Abstracts of the BCLA Annual Clinical Conference - London 1993

Journal of the British Contact Lens Association, Vol. 16, No. 4, pp 151-162, 1993 Printed in Great Britain

© 1993 British Contact Lens Association

Abstractsof the BCLAAnnual ClinicalC0nference- London1993 P A R A M E T E R STABILITY O F S O F T C O N T A C T L E N S E S D U R I N G W E A R

J. Veys and N. Efron During contact lens wear, the lens itself is subject to physical and environmental effects that can influence lens behaviour. For example, soft contact lenses dehydrate in the eye, the extent and rate of which appears to be primarily dependent on material type and lens thickness. Lens dehydration can result in a number of potentially adverse clinically relevant effects, leading to possible changes in lens fit, loss of oxygen performance and desiccation staining. A single centre, masked, randomised study was conducted to compare the parameter stability of Group I (low-water, nonionic) and Group IV (high-water, ionic) soft contact lenses in the eye and during disinfection, using video-based electronic measuring technology. Results show Group IV lenses to have

greater in vitro and in vivo parameter instability compared to Group I lenses during wear and with various disinfecting systems. However, except for heat, no adverse effect on contact lens fit, comfort or physiological impact on the cornea is demonstrated. Practitioners should be aware of the unique properties of different lens materials, and for optimum daily wear performance, a suitable lens should be matched to an appropriate lens care system.

Address for Correspondence Vistakon, The Braccans, London Rd, Bracknell, Berks RG12 2AT.

DISPOSABLES - THE WAY FORWARD

I. Davies Disposable contact lenses are one of the most significant advances in contact lenses in recent years. In the 5 years since Acuvue was launched, they have been fitted to over 2 million patients worldwide and are now the world's number one contact lens. Over the last 2 years, disposable lenses have been the subject of intense scrutiny by both professional and consumer media. This has led to questions being asked of practitioners by patients, and of manufacturers by practitioners. In this presentation, the studies reviewing the performance of disposable lenses, both positive and negative, will be reviewed. The lessons that have been learnt from these studies will be explored and the company response to the media discussed.

Safe contact lens wear is a partnership between manufacturer, practitioner and patient, all of whom must contribute. In this presentation, we shall explore the reasons why we have absolute confidence in the Acuvue disposable contact lens, the steps that we are taking to ensure the continued success of disposables, and ways in which the practitioner can address the questions and concerns of patients. Vistakon are committed to working with the profession to both maximise the benefits offered by disposability and to develop fully the contact lens market.

Address for Correspondence Vistakon, The Braccans, London Rd, Bracknell, Berks RG12 2AT.

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ABSTRACTSOFTHEBCLAANNUALCLINICALCONFERENCE- LONDON1993 A N A L T E R N A T I V E A P P R O A C H TO P R O G R A M M E D R E P L A C E M E N T

BJ. Shannon Patients and practitioners know that regular (frequen0 replacement of contact lenses is better because new lenses are consistently more comfortable and provide better vision. While one group of scientists is evaluating and recommending ways of assuring safe and comfortable contact lens wear, as has happened in programmed replacement, another group of scientists is studying and making recommendations on environmental issues that affect the well-being of animals and humans. Education of vision care professionals includes being taught about the visible spectrum, infra-red and ultra-violet (UV) radiation. However, up until recently those in the ophthalmic professions have not given UV radiation much thought in their day-to-day activities. UV radiation has caused many eye and health problems, including cataracts, pterygia, photokeratifis pigmentation, skin cancer and various allergic reaction. Astute, prudent con-

tact lens practitioners today need to understand how environmental changes, such as the thinning of the ozone layer, can affect professional vision-care. The workshop will discuss these critical clinical issues and recommend ways of providing contact lenses to patients, which ensure good comfort, vision and corneal physiology while at the same time providing safety from environmental changes. As it is medically appropriate to limit the amount of exposure to X-rays, it is now also recognised that it is important to limit the amount of exposure to UV radiation. The workshop will discuss how this can be accomplished very effectively with a new programmed replacement contact lens.

Address for Correspondence Permalens House, 1 Botley Rd, Hedge End, Southampton SO3 3HB.

FITHNG THE WESLEY-JESSEN OPTIFIT TORIC HYDROPHILIC LENS

W.A. Dishman

This workshop will discuss the proper methods of fitting the Wesley-Jessen OptiFit toric hydrophilic lens. Both the 38% and 55% water content (phemfilcon A) lenses will be compared, including: lens design; lens parameters; patient selection; fitting techniques; ordering tips; recommended care regimens; and problem-solving tips. OptiFit design and fitting

techniques will be compared to other types of toric lenses currently available.

Address for Correspondence Wesley-Jessen Ltd, 127 High St, Rickmansworth, Herts WD3 1AN.

M E N I C O N S U P E R EX, A N E W G E N E R A T I O N GAS P E R M E A B L E CONTACT L E N S

N.D. Cox The physiological advantages of high Dk rigid gas-permeable (RGP) materials over current hydrogel materials for extended wear have been shown by several investigators. However, many practitioners remain concerned at the complications arising from extended wear and are reluctant to use RGP lenses for this modality, perhaps because of the possibility of unforeseen complications, as occurred with hydrogels. Sixty patients were enrolled in a prospective practice-based study to assess the application of a new design RGP lens, employing a material with a Dk 162. Its usefulness for

problem-solving with existing wearers and for patients with no previous contact lens experience will be reported. Objective clinical findings are described together with subjective comments which are scored to evaluate patient satisfaction. The dimensional stability of trial lenses and prescription lenses is monitored throughout the duration of the study. The role of new generation RGP lenses in contemporary contact lens practice is discussed.

Address for Correspondence 28 Weymouth Street, London W1N 3FA.

MEETING THE FITHNG CHALI.ENGE OF THE 90S

K. Edwards Modern fitting of rigid gas-permeable (RGP) lenses is turning increasingly to system lenses which speed fitting and should provide an adequate fit in a high proportion of cases. However, there are still a significant minority of patients who need individually designed and fitted lenses. This workshop looks at the balance between system lenses and pre-

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scription options. It reviews the benefits of retaining a wide portfolio of lenses and materials to enable adequate fitting for a wide range of patients.

