A review of conventional, scleral and soft lenses
Contact Lens Update
Disregarding pioneering efforts that were more publicized than practical, the 1929 contact lens of Dallos really marked the beginning of the practical use of contact lenses. So contacts and the solutions used with them have been with us for nearly half a century. In 1943, Bier eliminated the need for fluid-filled lenses by drilling a hole to increase tearflow under the lens, while Touhy accomplished the same results five years later by reducing the lens size. Neill, Sohnges, Dickinson and others pursued this approach so that, until very recently, most contact lenses were modifications of those developed in the mid-1950's. All were made of a plastic called polymethyl methacrylate (PMMA) and cleaned, stored and wetted in much the same way . Almost 15 years ago, Wichterle 1 introduced hydroxyethyl methacrylate (HEMA) to the contact lens field. Hydrophilic, wearable for extended periods of time and extremely comfortable, the new soft lens was readily accepted in Europe despite its poor optical properties. With many of the technical problems now solved, this flexible, cross-linked polymer lens is becoming the method of choice for most American doctors and patients. Its future seems assured but present limitations allow ample room for coexistence of hard and soft lens materials. 2,3 To understand the problems involved in fitting a contact lens to a human cornea one must recognize the unusual condition which exists. The cornea is avascular. It is transparent and stays that way by virtue of a delicate water balance and a "metabolic pump" which requires atmospheric oxygen. This breaks down lactic acid into H20 and CO 2 which are discharged from the surface. 4,5.6 When a contact lens interferes with the process, resultant insult produces edema, loss of vision, discomfort, and ultimately, loss of epithelial tissue-a painful condition commonly called "overwear abrasion. "7,8 Under the tear layer, a cornea is covered with a thin multi-purpose precorneal film. Composed of mucopolysaccharide, water and oil layers, it prevents the cornea from drying and assures its integrity by maintaining a continuous layer of tears. 9,10 The deeper mucoid layer also is thought to aid in the utilization of oxygen and discharge of CO 2. The cornea is covered by this absorptive hydrophilic material, spread by the lid action, with a critical surface tension surpassing that of tears so that a continuous film will immediately form after every blink. The use of isotonic solutions of
water-soluble polymers has confirmed the feasibility of coating the contact lens or cornea to produce an effect similar to that provided by the hydrated conjunctival mucus. 11 . 12 The quality and quantity of the tears play an important role in contact lens wear.13 Inadequate secretion is given careful consideration (using the Schirmer tear test as standardized by Halberg and Behrens).14 However, when excessive and hypotonic tearing results from reflex stimulation by the lens, the relatively hypertonic fluid in the corneal tissue frequently produces edema when water is imbibed from the tears.
Vol. NS 15, No. 10, October 1975
Conventional Hard Lenses The most common regimen of hard lens care includes use of three solutions-wetting, soaking and cleansing-separately or in combination. Their use has long been established. 15 - 17 Wetting solutions reduce the interface tension between the lens and the tears, usually through the action of polyvinyl alcohol (PVA). The PVA alone, or in combination with other ingredients, also serves as a lubricant. These solutions generally contain benzalkonium chloride or thimerosal as preservatives and disodium edetate (EDTA) to enhance the activity of benzalkonium chloride against pseudomonas aeruginosa, and to prevent the development of resistant strains of the organism. Mercurial preservatives may be used alone or in combination with other agents. 18 ,19 A PMMA (hard) lens will absorb H20 in amounts from 1.5 percent to 3 percent of its weight. Changes in fitting characteristics resulting from this absorption can be avoided through the use of soaking solutions. 2o ,2 1 These are antiseptic and designed to resterilize themselves within four to eight hours after contamination from handling and wearing the lenses. This overnight storage reduces the chance of ocular infection and aids in the hydration and comfortable wear of lenses the next day. It should be pointed out that the surface must
Robert A. Koetting
By Robert A. Koetting
be cleaned before storage as remaining debris and microorganisms on the lens may exceed the disinfective capacity of the formulation. Hard lens cleaning solutions contain surfactants that are formulated in an alkaline pH to aid in dissolving denatured protein. They should be used prior to storing in a soaking solution to prevent inactivation of the soaking solution's preservative by proteinaceous deposits on the lenses. 22 - 24 At the present time a number of combination solutions have appeared on the market. These are designed to provide all three functions but are generally not as effective as the best single function solution. For example, the viscosity building and lubricating materials added to wetting agents tend to become quite thick and gummy in a storage case. They may even form hard crystals on the lip of the container and could be introduced into the eye to cause injury or discomfort. The contact lens wearer's desire to use the simple "one solution" method seems to result from the same human weakness which tempts him to try the ubiquitous home remedies that have ruined so many lenses and caused untold discomfort. Toothpaste does not make a good contact lens polish. In fact, some of the toothpaste ingredients tend to coat the lens and make it quite uncomfortable. The low pH of lemon juice makes it most undesirable as a proteinaceous deposit remover, yet many persons proclaim its value as a contact lens cleaner. Certain cigarette lighter fluids will dissolve greasy deposits from a lens surface but many contain solvents which will actually damage the plastic. It is difficult to explain why a patient would rather clean contacts with shampoo instead of the properly formulated materials which are readily available, but these amateur procedures constitute a continuing problem. Moreover, some commercially marketed solutions are not even compatible. A storage solution which contains boric acid, for instance, will form a precipitate when used with another manufactur-
Robert A. Koetting, 00, has an optometric practice limited to contact lenses in southwest St. Louis, Missouri. A continuing education lecturer on contact lens fitting, Dr. Koetting has done clinical investigation of several flexible lens materials. He received his doctor of optometry degree in 1947 from Southern College of Optometry in Memphis, Tennessee . He is past president and executive director of the philanthropic Optometric Center of St. Louis, an officer of a number of contact lens specialty groups, and has served on several American Optometric Association committees.
