Abstracts of the BCLA Annual Clinical Conference - London 1995

Journalofthe British ContactLensAssociation,Vol.18, No. 4, pp 129-142,1995 Printed in GreatBritain

© 1995BritishContactLensAssociation

Abstractsof the BCLAAnnual ClinicalC0nference- London1995 ASTIGMATISM CORRECTION WITH CONTACT LENSES C. Snyder Choice of contact lens material and design for the correction of astigmatism is individualised - a function of patient, ocular and refractive factors. In addition, the precision of optical correction may have a significant impact on visual performance and, therefore, ultimately on patient success with lens wear. The following issues related to clinical decisions in correcting astigmatism were reviewed. • The precision and completeness of astigmatic correction and

its relationship to visual comfort and visual performance. • The clinical challenge of choosing the appropriate contact lens type and design for astigmatic patients. • Empirical versus diagnostic fitting of toric hydrogel contact lenses. Address for Correspondence c/o CCLRU/CRCEtU', 22-32 King Street, Randwick, NSW 2031, Australia.

MEIBOMIAN GLAND DYSFUNCTION J. R. Larke Contact lens induced meibomian gland dysfunction affects approximately 10% of contact lens wearers. The aetiology, pathogenesis, differential diagnosis and treatment of this condition were described and illustrated.

Address for Correspondence Department of Optometry, UWIST, PO Box 905, Cardiff CF1 3XF, UK.

EXTENDED WEAR OF CONTACT LENSES - A VIABLE ALTERNATIVE TO REFRACTIVE SURGERY D. F o n n The presentation included a review of the physiological requirements for extended wear and the success of this modality when using soft and RGP lenses compared with current refractive surgical techniques. The aetiology of extended wear complications and how it may be possible

to eliminate these with highly permeable hydrogels were discussed.

Address for Correspondence School of Optometry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.

CONTACT LENS-RELATED KERATOPATHY O. D. Schein Corneal complications associated with .contact lens wear range from the transient and clinically insignificant to permanent visual loss from corneal scarring. Acute and chronic hypoxia underlie many of the adverse reactions including epithelial oedema, tight lens syndrome and neovascularisafion. Solution-related toxicity is common, doserelated and easily reversible. True solution allergies have become increasingly rare, although they may occasionally account for serious ocular surface manifestations such as superior limbic kerafitis. Corneal ulceration and stromal

keratitis resuk primarily from bacterial infection. However, both other organisms and non-infectious aetiologies must be considered. Strategies to reduce the incidence of contact lensrelated complications and to minimise their clinical impact, should they occur, were addressed. Address for Correspondence Dana Center for Preventive Ophthalmology, 116 Wilmer Building, Johns Hopkins Hospital, 600 North WoKe Street, Baltimore, MD 21287-9019, USA.

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ABSTRACI~ OFTHE BCLAANNUALCLINICALCONFERENCE -

LONDON1995

P R E S C R I B I N G C O N T A C T L E N S E S FOR SPORT

N. Efron With modern contact lens technology, there is no reason why ametropic sportspersons cannot compete with emmetropic opponents on an equal basis. The two major factors to be considered when prescribing contact lenses specifically for sport are (a) the nature of the sport and the demands it places on the eye and body (body contact, extreme movement, air flow, G-forces, vision), an (b) environmental factors (cold, altitude, dirt, aquatic, subaquatic, UV light). Careful attention must be given to contact lens fitting for endurance and combination sports. The special visual needs of presbyopic sportspersons and referees were assessed and useful hints for coaching staff offered. The issue of compliance can pose unique problems in the ophthalmic management of contact lens-wearing sportspersons. From an analysis of 92 different

sports, the following general conclusions were reached: (a) the lens of first choice in most instances is a regularly replaced (or disposable) soft lens of large diameter (/> 14.50mm), low water content (<~ 50%), and 'standard' centre thickness (/> O.07mm), (b) rigid lenses can be worn for some sports but are rarely the lens of first choice, (c) contact lenses are contraindicated (spectacles being preferred) for sports requiring critical static visual acuity (darts, archery, shooting), and (d) presbyopia should not be corrected with any form of monovision or bifocal contact lenses (a near spectacle over-correction is preferred).

Address for Correspondence UMIST, PO Box 88, Manchester M60 1QD, UK

PERMEABILITY, P U M P S A N D R E T I N A L PROTECTION R. M. Hill Explored here is just a part of the growing sophistication contact lens practice continues to acquire, including emerging oxygen strategies for achieving the most balanced (physiological and physical) outcome for each patient, and the growing role of contact lenses as protective devices. These and other advances assure a useful future for the

contact lens as an ophthalmic option well into the 21st century.

Address for Correspondence Ohio State University, College of Optometry, 338 West Tenth Avenue, Columbus, OH 43210-1240, USA.

H O W S U C C E S S F U L I S C O N T A C T L E N S W E A R A N D CAN I T B E IMPROVED?

D. Fonn The fact that approximately 10% of the North American population wear contact lenses supports the perception that this form of refractive correction is highly successful. However, some reports have indicated that a high percentage of patients discontinue lens wear each year, in spite of the fact that both lenses and care systems have improved significantly in the last few years. Contact lens manufacturers have reported tittle overall growth in the contact lens market which would support the observation that many patients discontinue

contact lens wear. This presentation described studies which have quantified abandonment and established reasons for soft and rigid lens wear discontinuation. Methods to improve the success and continuance of lens wear were presented.

Address for Correspondence School of Optometry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.

T H E B E N E F I T S O F R E G U L A R , P L A N N E D R E L A C E M E N T O F R I G I D GAS P E R M E A B L E CONTACT L E N S E S FOR DAILY W E A R

C Woods andN. Efron A study was conducted to investigate the benefits of planned replacement of rigid gas permeable (RGP) contact lenses. The study was a single-centre (n=42 subjects), doublemasked, randomised, 12-month investigation, involving two subject groups. Both groups wore Quantum II lenses (Dk 130) on a daily wear basis; subjects in group I replaced lenses every 3 months, whereas those in group II were not scheduled to replace lenses. All subjects wer~ existing RGP contact lens wearers with no contact lens-induced pathology (>grade 1). The ocular responses to lens wear were monitored. Compared with group II, group I patients displayed significantly less corneal staining (P=0.0035) and fewer lens deposits (P=0.0211). No significant differences were found between the two groups with respect to lens

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surface scratching, comfort, bulbar hyperaemia or tarsal changes. This study has shown that the regular replacement of rigid lenses reduces the level of corneal staining, which, in theory, should relate to a reduced risk of corneal infection. It is curious that, although the regular replacement of rigid lenses gave rise to fewer deposits, there was no significant difference in lens comfort between the two groups. The results of this study have demonstrated some benefits of regular replacement of RGP lenses.

Address for Correspondence Department of Optometry and Vision Sciences, UMIST, PO Box 88, Manchester M60 1QD, UK.

ABSTRACrSOFTHEBCLAANNUALCLINICALCONFERENCE- LONDON1995 EVALUATION OF THE CLINICAL PERFORMANCE CONTACT LENS

OF A DAILY-WEAR/DAILY-DISPOSABLE SOFT

S. Morgan and N. Efron A single-centre clinical trial was conducted to evaluate the safety and efficacy of a dally-wear/daily-disposable soft contact lens (DW-DD-SCL). Twenty-nine adapted soft contact lens wearers were fitted with the Premier TM DW-DD-SCL (Award plc) and ongoing progress was monitored in terms of ocular response and lens performance. These lenses are manufactured fl'om a non-ionic copolymer (HEMA vinyl pyrrolidone; Filcon 3a) using integrated cast moulding. The lenses were available in the following nominal variables: 14.4mm diameter, 8.7mm base curve, 0.14mm centre thickness (-3.00D lens) and 73% water content. The oxygen transmissibility (Dk/L) of a -2.50D lens (measured using the standard polarographic technique) averaged over the central 6ram zone was 20 × 10 -9 (cm/s) (ml O J m l × mm Hg); this value is superior to the Dk/L of most disposable lenses currently available [typically in the range 13 - 15 × 10 -9 (cm/sec) (ml O J m l × m m Hg)]. The following data were

obtained at the 1-month visit: mean comfort was graded as 4.4-+0.6 (on a scale from 0 to 5 [5 meaning 'cannot feel the lens']); mean vision (logMAR) at 90% contrast was 0.02+-0.10; 40% of lenses displayed slight temporal displacement; and no abnormal tissue responses were observed upon biomicroscopic observation. If costs were equal, 93% of patients would continue with these lenses in preference to their previous lenses. Overall, lens performance and ocular response to DW-DD-SCLs were satisfactory and the concept of dally disposability was well received by patients. Practitioners should consider DW-DD-SCLs to be a valuable alternative to current modalities of lens wear.