Address for Correspondence Bausch & Lomb (UK) Ltd, 106 London Rd, Kingston-uponThames, Surrey KT2 6QJ.

ABSTRACTSOFTHEBCLAANNUALCLINICALCONFERENCE- LONDON1993

ONE STEP HYDROGEN PEROXIDE DISINFECTION J. Tanner Hydrogen peroxide systems are the most popular in the UK for soft contact lens disinfection. The launch of Oxysept 1 Step this year marks the first significant change in their format since their UK introduction. The technology behind this new product is outlined, and objective and subjective per-

formances of the system are presented.

Address for Correspondence Allergan Optical, Coronation Rd, High Wycombe, Bucks HP12 3SH.

I N VIVO CONTACT LENS W E 1 T A B I L I T Y M. Guillon The in vivo wettabflity of a contact lens is a highly dynamic process. The process begins when a new lens is first inserted, and is in constant modification throughout use of that contact lens. This process includes a period when the in vivo wettabflity is optimal, enabling optimal subjective acceptance and an absence of ocular surface adverse effects. The aim of managing contact lenses must therefore be to identify for each patient, the contact lens type, care system and replacement frequency that permits optimal in vivo wettability during the length of use of the contact lens. The question of in vivo wettability cannot, however, be

approached in a too simplistic manner, as many factors contribute to the overall performance. In this presentation, we will review the current research information available with regard to the environmental, ocular contact lens and care wear related factors that affect performance. In conclusion, we will give general clinical guidelines for optimal clinical management.

Address for Correspondence Contact Lens Research Consultants, 16 Heath Dr, London NW3 7SL.

A EUROPEAN FITFING PHILOSOPHY FOR ASPHERIC, HIGH-Dk RGP CONTACT LENSES J.H. C. Kok Microbial keratitis, the most serious complication of contact lens wear, is most frequently associated with soft contact lenses. Rigid gas-permeable (RGP) lens wearers are less often affected. Increased use of high-Dk RGP lenses could reduce the number of cases of microbial keratitis. In Europe, aspheric high-Dk RGP lenses are very popular. I should like to present practical guidelines for computer-aided fitting of aspheric RGP lenses. Base curve selection using the ker-

atometer to determine the corneal topography will be given. This procedure is inexpensive, time-saving, and suitable for fitting either cosmetic contact lenses or lenses used to treat corneal pathology such as keratoconus.

Address for Correspondence Jan van Goyenkade 1, 1075 HN Amsterdam, The Netherlands.

CONTACT LENS PRACTICE IN G E R M A N Y A.K. Harle In 1959, the first course on 'contact lens fitting' began at the Berlin Advanced School of Ophthalmic Optics (SFOF) and in 1960-61 the subject 'contact lenses' was fully integrated into the curriculum of the Berlin College of Optometry. At that time, the Berlin School was the only German-speaking college in Europe at which the theory and practice of contact lens optics were part of the final examination. Based upon these historical facts, the paper will deal with the actual situation of contact lens care in Germany,

in which 68% of all contact lenses are fitted by optometrists and 32% by ophthalmologists. The lecture will not only cover the classification of all different kinds of contact lenses available and the state of the market, but will also describe the curricula relevant to optometry as well as clinical practice.

Address for Correspondence Schwabacer Str. 20, PO Box 2237, Furth, Germany.

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A B S T R A C T S O F T H E BCLA A N N U A L CLINICAL C O N F E R E N C E - L O N D O N 1993

A MEASUREMENT

OF CORNEAL METABOLISM IN THE HUMAN CORNEA

J. Larke The rate of metabolism in the human cornea has been extensively investigated, using the measurement of stromal swelling and apparent respiration rate. Both these measurements are indirect. We have developed a new technique which directly assesses the state of metabolism in the in vivo human cornea; this is the collection of corneal-derived lactate in vivo. Data will be presented on" the precision; intrasubject variability; the influence of gender; the influ-

ence of the menstrual cycle; ace; and circadian patterns. A close correlation with stromal swelling is demonstrated. The data give a clear and rather surprising view of corneal metabolism and the implications for contact lens wear will be discussed.

Address for Correspondence Dept. of Optometry, UWCC, Cardiff.

OXYGEN TRANSMISSIBILITY AS A POINT FUNCTION - A NEW SYSTEM FOR DESCRIBING OXYGEN SUPPLY TO THE CORNEA THROUGH A HYDROGEL LENS

I. Fatt and C.M. Ruben Oxygen transmissibflity (Dk/L) describes the ability of oxygen to be supplied to a cornea under a contact lens. Some investigators have adopted the harmonic average oxygen transmissibflity as the best way to describe performance of a contact lens on the eye. We show how the average oxygen transmissibility is related to the optical power of the lens through a simple mathematical formula. Furthermore, we propose that the average transmissibility should not be used, but rather oxygen transmissibility as a property at a point on the lens. In this way, oxygen transmissibility can tell us how

an epithelial cell directly under that point is affected by the lens. If such a cell becomes hypoxic, its physiological function will be impaired; this will influence the overall condition of the cornea. It is this overall condition that the clinician is more likely to observe rather than the condition of a single epithelial cell or a small collection of epithelial cells.

Address for Correspondence 406 Boynton Ave, Berkeley, California 94707, USA.

A NEW HYDROGEL MATERIAL FOR CONTACT LENSES

M.J.A. Port and R.J.W. Bowers A new range of hydrogel material is described. The chemistry of the polymer mimics that of natural cell membranes. The intrinsic properties of these biomimetic hydrogels imply that there is virtually zero deposition of proteins and lipids, no effect on water content with temperature, and no dehydration of lenses in the eye. Mechanical properties are the same as for conventional hydrogels of the same water content. Results are presented from the first clinical study using a 60% water content biomimefic hydrogel and a 58% conven-

tional material as a control. Thirty subjects were used. Normal vision was found at high and low contrasts, and there was no adverse response by ocular tissues to the material, no in vivo dehydration, and no protein deposition on the lens surfaces. The control lenses showed significant protein deposition and water loss.

