Silicone Hydrogels: A Clinical Look at Daily Wear with Silicone Hydrogels Lenses

A CLINICAL LOOK AT DAILY WEAR WITH SILICONE HYDROGEL LENSES

Advancements in contact lens technology allow clinicians to solve more and more of our contact lens wearing patients' problems. One of the most useful tools to be developed in recent years is Silicone Hydrogel lenses (CIBA Vision's Focus Night & Day and Bausch & Lomb's PureVision Lenses). The benefits of these lenses are clear in theory. Higher oxygen transmission ^1-3 should benefit most corneas and lead to improved ocular surface health during lens wear ^4;5 . The other characteristics of the lenses which make them different include the stiffness of the materials³ , lens design and lower water content. All these features may contribute to more successful lens wear. The good news is that with silicone hydrogel lenses the theory often translates into clinical reality when the lenses are used to solve problems and even as a lens of first choice.


AS A LENS OF FIRST CHOICE:

Some practitioners believe that the benefits of the silicone content of these lenses make silicone hydrogel lenses the first choice for all new fits because the oxygen benefits of the lenses may reduce complications in the future^4;5 . Certainly for extended or continuous wear patients, the oxygen benefits must make these the lens of choice⁶ . I have used silicone hydrogel lenses principally in the daily wear modaility and I wanted to share my clinical experiences with these lenses with the readers. In my practice, these types of lens are increasingly becoming the lenses of choice and certainly serve as a most useful problem solver.


Handling

One of the less talked about benefits of silicone hydrogel lenses is their ease of handling. Many new young contact lens wearers have considerable problems associated with the insertion and removal of their lenses. When this appears likely, I often choose a silicone hydrogel lens. This is especially the case for teenagers⁷ who could easily become discouraged because of the awkward aspects of lens insertion. Parents who are very concerned about their child's use of lenses are also reassured by the oxygen benefits of the lenses.


The Aging Eye

There are a group of presbyopes who want to wear contacts for the first time because of their desire to be able to go to a social event without wearing glasses. These are usually patients who have never worn lenses before and are discouraged about their dependency on bifocal glasses. Many of them have early signs of corneal edema such as microcysts and small striae. Oxygen to the cornea becomes an important issue for these patients and choosing a silicone hydrogel lens reassures the practitioner about the oxygen needs of the cornea.


The Sleeper

When patients ask to be fitted with contact lenses, a discussion about sleeping habits should be part of the history. Many patients nap on commuter trains and busses, couches during the afternoon or evenings and even during the opera. These patients deserve the protection of extra oxygen to reduce their chances of the complications of corneal edema during lens wear. Practitioners should certainly attempt to fit all of their "sleepers" in silicone hydrogel lenses.


AS A PROBLEM SOLVING LENS

Resolving Symptoms of Dryness

Figure 1 - click to enlarge

The most common complaint of hydrogel lens wearers⁸ and the most common reason for the discontinuation of soft lens wear is dryness^9;10 . Several studies have shown that symptoms of dryness, particularly late in the day, are endemic in the hydrogel lens wearing population⁸ . As a practitioner who wishes to keep patients in contact lenses, I spend a good deal of my clinical hours trying to solve this problem (Figure 1).

The reasons for the dryness during lens wear are complex. Certainly many of our patients are of an age when hormone changes, particularly for women in menopause and those on hormone replacement therapy, cause ocular surface changes that create symptoms of dryness even without contact lens wear¹¹ . Hormones affect the tears in many ways. Testosterone, which is reduced in post menopausal women and older men, affect the stimulation of the meibomian glands and the lacrimal glands. Reduced estrogen affects the mucous membranes of our bodies and is implicated in the drying of the conjunctiva.

Changes in tear chemistry with age include reduced tear flow, as measured by the Schirmer test, and complications associated with poor tear chemistry that lead to increased tear film evaporation. Tear osmolarity may increase and the secretions of the meibomian glands may be low or excessive. A mixture of these changes leads to stimulation of the sensory nerves of the conjunctiva and cornea, producing the symptoms of discomfort and dryness. Because of the exposure of the ocular surface to the elements of the day, these symptoms are increased in the evening.