Address for Correspondence Eurolens Research, Department of Optometry and Vision Sciences, UMIST, Manchester M60 1QD, UK.

THE USE OF PROCLF.AR BIOMIMETIC MATERIAL IN HYPERTHIN soFr

LENS DESIGNS

M. Port The objects of the experiments were: (1) To establish if the 60% Proclear material could be used for hyperthin lenses (tc 0.035ram) so that the transmissibility could be significantly improved over the current lens design (tc 0.07mm). (2) To establish if water content could be maintained with the 0.035mm tc and corneal desiccation staining avoided. (3) To establish the comfort with hyperthin designs. Three separate studies were conducted, each with 8-10 subjects. The first was a double-masked dally-wear trial where plano lenses of Proclear and Igel 58 (control) were made to the same design and had a tc of 0.035mm hydrated. Lenses were worn for 4 hours. The Proclear lenses maintained hydration to within 1% of the original values whereas the Igel lenses lost 9% of their water. The difference in relative dehydration was statistically significant (/%0.0001). The front surface drying time (FSDT) of the Proclear was 20sec and the Igel was half of this figure. Tear film acceptability was better

with the Proclear material. Lens comfort was strongly correlated with hydration and FSDT. In the second and third studied, the hyperthin lenses were worn overnight for 8h. In one study the lenses were powered -3.00DS and in the other powered plano. Central corneal swelling overnight was 5.0% with the plano lenses and 2.6% with the control eyes (no lens). Details of other clinical signs are given. In both studies lens dehydration of Proclear (1-2%) was the same as that seen in daily wear. The fluorescein staining patterns (corneal epithelium) produced from the studies were particularly interesting and may provide some additional evidence on the causes of SEALs.

Address for Correspondence 28 Alexandra Grove, North Finchley, London N12 8HG, U K

A R E C O N T A C T L E N S - A S S O C I A T E D PROBLEMS A P R I M A R Y M O T I V A T I O N A L F A C T O R F O R PRK PATIENTS?

G. Whittaker An analysis of 100 consecutive patients who have undergone PRK demonstrates the importance of contact lens nontolerance as a major factor in electing to have excimer laser treatment. At the time of making the decision to have PRK 41% of patients were not wearing contact lenses at all. Some of these individuals were intolerant to contact lenses and others had never tried contact lenses. The reasons for intolerance were discussed as were the motivational factors for those who had never worn contact lenses. Of the 59% still wearing contact lenses at the time the decision to have PRK was made, a substantial number (one third) had reduced wearing time.

Among other factors that influenced their decision were watersports (60/0), inconvenience of contact lens wear (19%) and adverse contact lens-related clinical signs (3%). A full breakdown of the contact lens-related reasons for electing to undergo PRK was given, emphasising the importance of the contact lens practitioner's role in the preselection of patients for PRK.

Address for Correspondence New Image Laser Eye Centre, 80 George Street, Edinburgh EH2 3BU, UIC

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CORNEAL BIOLOGY - THE MISSING LINK IN CONTACT LENS PRACTICE J. R. Larke Much is known of the gaseous transmission properties of contact lens materials and the short-term oxygen debt that they generate. However, the response of corneal metabolism to lens wear is wholly unknown. A technique for measuring in vivo corneal-derived lactate, described at a meeting of the Association 2 years ago was reviewed and the initial evidence

of metabolic adaptation to contact lens wear described.

Address for Correspondence Department of Optometry, UWlST, PO Box 905, Cardiff CP1 3XF, U K

THE INFLUENCE OF OXYGEN TRANSMISSIBILITY ON THE LIMBAL VASCULAR RESPONSE DURING CONTACT LENS W E A R E. Papas Soft contact lens wear is accompanied by limbal redness owing to engorgement and filling of limbal capillaries. In order to study the influence of lens oxygen transmissibility on this phenomenon and series of clinical studies were carried out in which up to 10 subjects wore a series of lenses of varying transmissibility (n=7), for an 8-h period. Limbal redness (LR) was graded from none (grade 0) to severe (grade 4) in each circumlimbal quadrant at baseline and at 8tl post-insertion. Similar observations were made with no lens wear over 8-h periods of both open and closed eye. The mean amount of induced LR observed was highly

correlated with the oxygen transmissibility of the contact lens in the region of the limbus, the line of best fit being of the form

ALR = (Dk/L + 7.4)/16.2 (R = 0.95) These results suggest that oxygen transmissibility is a major contributing factor in contact lens-induced limbal redness.

Address for Correspondence CCLRU, School of Optometry, UNSW, NSW 2052, Australia.

CONTACT LENS MANAGEMENT FOLLOWING PHOTOREFRACTIVE KERATECTOMY (PRK) J. Kersley, K. Edwards and D. A. Hough While corneal modelling can design the back surface geometry of contact lenses so that there will be a good physical relationship between the lens and the corneal surface, it can not take into account the influence of lens movement. On normal corneas lens mass and lid tension also play a part in the dynamics of lens fit. Where contact lens fitting is necessary following refractive surgery, fitting is Complicated by the unusual relationship between the relatively fiat central cornea and the steeper midperiphery. The effects of decentration and the potential for

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lens movement are far less predictable in these abnormal topographic environments. This paper demonstrates the problems encountered in fitting post-surgical eyes and endeavours to highlight the key variables that opfimise the static and dynamic fitting characteristics.

Address for Correspondence 143 Harley Street, London W I N 1DJ, UtC

ABSTRACTS OF T H E BCLA ANNUAL CLINICAL CONFERENCE - LONDON 1995

GAS P E R M E A B L E CONTACT LENSES IN THE VISUAL CORRECTION OF K E R A T O C O N U S J. Jackson, R. Gilmore, D. Fraser and T. Canavan Gas permeable contact lenses are routinely used in the optical correction of mild to moderate keratoconus. 1 In advanced cases, estimated to be in the order of 20% of keratoconic patients, corneal opacificafion and contact lens intolerance render keratoplasty inevitable. 2 In this study we reviewed case records of 55 keratoconic patients (18 females/37 males, mean age 27 years) referred to a regional hospital-based contact lens unit over a 5-year period. Forty-four of the patients had bilateral disease. Mean central corneal curvatures ranged from 4.50 to 8.40ram. Of the 55 patients assessed, 50 were subsequently fitted with contact lenses by an experienced contact lens practitioner. Forty-three patients continue to wear contact lenses and have done so for at least 1 year. Five patients initially opted for spectacles in preference to contact lenses and a further five reverted to spectacles because of contact lens intolerance or inconvenience. Only two eyes proceeded to corneal grafting during the course of the study. Subjective findings on the relative merits of contact lenses in the optical correction of keratoconus were recorded through the use of a patient questionnaire. Thirty-seven of 43 contact lens wearers who remained under review at the hospital contact lens clinic, 1 to 5 years after having been fitted, completed questionnaires. Results indicated that 68% of wearers used contact lenses for in excess of 7h per day. Fiftynine per cent judged contact lenses to be comfortable

although occasional episodes of acute discomfort were a significant inconvenience. Sixty-eight per cent of contact lens wearers achieved a contact lens corrected acuity of 6/9 or better. This contrasted sharply with 36% of patients who achieved a similar level of vision through spectacles. The proportions of patients failing to achieve a corrected acuity of at least 6/36 with contact lenses and spectacles were 7% and 32% respectively. Results indicate that although acute episodes of contact lens intolerance, lens loss, breakage and allergic type reactions are all to be expected in keratoconic contact lens wearers, the vast majority of wearers are adequately managed through the use of gas permeable lenses. REFERENCES

1 Lass, J.H., Lembach, R.G., et al. Clinical management of keratoconus, Ophthalmology, 97, 433-445 (1990). 2 Tuft, S.J., Moodaley, L.C., et al. Prognostic factors for the progression of keratoconus. Ophthalmology, 101, 439-447 (1994).