Address for Correspondence Dept. of Optometry and Vision Sciences, The City University, London.

BIFOCAL CONTACT LENSES: PREDICTING VISION FROM OPTICAL MEASUREMENT

R.L. Woods, J.E. Saunders, and M.J.A. Port While the main purpose of previous optical investigations of contact lenses has been to elucidate the effects of differences in design, there have been no previous reports of measurements of both optical performance and visual performance of the same contact lenses. We have compared optical and visual results and developed models to predict visual performance from the optical performance measurements of rigid concentric-design bifocal contact lenses. Optical performance was measured using an EROS solidstate modulation transfer function (MTF) system. Visual performance was measured with a monitor-based contrast sensitivity system, Pelli-Robson charts and high and low contrast visual acuity charts. Bifocal contact lenses were made in a back-surface design in both centre-distance and centre-near designs in polymethylmethacrylate (PMMA) by Pilkington VisionCare. The central optic zone diameter (COZD) varied

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from 1.8 to 3.4mm, while the peripheral optic zone diameter was fixed at 7.5mm. Multiple regression analysis models were empirically derived to include pupil size, decentration and COZD. Best predictions (adjusted R2 range 0.46 to 0.80) of visual performance were found with the MTF measurements made with a 4mm aperture. The average measured pupil diameter of the five presbyopic subjects was 2.8mm. The utility of these models indicated that the MTF is a useful measure of changes in lens design, and that given the correct conditions of measurement, good predictions of visual performance can be made. Hence, changes in the MTF of bifocal contact lenses are a useful indicator of changes in vision.

Address for Correspondence Queensland University of Technology, School of Optometry, GPO Box 2434, Brisbane, Australia.

ABSTRACPSOF THE BCLAANNUALCLINICALCONFERENCE- LONDON1993

IT'S A D I R T Y B U S I N E S S ; C L E A R I N G U P THE MESS CM. Schnider The issues surrounding contact lens care systems are extremely complex and in general poorly understood by contact lens practitioners and patients alike. Although many problems associated with toxicity and sensitivity have been minimised by the introduction of more contemporary preservatives, alternate disinfection techniques and disposable lenses, there are still many unanswered questions about the issue of lens care. Are enzymes necessary with rigid gaspermeable (RGP) lenses? Are abrasive cleaners more effective? Is it possible to change the optical quality or power of a rigid lens with digital cleaning? Is enzyme cleaning necessary with programmed replacement soft lenses? Does it vary by material group, patient characteristics, replacement frequency, etc? Does the state of the protein alter the frequency of adverse events, or is it simply the presence of protein? These and many more questions face the contact lens practitioner daily. Unfortunately, life is even more confusing for our patients, who often rely on advice from friends, relatives and chemists for selecting elements of the care regimen. This

paper will review findings relative to care systems for rigid and soft lenses, including: • The effect of enzyme cleaning on RGP lenses. • The effect of abrasive versus non-abrasive surfactants for RGPs. • Compatibility issues to consider when matching a care system with a contact lens material. • Protein uptake characteristics of different classes of rigid and soft lenses. • Studies on frequent replacement soft lenses and enzyme cleaning. The bottom line in considering the messy business of lens spoilation may be that the goal of eliminating care systems entirely is possibly in everyone's best interests.

Address for Correspondence Pacific University, College of Optometry, Forest Grove, Oregon, USA.

THE C O M P A R A T I V E S U R F A C E S P O I L A T I O N A N D C L I N I C A L P E R F O R M A N C E

OF TWO DAILY-

WEAR DISPOSABLE LENS SYSTEMS

L. Jones, V. Franklin, A. Home, and B. Tighe Twelve patients took part in a single-masked, randomised, cross-over study in which they wore Johnson & Johnson Acuvue lenses for 2 weeks and Bausch & Lomb Seequence lenses for 4 weeks on a daily-wear basis, while using a chlorine~release care system with the Acuvue lenses and a chlorhexidine-based tablet system with the Seequence lenses. Prior surfactant cleaning was undertaken with each system. Lens movement was similar with each system (p = MS). High contrast logMAR visual acuity was higher with the Acuvue lenses at both initial (p = 0.02) and final visits (p = 0.004), while low-contrast acuity indicated no difference initially (p = MS), but was higher with the Acuvue lenses on the final visit (p = 0.005). Although acuity with the Acnvue lenses was constant during the period of the trial, visual acuity diminished over the wearing period with the Seequence lenses. Visual quality, comfort, handling performance, simplicity of the care regimen and overall satisfaction was assessed by both interval and visual analogue scales. In all aspects except the care regimen (p = MS), Acuvue lenses were judged to be superior (p > 0.01). While in vivo slit-lamp microscopy revealed no statistically significant difference in the degree of deposition, independent

laboratory-based assays of lipid and protein revealed that the Acuvue lenses exhibited greater amounts of protein deposition (p = 0.0005) and that Seequence had increased levels of lipoidal spoflation (p = 0.01). Correlation between the measured reductions in visual acuity and the measured deposits indicate that it is primarily protein which causes the reduction in acuity seen with the Acuvue lenses (p = 0.02), which can be detected with low contrast charts, and that lipid is primarily responsible for reducing acuity with Seequence lenses (p > 0.01), which can be detected with both high and low contrast logMAR charts. Slit-lamp examination indicated that conjunctival staining in all four quadrants was significantly greater with the Acuvue lenses (p > 0.05). This study indicates that visual acuity with currently available disposable lens systems is excellent, but that certain patients are prone to reductions in visual performance even during short periods of wear, due to accumulation of deposits from the tear film.

Address for Correspondence Dept. of Chemistry, Aston University, Aston Triangle, Birmingham B4 7ET.