Given the sensitivity of the cornea, one would think that patients would benefit from the protective coverage that the soft contact lens provides to the cornea. Indeed some patients do experience real relief when lenses are fitted. For example, patients who wear soft lenses while cutting onions do not experience the stinging and excessive tearing that accompanies this task when lenses are not worn. However, the wearing of these same lenses causes increased symptoms of discomfort and dryness in most patients compared to those who do not wear hydrogel lenses. Apparently the dryness, discomfort sensations differ in origin or dimension from the stinging sensations and contact lenses stimulate one and protect from the other. Much more work is required to determine the factors that affect this most complicated world of symptoms.

In the meantime practitioners are faced with the challenge of reducing the symptoms of dryness that threaten continued contact lens wear. Clinically, we begin with a change of solutions. Lens wearers who have reduced wear time because of dryness may benefit from being placed on a non preserved care system such as Clear Care. By eliminating the preservatives and antibacterial chemicals that are found in other one step systems, the practitioner can then decide if the lens itself is the problem. If the symptoms persist and the lens appears to be the issue then my first choice for refitting is with a silicone hydrogel lens. Think of the number of variables that have been changed in this single move:

1. More oxygen will be available to the cornea. If there was subclinical oxygen deprivation of the cornea there certainly is no longer. This fact alone may change the sensory response of the ocular surface.

In the days of PMMA lens wear and the transition of patients from the oxygen impermeable material to the oxygen transmission of the newer rigid lens materials there were many problems. Patients would return to the clinic after refitting in gas permeables to say that they did not like the lenses because they were so much more aware of them in their eyes. This if course was due to the fact that the cornea had become resensitized and therefore more symptoms arose. With time the corneal metabolism improved and the patients adapted to the gas permeable lenses.

My experience clinically is the same. Some patients have reduced corneal symptomatolgy associated with their hydrogel lens wear. When first refitted with silicone hydrogels they are much more aware of the lenses. With time, however, the cornea reestablishes its healthy normal metabolism and the lenses feel better.

2. The lens will fit differently. Silicone hydrogel lenses are stiffer because of the silicone component and the reduced water content. This makes most patients more aware of the edges at first. I find that if a carefully fit the lenses, leaving time for settling and observing the lens edges, I can determine the best base curve¹² and reassure the patients that this sensation will reduce with wear. In most cases, on the follow-up visit 2 weeks later, the lens feels comfortable.

3. There will be less water in the lens and therefore potentially more water on the eye. When I discuss the concept of refitting the patient in silicone hydrogel lenses, they always wonder why I would switch to a lens that is lower in water content. In fact many of them have experienced my efforts to use higher water content lenses to improve their comfort. Once I explain that the lenses leave more of the tear film on the eye instead of in the lens, they seem satisfied. The proof of the experiment is always in the wearing and many of my patients are happily wearing silicone hydrogel lenses with fewer symptoms of dryness.

4. The tear film will interact differently with the contact lens surface. Many patients who have symptoms of dryness when wearing their hydrogel lenses have a dry looking lens surface. Tears that are sludging over the lens must create visual and physical problems. The tarsal plate has sensory nerve endings that likely respond to this surface interaction. By dramatically changing the interaction of the tears and the lens surface, patients will have a different sensation and hopefully have reduced dryness and improved comfortable wear time.


Reducing Redness

Many hydrogel lens wearing patients present with complaints of red eyes. They are comfortable and see well but their friends are always asking why their eyes are so red. This presenting complaint is the most satisfying of all to address with silicone hydrogel lenses. With almost 100% certainty, patients experience reduced redness with the wearing of these lenses^13;14 . One of the best clinical ways to demonstrate this is to use a digital camera to photograph the blood vessels of the bulbar conjunctiva and limbus at the same time of day on first visit (Figures 2 and 3, CCLR patient) and 1 to 2 weeks after wearing silicone hydrogel lenses (Figure 4, same CCLR patient after 1 week of daily wear with Focus Night & Day). The difference is clear.

