Twenty-five Years of Contact Lenses

Transcription

1 Cornea 19(5): , Lippincott Williams & Wilkins, Inc., Philadelphia Twenty-five Years of Contact Lenses The Impact on the Cornea and Ophthalmic Practice Timothy T. McMahon, O.D., and Karla Zadnik, O.D., Ph.D. Purpose. The history of contact lenses has occurred in the latter half of the 20th century. In particular, events in the 1970s through the 1980s related to the invention of soft, hydrogel contact lenses have revolutionized the contact lens industry and the eye care attached to it. This article recounts that history from the perspective of market forces, inventions, and discoveries about the physiologic functioning of the cornea. Methods. The relevant literature is critically reviewed. Results. Discoveries about the oxygen needs of the cornea and consumer pressure for clear, comfortable, around-the-clock vision have resulted in a history of rigid gas permeable and soft lenses that leads to today s contact lens picture. The short-term and long-term effects of chronic hypoxia and the levels of lens oxygen transmissiblity necessary to avoid them have been well-described. The advent of the soft lens, followed by the human experiment with initial extended-wear modalities, led to the advent of the disposable soft contact lens. Conclusions. In the past 25 years, the development and wide acceptance of soft contact lenses have revolutionized the management of refractive error and corneal diseases. Key Words: Contact lens Hydrogel Rigid gas permeable lens Extended-wear Daily-wear. In 1975, 25 years ago, the contact lens world was in the midst of a huge revolution that would change the face of eye care in America and much of the rest of the world. Most polymethylmethacrylate (PMMA) lenses were produced individually by small independently owned contact lens manufacturers for doctor clients; the soft lens was beginning to make a noticeable penetration into American and British marketplaces, leading the charge for large manufacturers to dominate the field. 1 3 Sparked by this change in contact lens materials, ophthalmic practice has never been the same. This review chronicles the past 25 years of contact lenses in ophthalmic practice and concentrates on the changes that new lens materials and care systems have had on patients, their corneas, and ophthalmic practice. The impact of these developments is greater than one would initially believe, resulting in new knowledge of corneal physiology and a much greater appreciation for the pathologic consequences of tampering with the normal human cornea. As well, contact lenses are routinely used in the management and Submitted February 8, Revision received March 21, Accepted March 27, From the Department of Ophthalmology and Visual Sciences (T.T.M.), University of Illinois at Chicago, Chicago, Illinois; and the College of Optometry (K.Z.), The Ohio State University, Columbus, Ohio, U.S.A. Address correspondence and reprint requests to Dr. Timothy McMahon, University of Illinois at Chicago, M/C 648, 1855 West Taylor Street, Chicago, IL 60612, U.S.A. treatment of ocular disease. Developments in the contact lens field have affected health care practitioners within the eye care domain and throughout medicine and dentistry in ways that have significantly changed the doctor patient relationship. Understanding the historical importance of the pioneers who developed the concept of the contact lens and the materials used provides a cornerstone for fully comprehending the impact of a little piece of plastic placed on a cornea. Additionally, we look at the knowledge gained in our understanding of corneal physiology, contact lens-associated corneal pathology, new roles for contact lenses in the treatment and management of corneal disease, and finally the impact of contact lenses on the doctor patient relationship. LENS MATERIALS The Soft Lens: The Otto Wichterle and Drahoslav Lim Story Behind the iron curtain in Prague, Czechoslovakia, a chemist and director of the Institute for Macromolecular Chemistry at the Czechoslovak Academy of Sciences was busy developing a polymer that could be used to construct artificial blood vessels and orbital implants. Professor Otto Wichterle (Fig. 1.) and his assistant Drahoslav Lim thought their new polymer hydroxyethylmethacrylate (HEMA) could be used to make contact lenses. 4 This was in the mid-1950s. An enterprising attorney named Martin Pollak, a major participant in a patent licensing and technology transfer company (National Patent Development Corporation in New York, NY, U.S.A.) was conducting business in Moscow and learned of a new contact lens being developed in Prague. He traveled from Moscow to Prague, happened upon Professor Wichterle, and became enthralled with potential prospects for the new material. Knowing nothing about contact lenses, Mr. Pollak was informed that the principal advantage of this new material was that fewer parameters were needed to fit a lens to the human cornea and that practitioners would be able to stock lenses and dispense them directly from their office. Pollak returned to the United States and recruited Robert Morrison, O.D., and eventually Allan Isen, O.D., to advise Wichterle on lens design issues and production issues. It was Professor Wichterle who developed the spincasting method for producing lenses from the gel polymer, initially constructing a prototype machine using his son s erector set in his kitchen. 5 Recognizing the need for serious financial backing, Pollak entered into a licensing agreement between Wichterle, National Patent Development Corporation, and Bausch & Lomb, Inc. ([B&L], Rochester, NY, U.S.A.), giving much of the worldwide rights to B&L for 730