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ABSTRACTSOFTHEBCLAANNUALCLINICALCONFERENCE- LONDON1993 A N E W S T A N D A R D I S E D SYSTEM F O R C O N T A C T L E N S D E P O S I T S

E.S. Mitchell, M.A. Hurst, and W.A. Douthwaite A new standardised method for classifying and quanitifying deposits on contact lenses is presented. This contact lens opacity grading system (CLOGS) uses a series of standard photographs of deposited soft contact lenses with which the lens in question can be compared. To facilitate classification, examples of film, granular, spot, and rust deposits are provided. Misclassification is limited by the provision of examples of artefacts which can occur during the viewing of a deposited lens. Five photographs of film deposits are provided for grading purposes. Any degree of deposit which falls between standard photographs are graded by interpolating between the nearest two photographs using a decimal scale. For example, if it was judged that the degree of deposit fell exactly between grades 2 and 3, it would be graded at 2.5. Both film and granular deposits are graded by comparison with these standard photographs. Spot and rust deposits are simply counted. Validation of the CLOGS system was carried out by grading and classifying a total of 79 photographs of a variety of

deposits on soft contact lenses. These deposits were classified and graded by two observers. Both intra- and interobserver agreement was quantified by computing the 95% confidence limits of the difference between test and retest scores. The 95% confidence limits for observers were _+0.76 and _+0.78 respectively (n = 79). When computing the interobserver results, the 95% confidence limit was +1.04 (n = 72). When judgements were made regarding the nature of film and granular deposits, agreement occurred 91.1% of the time. Although this system uses deposited soft contact lenses as standards, there is no reason why rigid gas-permeable lens deposits cannot also be classified by this system, since the deposits on either type of lens are similar in appearance. These results demonstrate the good repeatability of CLOGS and we therefore recommend this system for use in research and clinical environments.

Address for Correspondence Optometry Dept., University of Bradford, Richmond Rd, Bradford BD7 3DP.

TEARS, CARE S O L U T I O N S A N D S O F T L E N S S P O I L A T I O N

B. Tighe and V.J. Franklin A decade ago, the general morphology of soft lens deposition was well understood but little was known about its detailed composition or origin. In addition, until recently it was generally though that lysozyme was the only protein of significance associated with the spoilafion process. As our understanding of spoilation processes has improved and the popularity and availability of disposable lenses has increased, the role of care solutions has assumed greater importance.

Some significant pieces in the spoilation jigsaw have now been put into place. These will be used to show the way in which tears, surfactant cleaners, disinfection systems, and the lens itself all play important parts in this complex phenomenon.

Address for Correspondence Dept. of Chemistry, Aston University, Aston Triangle, Birmingham B4 7ET.

VISUAL P E R C E P T I O N A S LIMITED BY E Y E - L E N S O P T I C S

O. Wichterle An essential precondition of optimal visual correction is the quality of the image projected on the retinal surface. Thus, for patients with a well-developed power of accommodation, the eye-lens system should approach as nearly as possible to the exact optics of a photographic camera. For patients with a missing or strongly reduced accommodation capacity, precise optics offer a nice retinal image of objects placed in only one particular distance. Contrary to prescription glasses, contact lenses and intraocular lenses can

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simulate the missing accommodation to a certain extent. The alternatives of intentionally distorted lens optics will be discussed and their effect on the quality of the retinal image in relation to defocusing (i.e. to the varying distance of the projected object).

Address for Correspondence Institute of Czechoslovakia.

Macromolecular

Chemistry,

Prague,

ABSTRACTS OF THE BCLA ANNUAL CLINICAL CONFERENCE - LONDON 1993

ALTERNATIVES TO HEMA L. Jones For many years, corneal oedema has been of fundamental concern to the contact lens practitioner. Since the early days of sealed glass haptics, it has been apparent that contact lenses may only be worn successfully (for any period of time) if the oxygen available to the cornea beneath the lens is adequate to facilitate normal (or near-normal) corneal physiology. The production of hydrophilic lenses in the early 1960s from hydroxyethylmethacrylate (HEMA), and their subsequent commercial availability in the early 1970s, brought about a great resurgence in the field of contact lens practice. Their ease of fitting, longer wearing times and ease of adaptation soon resulted in rapid market growth. However, it was soon realised that even these lenses were not without their disadvantages. Their durability was significantly less than polymethylmethacrylate (PMMA) lenses, the required cleaning procedures were much more involved than initially envisaged, and complications such as giant papillary conjunctivitis and neovascularisafion soon sent manufacturers back to the drawing board. Practitioners have a duty to their patients to minimise the potential complications associated with contact lenses. One of the best ways of ensuring this is to provide patients with lenses which give the cornea as near-normal oxygenation as possible. It is therefore quite surprising to find that most hydrogel lenses currently being fitted are still of the original polyHEMA material developed in the early 1970s. For many years, researchers have attempted to establish the level of oxygen required at the anterior corneal surface to prevent any detectable oedematous response - the critical oxygen requirement (COR). The criteria and experimental techniques used to establish the COR have differed markedly and provided clinicians with a variety of conflicting information, with the most widely quoted figure available today being approximately 10%. The manner in which this level of oxygenation is provided to the cornea depends upon the transmissibility (Dk/t) of the material concerned. The most widely agreed figure for the minimum acceptable transmissibility is 24.1 × 10-9 units for daily wear and 87.0 × 10-9 during overnight or extended wear. The use of Dk/t values by contact lens companies to indicate lens performance may be misleading, due to a lack of standardisation. The materials are often quoted as having inflated Dk values and the thickness values used are usually quoted at a given centre thickness. While this provides useful comparative data between lenses, it provides little useful information about individual lens performance, particularly in the periphery, which becomes very important with high negative lenses. If the typical oxygen performance of a 38% HEMA ultrathin design and a standard thickness 70% lens is compared, it can be shown that the ultrathin lens affords reasonable oxygen delivery centrally, but exhibits very poor oxygen performance