Address for Correspondence Contact Lens Unit, Department of Ophthalmology, Royal Victoria Hospital, Grosvenor Road, Belfast BT12 6BA, Northern Ireland.

THE INTER-LABORATORY PRECISION OF POWER MEASUREMENT OF TORIC S O F t LENSES USING THE MOIRE DEFLECTOMETER D. A. Hough, A. Livnat and K. Eliezer A previous international inter-laboratory ring test has shown that the power measurement of toric soft lenses using traditional methods is difficult and imprecise. The purpose of this study was to determine the interlaboratory reproducibility of the measurement of powers and axis direction of toric soft lenses using the Moire deflectometer, a new instrument which uses the Moire effect and image processing software to objectively determine powers and optical quality. A representative range of commercially available toric soft lenses in three water contents were measured at five international centres, using a protocol consistent with internationally agreed ([SO) guidelines. The results of the ring test were statistically analysed according to the procedures set out by ISO. The results show that the use of the Moire deflectometer provides a significant improvement in the precision of such measurements when compared with

traditional methods. The validity of the study is assessed using ISO criteria. The presentation briefy introduced the technology of the Moire deflectometer and discussed the implications of the availability of this new technology for practitioners and lens manufacturers. The use of ring test data to establish tolerances which are then incorporated into lens specification standards within a regulated European marketplace was discussed. This is considered a contentious area by many practitioners. Other potential applications of the Moire deflectometer to contact lens measurements were briefly reviewed.

Address for Correspondence 4 Otter Way, Eaton Socon, St Neots, Huntingdon, Cambs PE19 3LB, UK.

A R E N ' T Y O U S I C C A D R Y EYE?

C. Snyder The 'dry-eye-ocular surface disease' coinplex with its variety of causes and clinical presentations makes it perhaps the most ill-defined of all ocular disorders. Consequently, a single test or treatment is unlikely to be the key to diagnosis and management. Even so, it is surprising with all of the research that has been done on the tears and the pre-ocular tear film that there is little consensus as to the relative importance of which clinical tests should be performed, procedures for administration, and how the results should be integrated for diagnosis and management.

As the quest for the best battery of clinical tests continues, the practitioner must make sense of what is known and use what is available to find guidance for today's patient management. Controversies surrounding the administration, interpretation, and usefulness of clinical testing of the tears and tear film were presented.

Address for Correspondence c/o CCLRU/CRCER;, 22-32 King Street, Randwick, NSW 2031, Australia.

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ANALYSIS OF THE TEAR FILM BY INFRARED THERMOGRAPHY

P. Morgan, A. Tullo and N. Efron Theory suggests that infrared radiation between 8-13~tm which leaves the eye emanates mainly from the tear film. This paper reports on the study of 36 dry eye patients and 27 age and sex-matched controls using an infrared detection apparatus; this was undertaken to evaluate non-contact thermal imaging systems in tear film assessment. Ocular temperature was shown to be greater in the dry eye group (32.28-+0.69°C compared with 31.94-+0.54°C; P<0.01). Investigation into the temperature variation across the ocular surface revealed a greater difference in temperature between the centre of the cornea and the limbus in the dry eye group (0.77_+0.28°C compared with 0.43_+0.19°C; P<0.01). This

variable was shown to be greater in patients with either a fast tear break-up time or a low Schirmer test result. It was demonstrated that dry eyes cooled more rapidly than controls (0.88_+0.23°C compared with 0.21_+0.27°C over a 7-sec period; P<0.0001). These results have assisted in the generation of a qualitative model of ocular temperature, and suggest that assessment of this type may be used for the objective analysis of the tear film.

Address for Correspondence Eurolens Research, Department of Optometry and Vision Sciences, UMIST, Manchester M60 1QD, UIL

A COMPARISON OF TECHNIQUES FOR EVALUATING THE PHYSICAL PROPERTIES OF H U M A N

J. P. Craig, P. A. Simmons, A. Tomlinson and S. Patel The technique of osmolality determination for human tears is technically difficult. This study investigated a simpler and possible alternative technique of critical angle refractive index measurement. The basis and comparability of Abb6 and digital refractometry with osmometry were also investigated. Following initial comparison of the techniques with aqueous NaC1 (0.5-1.4%), three successive tear samples were obtained from each of 40 normal, non-contact lens wearing subjects, mean age 29-+22 years, for analysis by freezing-point depression nanolitre osmometry and digital refractometry. The Lactoplate TM immunoassay provided an estimate of tear protein. Osmolality and both refractive index measurements were highly correlated with concentration, and with each other, for the range of NaC1 concentrations tested. For 0.9% NaClaq the mean value of osmolality was 292.0mOsm/kg and refractive index was 1.33422 (Abb6) and 1.33419 (digital). For human tears osmolality was found to be 303.7_+22.gmOsm/kg, refractive index (digital) 1.33698_+0.00110 and lactoferrin level (Lactoplate TM) test 1.64_+0.47mg/ml. No statistically

significant correlation was obtained between either refractive index or lactoferrin level and osmolality, but refractive index and lactoferfin level were significantly correlated (R2=0.413, P<0.001). The study demonstrated that the digital refractometer was comparable with the Abb6 refractometer, but allowed for analysis of nanolitre samples of human tears. The high correlation of refractometry and osmolality for aqueous NaC1 indicated comparability of the techniques in this instance, but this does not apply to human tears. Unlike tear osmolality, tear refractive index is dependent to a greater extent upon composition, as is suggested by its correlation with lactoferrin level. Therefore, refractometry is not acceptable as a direct replacement for osmometry in the assessment of lacrimal function.

Address for Correspondence Department of Vision Sciences, Glasgow Caledonian University, Cowcaddens Road, Glasgow G4 0BA, UIC

I N T E R A C T I O N O F T E A R L I P I D S W I T H S O F T C O N T A C T LENSES

B. J. Tighe, V. Franklin, K. Evans, L. Jones and U. Singh-Gill The study of lipoidal species and their interaction with the surface and matrix of the soft contact lens materials is important for the development of spoilation resistant contact lenses and successful ocular prostheses. Lipids are highly reactive molecules which interact not only with the surface of a contact lens, but are also readily absorbed into the matrix of the lens. Once chemically converted these species are less readily desorbed from the lens mahfx and may provide a site for further deposition to occur. Individual patient tear lipid composition varies considerably and physical factors related

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to the lens edge effects and surface rugosity can also contribute to the deposition profiles obtained, in addition to the expected dependence upon the material lens chemistry. This profiles the types of lipoidal species involved and the penetration into the lens matrix in the course of closely controlled clinical studies.

Address for Correspondence Biomaterials Research Unit, Aston University, Aston Triangle, Birmingham B4 7ET, UtC

ABSTRACTSOFTHEBCLAANNUALCLINICALCONFERENCE- LONDON1995

THE E P I D E M I O L O G Y O F C O R N E A L U L C E R A T I O N D U R I N G C O N T A C T L E N S W E A R O. D. Schein Although the experience of individual practitioners may provide important clues, the systematic assessment of large cohorts of patients and the use of controls are required to assess accurately the rate and risk factors of contact lensrelated ulcerative keratitis. Over the past 5 years, a number of major relevant studies have been performed in the UK and the United States. Despite different methodologies and conduct at different at different times and places, these studies have been remarkably consistent in their principal findings. These findings include the magnitude of overnight wear as a risk factor and the relatively small contribution to risk of hygiene-related factors and physical lens type. The absolute risk of ulcerative kerafitis associated with the

use of soft contact lenses (disposable or conventional) overnight is approximately one case per 300 users per year and for strictly daily wear use only approximately one case per 2500 users per year. Although risk factors other than overnight wear exist and were discussed, recent evidence suggests that overnight wear explains 50 to 75% of contact lens-related ulcerative keratitis.

Address for Correspondence Dana Center for Preventive Ophthalmology, 116 Wilmer Building, Johns Hopkins Hospital, 600 North Wolfe Street, Baltimore, MD 21287-9019, USA.

