How To Fit Soft Contact Lens

Transcription

1 FITTING BACKGROUND Soft lens fitting Myth or fact? Test your knowledge about today s soft lens fitting! For the contact lens industry, it seems paramount to know how soft lenses are fitted today. Manufacturers do not always seem to be fully aware of the complex and often confusing cascade of steps that eye care practitioners follow regarding the fitting of soft lenses. Well, they can rest assured, maybe. Many eye care practitioners are not sure, either. By Eef van der Worp and Helmer Schweizer

2 Soft lens fitting FITTING BACKGROUND To address this, the 2014 edition of the Dutch biennial contact lens meeting NCC and its 5 th anniversary, with a record attendance of 1,577 unique visitors on one or both days a workshop was scheduled to discuss the state of soft lens fitting anno The theme of the NCC2014 meeting was decoding the secret and that was exactly what this workshop intended to do. The intention was to dissect and analyze the way in which we are fitting soft lenses today, almost like x-raying soft lens fitting, and to reach consensus on the proper procedure. The aim of the workshop was to find common ground, and common sense, in the way in which we are fitting soft lenses today. This information may be of interest to the contact lens manufacturers as well. THE AIM OF THE WORKSHOP WAS TO FIND COMMON GROUND, AND COMMON SENSE, IN THE WAY WE ARE FITTING SOFT LENSES TODAY Optometrist and educator Helmer Schweizer, who is also Euromcontact president, acted as the panel discussion moderator. Apart from the authors of this paper, the workshop panel consisted of Matthew Lampa and Mark André both experts in the field from Pacific University College of Optometry in Oregon, USA and active in the soft lens industry. Also on the panel was Marco van Beusekom: the conference president of the successful NCC meeting and wellknown speaker on the topic of soft lens fitting. Devoted soft contact lens-fitting eye care professionals from the Netherlands, Belgium and other countries attending the NCC were invited to participate in the workshop and interact with a panel of representatives from the contact lens industry, which included contact lens educators and researchers. A total of 44 participants attended the interactive session. The proceedings were first published in the June 2014 issue of Contact Lens Spectrum. Looking at soft lens history, by the late 1960s, spin-cast and lathe-cut soft lenses were available in a number of countries. Up until then, RGP lenses had a monopoly in the market (consisting of corneal and scleral lens modalities). It was not until 1987 that the world of contact lenses was irrevocably changed with the introduction of disposable lenses. What is interesting is that soft lens fitting as a science and a skill has been downplayed over the last two decades or so as frequent replacement and disposable soft lenses have grown a logical development in itself. The downside is that fitting soft lenses has become a routine process without most of us actually realizing why we are doing things the way we are doing them. But more recently, developments have taken place that may encourage us to go back to the drawing board and have a second look at the way we fit soft lenses today. Silicone hydrogel lenses, now the number one lens material prescribed worldwide because of their excellent oxygen supply to the cornea, may make lens fitting more of a science and a skill again as the lens-to-cornea relationship has become more important because some of these lenses have a higher modulus compared to lenses manufactured in conventional soft lens materials. Also, measuring techniques, which up to recently were limited to central keratometry, have been upgraded: first to limbal-to-limbal corneal coverage topography instruments, and most recently to instruments that go into and beyond the limbal area (such as optical coherence tomography and eye surface profilers), thus helping us to better understand the shape of the corneo-scleral junction and the anterior sclera. See also the column (page 22) in this issue of GlobalCONTACT on the demise of radius in favor of height information and microns. Studies by Hall et al in the UK have indicated there is a direct relationship between corneo-scleral shape and soft lens fitting characteristics. Additionally, we have ways to better measure, analyze and understand the shape of soft contact lenses itself now. Last but not least: we are still facing high dropout rates, despite all of the material and contact lens care developments in recent years. It may therefore be time to see whether we can do things differently. Potentially, we may be off to a new beginning; some even