Soft Contact Lenses for Irregular Cornea - Optometry in Practice

Optometry in Practice 2010 Volume 11 Issue 2 77 – 90
Soft Contact Lenses for Irregular Cornea
Lynn White MSc FCOptom
Vision Care and Keratoconus Consultant to UltraVision, Leighton Buzzard
C-13831 3 CET points for optometrists and contact lens opticians
Introduction
Until recently, the term ‘irregular cornea’ (IC) generally referred to
corneas affected by conditions such as keratoconus, pellucid marginal
degeneration (PMD), grafting and trauma. Today, with the explosion
in refractive surgery and new treatments for ectasias, the term
‘irregular cornea’ covers a much wider range of conditions, including
post-laser-assisted in-situ keratomileusis (LASIK) and laser epithelial
keratomileusis (LASEK), post radial keratotomy (RK), astigmatic
keratotomy, photorefractive keratectomy and post intracorneal
rings (INTACS). Corneal collagen cross-linking, involving ultraviolet
activation of riboflavin applied to the cornea, is a treatment that is
increasingly used to halt the progression of keratoconus, often in
conjunction with a wide range of these refractive surgeries. Although
its efficacy in halting the progression of keratoconus is gradually being
accepted (Dilraj et al. 2009, Vinciguerra et al. 2009), contact lenses
are often still required postsurgically.
With the advent of improved designs and materials, soft lenses are
now a viable option for IC correction and have many advantages
for the patient in terms of ocular health and lifestyle. As a lens type
more familiar to the high street and less complex in fitting technique
than some specialist rigid lenses, practitioners can now extend their
range of soft lenses to accommodate patients with IC, particularly in
the area of postrefractive surgery. Although new soft lens designs for
these conditions are now available, not many papers have yet been
published detailing their performance.
Irregular corneal conditions
Keratoconus and pellucid marginal degeneration
These are naturally occurring ectasias of the cornea whose aetiology
is not fully understood. They are characterised by stromal thinning of
the cornea which then bulges forward under the influence of internal
ocular pressure. The corneal surface area may well be conserved by a
commensurate flattening of adjacent areas (Smolek & Klyce 2000). In
keratoconus, the steepest areas are mainly central or paracentral and
the condition is generally characterised by high-minus prescriptions,
with or without irregular astigmatism. PMD describes an ectasia that
is more closely located towards the limbus, often with low spherical
refractive error and against-the-rule astigmatism.
The result of these corneal changes is a reduction in acuity that cannot
be adequately corrected with spectacles. This is due to irregular
astigmatism and the effects of higher-order aberrations (HOAs), such
as coma and trefoil, induced by the irregular corneal shape (Alió &
Shabayek 2006). These aberrations result in the multiple images
and ghosting characterised by the conditions and may induce neural
insensitivity due to adaptation to poor retinal images (Ramkumar &
Geunyoung 2009).
Refractive surgery
Effective correction of refractive error by corneal surgery using RK was
perfected by Fyderov in the 1970s. It involves radial incisions in the
cornea, which change the corneal shape during the healing process.
Although still practised, this procedure has now been generally
superseded by photorefractive surgery, and approximately 17 million
LASIK procedures have been performed worldwide since 1983. Although
most surgeries are successful, some patients suffer regression, dry eyes
and visual disturbances due to the effects of HOAs and, in some cases,
development of ectasia. Many such postsurgical patients seek contact
lens correction in order to maintain their spectacle-free lifestyle.
These corneas can be difficult to fit, often requiring a reverse geometry
design as the central area of the cornea can be flatter relative to the
periphery when compared to a normal cornea.
Grafts
Indications for grafting include keratoconus, Fuchs endothelial
dystrophy, pseudophakic bullous keratopathy and viral keratitis or
indeed regrafting a previously failed graft. In the case of keratoconus,
corneas may be grafted if suitable contact lens fitting is not possible.
This may include poor vision even with a well-fitting, well-tolerated
contact lens or reasonably functional vision with a poorly tolerated
contact lens (Lim et al. 2000). Finally, grafting a keratoconic cornea
becomes necessary in the case of a very thin cornea or badly
scarred one.
The postoperative corneal shape resembles that of postrefractive
surgery and may be complicated by high irregular astigmatism or the
graft sitting proud of the host cornea.
However, grafts can take up to 18 months to settle fully and may
themselves pose a challenge to fit with a contact lens and therefore it
is in the patient’s best interest to try and maintain vision with contact
lenses for as long as possible.
Date of acceptance: 8 April 2010. Address for correspondence: L White, UltraVision, Commerce Way, Leighton Buzzard LU7 4RW, UK.
© 2010 The College of Optometrists
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Contact lenses for irregular cornea
Historically, most contact lenses for IC have had some rigid component:
rigid gas-permeables (RGPs), sclerals, semisclerals, semilimbals,
hybrids (RGP centre, soft skirt) and a piggy-backing system where
RGPs are worn over soft disposable lenses. With these choices, rigid
contact lenses act as a new, smooth-fronted surface to the cornea,
thus improving acuity markedly and restoring normal or near normal
vision to this patient group. In most UK hospitals, RGP lenses are
traditionally the first lens of choice for IC and the other lens options
are tried if RGPs fail for reasons of intolerance or fitting issues.
Soft lenses have historically been regarded as an option most suitable
for mild or moderate conditions only. The reasons for this are twofold:
it is difficult for many to understand how soft lenses can possibly
compensate for an IC, the assumption being that they simply mould
to the irregular corneal shape and thus replicate the irregularity.
Also, many feel that if soft lenses were manufactured thick enough
to mask irregularities, then they would significantly reduce oxygen
transmission, thus risking the development of neovascularisation
which would affect the success of a future graft.