in the periphery. If oxygenation was the only concern when fitting patients with soft lenses, then all patients would be fitted with high water content lenses. Indeed, high water content lenses have other advantages, particularly with respect to long-term comfort and handling. However, such lenses also have significant disadvantages, particularly concerning their durability, reproducibility, cost of care regimen, deposition and discolouration. In an attempt to overcome these problems, practitioners and manufacturers have begun to use hydrophilic lenses which are regularly replaced, hopefully before they become damaged, either physically or by deposits. Such systems may either use currently available hydrophflic lenses which are periodically replaced (planned or frequent replacement systems (FRS)) or may use one of the newer 'disposable' lenses. The replacement schedule for FRS systems tends to be decided upon by the practitioner concerned and tailored specifically to the needs of the patient, whereas the schedule for disposable systems is dictated by the manufacturer. Disposable lenses may be viewed as being the ultimate example of FRS. Behind the idea of disposability is the aim that such lenses will realise the following ideals: • The use of higher water content materials will reduce oedematous complications. • Poor durability is overcome as the lenses will be replaced before their useful life is over. • New manufacturing techniques using moulding technology will prevent reproducibility problems. • Visual performance and comfort will remain high as the patient is always wearing a 'fresh, clean lens'. • Grossly deposited and discoloured lenses are avoided, as they are discarded before significant spoilation can occur. This should reduce complications produced by using 'dirty lenses', including both inflammatory (e.g. giant papillary conjunctivitis) and infective (e.g. keratitis) complications. • Lens maintenance will be reduced to a minimum, as lenses will require little (if any) cleaning, due to their short duration of use. This should increase patient compliance. • Patient loyalty will be improved through an increased number of practice visits, thereby increasing practice profitability. The obvious question is 'Do frequently replaced lenses realise these ideals?'. These points will be addressed by this paper.

Address for Correspondence 38 Greenholm Rd, Eltham, London SE9 1UH.

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ABSTRACTS O F T H E BCLA ANNUAL CLINICAL CONFERENCE - LONDON 1993

PRESBYOPIC CONTACT LENS CORRECTION: INFLUENCE OF OCULAR FACTORS M. Guillon The fitting of presbyopic patients with contact lenses is still limited in success, despite the vast number of alternative modalities currently available which include monovision, mug tifocal simultaneous vision or bifocal alternating vision. Several factors contribute to the low usage of contact lenses to correct presbyopia, in particular: • Any contact lens correction compromises at least some aspect of vision. • Only limited consideration has been given to the influence of individual ocular factors when selecting a modality of correction. The current presentation will review the various ocular factors that should be considered when firing a presbyopic patient. It will consider the interaction between the contact lens and the ageing eye and find the most appropriate modality for the individual patient. The key ocular changes

associated with ageing will be reviewed in the context of the selection of contact lenses to correct presbyopia: • • • • • • • •

Accommodative power. Light transmission of the ocular media. Pupil characteristics. Retinal sensitivity. Visual performance. Anterior ocular segment topography. Corneal physiology. Tear characteristics.

In conclusion, general guidelines for a systematic approach to presbyopic contact lens correction will be given.

Address for Correspondence Contact Lens Research Consultants, 16 Heath Dr, London NW3 7SL.

RGP LENSES - WHAT'S HAPPENING? CM. Schnider The past 5 years in the contact lens industry have focused mainly on issues surrounding soft lenses - infections with extended wear, disposable lenses, frequent replacement programmes, and 'turn-your-brown-eyes-blue' products. However, the stalwart fans of rigid gas-permeable (RGP) lenses have continued their pursuit of perfection in lens selection, fitting and follow-up care. We will review various aspects of clinic performance related to RGP lenses.

Usage Rates • North America. • UK. • Australia. • Germany. • Japan.

Material Properties The chemist must design a lens material with a balance of bulk and surface properties, which will be easy to manufacture and biocompatible with the ocular surface. Its chemistry must leave it relatively inert with respect to chemicals that might be encountered in care systems, yet 'attractive' to the pre-ocular tear film. Properties which must be considered include:

Success Rates • Daily wear (CCLRU, Australia). • Extended wear (CCLRU, Australia). • Versus soft lenses (CCLRU, Australia). • Rigid versus soft (Form & Holden, Weiss, Johnson & Schnider). • Identifying long-term wearers (Sweeney, Australia).

• Manufacturing ease (affects product yields and modification ease). • Flexibility (governs design parameters, such as centre thickness, and affects visual performance on astigmatic eyes). • Memory or recovery from deformation (related to longterm stability of the lens, visual performance, and ease of verification). • Oxygen permeability (corresponds directly to ocular physiology and indirectly affects other characteristics). • Surface characteristics (can be governed by bulk properties of materials or by alteration of surface properties via treatments).

Complications • Relative risk (Stapleton, Dart & Minassian, UK). • Peripheral corneal complications (Andrasko; Schnider; Grohe & Lebwo, US).

Lens Design and Fitting The two primary goals of contact lens fitting are to achieve good vision and comfort. While visual performance is rarely an issue with RGP lenses, comfort has long been a stumbling block. Recent studies have investigated various aspects of improving initial comfort with rigid lenses: • • • • •

Lens diameter (Fonn, Canada). Peripheral curve design (Andrasko; Huber & Towle, US). Aspheric versus multicurve (Schnider, US). Edge shape and thickness (LaHood, Australia). Lens position (Sorbara, Canada).

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• Use of anaesthetics in fitting (Schnider & White, US).

RGP E W - Can it compete with refractive surgery? • Overview (materials, design and fitting, follow-up, complications). • Cost. • Convenience. • Safety. • Efficacy. Summary RGP lenses are very underused in many parts of the world, due largely to misunderstanding and apprehension on behalf of both patients and practitioners. Yet they offer advantages by way of cost, convenience and ocular health, and with the prudent use of extended wear options, may even offer patients a viable alternative to refractive surgery.

Address for Correspondence Pacific University, College of Optometry, Forest Grove, Oregon, USA.

A B f f I ' R A C I ~ O F T H E B C L A A N N U A L CLINICAL C O N F E R E N C E - L O N D O N 1993

POST-SURGICAL FITI'ING OF CONTACT LENSES E. MiUis The fitting of contact lenses after surgery is a specialised skill. The cornea is usually altered in shape and astigmatism is frequently a problem. In addition, the cornea may be compromised because of pathology, which was the original reason for surgery. Lens-related complications are more serious. The most common reasons for lens fitting are after: • Keratoplasty. • Cataract extraction. • Refractive surgery.

Post-keratoplastyfitting

piggy-back and Softperm lenses.