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er's wetting solution containing PVA, and the same can be said for a variety of artifical tears and irrigating solutions. A word should also be added concerning the many "accessory solutions" (such as Comfort Drops by Barnes-Hind, Blink-NClean by Allergan or Adapettes by Burton, Parsons & Co.) which have been introduced in recent years. Some contain polymers designed to supplement the mucoid covering of the corneal surface, others are solutions of non-ionic surfactants with varying amounts of viscosity-building agents added, while others are sold for the explicit purpose of cleaning and rewetting lenses on the eye. The specific action of these solutions is frequently misunderstood by patient, practitioner and pharmacist. Scleral Lenses Historically important, but of little current significance, the scleral lens is still used in certain specialized applications. Covering almost all of the exposed scleral conjunctiva, present day scleral lenses are designed to facilitate maximum tear circulation and do not require substantially different attention than smaller corneal lenses made of the same PMMA material. 25-27 Those few applications which do call for scleral lens use warrant serious consideration-prescriptions involving the use of a prism, highly astigmatic corneas, infants, and most common today, cosmetic lenses fitting in cases of aniridia (congenital absence of pupil), injury or serious eye disfigurement. 28,29 They are usually placed on the eye following preparation with conventional contact lens solutions. Naturally, cosmetic scleral lenses (or "shells" as they are called if no lens prescription is involved) require a regimen of care which is quite different in each individual case. A shell used following evisceration or loss of a cornea will probably be worn 24 hours a day, and aside from periodic cleaning, require the use of a prosthetic lubricant. 3o Soft Lenses Soft lenses were first described by Wichterle and Lim 1 in 1962. The present state of the art is marked by very rapid change. 31 ,32 Many similar lenses are under development in various parts of the world, distinguished only by minor differences in the cross-linked polymers, water content and fitting rationale. The material, a hydrophilic hydroxyethyl methacrylate (HEMA), usually absorbs water from about 40 percent to 60 percsnt of its own weight. Very stable lenses that are only about 12 per-
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cent H20 are being tried in Japan, while one British manufacturer uses a lens which is 80 percent H20 and designed to be worn continuously.33,34 (Photo 1, at right) Since the soft lens material is quite unmanageable in its hydrated state, changes involving fit or refractive considerations can be accomplished only by using another lens. They are somewhat fragile and tend to become coated, so the need for multiple replacements is immediately obvious. Mass-produced molded lenses sold with ten or a dozen in a package might seem quite practical, and indeed, the original developers foresaw this manner of marketing. Perhaps for the public good, however, the material is not easily molded. As it changes from liquid to a semi-rigid state in the process of polymerization, the volume decreases so that lenses cannot be accurately shaped. New methods are under development at the present time but the molding system is not yet a consideration. 35 Instead, most lenses produced in this country are spin cast-a technique which involves pouring polymerizing liquid into a rotating concave form. Optical properties are produced by centrifugal force. The greater the speed of rotation, the thinner the lens at its center. Spin casting requires exacting control but the problems are multiplied many times in the alternate manufacturing method. A lathe-cut lens is made from a button of dehydrated HEMA. It is fabricated following the same procedure used in manufacturing conventional hard lenses and hydrated by soaking in saline solution after the work is complete . Unfortunately, even the most minute changes in temperature, humidity, age or cross-linking of the polymer will produce significantly different results. The dehydrated material is brittle, and once hydrated, the parameters of the lens are never the same as they were before hydration. Nevertheless, lenses produced in this way pose optical superiority as a rule and can be fabricated to a wide range of para meters.36 Immediately after introduction of the soft lens, particularly in the United States, much emphasis was placed upon the control of pathogens. It was generally assumed that bacteria or fungi would penetrate the lens and grow in the intermolecular spaces. Researchers later determined that the pore size precluded this,37,38 while other studies showed that lenses developed cracks and fissures which could and did harbor certain microorganisms including pseudomonas
Photo 1-Soft Lens Placed on the Eye. Hydrophilic, wearable for extended periods of time, and extremely comfortable, the new soft lens is rapidly replaCing other types of contacts. aeruginosa. 39 ,40 Clinical experience seems to indicate that the growth of bacteria " on or in" is an academic consideration and that the soft lens in situ is not a case of infection. 41 The pathogen control mechanisms of the eye fluids are apparently as effective for soft lens wearers as they are for persons who wear no contacts at all. Just the same, a sterilization method for soft lenses remains a major consideration for FDA approval and only one method is currently acceptable. 42 ,43 At this writing, about 15 soft contact lenses are in various stages of investigation awaiting approval for use in the U.S. Only three have been accepted-the Soflens by Bausch & Lomb, Hydrocurve by Soft Lens, Inc. (both used for ophthalmic purposes) and the Softcon by WarnerLambert, restricted to therapeutic use. The "package" requires that all types be boiled when the lens has been removed from the eye. Although many methods of sterilization are used in Canada and throughout the world, nothing else is legally available to the U.S. soft lens wearer. Other soft lens care regimens are worthy of note, however. The simplest method of sterilization involves overnight storage in solutions containing chlorhexadene glucanate and thimerosal or iodophores, following daily prophylactic care with special cleaning products. These solutions provide the same convenience as conventional hard lens soaking and even employ the same type of case. The peroxide method is frequently used in Canada. Soaking a lens for ten minutes
Journal of the American Pharmaceutical Association
Robert A. Koetting
in three percent hydrogen peroxide renders it completely sterile and dislodges most foreign material from the surface. Unfortunately, the lens must be thoroughly rinsed since there is serious danger that residual peroxide may irritate the cornea. This involves extra steps and diligent patient control.44 Generally speaking, the soft lens disinfecting solutions currently in use have an acceptable, though not ideal, microbial kill rate or capacity. They are slower than an efficient single-function hard lens soaking solution and equal to, or somewhat slower in, resterilizing than the mUltipurpose hard lens solutions against two pseudomonas species. The soft lens solutions also are slower when challenged with common ocular bacterial contaminants and pathogens, including Candida a Ibicans, Escherichia coli, Proteus mirabilis and Staphylococcus aureus. 45 Some practitioners use standard autoclaving methods in the office. This renders trial contact lenses free of bacterial contaminants for use on other patients and sterile so that they can be stored for long periods of time without further attention. Aside from the obvious expense involved, this method probably could not be employed by patients at home on a daily basis because there are many unofficial reports that soft lenses deteriorate under exposure to such repeated high temperatures. Routine use of the small electric aseptor unit provided by Bausch & Lomb is an effective method of pathogen control and most patients are quite satisfied with it. Prevention of excessive contamination while the lens is off the eye is its major purpose. 46 (Photo 2, above right) Some practitioners have begun advising travelers to store lenses in a refrigerator at night if the boiling unit is not available for a day or two. Cool temperatures simply reduce the rate of microbial multiplication but represent a serious deviation from the FDA-approved regimen. Nevertheless, serious problems resulting from this revision of protocol have not been reported, and in view of the surface deposits compounded by heat, it may indeed be very practical advice . Soft lenses must be stored in an isotonic sodium chloride solution. According to the instructions in the approved Bausch & Lomb Kit it is prepared by adding one .250 g NaCI tablet to one ounce of distilled water. 47 A preserved isotonic solution also is available but approved for only one lens at this time. Normal saline solution can be prepared
Vol. NS 15, No. 10, October 1975
in many other ways. The danger is that patients will prepare large amounts of solution and be reluctant to discard the surplus, using it long after pathogen growth may have reached a significant level. Preparing the solution daily reduces this risk of extended storage. In an emergency situation, patients may be advised to add a one-gram USP salt tablet to four ounces of distilled water and discard the remainder after use . Salt tablets for the preparation of saline used with soft lenses must not contain additives. Adhesives, coating or any other ingredient may damage the patient's eye or lenses. (Although iodine was considered an unacceptable impurity at one time, limited research indicates that it is apparently harmless in concentrations commonly found in table salt.) The same must be said of prepared saline solutions. Injectable saline, ophthalmic irrigating solutions and the like contain preservatives. Benzalkonium chloride is the most serious contributor to severe problems because it is found in so many eye preparations and contact lens solutions. It binds to the lens polymer in a concentration which is many times the acceptable level. Wearers have experienced painful, though reversible, injury following ill-advised use of conventional hard lens soaking solutions with soft lenses .. 48 - 5o Last year the FDA approved the Hydrocurve lens manufactured by Soft Lens Incorporated of San Diego. The material is supplied by Automated Optics of New York and that firm plans to license other companies to produce the lens under a variety of names. None have reached the market at this writing. Prepared saline with .001 percent thimerosal added as a preservative is approved as a storage solution with these lenses. It is curious that one isotonic sodium chloride solution is suitable for use with a particular lens and another isotonic sodium chloride solution is legally restricted to use with a different lens. That is the current situation, however, and the "Boil-n-Soak" solution is sold " for use with Hydrocurve contact lenses." Soft lens clinicians agree that the foremost problem currently involves proteinaceous and mineral deposits which coat lens surfaces. Observable after periods varying from a few days to several years, this coating impairs vision and often produces mild infection or discomfort. The irregular surface of the foreign substance promotes the adherence of additional deposits and the protein is further solidified by
Photo 2- The Bausch & Lomb Aseptor Unit. Soft lenses in sealed vials are placed in the large office aseptor for routine bOiling. Patients perform pathogen control on a smaller scale by daily use of an individual-timed electrical heating unit which boils lenses in the case. the daily boiling process. Meibomian oils and foreign materials, including makeup, add the build up . Two cleaners for daily prophylactic lens care also have been approved for use with the Hydrocurve lens and are being tested with others at this writing. They are Soft Mate by Barnes Hind and Pliagel by Flow Pharmaceuticals . Lenses which are carefully cleaned upon removal will remain clear for extended periods of time , but the only method available to the Bausch & Lomb patient is the abrasive action of his own thumb and forefinger on the lens surface. Used with hot water or saline before the aseptor cycling, even such mechanical rubbing can be quite helpful because the half dozen soft lens cleaners which are commercially available in Canada and Europe have not been approved for use here. 50- 53 Lens coating also is prevented or controlled by buffering the saline solution used for storage. Proteinaceous deposits are less likely to form in alkaline media. A pH of 7.4 to 7 .8 is quite acceptable to corneal tissue and it is speculated that the addition of a small amount of sodium bicarbonate could eliminate many problems. Although such preventive measures are anticipated, the Bausch & Lomb Kit instructions have not been modified to date. Improper Handling Of the three soft lenses which have been approved for general use in the U.S., Warner-lambert's Softcon is prescribed only as a bandage and may be removed only by the physician . Consequently, there (Continued on page 587)
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Dickson/Rodowskas
4.
