SOFT LENS FITTING

The Future of Soft Contact Lens Fitting Starts Here

A workshop at the recent NCC2014 meeting set out to reach consensus on how soft lenses are fitted today.

By Eef van der Worp, BOptom, PhD, FAAO, FIACLE, FBCLA; Helmer Schweizer, MBA, FAAO, FBCLA, FIACLE, FEAOO; Matthew Lampa, OD, FAAO; Marco van Beusekom, BOptom, FIACLE; & Mark P. André, FAAO

At the 2014 Netherlands Contact Lens Congress (NCC), a biannual meeting that took place in March in Veldhoven, the Netherlands, a workshop was held to discuss the current state of soft contact lens fitting. The theme of the NCC2014 meeting was “Decoding the Secret,” and that was exactly what this workshop intended to do—to dissect and analyze the way in which we are fitting soft lenses today as well as to reach agreement on the proper procedure. In other words, the aim of the workshop was to find common ground, and common sense, in the way in which we are fitting soft contact lenses today.

It’s Time for a Change

Soft contact lens fitting and evaluation have been relatively downplayed over the last two decades or so (as frequent replacement and daily disposable soft lens modalities have grown); this has become a routine process in which most of us do not realize why we do things the way in which we do them. In the meantime, we are still experiencing high dropout rates, despite all of the lens material and contact lens care developments in recent years.

It may, therefore, be time to see whether we can do things differently. Using new technology—such as corneal topography, optical coherence tomography (OCT), and profilometry (e.g., the Eye Surface Profiler [ESP, Eaglet-Eye], Figure 1)—we’ve developed new insights into the shape of the anterior ocular surface. Additionally, we have ways to better measure and analyze the shape of soft contact lenses. These recent findings have brought us to a potential new beginning; some even say we’re at a crossroads that may change our approach regarding how we fit and evaluate soft contact lenses in the future.

Figure 1. Profilometry map.

Workshop Overview

Devoted soft contact lens-fitting eyecare professionals from the Netherlands, Belgium, and other countries attending the NCC were invited to participate in the workshop and to interact with a panel of representatives from the contact lens industry, contact lens educators, and researchers. A total of 44 participants attended the interactive session.

Helmer Schweizer, Euromcontact (the European Federation of National Associations and International Companies of Contact Lens [and Lens Care] Manufacturers) president as well as an optometrist and an educator, acted as the panel discussion moderator.

The first points that the audience and the panel discussed were the criteria for the evaluation of a “good” soft contact lens fit—centration, movement, and vision. The alignment of the posterior surface of the lens to the anterior ocular surface shape beyond the limbus drives centration and movement of a soft contact lens. New insights show us that practitioners shouldn’t expect the limbal area (or cornea-sclera junction) to necessarily have the concave shape that would be expected based on theoretical considerations expressed in older and even in current textbook chapters.

An important point was made that centration becomes particularly critical and relevant in toric and multifocal contact lenses. The focus of the workshop was then narrowed down specifically to spherical lenses alone, to avoid making the discussion unnecessarily complex.

The group also discussed physiological signs (e.g., hyperemia and corneal staining) and what the presence of such signs means in relation to how soft lenses are performing on the eye.

Keratometry was agreed upon as a means for establishing a baseline and possibly for selecting an initial lens type. However, its ability to predict soft lens base curve or behavior on-eye was called into question.

Finally, the group discussed what those base curve values on contact lens packaging really mean, and what impact corneal sagittal height, lens sagittal height, lens diameter, and back surface design have on soft contact lens fitting.

Following are specific statements that the consensus group and the panel discussed during the course of the workshop.

Statement #1: Eye Shape Is Different from What Traditional Textbooks Indicate

It appears that, more often than not, the shape of the cornea-sclera junction is best described as having tangent angles (Figure 2) rather than concave or convex curves, although individual limbal and anterior scleral shape differences occur.

Figure 2. An example of the tangential nature of the cornea-sclera junction in a normal eye.
COURTESY OF HANS KLOES, THE NETHERLANDS

Recent studies (Hall et al, 2013; Hall et al, 2011; van der Worp et al, 2010) also indicate that, for an average eye, the ocular surface beyond the cornea is nonrotationally symmetrical in nature. In an 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 can impact the position of the lens optics and, therefore, visual performance of the lens (Figure 3).

Figure 3. An example of a good soft contact lens fit, demonstrating on-eye centration (left) and one that is decentered slightly temporally (right).

Statement #2: Lens Centration Is Important

In the past, many of us were taught that larger soft contact lenses lead to better lens centration. Current knowledge that the nasal portion of the eye is more elevated may urge us to revisit this, as larger lenses may actually result in more (temporal) decentration.

It is very important to note from the discussion that lens diameter is considered a relative measure, meaning it should be evaluated relative to individual corneal diameter. For instance, Asian eyes generally have a smaller corneal diameter (Matsuda et al, 1992; Lam and Loran, 1991); therefore, a lens made specifically for Asian eyes might actually make sense.