Soft lenses as an option for irregular cornea
Custom soft lenses which are specifically designed to correct IC can
provide good vision, even in the presence of relatively significant
irregularities. Lenses manufactured from relatively low-Dk materials
can work successfully if the lens is not fitted too tightly and the patient
is followed up regularly to monitor wearing times. Many of these lens
types are now available in high-water-content hydrogel and silicone
hydrogel (SiH) materials, allowing sufficient oxygen transmission for
much longer wearing times (González-Méijome et al. 2006, Yamazaki
et al. 2006).
Some lenses are designed to have a direct relationship with the
central corneal curvature and others have fitting techniques based
more closely on the mid peripheral curves. Most of the companies
manufacturing such lenses advise that a fitting set should be utilised
to optimise fit, in the same manner as with RGP lens fittings. However,
unlike RGPS, soft lenses cannot be assessed with normal fluorescein
and, even if high-molecular fluorescein is used, it is difficult to obtain
useful fitting information. Thus, observation of the fit, movement,
rotation and acuity achieved is the best indicator of how well these
lenses fit.
Soft lenses designed specifically for IC drape and mould sufficiently
to limit pooling of tears under the lens, which in itself can contribute
to HOA effects but, generally, the front surface is also rigid enough
to mask much of the corneal irregularity. Additionally, as a soft lens
also partially rests on the sclera, it provides a steady platform for the
optical zone. Figure 1 (a) and (b) shows how corneal irregularity can
be compensated for by a custom soft lens. It should be noted that
astigmatism is not eliminated by most soft lenses (unless they are
very thick). Rather, the astigmatism becomes more regular, as shown
in Figure 1 (c) and (d), and therefore more amenable to correction with
a custom toric soft lens.
(a)
(c)
Figure 1. Keratoscopy of an irregular cornea (a) without and
(b) with lens in situ, demonstrating how astigmatism is transmitted
through the lens but is rendered more regular. (c) Topography of
irregular cornea; (d) topography of the same cornea with the
custom soft lens in place.
With modern lathe techniques, it is now possible to manufacture any
complex lens design with a high level of customisation, previously only
available with RGP lenses. Older lathes relied on turning techniques,
which produce rotationally symmetrical lenses, whereas newgeneration
lathes are driven by computer software, allowing complete
customisation. This allows, for example, manipulation of the periphery
of the lens independently of the base curve or even sections of a lens to
be lathe-cut with different parameters to the rest of the lens, opening
up a myriad of possibilities for lens design.
It is now possible to manufacture higher cylinder powers of up to
–16.00DC and, in theory, even to replicate the corneal shape on the
back surface of a soft lens. The topography mapping in Figure 2 shows
a difference map between the topography of a keratoconic cornea
(top) and of a lens button (bottom) cut using data input directly from
the topography to the lathe. The difference map on the right shows
that there is very little difference between the two surfaces.
Figure 2. Modern lathes can reproduce corneal shape exactly.
(a) Optoform lathe; (b) (right) difference map showing
(top) keratoconic cornea and (bottom) lens button cut from
topographic height data.
(b)
(d)
(a) (b)

With the advent of wavefront technology, it is now possible to
compensate for residual HOAs (de Brabander et al. 2003, Marsack
et al. 2007) by adjusting the optics of soft lenses. This can be very
beneficial in postrefractive surgery cases, where transmission of
internal HOAs can cause significant blur. However, this technology
requires more research as accommodation of the internal lens also
affects total HOA and patients may not tolerate having all HOAs
corrected if they have been adapted to them for a long time (Chen
et al. 2007, Sabesan & Yoon 2009).
Materials
Soft lens materials have continued to develop over the last few years
and now even complex lenses can be lathe-cut from high-watercontent
materials, including SiH. Benefits of high-water-content
lenses, particularly SiH, are:
• increased comfort, resulting in longer wearing times and increased
quality of life
• increased ocular health
• reduced lens irritability (thus reducing stimulus to rub eyes)
• reduced risk of corneal scarring
Quality of life issues
The general contact lens-wearing population has a wide choice of
contact lens designs and materials available to them and final lens
choice is often influenced by lifestyle, hobbies and visual requirements.
However, IC patients are more restricted as to which lens types are
available for their condition; visual acuity is often the main driver for
preferred lens choice by practitioners, with comfort and convenience
being secondary issues. Lim & Vogt (2002), in a review of lens types
fitted to a cohort of 130 keratoconus patients in The Western Eye
Hospital, reported that 96.1% were fitted with RGP lenses and this lens
type is usually the first lens of choice in most UK hospitals. However,
lack of tolerance can be an issue with some patients and care has to be
taken in order to ensure a correctly fitting lens.
The US Collaborative Longitudinal Evaluation of Keratoconus (CLEK)
study examined the changes in vision, corneal curvature, corneal status
(ie corneal scarring) and quality of life in patients with keratoconus
over a period of years. A total of 65% of these patients wore RGP lenses
and Zadnik et al. (1998) reported at baseline that 53% of patients
suffered from atopy, which often makes contact lens wear difficult
and uncomfortable, and that 53% had corneal scarring, a cause of
vision reduction. Barr et al. (2000) also showed that there was a causal
relationship between contact lens wear and corneal scarring and
suggested that scarring may be reduced by modifying the contact lens
fit. Therefore, it is essential to ensure that RGPs fit well on ICs and to
follow up such patients regularly. Baseline findings also indicated that
10% of patients could not wear lenses for leisure activities and 17.6%
could not wear lenses for reading at night (Wagner et al. 2007).
If contact lenses are poorly tolerated, they may only be comfortable
for a few hours. Driving, working, computer use, texting, reading, sport
and watching television all require reasonable vision and if a patient
can only manage reduced wearing times during the day, then the
‘quality vision’ time has to be managed carefully. Various strategies
are used, including wearing lenses in alternate eyes on alternate days,
wearing lenses for absolutely necessary functions only, eg driving, and
removing lenses after work or leaving them out at weekends.
