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The contact lens industry is in a state of constant evolution. It seems that new lens designs that improve the visual quality and safety of contact lens wear are introduced on a yearly basis. Today, the options are so diverse that we can provide contact lenses to meet the visual needs of almost any patient. From pediatric aphakes to elderly presbyopes, from patients with normal corneas to individuals with advanced corneal disease, the possibilities are nearly endless.
DAILY DISPOSABLE SOFT CONTACT LENSES
The current focus of soft contact lens manufacturers appears to be the development of new daily disposable lenses. Although the growth of this segment of the market has been relatively slow in the United States, use of these lenses is increasing rapidly in countries like Japan, Norway, and the United Kingdom. Data collected from those nations suggest that more than 30% of all new soft lens prescriptions are for dailies.1 With this in mind, it is not surprising that so many new daily lens options have become available. A few years ago, the first daily silicone hydrogel lens (SiHy) was introduced, and since then, we have seen new daily toric and multifocal designs as well. Although 1-Day Acuvue TruEye (Vistakon Division of Johnson & Johnson Vision Care, Inc.) is still the only commercially available SiHy daily lens in the United States, other lenses have been developed and are currently available in Europe. It is safe to say that these new SiHy lens options will soon be available in the United States as well.
Why this sudden expansion of the daily disposable contact lens market? It is likely because these lenses are very convenient and demonstrate the highest rates of patients' compliance among all modalities.2 For the patient, there is no longer a need to remove and clean their contacts. Given this simplicity, it would be reasonable to assume that these lenses are also safer and result in a lower incidence of microbial keratitis over other modalities. Unfortunately, recent epidemiological studies have failed to demonstrate this3,4; in fact, data from one study showed an increased risk of keratitis in daily disposable lens wearers when compared to reusable soft contact lens wearers.4 Although these data seem counterintuitive, one reasonable explanation is that there is a protective function in applying a lens with a disinfecting solution (reusable soft lens) that does not exist when using dailies, which are stored in saline.2
REUSABLE SOFT CONTACT LENSES
Although daily disposable lenses have grown in popularity, reusable soft lenses (biweekly, monthly, and quarterly replacement) are still by far the most commonly used modality worldwide. There are several reasons why these lenses have remained a popular option when patients are choosing contact lenses. Of these factors, overall cost to the consumer is likely the major advantage. When comparing the cost of a 1-year supply of daily disposables to biweekly or monthly replacement lenses, daily disposables are, on average, much more expensive. When discussing the cost of contact lens wear with our patients, however, it is important to consider the frequency of their lens wear. In a recent study conducted in the United Kingdom and published by Efron et al in 2011, the overall cost of lenses comparing different replacement modalities was examined. Their model showed that, although reusable lenses are indeed more cost-effective when worn full time (4-7 days/week), daily disposable lenses are more economical when worn on a part-time basis (1-3 days/week).5 Another major advantage of reusable soft lenses is the wide range of available lens types and parameters. Even though we have recently seen many new types of daily disposables, they are not a viable option for many patients. Currently, there is only one brand of multifocal daily disposable lens, and although there are multiple brands of toric dailies, none are designed to correct astigmatism at an oblique axis. Until a larger variety of daily lenses becomes available, biweekly and monthly lenses are still the best choice in many cases.
