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Contact Lens & Anterior Eye 37 (2014) 391–393

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Contact Lens & Anterior Eye

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ecoding soft lens fitting

The development of the first soft lenses date back to late 1950s-arly 1960s. In his excellent book ‘Contact Lenses – The Story’, Timowden [1] looks back at the origin of soft lenses, acknowledg-

ng the grandfather of soft lenses – Otto Wichterle. Apparently, onhristmas eve in 1961, Wichterle built what is regarded as the firstoft lens manufacturing device, which he made using a children’seccano set. A famous quote in the book by the grandfather himself

tates:

“A measure of a man is how he deals with those unexpected con-frontations with reality called change.” Otto Wichterle

Grand words that only a great visionary can proclaim. Ottoichterle was born in 1913, more than a century ago now, and

ied in 1998 in the Czech Republic. The development of soft lensesas a major achievement – one that hardly anyone in those earlyays believed in. By late 1960s, spin-cast and lathe-cut soft lensesere available in a number of countries. It was not until 1987

hat the world of contact lenses was irrevocably changed with thentroduction of disposable lenses, based on an idea by Danish oph-halmologist Michael Bay. What is interesting is that soft lens fittings a science and as a skill has been downplayed over the last twoecades or so as frequent replacement and disposable soft lensesave grown, which may be considered a logical development in

tself. The downside is that fitting soft lenses has become a routinerocess without most of us actually realizing why we are doinghings the way we do them. More recently, developments haveaken place that may urge us to have a second look at the waye fit soft lenses today. It would have been nice to have the per-

pective of the grandfather of soft lens fitting, Wichterle, regardinghese newest changes.

Silicone hydrogel lenses, now the number one lens material pre-cribed worldwide [2], may take us back to some degree to theoots of lens fitting, as the lens-to-cornea relationship seems toave become more important because many of these lenses have

higher modulus than conventional soft lens materials. Also, mea-uring techniques, up to recently limited to central keratometry,ave been upgraded: first to limbal-to-limbal corneal coverageopography instruments, and most recently to instruments thatan measure the limbal area and even beyond that (such as opticaloherence tomography [3–5] and eye surface profilometry [6,7]),

hus helping us better understand the shape of the corneo-scleralunction and the anterior surface. Studies by Hall et al. [8] havendicated that there is a direct relationship between corneo-scleralhape and soft lens fitting characteristics. Additionally, we have

ttp://dx.doi.org/10.1016/j.clae.2014.09.009367-0484/© 2014 British Contact Lens Association. Published by Elsevier Ltd. All rights r

ways to better measure, analyse and understand the shape andgeometry of currently used soft contact lenses.

Interestingly, despite all material, replacement frequency andcontact lens care developments in recent years, we are still facinghigh dropout rates [9,10] as alluded to at the 2014 BCLA ClinicalConference & Exhibition in Birmingham. It may therefore be timeto see whether we can do things differently. Potentially we may beoff to a new beginning, changing or altering our approach in theway we that we fit and evaluate soft lenses [11] going forward.

The NCC2014 meeting (the Dutch bi-annual contact lens meet-ing) earlier this year hosted a workshop to discuss the state of softlens fitting anno 2014. The theme of the meeting was ‘decoding thesecret’ and that was exactly what this workshop intended to do.Optometrist and educator Helmer Schweizer, who is also Eurom-contact president, acted as the panel discussion moderator. Apartfrom the author of this paper, the workshop panel consisted ofMatthew Lampa and Mark André, both experts in the field fromPacific University College of Optometry in Oregon (USA), and Marcovan Beusekom, conference president of the NCC meeting from theNetherlands and well-known speaker on the topic of soft lens fit-ting. The aim of the workshop was to find common ground, andcommon sense, in the way in which we are fitting soft lenses today.The proceedings of the NCC 2014 consensus group workshop werepresented in Contact Lens Spectrum of June 2014 under the title‘The Future of Soft Contact Lens Fitting Starts Here’ [12]. A few ofthe main points of the workshop are shared and further discussedhere.

1. Keratometry

One of the main ‘myths’ in the contact lens field may be the useof central keratometry measures to fit soft lenses. Taking centralkeratometry values is still valid and should be performed to obtaina baseline and thus, to be able to follow up and manage potentialtopographical changes. It can also play a role in lens selection (RGPversus soft, because of corneal versus refractive astigmatism). Butother than that, it may be time to admit that central keratometryis not a very useful indicator of soft lens behaviour on-eye or forselecting the initial base curve of the contact lens. This is backed upby work from Young [13] and Gundel [14] stating that there is a very

weak correlation between the central and peripheral K-readingsand soft contact lens fitting characteristics. Using sagittal heightdata has been proposed in the past [13,15,16], and using sagittalheight to better understand soft contact lens behaviour on-eye is

eserved.

