Clinical Performance: Comfort and Dryness

Kathryn Dumbleton - BSc (Hons), Uni of Wales1984 MCOptom 1985, MSc Uni of Waterloo 1988

Senior Researcher
Centre for Contact Lens Research (CCLR)
University of Waterloo, Ontario, Canada

Discomfort and dryness are the two most commonly cited reasons for discontinuing contact lens wear1 and it has been shown that dryness symptoms are experienced by up to 50% of soft contact lens wearers⁽²⁾.

Reducing or eliminating symptoms of discomfort and dryness for silicone hydrogel (SH) continuous wear (CW) patients is arguably even more important than for daily wear (DW) patients. Prospective CW wearers will be unlikely to succeed with this modality if they experience lens awareness or end of day dryness.
   

Studies at the CCLR have shown that 76% of subjects were successfully fitted with 8.6 mm base curve and 24% with 8.4mm Focus Night & DayTM lenses. It appears from Figure 1 that the 8.6 mm base curve lens was predominantly fitted on corneas whose steep K readings were flatter than 44D.

Figure 1: Distribution of steep keratometry readings for eyes fitted with 8.6 and 8.4 mm base curve Focus Night & Day lenses.

The 8.4mm base curve lens was favoured for k readings steeper than 45.50 D. For these steeper eyes, subjective discomfort with the 8.6 mm lens was also a useful signal for the need of a steeper lens, showing comfort scores for these subjects rising from 6.4 with the 8.6 lenses to 9.4 with the 8.4 lenses (Figure 2).

Figure 2: Subjective comfort scores during trial fitting of 8.6 mm and 8.4 mm base curve lenses on eyes with a range of steeper corneas

Figure 3 shows that the subjective comfort scores are the same for the 8.4 and 8.6mm base curves as long as the lens to cornea relationship is maintained. This demonstrates "fitting" and achievement of comfort is more critical with silicone hydrogels than conventional hydrogel lenses because of the higher modulus.

A number of studies have confirmed that SH lenses are perceived to be very comfortable by patients^(8,9) and are at least as comfortable as conventional lenses, when worn on a continuous wear basis^(6,10). It is important to note however that in some instances an "adaptation" period may be required, particularly if a patient is refitted from a thinner, less mobile, more flexible lens material.

Figure 3: Subjective comfort scores while wearing 8.6 and 8.4 mm base curve lenses.

Early clinical trials with SH lenses worn on a CW basis reported reduced levels of dryness symptoms, particularly at the end of the day, compared with conventional low and high water content lenses⁽¹⁰⁾. In the Focus Night & Day FDA study^(11,12), fewer subjects wearing Focus Night & Day lenses (19.8%) reported symptoms of dryness compared to the subjects wearing control hydrogel lenses (24.2%). The subjects also reported less dryness on waking and fewer unscheduled removals because of dryness with Focus Night & Day lenses. The difference in dryness between 30 nights CW silicone hydrogels wear and 6 nights EW low Dk control hydrogels is evident in Figure 4 from studies conducted at the CCLRU in Australia. In a 12 month contralateral clinical trial comparing PureVision and hydrogel control lenses, subjects rated the PureVision lenses as preferable on subjective scaling of comfort and dryness symptoms⁽¹³⁾.

Figure 4: Frequency of subjective dryness assessments at 12 and 24 months comparing SH and low Dk hydrogel lenses worn on an extended wear schedule.

There are many patients who experience dryness with conventional hydrogel materials; a large number of these may benefit from a reduction in symptoms with SH materials. To date, these reports of decreased dryness in normally symptomatic DW wearers have been largely anecdotal, however Sickenberger et al⁽¹⁴⁾ recently reported a more comfortable wearing time with less subjective dryness and greater end of day comfort with DW of Focus Night & Day lenses in a group of normally symptomatic patients.

Optimal fitting characteristics are essential with SH lenses. It is important that eye care practitioners ensure that the most appropriate SH lens design is fitted. CW patients who do experience dryness should try using lubricating drops in the morning and before going to bed. Preserved or non-preserved unit dose lubricants can be used, with the least viscous formulations being the most popular. Some patients report that inserting saline drops on waking is helpful. Patients should be cautioned to avoid contact between the bottle and the eye if the saline is used from a multi-dose container.

References

1. Pritchard N, Fonn D and Brazeau D. Discontinuation of contact lens wear: a survey. ICLC 1999;26:157-161

2. Doughty M, Fonn D, Richter D et al. A patient questionnaire approach to estimating the prevalence of dry eye symptoms in patients presenting to optometric practices in Canada. Optom Vis Sci 1997;74:624-631.

3. Efron N, Brennan NA, Currie JM, et al. Determinants of the initial comfort of hydrogel contact lenses. Am J Optom Physiol Opt 1986;63:819-23.

4. McMonnies CW. The critical initial comfort of soft contact lenses. Clin Exp Optom 1997;80:53-8.

5. Tighe B. Silicone hydrogel materials - how do they work? Silicone hydrogels. The rebirth of continuous wear contact lenses, D. Sweeney, Editor. Oxford, Butterworth-Heinemann 2000, pp 1-21.

6. Sweeney D, Keay L, Jalbert I, et al. Clinical performance of silicone hydrogel lenses. in Silicone hydrogels. The rebirth of continuous wear contact lenses, D. Sweeney, Editor. Oxford, Butterworth-Heinemann 2000, pp 90 - 149.

7. Dumbleton K, Chalmers R, Bayer S, Fonn D, McNally J. Lens base curve and subjective comfort with silicone hydrogel continuous wear lenses. Optom Vis Sci 2001; 78 (12s): 227.

8. Nilsson SE: 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. CLAO J 2001; 27; 3: 125-136.

9. Montero Iruzubieta J, Nebot Ripoll JR, Chiva J, et al. Practical experience with a high Dk lotrafilcon A fluorosilicone hydrogel extended wear contact lens in Spain. CLAO J 2001; 27: 41-6.

10. Fonn D, Pritchard N, Dumbleton K. Factors affecting the success of silicone hydrogels. in Silicone Hydrogels: The Rebirth of Continuous Wear Contact Lenses, D. Sweeney, Editor. Oxford, UK, Butterworth-Heinemann,2000, pp 214 - 234.

11. McNally J and McKenney C. A clinical look at a silicone hydrogel extended wear lens. Contact Lens Spectrum. January 2002:38-41.

12. Chalmers RL, McNally JJ, McKenney CD and Robirds SR. The role of dryness symptoms in discontinuation of wear and unscheduled lens removals with extended wear of silicone hydrogel materials. ARVO 2002, Abstract # 3088.

13. Brennan NA., Coles MLC, Comstock TL, Levy B. A 1-year prospective clinical trial of balafilcon A (PureVision) silicone-hydrogel contact lenses used on a 30-day continuous wear schedule. Ophthalmology 2002;109 (6); 1172 - 1177.

14. Sickenberger W, Schmied I, Schneider A and Gordon G. Are Fl-Si-Hydrogel-CL suitable for dry eye conditions in daily wear mode? AAO International Meeting April 2002.