2 TWENTY-FIVE YEARS OF CONTACT LENSES 731 of 1998, according to the International Association of Contact Lens Educators (personal communication, Sweeney D. International Association of Contact Lens Educators, 1999). Estimates by region indicate that 17 million people wear contact lenses in Asia, 17 million in Europe, 0.5 million in Australia, and 32 million in the United States (personal communication, Sweeney D. International Association of Contact Lens Educators, 1999). FIG. 1. Professor Otto Wicheterle. (Figure courtesy of Professor Jan Rocek.) the polymer and the manufacturing rights. B&L was prepared to bring their new lens to market in 1968 when the Food and Drug Administration (FDA) stepped in after many complaints from small, family owned, contact lens laboratories and indicated that this new lens was a drug and would have to go through the standard drug approval process. 6 B&L eventually received marketing approval from the FDA in 1971 for the Soflens. By 1973, the Griffin lens (Softcon, American Optical, Inc., now Ciba Vision Care, Inc., Duluth, GA, U.S.A.) was approved for daily-wear. The daily-wear soft lens was on its way to becoming the dominant product in the contact lens market. Within the next 10 years, additional polymers and a change in the exclusive distribution rights was subsequently converted to a nonexclusive license through litigation that opened the floodgates to competitors in the soft lens business. Demographics Today there are >25 hydrogel polymers on the U.S. market alone and scores of contact lens manufacturers with revenues in the hundreds of millions of dollars supplying millions of U.S. contact lens wearers. In 1975, there were only a couple of million soft lens wearers. By 1990, 76% (21.8 million) of lens wearers wore soft lenses and 24% (1.0 million polymethylmethacrylate [PMMA], 3.7 million rigid gas permeable [RGP]) used rigid lenses for a total of 26.5 million in the United States. In 1998 in the United States, 83% (27.6 million) of wearers used soft lenses and 17% (5.7 million) wore rigid lenses, totaling 33.3 million. 7 World wide there were approximately 75 million contact lens wearers as Extended-wear Contact Lenses HEMA-based hydrogels have always offered a certain degree of gas permeability. Refinements in the polymer formulations, including adding methacrylic acid, had the effect of elevating the water content of the lens polymer. Oxygen permeability is directly related (positively correlated) to the water content of the polymer and is inversely proportional to the thickness of the material. Thus, lens manufacturers were constrained by the boundaries of a very thin lens or a lens reaching such a high water content as to become dimensionally unstable, like a bag of water. Within these confines, sufficient oxygen permeability was achieved so that the FDA approved the first hydrogel extended-wear lens in 1979 for aphakia for the Permalens by Cooper Vision (Fairport, NY, U.S.A.) and the Hydrocurve lens from Continuous Curve Contact Lens Company (now Wesley-Jesson, DesPlaines, IL, U.S.A.). 5,6 The initial approval for 14 days of extended-wear rapidly decreased to 6 nights of continuous wear due to the appearance of complications not found during the FDA approval process The extended-wear lens was initially targeted to the aphakic patient who frequently was elderly and had difficulty with aphakic spectacles or with the insertion and removal of a contact lens. For many patients, the treatment plan was for a monthly visit to the doctor s office for cleaning and disinfection of the lenses. Myopic extended-wear was approved shortly after the aphakic lens approval in 1981, (the Hydrocurve and the Permalens) permitting myopic patients their first real opportunity to see well at all times. This was and is an extremely powerful elixir to the myope (and the older hyperope) as can be demonstrated by witnessing the explosion of refractive surgery procedures performed today. Recognition that extended-wear of hydrogel lenses carried an increased risk for serious complications, in part, led to a dramatic shift in the soft lens market The prevailing clinical opinion of the 1980s was that lens handling played a substantial role in the risk of microbial keratitis. In part, this general opinion led to the introduction of the disposable soft lens in 1987 by Vistakon (Jacksonville, FL, U.S.A.). The Acuvue disposable lens was initially introduced as a 2-week extended-wear lens to be worn and then thrown away. Initial claims were that this lens would be safer because lens handling was reduced to a minimum and the lens was replaced before potentially harmful contaminants could adhere to the lens. Although disposing of the lens on a regular basis did little to reduce the risk of serious complications, it did reduce the majority of nuisance complications and resulted in longer lasting contact lens comfort. 13,14 Vistakon s venture changed the face of the soft contact lens industry, and frequent replacement soft lenses are now the predominant lens type in the United States and Europe. Silicone Elastomer contact lenses were initially introduced to the market by Breger s Mueller-Welt Company (Chicago, IL, U.S.A.) as the Silcon lens. This was sold to Dow Corning (Detroit, MI, U.S.A.) in 1972 and reformulated as a coated silicone rubber lens in relatively small diameters for aphakia (Silsoft) and myopia (Silsight). 15 Extended-wear FDA approval was given for aphakia