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lso part of the international association of contact lens educators’IACLE) basic module on soft lens fitting [17]. Based on the sagittaleight fitting method, registering the total sagittal height of the

ens would make more sense in theory. One limitation of this is thatenses can have different back surface geometries and/or diametersnd still have the same sagittal height. Also, it is unclear how lensehydration on the eye would affect the total overall sagittal heightf the soft contact lens.

Lens diameter, from a clinical standpoint, may be potentiallyseful measure and alternative method for estimating the relativeagittal height of the cornea. Measuring corneal diameter is a dis-ussion in itself, but taking ‘white-to-white’ measurements of theornea (diagonally) with a corneal topographer could be one of theost preferred options. Recently, some contact lens manufactur-

rs have developed special ‘rulers’ to measure corneal diameter,nd if this is outside of a certain margin, then custom-made lensesre suggested. More and more companies are considering makingustom-made soft lenses for the non-standard eye.

. Base curve

Following up on the previous ‘myth’: base curve notation on aoft lens package (usually expressed in numbers with or withoutm) may not necessarily be the actual contact lens’ back surface

adius, at least not the one in the back surface optic zone (BOZR).t is more often than not questionable as to whether the lens actu-lly has an ‘8.3’ or ‘8.6’ mm spherical radius on its back surface. Inany cases, it is the calculated base curve equivalent (BCE), i.e., the

adius of a sphere that would have the same sagittal height overhe indicated diameter as the lens at hand. The lens’ back surfaceesign and diameter drive its actual sagittal height. For those lensrands that come with a choice of base curves (or BCEs), it shouldather be viewed as a sort of an indicator, more of a symbolic valuehan as the actual back surface curvature of the lens. Based on this,t appears that the single number on the lens box cannot definehe lens design or its fit. The total sagittal height and back surfaceesign of the lens seems to be of much more importance. From a

egal standpoint, though, some kind of base curve or base curvequivalent still needs to be on the package labelling at this point.

. Lens centration

It is suggested that more often than not, the corneo-scleralunction is best described as having tangent angles, rather thansing ‘curve’ terminology (like concave and convex) to define itshape, although individual limbal and anterior scleral shape differ-nces occur. New insights [4,5] show us that practitioners shouldn’txpect the limbal area, or corneo-scleral junction, to necessarilyave the concave shape that would be expected based on theoret-

cal considerations expressed in older and even current textbookhapters. In addition to this, these studies also indicate that, forhe average eye, the ocular surface beyond the cornea is non-otationally symmetrical in nature. It appears that, in the averageye, the entire nasal portion is typically flatter compared to thether quadrants. As a consequence, the nasal region typically isore elevated than in the other meridians – with a potentially

mportant clinical impact on soft contact lens centration. It mayxplain the commonly observed temporal decentration of soft con-act lenses – which is of importance in terms of the position ofhe lens optics and visual performance of the lens: especially withegards to toric lens designs, bifocal lens designs and surely myopia

ontrol lenses.

In the past, many of us were taught that larger soft contact lensesead to better lens centration. Current knowledge about the nasalortion of the eye being more elevated may urge us to revisit this.

or Eye 37 (2014) 391–393

Larger lenses may actually lead to more (temporal) decentration,at least in some cases. It should be noted that lens diameter is con-sidered a relative measure, meaning that it should be evaluatedrelative to the individual corneal diameter. For instance, Asian eyesgenerally are observed to have a smaller corneal diameter; there-fore, a specific lens for Asian eyes might actually make sense. Thediameter of the contact lens should be a specific amount (in mil-limetres) larger than the actual corneal diameter. All in all – thecontact lens diameter may be a better predictor than the base curveof lens behaviour on eye, including centration.

4. Lens movement

In the past, and even in some textbooks today, 1 mm of lensmovement is sometimes advocated as the optimal amount of softlens movement. However, with the average horizontal visible irisdiameter being 11.8 mm and average soft contact lens diameter inthe 14 mm range, this would bring the lens edge upon eye blinkingalmost right into the limbal zone, which may result in discomfort.The reality is that today’s soft lenses are often moving consider-ably less than 1 mm with an eye blink. This is backed up by recentresearch showing that 0.3 mm of soft contact lens movement in thenormal eye is more realistic. Troung et al. [18] recently showed thatpatients with lenses that move in the 0.1–0.4 mm range are mostcomfortable.

