Twenty-Five Years of Contact Lenses the Impact on the Cornea and Ophthalmic Practice

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 treatment of ocular disease. Developments in the contact lens field half of the 20th century. In particular, events in the 1970s through have affected health care practitioners within the eye care domain the 1980s related to the invention of soft, hydrogel contact lenses and throughout medicine and dentistry in ways that have signifi- have revolutionized the contact lens industry and the eye care cantly changed the doctor–patient relationship. attached to it. This article recounts that history from the perspec- Understanding the historical importance of the pioneers who tive of market forces, inventions, and discoveries about the physi- developed the concept of the contact lens and the materials used ologic functioning of the cornea. Methods. The relevant literature is critically reviewed. Results. Discoveries about the oxygen needs provides a cornerstone for fully comprehending the impact of a of the cornea and consumer pressure for clear, comfortable, little piece of plastic placed on a cornea. Additionally, we look at around-the-clock vision have resulted in a history of rigid gas the knowledge gained in our understanding of corneal physiology, permeable and soft lenses that leads to today’s contact lens picture. contact lens-associated corneal pathology, new roles for contact The short-term and long-term effects of chronic hypoxia and the lenses in the treatment and management of corneal disease, and levels of lens oxygen transmissiblity necessary to avoid them have finally the impact of contact lenses on the doctor–patient relation- been well-described. The advent of the soft lens, followed by the ship. “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 LENS MATERIALS lenses have revolutionized the management of refractive error and corneal diseases. Key Words: Contact lens—Hydrogel—Rigid gas permeable The Soft Lens: The Otto Wichterle and Drahoslav lens—Extended-wear—Daily-wear. 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 poly- In 1975, 25 years ago, the contact lens world was in the midst mer that could be used to construct artificial blood vessels and of a huge revolution that would change the face of eye care in orbital implants. Professor Otto Wichterle (Fig. 1.) and his assis- America and much of the rest of the world. Most polymethylmeth- tant Drahoslav Lim thought their new polymer hydroxyethylmeth- acrylate (PMMA) lenses were produced individually by small in- acrylate (HEMA) could be used to make contact lenses.4 This was dependently owned contact lens manufacturers for doctor clients; in the mid-1950s. An enterprising attorney named Martin Pollak, a the “soft lens” was beginning to make a noticeable penetration into major participant in a patent licensing and technology transfer American and British marketplaces, leading the charge for large company (National Patent Development Corporation in New York, manufacturers to dominate the field.1–3 Sparked by this change in NY, U.S.A.) was conducting business in Moscow and learned of a contact lens materials, ophthalmic practice has never been the new contact lens being developed in Prague. He traveled from same. This review chronicles the past 25 years of contact lenses in Moscow to Prague, happened upon Professor Wichterle, and be- ophthalmic practice and concentrates on the changes that new lens came enthralled with potential prospects for the new material. materials and care systems have had on patients, their corneas, and Knowing nothing about contact lenses, Mr. Pollak was informed ophthalmic practice. The impact of these developments is greater that the principal advantage of this new material was that fewer than one would initially believe, resulting in new knowledge of parameters were needed to fit a lens to the human cornea and that corneal physiology and a much greater appreciation for the patho- practitioners would be able to stock lenses and dispense them logic consequences of tampering with the normal human cornea. directly from their office. Pollak returned to the United States and As well, contact lenses are routinely used in the management and recruited Robert Morrison, O.D., and eventually Allan Isen, O.D., to advise Wichterle on lens design issues and production issues. It Submitted February 8, 2000. Revision received March 21, 2000. Ac- was Professor Wichterle who developed the spincasting method cepted March 27, 2000. for producing lenses from the gel polymer, initially constructing a From the Department of Ophthalmology and Visual Sciences (T.T.M.), prototype machine using his son’s erector set in his kitchen.5 Rec- University of Illinois at Chicago, Chicago, Illinois; and the College of ognizing the need for serious financial backing, Pollak entered into Optometry (K.Z.), The Ohio State University, Columbus, Ohio, U.S.A. Address correspondence and reprint requests to Dr. Timothy McMahon, a licensing agreement between Wichterle, National Patent Devel- University of Illinois at Chicago, M/C 648, 1855 West Taylor Street, opment Corporation, and Bausch & Lomb, Inc. ([B&L], Roches- Chicago, IL 60612, U.S.A. ter, NY, U.S.A.), giving much of the worldwide rights to B&L for

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of 1998, according to the International Association of Contact Lens Educators (personal communication, Sweeney D. Interna- tional 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).