Soft Contact Lenses for Irregular Cornea
If lens wear has to be discontinued for ocular health or refitting
reasons, then IC patients are at a real disadvantage, especially as most
employers have little understanding of the issues involved. Patients
with significant IC have the disadvantage of having to cope with good
acuity when wearing contact lenses but poor vision once they remove
them, as they cannot see well with spectacles.
Thus, increasing wear time with a comfortable contact lens type can
be a useful option for this patient group. Current lens modalities used
to achieve this include piggy-backing, large RGP lenses, semisclerals,
sclerals and hybrid lenses. Due to the improvements in design
and materials, soft lenses now offer a realistic alternative to rigid
materials.
Disposable soft lenses
Soft toric disposable lenses, such as Bausch & Lomb Soflens 66
and Purevision, Biofinity torics, Coopervision Frequency Excel and
Frequency XR, can all be used in mild and early uncomplicated
keratoconus to good effect. If the level of astigmatism is higher than
can be corrected by such disposables, the practitioner can choose
from a number of lathe-cut toric prescription lenses in a wide range
of materials, diameters and base curves. When vision can no longer be
satisfactorily corrected with normal soft lenses, then it is time to move
on to specialist lenses.
Custom soft lenses for IC
Points to take into account when considering the move to a dedicated
IC soft lens:
• Has the patient developed high levels of astigmatism?
• With standard lenses, is there more than 4mm post-blink
movement?
• Does the edge of the lens lift off the cornea (edge fluting)?
• Is there general lens instability, leading to patient discomfort and
variable vision?
• Does the patient experience ghosting and/or multiple images?
The ghosting and multiple image effects are due to the presence
of HOAs, such as coma and trefoil, and in many cases they can be
difficult to eliminate with any lens type, rigid or soft. Occasionally
this may be due to HOAs produced by the back corneal surface or the
crystalline lens surfaces which were previously compensated for by
the cornea before it became distorted. HOAs can also be an issue with
postrefractive surgery cases.
Fitting procedures for soft lenses for irregular
cornea
The various commercially available soft lens types for IC vary in fitting
criteria. Some, such as Acuity Soft K, are based closely on the shape
of the cone and therefore have a steeper range of base curves in their
trial lenses, while others, such as Soflex and KeraSoft, have a flatter
range as they rely on fitting the mid-periphery rather than the steepest
areas. Therefore it is essential to be aware of the type of cornea being
fitted and the location of the steepest and flattest areas. Only then
can the most appropriate lens design be decided upon.
Measuring the cornea
Traditionally contact lenses of all types have been fitted based on
measurements of the cornea using keratometry. Keratometers,
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however, can only measure a central area 4mm in diameter. In many
IC conditions such as keratoconus and particularly PMD, the steepest
area of the cornea may be significantly decentred, with the result that
meaningful readings may be difficult to achieve with keratometry.
Topography
Most practitioners employing topography use Placido-based machines
and, depending on type, many of these struggle to record complex
corneal shapes accurately, especially in the presence of corneal scarring
or INTACS. This type of topography rarely gives information past
6–7mm and even Scheimpflug scanning topography (eg Pentacam) will
not give any information about the corneoscleral junction. Peripheral
assessment is very useful in obtaining a good soft lens fit, especially in
cases of PMD where the steepest area of the cornea is often very near
the limbus.
The general convention in topographic mapping is that the steeper
areas are denoted by colours at the red end of the spectrum and the
flatter ones by colours at the blue end. A ‘normal’ spherical cornea
will show a generalised green appearance, slightly flattening off
towards blue at the periphery. Regular astigmatism is represented
by a ‘bow-tie’ pattern, which represents the toric surface of the
cornea. Figure 3 shows mild astigmatism of –1.00DC axis 170 on
a normal cornea.
Figure 3. Topographic representation of a normal cornea with
–1.00DC of astigmatism axis 170.
Topography of irregular corneas
Topography software for Placido-based topography creates elevation
data, comparing corneal height data to a reference curve, and is
based on the assumption that the highest point of the cornea is
approximately at the geometric centre of the cornea. As a result
of this assumption, the more extreme the displacement of the
cone or irregularity, the more likely the software is to distort the
mapping (Klein 1997). It is for this reason that, currently, direct
translation of topographic data into lathe software does not result
in an accurate back-surface match for decentred cones. Figure 4
shows the topographic mapping of various irregular conditions using
Placido-based topography.
Central/nipple cone Moderate cone
Offset cone Low cone
Pellucid marginal degeneration Post-laser-assisted in-situ
keratomileusis (LASIK)
Post-LASIK ectasia Post-graft
Figure 4. Topographic appearance (Placido-based topography) of
several irregular corneal conditions.
However, topography information can be very useful – it gives a clear
indication of the abnormality of the corneal shape, can aid diagnosis
and early detection of conditions and is extremely useful in tracking
corneal shape changes. It can indicate where reverse geometry lenses
may be more useful and identify the position of the steepest part of
the cornea.
Advanced keratoconus: central/nipple cone
Characterised by a central steep area and a flatter periphery, this type
of cornea is typically regular and symmetrical in shape and represents
the classical keratoconus shape of central, conical bulging. In these
cases, refraction is usually high-minus with or without significant
astigmatism. First choice would be a lens at the steeper end of the
trial set range and often these cases require reduced diameter lenses.
If periphery manipulation is possible, these cases benefit from lenses
with steep base curves and flatter peripheries.

Moderate cone
The majority of keratoconic cones tend to be inferior, although
some can be superior. There are usually significant levels of irregular
astigmatism and moderate myopia. Ghosting can be an issue due to
moderate levels of HOA and coma.