Aphakia The fitting of lenses for aphakia is less common since the advent of the intra-ocular lens (IOL) implant, but is still needed whenever IOLs are contraindicated. It is sometimes used to cope with post-operative astigmatism occurring after insertion of an IOL. Additionally, contact lenses are used in cases of paediatric aphakia. Fitting in aphakic patients may be complicated by the presence of surgically formed drainage blebs when a combined operation to treat glaucoma and to remove a cataract has been performed.

The aim is to improve vision. Therapeutic uses include:

Post-refractive surgery • Protection of graft epithelium. • Splinting and moulding. • Epithelial loss. Fitting lenses differs in the phakic and aphakic eye. Spherical, elliptical, parabolar and toric lenses may all be used as may gas permeable and soft lenses. The selection and fitring of the main types of lens will be discussed and, if time permits, the use of more advanced fitting techniques, such as

New techniques for treating refractive errors are now available, albeit still on trial. In the future, some of these patients may request contact lens correction for any residual error. The corneal topography has been altered and lens fitting will need to be considered in this light.

Address for Correspondence 78 Harley St, London W1N 1AE

FREQUENT LENS REPLACEMENT VERSUS LENS HYGIENE

J.H. Kersley The paper presented concerned an overall picture of lenses as affected by disposable lenses. Since the boom in soft contact lens wear, we have been asking for cheap frequently replaceable lenses for years. Finally we have them but we are unhappy. Disposable lenses did break the mould, but while altering soft contact lens concepts forever, they have introduced other problems. Although different materials, shapes and sizes are used, they are basically similar to any other soft contact lenses. However, they impose on us both administrative and ethical restrictions. The major breakthrough has been our ability to replace conventional lenses more frequently at a fraction of the cost. These cost reductions are borne both by the manufacturer and the practitioner, but should not result in short-cuts on either part. The organisation of paperwork devised by the manufacturers and carried through into practices has also contributed to keeping costs down. We must keep a clear head with the concepts of daily wear, flexible wear, extended wear, and particularly patient education. The latter is not possible unless we ourselves under-

stand it in detail, so that we can pass on the urgency and relevance of the minutiae of lens hygiene to our patients. The problem with gatherings such as the BCLA Congress is that such preaching as occurs is to the converted - the few. Most practitioners do not involve themselves in these events and rely on the daily press to present or misrepresent information to the public. Hygiene systems should be efficient but also need to be simple. An efficient but complicated system will be debased by misuse, while a less efficient but simple system may often fare better but only with proper instruction and follow-up. The development of own-label systems is to be deplored, as the plethora of names makes it difficult for the expert to give good advice and impossible for the amateur or the pharmacist. The current lens forms and the options for good hygiene were reviewed.

Address for Correspondence 143 Harley St, London W I N 1DJ.

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ABKFRACTSOFTHE BCLAANNUALCLINICALCONFERENCE- LONDON1993

OXYGEN PERMEABILITY- AN UPDATE I. Fatt a n d C.M. Ruben

The single most important advantage of hydrogel and rigid gas-permeable (RGP) contact lenses over the earlier polymethylmethacrylate (PMMA) lenses is oxygen diffusion through the lens from the air to the cornea. During development of hydrogel and RGP lenses over the past 20 to 30 years, the oxygen permeability (Dk) of the lens material has been widely discussed and advertised in the contact lens literature. This has been despite the lack of standard methods for measuring this quantity or of reference materials for standardising the measuring equipment being used. Measuring methods and standard reference samples have not been a problem for hydrogel materials because oxygen permeability is related to water content by a simple mathematical formula. K water content of a hydrogel is not known, it can be easily measured by a hand-held refractometer. RGP materials have been a far greater challenge. Permeability cannot be inferred from some easily measured property. Several methods for measuring permeability have been proposed but only one, the polarographic method, has reached the level of an internationally recognised standard procedure. The International Standards Organisation (ISO) has issued ISO Standard No. 9913, Optics and Optical Instruments - Contact Lenses - Determination of Oxygen Permeability and Transmissibility. Standard No. 9913 is applicable to both hydrogel and RGP materials. It calls for boundary layer and edge effect corrections. Standard No. 9913 offers HEMA 38% water content as a reference material for hydrogels, but there are no RGP reference materials. ISO Standard No. 9913 recommends measurement on a series of samples of different thicknesses of a given material. The plot of reciprocal measured transmissibility versus sample thickness is fitted to a straight line by the least squares regression method. The reciprocal of t h e slope of this line is permeability, free of boundary layer effects. Standard No. 9913 does not offer a procedure for statistical evaluation of the permeability as calculated from the reciprocal slope although such methods are known. Furthermore, when measured data are collected and analysed on a spreadsheet computer program, the standard deviation of the permeability is automatically displayed. A correction for edge effect that arises because of the finite diameter of the polarographic cathode is recommended by Standard No. 9913 and the method for making the correction is described. Standard No. 9913 makes no mention of RGP-reference materials. Recently a set of six RGP materials, each from a single lot and with Dk range from 14 to 159, has been deposited in US repositories. These samples are available at reasonable cost so that users of Dk-measuring equipment can compare their results with those from other laboratories who have made measurements on the reference materials. The first set of measurements on the reference materials