3 732 T.T. MCMAHON AND K. ZADNIK in 1981 and myopia for 30 days in Although initial experience was reportedly quite positive, silicone elastomer lenses generally were not well-tolerated by myopic patients with frequent complaints of poor wetting and discomfort. 6,16 22 B&L acquired the lens in 1985 and continues to provide the lenses in aphakic powers only. This lens has become the lens of choice for pediatric aphakia. Due to the high relative risk for infectious microbial keratitis, the frequency of extended-wear using the HEMA-based hydrogels gradually decreased during the 1990s. The primary culprit for the heightened risk of infection appears to be a cascade of events produced by hypoxia. The desire by patients to have their vision corrected at all times has not waned. In response to this desire, expressed in the volume of patients undergoing refractive surgery, contact lens manufacturers have aggressively sought new materials that will reduce the hypoxia induced while wearing a lens during closed-eye periods. As previously mentioned, all HEMA-based materials oxygen permeability is constrained by either water content or thickness. Unfortunately, the constraints do not permit a lens to be made that can be tolerated or that will survive the rigors of handling or wearing that delivers the oxygen levels needed in the cornea under closed-eye conditions. Therefore, novel materials were needed that would not be limited by these boundaries. As of this writing, two such polymers are available. These are balifilcon A (PureVision; Bausch and Lomb) and lotrafilcon A (Focus Night and Day; Ciba Vision Care, Inc.). Both of these polymers are referred to as silicone hydrogels, and each exceeds 90 barrers of permeability. Rigid Gas Permeable Lenses, the Story of Siloxane The earliest known lenses were rigid. The first to describe the principle of the optical effect of the contact lens was Leonardo Da Vinci in 1508 using a glass bowl of water. Rene Descartes described the neutralizing power of the cornea using a water-filled glass tube in 1636 in his studies of astigmatism and has been credited for being the first to actually describe the use of a contact lens. 23 Thomas Young applied the same principle in his studies of accommodation in 1801, and Sir John Herschel clearly described a glass contact lens to be used on a distorted cornea in ,6 The early lenses used for clinical purposes were also made from cut or blown glass and were permitted for only extremely short wearing times and very limited uses. Fick first described corneal lenses, and attempts were made by several investigators to use these early lenses for the correction of aphakia, keratoconus, and injury. 6,23 The first plastic lenses were large scleral designs. William Feinbloom marketed the first partially plastic lens in 1936 as a scleral lens, with the central portion being made of glass and the peripheral portion being made of PMMA. Theodore Obrig, John Mullen, and Istvan Gyorrfy were the first to make an all plastic lens between 1938 and Obrig laboratories were established in New York in the 1940s to make plastic scleral lenses. It is interesting to note that, while conducting studies in the laboratory, it was here that Obrig accidentally noted that sodium fluorescein could be used with a black light to evaluate the tear layer behind a contact lens. Kevin Tuohy, a technician in Obrig s lab is generally acknowledged as the inventor of the plastic corneal contact lens. PMMA served as the primary material until the late 1970s when gas permeable materials were introduced. In 1978, the first gas permeable material was approved by the FDA. Cellulose acetate butyrate lenses were used for both daily- and extended-wear, although they were only approved for daily-wear. Then eventually were discontinued due to problems with dimensional stability. Norman Gaylord, a polymer chemist, Leonard Seidner, an optometrist, and his brother Joseph Seidner, an engineer, developed a gas permeable polymer commonly known as silicone/acrylate ; the proper term is polysiloxanylalkyl acrylic ester and alkyl acrylic ester. Syntex Laboratories (AZ, U.S.A.) bought the material and marketed the first widely used gas permeable lens known as the Polycon (silafilcon A) lens in Since then, a wide variety of rigid gas permeable polymers have been brought to market worldwide (Table 1). The early siloxane/acrylate lenses provided limited oxygen permeability with permeabilities <30 barrers. These lenses were also more difficult to make, resulting in marked differences in laboratory-specific quality of product. Due to the siloxane in the materials, surface wetting problems were common, and patients frequently complained of end-of-day dryness. During the mid-1980s, the focus of the ophthalmic community was on the need for greater oxygen permeability, which resulted in a new class of gas permeable lenses known as the high Dk siloxane/acrylate lenses. These materials had permeability values ranging from 30 barrers to the mid-50 barrers. The increased permeability was primarily achieved through the addition of higher amounts of siloxane to the polymer. Although this was a successful strategy for elevating the oxygen flux through the material, it also made the lenses less wettable and, hence, less well-tolerated by the wearer. Enter fluorine. Although fluorine had been considered very early in the development of rigid contact lenses, it was not until the early 1990s that the contact lens industry fully grasped the advantage of this molecule. Adding fluorine to the polymer mix enhanced the wetting properties of the lens and improved comfort and visual performance of the lenses. Fluorine also elevated the permeability of these plastics a well. These fluoro-siloxane/acrylates, com- TABLE 1. Rigid gas permeable contact lens materials Brand name Material Dk Cellulose acetate butyrate (CAB) Meso Porofocon A 12.3 RX 56 Porofocon A 12.5 Low Dk siloxane/acrylate Polycon II Silafocon A 12.0 Paraperm O2 Pasifocon A 15.6 Boston II Pasifocon A 14.6 Optacryl SGP-1 Telefocon A 12.0 OP-2 Lotifocon A 15.9 High Dk siloxane/acrylate Paraperm EW Pasifocon C 56.0 Boston IV Pasifocon B 28.7 SGP-2 Telefocon B 43.5 SGP-3 Unifocon A 43.5 Fluoro-siloxane/acrylate Menicon SFP Melafocon A Menicon Z Tisilfocon A Fluoroperm 30 Paflucon C 30.0 Fluoroperm 60 Paflucon B 60.0 Fluoroperm 92 Paflucon A 92.0 Fluoroperm 151 Paflucon D Paragon HDS Paflucon B 58.0 Boston VII Satafocon A 73.0 Boston ES Enflucon A 36.0 Boston EO Enflucon B 82.0 Equalens Itafluorocon A 64.0 Fluorex 300 Flusifocon C 30.0 Fluorex 500 Flusifocon B 50.0 Fluorex 700 Flusifocon A 70.0