5.
6.
7.
sumer Attitudes Toward Prescription Prices by Selected Consumer Characteristics," unpublished masters thesis, Oregon State University (Aug. 1968) Task Force on the Roles of Practitioner and the Subprofessional in Pharmacy. "Report on the Task Force on the Roles of the Practitioner and the Subprofessional in Pharmacy," JAPhA, NS9 (8), 415 (Aug. 1969) Barker, K.N., and Smith, M.C., " Deficiencies of the Task Force Criteria for Identifying Subprofessional Tasks, " Am. J. of Hosp. Pharm., 29 (9), 734 (Sept. 1969) Ryan , M.R , " An Analysis of the Work of Fifty Community Pharmacists in Northern Mississippi. " unpublished PhD dissertation, University of Mississippi (May 1973) Task Force on the Pharmacist's Clinical Role, " Report of
Robert Koetting (Continued from page 577) is little need for patient instruction because all of the handling should be accomplished by his physician. These people are ordinarily under reasonably close medical supervision and serious problems are rare, In the case of the Bausch & Lomb Soflens, however, minor problems have resulted from misinterpretation of the instructions. The printed package insert contains a good deal of extraneous information and patients are often confused.53 These mistakes seem to be the most often repeated1, Excessive or incorrect use of cosmetics frequently causes severe abrasion when the materials become lodged in or under a lens.54 2, Soft lenses stored in conventional hard lens solution containing benzalkonium chloride produce serious corneal irritation, 3. Lenses stored in tap water instead of saline solution result in stinging and corneal edema upon application. There is also serious possibility of microbial contamination, 4, Disregarding regular use of the aseptor allows the development of fungus colonies on the lens surface, 5. Use of injectable saline (containing preservatives) for storage produces discomfort and occasionally serious corneal insult. 6, Use of salt· tablets which are the wrong size or those containing additives to improve the flavor or act as an adhesive may ruin the lens and are usually a source of irritation when the lens is worn, The foregoing certainly leads to a practical conclusion of this review, Closer cooperation between the pharmacist and the optometrist can prevent many such problems. Both professions have a serious obligation to the public welfare and all parties will benefit from a free and frequent exchange of scientific information. The FDA position that new lens materials are drugs and the resultant awareness of a mutual interest should accelerate a diVol. NS 15, No. 10, October 1975
the Task Force on the Pharmacist's Clinical Role," JAPhA, NS11 (9), 482 (Sept. 1971) 8. Graber, J.B., and Brodie, D.C. (eds.), Proceedings of an Invitational Conference on Pharmacy Manpower, National Center for Services Research and Development. Rockville, Md. (Jan . 1971) 9 . Work sampling is one of several job analysis techniques available. For a description of work sampling see Barnes, R.M., Work Sampling, 2nd ed., John Wiley & Sons, New York (1957); or see Heiland, R.E. , and Richardson , W.J., Work Sampling, McGraw-Hili, New York (1957) 10. Barker, K.N. , " An Analysis of the Work and Utilization of the Pharmacist in Small Mississippi Hospitals to Estimate Some Effects of the Introduction of Pharmacy Auxiliary
alogue long overdue . After all, contact lenses and the solutions used with them have been with us for nearly half a century,
•
References 1. Wichterle, 0 ., and Lim, D., " Hydrophilic Gel Lens for Biological Use, " Nature, 185 117- 118 (1960) 2. Mandell, R , Korb, D.R , Sarver, M., and Poster, M. , " The State of the Art," J. Am. Optom. Assn., 44 (3), 229- 236 (March 1973) 3. Feldman , GR, et al., "The Soft Lens Situation: Using Today's Materials," Contacto, 17 (3),7 - 30 (June 1973) 4. Fatt, I., "Oxygen Supply to the Contact Lens Through Hydrogel Contact Lens, " The Contact Lens, 14 (1), 3-5 (Oct. 1972) 5. Hill, RM., and Fatt, I., " How Dependent is the Cornea on the Atmosphere?," Am. J. Optom., 35 (10),873- 876 (Oct. 1964) 6. Ullen , R., "Transparency, Edema, and Contact Lenses, Part I, 11 (8), 1- 4 (Oct. 1971); Part II, 11 (9), 1,2 (Nov. 1971); Part 111,11 (10), 1- 4 (Dec. 1971) 7. Kennedy, J.R. , "Corneal Abrasion Considerations," Contacto, 16 (2),69 - 72 (June 1972) 8 . Korb, D.R. , " Edematous Corneal Formations, " J. Am. Optom. Assn., 44 (3), 246 - 253 (March 1973) 9 . Lemp, M.A ., Holly, F.J., Iwata , S. , and Dohlman, C.H., " The Precorneal Tear Film," Archives of Ophthal., 83 (1), 89- 94 , (1970) 10. Rankin, B.F., and Trager, S.F., " Wetting of Contact Lenses," J. Optom. & Archives of Am. A cad. Optom., 47 (9), 698 - 702 (Sept. 1970) 11 . Koetting , R. A., "The Effect of Polyvinyl pyrollidone with Hydroxyethylcellulose on Three and Nine O'Clock Staining," Contacto, 15 (2) (June 1971) 12. Lemp, M., and Holly, F.J. , " Ophthalmic Polymers and Ocular Wetting Agents, " Annals of Ophthal., 15- 20 (Jan . 1972) 13. Hill , J.F., "Tear Analysis for Successful Contact Lens Wear," Optom. Weekly, 64 (39),943- 946 (Sept. 27,1973) 14. Halberg, G.P. and Behrens, C., " Standardized Schirmer Tear Test," Am. J. Ophthal., 51 (5), 840- 842 (May 1961) 15. Dabezies, D .H., "Contact Lenses and Their Solutions: A Review of Basic Principles," Eye, Ear, Nose & Throat Monthly, Parts I, II, & III (Jan ., Feb., March 1966) 16. Weston, J.H. , "The Preparation of Bacteria Free Solutions for Contact Lenses," Optical World, 1 (4), 23- 24 (Sept ., Oct. 1972) 17. Koetting, R.A., " The Solution May Be the Problem," Optom. Mgmt. 7 (8), 9- 13 (Aug. 1971) 18. Cureton, G.L., "New Perspectives on Solutions for Hard & Soft Contact Lenses," Mftg. Optics Inti., 71 (10), 503 510 (Oct. 1973) 19. Charles, A.M., "A Test System for Evaluating the Bactericidal Capabilities of Hard Lens Solutions," J. Contact Lens SOCiety of Am., 6 (3), 40- 46 (Oct. 72) 20. Koetting, R.A., "Minimizing Problems Resulting from Changes in Contact Lens Radius, " The Optom. Weekly (Oct. 24, 1963) 21 . Koetting, R.A. , "The Interpretation of Contact Lens Base Curve Changes, " Optom. Weekly, 57 (52) (Dec. 29, 1966) 22. Baldone, J.A ., "Contact Lens Cleaning Updated," Contact Lens Medical Bulletin, 4 (2), 9- 12 (April, June 1971) 23. Elstrom, G.P., "Contact Lens Cleaner," J. Am. Optom. Assn., 45 (4),450 (April 1973) 24. Young, W., and Hill, R.M., "Cholesterol Levels of Human Tears," J. Am. Optom. Assn., 45 (4), 424 - 428 (April 1943) 25. Elliott, D.O., "Venting and Fenestration," J. Am. Optom. Assn., 42 (3),255 (March 1971) 26 . Fletcher, R.J., ed., "A Personal Technique of Haptic Lens
