Managing Keratoconus in Optometric Practice - Optometry in Practice

Optometry in Practice Vol 5 (2004) 69–78
Managing Keratoconus in Optometric
Practice
Cindy Tromans PhD MCOptom
Department of Optometry, Manchester Royal Eye Hospital, Manchester, UK
Accepted for publication 17 May 2004
Introduction
Keratoconus is usually classified as an asymmetric,
progressive ectasia of the cornea. It is non-inflammatory
and is characterised by thinning, steepening and scarring
of the central cornea (Krachmer et al. 1984, Rabinowitz
1998). The disease progresses from initial symptoms of
mild visual disturbance and frequent changes to the
spectacle prescription to severe visual impairment in the
latter stages of the disease from corneal scarring and
hydrops. The management of this condition is
predominantly optometric in the early stages through the
provision of spectacles or contact lenses. As the disease
progresses specialist contact lens fitting may be required
and when these options have been exhausted, surgical
intervention may be indicated (Lass et al. 1990).
The aim of this review is to familiarise the optometrist in
primary optometric practice with the relevant literature,
signs, symptoms and non-surgical management options
for keratoconus.
Incidence and Prevalence
Many studies have been conducted to estimate the
incidence and prevalence of keratoconus. The incidence
of keratoconus in the population has been reported at
between 50 and 230 in 100 000 (or approximately 1 in
2000) in various studies and the prevalence at 54.5 per
100 000 in the USA (Kennedy et al. 1986, Rabinowitz
1998). Keratoconus has been documented as occurring in
all ethnic groups with no male or female preponderance.
Pearson et al. (2000) have shown that Asians in the UK
have a fourfold increase in incidence compared to
Caucasian patients when presenting to the Hospital Eye
Service. The majority (89.5%) of the Asian group were of
Indian ethnic origin. These data are of interest and
significance as keratoconus may therefore have a higher
prevalence in areas where there are large ethnic
communities and therefore may present more frequently
to primary optometric practice in those areas.
Address for correspondence: Dr C Tromans, Department of Optometry,
Manchester Royal Eye Hospital, Oxford Road, Manchester M13 9WH, UK
© 2004 The College of Optometrists
69
Aetiology
There has been much speculation on the aetiology of
keratoconus and research into this area has been ongoing
for many years. Teng in 1963 performed electron
microscopic studies of the keratoconic cornea and
suggested that the initial changes in keratoconus were
related to degradation of the epithelial basement
membrane material. Advances in molecular techniques
and immunohistochemistry have led workers to base their
theories on: (1) abnormal processing of the free radicals
and superoxides in keratoconic corneas; (2) build-up of
destructive aldehydes and/or peroxynitrites in the cornea;
(3) cells that are damaged irreversibly undergo the
process of programmed cell death (apoptosis); (4) cells
that are damaged reversibly undergo wound healing or
repair. Kenney et al. (2000) summarise this work and
hypothesise that various factors, eg ultraviolet radiation,
atopy, mechanical eye rubbing and poorly fitting contact
lenses, can cause either oxidative damage or disruption to
the cellular structure or function. If the cells are
irreversibly damaged they undergo apoptosis, but if the
cells are only partially damaged, they undergo a repair
process. This leads to an increase in the activity of
degradative enzymes, focal sites of wound healing and
tissue remodelling, which lead to focal areas of corneal
thinning and fibrosis.
Genetics
Although the most common presentation of keratoconus
is sporadic (Kennedy et al. 1986), it has long been
recognised that some patients have a significant family
history of the disease. Edwards et al. (2001) reviewed the
role of genetics in keratoconus and show that numerous
studies confirm the inheritability of keratoconus but note
that most of the studies are largely point prevalence-type
studies and, since the nature of the disease is slowly
progressive, the detection rates of family members will
depend on the sensitivity of diagnostic criteria used. The
advent of computerised corneal mapping systems has

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facilitated earlier detection of irregular astigmatism and
forme fruste keratoconus and, subsequently, familial
prevalence rates have increased. Using corneal
topographical findings, Rabinowitz et al. (1990) have
shown that 50% of randomly selected members of families
of keratoconic subjects had minor topographical
abnormalities. Further follow-up of groups like these is
necessary to establish if these abnormal corneas progress
to keratoconus.