Offset cone/low cone
Although most cones tend to be inferior, they can occur at any
position. Ones that are significantly offset often cause problems with
any contact lens fitting because the lenses tend to decentre, as they
settle on the highest point of the cornea. With a soft lens, increasing
the diameter often aids centration. Refraction can be more varied in
these cases, tending towards a lower-minus sphere and higher levels
of astigmatism.
Pellucid marginal degeneration
This term describes a low cone which is close to the limbal area. The
topography is characterised by a ‘crab claw’ or ‘kissing bird’ shape
and the refraction result is usually against-the-rule astigmatism with
low levels of minus spherical correction or even plus spheres. Patients
often have reasonable spectacle acuity (around 6/12–6/7.5) which is
marred by high levels of ghosting due to significant levels of coma.
Again, these corneas are difficult to fit easily with any lens type
because of centration issues and, in extreme cases, the topography
can be misleading. In many cases, fitting much steeper than indicated
by the flatter areas shown in topography can provide a better fit. If
periphery manipulation is available, then a steeper periphery may be
useful in these cases.
Post-graft
Post-graft corneas are usually characterised by a flat central area and
a steeper periphery, especially on grafted keratoconic corneas. These
corneas can benefit from reverse geometry fittings, ie a flat base curve
with a relatively steeper periphery.
Post-LASIK/postrefractive surgery
These cases most closely resemble grafted corneas in that the
central cornea is often relatively flatter than the periphery and
will often benefit from reverse geometry fittings. However, they
may also respond to more ‘normal’ fittings, as occasionally the
topography reading for the mid peripheral cornea can indicate a
flatter reading than is actually the case. A tricurve lens design often
has more flexibility than a bicurve design in coping with this type of
corneal shape.
Post-LASIK ectasia
Post-LASIK ectasia cases have the disadvantage of having a cone
superimposed on a cornea that is already centrally flattened by
refractive surgery. They will often demonstrate high levels of HOA,
particularly coma, and can respond well to a more customised design,
specifically steepening the periphery in the area of the cone and
flattening in the opposite area.
Assessing the fit of custom soft lenses for irregular
cornea
As custom soft lenses have more substance than disposable lenses, the
optimum lens movement may be greater, ie in the range of 2–3mm,
and the movement on upward gaze will be much greater than that of
Soft Contact Lenses for Irregular Cornea
straight-ahead gaze. In many ways, these lenses will move more like
a large RGP than a typical disposable soft lens. This can be misleading
to the novice fitter, as a steeply fitting lens can often be mistaken for
an optimum fit. Most of these lens types perform best when the lens is
fitted so that the lens moves freely in the mid peripheral area, because
a tight fit will result in eventual moulding of the peripheral lens to the
sclera, thus altering the fit.
Flat fits
A flat fit is often indicated by a decentred lens or one that moves
excessively on push-up test and drops markedly on upward gaze. If
a toric fitting lens is used, the laser marks used to gauge rotation will
often swing back and forth in an irregular fashion. In many cases of
keratoconus, a flat fit will result in fluting at the inferior limbus. Patient
acuity will usually become worse on staring.
Steep fits
A steeply fitting lens will often have bubbles trapped underneath the
lens which do not easily dispel with blinking or on settling. Even if the
lens moves reasonably on upward gaze, a tight fit will often cause
dragging of the bulbar conjunctiva on straight-ahead gaze. It is always
wise to allow an ‘optimal lens’ to settle for at least 30 minutes to
check that it does not become tight over time.
Assessing overrefraction in soft lens fittings
Generally, to attain the best acuity and to minimise ghosting
effects from HOAs, a careful toric overrefraction is required. Some
lens types do not allow for high-cyl correction and, in these cases,
a spectacle overrefraction can be worn. It can be difficult to obtain
accurate spectacle refraction in cases where the corneal surface is
very irregular. Retinoscopy can be difficult due to split or distorted
images and even topography or autorefraction may be impossible.
Thus, carrying out refractive procedures with the lens in situ may be
more helpful.
• In many cases, the cylinder found by refraction will match that
found on topography fairly closely; in other cases, the cyl axis can
be almost 90° offset from that indicated in the topography. Much
depends on the level of irregularity of the corneal surface and the
peripheral fit of the soft lens. Steep-fitting lenses will create pooling
of tears, resulting in poor, fluctuating vision which is often much
better immediately after a blink.
• Topography or autorefraction over the top of the lens will give a
good estimation of the cyl required and allows a good starting point
for subjective overrefraction. However, these readings should be
taken as a guide only.
• The presence of HOAs tends to confuse IC patients. They find it
difficult to choose between ‘darker but more ghosting’ and ‘less
ghosting but fainter’ when viewing letters and do not generally
respond well to small changes (0.25D) in overrefraction. It is often
useful to start with an approximation of the sphere and concentrate
on refining the cylinder (which may be high) first before attempting
to finalise the spherical component.
• Allowing patients themselves to rotate the cyl in a trial frame can
often more accurately establish the required axis as, in some cases,
using cross-cyl can confuse patients due to the effects of HOAs.
• Good vision that can only be maintained when the patient stares
and does not blink may indicate a flat fit or simply that the lens has
not yet settled.
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Currently available custom soft lenses for
irregular cornea
Whereas specialised RGP lenses are manufactured by several major
companies and many independent laboratories, not many companies
produce dedicated soft lenses for IC. Some of the custom soft lenses
for IC available in the USA and UK are described below.
Hydrocone by Medlens (USA)
This is a tricurve lens and all curves are aspheric, with the central
curve computed by a complex polynomial formula; it approximates
hyperbolic aspheres in larger sagittal depths. The paracentral curve
is similar in design to the base curve of a standard soft lens and the
8.6mm radius curve with a 14.8mm diameter should fit the majority
of eyes.