Workers," unpublished PhD dissertation, University of Mississippi (May 1971) 11 . Rodowskas, C.A., and Gagnon, J.P., " Personnel Activities in Prescription Departments of Community Pharmacies," JAPHA, NS 12 (8), 407 (Aug. 1972) 12. Morsh, J.E., Madden, J.M., and Christal, HE, Job Analysis in the United States Air Force, National Technical Information Service, Springfield, Va., 3 (1961) 13. Ibid. 14. Siegel, S., Nonparametric Statistics for the Behavioral Sciences, McGraw-Hili, New York, 184 (1956) 15. Task Force on the Roles of the Practitioner and the Subprofessional in Pharmacy, op. cit. 16. Blacklock , H.M., Social Statistics, McGraw-Hili, New York, 169 (1960) Fitting, " Part 9, The Contact Lens, 2 (7), 22- 30 (April 1970) 27 . Redford, CA, " Who Wants to Bother With Haptic Lenses? " Radharc, 16 (2),35 - 38 (March - April, 1972) 28 . Heyman, L.S ., " Cosmetic Lenses, " J. Contact Lens Society of Am., 6 (1), 16- 18 (April 1972) 29 . LeGrand , J.A., " Scleral Cosmetic Shells and Lenses," Inti. Ophtha/. Clinics, 10 (4), 763- 776 (Winter 1970) 30. Koetting, R.A ., "The Ocular Prosthesis in Optometric Practice," Optom. Weekly, 36 (5) (March 1965) 31 . Hill, J.F., " Physical and Physiological Differences in Fitting Soft Contact Lenses," Optom. Weekly, 64 (26), 621 623 (June 28, 1973) 32. Slatt, 6. , and Stein, H.: ·" Comparison of Hydrophilic Lenses, " Contact Lens Medical Bulletin, 5 (3 & 4) 7- 12 (July & Dec . 1972) 33. Harris, M.G., Hall, K., and Dye, R , " The Measurement and Stability of Hydrophilic Lens Dimensions," Am. J. Optom., 50 (7), 546 - 552 (July 1973) 34. DeCarie, J., " Developing Hydrophilic Lenses for Continuous Wear," Contacto, 16 (1), 39 - 42 (March 1972) 35 . O'Driscoll, K.F., The Nature and Chemistry of High Polymers, Reinhold, London (1964) 36. " Symposium on the Flexible Lens, the Future of the Flexible Lens vs. Rigid Lenses," C.V. Mosby, St. Louis, Mo. (1972) 37. Haberich, F.J ., "Physiological Aspects in Fitting of Hard and Soft Contact Lenses," Contact-Linse, 7 (3), 6- 11 (July 15, 1973) (German) 38. Matas, B.R., Spencer, W.H., and Hayes, TL, "Scanning Electron Microscopy of Hydrophilic Contact Lenses, " Archives Ophthal., 88 (3), 287-295 (Sept. 1972) 39. Charles, A.M., "Techniques for the Isolation of Micro-organism for Contact Lenses," J. Am. Optom. Assn., 43 (6), 661-662 (June 1972) 40. Milauskas, A.T ., "Pseudonomas Aeruginosa Contamination of Hydrophilic Contact Lenses and Solutions, " Am. Acad., Opthal. & Otolaryngology Transactions, 76 (2), 511-516 (March- April 1972) 41. Bernstein, H.N ., " Fungal Growth Into a Bionite Hydrophilic Contact Lens," Annals of Ophthal., 5 (3), 317-322 (March 1973) 42 . Mote, E., Filppi, J.A., and Hill, R., " Does Heating Arrest Organism in Hydrophilic Cases? ," J. Am. Optom. Assn., 43 (3), 302 - 304 , (March 1972) 43. Cumming , J.S., "The Food and Drug Adminstration" the Law, and Flexible Hydrophilic Contact Lenses," J. Am. Optom. Assn. , 43 (3), 259- 261 (March 1972) 44. Cureton , G.L., "New Perspectives on Solutions for Hard and Soft Contact Lenses," Mftg. Optics Inti., 26 (10), 503- 511 (Oct. 1973) 45. Cureton, GL, and Sibley, M.J., " Soft Contact Lens Solution, Past, Present and Future ," J. Amer. Opt. Assn., 45 (3),285-291 (March 1974) 46. Knoll, H.A., "Microbiology and Hydrophilic Contact Lenses, " Am. J Optom., 48 (10), 840- 844 (Oct. 1971) 47. Bausch & Lomb Instructions for Wearers of Soflens Contact Lenses, package insert, Rochester, N.Y . (1971) 48 . Bailey, W.R., " Preservatives for Contact Lens Solutions," Contact Lens Society of Am., 6 (3), 33 - 39 (Oct. 1972) 49. Sibley, M.J., and Yung, G., "A Technique for the Determination of Chemical Binding to Soft Contact Lenses, " Am. J. . Optom. 50 (9), 710-714 (Sept. 1973) 50. Krezanoski, J.Z., " Pharmaceutical Aspects of Cleaning and Sterilizing Flexible Contact Lenses," Ophthal. Optician, 12 (20), 1035- 1037 (Oct. 14, 1972) 51. Sagan, W., and Schwaderer, K.N., "A New Cleaning Technique for Hydrophilic Lenses, " J. Am. Optom. Assn., 45 (3), 267 .. 279 (March 1974) 52. Trager, S.Y., " Solutions for Soft Lenses," Mftg. Optics Inti, 25 (10), 403- 405 (May 1972) 53 . Koetting, R.A ., "It's An Emergency," Optom. Mgmt. , 10 (3),22- 26 (March 1974) 54 . Mulrooney, G., " Soft Contact Lenses, Cosmetics, and Medication," Canadian J Optom., 33 (3),74 (Dec. 1971)
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Disregarding pioneering efforts that were more publicized than practical, the 1929 contact lens of Dallos really marked the beginning of the practical use of contact lenses. So contacts and the solutions used with them have been with us for nearly half a century. In 1943, Bier eliminated the need for fluid-filled lenses by drilling a hole to increase tearflow under the lens, while Touhy accomplished the same results five years later by reducing the lens size. Neill, Sohnges, Dickinson and others pursued this approach so that, until very recently, most contact lenses were modifications of those developed in the mid-1950's. All were made of a plastic called polymethyl methacrylate (PMMA) and cleaned, stored and wetted in much the same way . Almost 15 years ago, Wichterle 1 introduced hydroxyethyl methacrylate (HEMA) to the contact lens field. Hydrophilic, wearable for extended periods of time and extremely comfortable, the new soft lens was readily accepted in Europe despite its poor optical properties. With many of the technical problems now solved, this flexible, cross-linked polymer lens is becoming the method of choice for most American doctors and patients. Its future seems assured but present limitations allow ample room for coexistence of hard and soft lens materials. 