Twin studies are of great importance in establishing a
genetic origin of a disease and there are studies of at least
18 sets of monozygotic twins, in which one or both of the
pair show some degree of keratoconus. Most of these
studies were reported before the use of videokeratoscopy
but they have generally reported monozygotic twins
concordant rather than discordant for keratoconus. This
strongly supports a genetic aetiology.
Molecular genetic techniques are rapidly identifying genes
associated with ophthalmic conditions, eg corneal
dystrophies. Most work to date in keratoconus has been in
rare family groups where there is a significant number of
known keratoconics. Linkage analysis has been used: this
identifies chromosomal regions shared by affected family
members and identifies novel genes mapped to these
areas. However, linkage analysis between different families
is not valid because of presumed heterogeneity; presently
molecular genetic analysis is only possible in very
restricted numbers and so progress is extremely slow and
a unifying molecular cause for keratoconus has yet to be
found.
Associated Diseases
Keratoconus has also been associated with many
conditions. Down’s syndrome has been reported to have a
higher incidence of keratoconus of between 5.5% and 15%
by several authors. A study by Doyle et al. (1998) detected
2% incidence of overt keratoconus and 6% subclinical
keratoconus in a cohort of individuals with Down’s
syndrome. This is considerably higher than the incidence
of around 50 per 100 000 (0.05%) quoted above for the
general population.
Connective tissue disorders have been reported in
association with keratoconus but these have been based
upon rare reports of associations of keratoconus with
disorders of collagen metabolism such as osteogenesis
imperfecta, Ehrlers–Danlos syndrome and joint
hypermobility (Rabinowitz 1998). Reports in the
literature also associate keratoconus with mitral valve
prolapse (Lichter et al. 2000).
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Atopy
Atopy is defined as a tendency to develop hypersensitivity
reactions, eg hayfever, allergic asthma and eczema, and
several studies have demonstrated that keratoconus is
associated with atopic conditions. Harrison et al. (1989)
found that 56.7% of the patients in their study had at least
one atopic condition, with 28.4% having asthma, 31.3%
eczema and 37.3% hayfever. The nature of the association
remains elusive, but eye rubbing may be a contributing
factor as this study showed that unilateral keratoconus
occurred more frequently on the side of the dominant
hand.
Eye rubbing
Eye rubbing has been long been indicated as a
contributory factor in the aetiology of keratoconus.
Kennedy et al. (1986) reported a high number of
keratoconic patients admitting excessive eye rubbing.
However, as mentioned above, a high proportion of atopic
individuals also have keratoconus. It is therefore difficult
to determine whether it is the atopy in these individuals
which causes eye rubbing, and then coincidentally,
associated keratoconus. However, eye rubbing has been
suggested as the cause of chemical changes in the cornea
(Kenney et al. 2000) leading to stromal thinning but there
is insufficient hard evidence to support a causal link
between eye rubbing and keratoconus (Edwards et al.
2001).
Personality
The observation is often made that patients with
keratoconus tend to have a certain type of personality, in
that they appear to be more demanding and obsessed with
their condition. References have been made on this
subject in the literature: Cooke et al. (2003) compared a
group of contact lens-wearing high myopes with
keratoconus subjects who were also wearing lenses and
found that there was little evidence to suggest that
keratoconics differ significantly in personality from their
myopic counterparts. The report did not substantiate the
idea that keratoconics had particular personality traits.
Signs and Symptoms
Apical protrusion is the major feature of keratoconus. The
apex of the cornea protrudes to give the cornea a conical
shape (Figure 1) and in later stages of the disease this can
lead to Munson’s sign, where an angular curve is assumed
by the lower lid margin when the patient looks down
(Figure 2).

Figure 1. Profile of the cornea in
keratoconus.
Figure 4. Stromal thinning and apical
scarring.
Figure 7. Profile of the cornea in
keratoglobus (courtesy of KW Pullum).
Figure 10. Rigid gas-permeable contact
lens with apical clearance.
Figure 2. Munson’s sign. Figure 3. Vogt’s striae.
Figure 5. A resolved hydrops with splits
in Descemet’s membrane still evident.
Figure 8. Corneal topographical map in
subclinical keratoconus.
Figure 11. Flat-fitting rigid gaspermeable
contact lens (courtesy of
KW Pullum).
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Managing Keratoconus in Optometric Practice
Figure 6. Profile of the cornea in
pellucid marginal degeneration.