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.8–12 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 FIG. 1. Professor Otto Wicheterle. (Figure courtesy of Professor Jan Rocek.) cleaning and disinfection of the lenses. Myopic extended-wear was approved shortly after the aphakic lens approval in 1981, (the the polymer and the manufacturing rights. B&L was prepared to Hydrocurve and the Permalens) permitting myopic patients their bring their new lens to market in 1968 when the Food and Drug first real opportunity to see well at all times. This was and is an Administration (FDA) stepped in after many complaints from extremely powerful elixir to the myope (and the older hyperope) as small, family owned, contact lens laboratories and indicated that can be demonstrated by witnessing the explosion of refractive this new lens was a “drug” and would have to go through the surgery procedures performed today. standard drug approval process.6 B&L eventually received mar- Recognition that extended-wear of hydrogel lenses carried an keting approval from the FDA in 1971 for the Soflens. By 1973, increased risk for serious complications, in part, led to a dramatic 8–11 the Griffin lens (Softcon, American Optical, Inc., now Ciba Vision shift in the soft lens market. The prevailing clinical opinion of Care, Inc., Duluth, GA, U.S.A.) was approved for daily-wear. The the 1980s was that lens handling played a substantial role in the daily-wear soft lens was on its way to becoming the dominant risk of microbial keratitis. In part, this general opinion led to the product in the contact lens market. Within the next 10 years, ad- introduction of the disposable soft lens in 1987 by Vistakon (Jack- ditional polymers and a change in the exclusive distribution rights sonville, FL, U.S.A.). The Acuvue disposable lens was initially was subsequently converted to a nonexclusive license through liti- introduced as a 2-week extended-wear lens to be worn and then gation that opened the floodgates to competitors in the soft lens thrown away. Initial claims were that this lens would be safer business. because lens handling was reduced to a minimum and the lens was replaced before potentially harmful contaminants could adhere to Demographics the lens. Although disposing of the lens on a regular basis did little Today there are >25 hydrogel polymers on the U.S. market to reduce the risk of serious complications, it did reduce the ma- alone and scores of contact lens manufacturers with revenues in jority of “nuisance” complications and resulted in longer lasting the hundreds of millions of dollars supplying millions of U.S. contact lens comfort.13,14 Vistakon’s venture changed the face of contact lens wearers. In 1975, there were only a couple of million the soft contact lens industry, and frequent replacement soft lenses soft lens wearers. By 1990, 76% (21.8 million) of lens wearers are now the predominant lens type in the United States and Europe. wore soft lenses and 24% (1.0 million polymethylmethacrylate Silicone Elastomer contact lenses were initially introduced to [PMMA], 3.7 million rigid gas permeable [RGP]) used rigid lenses the market by Breger’s Mueller-Welt Company (Chicago, IL, for a total of 26.5 million in the United States. In 1998 in the U.S.A.) as the Silcon lens. This was sold to Dow Corning (Detroit, United States, 83% (27.6 million) of wearers used soft lenses and MI, U.S.A.) in 1972 and reformulated as a coated silicone rubber 17% (5.7 million) wore rigid lenses, totaling 33.3 million.7 World lens in relatively small diameters for aphakia (Silsoft) and myopia wide there were approximately 75 million contact lens wearers as (Silsight).15 Extended-wear FDA approval was given for aphakia

Cornea, Vol. 19, No. 5, 2000 732 T.T. MCMAHON AND K. ZADNIK in 1981 and myopia for 30 days in 1983. Although initial experi- though they were only approved for daily-wear. Then eventually ence was reportedly quite positive, silicone elastomer lenses gen- were discontinued due to problems with dimensional stability. erally were not well-tolerated by myopic patients with frequent Norman Gaylord, a polymer chemist, Leonard Seidner, an optom- complaints of poor wetting and discomfort.6,16–22 B&L acquired etrist, and his brother Joseph Seidner, an engineer, developed a gas the lens in 1985 and continues to provide the lenses in aphakic permeable polymer commonly known as “silicone/acrylate”; the powers only. This lens has become the lens of choice for pediatric proper term is polysiloxanylalkyl acrylic ester and alkyl acrylic aphakia. ester. Syntex Laboratories (AZ, U.S.A.) bought the material and Due to the high relative risk for infectious microbial keratitis, marketed the first widely used gas permeable lens known as the the frequency of extended-wear using the HEMA-based hydrogels Polycon (silafilcon A) lens in 1979. Since then, a wide