ARE SILICONE HYDROGELS SUITABLE FOR DRY EYE CONDITIONS IN A DAILY WEAR MODALITY?

Wolfgang Sickenberger MS., Dipl. Ing. (FH) AO

Wolfgang Sickenberger graduated from the University of Applied Sciences Aalen, Germany, in 1989 and has practiced in Germany since then. In 1995 he became head of Professional Services at Ciba Vision, Germany and he is also a part time educator at the Universities of Applied Sciences in Aalen and Jena. He received his Master's degree in Clinical Optometry in 1998 at the Pennsylvania College of Optometry. In his private practice his interests are in the fields of dry eye and the tear film. He is also well known in Germany as an author of the textbook “Classification of slit lamp findings”. In March 2004 Wolfgang Sickenberger will move to the University of Applied Sciences in Jena, Germany to take up the position of Associate Professor.

When suffering from dry eye, contact lens wearers complain of a persistent feeling of ocular dryness and itchiness, which may trigger excessive blinking. The condition affects a significant percentage of the population, and ocular dryness is the most common adverse symptom associated with contact lens wear, which may lead to shorter wear times and at worst total contact lens intolerance. Although there are a range of wetting solutions that can be used to help alleviate the symptoms of dry eye for contact lens wearers, there is still a large unmet need for alternative methods of preventing dry eye.

A recent consumer study from Germany indicates that almost 50% of contact lens wearers complain of dryness (Figure 1). Consequently a major challenge in our contact lens practice in Germany has been to solve the dryness complaints of our patients. It has been suggested that silicone hydrogel lenses may help to reduce dehydration effects during lens wear and it is this potential that leads us to investigate whether silicone hydrogels can overcome the complaints of dry eye patients when worn in a daily wear mode.

Figure 1: GfK Consumer Study. Germany Top 7 complaints reported by CL wearers (n = 456)	Dehydration of a SCL on eye

We conducted a short study of 30 of our patients that had previously worn frequent replacement conventional soft contact lenses, or rigid contact lenses for at least 6 months and who had a history of dry eye or marginal dry eye symptoms. A breakdown of the percentage of patients reporting a range of subjective symptoms with their previous lens wear history is given in Table 1.

Table 1. Percentage of patients reporting subjective symptoms with their previous contact lenses

Our 30 patients were fitted with silicone hydrogel contact lenses in a daily wear mode and were examined at baseline and after 1 week, 2 weeks, 1 month and 3 months of lens wear. Patients were asked to wear their lenses for at least 4 hours before attending the follow-up examinations. At each visit we examined the anterior section of the eye, evaluated the contact lenses, and evaluated the quality and the quantity of the tear film. Patients were also asked to subjectively assess their symptoms of dryness and comfort via a questionnaire. Throughout the study, patients were encouraged to continue with their own lens care products.

After 3 months of daily wear with silicone hydrogels the most dramatic improvements were seen in wear time with some patients now able to wear contact lenses over the whole day. Previously only 25% of patients could wear lenses for 12 hours or more, but with silicone hydrogels this increased to 64% (Figure 2).

Figure 2: Improvement in comfortable wear time after 3 months with silicone hydrogels

In addition patients reported less sensations of dryness (p<0.001) and grittiness (p=0.03), whiter eyes (p<0.001)(Figure 3), less haloes (p=0.03), less blurry (p=0.002) and unstable vision (p=0.002) and less problems with contact lens removal (p<0.001), and improved comfort at the end of the day (p=0.003)(Figure 4).

Figure 3: Improvement in redness after 3 months with silicone hydrogels

Figure 4: Improvement in end of day comfort after 3 months with silicone hydrogels

We also took a closer look at the subgroup of 19 patients that were intensive personal computer (PC) users. These lens wearers are more likely to experience dryness due to a reduced blink rate and comfortable wear time is particularly important for these wearers. All of our PC users were able to increase their wear time with silicone hydrogels by at least 2 hours. Of the 19 PC users we examined, all but one could wear silicone hydrogels for 12 hours or more (Table 2).

A number of features of silicone hydrogels may contribute to the reduction in sensations of dryness and increased wear time. In addition to high oxygen transmissibility these may include improved wetting qualities, low water content, and a low dehydration tendency. In classic hydrogel materials, oxygen transport is exclusively maintained by the water phase whereas in silicone hydrogels it is the silicone phase that is responsible for oxygen transport.

The high oxygen transmissibility of silicone hydrogels avoids physiological changes to the cornea and conjunctiva and it is the water content that provides ion transport and fluid exchange. As a consequence of the low water content, silicone hydrogel materials are more resistant to the effects of dehydration. In addition, the surfaces of silicone hydrogel lenses appear to be less susceptible to deposition. Surface deposits on contact lenses are associated not only with a reduction in comfort and visual acuity, but can also initiate allergic reactions, all of which contribute to wearer dissatisfaction.

Our experience with silicone hydrogels for patients with dry eye shows that extended wear is not the only segment of the contact lens market that can benefit from these highly oxygen permeable materials. Practitioners may wish to consider silicone hydrogels for daily wear when fitting patients with dry eye symptoms and for patients whose work or home environment may make them susceptible to the effects of dehydration.