T H E I N C I D E N C E O F C O N T A C T LENS-INDUCED KERATITIS IN S W E D E N A N D ITS RELATION TO LENS TYPE AND WEAR SCHEDULE

S.E. Nilsson and P. Montan In a 3-month prospective study, all cases of contact lensinduced keratitis (epithelial defects with an underlying infiltrate or ulcer) among cosmetic wearers in Sweden were collected and analysed for risk factors in relation to lens type and wear schedules. Every ophthalmologist in Sweden was invited to participate, and all responded. Viral cases were excluded. The number of lens wearers in Sweden subdivided by lens type and wear schedule was obtained in a parallel 3month study among 71% of the lens fitters, who counted all their wearers, recording lens types and wear schedule as well as revisit and replacement schedules. The annualised incidence per 10 000 wearers was 1.48 for daily wear (DW) of rigid gas permeable lenses, 2.16 for DW and 10.00 for extended wear (EW) of disposable soft lenses and 2.17 for DW and 13.33 for EW of conventional soft lenses. Thus, EW was associated with a significantly (P<0.01-0.001) higher (5-6 times) risk of keratitis than DW. There were no other significant differences between the incidence figures. The Swedish figures were approximately half as large as those

reported from the USA. Of the lesions, only 12% were located within the pupillary area and only 8% were corneal ulcers. Only three patients (12%) suffered a decrease in visual acuity: 2, 3 and 5 Snellen lines, respectively. Severe keratitis was significantly (P<0.01) more common among conventional soft lens wearers (all ulcers, all lesions within the pupillary area and all decrease in visual acuity) than among wearers of disposable lenses. In another study, all hospitalised (and more severe) cases of contact lens-induced keratitis in Sweden over a 3-year period were reviewed retrospectively. The results showed that in relation to such cases, daily wear of disposable lenses (0.16/10000 wearers) was associated with significantly (P<0.05-0.01) less risk than daily wear of other lens types.

Address for Correspondence Department of Ophthalmology, University of Hnktiping and St Erik's Eye Hospital, The Karolinska Institute, Stockholm, Sweden.

WHICH SOLUTIONS MAINTAIN THE EPITHELIAL SURFACE BETrER - HYDROGEN PEROXIDE OR BIGUANIDE?

G. Wilson In a clinical setting it is difficult to evaluate the effects of solutions on the corneal surface. Patients respond to the immediate sensation of a solution and lens when placed on the eye, and find it difficult to judge the effects of the solution itself over a long period of time. A laboratory method of looking at the amount of light scattered by corneal surface cells is useful for examining the effects of different solutions held in contact with the epithelial surface (Bachman and Wilson, Invest. Ophthalmol. Vis. Sci., 2 6 (11), 116-121, 1985). We tested two commercially available solutions containing the preservative bignanide, and three solutions containing hydrogen peroxide. The solutions tested were: ReNu MultiPurpose Solution and ReNu Saline (Bausch and Lomb), and SoftWear Saline, neutralised AOSept and Solocare (Ciba Vision). The solutions were compared with each other, and with Basic Tear Solution (BTS), which has been shown to maintain the surface of the epithelium for up to 150min. Each of the seven solutions was tested five times on excised rabbit

corneas. The results showed that the above solutions containing biguanide or hydrogen peroxide can be held safely in contact with the epithelial surface for up to 150rain. This period far exceeds the time they d e likely to be ion contact with the human eye when used with contact lenses. AOSept and ReNu Saline performed better than other solutions (ANOVA P<0.01) AOSept performed significantly better than BTS (P<0.01), and ReNu Saline was not significantly different (P>0.05) It is concluded that both hydrogen peroxide and biguanide in the above solutions are benign, and can remain in contact with the corneal surface for longer times than are likely in contact lens wear.

Address for Correspondence Department of Physiological Optics, The University of Alabama at Birmingham, Worrell Building, 924 South 18th Street, Birmingham, Alabama 35294-4390, USA.

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ABSTRACTS O F T H E BCLA ANNUAL CLINICAL CONFERENCE - LONDON 1995

A M U L T I - S O L U T I O N C O M P A R I S O N O F G R O U P I I A N D G R O U P IV D I S P O S A B L E L E N S E S

L. Jones, V. Franklin, K. Evans, R. Sariri and B. Tighe This study investigated the deposition encountered in group II and group IV monthly disposable lenses when cleaned and disinfected with a variety of solutions. Ten male subjects were fitted with a group II lens (Lunelle 'Rythmic') in one eye and a group IV lens (Vistakon 'Surevue') in the other. The lens types were randomised and masked from both subjects and practitioner. The lenses were replaced on a monthly basis, while subjects sequentially and randomly cycled through five solution systems. The solution systems were masked from the practitioner. The five solutions used were a one-step peroxide, two-step peroxide, chlorine, dymed and polyquad based systems. Results showed that significantly more lipid was deposited on group II lenses and substantially more protein was

deposited on group IV lenses, in both the surface and the bulk. The systems overall were similar in their control of both lipid and protein deposition, but significant inter-subject variation was seen. While multi-purpose solutions had little deleterious effects on the deposited layer, with the majority of the deposited protein retaining its activity, hydrogen peroxide-based systems resulted in significant denaturation of the deposited lysozyme.

Address for Correspondence Biomaterials Research Unit, Aston University, Piston Triangle, Birmingham B4 7E-~I", UK.

INVESTIGATION OF THE EFFICACY OF SINGLE PURPOSE SURFACTANT CI.FANERS AND MULTIPURPOSE CLEANING SOLUTIONS

V. Franklin The initial stages of contact lens spoilation are rapid with respect to the deposition of tear components, in particular, lipids and proteins. This early stage deposition is followed by diffusion, immobilisation and chemical conversion of the biological components involved in ocular spoilation. In addition, extrinsic factors, such as care solutions, cosmetics, skin lipids, drugs and tobacco smoke may all play an important part in the spoilation process. Our work has shown that different care systems have different effects on this deposited biological layer and care systems can alter the course of subsequent tear interactions. One example is surfactant cleaners which differ quite dramatically in their efficiency and, of course, partial cleaning produces a partially modified lens surface. This partially modified biofilm may then interact, in a completely different manner from the uncleaned lens, upon re-insertion of the contact lens. Disinfection systems have little or no intrinsic cleaning

ability. They may, however, chemically convert the deposited biological components. Their efficacy may also be reduced by heavy surface deposition. The detailed efficacies of single purpose and multipurpose polycationic cleaners which are now available in the UK (ReNu, Optifree, Complete), on the biological species involved in the spoilafion process are of great potential importance in contact lens-tear interaction understanding, and are at present unclear. This paper is concerned with furthering the understanding of the efficacies of these solutions in removing the deposition from the contact lens and the effect of any residual deposition on the contact lenstear film interaction.

Address for Correspondence Biomaterials Research Unit, Aston University, Aston Triangle, Birmingham B4 7ET, UK.

CONTACT LENSES: BEYOND REFRACTIVE ERROR

R.M. Hill On even cursory inspection, the contact lens field reveals a remarkable diversity among the sciences and technologies it draws upon, the ocular and visual anomalies it addresses, and the frontiers (anatomical, physiological, biochemical, immunological, microbiological, psychological . . .) it continues to challenge. Surveyed here is just one laboratory's view of the remarkable opportunities the contact lens has provided, not only to the direct benefit of our patients, but towards an ultimate understanding of those tissues and the underlying processes being dealt with. Questions thought of.in the 1950s

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and their answers which required the best and most creative strategies of their times, are now taken as long established fundamentals of our field. Yet, each represents an individual triumph for our patients, our practitioners, and our science and continue to contribute to the vigour and the excitement which has sustained all of our interests over those decades, and will do so into the next century.

Address for Correspondence Ohio State University, College of Optometry, 338 West Tenth Avenue, Columbus, OH43210-1240, USA.