variety of gradually decreased during the 1990s. The primary culprit for the rigid gas permeable polymers have been brought to market world- heightened risk of infection appears to be a cascade of events wide (Table 1). produced by hypoxia. The desire by patients to have their vision The early siloxane/acrylate lenses provided limited oxygen per- corrected at all times has not waned. In response to this desire, meability with permeabilities <30 barrers. These lenses were also expressed in the volume of patients undergoing refractive surgery, more difficult to make, resulting in marked differences in labora- contact lens manufacturers have aggressively sought new materials tory-specific quality of product. Due to the siloxane in the mate- that will reduce the hypoxia induced while wearing a lens during rials, surface wetting problems were common, and patients fre- closed-eye periods. As previously mentioned, all HEMA-based quently complained of end-of-day dryness. During the mid-1980s, materials’ oxygen permeability is constrained by either water con- the focus of the ophthalmic community was on the need for greater tent or thickness. Unfortunately, the constraints do not permit a oxygen permeability, which resulted in a new class of gas perme- lens to be made that can be tolerated or that will survive the rigors able lenses known as the “high Dk” siloxane/acrylate lenses. These of handling or wearing that delivers the oxygen levels needed in materials had permeability values ranging from 30 barrers to the the cornea under closed-eye conditions. Therefore, novel materials mid-50 barrers. The increased permeability was primarily achieved were needed that would not be limited by these boundaries. As of through the addition of higher amounts of siloxane to the polymer. this writing, two such polymers are available. These are balifilcon Although this was a successful strategy for elevating the oxygen A (PureVision; Bausch and Lomb) and lotrafilcon A (Focus Night flux through the material, it also made the lenses less wettable and, and Day; Ciba Vision Care, Inc.). Both of these polymers are hence, less well-tolerated by the wearer. referred to as silicone hydrogels, and each exceeds 90 barrers of Enter fluorine. Although fluorine had been considered very early permeability. in the development of rigid contact lenses, it was not until the early 1990s that the contact lens industry fully grasped the advantage of Rigid Gas Permeable Lenses, the Story of Siloxane this molecule. Adding fluorine to the polymer mix enhanced the The earliest known lenses were rigid. The first to describe the wetting properties of the lens and improved comfort and visual principle of the optical effect of the contact lens was Leonardo Da performance of the lenses. Fluorine also elevated the permeability Vinci in 1508 using a glass bowl of water. Rene Descartes de- of these plastics a well. These fluoro-siloxane/acrylates, com- scribed 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 TABLE 1. Rigid gas permeable contact lens materials 23 lens. Thomas Young applied the same principle in his studies of Brand name Material Dk accommodation in 1801, and Sir John Herschel clearly described Cellulose acetate butyrate (CAB) 2,6 a glass contact lens to be used on a distorted cornea in 1827. The Meso Porofocon A 12.3 early lenses used for clinical purposes were also made from cut or RX 56 Porofocon A 12.5 Low Dk siloxane/acrylate blown glass and were permitted for only extremely short wearing Polycon II Silafocon A 12.0 times and very limited uses. Fick first described corneal lenses, Paraperm O2 Pasifocon A 15.6 and attempts were made by several investigators to use these early Boston II Pasifocon A 14.6 6,23 Optacryl 60 18.0 lenses for the correction of aphakia, keratoconus, and injury. SGP-1 Telefocon A 12.0 The first plastic lenses were large scleral designs. William Fein- OP-2 Lotifocon A 15.9 High Dk siloxane/acrylate bloom marketed the first partially plastic lens in 1936 as a scleral Paraperm EW Pasifocon C 56.0 lens, with the central portion being made of glass and the periph- Boston IV Pasifocon B 28.7 eral portion being made of PMMA. Theodore Obrig, John Mullen, SGP-2 Telefocon B 43.5 SGP-3 Unifocon A 43.5 and Istvan Gyorrfy were the first to make an all plastic lens be- Fluoro-siloxane/acrylate tween 1938 and 1940.5 Obrig laboratories were established in New Menicon SFP Melafocon A 159.0 York in the 1940s to make plastic scleral lenses. It is interesting to Menicon Z Tisilfocon A 250.0 Fluoroperm 30 Paflucon C 30.0 note that, while conducting studies in the laboratory, it was here Fluoroperm 60 Paflucon B 60.0 that Obrig accidentally noted that sodium fluorescein could be Fluoroperm 92 Paflucon A 92.0 used with a black light to evaluate the tear layer behind a contact Fluoroperm 151 Paflucon D 151.0 Paragon HDS Paflucon B 58.0 lens. Kevin Tuohy, a technician in Obrig’s lab is generally ac- Boston VII Satafocon A 73.0 knowledged as the inventor of the plastic corneal contact lens. Boston ES Enflucon A 36.0 Boston EO Enflucon B 82.0 PMMA served as the primary material until the late 1970s when Equalens Itafluorocon A 64.0 gas permeable materials were introduced. In 1978, the first “gas Fluorex 300 Flusifocon C 30.0 permeable” material was approved by the FDA. Cellulose acetate Fluorex 500 Flusifocon B 50.0 Fluorex 700 Flusifocon A 70.0 butyrate lenses were used for both daily- and extended-wear, al-