The diameter of a soft contact lens should be a specific amount (in millimeters) larger than the actual corneal diameter. All in all, contact lens diameter may be a better predictor than base curve is of lens behavior on eye.

Statement #3: 1mm of Lens Movement Is Not Optimal for Soft Lenses

In the past, and even in some textbooks today, 1mm of lens movement is sometimes advocated as optimal for soft lenses. However, with the average horizontal visible iris diameter (HVID) of 11.8mm (André et al, 2001) and average soft contact lens diameter in the 14mm range, 1mm of lens movement upon blinking would bring the lens edge almost into the limbal zone, which may result in discomfort.

In reality, today’s soft contact lenses are often moving considerably less than 1mm with blinking. This is backed up by recent research indicating that 0.3mm of soft contact lens movement in a normal eye is more realistic (Wolffsohn et al, 2009). Troung et al (2014) recently showed that patients whose lenses move about 0.1mm to 0.4mm during blinking are most comfortable.

The group also discussed different lens movement assessment techniques; the push-up test, lens-lag (with eye movement and post-blinking), and even rotational movement of the lens were all considered. The consensus group agreed that measuring soft contact lens movement in increments of 0.1mm in clinical practice is not feasible.

Helmer Schweizer suggested a simple, but clinically useful, method of assessing soft lens movement that can be performed even if a slit lamp is not available. The average visible iris diameter vertically is approximately 11.5mm, so for a contact lens diameter of 14.0mm, there is 2.5mm difference. That would mean that there is 1.25mm 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 0.6mm of movement.

Apart from comfort issues, excessive soft lens movement was linked to variation/fluctuation in vision and, in some cases, to the development of localized contact lens-induced papillary conjunctivitis (CLPC). It was stated that variable or suboptimal vision may also be a potential indicator of poor lens fit.

Statement #4: We Cannot Assume that Silicone Hydrogel Lenses Move More Compared to Conventional Hydrogels

The consensus group could not decide universally on whether conventional hydrogel lenses move more or less compared to silicone hydrogel lenses. Lens movement may depend on many other variables than material alone (such as lens edge shape and back surface geometry, among others). In general, we should not assume that silicone hydrogels move more compared to conventional hydrogels.

Statement #5: Lens Movement Is Crucial for Tear Film Exchange and Debris Removal

Soft contact lenses that appear to have no or minimal movement may be very comfortable. Unfortunately, such lenses may exhibit very little tear exchange. A constant supply of fresh tears beneath the lens is considered crucial for good eye health, and tight lenses may eventually result in some of the problems that we see in today’s contact lens practice. Inflammatory conditions, such as corneal infiltrates, may result from a reaction to the toxins released from the debris trapped in the tear film behind the lens.

The consensus group agreed that, in general, non-moving lenses would “make them nervous” and would not guarantee good eye health in long-term soft contact lens wear. Therefore, because a tight-fitting lens or a lens edge that digs into the conjunctiva may be more comfortable initially compared to a lens that exhibits adequate movement, the fit of a soft lens that provides very high initial comfort needs to be carefully verified. We also agreed that initial comfort is not a good indicator of successful long-term lens wear. If anything, it may be the opposite.

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 compared to those that have a good lens-to-ocular-surface relationship due to decentration onto the conjunctiva. Steeper-fitting lenses sometimes move more on the eye because of a less-than-ideal lens-to-ocular-surface relationship, allowing the eyelids to have more “grip” on the lens. We could not agree 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 provide 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 (or the lack thereof) in the near future.

Statement #6: Physiological Signs Are Important to Consider in Lens Performance

The group also agreed that beyond lens movement, physiological signs, such as hyperemia, impingement of conjunctival vessels, and corneal staining, may be important to consider with regard to lens performance on-eye because they could result from a poor lens fit. Marco van Beusekom introduced the term “physiological management” for this during the workshop.

Conjunctival impression rings were also brought up as a variable, but the general consensus was that not enough evidence currently exists to indicate that conjunctival impression and/or conjunctival staining are reliable indicators of soft lens success or potential predictors of lens failure. Scleral lens fitting has demonstrated that patients can be very comfortable and successful with some significant lens impression into the conjunctiva.

Statement #7: Central Keratometry Measurements Are Not Useful in Predicting Soft Lens Fitting Characteristics

The consensus group decided that determining central keratometry values is still valid; it is necessary to establish a baseline and, thus, to serve as a reference for follow up and in managing potential topographical changes. Keratometry values also can play a role in lens selection (GP versus soft, because of corneal versus refractive astigmatism).

The group also agreed that keratometry is not a very useful indicator of soft lens behavior on-eye or for selecting the initial base curve of a contact lens. This is backed up by work from Young (1992) and Gundel et al (1986) stating that there is a very weak correlation between the central and peripheral K-readings and soft contact lens fitting characteristics.