say at a crossroads, at which we may change our approach in the way we fit and evaluate soft lenses in the future. Presented in this article are eight Myth or Fact? statements to test your knowledge of the general beliefs or consensus, if you prefer about today s soft lens fitting and today s soft lens practice. Taking central keratometry measures is a useful method of predicting soft lens fitting characteristics. Taking central keratometry values is still valid and should be done to have a baseline and thus to be able to follow up and manage potential topographical changes, the group decided. It also can play a role in lens selection (GP versus soft, because of corneal versus refractive astigmatism). But, the group universally agreed that keratometry is not a very useful indicator of soft lens behavior on-eye or for selecting the initial base curve of the contact lens. This is backed up by work from Graeme Young and Ralph Gundel stating there is a very weak correlation between the central and peripheral K-readings and soft contact lens fitting characteristics. Using sagittal height data has been proposed in the past and using sagittal height to better understand soft contact lens behavior on-eye is also part of the international association of contact lens educators (IACLE) basic module on soft lens fitting. Based on the sagittal height fitting method, registering the total sagittal height of the lens would make more sense in theory. One limitation of this is that lenses can have different back surface geometries and/or diameters and still have the same sagittal height. Also, it is unclear what effect lens dehydration on the eye would have on the total overall sagittal height of the soft contact lens. GlobalCONTACT

3 FITTING BACKGROUND Soft lens fitting 1 Fig. 1: Example of height topography (Eye Surface Profiler Eaglet Eye), providing ocular sagittal height data Lens diameter was discussed from a clinical standpoint as a potentially useful measure and alternative method for estimating the relative sagittal height of the cornea. Measuring corneal diameter is a discussion in itself, but taking white-to-white measurements of the cornea (diagonally) with a corneal topographer could be the best, or most preferred, option according to the experts on the panel. The base curve values on lens packaging represents the actual contact lens back surface shape. Following up on the previous myth, the group indicated that base curve notation on a soft lens package (usually expressed in numbers with or without mm) is not necessarily considered to be the actual contact lens back surface radius, at least not in the back surface optic zone (BOZR). It is more often than not questionable as to whether the lens actually has an 8.3 or 8.6 mm spherical radius on its back surface. In many cases, it is the calculated base curve equivalent, i.e., the radius of a sphere that would have the same sagittal height over the indicated diameter as the lens at hand. The lens back surface design and diameter drives its actual sagittal height. Therefore, in the case of non-spherical back surfaces, it may be more appropriate to call it a base curve equivalent (BCE) rather than a base curve. Anyhow, for those lens brands that come with a choice of base curves/bces, it should rather be viewed as a sort of indicator, more of a symbolic value than as the actual back surface curvature of the lens. So, a single number on the lens box can certainly not define the lens fit. The total sagittal height and back surface design of the lens is of much more importance. But from a legal standpoint, some kind of base curve or base curve equivalent still needs to be on the package labelling today. The anterior ocular surface shape consists of a steep curve (the cornea) and a fl at curve (the sclera) and a marked transition between those two. It is suggested that more often than not, the corneo-scleral junction is best described as having tangent angles rather than using curve terminology (like concave and convex) to define its shape, although individual limbal and anterior scleral shape differences occur. New insights show us that practitioners shouldn t expect the limbal area, or corneo-scleral junction, to necessarily have the concave shape that would be expected based on theoretical considerations expressed in older and even current textbook chapters. In other words, it appears that our textbooks need to be rewritten to be in line with recent studies like the ones from Pacific University and Lee Hall. These studies also may contain valuable information for scleral lens geometry and manufacturing, as well as soft lens design and fit, it seems. LENS CENTRATION BECOMES PARTICULARLY CRITICAL AND RELEVANT