The anterior surface has a central optical portion, which quickly tapers
to a thinner flange curve to maximize oxygen to the cornea. It has
about the same total lens mass as a standard high-plus soft lens. When
residual astigmatism indicates that a toric lens is needed, double slaboff
ballasting is used to stabilise lens rotation.
A case report by Patrick Caroline and Mark Andre in Contact Lens
Spectrum (March 2008) describes a Hydrocone fitting where the
patient achieved 20/30 acuity. The patient had become intolerant to
his well-fitting RGP lenses and could achieve 14–16 hours’ wear with
these lenses.
Flexlens by Walmans (USA)
This type of soft lens is fitted more closely to the central cone. It is
a tricurve lens with centre thickness between 0.40 and 0.45mm,
incorporating a second curve around 1.20–1.80mm flatter than base
curve and a scleral curve between 2.20 and 2.80mm flatter.
As an example, a cornea with K readings of 6.50 × 180/5.90 × 90
would be fitted with a first-choice lens of 6.20 based on the average
K reading.
The lenses are available in spherical powers ±50.00 and it is suggested
that a diagnostic fitting set be used to obtain the best results.
Soft K by Acuity (UK)
The Acuity Soft K (Table 1) lens is manufactured from a fairly stiff
material and is designed to mask astigmatism up to 11.00DC. The
first-choice lens is based on the average K reading of the cornea and
available base curves range between 5.40 and 7.60mm.
The fit of these lenses can be altered by adjusting the peripheral curves.
Thus, if the fit appears tight, then the periphery can be flattened by
ordering a +1 or +2 edge fit. If it is too loose, then the periphery can be
tightened by ordering –1 or –2 edge fit.
With this design, altering the peripheral fit may require some adjustment
of power to allow for change of fit. It is therefore recommended that,
when fitting a large number of Acuity soft lenses on advanced cones, a
set of fitting lenses with a flatter periphery is used to obtain optimum
overcorrection results.
Table 1. Parameters of the Acuity Soft K lens
Soft K
Material 61% anionic Filcon II (modulus 0.75)
Design Back surface toric design (?)
Parameters 5.40 through 7.60 in 0.20 steps (in
between and custom cones to order)
Diameter 14.50 or custom
Periphery –2, –1, standard, +1, +2, +3
Rx range +20.00 to –40.00
Dk 26 × 10-11
Centre thickness 0.20mm
Soft K by Soflex
The Soft K design (Table 2) is available in hydrogel and lathe-cut SiH.
Although there are limited toric powers in the hydrogel material, a
full range of toric powers up to 11.00DC is available in SiH. This design
of lens has pressure-balancing holes to equalise pressure between the
back and front of the lens, which aids fitting in more complex corneal
shapes.
Table 2. Parameters of the Soflex Soft K and SiH Soft K
Soft K SiH Soft K
Material Filcon 2 II water
content 67%
Design Back toric with
prism ballast
Parameters Base curves 7.00,
7.30, 7.60, 7.90,
8.20 Diameter
14.20mm
Rx range +10.00 to –20.00
Cyls: –0.50 to
–2.00 any axis
Silicone hydrogel (Filcon
II 3 water content 74%
modulus 0.39)
Back toric with prism
ballast
Dk 30 × 10–11 57 × 10–11
Centre
thickness
0.36mm 0.36mm
Base curves 7.30, 7.60,
7.90, 8.20 Diameter
14.20mm
+10.00 to –20.00
Cyls: to order, any axis
This lens is designed with a spherical optic zone and an aspheric
periphery. The front surface has three zones: a thick optic zone to
improve optical quality, a lenticular zone for structural stabilisation
and the peripheral zone (Figure 5).

Figure 5. Design of the Soft K lens and Soft K toric lens, available
from Soflex.
Soflex fitting
For both materials, fitting instructions are the same:
• Start with 7.60 lens and leave to settle for 30 minutes.
• Optimum movement is 0.7–1.00mm.
• The lens should be centred.
• There should be no air bubbles.
• There should be no edge lift.
• Vision should be acceptable with sph-cyl overrefraction.
Soft K is fitted more to the mid-periphery, in contrast to Hydrocone or
Flexlens, and a trial set is supplied for fitting purposes. It is suggested
that the 7.60 base curve lens is chosen as the first-choice lens and then
this is assessed by slit lamp to determine whether one needs to go
steeper or flatter.
KeraSoft Range by UltraVision
There are currently three versions of the KeraSoft lens: KeraSoft2,
KeraSoft3 and KeraSoft IC (Table 3). KeraSoft2 is produced in
Hydroxyfilcon BII and has a back surface toric design. As the newer
KeraSoft versions are manufactured from different materials and
are front surface toric designs, they cannot be ordered from current
KeraSoft2 lenses that the patient may be wearing. The KeraSoft3 lens
is manufactured in SiH only. KeraSoft IC is produced in both a highwater-content
hydrogel option and a SiH option. The fitting lenses
are supplied in the hydrogel material and have been designed so
that final lenses can be ordered in either material using the same
fitting set.
Only the KeraSoft IC lens can be fully customised, allowing changes
to base curve, diameter, periphery (from flat 4 to steep 4), optical
zone and the periphery. Sector management control can be utilised to
fit more complex ICs and, with this option, individual sections of the
periphery can be steepened and flattened as desired.