has been made in our laboratory in Berkeley, California. The data are now available and will be published as soon as possible. The Dk values at 35 ° C using the procedure of Standard No. 9913 with correction for boundary layer but not for edge effect are: Menicon SF-P, 159E-11 (+11E-11); Menicon Ex, 85E-11 (+1.4E-11); Quantum II, 128E-11 (_+9E-11); Equalens, 64E-11 (+_2.4E-11); Fluoroperm 30, 37E-11 (+_2.4E-11); and Polycon II, 14E-11 (+1.0E-11). The units of Dk are (cm2/sec) (ml Q / m l × mmHg); the numbers in parentheses are standard deviation. When corrected for edge effect, the Dk values become: Menicon SF-P, 126E-11 (_+6E-11); Menicon EX, 64E-11 (+1.3E-11); Quantum II, 99E-11 (+7E-11); Equalens, 48E-11 (+0.5E-11); Fluoroperm 30, 28E-11 (+1.2E-11); and Polycon II, 10E-11 (_+0.5E-11). The Dk values uncorrected for edge effect have standard deviations that range from 2% to 7% of the Dk value. When corrected for edge effect, the standard deviations are somewhat smaller. Statistical theory states that the difference between two Dk values will have a standard deviation that is the square root of the sum of the squares of each standard deviation. The two pairs of materials we wish to compare are Menicon SF-P and Quantum II, and Menicon EX and Equalens. The difference in Dk between Menicon SF-P and Quantum II (both with and without edge-effect correction) is more than the square root of the sum of the squares of each standard deviation, so that we can say with at least 95% confidence that Dk of Menicon SF-P is greater than that of Quantum II. We can also say with 95% confidence that Menicon EX has a higher Dk than Equalens. A permeability study on the same RGP materials as in the reference material repositories but not from a repository has been made by the gas-to-gas procedure in the laboratories of Polymer Technology Corporation, Wilmington, Massachusetts, USA. They report Dk values as Menicon SF-P, 105E-11; Menicon EX, 70E-11; Quantum II, 130E-11; Equalens, 65E-11; Fluoroperm 30, 41E-11; Polycon II, 12E-11. These results are gratifying because they show that two different laboratories using different methods on the same materials (but of different lots) can arrive at substantially the same Dk values. The ready availability of equipment for measuring Dk by an ISO standard procedure and the availability of reference materials should remove a great deal of uncertainty and confusion surrounding the Dk of RGP materials. These conclusions should not be construed to mean that when fitted to the eye, a lens of one material will perform better than another. Much more than Dk is involved in satisfactory performance of an RGP lens on a patient's eye.

Address for Correspondence 406 Boynton Ave, Berkeley, California 94707, USA.

ENDOTHELIAL RESPONSE TO CONTACT LENS WEAR D. Epstein

It is now well established that contact lenses cause substantial changes in the morphology of the corneal endothelinm after a few years of wear. It is, however, not clear whether these changes alter the functional reserve of the endothelial pump system, which in turn is responsible for maintaining corneal transparency. The significance of lens wear endothelial pathology will be discussed, and inferences will be made about the possible implications of this pathology for normal corneal

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function in the ageing contact lens wearer. Circumstantial evidence will be presented from other known causes of similar morphological changes in the endothelinm to support or refute different scenarios regarding the long-term significance of contact lens-induced endothelial pathology.

Address for Correspondence University Hospital, Uppsala, Sweden.

ABSTRACTSOF THE BCLAANNUALCLINICALCONFERENCE- LONDON1993 COMPLICATIONS LENSES

AND SYMPTOMS

IN DISPOSABLE

AND CONVENTIONAL

SOFt

DAILY WEAR

E.C. Poggio and M.B. Abelson In order to estimate the rates of occurrence of complications and symptoms for patients using disposable and conventional soft lenses, we conducted two historical cohort studies of a total of 4,387 myopic, cosmetic soft contact lens wearers. Data were abstracted from 1987-89 office records of selected eye care practitioners in the US and Denmark. In one study, the prevalence of complications for disposable extended wear lens users was not significantly different from the prevalence for conventional daily wear lens users. However it was significantly lower than the prevalence for conventional extended wear lens users. Also, disposable

extended wear users reported symptoms significantly less frequently at routine scheduled visits as compared to both conventional daily and conventional extended wear users. In the second study, the prevalence of complications and the frequency of reporting symptoms at routine scheduled visits were both found to be significantly lower for disposable daily wear lens users than for conventional daily wear lens users.

Address for Correspondence Abt Associates, Cambridge, Massachusetts 02138, USA.

POSTER PRESENTATIONS

1. Physical Properties and Ocular Retention of W e t t i n g Solutions

V.J. Franklin, U. Singh-Gill, P. Sariri, and B.J. Tighe This poster discusses the properties of wetting capability, pH, viscosity, and tonicity of currently available hard lens wetting solutions. It shows how these have changed over the last decade, and how the properties of these solutions affect their retention in the eye in relation to models for tear film stability.

also by computerised video cornea topography. Rigid gas-permeable contact lenses were fitted with base curves steeper than central corneal radii. Measurements were taken immediately after removal of contact lenses and again some time later. It is postulated that the orthokeratology effect is greater in eyes in which radial keratotomy was performed than in normal eyes.

Address for Correspondence PO Box 3868, Jerusalem, Israel.

Address for Correspondence Speciality Materials Research Group, Aston University, Aston Triangle, Birmingham, UK.

4. Observations of a High W a t e r C o n t e n t Elliptical Toric L e n s

J. Stevenson 2. T e a r Deposition on 'Spoilation-Resistant' M a t e r i a l s . A Preliminary Study

U. Singh-Gill, V.J. Franklin, L. Jones, P. Sariri, and B.J. Tighe At the beginning of the decade, Montague Ruben, an eminent authority on contact lens wear, wrote: q'he manufacturers must, therefore, face the challenging problem of bringing new or modified soft lens material to avoid or overcome the problem of soft lens spoilation'. The succeeding years have, unfortunately, not produced a single commercially available material that answers this challenge in any absolute sense. There are, however, several materials which are claimed, or believed, to resist spoilation more effectively than polyhydroxyethylmethacrylate (polyHEMA). This poster compares the relative resistance to ocular deposition processes of several materials, both new and well established, using in vivo and in vitro spoilation methods with a comprehensive range of analytical techniques. This will include the first presentation of results obtained with a new gas plasma probe technique.

Address for Correspondence Speciality Materials Research Group, Aston University, Aston Triangle, Birmingham, UK. 3. The Effect of Contact Lenses on Corneal Curvature After R a d i a l K e r a t o t o m y ( P r e l i m i n a r y Report)

L. Rose and H. Zauberman The purpose of this paper is to assess the extent of modifying corneal curvature by contact lenses following radial keratotomy for correction of myopia, with resultant overcorrection. Corneal curvatures were measured by keratometry and

Following a general realisation of the oxygenation needs of the cornea, there has been a trend towards higher water content soft contact lenses. However most of the commonly fitted soft toric lenses are made in low water content materials. Combined with thick lens designs, most soft toric lenses fall far short of corneal physiological requirements. 1 WCE toric has been developed to meet these demands. It is a 60% water content dynamically stabilised lens with an elliptical back surface. Elliptical designs have been successful with both rigid lenses 2 and hydrophflic lenses. 3 WCE Toric is the first toric lens with an elliptical back surface design. Case records will be used to illustrate WCE Toric performance over a 3-month period - showing patient acceptance, ocular physiology and predictability of stabilisation.