4 TWENTY-FIVE YEARS OF CONTACT LENSES 733 monly known as the fluoropolymers by class, had become the lens materials of choice by the mid-1990s. Oxygen permeability values have reached 200 barrers for some materials. With each new version, less siloxane is used, reducing the importance of this compound in today s lenses. However, siloxane s place in the archives of contact lens history remains an important one. The Hybrid Materials A novel lens design merits singular mention here. Precision- Cosmet (Minneapolis, MN, U.S.A.), a small laboratory in Minnesota, developed a method of producing a lens with a low oxygen permeable gas permeable center surrounded by a hydrogel skirt. The concept was ingenious obtain rigid lens optics with soft lens comfort! Their first version was called Saturn. The company was eventually acquired by Pilkington-Barnes Hind (now Wessley- Jessen, DesPlaines, IL, U.S.A.). Two other versions came to market, Saturn II and SoftPerm. The improved versions were needed because of significant fitting problems encountered with the lenses, which resulted in many lens fitters avoiding this product. In the latest version, SoftPerm, the rigid center uses the Polycon material (silafocon A). Additionally, the lens tended to tighten with time, ripped easily, and had low oxygen permeability resulting in corneal edema and neovascularization as common complications. The concept was brilliant, but the execution was less than desired by a large margin. THE IMPACT OF CONTACT LENS WEAR ON CORNEAL PHYSIOLOGY The earliest evidence of the relative importance of an interruption in the availability of atmospheric oxygen was noted by Fick 24,25 in the late 1800s; he described a misting of the cornea after wearing a glass scleral lens. Later, the frequency of corneal clouding with lens wear raised concerns about the safety of contact lens wear It is clear that all contact lenses produce a barrier to the oxygen available to the cornea This barrier will decrease the partial pressure of atmospheric oxygen at the corneal surface and, hence, will result in a reduced flow into the cornea. 37 It is also clear that the cornea is unique in that it obtains the majority of the oxygen needed for metabolic activity via uptake directly from the oxygenated tear-film and lesser amounts from perilimbal capillaries and the anterior chamber. When a contact lens is on the cornea, atmospheric oxygen is available through two primary pathways: pumping of oxygenated tears around and under the lens and diffusion through the lens. Fatt and St. Helen 33 have described the most commonly reported method for determining the diffusion of flow through a contact lens material. The rate of diffusion of a gas (J) is determined by the following formula: J (P 1 P 2 )Dk/L Where D is the diffusivity and k is the solubility of a specific gas in the material, L (sometimes referred to as t) is the lens thickness, and P 1 and P 2 are the gas tensions at the two lens surfaces. The term Dk is known as the permeability of the material and represents a variable that can be calculated but not measured. The term is devoid of material thickness and boundary effects. It is the term used by the contact lens industry to compare one lens material to another in terms of oxygen flux. Dk/L is the transmissibility or transmissivity of a lens. This term is measured and is germane to the lens itself. The level of oxygen under a contact lens has been measured supporting the notion that the higher the Dk/L for oxygen of a lens the higher the oxygen levels under the lens Under the closed-eye environment, the partial pressure of oxygen at the corneal surface is reduced from 20.9% to approximately 8%. With HEMA-based hydrogels and many rigid lenses, this low level of initial oxygen supply results in diffusion levels that are below safe minimum levels to maintain normal corneal integrity. Holden and Mertz 41 have defined the critical transmissibility levels under which corneas do not swell for daily-wear as being Dk/L avg and Dk/L avg for overnight, closed-eye wearing conditions. These have become known as the Holden Mertz criteria. Another way of looking at this is to define the critical minimum partial pressure of oxygen at the corneal surface needed to avoid corneal edema. In 1970, Polse and Mandell 32 defined this level as being %. Over the next 15 years, the critical PO 2 level has been revised to between 10 13% These newer values are consistent with the 3 4% overnight swelling normally seen without lens wear where the PO 2 is around 8%. Tear pumping has been determined to be a supplementary route for providing oxygen to the cornea Investigators have found that there is a 10 20% volume exchange under a rigid lens per blink, whereas only a 1% per blink exchange with soft lenses. 45 Radke et al. 48 have recently postulated that the exchange of tears under a contact lens is best explained by a tear mixing model rather than by a flow model. Regardless, the exchange rate under rigid lenses, and to a greater extent soft lenses, is insufficient to meet the oxygen needs of the cornea. A great deal has been learned about the mechanism of hypoxiainduced corneal edema, stimulated by the need to understand the origin of Fick s corneal misting 24,25 or Sattler s veil 28 or Korb s central circular clouding, 49,50 all describing the loss of transparency secondary to corneal edema. Oxygen is a necessary metabolite for aerobic respiration (carbohydrate metabolism), which accounts for about 15% of the glucose substrate metabolized. This minority share of the glucose metabolism provides the majority of the energy needed for corneal metabolic activity due to the cornea s high metabolic efficiency. Reduction in the available O 2 supply results in a greater percentage of anaerobic respiration. Anaerobic respiration leads to a build-up of lactate, a byproduct resulting in stromal acidosis that rapidly decreases the endothelial cell aqueous pump function. The reduction in the endothelial pump function results in a decrease in stromal hydration control and, hence, corneal edema. However, anaerobic respiration is not solely responsible for contact lens-induced corneal edema. Other factors, including alterations in epithelial permeability, carbon dioxide levels under the contact lens, the breakdown of trapped debris under the lens affecting tear ph, and elevated corneal temperature, also play important roles. 