2,3 To understand the problems involved in fitting a contact lens to a human cornea one must recognize the unusual condition which exists. The cornea is avascular. It is transparent and stays that way by virtue of a delicate water balance and a "metabolic pump" which requires atmospheric oxygen. This breaks down lactic acid into H20 and CO 2 which are discharged from the surface. 4,5.6 When a contact lens interferes with the process, resultant insult produces edema, loss of vision, discomfort, and ultimately, loss of epithelial tissue-a painful condition commonly called "overwear abrasion. "7,8 Under the tear layer, a cornea is covered with a thin multi-purpose precorneal film. Composed of mucopolysaccharide, water and oil layers, it prevents the cornea from drying and assures its integrity by maintaining a continuous layer of tears. 9,10 The deeper mucoid layer also is thought to aid in the utilization of oxygen and discharge of CO 2. The cornea is covered by this absorptive hydrophilic material, spread by the lid action, with a critical surface tension surpassing that of tears so that a continuous film will immediately form after every blink. The use of isotonic solutions of
water-soluble polymers has confirmed the feasibility of coating the contact lens or cornea to produce an effect similar to that provided by the hydrated conjunctival mucus. 11 . 12 The quality and quantity of the tears play an important role in contact lens wear.13 Inadequate secretion is given careful consideration (using the Schirmer tear test as standardized by Halberg and Behrens).14 However, when excessive and hypotonic tearing results from reflex stimulation by the lens, the relatively hypertonic fluid in the corneal tissue frequently produces edema when water is imbibed from the tears.
Vol. NS 15, No. 10, October 1975
Conventional Hard Lenses The most common regimen of hard lens care includes use of three solutions-wetting, soaking and cleansing-separately or in combination. Their use has long been established. 15 - 17 Wetting solutions reduce the interface tension between the lens and the tears, usually through the action of polyvinyl alcohol (PVA). The PVA alone, or in combination with other ingredients, also serves as a lubricant. These solutions generally contain benzalkonium chloride or thimerosal as preservatives and disodium edetate (EDTA) to enhance the activity of benzalkonium chloride against pseudomonas aeruginosa, and to prevent the development of resistant strains of the organism. Mercurial preservatives may be used alone or in combination with other agents. 18 ,19 A PMMA (hard) lens will absorb H20 in amounts from 1.5 percent to 3 percent of its weight. Changes in fitting characteristics resulting from this absorption can be avoided through the use of soaking solutions. 2o ,2 1 These are antiseptic and designed to resterilize themselves within four to eight hours after contamination from handling and wearing the lenses. This overnight storage reduces the chance of ocular infection and aids in the hydration and comfortable wear of lenses the next day. It should be pointed out that the surface must
Robert A. Koetting
By Robert A. Koetting
be cleaned before storage as remaining debris and microorganisms on the lens may exceed the disinfective capacity of the formulation. Hard lens cleaning solutions contain surfactants that are formulated in an alkaline pH to aid in dissolving denatured protein. They should be used prior to storing in a soaking solution to prevent inactivation of the soaking solution's preservative by proteinaceous deposits on the lenses. 22 - 24 At the present time a number of combination solutions have appeared on the market. These are designed to provide all three functions but are generally not as effective as the best single function solution. For example, the viscosity building and lubricating materials added to wetting agents tend to become quite thick and gummy in a storage case. They may even form hard crystals on the lip of the container and could be introduced into the eye to cause injury or discomfort. The contact lens wearer's desire to use the simple "one solution" method seems to result from the same human weakness which tempts him to try the ubiquitous home remedies that have ruined so many lenses and caused untold discomfort. Toothpaste does not make a good contact lens polish. In fact, some of the toothpaste ingredients tend to coat the lens and make it quite uncomfortable. The low pH of lemon juice makes it most undesirable as a proteinaceous deposit remover, yet many persons proclaim its value as a contact lens cleaner. Certain cigarette lighter fluids will dissolve greasy deposits from a lens surface but many contain solvents which will actually damage the plastic. It is difficult to explain why a patient would rather clean contacts with shampoo instead of the properly formulated materials which are readily available, but these amateur procedures constitute a continuing problem. Moreover, some commercially marketed solutions are not even compatible. A storage solution which contains boric acid, for instance, will form a precipitate when used with another manufactur-
Robert A. Koetting, 00, has an optometric practice limited to contact lenses in southwest St. Louis, Missouri. A continuing education lecturer on contact lens fitting, Dr. Koetting has done clinical investigation of several flexible lens materials. He received his doctor of optometry degree in 1947 from Southern College of Optometry in Memphis, Tennessee . He is past president and executive director of the philanthropic Optometric Center of St. Louis, an officer of a number of contact lens specialty groups, and has served on several American Optometric Association committees.