Figure 9. Corneal topographical map in
advanced keratoconus.
Figure 12. Rigid gas-permeable contact
lens with three-point touch (courtesy of
KW Pullum).

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Irregular astigmatism is usually the first sign of
keratoconus. It is often detected by the optometrist during
a routine eye examination, alerted by changes in
refraction, degree of astigmatism, drop in visual acuity
(VA) and distorted retinoscopy reflex. Keratometry mires
and keratoscopy show distortion and can be used to detect
subclinical corneal distortion before VA is affected.
Fleischer ring is a yellowish incomplete ring around the
cone and is formed by deposition of haemosiderin
superficial to Bowman’s membrane. It is often best seen
under blue light illumination on the slit lamp.
Vogt’s striae are striae seen centrally in the posterior
corneal stroma, just anterior to Descemet’s membrane
surface. They occur as the disease progresses (Figure 3).
They are often vertically oriented, but are usually aligned
in the meridian of the greatest curvature.
Stromal thinning is not always apparent early in the
disease process but almost always presents in later disease
(Figure 4).
Apical scarring occurs in most cases and is considered to
be part of the disease process, although it can be
exacerbated by rigid lens wear in keratoconus (Figure 4).
Hydrops is an acute, painful episode caused by a rupture
in Descemet’s membrane. Aqueous humour floods into the
cornea, causing gross oedema and loss of VA. It resolves
after a period of months, often leaving scarring (Figure 5).
Other Corneal Ectasia
There are other ectasia which, although rare, may be
confused with keratoconus in the early stages of the
disease process.
Pellucid marginal degeneration (PMD)
In PMD, the inferior part of the cornea thins, allowing the
cornea to sag and protrude inferiorly (Figure 6). This can
often be confused with a low-centred cone, but this can be
distinguished from keratoconus as there is typically a high
level of against-the-rule astigmatism on refraction which,
on correction, can give good VA (Biswas et al. 2000).
Keratoglobus
Keratoglobus is a rare disorder in which most of the
cornea is thinned and protrudes (Figure 7). Management
is consistent with that for keratoconus, although scleral
contact lenses may have to be used sooner rather than
72
later. There is a higher risk of perforation in keratoglobus
and some authors contradindicate the use of contact
lenses (Rabinowitz 1998).
Assessing the Shape and Curvature of the
Cornea in Keratoconus
Keratometry
In keratoconus, the keratometry mires are typically
distorted, showing irregular astigmatism and inferior
steepening. As the disease progresses the mires become
more distorted and often progress to ‘off-the-scale’
readings. Keratometry can therefore only reliably give
measures of corneal curvature in the early stages of the
disease but it is a useful tool in the diagnosis of early
keratoconus as it will detect irregular astigmatism
(Rabinowitz 1998).
Corneal topography
Videokeratoscopy is a useful tool to obtain clinical
information about the shape of the cornea (Corbett et al.
1999). Most instruments use Placido-based
videokeratoscopy which projects a series of concentric
rings (mires) on to the cornea. The mires are analysed and
digitised to produce three-dimensional information about
the cornea in the form of a colour-coded map. In
keratoconus, the irregular astigmatism will cause the
mires to become distorted with irregular spacing which
will be reflected as a change in colour on the map. Corneal
topography allows the detection of keratoconus, even in
the early subclinical stages of the disease, as the patterns
of mire distortion are easily recognised. The colour-coded
maps also provide a means of pattern recognition. In
addition, corneal indices are generated to aid data
interpretation. The two most useful indices are surface
asymmetry index (SAI) and surface regularity index (SRI).
Both of these indices increase in value as the cornea
becomes progressively more distorted. Figure 8 shows
subclinical keratoconus, where there is distortion of the
mires indicating irregular astigmatism, yet the patient is
asymptomatic and has good corrected VA. Figure 9 shows
a typical pattern in a more advanced case of keratoconus
where the colour coding indicates a much steeper cornea
(red) and some of the data is absent due to extreme
distortion of the mires. The pattern also indicates the
location of the steepest area of the cornea, which is the
cone location.
FDACL method
The first definite apical clearance lens (FDACL) method of

assessing corneal curvature and disease progression was
developed as a tool in the Collaborative Longitudinal
Evaluation of Keratoconus (CLEK) Study (Edrington et al.