Cornea, Vol. 19, No. 5, 2000 TWENTY-FIVE YEARS OF CONTACT LENSES 733 monly known as the fluoropolymers by class, had become the lens transmissivity of a lens. This term is measured and is germane to materials of choice by the mid-1990s. Oxygen permeability values the lens itself. The level of oxygen under a contact lens has been have reached 200 barrers for some materials. With each new ver- measured supporting the notion that the higher the Dk/L for oxy- sion, less siloxane is used, reducing the importance of this com- gen of a lens the higher the oxygen levels under the lens.38–40 pound in today’s lenses. However, siloxane’s place in the archives Under the closed-eye environment, the partial pressure of oxy- of contact lens history remains an important one. gen at the corneal surface is reduced from 20.9% to approximately 8%. With HEMA-based hydrogels and many rigid lenses, this low The Hybrid Materials level of initial oxygen supply results in diffusion levels that are A novel lens design merits singular mention here. Precision- below safe minimum levels to maintain normal corneal integrity. 41 Cosmet (Minneapolis, MN, U.S.A.), a small laboratory in Minne- Holden and Mertz have defined the critical transmissibility lev- sota, developed a method of producing a lens with a low oxygen els under which corneas do not swell for daily-wear as being −9 ס −9 ס permeable gas permeable center surrounded by a hydrogel skirt. Dk/Lavg 24.1 × 10 and Dk/Lavg 87×10 for overnight, The concept was ingenious—obtain rigid lens optics with soft lens closed-eye wearing conditions. These have become known as the comfort! Their first version was called Saturn. The company was “Holden–Mertz criteria.” Another way of looking at this is to eventually acquired by Pilkington-Barnes Hind (now Wessley- define the critical minimum partial pressure of oxygen at the cor- Jessen, DesPlaines, IL, U.S.A.). Two other versions came to mar- neal surface needed to avoid corneal edema. In 1970, Polse and 32 ket, Saturn II and SoftPerm. The “improved” versions were needed Mandell defined this level as being 1.5–2.5%. Over the next 15 because of significant fitting problems encountered with the years, the critical PO2 level has been revised to between 10– 42–44 lenses, which resulted in many lens fitters avoiding this product. In 13%. These newer values are consistent with the 3–4% over- the latest version, SoftPerm, the rigid center uses the Polycon night swelling normally seen without lens wear where the PO2 is material (silafocon A). Additionally, the lens tended to tighten around 8%. with time, ripped easily, and had low oxygen permeability result- Tear pumping has been determined to be a supplementary route 45–47 ing in corneal edema and neovascularization as common compli- for providing oxygen to the cornea. Investigators have found cations. The concept was brilliant, but the execution was less than that there is a 10–20% volume exchange under a rigid lens per 45 desired by a large margin. blink, whereas only a 1% per blink exchange with soft lenses. 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 THE IMPACT OF CONTACT LENS WEAR ON than by a flow model. Regardless, the exchange rate under rigid CORNEAL PHYSIOLOGY lenses, and to a greater extent soft lenses, is insufficient to meet the oxygen needs of the cornea. The earliest evidence of the relative importance of an interrup- A great deal has been learned about the mechanism of hypoxia- tion in the availability of atmospheric oxygen was noted by induced corneal edema, stimulated by the need to understand the 24,25 Fick in the late 1800s; he described a misting of the cornea origin of Fick’s “corneal misting”24,25 or Sattler’s “veil”28 or after wearing a glass scleral lens. Later, the frequency of corneal Korb’s “central circular clouding,”49,50 all describing the loss of clouding with lens wear raised concerns about the safety of contact transparency secondary to corneal edema. Oxygen is a necessary 26–31 lens wear. metabolite for aerobic respiration (carbohydrate metabolism), It is clear that all contact lenses produce a barrier to the oxygen which accounts for about 15% of the glucose substrate metabo- 32–36 available to the cornea. This barrier will decrease the partial lized. This minority share of the glucose metabolism provides the