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er's wetting solution containing PVA, and the same can be said for a variety of artifical tears and irrigating solutions. A word should also be added concerning the many "accessory solutions" (such as Comfort Drops by Barnes-Hind, Blink-NClean by Allergan or Adapettes by Burton, Parsons & Co.) which have been introduced in recent years. Some contain polymers designed to supplement the mucoid covering of the corneal surface, others are solutions of non-ionic surfactants with varying amounts of viscosity-building agents added, while others are sold for the explicit purpose of cleaning and rewetting lenses on the eye. The specific action of these solutions is frequently misunderstood by patient, practitioner and pharmacist. Scleral Lenses Historically important, but of little current significance, the scleral lens is still used in certain specialized applications. Covering almost all of the exposed scleral conjunctiva, present day scleral lenses are designed to facilitate maximum tear circulation and do not require substantially different attention than smaller corneal lenses made of the same PMMA material. 25-27 Those few applications which do call for scleral lens use warrant serious consideration-prescriptions involving the use of a prism, highly astigmatic corneas, infants, and most common today, cosmetic lenses fitting in cases of aniridia (congenital absence of pupil), injury or serious eye disfigurement. 28,29 They are usually placed on the eye following preparation with conventional contact lens solutions. Naturally, cosmetic scleral lenses (or "shells" as they are called if no lens prescription is involved) require a regimen of care which is quite different in each individual case. A shell used following evisceration or loss of a cornea will probably be worn 24 hours a day, and aside from periodic cleaning, require the use of a prosthetic lubricant. 3o Soft Lenses Soft lenses were first described by Wichterle and Lim 1 in 1962. The present state of the art is marked by very rapid change. 31 ,32 Many similar lenses are under development in various parts of the world, distinguished only by minor differences in the cross-linked polymers, water content and fitting rationale. The material, a hydrophilic hydroxyethyl methacrylate (HEMA), usually absorbs water from about 40 percent to 60 percsnt of its own weight. Very stable lenses that are only about 12 per-
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cent H20 are being tried in Japan, while one British manufacturer uses a lens which is 80 percent H20 and designed to be worn continuously.33,34 (Photo 1, at right) Since the soft lens material is quite unmanageable in its hydrated state, changes involving fit or refractive considerations can be accomplished only by using another lens. They are somewhat fragile and tend to become coated, so the need for multiple replacements is immediately obvious. Mass-produced molded lenses sold with ten or a dozen in a package might seem quite practical, and indeed, the original developers foresaw this manner of marketing. Perhaps for the public good, however, the material is not easily molded. As it changes from liquid to a semi-rigid state in the process of polymerization, the volume decreases so that lenses cannot be accurately shaped. New methods are under development at the present time but the molding system is not yet a consideration. 35 Instead, most lenses produced in this country are spin cast-a technique which involves pouring polymerizing liquid into a rotating concave form. Optical properties are produced by centrifugal force. The greater the speed of rotation, the thinner the lens at its center. Spin casting requires exacting control but the problems are multiplied many times in the alternate manufacturing method. A lathe-cut lens is made from a button of dehydrated HEMA. It is fabricated following the same procedure used in manufacturing conventional hard lenses and hydrated by soaking in saline solution after the work is complete . Unfortunately, even the most minute changes in temperature, humidity, age or cross-linking of the polymer will produce significantly different results. The dehydrated material is brittle, and once hydrated, the parameters of the lens are never the same as they were before hydration. Nevertheless, lenses produced in this way pose optical superiority as a rule and can be fabricated to a wide range of para meters.36 Immediately after introduction of the soft lens, particularly in the United States, much emphasis was placed upon the control of pathogens. It was generally assumed that bacteria or fungi would penetrate the lens and grow in the intermolecular spaces. Researchers later determined that the pore size precluded this,37,38 while other studies showed that lenses developed cracks and fissures which could and did harbor certain microorganisms including pseudomonas
Photo 1-Soft Lens Placed on the Eye. Hydrophilic, wearable for extended periods of time, and extremely comfortable, the new soft lens is rapidly replaCing other types of contacts. aeruginosa. 39 ,40 Clinical experience seems to indicate that the growth of bacteria " on or in" is an academic consideration and that the soft lens in situ is not a case of infection. 41 The pathogen control mechanisms of the eye fluids are apparently as effective for soft lens wearers as they are for persons who wear no contacts at all. Just the same, a sterilization method for soft lenses remains a major consideration for FDA approval and only one method is currently acceptable. 42 ,43 At this writing, about 15 soft contact lenses are in various stages of investigation awaiting approval for use in the U.S. Only three have been accepted-the Soflens by Bausch & Lomb, Hydrocurve by Soft Lens, Inc. (both used for ophthalmic purposes) and the Softcon by WarnerLambert, restricted to therapeutic use. The "package" requires that all types be boiled when the lens has been removed from the eye. Although many methods of sterilization are used in Canada and throughout the world, nothing else is legally available to the U.S. soft lens wearer. Other soft lens care regimens are worthy of note, however. The simplest method of sterilization involves overnight storage in solutions containing chlorhexadene glucanate and thimerosal or iodophores, following daily prophylactic care with special cleaning products. These solutions provide the same convenience as conventional hard lens soaking and even employ the same type of case. The peroxide method is frequently used in Canada. Soaking a lens for ten minutes
Journal of the American Pharmaceutical Association
Robert A. Koetting
in three percent hydrogen peroxide renders it completely sterile and dislodges most foreign material from the surface. Unfortunately, the lens must be thoroughly rinsed since there is serious danger that residual peroxide may irritate the cornea. This involves extra steps and diligent patient control.44 Generally speaking, the soft lens disinfecting solutions currently in use have an acceptable, though not ideal, microbial kill rate or capacity. They are slower than an efficient single-function hard lens soaking solution and equal to, or somewhat slower in, resterilizing than the mUltipurpose hard lens solutions against two pseudomonas species. The soft lens solutions also are slower when challenged with common ocular bacterial contaminants and pathogens, including Candida a Ibicans, Escherichia coli, Proteus mirabilis and Staphylococcus aureus. 45 Some practitioners use standard autoclaving methods in the office. This renders trial contact lenses free of bacterial contaminants for use on other patients and sterile so that they can be stored for long periods of time without further attention. Aside from the obvious expense involved, this method probably could not be employed by patients at home on a daily basis because there are many unofficial reports that soft lenses deteriorate under exposure to such repeated high temperatures. Routine use of the small electric aseptor unit provided by Bausch & Lomb is an effective method of pathogen control and most patients are quite satisfied with it. Prevention of excessive contamination while the lens is off the eye is its major purpose. 46 (Photo 2, above right) Some practitioners have begun advising travelers to store lenses in a refrigerator at night if the boiling unit is not available for a day or two. Cool temperatures simply reduce the rate of microbial multiplication but represent a serious deviation from the FDA-approved regimen. Nevertheless, serious problems resulting from this revision of protocol have not been reported, and in view of the surface deposits compounded by heat, it may indeed be very practical advice . Soft lenses must be stored in an isotonic sodium chloride solution. According to the instructions in the approved Bausch & Lomb Kit it is prepared by adding one .250 g NaCI tablet to one ounce of distilled water. 47 A preserved isotonic solution also is available but approved for only one lens at this time. Normal saline solution can be prepared
Vol. NS 15, No. 10, October 1975
in many other ways. The danger is that patients will prepare large amounts of solution and be reluctant to discard the surplus, using it long after pathogen growth may have reached a significant level. Preparing the solution daily reduces this risk of extended storage. In an emergency situation, patients may be advised to add a one-gram USP salt tablet to four ounces of distilled water and discard the remainder after use . Salt tablets for the preparation of saline used with soft lenses must not contain additives. Adhesives, coating or any other ingredient may damage the patient's eye or lenses. (Although iodine was considered an unacceptable impurity at one time, limited research indicates that it is apparently harmless in concentrations commonly found in table salt.) The same must be said of prepared saline solutions. Injectable saline, ophthalmic irrigating solutions and the like contain preservatives. Benzalkonium chloride is the most serious contributor to severe problems because it is found in so many eye preparations and contact lens solutions. It binds to the lens polymer in a concentration which is many times the acceptable level. Wearers have experienced painful, though reversible, injury following ill-advised use of conventional hard lens soaking solutions with soft lenses .. 48 - 5o Last year the FDA approved the Hydrocurve lens manufactured by Soft Lens Incorporated of San Diego. The material is supplied by Automated Optics of New York and that firm plans to license other companies to produce the lens under a variety of names. None have reached the market at this writing. Prepared saline with .001 percent thimerosal added as a preservative is approved as a storage solution with these lenses. It is curious that one isotonic sodium chloride solution is suitable for use with a particular lens and another isotonic sodium chloride solution is legally restricted to use with a different lens. That is the current situation, however, and the "Boil-n-Soak" solution is sold " for use with Hydrocurve contact lenses." Soft lens clinicians agree that the foremost problem currently involves proteinaceous and mineral deposits which coat lens surfaces. Observable after periods varying from a few days to several years, this coating impairs vision and often produces mild infection or discomfort. The irregular surface of the foreign substance promotes the adherence of additional deposits and the protein is further solidified by
Photo 2- The Bausch & Lomb Aseptor Unit. Soft lenses in sealed vials are placed in the large office aseptor for routine bOiling. Patients perform pathogen control on a smaller scale by daily use of an individual-timed electrical heating unit which boils lenses in the case. the daily boiling process. Meibomian oils and foreign materials, including makeup, add the build up . Two cleaners for daily prophylactic lens care also have been approved for use with the Hydrocurve lens and are being tested with others at this writing. They are Soft Mate by Barnes Hind and Pliagel by Flow Pharmaceuticals . Lenses which are carefully cleaned upon removal will remain clear for extended periods of time , but the only method available to the Bausch & Lomb patient is the abrasive action of his own thumb and forefinger on the lens surface. Used with hot water or saline before the aseptor cycling, even such mechanical rubbing can be quite helpful because the half dozen soft lens cleaners which are commercially available in Canada and Europe have not been approved for use here. 50- 53 Lens coating also is prevented or controlled by buffering the saline solution used for storage. Proteinaceous deposits are less likely to form in alkaline media. A pH of 7.4 to 7 .8 is quite acceptable to corneal tissue and it is speculated that the addition of a small amount of sodium bicarbonate could eliminate many problems. Although such preventive measures are anticipated, the Bausch & Lomb Kit instructions have not been modified to date. Improper Handling Of the three soft lenses which have been approved for general use in the U.S., Warner-lambert's Softcon is prescribed only as a bandage and may be removed only by the physician . Consequently, there (Continued on page 587)
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Dickson/Rodowskas
4.