ABSTRACYSOFTHEBCLAANNUALCLINICALCONFERENCE- LONDON1995

POSTER PRESENTATIONS 1. Is it possible to develop a fast, accurate technique to upgrade patients from one toric lens to another without the need to refit? M. M. Bark Practitioners realise the importance of continually keeping abreast with new advances in contact lens materials and changing technology. Upgrading patients to higher oxygen transmissible materials and improved lens designs are also essential for the success of the contact lens business, but this involves a significant amount of chair time, especially if the lenses are complex to tit. We decided to find out if it was possible to develop fast, accurate switching recommendations for practitioners to upgrade patients from one toric lens to another, preferably without the need to refit. Forty-five patients wearing a low water (LWC) toric lens (Ciba-Vision 'Torisoft') were evaluated for base curve fitting, stabilisation and visual performance and then retired with a high water (HWC) toric lens (Ciba-Vision ~NCE Toric'). After 1 week of WCE toric lens wear they were re-evaluated following the same criteria. We found that the WCE torics stabilised within 10 degrees of the original Torisoft lenses in 90% of cases. There was a clearly defined relationship between patients who were originally wearing 8.6 and who were retired with steep base curve (this happened in 88% cases), and with patients being fitted from 8.9 and 9.2 toflat (92.5% cases) At the end of 1 week of wear the WCE toric lenses gave statistically better overall comfort and visual acuity. From our results, if a patient needs upgrading from the traditional LWC toric lens to a HWC toric lens, we can predict with a high degree of accuracy the required axis and base curve and prescription to give at least the same if not a better overall result. Thus we can conclude it is possible to determine in a fast and accurate manner equivalent fittings and predictability of one toric lens compared with another, in order to successfully upgrade patients without the need to refit. This obviously saves valuable chair time for practitioners.

Address for Correspondence CibaVision ( U K ) Ltd, Southampton, UK.

Flanders

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2. Can patients truly discern between different monthly frequent replacement lenses? M. M. Bark Monthly frequent replacement lenses, often the first choice for fitting in practices, offer differences in designs, materials and such additional features as visible handling tints and ultraviolet light filters. To determine whether there is a significant difference between different types of monthly replacement lenses, we carried out a single-masked, contralateral evaluation of three different mid/high water contact lenses, both subjectively and objectively. One group of patients was randomly assigned Focus lenses in one eye and Medalfist 66 in the other, and another group wore Focus and Precision UV. There was no significant difference between any of the lenses in physiological performance or the distribution of fits, although the mean subjective assessment of vision on insertion and removal of the lenses at the end of the 1-month wearing period was judged to be better with Focus than with Medallist 66 (P<0.05). Asked to state a preference for one lens over the other at each follow-up visit, 60% of practitioners preferred Focus compared with 26% who preferred Medallist 66, and in the second group 38% each preferred Focus and Precision UV. For handling, 50% of patients preferred Focus and 32% preferred Medallist 66, while in the other group 44% preferred Focus and 37% preferred Precision UV. Overall,

patient preferences for Focus and Medallist 66 were 52% and 37% prospectively, and for Focus and Precision UV, they were 44% and 45%. We can conclude that while physiological performance is similar over 3 months, there are discernible differences in preference for some types of monthly disposable lenses by both practitioners and patients.

Address for Correspondence CibaVision ( U K ) Ltd, Southampton, UK.

Flanders

Road,

Hedge

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3. Efficacy of soft contact lens disinfection systems against Acanthamoeba on the contact lens surface C. G. Begley and If. Liedel We compared the efficacy of three widely used contact lens disinfection systems, AOSept, Opti-Free and Re-Nu, and their associated cleaners, against an ocular isolate of Acanthamoeba. Twenty-seven worn Ciba NewVue lenses were quartered, heat sterilised and immersed for 2h in a solution containing 3×10 ° ml Acanthamoeba. Lenses were then randomly divided into three groups, with group A lenses exposed to cleaner and saline rinse only, group B to disinfection only and group C to both cleaner and disinfection. One-quarter of each lens served as a control and the other three-quarters were experimental. Lens cleaning and disinfection steps were performed following the manufacturer's instructions, and the experiment was carried out in the cases provided by the manufacturer. Quantification of the number of viable Acanthamoeba organisms remaining on the lens after each step of the disinfection system was determined using trypan blue exclusion. An observer unaware of the treatment used counted live trophozoites and cysts on the lens surface. Group A lenses (cleaner and saline rinse only) showed no significant difference between the treatments, or the treatments and the control. The control for group A lenses consisted of rubbing the lens quarter with saline. Group B lenses (disinfection only) demonstrated a significant, although less marked, difference (P=0.0001) between the treatments and the control. In addition AOsept with AODisc was significantly more effective (P=0.0252) than either Opti-Free or Re-Nu. In group C (cleaning and disinfection), the control lens quarters were significantly different (P=0.037) from the experimental, but there was no significant difference between the treatments. Our results demonstrate that, in the absence of cleaning or digitally rubbing the lens surface, disinfection with AOSept was most effective against viable Acanthamoeba. These results also underscore the importance of thoroughly rubbing the contact lens surface to decrease the number of viable Acanthamoeba organisms.

Acknowledgement This project was supported by a grant from Ciba Vision Corporation.

Address for Correspondence Indiana University School of Optometry, 800 E Atwater Avenue, Bloomington, IN 47405, USA.

4. Studies of polycationic materials and their deposition characteristics K. French, R. Sariri, V. Franklin and B. J. Tighe Previous studies on the interaction of proteins on the contact lens matrix have demonstrated the relative ability of certain hydrogel materials to withstand ocular deposition. However, very little work has included the study of materials with a positive surface charge. With the increasing use of cationic polymers as antibacterial agents in disinfecting regimes and

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ABSTRACTSOFTHEBCLAANNUALCLINICALCONFERENCE- LONDON1995

5. Anti-bacterial biomaterials K~ French, M. Eccleston and B. J. Tighe The contact lens and the vascular catheter share significant problems associated with bacterial infection. In the case of both devices introduction of a synthetic material to a body site is, on occasion, associated with bacterial invasion which can have catastrophic consequences. Novel strategies have been proposed to deal with such situations; some are in their relative infancy while others have been demonstrated to be successful in a clinical environment. Many of these strategies are associated with the introduction, generation or release of charged species. Examples of current activities in the area were described and the concept of the antibacterial contact lens discussed.

correction. Studies have shown that an active, positive approach towards contact lens fitting will result in an increased number of contact lertses being fitted. This study was conducted by four practitioners in two centres to investigate if this is the case in the UK. Each practitioner noted the details of 40 successive noncontact lens wearing patients who consulted them for a routine eye examination. Subjects were eligible for entry if they were between the ages of 18-60, had no obvious pathology which would prevent them wearing contact lenses, had spectacle prescriptions between -8.00D to +5.00D and had a maximum cylindrical correction of 0.75D. The subjects were divided into two equal groups. The first group consisted of subjects with whom contact lenses were only discussed if the subjects solicited the discussion. The second group consisted of subjects who were actively invited to discuss contact lenses and were given written information informing them of the potential benefits of lenses and enquiring if they would like to try contact lenses for 2 weeks, at no charge. If they were interested they were fitted with a monthly disposable lens, given instructions on handling and disinfection and dismissed for 2 weeks. Upon completion of this time period the patients were asked if they would like to continue with lenses, which they would subsequently have to pay for. Approximately six times more patients were fitted with contact lenses by adopting a proactive approach.

Address for Correspondence Biomaterials Research Unit, Aston University, Aston Triangle, Birmingham B4 7ET, UK.

Address for Correspondence Collett & Jones Opticians, 103 Main Road, Sidcup, Kent DA14 6ND, UIC

6. The spoilation and clinical performance of 1-monthly versus 3-monthly disposable contact lenses

8. Further studies on the interaction of the biochemical species of the ocular environment and soft contact lenses

the known ability of these agents to adhere to lens materials, the need to investigate the role of cationic substrates in lens spoilation was recognised. This poster described the studies of the interaction of specific proteins with the cationic charged surface of materials of varying composition, along with the general deposition phenomena. The poster also described the potential antibacterial nature of such polycationic materials. Address for Correspondence Biomaterials Research Unit, Aston University, Aston Triangle, Birmingham B4 7ET, UK.