pressure of atmospheric oxygen at the corneal surface and, hence, majority of the energy needed for corneal metabolic activity due to 37 will result in a reduced flow into the cornea. It is also clear that the cornea’s high metabolic efficiency. Reduction in the available the cornea is unique in that it obtains the majority of the oxygen O2 supply results in a greater percentage of anaerobic respiration. needed for metabolic activity via uptake directly from the oxygen- Anaerobic respiration leads to a build-up of lactate, a byproduct ated tear-film and lesser amounts from perilimbal capillaries and resulting in stromal acidosis that rapidly decreases the endothelial the anterior chamber. When a contact lens is on the cornea, atmo- cell aqueous pump function. The reduction in the endothelial pump spheric oxygen is available through two primary pathways: pump- function results in a decrease in stromal hydration control and, ing of oxygenated tears around and under the lens and diffusion hence, corneal edema. However, anaerobic respiration is not solely 33 through the lens. Fatt and St. Helen have described the most responsible for contact lens-induced corneal edema. Other factors, commonly reported method for determining the diffusion of flow including alterations in epithelial permeability, carbon dioxide lev- through a contact lens material. The rate of diffusion of a gas (J) els under the contact lens, the breakdown of trapped debris under is determined by the following formula: the lens affecting tear pH, and elevated corneal temperature, also 27,51–55 .P −P)Dk/L play important roles) ס J 1 2 Short-term and long-term changes in corneal structure and func- Where D is the diffusivity and k is the solubility of a specific gas tion associated with lens wear have been identified (Table 2). An in the material, L (sometimes referred to as t) is the lens thickness, important observation is that chronic, long-term effects are quite and P1 and P2 are the gas tensions at the two lens surfaces. The different in some respects than the impact of acute hypoxia. For term Dk is known as the permeability of the material and repre- example, with chronic exposure to low level hypoxia under a sents a variable that can be calculated but not measured. The term contact lens, the epithelium and stroma thin with time instead of is devoid of material thickness and boundary effects. It is the term thicken. This presumably represents a compensatory reaction to a used by the contact lens industry to compare one lens material to long-term change in corneal metabolism. Additionally, long-term another in terms of oxygen flux. Dk/L is the transmissibility or lens wear has been associated with reduced recovery from corneal

Cornea, Vol. 19, No. 5, 2000 734 T.T. MCMAHON AND K. ZADNIK

TABLE 2. Changes in function and structure of the cornea with levels, and bacterial adherence to desquamated epithelial cells in contact lens wear 109 subjects using a variety of soft and RGP materials of varying Short-term Long-term Dk levels. They provide clear evidence of increased bacterial binding, decreased desquamation frequency, and larger cells in eyes Corneal Epithelium Reduced aerobic respiration Increased fragility wearing lower Dk/L materials compared to high Dk/L lenses. Increased anaerobic respiration Microcysts Immune mediated adverse responses are common ocular com- Elevated oxygen uptake Reduction in the oxygen uptake rate plications to lens wear. Important examples of this class of com- Elevated lactate levels Elevated lactate levels Edema Thinning plications include contact lens-associated superior limbic kerato- Reduced mitotic rate Reduced mitotic rate conjunctivitis,76 peripheral corneal ulcers,77 central sterile infil- Reduced glycogen stores Reduced glycogen stores 78 79 Reduced transcorneal potential Decrease in corneal sensitivity trates, and giant papillary conjunctivitis. Stroma Mechanical injury can be subclinical with microtrauma to cor- Edema Thinning neal epithelial cells. For example, RGP wear can have a tendency Posterior striae Vascularization Endothelium to physically injure and causes premature shedding of epithelial Endothelial blebs Decreased cell density cells. Clearly, clinically evident injury to the cornea is common in Decreased aqueous pump function Decreased aqueous pump function all types of lenses and under all wearing regimens. Osmotic injury Polymegathism Pleomorphism refers to lens-mediated environments where the tear-film becomes Endothelial bedewing 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 scatter- edema, implicating the chronic hypoxia environment with a reducing and photophobia, yielding further tearing and hypotonicity, so tion in endothelial pump function and epithelial barrier func- on and so on. Dellen formation would fall into this category, as 51,56–63 tion. well, through dehydration mechanisms.