5.
6.
7.
sumer Attitudes Toward Prescription Prices by Selected Consumer Characteristics," unpublished masters thesis, Oregon State University (Aug. 1968) Task Force on the Roles of Practitioner and the Subprofessional in Pharmacy. "Report on the Task Force on the Roles of the Practitioner and the Subprofessional in Pharmacy," JAPhA, NS9 (8), 415 (Aug. 1969) Barker, K.N., and Smith, M.C., " Deficiencies of the Task Force Criteria for Identifying Subprofessional Tasks, " Am. J. of Hosp. Pharm., 29 (9), 734 (Sept. 1969) Ryan , M.R , " An Analysis of the Work of Fifty Community Pharmacists in Northern Mississippi. " unpublished PhD dissertation, University of Mississippi (May 1973) Task Force on the Pharmacist's Clinical Role, " Report of
Robert Koetting (Continued from page 577) is little need for patient instruction because all of the handling should be accomplished by his physician. These people are ordinarily under reasonably close medical supervision and serious problems are rare, In the case of the Bausch & Lomb Soflens, however, minor problems have resulted from misinterpretation of the instructions. The printed package insert contains a good deal of extraneous information and patients are often confused.53 These mistakes seem to be the most often repeated1, Excessive or incorrect use of cosmetics frequently causes severe abrasion when the materials become lodged in or under a lens.54 2, Soft lenses stored in conventional hard lens solution containing benzalkonium chloride produce serious corneal irritation, 3. Lenses stored in tap water instead of saline solution result in stinging and corneal edema upon application. There is also serious possibility of microbial contamination, 4, Disregarding regular use of the aseptor allows the development of fungus colonies on the lens surface, 5. Use of injectable saline (containing preservatives) for storage produces discomfort and occasionally serious corneal insult. 6, Use of salt· tablets which are the wrong size or those containing additives to improve the flavor or act as an adhesive may ruin the lens and are usually a source of irritation when the lens is worn, The foregoing certainly leads to a practical conclusion of this review, Closer cooperation between the pharmacist and the optometrist can prevent many such problems. Both professions have a serious obligation to the public welfare and all parties will benefit from a free and frequent exchange of scientific information. The FDA position that new lens materials are drugs and the resultant awareness of a mutual interest should accelerate a diVol. NS 15, No. 10, October 1975
the Task Force on the Pharmacist's Clinical Role," JAPhA, NS11 (9), 482 (Sept. 1971) 8. Graber, J.B., and Brodie, D.C. (eds.), Proceedings of an Invitational Conference on Pharmacy Manpower, National Center for Services Research and Development. Rockville, Md. (Jan . 1971) 9 . Work sampling is one of several job analysis techniques available. For a description of work sampling see Barnes, R.M., Work Sampling, 2nd ed., John Wiley & Sons, New York (1957); or see Heiland, R.E. , and Richardson , W.J., Work Sampling, McGraw-Hili, New York (1957) 10. Barker, K.N. , " An Analysis of the Work and Utilization of the Pharmacist in Small Mississippi Hospitals to Estimate Some Effects of the Introduction of Pharmacy Auxiliary
alogue long overdue . After all, contact lenses and the solutions used with them have been with us for nearly half a century,
•
References 1. Wichterle, 0 ., and Lim, D., " Hydrophilic Gel Lens for Biological Use, " Nature, 185 117- 118 (1960) 2. Mandell, R , Korb, D.R , Sarver, M., and Poster, M. , " The State of the Art," J. Am. Optom. Assn., 44 (3), 229- 236 (March 1973) 3. Feldman , GR, et al., "The Soft Lens Situation: Using Today's Materials," Contacto, 17 (3),7 - 30 (June 1973) 4. Fatt, I., "Oxygen Supply to the Contact Lens Through Hydrogel Contact Lens, " The Contact Lens, 14 (1), 3-5 (Oct. 1972) 5. Hill, RM., and Fatt, I., " How Dependent is the Cornea on the Atmosphere?," Am. J. Optom., 35 (10),873- 876 (Oct. 1964) 6. Ullen , R., "Transparency, Edema, and Contact Lenses, Part I, 11 (8), 1- 4 (Oct. 1971); Part II, 11 (9), 1,2 (Nov. 1971); Part 111,11 (10), 1- 4 (Dec. 1971) 7. Kennedy, J.R. , "Corneal Abrasion Considerations," Contacto, 16 (2),69 - 72 (June 1972) 8 . Korb, D.R. , " Edematous Corneal Formations, " J. Am. Optom. Assn., 44 (3), 246 - 253 (March 1973) 9 . Lemp, M.A ., Holly, F.J., Iwata , S. , and Dohlman, C.H., " The Precorneal Tear Film," Archives of Ophthal., 83 (1), 89- 94 , (1970) 10. Rankin, B.F., and Trager, S.F., " Wetting of Contact Lenses," J. Optom. & Archives of Am. A cad. Optom., 47 (9), 698 - 702 (Sept. 1970) 11 . Koetting , R. A., "The Effect of Polyvinyl pyrollidone with Hydroxyethylcellulose on Three and Nine O'Clock Staining," Contacto, 15 (2) (June 1971) 12. Lemp, M., and Holly, F.J. , " Ophthalmic Polymers and Ocular Wetting Agents, " Annals of Ophthal., 15- 20 (Jan . 