Lyndon Jones, Valerie Franklin, Kathryn Evans, Rayhenah Sariri and Brian Tithe This study investigated the clinical performance and deposition encountered in group II disposable lenses when replaced on a 1-monthly versus 3-monthly basis. Twelve subjects were fitted with a group II lens (PBH 'Precision UV'), which was either replaced every month for 3 months or worn for 3 months before replacement occurred. The lens wearing periods were randomised and masked from the practitioner assessing the lenses. During the period of the study the subjects used a multipurpose cleaning and disinfecting system. Visual quality, high and low contrast acuity and comfort were unaltered with either replacement schedule, but overall satisfaction was significantly greater with the shorter replacement schedule (P=0.04). Front surface wettability revealed a large degree of intersubject variability and was reduced at the 3-month visit with the longer wearing period lenses (P=0.0003). Visible deposition also increased with wearing time (P=0.05). Laboratory-based analytical results showed that both gross lipid and gross protein significantly increased in the 3-month lenses compared with the 1-month lenses, with 50% reduction in lipid accumulation and 60% reduction in protein deposition. These findings support the premise behind the use of regular replacement in the management of contact lens deposition. Address for Correspondence Biomaterials Research Unit, Aston University, Agton Triangle, Birmingham B4 7ET, UK. 7. Reactive or proactive contact lens fitting - does it m a k e a difference?

Lyndon Jones, Deborah Jones, Claire Langley and Mark Houlford Contact lens penetration in the UK is lower than that found in many other European countries, currently running at approximately 4% of those patients requiring visual 138

V. Franklin, K. Evans, L. ]ones, 17. Sariri, U. Singh-Gill and B. ]. Tighe Previous studies on the interaction of proteins and lipids on and within the contact lens matrix have demonstrated differences between patient tear chemistries and the relative ability of 'deposit resistant' contact lenses to withstand ocular deposition. This type of analysis requires the use of highly sensitive analytical techniques in conjunction with carefully controlled clinical trials and in parallel with in vitro studies of the deposition processes. This poster described further studies into the deposition phenomena over varying time intervals and wear schedules. Interesting variations between the types of materials and patient tear chemistries and ways of presenting data relating to these factors were observed. Address for Correspondence Biomaterials Research Unit, Aston University, Aston Triangle, Birmingham B4 7ET, UtC 9. The interaction of care solutions with tear c o m p o n e n t s deposited on soft contact lenses

V. Franklin, R. Sariri, K. Evans, L. Jones, J. Ma, A. Mann, U. Singh-Gill and B. J. Tithe This poster compared the relative effects of some currently available single-purpose cleaning solutions, multi-purpose solutions and disinfecting solutions on the biochemical species involved in ocular deposition processes. These effects included the effect on biological activity of the proteins, the uptake from the tear fluid and leaching profiles from the lens matrix of these species together with the chemical conversion of such biochemical species and their potential effect on the inflammatory response of the eye on re-insertion of the contact lens. Address for Correspondence Biomaterials Research Unit, Aston University, Aston Triangle, Birmingham B4 7E~, UK.

ABSTRACIX3 OF T H E BCLA ANNUAL CLINICAL CONFERENCE - LONDON 1995

10. Interaction of tear lipids with soft contact lenses

E Franklin, K. Evans, L. Jones, U. Singh-Gill and B. J. Tighe The study of lipoidal species and their interaction with the surface and matrix of the soft contact lens materials is important for the development of spoliation-resistant contact lenses and successful ocular prostheses. Lipids are highly reactive molecules which interact not only with the surface of a contact lens, but are also readily absorbed into the matrix of the lens. Once in the lens matrix these species are no longer in close contact with the antioxidants in the superficial tear layer and may undergo chemical conversion as a result of exposure to a cleaning regime. Once chemically converted the species are less readily desorbed from the lens matrix and may provide a site for further deposition to occur. Individual patient tear lipid composition varies considerably and physical factors related to the lens edge effects and surface rugosity can also contribute to the deposition profiles obtained, in addition to the expected dependence upon the material lens chemistry. This poster profiles the types of lipoidal species involved and the penetration into the lens matrix in the course of closely controlled clinical studies.

Address for Correspondence Biomaterials Research Unit, Aston University, Aston Triangle, Birmingham B4 7E'T, UK 11. Problems, problems, problems! D. Jones and L. Jones Contact lens practitioners are sometimes faced with contact lens patients with complications outside those normally encountered in clinical practice. This poster photodocumented 20 unusual cases which have presented to the authors in their private practice, which have required some complicated management decisions. Each case was succinctly described, a photograph presented and the method of management outlined.

Address for Correspondence Collett & Jones Opticians, 103 Main Road, Sidcup, Kent DA14 6ND, UIC 12. Contact lens m a n a g e m e n t of corneal vascularisation M. Lloyd Observation of corneal vascularisation in contact lens practice with a slit-lamp biomicroscope is frequently estimated rather than actually measured with a graticule. This can tead to variations in the amount of corneal vascularisation that is deemed acceptable, creating variable patient management. This poster showed examples of differing grades of corneal vascularisation induced by long-term low-water contact lens wear. Depending on the level of vascularisation patients will be advised to change to a different lens option (high water soft lens, hard gas permeable or to discontinue lens wear). For each slide a range of responses from 10 practitioners on how to manage each patient is given together with the estimated and the actual degree of vascularisation. Examples were given between 1.00mm and 2.00mm vascularisation showing agreement between practitioners on when an HGP lens should be fitted and when the use of even a high water content soft lens was unacceptable The poster is intended as a pictorial guide for management of patients presenting with varying degrees of contact lensinduced corneal vascularisation. Address for Correspondence 126 Ennerdale Road, Kew, Surrey TW9 2DH, UK. 13. The role of absorbed vitronectin in contact lensinduced inflammatory p r o c e s s e s A. Mann, V. Franklin, N. Bretherton, B. J. Tighe and M. GuiUon

Vitronectin is now well established as an important inflammatory marker and has an important proactive role in modulating the conversion of plasminogen to plasmin. Cleavage of vitronectin by plasmin eliminates plasminogen activator inhibitor (PAl) binding, resulting in local upregulation of plasmin formation, thereby controlling an important regulatory mechanism in wound repair. We have previously demonstrated the value of a cell-based assay for the study of vitronectin in the ocular environment in the presence of a contact lens. Our aim was to evaluate the potential influence of the contact lens and lens material on the vitronectin-mediated inflammatory process. The hypothesis tested was that the microclimate of the post-lens, rather than the pre-lens, tear film, particularly during closed eye wear, creates a favourable environment for up-regulation of the contact lens-induced immunological response. The cell-based assay using 3T3 cells in conjunction with anti-human fibronectin and vitronectin was carried out on group II and iV lens materials with a common group of patients under similar wear conditions. The location of vitronectin on the lenses studied confirmed that the post-lens microclimate, particularly towards the periphery, is rich in vitronectin to a degree that is capable of influencing localised plasmin production. This production of a microclimate is influenced by lens material, in particular its anionic nature, a fact confirmed by in vitro studies. We concluded that the contact lens provides a vitronectin-rich microcllmate in contact with the cornea, which is influenced by the nature of the lens materials, particularly material ionicity. We believe that the consequent enhanced plasmin production and thus susceptibility to localised tissue damage, following an initial insult, coupled with fibronectin cleavage and a resultant loss of tissue repair capability, provides an important element in the understanding of contact lens-induced inflammatory processes including ulcers.

Address for Correspondence Biomaterials Research Unit, Aston University, Aston Triangle, Birmingham B4 7ET, UK. 14. The effects of microwave irradiation on soft contact lens variables N. M. Quesnel, P. Simonet and C. Giasson Several authors in recent literature have experimented with the use of standard microwave ovens as an alternative method for soft contact lens disinfection. However, no previous investigation has checked the effect of multiple repeated exposures to microwave irradiation on clear and tinted soft contact lenses with identical parameters. The purpose of this study was to evaluate the effects of microwave disinfection on optical variables of unused lenses from group i of the FDA material classification. A total of 20 afocal lenses including 10 Hydron Z6 and 10 CSI were used, half of these lenses were tinted aqua. Each lens was placed in a Ciba AOSept case filled with unpreserved saline and all lenses were disinfected together for 120sec in a standard microwave oven (2450MHz, 650W) with a rotating plate. The lens variance, including back vertex power, back optic zone radius (BOZR) and water content were measured at baseline and after 30, 60 and 90 disinfection cycles. The results indicated that there were no statistically (one-way ANOVA P=0.05) or clinically significant changes in the refractive power and BOZR after 90 disinfection cycles. But our results showed a statistically significant change in water content for all lenses (range -0.1% to +0.9%). Although these differences are smaller than the experimental error they are not clinically significant. These findings indicate that microwave disinfection could be a feasible alternative to current disinfection methods; however, further studies on the effects of microwave irradiation on worn soft lenses are needed.