Pathophysiologic Correlates of Contact Lens Wear Over the past 25 years, great strides have been made in under- NEW USES FOR CONTACT LENSES: THE standing the pathophysiology of the adverse events found with MANAGEMENT OF DISEASE, SURGERY contact lens wear. These events can be grouped into four major AND TRAUMA categories: hypoxia mediated events, immune events, mechanical events, and osmotic events. These categories are not mutually Over the past 25 years, contact lenses have been used to manage exclusive and more than one category can be in play for a par- corneal disease, in postoperative care, and in vision rehabilitation ticular complication. Of these groupings, hypoxia and immune after disease, surgery, and trauma by serving as a vehicle to deliver events have the greatest risks for loss of vision. drugs, as a bandage, “optically” as a new corneal surface, and as The effect of hypoxia has been cited previously to have pro- a prosthetic device. Delivery of ophthalmic drugs via soft lenses 80 found effects on the structure and function of the various layers of was considered early on after hydrogels were introduced. Poten- the cornea. It is now generally believed that hypoxia plays a dom- tial uses included lenses used as a vehicle for glaucoma medica- 81–85 inant role in the causal mechanism of infectious keratitis associ- tions and antimicrobials. The belief was that using a con- ated with contact lens wear. Epidemiologic evidence in the United trolled delivery method over time would prove to be superior to States (late 1980s) and recently from Europe demonstrates that the pulse dosing via eye drops in sustaining therapeutic drug levels relative risk of infectious keratitis increases with increased expo- and permitting lower drug concentrations, reducing complications. sure to hypoxia. Cheng et al.64 from the Netherlands have recently Several investigators determined that hydrogel lenses deliver drug confirmed prior U.S. evidence indicating that the estimated annu- via a passive diffusion mechanism, appropriately adjusted for 81,82 alized incidence of infection is 1.1 per 10,000 (95% CI, 0.6–1.7) drug–lens binding properties. The diffusion rate was also re- for RGP daily-wear, 3.5 per 10,000 (95% CI, 2.7–4.5) for daily- lated to tear pH and tear volumes and, thus, was somewhat difficult wear soft lenses, and 20.0 per 10,000 (95% CI, 10.3–35.0) for to control. The use of hydrogel lenses for drug delivery never extended-wear soft lenses. Poggio et al.10 have shown that the achieved wide usage and is rarely employed today. Porcine colla- duration of the hypoxia also is related to risk of infection. Hypoxia gen also was investigated and briefly used in the 1980s for wound appears to affect the increase in risk through a number of channels. healing and drug delivery. These devices intentionally broke down These include reduction in mitotic rate resulting in older and, when exposed to tear enzymes, thus dissolving within a few days. consequently, larger cells being present at the corneal surface, Due to cost, handling difficulties, and comparable performance to alterations in epithelial permeability, increased epithelial fragility, hydrogels, these devices were popular for only a few years. and increased microbial adherence to corneal epithelial cells after exposure to hypoxia.61,65–71 The weakened and damaged cells Bandage Lenses provided a locus for infection. Increased cell adhesion by cytotoxic Using lenses for “bandage” or therapeutic purposes has gained strains of bacteria provides for direct cellular invasion by these wider appeal over the past 2 decades. Therapeutic uses include strains. barrier function and an adjunct to surface healing,80,86–95 tampon- Interestingly, new high oxygen flux lenses both (soft and rigid) ade,96,97 and pain management.75,98–100 There is even the odd use appear to reduce bacterial adhesion in eyes wearing high Dk lenses of hydrogel lenses by otolaryngology for the healing of tympanic compared to lower Dk materials.71–74 Ren et al.75 reported on a membranes.101 Hydrogel lenses, being supple and conforming, 3-year randomized clinical trial evaluating corneal cell desquama- make nearly ideal bandages. Thin, minimally movable lens designs tion rate, surface epithelial cell size, tear lactate dehydrogenase have been developed to help protect the injured cornea from ex-

Cornea, Vol. 19, No. 5, 2000 TWENTY-FIVE YEARS OF CONTACT LENSES 735 ternal forces, such as the wiping action of the eyelids. This barrier provements from 20/200 to 20/40 in such cases after contact lens permits the sliding action at the leading edge of the adjacent epi- application. thelium, a critical part of the healing process to progress unim- peded. This barrier function can also be employed to protect the Keratoconus and the Other healthy cornea from rough and scarred eyelids found in cicatricial Noninflammatory Disorders disease. A last role is in conjunction with corneal gluing of per- The role for contact lenses in keratoconus and pellucid marginal 102,103 forations. Here the lens serves to reduce lid irritation caused degeneration is an ancient one. Some of the earliest uses for con- by the rough glue surface and to aid in retaining the glue at the tact lenses included patients with keratoconus.5,6,23 The primary wound site. lens type used throughout the world today for keratoconus is the Tamponade is a relatively uncommon role for contact lenses. rigid gas permeable corneal lens. Numerous other approaches to The three principal areas involve stopping leaky cataract wounds, the optical management of these disorders have been tried. These stopping leaky filtering blebs, and plugging small corneal leaks include scleral lenses, hybrid lenses (Softperm), and specially de- associated with corneal melts or lacerations.96,97,104–106 signed soft lenses.117–120 Additionally, combining a soft lens with Pain management involves reducing the stimulation of corneal a rigid lens in a piggy-back fashion has also seen success in some nerve endings found with loosely adherent epithelium and during patients who are intolerant to RGPs