Lens wettability is assessed from a combination of the pattern, size and speed of tear breakup, stability of the tear film and the lipid layer appearance. There are several different scales based on these factors that are used to grade lens wettability, two of which are described below:

The presence and assessment of lens deposits is best observed immediately after a blink. Further assessment can be made when the tear film begins to thin though this may overestimate the level of deposits. Poor wettability must not be taken into account when assessing deposits. These are examples of grading scales that may be used.

Figure 1 shows deposits in the form of film or haze. These deposits are observed on all types of lenses, but may be more prevalent on silicone hydrogel lenses than on disposable lenses ⁷-⁸. Film or haze appears as a fine white or greyish layer on the lens surface with a streaky or meshwork appearance. Figure 2 shows globules which are a build up of small to medium sized greyish balls adherent to the lens. This haze and globule-type deposition generally occurs at higher levels on the front compared to the back surface of lenses.

Patient variability
Deposition levels seem to be similar whether lenses are worn on a 6N or 30N schedule (see Figure 1)

Figure 1

Enlarge

However some patients may be predisposed to develop higher levels of deposition more rapidly ⁸. This may be due to the interaction of factors such as tear film composition, ocular surface, environment, the lens material, the relative stiffness of the lenses and contaminant characteristics ⁹.

Patient management
When these deposits are severe, patients may report symptoms such as blurry or misty vision, discomfort and irritation. These are dependent on the severity of the deposits. Patients should be encouraged to remove, rub and rinse their lenses as these deposits can usually be easily removed with cleaning. If the deposit remains the lens should be replaced ⁸. Some patients tend to develop lens deposits rapidly, regardless of whether they are wearing the lenses on a 6N or 30N schedule, and may need to remove lenses for cleaning frequently, often every two to three days. In our experience development of deposits does not preclude the patient from continuing in otherwise successful 30N CW of silicone hydrogels.

Laboratory assays
In contrast to clinical observation that shows similar amounts of deposits on silicone and conventional lenses, laboratory analyses show that etafilcon A attracts substantially greater quantities of lysozyme and IgA than silicone hydrogel materials ^10-11. However, these results are not necessarily contradictory as visible lens deposits have little relation to the actual amount or type of protein that is assayed from the lens.

Biochemical analysis suggests the deposits on silicone hydrogel lenses are primarily lipid in composition. The globules are similar in appearance to the deposits found on rigid gas permeable (RGP) lenses. High levels of lipid accumulation are found on siloxanyl alkyl acrylate RGP lenses ¹². Non-ionic polymer matrices and higher water content tend to increase lipid deposition on hydrophilic lenses.

Clinical relevance
Patients with contact lens induced papillary conjunctivitis (CLPC) generally have more deposits on their lens surfaces, however no correlation has been found between CLPC and the amount of protein deposits ^13-14. The current hypothesis is that it is denatured protein that may trigger the immune response found in CLPC ¹⁵. The lens surfaces of recovered CLPC patients and asymptomatic patients are similar ¹⁶. Therefore the level of deposition cannot be used to predict the likelihood of a patient developing CLPC.

Lower levels of deposits do not always cause symptoms or lens related adverse responses. Brennan (2002) found that patients' ratings of comfort and dryness in their studies were better with the silicone hydrogel lenses, even though these had slightly higher levels of deposition. In addition the patients wearing these had similar tarsal conjunctival redness and roughness, visual acuity and lens wettability. The relatively low levels of deposition and good wettability, as well as the high levels of comfort and satisfaction that patients experience, suggest that the new coating technology has made silicone hydrogel lenses more biocompatible and have overcome the earlier problems associated with silicone materials ¹.

References

1. Brennan NA, Coles ML, Comstock TL and 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.

2. Montero Iruzubieta J, Nebot Ripoll JR, Chiva J, Fernandez OE, Rubio Alvarez JJ, Delgado F, Villa C and Traverso LM. Practical experience with a high Dk lotrafilcon A fluorosilicone hydrogel extended wear contact lens in Spain. Cont Lens Assoc Ophthalmol J 2001; 27:41-46.

3. Long B, Robirds S and Grant T. Six month of in practice experience with a high Dk lotrafilcon A soft contact lens. Cont Lens Ant Eye 2000; 23:112-118.

4. Morgan PB and Efron N. Comparative clinical performance of two silicone hydrogel contact lenses for continuous wear. Clin Exp Optom 2002; 85(3):183-192.

5. Siegel DJ and Spilkin J. A comparison of on-eye performance and patient assessment of the Bausch & Lomb PUREVISION™ lens and CIBA Focus NIGHT & DAY™ lens when worn on a 7-day EW cycle for one month. Cont Lens Ant Eye 2000; 23(4):162.

6. Grant T and Amos C. The daily wear clinical performance of a surface treated high Dk hydrogel. Optom Vis Sci 2001; 7412s:202.

7. Fonn D, Pritchard N and Dumbleton K. Factors affecting the success of silicone hydrogels. In: Sweeney D: Silicone Hydrogels: the rebirth of continuous wear contact lenses. Oxford, Butterworth-Heinemann, 2000, pp. 219-222.

8. Sweeney D. Silicone Hydrogels: the rebirth of continuous wear contact lenses. Oxford, Butterworth-Heinemann, 2000, pp. 125-128.

9. Bontempo AR and Rapp J. Protein and lipid deposition onto hydrophilic contact lenses in vivo. CLAO J 2001; 27(2):75-80.

10. McKenney C, Becker N, Thomas S, et al. Lens deposits with a high Dk hydrophilic soft lens. Optom Vis Sci 1998; 75:276.

11. Jones LW, Senchyna M, Louie D, May C, Schubert N and Dumbleton K. Invest Ophthalmol Vis Sci 2000; 41(4):S71.

12. Bontempo AR and Rapp J. Lipid deposits on hydrophilic and rigid gas permeable contact lenses. CLAO J 1994; 20(4):242-245.

13. Grant T, Holden B, Rechberger J, et al. Contact lens related papillary conjunctivitis (CLPC): Influence of protein accumulation and replacement frequency (ARVO Abstract). Invest Ophthalmol Vis Sci 1989; 30:S166.

14. Richard N, Anderson J, Tasevska Z, et al. Evaluation of tear protein deposits on contact lenses with patients with and without giant papillary conjunctivitis. CLAO J 1992; 18:143-147.

15. Hart D, Schkolnick J, Bernstein S, et al. Contact lens induced giant papillary conjunctivitis: A retrospective study. J Am Optom Assoc 1989; 60:195-204.

16. Fowler S, Greiner J and Allansmith M. (1979). Soft contact lenses from patients with giant papillary conjunctivitis. Am J Ophthalmol 1979; 88:1056-1061.