Address for Correspondence 122 Stifling Crescent, Hedge End, Southampton SO3 4SJ.

References i Holden, B.A. and Mertz, G.W. Critical oxygen levels to avoid corneal oedema for daily and extended wear contact lenses. Incest. Ophthalmol. Vis. Sci., 25, 1161-1167 (1984). 2 Killpartrick, M.R. The Persecon E. Optician, Feb 4, (1983). a Killpartfick, M.IL, Achatz, M., and Markus, W. Weicon 38 elliptical soft lenses - design philosophy and multicentre field study results. Optician, Dec 3 (1982). 5. Lysozyme a n d G r o u p IV L e n s e s . Location, Mobility a n d Biological Activity

P. Sariri, V.J. Franklin, S. Singh-Gill, and BJ. Tighe A number of studies have indicated that protein accumulation is highly material dependent. In particular, high water content ionic (Group IV) lenses deposit to a greater degree than

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ABSTRACTSOFTHE BCLAANNUALCLINICALCONFERENCE- LONDON1993 lenses fabricated from non-ionic materials. The penetration of proteins into the lens matrix is as important as how much protein deposits as a surface film. The mobility and biological activity of the protein is another important aspect of their behaviour. Lysozyme, which is a small positively charged and relatively comformationally stable protein, is known to penetrate the tens matrix of Group IV lenses. This poster assembles information from techniques that enable, for the first time, the location (surface or bulk) and 'intactness' (biological activity) of lysozyme on lenses to be monitored.

Address for Correspondence 122 Stifling Crescent, Hedge End, Southampton SO3 4SJ. 6. The Use of the EyeSys Keratoscope in Hospital a n d

General Contact Lens Practice C.L.K. Astin, N. Burnett-Hodd, and D. Rustin Detailed information about the topography of the cornea is becoming increasingly valuable both for diagnosis of ocular conditions, baseline measurement and monitoring of the corneal response to surgical treatment, or contact lens fitting. The EyeSys video keratoscope is a good example of the most up-to-date developments in keratoscopy and its description of topography in the form of colour-mapping facilitates the understanding of corneal contour changes. The linked computer can be used to store and compare a huge amount of corneal topographical data. This paper describes its uses, advantages and disadvantages and gives several illustrative case descriptions. These include keratoconus, corneal transplant, excimer laser treatment, and post-operative corneal distortion, in addition to ametropes being fitted with contact lenses or demonstrating unusual corneal contours.

Address for Correspondence 9 Courtfields, Harpenden, Herts AL5 5RX. 7. Correcting the Disfigured Eye in the Prosthetic Hydrogel Contact Lens W.A. Dishman and C. Barron Traditionally scleral shells and hard and rigid contact lenses have been used to correct both the cosmetic appearance and visual function of the disfigured eye. More recently, hydrogel lenses have become more popular for these purposes. They have grown in popularity with both patients and practitioners because of their inherent stability on the eye without loss of comfort. Fitting procedures are also relatively simple compared to other prosthetic lenses. Improvements in tinted and coloured lens technology have expanded the range of products available to allow more patients with a wider range of abnormalities to be fitted with hydrogel prosthetic lenses to produce a very pleasing cosmetic effect and appropriate visual correction if necessary. Two cases will be presented which illustrate the use of hydrogel prosthetic lenses. Case one describes a 27-year-old

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Hispanic female with a non-sighted eye secondary to a failed corneal graft. Case two describes a 42-year-old AfricanAmerican female with a partially sighted eye secondary to extraction of the crystalline lens and resulting iris trauma. In both cases, the fitting procedures, lens design, and follow-up care will be presented.

Address for Correspondence Wessley - Jessen Corporation, 400 West Superior, Chicago IL 60610-3496, USA.

8. Measuring Lid Margin and Palpebral Conjunctival Sensitivity D.P. McGowan A test group of 30 carefully selected subjects was used to measure lid margin and palpebral conjunctival sensitivity. A Cochet-Bonnet aesthesiometer held in a Bleshoy applicator was used, mounted on a slit-lamp, for a magflified binocular view allowing easy movement in all directions. The aethesiometer was calibrated using a sensitive pan-balance. Touch sensitivity was measured using a threshold method with repeated readings. Particular areas of investigation included a comparison of sensitivity of upper and lower lid, central and lateral lid, the anterior dry epithelium, marginal angle and palpebral conjunctiva, as well as their relationship to corneal sensitivity and innervation. The investigation found that the lid-touch threshold varied greatly between individuals. It was also shown that no significant variation existed between the upper and lower lids and central and lateral lids. However, there was a significant variation in sensitivity between the three types of conjunctival tissue tested. The marginal angle was significantly most sensitive with a small decline in sensitivity in the anterior dry epithelium and a dramatic decline in the palpebral conjucfiva. These tissues also exhibited significant variation with respect to their position in the lids. The average lid margin sensitivity was found to be 12 times less sensitive than published data on corneal sensitivity. It was concluded that the main factor governing sensitivity is the level of innervation of that particular tissue and this relates to the distribution of free nerve endings found within the margins, rather than the complex nerve endings also found here. The findings also implicate that lid margin sensitivity plays little role in sensory adaptation to contact lenses as the cornea is 12 times more sensitive. The main criticism of the method and equipment used was that the Cochet-Bonnet aesthesiometer has a linear scale, whereas the relationship of filament length to pressure exerted was found to be logarithmic. It was concluded that an instrument with a logarithmic scale based on its calibration would be a great improvement.

Address for Correspondence 10 Croft Edge, Oxton, Birkenhead, Wirral, Merseyside L43 5UD.