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ABSTRACTSOFTHEBCLAANNUALCLINICALCONFERENCE-LONDON1995 Address for Correspondence Ecole d'Optometrie, University of Montreal, CP 6128 succursale Centre-Ville, Montreal, Quebec, Canada H3C 3J7.

Address for Correspondence Biomaterials Research Unit, Aston University, Aston Triangle, Birmingham B4 7ET, UK.

15. Protein mobility and activity in hydrogel contact lenses t?. Sariri, K. Evans, V. Franklin, U Singh-Gill and B. J. Tighe The problem of deposit formation of soft contact lenses frequently begins with the adsorption of protein at an interface and is followed rapidly by adsorption of secondary and tertiary protein layers and the competitive adsorption of other biochemical species. Additionally, some components, such as lipids, begin to diffuse into the lens matrix and are held within it. The initiating processes in all these interactions are referred to as biological interface conversion processes and they can be readily studied in the eye whereas they can only be studied with considerable difficulty in, for example, blood contact devices. The advent of disposable and frequent replacement lenses has not overcome the problems associated with lens-tear interactions. Indeed, the widespread use of high water content ionic lenses (e.g. FDA Group 4; Etafilcon and V'Lfilcon) has meant that the problem is more acute. Although it is widely accepted that proteins such as lysozyme interact strongly with group 4 materials, no systematic study has been made of the relative interaction of tear proteins with these lenses, the subsequent mobility of the proteins and the effect of interaction on their biological activity. This poster addressed these three questions.

17. The locus of contact lens spoilation: a story with two sides U. Singh-Gill and B. J. Tighe The term lens spoflation is used to encompass physical and chemical changes occurring both on and within the expanded gel network of hydrogel soft contact lenses. Even with the trend towards disposability and frequent replacement it is still a major and significant problem encountered during lens wear that can impair the optical properties of the lens or produce symptoms of discomfort and even intolerance to the wearer. The current techniques which are available to study protein and lipid absorption are limited and generally do not provide all the information desired. We have developed a combination of technologies, a novel plasma etching and emission monitoring system (PEEMS), to advance our understanding and knowledge of the interaction of the biological species involved in the process for the tear film and the contact lens surfaces. The technique has been used to address several questions: Which tear components penetrate into the lens matrix? How far do these species penetrate? What factors affect the deposition and penetration? The information that has emerged has been concerned with the absorption processes that occur on the posterior and anterior surfaces of a lens as a function of lens material properties together with tear film structure, composition and break-up time.

Address for Correspondence Biomaterials Research Unit, Aston University, Aston Triangle, Birmingham B4 7ET, UtC 16. Acidic and basic impurities in soft contact lens manufacture R. Sariri, A. Mann, K. Evans, K J. Franklin and B. J. Tighe One of the problems in the manufacture of polyHEMA lenses is that it is impossible to obtain the monomer in a state that is completely free of methacrylic acid. Previous studies have shown the importance of the surface and structural properties on protein interactions with soft contact lenses. Surface charge such as that produced by methacrylic acid is particularly important in the absorption profiles obtained. Only small quantifies of charge are required to produce this type of deposition. Although N-vinyl pyrrolidone can be prepared in a pure state the problems associated with this monomer is that it polymerises relatively ineffectively in conjunction with monomers such as HEMA and methyl methacrylate with which it is combined in contact lens manufacture. Any unreacted monomer and soluble low molecular weight polymer is conveniently extracted at the hydration stage and these washings discarded before the lens is finally placed in storage solution and despatched to the practitioner. Levels of residual N-vinyl pyrrolidone in various commercial products are compared. Tracial impurities in soft contact lens manufacture may manifest themselves in different ways. Two of the most important are (1) the presence of monomer impurities that become incorporated in the polymer; and (2) the presence of residual unpolymerised monomer that i s subsequently leached out of the lens. Manufacturers are extremely careful to set quality assurance standards that ensure that the levels of such 'impurities' are carefully controlled. This poster describes the results of a comparative study of two aspects of currently available commercial products: (1) the effect of residual methacrylic acid contaminants on the surface ionicity of polyHEMA lenses. (2) The effects of residual N-vinyl pyrrolidone (NVP) on the leachable monomer content of NVP-containing lenses. 140

Address for Correspondence Biomaterials Research Unit, Aston University; Aston Triangle, Birmingham B4 7ET, UIC 18. Analysis of corneal topography maps from contact lens wearers seeking an opinion on photorefractive keratectomy C. F. Steele Corneal topographic mapping is an essential part of the preassessment of prospective PRK patients. This is particularly important with contact lens wearers who may be suffering asymptomatic contact lens-induced corneal warpage of varying severity. Between June 1993 and December 1994, there were 86 patients who sought an opinion regarding PRK who were currently wearing contact lenses. All subjects in this study had their contact lenses removed from their eyes for no more than 48h before assessment. There were four hard PMMA (eight eyes), 47 soft (92 eyes) and 35 (69 eyes) RGP contact lens wearers. Each subject underwent a routine ophthalmological examination which included corneal topographic evaluation of each eye using the Tomey topographic modelling system. The topographic maps were then categorised into (i) round/oval (ii) astigmatic bow-tie (with-the-rule) (iii) astigmatic bow-fie (against the rule), (iv) inferior astigmatism (v) superior astigmatism, (vi) irregular. These topographic maps were analysed by three observers independently following agreement on the classification protocol, in which all patients' names and unit numbers were masked. The results were compared with a randomly selected control group of non-contact lens wearers (n=34; 68 eyes). In the control, hard, soft and RGP groups all three observers agreed in 81%, which compared with 100%, 93.3% and 89.8% of cases respectively. In the control group 22% were classified as irregular which compared with 100% for hard lenses, 38.1% in soft and 44.8% in RGP lens wearers. Other factors including surface regularity index (SRI) and surface asymmetry index (SAI) were also analysed. Although the difference between SAI and SRI values for each group were statistically significant, the indices proved

ABSTRACTS OF T H E BCLA ANNUAL CLINICALCONFERENCE - L O N D O N 1995

to be only of very limited clinical value. The importance of these results were discussed in relation to PRK and recommendations given on interpreting irregular topographic maps.

Address for Correspondence Optometry Department, Sunderland Eye Infirmary, Queen Alexandra Road, Sunderland SR2 9HP, UK. 19. Follow-up of two rigid contact lens patients with contact lens-induced corneal warpage using the videokeratography system TMS-1 C. F. Steele Clinically significant changes in corneal topography can be associated with daily or extended wear of rigid or soft contact lenses. Corneal warpage is the term used to describe these changes in corneal shape, a term originally used by Harstein (1965). The emergence of computerassisted videokeratographic analysis has provided a sensitive tool for assessing normal and pathological corneal contour and for monitoring changes over time. Two female patients, who were long-term rigid PMMA and GP lens wearers, were followed-up over a 5-month period following cessation of contact lens wear in their right eyes. This was after the diagnosis of contact lens-induced warpage. Corneal topography using the Tomey topographical mapping system (TMS-1) was carried out at regular intervals and spectacle refraction and changes in visual acuity were recorded. These chronological corneal maps, which originally exhibited grossly warped topographic images, returned to normal with maps showing regular bow-tie astigmatism. The regular bow-tie patterns had been previously completely masked. A chronological presentation of the TMS colour coded maps was made with the accompanying refractive data spectacular microscopy results and slit-lamp fluorescein photographs. General discussion on how these patients were re-fitted with contact lenses is included. Address for Correspondence Optometry Department, Sunderland Eye Infirmary, Queen Alexandra Road, Sunderland SR2 9HP, UK. 20. Old mother nature's recipes; tears, lung surfaetant and synovial fluid S. R. Tonge and B. J. Tighe The eye, the lung and the articulating joints within the body depend for their successful function on fluids that have certain common features such as spreading and lubrication. The ways in which these properties are achieved show certain fascinating similarities and differences. This poster compared and contrasted the structure, composition and function of tears, lung surfactant and synovial fluid highlighting the problems associated with the production of synthetic equivalents.