1996). A series of rigid contact lenses is applied to the
cornea and the flattest lens that shows an apical clearance
pattern determines corneal curvature and can be used to
monitor the progression of corneal steepening. This is a
useful technique that is repeatable and without the known
errors that can arise from keratometry and corneal
topographical techniques (Edrington et al. 1998).
Disease Onset and Progression
The age of onset of the disease is typically reported to be
in the late teenage years; however, it can be difficult to
pinpoint because of the gradual onset and asymmetric
nature of the disease and so diagnosis is often reported at
a later age. The disease is progressive, although it has been
reported that stabilisation may occur in some patients
after 3–8 years (Krachmer et al. 1984).
Before considering the management options available to
the optometrist and contact lens practitioner, it is a good
idea to try and classify the degree and type of keratoconus.
A suggested guide would be
• Early: keratometry (K) in normal ranges with or
without distortion of keratometry mires and reasonable
corrected spectacle VA.
• Moderate: when central Ks begin to steepen (K <
7.20mm) and other signs such as striae and Fleischer’s
ring are present.
• Advanced: steeper (K < 6.0mm), with the added signs of
stromal thinning and apical scarring.
• Severe: in a very steep cone (K < 5.0mm), globic cones
or if there has been an episode of hydrops.
Spectacle Lens Correction
As the cornea steepens, the refraction tends towards
increasing myopia and astigmatism and most patients will
wear some form of spectacle correction in the early stages
of the disease. However, the spectacle prescription may
change frequently and can be limited if the degree of
astigmatism is high and not tolerable to the wearer in
spectacle lens form. In addition, the irregular nature of the
astigmatism may give an unsatisfactory level of best
corrected visual acuity. Also, if the disease is
asymmetrical there may be an intolerable degree of
anisometropia.
73
Managing Keratoconus in Optometric Practice
Spectacles, however, despite these problems are the initial
form of visual correction and in the early stages of disease
can provide surprisingly good acuity (Zadnik et al. 1996)
and VA measurement and subjective refraction are
reasonably repeatable (Davis et al. 1998).
Contact Lens Correction
Contact lens fitting is by far the most common and
successful method of correction of the keratoconic eye.
There are many lens designs to choose from and some are
more successful than others at fitting different stages of
the disease and cone types. The majority of keratoconic
patients will be fitted with rigid gas-permeable lenses,
although there are other lens types which may be
employed and these are discussed later.
Cone Classification
It is also important to try to classify the position and size
of the cone as this may influence the contact lens fitting
method selected. The best way to do this is to use a
corneal topography device, as described above, where the
profile of the entire cornea can be considered. A handheld
keratoscope or Placido disc will also allow
determination of the affected areas of the cornea. Perry et
al. (1980) described different cone types (round and oval)
which may require different contact lens fitting
approaches. The following types can be recognised:
• Round or nipple cones are generally small in diameter
and most commonly occur slightly below the visual
axis, with varying degrees of conicity.
• Oval cones show a larger conical area which lies further
away from the visual axis in the inferior part of the
cornea. If the area of thinning is very low then there is
the need to differentiate the diagnosis between an
advanced oval cone and pellucid marginal
degeneration.
• Globus cones have been described as very-largediameter
cones involving up to three-quarters of the
corneal surface.
Rigid Lens Fitting Philosophies
The question of the most appropriate fitting philosophy
has been the subject of debate amongst practitioners for
many years. The three main philosophies are:

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Figure 13. Softperm TM lens. Figure 14. Piggyback system with a
silicone hydrogel lens as the bandage
component (courtesy of C O’Donnell and
Maldonado-Codina).
Figure 16. Vortex staining (courtesy of
KW Pullum).
1. Apical clearance: the lens is supported fully on the
paracentral cornea with no touch on the cone (Figure 10).
Although this approach may seem ideal since there is a
relationship between apical touch and corneal scarring
(see later). The main problem with this philosophy is that
vision can be suboptimal. Fitting a steep lens may also
induce oedema due to diminished tear exchange.
2. Flat-fitting: the entire weight of the lens bears on the
cone with a wide edge stand-off (Figure 11). This apical
touch gives better VA and uncorrected vision may be
improved immediately after lens removal due to an
orthokeratology effect. Flat-fitting lenses are associated
with the development or acceleration of apical staining.
This in turn has been established as a risk factor for the
development of scarring (Barr et al 2000).