Soft Contact Lenses for Irregular Cornea
Table 3. Parameters of the UltraVision KeraSoft range
Material Hioxyfilcon BII Silicone
hydrogel
(Filcon II 3
water content
74% modulus
0.39)
Design Back surface
toric bicurve
Wavefront
aberration
control
(spherical
aberration)
Trial set Trial set
8.00–8.60
plano
Rx range Base curves
8.00–8.60 in
0.20 steps
Diameters
14.00, 14.50,
15.00mm
Powers +30.00
to –30.00
Cyls to 11.00
any axis
Add to +3.00
Front surface
toric bicurve
Wavefront
aberration
control
(spherical
aberration)
Prism ballast
Trial set
8.00–8.60
powered
Base curves
8.00–8.60 in
0.20 steps
Diameters
14.00, 14.50,
15.00mm
Powers +30.00
to –30.00
Cyls to 15.00
any axis
Add to +3.00
Filcon II 2
hydrogel water
content 77%
and silicone
hydrogel (Filcon
II 3 water
content 74%
modulus 0.39)
Front surface
toric tricurve
Wavefront
aberration
control
(spherical
aberration)
Prism ballast
Trial set
7.80–8.80
plano standard
periphery plus
8.20/flat2
periphery and
8.60/steep2
periphery
Base curves to
order
Diameters
14.00, 14.50,
15.00mm
Powers +30.00
to –30.00
Cyls to 15.00
any axis
Periphery
customised to
order
Dk 15 × 10 –11 60 × 10 –11 Hydrogel: 53 ×
10 –11
SiH:60 × 10 –11
Centre
Thickness
® ® ®
0.30 0.30 0.40 (standard)
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Patient suitability
All of these lens types can be used for IC with varying levels of success.
Best results are achieved when fitting a cornea that has not been
previously fitted with rigid lenses. Flat-fitting RGPs in particular can
significantly distort the cornea but even well-fitting, or slightly apical
clearance lenses, can cause changes to corneal shape (Hill & Rengstorff
1974, McMonnies 2005, Swarbrick et al. 2004).Thus, allowance should
be made for ‘demoulding’ effects when refitting a patient from RGPs
to soft lenses. In general, the major corneal shape changes take place
within the first 3 months of soft lens wear and most patients can
tolerate the resulting vision fluctuations during this time, if suitably
motivated. If optimal visual acuity is of prime importance to the
patient, then refitting one eye at a time should be considered. Corneas
that have significant scarring from badly fitted contact lenses will take
longer to settle and thus patient management is very important.
Case studies
Lack of RGP tolerance: Acuity Soft K (courtesy of Michael
Bunn FADO)
A 42-year-old general practitioner was diagnosed with uniocular
keratoconus 20 years previously in the left eye (LE). He was unable
to tolerate RGP lenses very well and, as he could see with spectacles
with the right eye (RE), he discontinued wear after 5 years but had to
give up his private pilot’s licence as a consequence. Fifteen years later,
he was pleased to find soft lenses were an option and wished to try to
regain his pilot’s licence.
K readings were 6.60 × 55.5.80 × 135 and a Rose K of base curve
6.50 gave a good fit. This gave a good starting point for using the
Acuity Soft K 61 base curve 6.50. This lens produced a central bubble
which displaced very easily and the lens appeared mobile. The lens
was changed for a 6.40 base curve which fitted much better – the
central bubble dissipated after a few blinks. However, the edge fit
now appeared tight, so it was flattened to a +1.00 which gave an
excellent fit.
Final lens: 6.40/14.50/–6.50SK+1.00, which gave 6/6+4 acuity.
The patient was comfortable and was able to regain his pilot’s licence
and resume flying.
Change of soft lens material: Soflex SiH Soft K (courtesy of
Soflex Contact Lenses)
Patient DM
The patient was a 30-year-old woman who underwent LASIK in 2002
and subsequently developed ectasia in the LE. She was fitted with a
soft lens of moderate Dk and developed early neovascularisation due
to long wearing times (over 14 hours). She discontinued wear and
underwent corneal collagen cross-linking. On assessing for contact
lens wear post collagen cross-linking, she was intolerant to RGP lenses
and therefore was fitted with Soflex Soft K in 74% SiH material.
LE: Sim Ks at fitting appointment: 6.74 × 41/7.13 × 131
LE: spectacle Rx: 6/18 –3.50/–1.75 × 35 6/12–
Figure 6. Left eye topography for patient DM (a) before and (b) 1
month after collagen cross-linking.
As per fitting guide instructions, a lens of 7.60/14.20 base curve
was inserted and allowed to settle. However, the patient reported
significant lid sensation and excessive movement, greater than 2mm,
was observed. The next steepest lens was therefore inserted, base
curve 7.30/14.20. This lens settled very well and gave no lid sensation.
Movement was now reduced to 1mm and the following lens was
supplied:
L: 7.30/14.20/–4.75DS VA 6/10–
One-month follow-up showed full regression of neovascularisation
with 10 hours’ comfortable wearing time.
Refitting from RGP to soft: KeraSoft IC
Patient HP
www.kerasoft.co.uk
HP, a 28-year-old male, was diagnosed with keratoconus at the age of
16. The LE advanced more than the RE and he wore RGP lenses from
the age of 18 years old. He presented wearing the same right lens he
was prescribed at 18 and his immediate issue was the left lens which
continually fell out and was generally uncomfortable. His hospital
eye department had attempted to refit both eyes with RGPs but any
improvement in fit resulted in a lower visual acuity.
HP was interested in being refitted with soft lenses due to the general
fitting issues with the LE and the overall discomfort level and restricted
wearing time he had with RGP lenses. Refitting the LE was a priority
and he would consider refitting the RE once the LE had stable reliable
vision. He did not want to consider a refit with an RGP for the RE at
this time, despite the age of the lens, as he was worried he might end
up with problems with both eyes at the same time (due to his previous
fitting experiences).

Initial findings
No details of RGP lenses being worn were available and he had no
spectacles.
Acuity with RGP lenses
RE: 6/12 +2.00 overrefraction visual acuity (VA) 6/12
LE: 6/19 No overrefraction improved acuity
Spectacle refraction
RE: Vision 6/19 no improvement
LE:

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KeraSoft IC SiH (sector management control) fitting
RE: 8.40/15.00/FLT1/STP2/–1.50/-5.25 × 50 A1: 30 / A2: 150 / A3: 220
/ A4: 320 VA 6/8
HP was warned that vision in the RE with the KeraSoft IC would vary as
the cornea settled down during the post-RGP demoulding phases.