Figure 2 - click to enlarge	Figure 3 - click to enlarge
Figure 4 - click to enlarge

Filamentary Keratitis

Patients with severe dry eyes such as those with Sjogren's Syndrome, can experience extreme discomfort when their corneas form filaments. These patients must be handled carefully as their autoimmune disease and dry eyes leave them open to infections and severe rejection of contact lenses. However, those that can be helped with the use of lenses often do well with silicone hydrogel lenses in my practice. Unfortunately many of these patients also have rheumatoid arthritis and therefore cannot readily handle the lenses. This can be solved by training family members to remove, insert and disinfect the lenses. If the patient can tolerate the lenses the relief is overwhelming and often the cornea will heal to the point where no lenses need to be worn.


SUMMARY

Silicone hydrogel lenses are an extremely useful tool in fitting patients and in solving their problems. Clinicians who have not had occasion to use these lenses should embrace their benefits. Although not every patient can wear the lenses and some may have clinical problems directly associated with the lens material, many patients benefit from the design and oxygen transmissibility. By using these lenses we can keep more of our patients wearing contact lenses and prevent some of the complications that have arisen in the past with more conventional lenses.


Reference List

1. Alvord L, Court J, Davis T, Morgan CF, Schindhelm K, Vogt J et al. Oxygen permeability of a new type of high Dk soft contact lens material. Optom.Vis.Sci. 1998; 75 :30-6.

2. Morgan CF, Brennan NA, Alvord L. Comparison of the coulometric and polarographic measurement of a high-Dk hydrogel. Optometry and Vision Science 2001; 78 :19-29.

3. Tighe B. In: Sweeney D, ed. Silicone Hydrogels: the rebirth of continuous wear contact lenses . Oxford: Butterworth-Heinemann, 2000: 1-21.

4. Covey M, Sweeney DF, Terry R, Sankaridurg PR, Holden BA. Hypoxic effects on the anterior eye of high-Dk soft contact lens wearers are negligible. Optometry and Vision Science 2001; 78 :95-9.

5. Nilsson SE. Bacterial keratitis and inflammatory corneal reactions: possible relations to contact lens oxygen transmissibility: the Harold A. Stein Lectureship 2001. Contact Lens Association of Ophthalmologists Journal 2002; 28 :62-5.

6. Fonn D, du T, Simpson TL, Vega JA, Situ P, Chalmers RL. Sympathetic swelling response of the control eye to soft lenses in the other eye. Investigative Ophthalmology and Visual Science 1999; 40 :3116-21.

7. Soni S, Horner D. Keeping teens healthy in contact lenses. Contact Lens Spectrum 1995; 10 :20-7.

8. Begley CG, Caffery B, Nichols KK, Chalmers R. Responses of contact lens wearers to a dry eye survey. Optometry and Vision Science 2000; 77 :40-6.

9. Pritchard N, Fonn D, Brazeau D. Discontinuation of contact lens wear: a survey. International Contact Lens Clinic 1999; 26 :157-62.

10. Young G, Veys J, Pritchard N, Coleman S. A multi-centre study of lapsed contact lens wearers. Ophthalmic and Physiological Optics 2002; 22 :516-27.

11. Mathers WD, Stovall D, Lane JA, Zimmerman MB, Johnson S. Menopause and tear function: the influence of prolactin and sex hormones on human tear production. Cornea 1998; 17 :353-8.

12. Dumbleton KA, Chalmers RL, McNally J, Bayer S, Fonn D. Effect of lens base curve on subjective comfort and assessment of fit with silicone hydrogel continuous wear contact lenses. Optom.Vis.Sci. 2002; 79 :633-7.

13. Dumbleton KA, Chalmers RL, Richter DB, Fonn D. Vascular response to extended wear of hydrogel lenses with high and low oxygen permeability. Optom.Vis.Sci. 2001; 78 :147-51.

14. Papas EB, Vajdic CM, Austen R, Holden BA. High-oxygen-transmissibility soft contact lenses do not induce limbal hyperaemia. Current Eye Research 1997; 16 :942-8.