3. Three-point touch: currently the most widely accepted
method. The aim is to distribute the weight of the lens
between the cone and the peripheral cornea. The fit
should show an apical contact area of 2–3mm and a mid
peripheral contact annulus (Figure 12). The area of mid
peripheral touch may be more crescent-shaped, where
there is vertical asymmetry of the cone.
74
Rigid Lens Designs
Multicurve
Standard multicurve designs may suffice in early
keratoconus but there are also many more specialized
multicurve designs for advanced disease. The main
advantage of using a multicurve is that the lens
parameters are known and can be altered to suit, eg
flatten, or tighten peripheral curves or change back optic
zone radius (BOZR). The other advantage of this design is
that the lens can be ordered in the material of choice.
Spherical lenses to fit the periphery
These multicurve lenses are based on the principle that
the corneal periphery remains relatively unchanged in
early to moderate disease. The lenses have essentially
normal peripheral curves but with a much steeper BOZR.
The cone radius is selected from central Ks and there are
a number of different peripheries for each cone radius to
choose from.
Elliptical / aspheric
Figure 15. Sealed rigid gas-permeable
scleral lens on a keratoconic eye
(courtesy of KW Pullum).
Figure 17. Dimpling. Figure 18. Nebulae.
Part or fully aspheric lenses designed for normal eyes can
be useful in early disease. However, there are lenses
designed specifically for keratoconus, an example of which

is bi-elliptical in design, where the peripheral zone is
flattened using a second ellipsoidal curve of the same
eccentricity but flatter vertex radius than the first. It has
a large optic zone which makes it useful on eyes with large
pupils and for oval-type cones. The main disadvantage is
that it is essentially an apical bearing lens. Other aspheric
keratoconic designs are available that can be a useful firstchoice
lens as they can enhance comfort due to the
blended lens surface.
Offset lenses
The centre of curvature of the back peripheral curve is
offset to the opposite side of the central axis, thereby
virtually eliminating any transition. This controls the
degree of axial edge lift, which is useful in keratoconus as
large axial edge lifts are often required since the
peripheral cornea remains relatively normal in curvature
whilst the central cornea increases in curvature during the
disease process. They are sometimes called a continuous
bicurve lens or a contralateral offset lens. The main
advantages of this design are comfort, because of the
minimal transition, and the large edge lifts that can be
achieved.
Small-diameter or apical
This is an old design, originally for use with polymethyl
methacrylate (PMMA) lenses. The advent of gaspermeable
materials has led to the safe use of largerdiameter
lenses. Small-diameter lenses are now only used
to achieve apical clearance and for fitting steep, central
nipple-type cones. They have the disadvantage that they
can be unstable on the eye.
Large-diameter lenses
Large multicurve designs of up to 12.5mm can be very
useful. They are not a lens of first choice but can be useful
when dealing with decentred cones or larger oval cones as
stability is hard to achieve with smaller-diameter lenses.
Using lenses of this size, which are also usually bearing on
the cone apex, can result in epithelial / stromal scarring.
This should be reflected in material choice, which should
generally be high-Dk.
Axial profile fitting
This is a relatively new design where the principle is to
base the fitting on the profile of the cornea rather than to
the base curve and to specify parameters according to the
axial profile of the lens rather than specific measurements
of curvature. Various edge configurations are available to
control edge lift.
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Other Lens Types
Kerasoft TM
Managing Keratoconus in Optometric Practice
The Kerasoft lens can be used for mild to moderate
keratoconus when there is intolerance to a rigid lens. It is
a relatively thick, toric soft lens made from a 49% waterretentive
material. It has the comfort of a soft lens,
cylindrical power up to –11.00D, 1 / 2-degree axis steps and
is fitted by refraction over a plano diagnostic lens. A, B
and C series allow for variations in peripheral corneal
radius.
Softperm TM
Hybrid lenses, of which Softperm is the latest generation
(Figure 13), have a rigid gas-permeable centre with a 25%water-content
hydroxyethyl methacrylate (HEMA)-based
soft skirt which are bonded by a co-polymerization
process. A hybrid lens can offer increased comfort and
stabilisation but may increase the risk of
neovascularisation if the lens is too tight and if it is worn
for inappropriate lengths of time.