Conclusion
Over the last few years, soft lens options for IC have improved so that
extended wearing periods are now possible for this patient group with
reduced risk of neovascularisation. Good visual acuities can be attained,
in some cases equal to those experienced by rigid lens wearers. These
lens types now offer an alternative if patients become intolerant to
RGP lenses and, indeed, may be considered as a first lens choice for
patients who do not wish to have RGP lenses for reasons of lifestyle or
comfort. The fitting technique of such lenses is comparable to ‘normal’
prescription toric lenses and much of the same principles apply.
It is important to take into account quality-of-life issues as well as
final acuity when assessing patients with IC for contact lens wear. This
patient group requires comfortable, functional vision during the whole
of a day rather than for restricted periods, as they cannot resort to
spectacle lens wear if lenses become uncomfortable. Many patients
would accept a slight reduction of acuity if this meant they could wear
contact lenses without having to plan their day around lens wear.
As refitting from RGP contact lenses to soft lenses will often involve
a period of time when the cornea changes shape, it may be useful
to explore the possibility of soft lens fittings before moving to rigid
lenses.
Summary
This article discusses dedicated soft lenses for irregular corneas,
describing how they work compared to other lens modalities.
Various types of these soft lenses are listed, with descriptions of
the range of base curves and powers available. Fitting techniques
are discussed, using case studies as an illustration. A description
of how to use topography to guide the fitting of these lenses is
also included.
References
Alió JL, Shabayek MH (2006) Corneal higher order aberrations: a
method to grade keratoconus. J Refract Surg 22, 539–45
Barr J T, Zadnik K, Wilson B S et al. (2000) Factors associated with
corneal scarring in the Collaborative Longitudinal Evaluation of
Keratoconus (CLEK) study. Cornea 19, 501–7
Caroline P, Andre M (2008) Soft lenses for keratoconus. Contact
Lens Spectrum March. Available online at:
http://www.clspectrum.com/article.aspx?article=101460
Chen L, Artal P, Gutierrez D et al. (2007) Neural compensation for
the best aberration correction. J Vision 7, 1–9
de Brabander J, Chateau N, Marin G et al. (2003) Simulated
optical performance of custom wavefront soft contact lenses for
keratoconus. Optom Vis Sci 80, 637–43
Dilraj SG, Gagandeep SB, Rajeev J et al. (2009) Corneal
collagen crosslinking using riboflavin and ultraviolet-A light
for keratoconus. One-year analysis using Scheimpflug imaging.
J Cataract Refract Surg 35, 425–32
González-Méijome J M, Jorge J, de Almeida J B et al. (2006) Soft
contact lenses for keratoconus: case report. Eye Contact Lens 32,
143–7
Hill J F, Rengstorff R H (1974) Relationship between steeply fitted
contact lens base curve and corneal curvature changes. Am J Optom
Physiol Opt 51, 340–2
Klein S A (1997) Axial curvature and the skew ray error in corneal
topography. Optom Vision Sci 74, 931–44
Lim N, Vogt U (2002) Characteristics and functional outcomes of
130 patients with keratoconus attending a specialist contact lens
clinic. Eye 16, 54–60
Lim L, Pesudovs K, Coster D J (2000) Penetrating keratoplasty for
keratoconus: visual outcome and success. Ophthalmology 107,
1125–31
Marsack J D, Parker K E, Niu Y et al. (2007) On-eye performance
of custom WaveFront guided soft contact lenses in a habitual soft
lens wearing keratoconic patient. J Refract Surg 23, 960–4
McMonnies CW (2005) The biomechanics of keratoconus and rigid
contact lenses. Eye Contact Lens 31, 80–92
Ramkumar S, Geunyoung Y (2009) Visual performance after
correcting higher order aberrations in keratoconic eyes. J Vision 9,
1–10
Sabesan R, Yoon G (2009) Visual performance after correcting
higher order aberrations in keratoconic eyes. J Vision 9, 1–10
Smolek M K, Klyce S D (2000) Is keratoconus a true ectasia? An
evaluation of corneal surface area. Arch Ophthalmol 118, 1179–86
Swarbrick HA, Hiew R, Kee A V et al. (2004) Apical clearance rigid
contact lenses induce corneal steepening. Optom Vision Sci 81,
427–35
Vinciguerra P, Albè E, Trazza S et al. (2009) Refractive, topographic,
tomographic, and aberrometric analysis of keratoconic eyes
undergoing corneal cross-linking. Ophthalmology 116, 369–78
Wagner H, Barr J T, Zadnik K (2007) Collaborative Longitudinal
Evaluation of Keratoconus (CLEK) study: methods and findings to
date. Contact Lens Anterior Eye 30, 223–32
Yamazaki E S, da Silva V C, Morimitsu V et al. (2006) Keratoconus
special soft contact lens fitting. Arq Bras Oftalmol 69, 557–60
Zadnik K, Barr J T, Edrington T B et al. (1998) Baseline findings in
the Collaborative Longitudinal Evaluation of Keratoconus (CLEK)
study. Invest Ophthalmol Vis Sci 39, 2537–46

Multiple choice questions
This paper is reference C-13831. Three points are available for
optometrists and contact lens opticians. Please use the inserted
answer sheet. Copies can be obtained from Optometry in Practice
Administration, PO Box 6, Skelmersdale, Lancashire WN8 9FW. There
is only one correct answer for each question.
1. Which of the following statements regarding corneal grafts
is true?