or who demonstrate a history healing. Bandage contact lenses have proven to be a great asset in of recurrent erosions.121,122 controlling discomfort associated with bullous keratopathy.75,100 Within the corneal lens domain, significant controversy exists in Frequently, placing a high water content lens on the affected eye the ophthalmic community regarding the best and safest manner can completely eliminate discomfort for days at a time. Overnight for managing keratoconus. By lumping the myriad of lens-fitting wear for this purpose is the rule, with durations upward of a month. strategies into three philosophical groups, one finds opposing Postoperative pain management after phototherapeutic keratec- views on how best to care for patients with this disorder. These tomy relies heavily on the placement of a hydrogel lens for the groupings are large and flat with the purpose of splinting the initial 2–3-day period of epithelial healing.87,98,99,107 Before using cornea to establish more normal shape and to retard disease pro- these devices, it was common to need scheduled narcotics to con- gression,123,124 divided support with apical contact with no inten- 125,126 trol the pain. In fact at one point early in the trials for myopic tion to alter the topography of the cornea, and apical clear- phototherapeutic keratectomy in the United States, there was se- ance fitting to avoid trauma to the thinned apical area to reduce the 127,128 rious concern that the FDA would not approve such a painful likelihood of scar formation. Embroiled within this contro- procedure to treat refractive error. Therefore, in a strange twist of versy is the yet unknown cause of keratoconus. Some authorities fate, contact lenses made it possible for laser refractive surgery believe that contact lenses and/or eye rubbing can produce kera- procedures to go forward and receive FDA approval for marketing toconus, and some investigators think contact lens wear, particu- in the United States. larly the fitting philosophy, can alter the course of the disease 129–136 A change in the standard of care for the management of corneal progression—for better or for worse. abrasions occurred in the 1990s. Reports surfaced of microbial keratitis after patching for corneal abrasions in contact lens wear- Penetrating and Lamellar Keratoplasty ers.108 Recommendations not to patch abrasions during the first 24 Contact lenses play an important role in the postkeratoplasty hours after a contact lens-related abrasion to avoid incubating an armamentarium of vision correction options. Although visual out- occult microbial infection of the cornea quickly followed.109,110 comes have improved remarkably since the introduction of pen- Subsequent to these reports, several studies recommended aban- etrating keratoplasty in 1952, one-third to one-half of all cases doning pressure patching with evidence supporting no improve- achieve their maximum visual acuity with a contact lens, compared ment in comfort and an absence of increased healing rates.111–113 to spectacles or no correction. The indications of contact lenses On the other hand and related to their use in the postoperative pain after keratoplasty have included anisometropia, high regular astig- management regimen, hydrogel bandage lenses—along with topi- matism, irregular astigmatism, concurrent aphakia, and contact cal nonsteroidal antiinflammatory agents and topical antibiotics— lens wear in the fellow eye. In the majority of cases, rigid corneal have been recommended in the general management of corneal lenses have been employed, although daily-wear and extended- 137–142 abrasions.114–116 The advantages to this approach are reduced dis- wear hydrogel lenses have been used. comfort, increased healing rates, maintenance of binocular vision, Rigid lens designs used for eyes with corneal transplants include and direct visualization of the wound during healing. high Dk materials, spherical base curve designs, aspheric designs, One of the most powerful and satisfying uses for contact lenses and bitoric lenses. Lenses are almost always equal to or larger than is their application in visual rehabilitation. In the presence of very the size of the graft. Lenses fitted entirely within the graft tend to high refractive errors and corneal irregularities, rigid contact lenses be too unstable and are prone to frequent dislodgment. can have a dramatic impact on visual acuity, even in the presence Complications include corneal abrasions, suture lysis, corneal of significant scarring. The application for lenses in vision reha- neovascularization, suture abscesses, and infectious keratitis. To bilitation include keratoconus and the other noninflammatory thin- date, no relationship has been found between contact lens wear and ning disorders (except keratoglobus), postpenetrating and lamellar corneal allograft rejection. corneal grafts, corneal lacerations, aphakia, postrefractive surgery, as well as inflammatory and infectious corneal scarring. Pathologic Aphakia myopia and nanophthalmus are greatly helped by contact lens use. Before the introduction and popular use of intraocular lenses, In the +30 diopters (D) hyperope or −25 D myope, spectacles will contact lenses were a popular choice for correcting aphakia. Ini- rarely provide acceptable visual acuity. It is common to see im- tially, PMMA was used; but later, hydrogels were enthusiastically

Cornea, Vol. 19, No. 5, 2000 736 T.T. MCMAHON AND K. ZADNIK prescribed for this group of patients. Extended-wear was also first COMMERCIAL MARKETING STRATEGIES: thought of for the aphakic patient who had difficulty with insertion DECISIONS THAT HAVE CHANGED THE FACE 143–147 and removal of the lenses. OF THE OPHTHALMIC MARKET PLACE

