The Untapped Use of Silicone Hydrogels

Professor Dennis Burger, OD, FAAO Dennis Burger graduated from the School of Optometry, at the University of California, where he is currently Clinical Professor and senior mentor in the contact lens residency program. He is also senior optometrist at the Kaiser-Permanente Medical Center in Oakland. His special interests include pediatric contact lenses, bifocal contacts, and keratoconus. Professor Burger has been active in many organizations serving as President of the California Chapter of the AAO, an executive board member in the Cornea and Contact Lens Section, Chairman of the Clinical Faculty at U.C. Berkeley, as well as serving as a board member in his local society. He has authored a number of articles including many on keratoconus and is a co-investigator in the Collaborative Longitudinal Evaluation of Keratoconus Study (CLEK Study).

Practitioners are frequently reluctant to prescribe conventional hydrogel contact lenses for their pediatric patients because of the potential problems which may occur as a result of low oxygen transmissibility. The advent of highly oxygen permeable silicone hydrogel materials has given us greater confidence to prescribe these lenses to our younger patients.

In addition to their therapeutic use in pediatric care [1-3], contact lenses have significant potential to manage and/or correct a number of visual conditions for pediatric patients [4]. We are all aware of the benefits of contact lenses for high myopes, including improvements in peripheral vision, and less image minification compared with spectacle correction. Similar improvements are achieved in hyperopic patients who benefit from the increase in visual field and a more normalized image with less magnification.

The two main reasons for vision correction in young children are to correct accommodative esotropia and to prevent amblyopia. Consider the hyperopic accommodative esotrope. These patients benefit from contact lenses because there is lower accommodative and convergence demands with contact lenses compared to spectacles (Fig 1 and 2) [4].

Figure 1, Esotropia	Figure 2, Esotropia with contact lens wear

There are also advantages to contact lens correction for intermittent exotropes. Treatment effects by over-minusing in contact lenses are greater than the results which can be achieved in glasses, and as a result the frequency with which the exotropia is manifest may be significantly reduced (Fig 3 and 4).

Figure 3, Intermittent exotropia	Figure 4, Exotropia with contact lens wear

As practitioners we are all aware of the problems that anisometropia can cause. Patients wearing glasses have the problem of unequal image size that makes it difficult if not impossible to fuse. A contact lens correction results in less difference in image size between the two eyes, improving fusion and helping to prevent the suppression that would otherwise result (Fig 5 and 6) [4-6]. Patients who have large amounts of anisometropia may develop amblyopia and must be aggressively treated. Patching for at least 4 hours a day is generally still required to diminish the amblyopia which may otherwise develop [7]. While it is not recommended to patch an eye wearing a lens of low oxygen transmissibility – in these cases the contact lens needs to be removed - with silicone hydrogel lens wear, a period of patching each day will not result in significant hypoxic responses. 

Figure 5, Anisometropia (10D)	Figure 6, Anisometropia with contact lens wear

Pediatric nystagmus patients may benefit greatly from contact lens correction [8,9]. These patients have reduced visual acuity as a result of their involuntary eye movement. They also frequently have high refractive errors.  Consequently, when they wear glasses they do not constantly look through the center of the lens and they may experience optical distortion. Many nystagmus patients lessen their involuntary eye movements by turning their head to achieve a “null point”. The null point is the point where the nystagmus is most dampened and is often accomplished by turning the head and then looking in an extreme position of gaze to help stabilize the nystagmus. Significant distortion can occur for patients with a -10.00 D correction looking through the periphery of the spectacle lens. Correction with silicone hydrogel contact lenses allows these patients to look through the center of the lens at all times as their eyes move, allowing the vision to be improved even with extreme head turns.

The benefits of using silicone hydrogels for therapeutic purposes has been established [10-12], but they also offer a number of advantages in terms of correcting the vision of pediatric patients [13, 14]. Even though many of these conditions can be better corrected with contact lenses than with spectacles, practitioners have not been confident to fit children. They are concerned about many issues ranging from simply the mechanics of fitting the lenses to teaching the parents to handle the lenses (Fig 7). While rigid gas permeable lenses are frequently considered to be a safe option for children, they are not commonly prescribed because of the fitting and adaptation process which is required for these lenses. We are all aware of the excellent immediate comfort afforded by soft lenses. In children, comfort is especially important since a child will not be motivated to wear a lens that is irritating. Soft lenses also are less likely to displace or come out of the eye, particularly if the eye is rubbed. The advent of silicone hydrogels makes prescribing contact lenses for children a little easier for everyone.

Figure 7

The main advantage of silicone hydrogel contact lenses is the fact that these materials are highly oxygen-transmissible, which means that patients wearing them do not suffer from the complications associated with hypoxia. Lenses can be worn with the eyes closed, whether just for naps or for a week at a time, which means less need for lens handling by parents or by the pediatric patient. Additionally some of the silicone hydrogel lenses have a stiffer modulus, making the lens easier to handle for the child or his parents, when they do have to handle the lens. Very thin soft lenses are very difficult to insert in children; the stiffer silicone hydrogel lens allows for easier application.

With the increase in parameters of both spherical and toric lenses in these materials, I would expect the use of silicone hydrogel lenses to continue to rise. Don’t be afraid to fit challenging young patients. You are using the right materials, and more even more options are on the way.

References

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13. Sankaridurg P. Contact lenses for tweens. Silicone Hydrogels Website, March 2004.
14. Sim I. Pediatric contactology: kids and contacts. Silicone Hydrogels Website, March 2004