IN TORIC, MULTIFOCAL AND MYOPIA CONTROL CONTACT LENSES. In addition to this, these studies also indicate that, for the average eye, the ocular surface beyond the cornea is non-rotationally symmetrical in nature. It appears that, in the average eye, the entire nasal portion is typically flatter compared to the other quadrants. As a consequence, the nasal region appears more elevated compared to the other meridians with a potentially important clinical impact on soft contact lens centration. This may explain the commonly observed temporal decentration of soft contact lenses which is important in terms of the position of the lens optics and visual performance of the lens. An important point was made that centration becomes particularly critical and relevant in toric, multifocal and myopia control contact lenses. The focus of the workshop was then narrowed down specifically to spherical lenses alone, to avoid making the discussion unnecessarily complex. Larger soft contact lenses lead to better lens centration. In the past, many of us were taught that larger soft contact lenses lead to better lens centration. Current knowledge about the nasal portion of the eye being more elevated may urge us to revisit this, as larger lenses may actually lead to more (temporal) decentration. It is very important to note from the discussion that lens diameter is considered a relative measure, meaning that it should be evaluated relative to the individual corneal diameter. For instance, Asian eyes generally are observed to have a smaller corneal diameter; therefore, a specific lens for Asian eyes might actually make sense. The diameter of the contact lens should be a specific amount (in millimeters) larger than the actual corneal diameter. All in all the contact lens diameter may be a better predictor of lens behavior on eye, including centration, than the base curve. 30 GlobalCONTACT 3-14

4 Soft lens fitting FITTING BACKGROUND 1 mm of lens movement is the desired amount of movement in soft lens wear. In the past, and even in some textbooks today, 1 mm of lens movement is sometimes advocated as the optimal amount of soft lens movement. However, given the average horizontal visible iris diameter (11.8 mm) and the average soft contact lens diameter in the 14 mm range, this would bring the lens edge upon eye blinking almost right into the limbal zone, which may result in discomfort. The reality is that today s soft lenses are often moving considerably less than 1 mm with blink. Recent research shows that 0.3 mm of soft contact lens movement in the normal eye is more realistic. Tan Troung et al in a recent paper in Optometry & Vision Science showed that patients with lenses that move in the mm range are most comfortable. Silicone hydrogels move more on the eye than conventional hydrogels do. Maybe in contrast with general belief, the consensus group could not decide universally whether conventional hydrogel lenses move more or move less than silicone hydrogel lenses do. Lens movement may depend on many more variables (like lens edge shape and back surface geometry, among others) than material alone. In general, it should not be assumed that silicone hydrogels move more than conventional hydrogels do. Different lens movement assessment techniques were discussed with the group; the push-up test, lens-lag (with eye movement and post-blinking) and even rotational movement of the lens were all taken into consideration. The consensus group agreed that measuring soft contact lens movement in increments of 0.1 mm in clinical practice is not feasible. Helmer Schweizer suggested a simple but clinically useful method of assessing lens movement that can be performed even if a slit lamp is not available. The average visible iris diameter vertically is approximately 11.5 mm, and if the contact lens diameter is 14.0 mm, then there is a 2.5 mm difference. That would mean there is 1.25 mm between the edge of the contact lens and the limbus on each side. If we observe half of this distance in movement of the contact lens on the eye, this would mean roughly 0.6 mm of movement. Apart from comfort issues, excessive movement was linked to variation/fluctuation in vision and may in some cases lead to the development of localized CLPC (contact lens-induced papillary conjunctivitis). It was stated that variable or suboptimal vision may also be a potential indicator of poor lens fit. Initial lens wear comfort is a good indicator of lens success. Soft contact lenses that appear to have no or minimal movement may be very comfortable. Unfortunately, these lenses may exhibit very little tear exchange. Fresh tears beneath the lens is considered crucial for good eye health, and tight lenses may be