Maybe in contrast with the general belief, the consensus groupcould not universally decide whether conventional hydrogel lensesmove more or move less than silicone hydrogel lenses do. Lensmovement may depend on many more variables (like lens edgeshape and back surface geometry, among others) than mate-rial alone. In general, it was concluded that it should not beassumed that silicone hydrogels move more than conventionalhydrogels.

Soft contact lenses that appear to have no or minimal move-ment may be very comfortable. Unfortunately, these lenses mayexhibit very little tear exchange. Fresh tears beneath the lens isconsidered crucial for good eye health, and tight lenses may be aprecursor to some of the problems we see in today’s contact lenspractice. Inflammatory reactions, like corneal infiltrates, may be areaction to the toxins released from the debris trapped in the tearfilm behind the lens. The consensus group was in agreement thatnon-moving lenses in general ‘would make us nervous’ and wouldnot be a guarantee for good eye health in long-term soft contactlens wear. A tight-fitting lens or a lens edge that digs into the con-junctiva may be more comfortable than a well-fitting lens, but isnot good for long-term eye health. Thus, the fit of a very high initialcomfort lens has to be carefully verified. It was generally agreedthat initial comfort is not a good indicator of successful long-termlens wear. If anything, it may be the reverse.

Another interesting, and quite trivial, question is whether thereis a correlation between lens movement and tear film exchange.Many of us have observed that flat-fitting soft contact lenses maymove the same, or even 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 ofa less than ideal lens-to-ocular-surface relationship, allowing theeyelids to have more “grip” on the lens. In summary: although itseems clear that lens movement is essential for healthy soft lenswear, at this point it is unclear whether more movement is equiv-alent to more tear film exchange. New imaging techniques maypotentially help us to better understand post-soft lens tear film

thickness, and thus may be able to provide better insights intotear film exchange behind the lens. There certainly is a desire andneed to define and develop a method to identify tear film exchangeand/or the lack thereof in the near future.

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Physiological signs like hyperemia, impingement of conjuncti-al vessels and corneal staining may be important signs to considern lens performance on-eye in addition to lens movement. Marcoan Beusekom introduced the term ‘physiological management’ forhis. Conjunctival impression rings were also brought up as a vari-ble – but general consensus was that there is not enough evidences of now that conjunctival impression and/or conjunctival stainings a reliable indicator of a soft lens success or a potential predictorf lens failure. Scleral lens fitting may have shown us that patientsan be very comfortable and successful with some significant lensmpression into the conjunctiva.

Another point of interest that may need further investigation ishat soft lenses do induce corneal topographical changes. Similaro rigid gas permeable lenses, soft lenses can have an impact onhe cornea and on corneal shape. Corneal deformations as a resultf suboptimal soft lens fittings are not as uncommon as many mayhink. If practitioners would remove soft lenses at every follow-upisit and perform corneal topography, they would be surprised byhe amount of unwanted changes that can take place beneath a softens [19–22]. This could serve, in addition to the ones mentionedbove, as a potential valuable clinical tool to evaluate soft contactens fit on-eye.

. Potential future steps

The traditional approach to soft lens fitting may not be suf-cient to optimally serve the full range of eyes in our practicesoing forward, and many of the current ideas we have aboutoft lens fitting may no longer apply. A few recommendationsan be made based on the statements above. As a request tohe industry, more diameter options would be highly preferred.nd although sagittal height information, as stated before, mayot be a perfect measure, it would be a good start and possi-ly a good indicator for how the sagittal height changes whenwitching from one lens brand to another. In general – a goodtart would be to have more knowledge about back surface designnd/or sagittal depth of the lens, as this could potentially helpye care practitioners to better serve their patients (is it a mono-urve, a bi-curve, tri-curve or an aspherical design?). To have thisnformation available, on the package or listed in overviews likehe ACLM Contact Lens Year Book (available through the BCLAor members) or US-based Tyler’s Quarterly or product cataloguesould be highly desirable. Of course, many factors contribute to

oft lens comfort and to potential dropout rates [23], and look-ng at lens fit and design may not solve all of our problems. Butt may be one piece of the puzzle, one that potentially is oftentimesverlooked.