Although it is uncommon to review marketing issues in a pres- Trauma tigious peer-reviewed journal, we would be seriously remiss if Major eye trauma frequently results in significant corneal scar- several landmark decisions and strategies from the 1980s were not ring, pupil dyscoria, aphakia, and lid abnormalities. Several inves- discussed here. There are three events that will go down in history tigators have shown that contact lenses offer a valuable means for as substantially affecting the way eye care is delivered today. correcting residual vision after ocular trauma.148–150 McMahon et These are the optical chain story, the Johnson and Johnson deci- al.149 have sounded a note of caution, however. In their large urban sion, and the birth of the mail order business. center series of more than 100 major injuries, almost 50% of cases Before the development of the soft lens, eye care provided by ceased wearing lenses after 12 months even if the lenses were optometrists and ophthalmologists in the United States was almost comfortable and vision was greatly improved. Additionally, al- exclusively conducted in a private office setting. Spectacles were though more than two-thirds of cases were corneal or cornea- made available to patients through small family owned optical scleral lacerations, the primary reason for lens use was for the shops (most commonly used by ophthalmologists) or directly from correction of concurrent aphakia. the office (route preferred by most optometrists). In the 1970s, there were about twice as many optometrists as ophthalmologists. Postrefractive Surgery Half of the U.S. patient population was seen by ophthalmologists Only a few refractive surgery patients require postoperative op- and the remaining were seen by optometrists. Optical shops began tical correction with a contact lens. The primary reasons for con- hiring optometrists and, less commonly, ophthalmologists began to tact lens use in these cases include undercorrection, overcorrec- attract patients at shopping malls in the early 1970s. After the tion, anisometropia, irregular and high astigmatism, as well as introduction of the soft lens, the popularity, success, and numbers glare and halos at night.151–156 Historically, most of these patients of these shops increased dramatically. Many of these shops were have been difficult to fit due to the irregular corneal curvature and purchased and banded together to form optical chains. The chains oblate shape of the cornea. Additionally, many of the cases had offered local convenience and frequently lower prices for services sought refractive surgery because of previous contact lens failure. and introduced the world of mass marketing and advertising of Regardless of these barriers to success, lens wear can commonly eyeglasses to the American public. Today, nearly half of all provide a tolerable means of vision correction. 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 Infectious and Inflammatory Scarring years ago. In general, corneal scarring limits uncorrected and spectacle In 1981, Frontier Contact Lenses, a small Jacksonville, Florida, corrected visual acuity primarily through associated irregular soft lens manufacturer (later renamed Vistakon), was acquired by astigmatism rather than because of opacification of portions of the the healthcare product giant Johnson and Johnson, Inc. Johnson cornea. Therefore, contact lenses, primarily rigid lenses, can fre- and Johnson bought the rights to a stabilized soft molding process quently provide excellent vision after serious corneal infection or from a Danish firm in 1984. This technology permitted Vistakon to episodes of inflammatory disease with residual scarring.150 The produce vast numbers of soft lenses inexpensively and reproduc- authors’ experience suggest that careful attention should be placed ibly. The initial goal was to provide a safer extended-wear lens, on reducing the bearing on the scar by the lens where possible. one that would only be handled once and then discarded after a Chronic rubbing by the lens leads to reduced tolerance, increased period of use. At the time, hygiene and lens handling were thought risk of corneal vascularization, and in some cases, an increase in to be a source of the higher incidence of infections found with the whiteness of the opacity. extended-wear lenses, justifying this approach. Although their strategy actually failed, in that disposable lenses are not safer for Prosthetic Lenses extended-wear than are conventional extended-wear lenses (for Before approximately 1980, the disfigured eye was prescribed a serious complications), Vistakon succeeded in changing the soft painted scleral shell fitted and finished by an ocularist, to improve lens industry by providing a product that appealed greatly to pa- cosmesis. In the early 1980s, several labs around the world began tients and that reduced the frequency of lens spoilage-related com- tinting, dying, and using photographic inlays to produce contact plications. Additionally, Johnson and Johnson’s Vistakon is gen- lenses that could restore some or all of the natural appearance to erally regarded as the first contact lens manufacturer to make a the eye. There are at least eight firms within the United States that multimillion dollar commitment to direct advertising of their pre- will produce such lenses. They are most successful with darkly scription product to consumers. The idea was to drive patients into pigmented eyes because brown eyes tend to lack visibly significant doctors’ offices requesting their product. This strategy worked. iris detail, and the anterior angle shadow (seen as a dark ring at the Vistakon holds the majority of the disposable/frequent replace- periphery) is much less apparent and, thus, is easier to match the ment lens market share in the United States and is a major dis- normal eye.157,158 Today, for disfigured eyes where there is a tributor worldwide. Today, pharmaceutical companies advertise formed eye where the surface is not unduly rough and irregular and prescription drugs frequently in print, via radio, and in television in the absence of severe enophthalmus, hydrogel prosthetic and markets throughout the country directly to patients. It started with (less commonly) rigid corneal prosthetic lenses are the choice for disposable contact lenses. restoring a more normal appearance. The third major event pertains to the introduction of mail order

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