27,51 55 Short-term and long-term changes in corneal structure and function associated with lens wear have been identified (Table 2). An important observation is that chronic, long-term effects are quite different in some respects than the impact of acute hypoxia. For example, with chronic exposure to low level hypoxia under a contact lens, the epithelium and stroma thin with time instead of thicken. This presumably represents a compensatory reaction to a long-term change in corneal metabolism. Additionally, long-term lens wear has been associated with reduced recovery from corneal

5 734 T.T. MCMAHON AND K. ZADNIK TABLE 2. Changes in function and structure of the cornea with contact lens wear Short-term Corneal Epithelium Reduced aerobic respiration Increased anaerobic respiration Elevated oxygen uptake Elevated lactate levels Edema Reduced mitotic rate Reduced glycogen stores Reduced transcorneal potential Stroma Edema Posterior striae Endothelium Endothelial blebs Decreased aqueous pump function Long-term Increased fragility Microcysts Reduction in the oxygen uptake rate Elevated lactate levels Thinning Reduced mitotic rate Reduced glycogen stores Decrease in corneal sensitivity Thinning Vascularization Decreased cell density Decreased aqueous pump function Polymegathism Pleomorphism Endothelial bedewing edema, implicating the chronic hypoxia environment with a reduction in endothelial pump function and epithelial barrier function. 51,56 63 Pathophysiologic Correlates of Contact Lens Wear Over the past 25 years, great strides have been made in understanding the pathophysiology of the adverse events found with contact lens wear. These events can be grouped into four major categories: hypoxia mediated events, immune events, mechanical events, and osmotic events. These categories are not mutually exclusive and more than one category can be in play for a particular complication. Of these groupings, hypoxia and immune events have the greatest risks for loss of vision. The effect of hypoxia has been cited previously to have profound effects on the structure and function of the various layers of the cornea. It is now generally believed that hypoxia plays a dominant role in the causal mechanism of infectious keratitis associated with contact lens wear. Epidemiologic evidence in the United States (late 1980s) and recently from Europe demonstrates that the relative risk of infectious keratitis increases with increased exposure to hypoxia. Cheng et al. 64 from the Netherlands have recently confirmed prior U.S. evidence indicating that the estimated annualized incidence of infection is 1.1 per 10,000 (95% CI, ) for RGP daily-wear, 3.5 per 10,000 (95% CI, ) for dailywear soft lenses, and 20.0 per 10,000 (95% CI, ) for extended-wear soft lenses. Poggio et al. 10 have shown that the duration of the hypoxia also is related to risk of infection. Hypoxia appears to affect the increase in risk through a number of channels. These include reduction in mitotic rate resulting in older and, consequently, larger cells being present at the corneal surface, alterations in epithelial permeability, increased epithelial fragility, and increased microbial adherence to corneal epithelial cells after exposure to hypoxia. 61,65 71 The weakened and damaged cells provided a locus for infection. Increased cell adhesion by cytotoxic strains of bacteria provides for direct cellular invasion by these strains. Interestingly, new high oxygen flux lenses both (soft and rigid) appear to reduce bacterial adhesion in eyes wearing high Dk lenses compared to lower Dk materials Ren et al. 75 reported on a 3-year randomized clinical trial evaluating corneal cell desquamation rate, surface epithelial cell size, tear lactate dehydrogenase levels, and bacterial adherence to desquamated epithelial cells in 109 subjects using a variety of soft and RGP materials of varying Dk levels. They provide clear evidence of increased bacterial binding, decreased desquamation frequency, and larger cells in eyes wearing lower Dk/L materials compared to high Dk/L lenses. Immune mediated adverse responses are common ocular complications to lens wear. Important examples of this class of complications include contact lens-associated superior limbic keratoconjunctivitis, 76 peripheral corneal ulcers, 77 central sterile infiltrates, 78 and giant papillary conjunctivitis. 79 Mechanical injury can be subclinical with microtrauma to corneal epithelial cells. For example, RGP wear can have a tendency to physically injure and causes premature shedding of epithelial cells. Clearly, clinically evident injury to the cornea is common in all types of lenses and under all wearing regimens. Osmotic injury refers to lens-mediated environments where the tear-film becomes hypotonic, resulting in epithelial swelling. This is a secondary phenomena such as can found with chronic tearing when wearing a chronically irritating lens that produces notable forward scattering and photophobia, yielding further tearing and hypotonicity, so on and so on. Dellen formation would fall into this category, as well, through dehydration mechanisms. NEW USES FOR CONTACT LENSES: THE MANAGEMENT OF DISEASE, SURGERY AND TRAUMA Over the past 25 years, contact lenses have been used to manage corneal disease, in postoperative care, and in vision rehabilitation after disease, surgery, and trauma by serving as a vehicle to deliver drugs, as a bandage, optically as a new corneal surface, and as a prosthetic device. Delivery of ophthalmic drugs via soft lenses was considered early on after hydrogels were introduced. 