In addition to the items mentioned above – new technologyopefully can help us better understand the shape of the anteriorcular surface, and maybe even can be of assistance is soft lensvaluation on-eye and/or with assessing tear film exchange. It has

een estimated that the stock lenses we have available today willt at probably 80% of the corneas we see. But for the other part oft least 20%, more customization of lenses may be needed and/oresired.

or Eye 37 (2014) 391–393 393

Working together – manufacturers, educators, researchers, eyecare practitioners and professional organisations like the BCLA – wecould all help elevate soft contact lens fitting to the next level. This,and new technologies, may enable us to improve our understandingof soft contact lens fitting in the future.

It appears that the famous words of Otto Wichterle (“A measureof a man is how he deals with those unexpected confrontations withreality called change”) echo back to us once again.

References

[1] Bowden T. Contact lenses – the story. Bower House Publications; 2009, ISBN978-0-9556719-0-6.

[2] Morgan PB, Woods CA, Tranoudis IG, Helland M, Efron N, Teufl M, et al. Inter-national contact lens prescribing 2013. Contact Lens Spectr 2014;1:30–5.

[3] Sorbara L, Maram J, Fonn D, Woods C, Simpson T. Metrics of the normalcornea: anterior segment imaging with the Visante OCT. Clin Exp Optom2010;93:150–6.

[4] Van der Worp E, Bornman D, Ferreira DL, Faria-Ribeiro M, Garcia-Porta N,González Meijome JM. Modern scleral contact lenses: a review. Contact LensAnterior Eye 2014;37:240–50.

[5] Hall LA, Hunt C, Young G, Wolffsohn J. Factors affecting corneoscleral topogra-phy. Invest Ophthalmol Vis Sci 2013;54:3691–701.

[6] Iskander D. The clinical utility of the Eye Surface Profiler. In: ARVO meeting.2013, poster 533.

[7] Jongsma FH, de Brabander J, Hendrikse F, Stultiens BA. Development of a widefield height eye topographer: validation on models of the anterior eye surface.Optom Vis Sci 1998;75:69–77.

[8] Hall LA, Young G, Wolffsohn JS, Riley C. The influence of corneoscleral topog-raphy on soft contact lens fit. Invest Ophthalmol Vis Sci 2011;52:6801–6.

[9] Wolffsohn JS. BCLA Pioneers Lecture – evidence basis for patient selection: howto predict contact lens success. Contact Lens Anterior Eye 2014;37:63–4.

10] Naroo SA. Contact lens dropouts – ‘must try harder’. Contact Lens Anterior Eye2012;35:95.

11] Wolffsohn JS, Hunt OA, Basra AK. Simplified recording of soft contact lens fit.Contact Lens Anterior Eye 2009;32:37–42.

12] 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;6:44–55.

13] Young G. Ocular sagittal height and soft contact lens fit. J BCLA 1992;15:45–9.14] Gundal R, Cohen H, DiVergilio D. Peripheral keratometry and soft lens fitting.

Int Eyecare 1986;2:611–3.15] Andre M, Davis J, Caroline P. A new approach to fitting soft contact lenses.

Eyewitness 2001;2:1–4.16] Bibby MM. Sagittal depth considerations in the selection of the base curve

radius of a soft contact lens. Am J Optom Vis Sci 1979;56:407–13.17] Spherical soft contact lens fitting and the effects of parameter changes.Fonn D,

editor. The IACLE contact lens course. 1st ed. Sydney, Australia: IACLE; 1997.Lecture 3.2. Available on-line at: http://www.iacle.org

18] Truong TN, Graham AD, Lin MC. Factors in contact lens symptoms: evidencefrom a multistudy database. Optom Vis Sci 2014;91(2):133–41.

19] Schornack M. Hydrogel contact lens-induced corneal warpage. Contact LensAnterior Eye 2003;26:153–9.

20] Van der Worp E. Backstage – part I: do we know what is happening behind asoft lens? Global Contact 2014;67(1):20–4.

21] Van der Worp E. Backstage – part II: do we know what is happening behind asoft lens? Global Contact 2014;2(67):20–4.

22] McKernan AL, O’Dwyer V, Mannion LS. The influence of soft contact lens wearand two weeks cessation of lens wear on corneal curvature. Contact Lens Ante-rior Eye 2014;37:31–7.

23] Chalmers R. Overview of factors that affect comfort with modern soft contactlenses. Contact Lens Anterior Eye 2014;37:65–76.

Eef van der Worp (BOptom, PhD, FAAO, FIACLE,

FBCLA, FSLS)

E-mail address: eefvanderworp@netherlens.com

5 September 2014