Using sagittal height data to improve soft lens fitting has been proposed in the past (André et al, 2001; Young, 1992). In addition, using sagittal height data to better understand soft contact lens behavior on-eye is part of the International Association of Contact Lens Educators’ (IACLE) basic module on soft lens fitting (Fonn, 1997). Based on the sagittal height fitting method, registering the total sagittal height of a soft lens would, in theory, make more sense. One limitation of this is that lenses can have different back-surface geometries and/or diameters and still have the same sagittal height (Figure 4). Also, it is unclear what effect on-eye lens dehydration has on the total overall sagittal height of a soft contact lens.

Figure 4. The right half shows a spherical back surface lens design with radius 8.6mm across the total back surface. The left half (red) shows an aspheric back surface design with the same sagittal height and diameter as the right half. Thus, the calculated base curve equivalent of the left lens is the same as the actual base curve of the right one.

Lens diameter was discussed as a very useful clinical measurement and an alternative method for estimating the relative sagittal height of the cornea. Measuring corneal diameter is a discussion in itself, but the experts on the panel agreed that taking white-to-white measurements of the cornea on a diagonal using a corneal topographer could be the best, or most preferred, method.

Statement #8: The Base Curve Values on Soft Lens Packaging Are Symbolic Values

The indicated base curve on a soft lens package (usually expressed in numbers, with or without mm) is by many considered to be the actual back-surface radius of the packaged lens, or at least the back-surface radius of the optic zone (BOZR). However, it is more often than not questionable as to whether the lens actually has an 8.3mm or 8.6mm 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. A 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 indicate on the label “base curve equivalent” (BCE) rather than “base curve.”

At any rate, for lens brands that come with a choice of base curves/BCEs, we should rather view it as more of a symbolic value. That single number on the lens box certainly does not define the lens fit. The total lens sagittal height and back surface design is of much more importance. However, from a legal standpoint, it was agreed that some kind of base curve or BCE value still needs to be on lens package labeling today.

Statement #9: More Diameter Variability and Sagittal Height/Lens Design Information Is Needed

We estimate that the stock lenses that we have available today will fit at least 80% of the corneas that we see. Our concern is for the other 20 percent. We feel that it would be in the best interest of those patients to develop additional lens diameters rather than base curves. This may result in better fitting and more comfortable lenses for not-so-standard eyes.

Another consideration that the consensus group wants to suggest to the industry is to provide sagittal height values of currently available soft contact lenses. Studies at the University of Maastricht show that marked differences exist in sagittal height among different commercially available frequent replacement silicone hydrogel lenses (van der Worp, 2014). Different lens brands with the same labeled base curve value also had marked differences in sagittal height, with potentially significant clinical on-eye performance in terms of lens behavior. Although, as stated previously, sagittal height information may not be a perfect measure, it would be a good start and possibly a good indicator for what we change when switching from one lens brand to another.

Another item revealed to be high on the discussion group’s wish list is for manufacturers to disclose more information about lenses’ back surface designs—whether they have a monocurve, bicurve, tricurve, or an aspherical design.

The Future

In summary, the traditional approach to soft lens fitting may not be sufficient to optimally serve the full range of eyes in our practices. We may be at a crossroads; the discussion group agreed 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 to be essential for good eye health in the long run. But we need to reconsider the “1mm optimal movement” guideline: current knowledge shows that movement of up to 0.5mm is more realistic and desirable.

Finally, as a request to the industry, more lens diameter options and more knowledge about lens sagittal height and the actual back surface design would help eyecare practitioners to better serve their patients. Making this information available on blister packs or listed in overviews such as Tyler’s Quarterly, Contact Lenses & Solutions Summary, or product catalogues would be highly desirable.

If all of us—industry, educators, researchers, and eyecare practitioners in clinical practice—work together, we can help elevate soft contact lens fitting to the next level. In addition, new technologies such as OCT and profilometry may enable us to measure ocular sagittal height and to improve our understanding of soft contact lens fitting in the future. CLS

The views and statements expressed in this article are those of the workshop and its participants and are not necessarily those of Contact Lens Spectrum.

Acknowledgements:

The authors thank the members of the “Future of Soft Lens Fitting” NCC2014 Consensus Group: Carsten Avermann, Eelko Bakker, Ronald Basseleur, Marjan Beumer, Sabrina Bockhoven-Grine, Christine Boer, G.H. Boer, Wim Borst, Christophe Collette, Ilse Joyce Dijksterhuis, Diana Doorduin, Sieuwke Douna, Edward Geeve, Petra Groen, Roland Hemmer, Hanka Jongman, Jack Kostelijk, Jeanine Lammers, D. Last, Frans Littooij, Astrid Lourens-van Os, Jeroen Mulder, Niels Mulder, Herman Obbink, Dirkje Oostenveld, John Phielix, D. Schaper, John Schilder, Lex Klein Schiphorst, Roel Schwedler, Sarah Smit, Gudrun Sturing-Kempin, Elga van Braam, Henri Van Eek, Jennifer van Hassel, Augusta van Lingen, Hendri van Veen, Jeroen van der Heijden, William van der Zalm, Karel Vandeputte, Andre Verhoeve, Lindsey Verhoeve, Ton Weijsenfeld, and Gea Wiggers.

For references, please visit www.clspectrum.com/references and click on document #223.