a precursor to some of the problems we see in today s contact lens practice. Inflammatory reactions, like corneal infiltrates, may be a reaction to the toxins released from the debris trapped in the tear film behind the lens. The consensus group was in agreement that non-moving lenses in general would make us nervous and would not guarantee good eye health in long-term soft contact lens wear. Because a tight-fitting lens or a lens edge that digs into the conjunctiva may be more comfortable than a well-fitting lens, the fit of a very high initial comfort lens has to be carefully verified. It was generally agreed that initial comfort is not a good indicator for successful long-term lens wear. If anything, it may be the reverse, and the group agreed that initial comfort alone should not be used as an indicator of lens success. Advertisement

5 FITTING BACKGROUND Soft lens fitting 2 Fig. 2: Contact lens diameter may be a better predictor of lens behavior on eye, including centration, than the base curve Soft lens movement on-eye leads to better tear film exchange. The group was uncertain about the correlation between lens movement and tear film exchange. Many of us have observed that flat-fitting soft contact lenses may move less than those with a good lens-to-ocular-surface relationship due to decentration onto the conjunctiva. Steeper-fitting lenses sometimes move more on the eye because the eyelids have more grip on the lens. We could not agree at this point whether more movement is equivalent to more tear film exchange. The group did agree, however, that lens movement is essential for healthy soft lens wear. New imaging techniques may potentially help us to better understand post-soft lens tear film thickness, and thus may offer better insights into tear film exchange behind the lens. The consensus group concluded that there is a desire and need to define and develop a method to identify tear film exchange and/or the lack thereof in the near future. Physiological signs like hyperemia, impingement of conjunctival vessels and corneal staining may be important signs to consider in lens performance on-eye in addition to lens movement. Marco van Beusekom introduced the term physiological management for this. Conjunctival impression rings were also brought up as a variable but general consensus was that there is not enough evidence at this time that conjunctival impression and/or conjunctival staining is a reliable indicator of soft lens success or a potential predictor of lens failure. Scleral lens fitting may have shown us that patients can be very comfortable and successful with some significant lens impression into the conjunctiva. CONCLUSIONS & RECOMMENDATIONS The traditional approach to soft lens fitting may not be sufficient to optimally serve the full range of eyes in our practices. Also, many of the current ideas we have about soft lens fitting may no longer be accurate. For instance, it was agreed upon by the discussion group that base curve and keratometry values, as well as traditional soft lens fitting rules, may be obsolete. Soft contact lens movement on-eye was agreed upon to be essential for good eye health in the long run. But the 1 mm optimal movement guideline needs to be reconsidered: current knowledge shows that movement of up to 0.5 mm is more realistic and desirable. A few recommendations made by the consensus group also reflect on the contact lens manufacturers. As a request to the industry: more diameter options and more knowledge about back surface design would help eye care practitioners to better serve our patients for instance, is it a monocurve, bicurve, tricurve, or an aspherical design? To have this information available, either on the blister pack or listed in overviews like Tyler s Quarterly or product catalogues, would be highly desirable. In the group discussion it was estimated that the stock lenses we have available today will fit at least 80% of the corneas we see. Our concern is for the other 20%. We feel it would be in the best interest of those patients to develop additional lens diameters rather than developing new base curves. This may result in better fitting and more comfortable lenses for the not-so-standard eyes. Another consideration the consensus group in the workshop wants to give to the industry is to provide eye care practitioners with the sagittal height values of currently available soft contact lenses. Studies at the University of Maastricht show that marked differences in sagittal height exist among different commercially available frequent replacement silicone hydrogel lenses. Different lens brands with the same labelled base curve value also had marked differences in sagittal height, with