(a) Vision is stable post-graft in approximately 6 weeks
(b) Grafting patients with IC allows them to be fitted easily with
contact lenses afterwards
(c) An indication for grafting a patient with keratoconus and a clear
cornea is intolerance to contact lens wear
(d) Post-graft corneas require soft lenses with a flatter peripheral
fitting
2. Regarding RGP wearing time for patients with IC, which of the
following statements is true?
(a) Most patients wear RGP lenses all day long comfortably
(b) Comfortable wear time of 8 hours per day would be considered
sufficient
(c) RGP wear is not particularly affected by allergies
(d) Wear time can be reduced by dry-eye symptoms
3. Which of the following statements is false regarding soft lenses
for IC?
(a) Only low levels of astigmatism can be corrected
(b) Some patients may choose to trade the visual acuity achieved with
RGP lenses for the longer wearing times of soft lenses
(c) Good vision may be obtained with disposable lenses in early
keratoconus
(d) Specialist soft lenses can provide good vision, even in the presence
of relatively significant corneal irregularities
4. What percentage of RGP wearers could not wear lenses for leisure
activities according to the CLEK study?
(a) 10%
(b) 17%
(c) 22%
(d) 53%
5. Regarding topography in patients with ICs, which of the following
statements is incorrect?
(a) Placido disc-based machines are less accurate in the presence of
corneal scarring
(b) Most topographers do not give information about the corneoscleral
junction
(c) Central corneal assessment is vital in obtaining a good soft lens fit
in cases of PMD
(d) Topography software assumes that the highest point of the cornea
is approximately at the geometric centre of the cornea
6. Corneal collagen cross-linking involves use of riboflavin and which
kind of light source?
(a) Ultraviolet
(b) Laser
(c) Infrared
(d) Light-emitting diode
Soft Contact Lenses for Irregular Cornea
7. Which of the following is correct when referring to overrefracting
soft lenses for IC?
(a) HOAs have no effect on subjective refraction
(b) Using an autorefractor will give guidance as to levels of
astigmatism
(c) An autorefractor will accurately supply a full sphere overrefraction
(d) Often a spherical overrefraction is all that is required
8. Which of the following statements is false concerning movement
of soft lenses for IC?
(a) Lens movement should be the same amount as for disposable soft
lenses
(b) An inexperienced practitioner could mistake a steep-fitting custom
lens for an optimum fit
(c) Movement of 2–3mm is acceptable as long as the patient is
comfortable
(d) A lens should be allowed to settle for at least 30 minutes prior to
fit assessment
9. Which of the following is correct regarding the fitting of
postrefractive surgery cases?
(a) The central cornea is often steeper than the periphery
(b) HOAs are never a problem with this patient group
(c) A bicurve lens is preferred to a tricurve lens with these patients
(d) Reverse geometry lenses are often needed
10. With regard to modern lathing techniques, which of the following
is true?
(a) Lenses have to be rotationally symmetrical
(b) Soft lenses cannot be customised as easily as RGPs
(c) It is only possible to apply cylinders up to –13.00DC
(d) None of the above
11. When refitting from RGP lens modality to soft lenses in cases of IC,
which of the following statements is true?
(a) It is easier to refit from RGP to soft lenses rather than the other way
around
(b) Vision can fluctuate for several weeks before settling
(c) It is always best to refit both eyes at the same time
(d) Flat-fitting RGPs cause less corneal distortion than steep-fitting
ones
12. What percentage of patients were atopic in the 1998 study by
Zadnik et al.?
(a) 65%
(b) 53%
(c) 17%
(d) 62%
13. How much astigmatism do the manufacturers of the Acuity Soft K
lens claim to be able to mask?
(a) Up to 9DC
(b) Up to 10DC
(c) Up to 11DC
(d) Up to 12DC
14.Regarding PMD, which of the following statements is incorrect?
(a) These patients tend to have a low cone close to the limbus
(b) These patients usually have visual acuity worse than 6/36
(c) Topography results can be misleading
(d) If peripheral manipulation is available, then a lens with a steeper
periphery may be beneficial
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15. Regarding HOAs, which of the following statements is incorrect?
(a) They can result in ghosting
(b) They can result in multiple images
(c) Wavefront technology can compensate for residual HOAs
(d) Post-LASIK ectasias will very rarely demonstrate coma
CPD information
Now update your CPD record with this article. If you have
completed the CET questions, the details for this article can be
downloaded from CETOptics (at the end of the month). If you
have not completed the CET questions you can cut and paste
the relevant details (title/learning outcomes etc.) from the pdf
copy of the article which is posted on the College website.
Once you have downloaded the details of the article, answer
the reflective questions to complete the CPD activity.
If you wish, you can type your reflections into the box below and
then copy them into your online record.
Reflection
1. What impact has your learning had, or might it have, on:
• your patients or other service users (eg those who refer
patients to you, members of staff whom you supervise)?
• service delivery?
• yourself (improved knowledge, performance, confidence)?
• your colleagues?
2. How might you assess/measure this impact?
To access CPD Online please click on the following link:
college-optometrists.org/cpd

Continuing Professional Development (CPD)
Soft Contact Lenses for Irregular Cornea
The College of Optometrists recognises ongoing CPD to be valuable and desirable both in terms of professional advancement
and also enhanced service quality to patients.
On the following pages we publish articles that provide CPD outside the General Optical Council’s core competencies but that
have a direct relevance to optometric practice.
Many optometrists strive to improve and broaden their knowledge and skills after they become registered. The College’s
voluntary CPD scheme enables this personal development to be documented and kept securely, to be used by the individual
optometrist for a number of purposes such as for job applications, performance reviews and potentially for revalidation.
For more information visit www.college-optometrists.org.
Note: All CET-accredited articles can also be used for CPD purposes. Optometry in Practice publishes sample CPD
exercises for all CET-accredited articles, which can be copied to your CPD record. These are printed after the Multiple
Choice Questions, and are also available as interactive pdfs online.
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