1972) 13. Hill , J.F., "Tear Analysis for Successful Contact Lens Wear," Optom. Weekly, 64 (39),943- 946 (Sept. 27,1973) 14. Halberg, G.P. and Behrens, C., " Standardized Schirmer Tear Test," Am. J. Ophthal., 51 (5), 840- 842 (May 1961) 15. Dabezies, D .H., "Contact Lenses and Their Solutions: A Review of Basic Principles," Eye, Ear, Nose & Throat Monthly, Parts I, II, & III (Jan ., Feb., March 1966) 16. Weston, J.H. , "The Preparation of Bacteria Free Solutions for Contact Lenses," Optical World, 1 (4), 23- 24 (Sept ., Oct. 1972) 17. Koetting, R.A., " The Solution May Be the Problem," Optom. Mgmt. 7 (8), 9- 13 (Aug. 1971) 18. Cureton, G.L., "New Perspectives on Solutions for Hard & Soft Contact Lenses," Mftg. Optics Inti., 71 (10), 503 510 (Oct. 1973) 19. Charles, A.M., "A Test System for Evaluating the Bactericidal Capabilities of Hard Lens Solutions," J. Contact Lens SOCiety of Am., 6 (3), 40- 46 (Oct. 72) 20. Koetting, R.A., "Minimizing Problems Resulting from Changes in Contact Lens Radius, " The Optom. Weekly (Oct. 24, 1963) 21 . Koetting, R.A. , "The Interpretation of Contact Lens Base Curve Changes, " Optom. Weekly, 57 (52) (Dec. 29, 1966) 22. Baldone, J.A ., "Contact Lens Cleaning Updated," Contact Lens Medical Bulletin, 4 (2), 9- 12 (April, June 1971) 23. Elstrom, G.P., "Contact Lens Cleaner," J. Am. Optom. Assn., 45 (4),450 (April 1973) 24. Young, W., and Hill, R.M., "Cholesterol Levels of Human Tears," J. Am. Optom. Assn., 45 (4), 424 - 428 (April 1943) 25. Elliott, D.O., "Venting and Fenestration," J. Am. Optom. Assn., 42 (3),255 (March 1971) 26 . Fletcher, R.J., ed., "A Personal Technique of Haptic Lens
Workers," unpublished PhD dissertation, University of Mississippi (May 1971) 11 . Rodowskas, C.A., and Gagnon, J.P., " Personnel Activities in Prescription Departments of Community Pharmacies," JAPHA, NS 12 (8), 407 (Aug. 1972) 12. Morsh, J.E., Madden, J.M., and Christal, HE, Job Analysis in the United States Air Force, National Technical Information Service, Springfield, Va., 3 (1961) 13. Ibid. 14. Siegel, S., Nonparametric Statistics for the Behavioral Sciences, McGraw-Hili, New York, 184 (1956) 15. Task Force on the Roles of the Practitioner and the Subprofessional in Pharmacy, op. cit. 16. Blacklock , H.M., Social Statistics, McGraw-Hili, New York, 169 (1960) Fitting, " Part 9, The Contact Lens, 2 (7), 22- 30 (April 1970) 27 . Redford, CA, " Who Wants to Bother With Haptic Lenses? " Radharc, 16 (2),35 - 38 (March - April, 1972) 28 . Heyman, L.S ., " Cosmetic Lenses, " J. Contact Lens Society of Am., 6 (1), 16- 18 (April 1972) 29 . LeGrand , J.A., " Scleral Cosmetic Shells and Lenses," Inti. Ophtha/. Clinics, 10 (4), 763- 776 (Winter 1970) 30. Koetting, R.A ., "The Ocular Prosthesis in Optometric Practice," Optom. Weekly, 36 (5) (March 1965) 31 . Hill, J.F., " Physical and Physiological Differences in Fitting Soft Contact Lenses," Optom. Weekly, 64 (26), 621 623 (June 28, 1973) 32. Slatt, 6. , and Stein, H.: ·" Comparison of Hydrophilic Lenses, " Contact Lens Medical Bulletin, 5 (3 & 4) 7- 12 (July & Dec . 1972) 33. Harris, M.G., Hall, K., and Dye, R , " The Measurement and Stability of Hydrophilic Lens Dimensions," Am. J. Optom., 50 (7), 546 - 552 (July 1973) 34. DeCarie, J., " Developing Hydrophilic Lenses for Continuous Wear," Contacto, 16 (1), 39 - 42 (March 1972) 35 . O'Driscoll, K.F., The Nature and Chemistry of High Polymers, Reinhold, London (1964) 36. " Symposium on the Flexible Lens, the Future of the Flexible Lens vs. Rigid Lenses," C.V. Mosby, St. Louis, Mo. (1972) 37. Haberich, F.J ., "Physiological Aspects in Fitting of Hard and Soft Contact Lenses," Contact-Linse, 7 (3), 6- 11 (July 15, 1973) (German) 38. Matas, B.R., Spencer, W.H., and Hayes, TL, "Scanning Electron Microscopy of Hydrophilic Contact Lenses, " Archives Ophthal., 88 (3), 287-295 (Sept. 1972) 39. Charles, A.M., "Techniques for the Isolation of Micro-organism for Contact Lenses," J. Am. Optom. Assn., 43 (6), 661-662 (June 1972) 40. Milauskas, A.T ., "Pseudonomas Aeruginosa Contamination of Hydrophilic Contact Lenses and Solutions, " Am. Acad., Opthal. & Otolaryngology Transactions, 76 (2), 511-516 (March- April 1972) 41. Bernstein, H.N ., " Fungal Growth Into a Bionite Hydrophilic Contact Lens," Annals of Ophthal., 5 (3), 317-322 (March 1973) 42 . Mote, E., Filppi, J.A., and Hill, R., " Does Heating Arrest Organism in Hydrophilic Cases? ," J. Am. Optom. Assn., 43 (3), 302 - 304 , (March 1972) 43. Cumming , J.S., "The Food and Drug Adminstration" the Law, and Flexible Hydrophilic Contact Lenses," J. Am. Optom. Assn. , 43 (3), 259- 261 (March 1972) 44. Cureton , G.L., "New Perspectives on Solutions for Hard and Soft Contact Lenses," Mftg. Optics Inti., 26 (10), 503- 511 (Oct. 1973) 45. Cureton, GL, and Sibley, M.J., " Soft Contact Lens Solution, Past, Present and Future ," J. Amer. Opt. Assn., 45 (3),285-291 (March 1974) 46. Knoll, H.A., "Microbiology and Hydrophilic Contact Lenses, " Am. J Optom., 48 (10), 840- 844 (Oct. 1971) 47. Bausch & Lomb Instructions for Wearers of Soflens Contact Lenses, package insert, Rochester, N.Y . (1971) 48 . Bailey, W.R., " Preservatives for Contact Lens Solutions," Contact Lens Society of Am., 6 (3), 33 - 39 (Oct. 1972) 49. Sibley, M.J., and Yung, G., "A Technique for the Determination of Chemical Binding to Soft Contact Lenses, " Am. J. . Optom. 50 (9), 710-714 (Sept. 1973) 50. Krezanoski, J.Z., " Pharmaceutical Aspects of Cleaning and Sterilizing Flexible Contact Lenses," Ophthal. Optician, 12 (20), 1035- 1037 (Oct. 14, 1972) 51. Sagan, W., and Schwaderer, K.N., "A New Cleaning Technique for Hydrophilic Lenses, " J. Am. Optom. Assn., 45 (3), 267 .. 279 (March 1974) 52. Trager, S.Y., " Solutions for Soft Lenses," Mftg. Optics Inti, 25 (10), 403- 405 (May 1972) 53 . Koetting, R.A ., "It's An Emergency," Optom. Mgmt. , 10 (3),22- 26 (March 1974) 54 . Mulrooney, G., " Soft Contact Lenses, Cosmetics, and Medication," Canadian J Optom., 33 (3),74 (Dec. 1971)
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