Address for Correspondence Biomaterials Research Unit, Aston University, Aston Triangle, Birmingham B4 7ET, UK 21. Studies of in vivo versus in vitro wettability of soft contact lenses S. R. Tonge, J. Ma, L. Jones and B. J. Tighe Comparison of the dynamic and static wettability measurements of a number of commercially available and novel hydrogels has been made using both in vivo and in vitro measurements. In vivo wettability was assessed in a number of controlled, double-masked, crossover clinical studies by ufilising a novel NIBUT device, the 'Loveridge grid'. Static in vitro wettability was assessed by using a modified goniometer, using coherent laser light to investigate the effect of various solution systems on the wettability of

previously unworn hydrogel lenses. Similar dynamic measurements were made with a purpose-designed computer-controiled wetting balance. Additional data on the behaviour of both natural (tear) and synthetic (solution) systems were obtained with both pulsating bubble surfactometer and Langmuir Trough.

Address for Correspondence Biomaterials Research Unit, Aston University, Aston Triangle, Birmingham B4 7ET, UK. 22. How do the new polymeric antibacterials work? S. R. Tonge and B. Tighe The antibacterial mode of action of polyhexanide is similar to that of the tear protein lysozyme. To illustrate this similarity the structure of lysozyme was analysed using a molecular modelling technique and the structural features responsible for interactions with, and disruption of, bilayer membranes was demonstrated graphically. In vitro surface chemical investigations, including Langmuir film studies, showed that the interaction between polyhexanide and lipid monolayers analogous to those found in bacterial cellular membranes were similar to those of lysozyme. These studies demonstrate that the polymeric antibacterial agents currently used in multipurpose contact lens solutions act by both ionic and hydrophobic interactions with cellular membranes and, as such, mimic more closely the action of the native antibacterial protein present in tear fluid.

Address for Correspondence Biomaterials Research Unit, Aston University, Aston Triangle, Birmingham B4 7E~, UK 23. Soft contact lenses for Asian eyes? K. O. Tan Most contact lenses available in Asia are designed and manufactured in Western countries. Although the ocular characteristics between the Asian and Caucasian are not fully understood, some practitioners in Asia prefer to judge the fitting solely based on the 'comfort' of the lens. It is thus interesting to investigate the clinical performance of some hydrogel lenses on Asian eyes. This study was conducted at two centres (Hong Kong Polytechnic and Singapore Polytechnic). Ten soft contact lens wearers (aged 16-33 years) were recruited in each centre. Six different types of lenses (Weicon 38E, Hydron Z6, Medallist, Acuvue, Focus and SeeQuence) were fitted on one eye. The fittings were assessed 20rain later by five optometrist at each centre, and the comfort levels were graded subjectively on a 0 to 100 scale. The results showed that comfort levels were not significantly different among the lenses tested in both centres (P>0.05). However, there were significant differences (P>0.05) in fitting characteristics in both centres. Fitting of most lenses was significantly more acceptable (P>0.05); however, Acnvue and SeeQuence were found to be significantly fighter (P>0.05). In conclusion, there is no single lens that suits every Asian eye. Some lenses are equally comfortable; however, the fitting could be tighter when compared with the others. Thus, judging fit based on 'comfort' without proper fitting assessment may result in prescribing a tight lens. This should be of concern to those busy optical practices in Asia where some practitioners judge the suitability of a lens solely based on the 'comfort' levels and without fitting assessment. Trial fitting assessment on every patient is still the best way to select the appropriate lenses for Asian eyes. Also, fitting behaviour of a lens in one patient is not an adequate predictor of that lens performance with other patients.

Address for Correspondence CibaVision Group Management Inc., 171 Chin Swee Road, 02-05/08 San Centre, Singapore 0316.

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ABSTRACTSOFTHEBCLAANNUALCLINICALCONFERENCE- LONDON1995

24. The implication of post-PRK corneal topographical changes for the contact lens practitioner G. Whittaker A number of factors, both procedural and physiological, may influence the visual outcome following PRIL In a group of 126 patients (with a pretreatment refraction of -1.25 to -7.50D) 88% achieved 6/10 or better unaided vision; the remaining 11% would clearly require an optical correction for certain tasks. Contact lenses should be available as an option for these patients. The post-PRK cornea will typically have a flattened central zone compared with the pretreatment values, the periphery and mid-periphery will however remain relatively unchanged. This clearly has major implications for the contact lens fitter. The usefulness of pre~ and post-treatment keratometry values in the fitting of contact lenses post-PRK were examined and contrasted with the use of corneal mapping techniques in fitting the post-PRK cornea. The difficulties encountered in fitting RGP lenses to what is essentially a flattened central zone and steep periphery were examined using a number of case studies and computer simulation of rigid lens fits to demonstrate the changes seen in the corneal shape post-PRIC Address for Correspondence New Image Laser Eye Centre, 80 George Street, Edinburgh EH2 3BU, UK. 25. Therapeutic contact lens management K. H. Weed Therapeutic contact lenses are a rewarding area of optometric practice. Within Sunderland Eye Infirmary a diversity of ocular conditions present, creating a wide range of challenges. A variety of case histories were discussed and the practicability of their practice management. A traumatic cataract caused by a flying contact lens lid required an aphakic hydrogel contact lens with an opaque iris print. Two cases of perforating injury resulting in opaque corneas were shown. In one case, the lens was ordered from a trial set, the other prosthetic contact lens was hand painted to match a photograph sent to the manufacturer. A hydrogel occlusive pupil contact lens was used to cover a dense white inoperable cataract caused by recurrent uveitis in rheumatoid arthritis. This type of contact lens is also used for diplopia therapy. A prosthetic scleral shell was made for a chemical burn injury which presented with symblepharon. Address for Correspondence Optometry Department, Sunderland Eye Infirmary, Queen Alexandra Road, Sunderland SR2 9HP, UK. 26. Designing lenses for the post-refi'active surgery eye If. H. Edwards, D. A. Hough and H. J. Kersley Surgical procedures to correct refractive error are increasing in popularity. While good success rates have been claimed, these can be seen to be a function of the type of procedure (RK or PRK), the degree of presenting ametropia and the ablation zone diameter (in PRK).

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With a reported 20% or more of patients requiring postsurgical correction, usually with contact lenses, there are significant challenges for the contact lens practitioner in obtaining a satisfactory fit over the abnormal corneal topography. Conventional rigid lens fitting will usually result in steep central fitting and/or flat peripheral fitting. In order to develop lens designs specifically to fit postsurgical corneas, specific computer software has been developed to permit the modelling of corneal contour in these eyes and a back surface geometry has been evolved to cope with the relatively steep mid-peripheral cornea which lies outside the flattened corneal central zone. This poster delineated the current problems of lens fitting and provided details of how the post-surgical cornea can be modelled on computer. New terminology is adopted and a justification given for its use. A broad outline of the fitting characteristics of the proposed new lens design was reviewed.

Address for Correspondence Bausch & Lomb (Ut0 Ltd, 108 London Road, Kingston-uponThames, Surrey KT2 6TN, UK. 27. Ocular response to AOSept, ReNu and Opti-Free in a prospective study of high school-aged soft contact lens wearers P. S. Soni The purpose of our 3-year prospective study was to compare high school-aged patients, randomised into wearing soft contact lenses and spectacles, in terms of ocular health, refractive status and self esteem. This report focused on ocular response to the lens care systems used through the first 18 months of the investigation. Eighty-four patients were randomly fitted with either CibaSoft Visitint or CibaSoft Standard (STD) contact lenses. Three lens care systems, AOSept, ReNu, and Opti-Free were randomly prescribed to the patients. Corneal oedema, neovascularisation, corneal staining with fluorescein, conjunctival and limbal injection, and hyperaemia were graded at dispensing and at 6, 12, and 18-month visits. There were no significant differences between the groups at baseline. At 6 months a statistically significant difference (P=0.0131) was found for corneal staining among the three systems combined. At 12 months significant differences were found for corneal oedema (P=0.0404) and neovascularisation (P=0.0315) among the systems. At 18 months generalised conjunctival hyperaemia was seen as significantly different (P=0.0234) among the systems along with greater limbal vessel involvement (P=0.0015) and neovascularisation (P=0.0238). The cornea, limbal vessels and the conjunctiva responded differently to the lens care systems used in this study. Overall, patients using AOSept presented with less corneal staining and minimal inflammatory response than patients using ReNu and Opti-Free. Address for Correspondence School of Optometry, Indiana University, 800 East Atwater Avenue, Bloomington, IN 47405, USA.