potentially significant effects in clinical on-eye performance in terms of lens behavior. Although sagittal height information, as stated before, may not be a perfect measure, it would be a good start and possibly a good indicator for how the fit changes when switching from one lens brand to another. Working together manufacturers, educators, researchers and eye care practitioners in clinical practice could help elevate soft contact lens fitting to the next level. This and new technologies may enable us to improve our understanding of soft contact lens fitting in the future. Hopefully at future events, like the EFCLIN meeting and other contact lens meetings around the world, further discussion on the topic can take place and reveal what steps we need to take in the future. ACKNOWLEDGEMENTS This article is based on the proceedings of the NCC 2014 consensus group workshop publication in Contact Lens Spectrum of June 2014 under the title The future of soft contact lens fitting starts here. We would like to thank PentaVision LLC for allowing us to reprint parts of that article. REFERENCES Andre M, Davis J, Caroline P. A New approach to fitting soft contact lenses. Eyewitness 2001;2:1-4 Bowden T. Contact Lenses The Story. Bower House Publications, ISBN Fonn D (Ed.). Spherical soft contact lens fitting and the effects of parameter changes. In: The IACLE Contact Lens Course 1st ed., Lecture 3.2. IACLE, Sydney Australia; Available on-line at: Gundal R, Cohen H, DiVergilio D. Peripheral keratometry and soft lens fitting. Int Eyecare 1986;2:611-3 Hall LA, Hunt C, Young G, Wolffsohn J. Factors affecting corneoscleral topography. Invest Ophthalmol Vis Sci 2013;54: Hall LA, Young G, Wolffsohn JS, Riley C. The influence of corneoscleral topography on soft contact lens fit. Invest Ophthalmol Vis Sci 2011;52: GlobalCONTACT 3-14

6 Soft lens fitting FITTING BACKGROUND Truong TN, Graham AD, Lin MC. Factors in contact lens symptoms: evidence from a multistudy database. Optom Vis Sci. 2014;91(2): Van der Worp E, Graf, T, Caroine P. Exploring Beyond the Corneal Borders. Contact Lens Spectrum 2010;6:26-32 Van der Worp E, Schweizer H, Lampa M, Van Beusekom M, Andre M. The futureof soft contact lens fitting starts here. Contact Lens Spectr 2014;6: Wolffsohn JS, Hunt OA, Basra AK. Simplified recording of soft contact lens fit. Cont Lens Anterior Eye 2009;32:37-42 Young G. Ocular sagittal height and soft contact lens fit. J BCLA 1992;15:45-49 Eef van der Worp, BOptom, PhD, FAAO, FIACLE, FBCLA, FSLS is an educator and researcher. He received his optometry degree from the Hogeschool van Utrecht in the Netherlands (NL) and has served as a head of the contact lens department at the school for over eight years. He received his PhD from the University of Maastricht (NL) in He is a fellow of the AAO, IACLE, BCLA and the SLS. He is currently affiliated with the University of Maastricht as an associate researcher, a visiting scientist at Manchester University (Manchester UK) and adjunct Professor at the University of Montreal University College of Optometry (CA) and adjunct assistant Professor at Pacific University College of Optometry (Oregon, USA). He is lecturing extensively worldwide and is a guest lecturer at a number of Universities in the US and Europe. Helmer Schweizer, Optometrist and MBA, FEAOO, FAAO, FBCLA, FIACLE, VDCO, WVAO, SBAO Past and current President of Euromcontact and Chairman European Contact Lens Forum 2012 Recipient of the EFCLIN Award The future of soft lens fitting NCC2014 consensus group: Helmer Schweizer (moderator) Matthew Lampa Mark André Marjan Beumer Christophe Collette Christine Boer John Schilder Ronald Basseleur Sarah Smit Elga van Braam Dirkje Oostenveld Eelko Bakker Carsten Avermann Andre Verhoeve Frans Littooij Karel Vandeputte Panel Participants Marco van Beusekom Eef van der Worp Hendri van Veen Jennifer van Hassel John Phielix Jack Kostelijk G.H. Boer Lindsey Verhoeve Roel Schwedler Herman Obbink Jeroen van der Heijden Gudrun Sturing-Kempin Niels Mulder Henri Van Eek Jeroen Mulder D. Schaper William van der Zalm Gea Wiggers Wim Borst Petra Groen Lex Klein Schiphorst Ilse Joyce Dijksterhuis Ton Weijsenfeld Sabrina Bockhoven-Grine Sieuwke Douna D. Last Jeanine Lammers Augusta van Lingen Hanka Jongman Roland Hemmer Edward Geeve Astrid Lourens-van Os Diana Doorduin Advertisement The world famous NIMO technology and bene ts in a brand new ALL IN ONE motorized instrument Up to 121 IOL measured in a single click! Flexible Matrix tray de nition One time calibration Dry or Wet measurement Non-moving IOL Matrix tray for an easy water management Lambda-X s.a. Av. Robert Schuman 102 B-1400 Nivelles Belgium Tel. : +32 (0) Fax. : +32 (0) info@lambda-x.com