80 Potential uses included lenses used as a vehicle for glaucoma medications and antimicrobials The belief was that using a controlled delivery method over time would prove to be superior to pulse dosing via eye drops in sustaining therapeutic drug levels and permitting lower drug concentrations, reducing complications. Several investigators determined that hydrogel lenses deliver drug via a passive diffusion mechanism, appropriately adjusted for drug lens binding properties. 81,82 The diffusion rate was also related to tear ph and tear volumes and, thus, was somewhat difficult to control. The use of hydrogel lenses for drug delivery never achieved wide usage and is rarely employed today. Porcine collagen also was investigated and briefly used in the 1980s for wound healing and drug delivery. These devices intentionally broke down when exposed to tear enzymes, thus dissolving within a few days. Due to cost, handling difficulties, and comparable performance to hydrogels, these devices were popular for only a few years. Bandage Lenses Using lenses for bandage or therapeutic purposes has gained wider appeal over the past 2 decades. Therapeutic uses include barrier function and an adjunct to surface healing, 80,86 95 tamponade, 96,97 and pain management. 75, There is even the odd use of hydrogel lenses by otolaryngology for the healing of tympanic membranes. 101 Hydrogel lenses, being supple and conforming, make nearly ideal bandages. Thin, minimally movable lens designs have been developed to help protect the injured cornea from ex-

6 TWENTY-FIVE YEARS OF CONTACT LENSES 735 ternal forces, such as the wiping action of the eyelids. This barrier permits the sliding action at the leading edge of the adjacent epithelium, a critical part of the healing process to progress unimpeded. This barrier function can also be employed to protect the healthy cornea from rough and scarred eyelids found in cicatricial disease. A last role is in conjunction with corneal gluing of perforations. 102,103 Here the lens serves to reduce lid irritation caused by the rough glue surface and to aid in retaining the glue at the wound site. Tamponade is a relatively uncommon role for contact lenses. The three principal areas involve stopping leaky cataract wounds, stopping leaky filtering blebs, and plugging small corneal leaks associated with corneal melts or lacerations. 96,97, Pain management involves reducing the stimulation of corneal nerve endings found with loosely adherent epithelium and during healing. Bandage contact lenses have proven to be a great asset in controlling discomfort associated with bullous keratopathy. 75,100 Frequently, placing a high water content lens on the affected eye can completely eliminate discomfort for days at a time. Overnight wear for this purpose is the rule, with durations upward of a month. Postoperative pain management after phototherapeutic keratectomy relies heavily on the placement of a hydrogel lens for the initial 2 3-day period of epithelial healing. 87,98,99,107 Before using these devices, it was common to need scheduled narcotics to control the pain. In fact at one point early in the trials for myopic phototherapeutic keratectomy in the United States, there was serious concern that the FDA would not approve such a painful procedure to treat refractive error. Therefore, in a strange twist of fate, contact lenses made it possible for laser refractive surgery procedures to go forward and receive FDA approval for marketing in the United States. A change in the standard of care for the management of corneal abrasions occurred in the 1990s. Reports surfaced of microbial keratitis after patching for corneal abrasions in contact lens wearers. 108 Recommendations not to patch abrasions during the first 24 hours after a contact lens-related abrasion to avoid incubating an occult microbial infection of the cornea quickly followed. 109,110 Subsequent to these reports, several studies recommended abandoning pressure patching with evidence supporting no improvement in comfort and an absence of increased healing rates On the other hand and related to their use in the postoperative pain management regimen, hydrogel bandage lenses along with topical nonsteroidal antiinflammatory agents and topical antibiotics have been recommended in the general management of corneal abrasions The advantages to this approach are reduced discomfort, increased healing rates, maintenance of binocular vision, and direct visualization of the wound during healing. One of the most powerful and satisfying uses for contact lenses is their application in visual rehabilitation. In the presence of very high refractive errors and corneal irregularities, rigid contact lenses can have a dramatic impact on visual acuity, even in the presence of significant scarring. The application for lenses in vision rehabilitation include keratoconus and the other noninflammatory thinning disorders (except keratoglobus), postpenetrating and lamellar corneal grafts, corneal lacerations, aphakia, postrefractive surgery, as well as inflammatory and infectious corneal scarring. Pathologic myopia and nanophthalmus are greatly helped by contact lens use. In the +30 diopters (D) hyperope or 25 D myope, spectacles will rarely provide acceptable visual acuity. It is common to see improvements from 20/200 to 20/40 in such cases after contact lens application. Keratoconus and the Other Noninflammatory Disorders The role for contact lenses in keratoconus and pellucid marginal degeneration is an ancient one. Some of the earliest uses for contact lenses included patients with keratoconus. 