GAS-PERMEABLE CONTACT LENSES
Hard contact lenses were once at the forefront of contact lens practice. In the 1950s and 60s, these non-gas permeable lenses, made of polymethyl methacrylate, were commonly fit and were widely popular. The invention of the first hydrogel contact lens material (HEMA) by Otto Wichterle and Drahoslav Lim in the late 1950s was the first step toward the eventual decline of the hard contact lens market. Due to greater initial comfort and ease of use, soft lenses quickly became the favored form of contact lens correction. Today, polymethyl methacrylate is a thing of the past, and lenses made with new gas-permeable materials (GP) can provide flawless vision and excellent oxygen transmissibility to the cornea. In many ways, visual quality with GP lenses is far superior to what we can achieve with a soft contact, yet they only account for approximately 8% of all contact lens wear.6 GP lenses are ideal for patients with high amounts of astigmatism or those with complex “hard-to-fit” corneas and are usu- ally the only option for individuals with irregular corneal astigmatism. When fitting patients with normal prolate corneas, spherical GP lenses work well most of the time. These lenses will vary slightly based on the manufacturer, but they are all relatively similar in design and have not changed significantly in recent years. New GP lens designs seem to cater to the growing population of presbyopes with a multitude of multifocal designs within the corneal GP realm of translating and aspheric progressive lenses.7
Long-standing myopic control with orthokeratology lenses is an additional target market for the GP-fitting niche. The ease and precision of reshaping the cornea with specially designed GP lenses in practice has proven to be a mainstay, especially in East Asian countries. The general idea behind orthokeratology is to flatten the curvature of the central cornea through overnight wear of a reverse geometry corneal GP lens.8 Reduction in myopia’s progression is thought to be the result of peripheral myopic defocus secondary to the corneal reshaping process.9
Semi-scleral and scleral GP lenses are the newest approach to managing patients with corneal ectasia secondary to conditions like keratoconus and pellucid marginal degeneration. Although the idea of large-diameter scleral contact lenses dates back more than 125 years, modern scleral GPs bear little resemblance to their ancestors. In the past, the common concern with the use of scleral lenses was the limited level of oxygen transmission to the cornea. Through the use of newer, more oxygen-permeable (higher Dk) materials, these lenses have once again become a viable option. By vaulting the entire cornea and landing on the conjunctiva, scleral lenses simultaneously correct for any corneal astigmatism (regular or irregular) and provide enhanced comfort compared with corneal GP lens designs. Despite the fact that these large lens designs are, on average, more expensive than traditional corneal GPs, they have recently gained popularity among many contact lens practitioners.
Although there have been many advances recently in terms of contact lens options, lens manufacturers are still working to improve overall patient safety and vision. It can sometimes be difficult to determine which lens will work best for your patient, so it is important to keep an open mind and consider the wide array of lens options available to you.
Chirag Patel, OD, is the cornea and contact lens research fellow at the Texas Eye Research and Technology Center and The University of Houston College of Optometry. He acknowledged no financial interest in the products or companies mentioned herein. Dr. Patel may be reached at email@example.com.
Sophia Asaria, OD, is a cornea and contact lens resident at The University of Houston College of Optometry. She acknowledged no financial interest in the products or companies mentioned herein. Dr. Asaria may be reached at firstname.lastname@example.org
- Efron N, Morgan P, Helland M, et al. Daily disposable contact lens prescribing around the world. Cont Lens Anterior Eye. 2010;33:225-227.
- Morgan P, Efron N, Toshida H, Nichols J. An international analysis of contact lens compliance. Cont Lens Anterior Eye. 2011;34:223-228.
- Stapleton F, Keay L, Edwards K, et al. The incidence of contact lens-related microbial keratitis in Australia. Ophthalmology. 2008;115:1655-1662.
- Dart JKG, Radford CF, Minassian D, et al. Risk factors for microbial keratitis with contemporary contact lenses. A case-control study. Ophthalmology. 2008; 115:1647-1654.
- Efron S, Efron N, Morgan P, Morgan S. A theoretical model for comparing UK costs of contact lens replacement modalities. Cont Lens Anterior Eye. 2012;35:28-34.
- Nichols J. Contact Lenses 2009. Contact Lens Spectrum. 2010;25(1).
- Efron N. Obituary. Rigid contact lenses. Cont Lens Anterior Eye. 2010;33:245-252.
- Caroline PJ. Contemporary orthokeratology. Cont Lens Anterior Eye. 2001;24:41-46.
- Smith III EL. Optical treatment strategies to slow myopia progression: effects of the visual extent of the optical treatment zone [published online ahead of print January 3, 2013]. Experimental Eye Research. 2012. http://dx.doi.org/10.1016/j.exer.2012.11.019.