogel lenses. Fortunately, changing to a different lens care product generally will solve the problem.

References

1. Jones L. Understanding Incompatibilities. Contact Lens Spectrum. 2004;19:4-8.

2. Amos C. A clinical comparison of two soft lens care systems used with silicone hydrogel contact lenses. The Optician. 2004;227:16-20.

3. Amos C. Performance of a new multipurpose solution used with silicone hydrogels. The Optician. 2004;227:18-22.

4. Szczotka-Flynn LB, Diaz-Insua M. Risk of Infiltrates and CLPC With Traditional Hydrogel and Silicone Hydrogel Extended Wear: A Meta Analysis. Invest. Ophthalmol. Vis. Sci. [ARVO Abstract]. 2005;46:2067-.

5. Skotnitsky CC, Sweeney DF, Naduvilath TJ, Sankaridurg PR. The Incidence of Local and General Contact Lens Induced Papillary Conjunctivitis in Silicone Hydrogel Contact Lenses. Invest. Ophthalmol. Vis. Sci. [ARVO Abstract]. 2005;46:2064-.

6. Jalbert I, Sweeney DF, Holden BA. Epithelial split associated with wear of a silicone hydrogel contact lens. CLAO J. 2001;27:231-233.

7. Jones L, Macdougall N, Sorbara LG. Asymptomatic corneal staining associated with the use of balafilcon silicone-hydrogel contact lenses disinfected with a polyaminopropyl biguanide-preserved care regimen. Optom Vis Sci. 2002;79:753-761.

8. Sankaridurg PR, Holden BA, Jalbert I. Adverse events and infections: which ones and how many? In: Sweeney, DF, ed Silicone hydrogels: Continuous-wear contact lenses. Edinburgh: Butterworth-Heinemann; 2004: 217-274.

9. Morgan PB, Efron N, Hill EA et al. Incidence of keratitis of varying severity among contact lens wearers. Br J Ophthalmol. 2005;89:430-436.

10. McKenney CD, McNally J, Chalmers R. The Influence of Patient Factors and Wearing Schedule on the Rate of Corneal Inflammatory Events Among Wearers of Lotrafilcon A Lenses. Invest. Ophthalmol. Vis. Sci. [ARVO Abstract]. 2003;44:3717-.

11. Sweeney DF, du Toit R, Keay L et al. Clinical performance of silicone hydrogel lenses. In: Sweeney, DF, ed Silicone hydrogels: continuous-wear contact lenses. Oxford: Butterworth-Heinemann; 2004: 164-216.

12. Dart JKG, Stapleton F, Minassian D. Contact lenses and other risk factors in microbial keratitis. Lancet. 1991;338:650-653.

13. Schein OD, Glynn RJ, Poggio EC et al. The relative risk of ulcerative keratitis among users of daily-wear and extended-wear soft contact lenses. N Engl J Med. 1989;321:773-778.

14. Edwards K, Keay L, Naduvilath T et al. Risk Factors for Contact Lens Related Microbial Keratitis in Australia. Invest. Ophthalmol. Vis. Sci. [ARVO Abstract]. 2005;46:926-.

15. Stapleton F, Edwards K, Keay L et al. The Incidence of Contact Lens Related Microbial Keratitis in Australia. Invest. Ophthalmol. Vis. Sci. [ARVO Abstract]. 2005;46:5025-.