5,6,23 The primary lens type used throughout the world today for keratoconus is the rigid gas permeable corneal lens. Numerous other approaches to the optical management of these disorders have been tried. These include scleral lenses, hybrid lenses (Softperm), and specially designed soft lenses Additionally, combining a soft lens with a rigid lens in a piggy-back fashion has also seen success in some patients who are intolerant to RGPs or who demonstrate a history of recurrent erosions. 121,122 Within the corneal lens domain, significant controversy exists in the ophthalmic community regarding the best and safest manner for managing keratoconus. By lumping the myriad of lens-fitting strategies into three philosophical groups, one finds opposing views on how best to care for patients with this disorder. These groupings are large and flat with the purpose of splinting the cornea to establish more normal shape and to retard disease progression, 123,124 divided support with apical contact with no intention to alter the topography of the cornea, 125,126 and apical clearance fitting to avoid trauma to the thinned apical area to reduce the likelihood of scar formation. 127,128 Embroiled within this controversy is the yet unknown cause of keratoconus. Some authorities believe that contact lenses and/or eye rubbing can produce keratoconus, and some investigators think contact lens wear, particularly the fitting philosophy, can alter the course of the disease progression for better or for worse Penetrating and Lamellar Keratoplasty Contact lenses play an important role in the postkeratoplasty armamentarium of vision correction options. Although visual outcomes have improved remarkably since the introduction of penetrating keratoplasty in 1952, one-third to one-half of all cases achieve their maximum visual acuity with a contact lens, compared to spectacles or no correction. The indications of contact lenses after keratoplasty have included anisometropia, high regular astigmatism, irregular astigmatism, concurrent aphakia, and contact lens wear in the fellow eye. In the majority of cases, rigid corneal lenses have been employed, although daily-wear and extendedwear hydrogel lenses have been used Rigid lens designs used for eyes with corneal transplants include high Dk materials, spherical base curve designs, aspheric designs, and bitoric lenses. Lenses are almost always equal to or larger than the size of the graft. Lenses fitted entirely within the graft tend to be too unstable and are prone to frequent dislodgment. Complications include corneal abrasions, suture lysis, corneal neovascularization, suture abscesses, and infectious keratitis. To date, no relationship has been found between contact lens wear and corneal allograft rejection. Aphakia Before the introduction and popular use of intraocular lenses, contact lenses were a popular choice for correcting aphakia. Initially, PMMA was used; but later, hydrogels were enthusiastically

7 736 T.T. MCMAHON AND K. ZADNIK prescribed for this group of patients. Extended-wear was also first thought of for the aphakic patient who had difficulty with insertion and removal of the lenses Trauma Major eye trauma frequently results in significant corneal scarring, pupil dyscoria, aphakia, and lid abnormalities. Several investigators have shown that contact lenses offer a valuable means for correcting residual vision after ocular trauma McMahon et al. 149 have sounded a note of caution, however. In their large urban center series of more than 100 major injuries, almost 50% of cases ceased wearing lenses after 12 months even if the lenses were comfortable and vision was greatly improved. Additionally, although more than two-thirds of cases were corneal or corneascleral lacerations, the primary reason for lens use was for the correction of concurrent aphakia. Postrefractive Surgery Only a few refractive surgery patients require postoperative optical correction with a contact lens. The primary reasons for contact lens use in these cases include undercorrection, overcorrection, anisometropia, irregular and high astigmatism, as well as glare and halos at night Historically, most of these patients have been difficult to fit due to the irregular corneal curvature and oblate shape of the cornea. Additionally, many of the cases had sought refractive surgery because of previous contact lens failure. Regardless of these barriers to success, lens wear can commonly provide a tolerable means of vision correction. Infectious and Inflammatory Scarring In general, corneal scarring limits uncorrected and spectacle corrected visual acuity primarily through associated irregular astigmatism rather than because of opacification of portions of the cornea. Therefore, contact lenses, primarily rigid lenses, can frequently provide excellent vision after serious corneal infection or episodes of inflammatory disease with residual scarring. 150 The authors experience suggest that careful attention should be placed on reducing the bearing on the scar by the lens where possible. Chronic rubbing by the lens leads to reduced tolerance, increased risk of corneal vascularization, and in some cases, an increase in the whiteness of the opacity. Prosthetic Lenses Before approximately 1980, the disfigured eye was prescribed a painted scleral shell fitted and finished by an ocularist, to improve cosmesis. In the early 1980s, several labs around the world began tinting, dying, and using photographic inlays to produce contact lenses that could restore some or all of the natural appearance to the eye. There are at least eight firms within the United States that will produce such lenses. They are most successful with darkly pigmented eyes because brown eyes tend to lack visibly significant iris detail, and the anterior angle shadow (seen as a dark ring at the periphery) is much less apparent and, thus, is easier to match the normal eye. 157,158 Today, for disfigured eyes where there is a formed eye where the surface is not unduly rough and irregular and in the absence of severe enophthalmus, hydrogel prosthetic and (less commonly) rigid corneal prosthetic lenses are the choice for restoring a more normal appearance. COMMERCIAL MARKETING STRATEGIES: DECISIONS THAT HAVE CHANGED THE FACE OF THE OPHTHALMIC MARKET PLACE Although it is uncommon to review marketing issues in a prestigious peer-reviewed journal, we would be seriously remiss if several landmark decisions and strategies from the 1980s were not discussed here. There are three events that will go down in history as substantially affecting the way eye care is delivered today. These are the optical chain story, the Johnson and Johnson decision, and the birth of the mail order business. Before the development of the soft lens, eye care provided by optometrists and ophthalmologists in the United States was almost exclusively conducted in a private office setting. Spectacles were made available to patients through small family owned optical shops (most commonly used by ophthalmologists) or directly from the office (route preferred by most optometrists). In the 1970s, there were about twice as many optometrists as ophthalmologists. Half of the U.S. patient population was seen by ophthalmologists and the remaining were seen by optometrists. Optical shops began hiring optometrists and, less commonly, ophthalmologists began to attract patients at shopping malls in the early 1970s. After the introduction of the soft lens, the popularity, success, and numbers of these shops increased dramatically. Many of these shops were purchased and banded together to form optical chains. The chains offered local convenience and frequently lower prices for services and introduced the world of mass marketing and advertising of eyeglasses to the American public. Today, nearly half of all Americans get their eye care from optical chains. Fully 50% of all new contact lens fittings are performed in optical chains. This health care delivery vehicle is a serious force. It barely existed 25 years ago. In 1981, Frontier Contact Lenses, a small Jacksonville, Florida, soft lens manufacturer (later renamed Vistakon), was acquired by the healthcare product giant Johnson and Johnson, Inc. Johnson and Johnson bought the rights to a stabilized soft molding process from a Danish firm in This technology permitted Vistakon to produce vast numbers of soft lenses inexpensively and reproducibly. The initial goal was to provide a safer extended-wear lens, one that would only be handled once and then discarded after a period of use. At the time, hygiene and lens handling were thought to be a source of the higher incidence of infections found with extended-wear lenses, justifying this approach. Although their strategy actually failed, in that disposable lenses are not safer for extended-wear than are conventional extended-wear lenses (for serious complications), Vistakon succeeded in changing the soft lens industry by providing a product that appealed greatly to patients and that reduced the frequency of lens spoilage-related complications. Additionally, Johnson and Johnson s Vistakon is generally regarded as the first contact lens manufacturer to make a multimillion dollar commitment to direct advertising of their prescription product to consumers. The idea was to drive patients into doctors offices requesting their product. This strategy worked. Vistakon holds the majority of the disposable/frequent replacement lens market share in the United States and is a major distributor worldwide. Today, pharmaceutical companies advertise prescription drugs frequently in print, via radio, and in television markets throughout the country directly to patients. It started with disposable contact lenses. The third major event pertains to the introduction of mail order

8 TWENTY-FIVE YEARS OF CONTACT LENSES 737 contact lens establishments. Mail order shops started in the late 1980s as small businesses; they were frequently initially established as small local labs, which then branched out into a direct access line of business. Early on, these businesses operated at the fringes of state laws regulating the provision of contact lenses within their respective states. Some states drove the mail order houses out of business within their state only to find them set up in a neighboring state. State laws limiting a patient s access to his or her prescription for contact lenses and glasses as well as hesitancy to release prescriptions by their doctors severely curtailed growth of these businesses until Eye Glasses I was promulgated by the Federal Trade Commission. The Federal Trade Commission mandated that a patient had a right to his or her prescriptions. Lastly, the contact lens industry had largely tried to avoid selling products to these shops. A recent series of lawsuits by various state Attorneys General alleges that this restriction harms the American public (in essence through a means of price fixing). The contact lens companies have largely settled the suits and sell products to any and all legal establishments. As a result, the mail order contact lens business is flourishing. Today not only can contact lenses be obtained easily through the mail but prescription drugs and orthopedic devices are provided via this vehicle as well. In some cases, a health care plan may even mandate delivery through this mechanism. In very recent days, the Internet has become a source for contact lenses and pharmaceuticals, opening yet another channel for patients. REFERENCES 1. Goodlaw EI. How corneal contacts were born. Contact Lens Forum 1978;2: Hoffstetter HW, Graham R. Leonardo and contact lenses. AmJOptom 1953;30: Historical development. In: Mandell R, ed. Contact lens practice. 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