Piggyback lenses
This method can be used for rigid lens intolerance or
where there is epithelial damage which is compromising
contact lens wear. The piggyback lens system involves
fitting a rigid lens on top of a soft lens (Figure 14) which
acts as a bandage, increasing the comfort and protecting
the apex of the cone. It is recommended that high-Dk
lenses are used in combination with a high-water-content
bandage lens. The advent of silicone hydrogel lenses has
added a new dimension to this approach, with an
ultrahigh-Dk bandage lens making this technique a more
attractive option (O’Donnell & Maldonado-Codina 2004).
Scleral lenses
Scleral lenses still play a role in the management of
keratoconus, where corneal lens fitting is rendered
impossible in advanced disease and when surgical
intervention is not advisable due to severe atopic eye
disease or a vascularised cornea (Tan et al. 1995). Until
relatively recently, scleral lenses were manufactured in
PMMA using either preformed lens designs or by moulding
a lens from an impression taken of the eye to give an exact
fit. The disadvantages of using PMMA sclerals are low
wearing times (principally due to oedema) and the risk of
neovascularisation. However, the significant advances in
gas-permeable materials in recent years have produced
materials of sufficiently high Dk to allow sufficient oxygen
transmission through the required thickness of lens that is

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necessary in a scleral. At present rigid gas-permeable
sclerals are fitted in a preformed design and are lathe-cut.
These lenses can be fitted sealed with saline on to the eye
so that the irregular corneal surface is completely
neutralised and have proven to be useful in difficult cases
(Figure 15).
Complications of Contact Lens Wear in
Keratoconus
Contact lens wearers with keratoconus are susceptible to
the usual types of contact lens-related complications. The
following represent some of the complications more
commonly seen in keratoconus.
Vortex staining
Vortex staining is a swirling pattern of staining caused by
migration of dead epithelial cells from the basal cell layer
upwards to the epithelial surface (Figure 16). It is an
indication that the epithelium has been compromised. It
can be observed in corneas wearing flat-fitting lenses
which insult the epithelium. It can be resolved by
discontinuing contact lens wear, refitting with a steeper
lens to alleviate pressure on the cone and using a higher-
Dk lens material to enhance oxygenation of the cornea.
Dimpling
Dimpling is caused by bubbles forming beneath the
contact lens. They are effectively smooth foreign bodies
trapped under the lens which indent the epithelium and
can be seen clearly on instillation of fluorescein (Figure
17). Dimpling is often seen when using normal rigid gaspermeable
lens designs in early keratoconus, as the BOZD
is too large for the steepening cornea. Most keratoconic
lens designs have smaller BOZDs to contour the lens to the
steeper cornea and thus eliminate this problem. If using
standard designs, then reducing BOZD and adding further
peripheral curves should help to solve this problem or
alternatively try a keratoconus design.
Nebulae
Nebulae are discrete scars normally caused by wearing a
flat-fitting lens (Figure 18). They are usually quite small
and occur in the superficial stroma and may be slightly
raised. They can be abraded by the contact lens and so
cause discomfort and reduced wearing time. Also VA may
be reduced if they are on the visual axis. Treatment
consists of mechanical debridement or removal with an
excimer laser.
76
Stromal scarring
Stromal scarring is inevitable in later stages of the disease
process and affects VA to varying degrees, depending upon
location and severity. Also photosensitivity may be
increased due to glare. When reduced VA or glare is
interfering with quality of life, then referral for surgical
intervention is indicated.
Neovascularisation
Neovascularisation is usually observed from overwear of
contact lenses, especially hybrid lenses, larger-diameter
lenses which cross the limbus and scleral lenses. It is a
complication which should be avoided at all costs as it
may seriously jeopardise the success of future corneal
transplant surgery. Any signs of neovascularisation should
be dealt with in the early stages, with reduced wearing
time and refitting, and the opinion of a corneal specialist
should be sought.
When to Refer
Many patients with keratoconus can be managed in
optometric practice, especially in the early to moderate
stages of the disease. However the following should be
considered as suggested referral criteria:
• when the patient cannot obtain good enough acuity or
sufficient contact lens wearing time to carry on with
employment and driving or when quality of life is
impaired
• when complications develop such as scarring,
neovascularisation and hydrops
• if the practitioner feels that he or she does not have the
lens types or expertise to fit the patient with lenses,
then referral to a specialist contact lens centre or
hospital should be considered
Acknowledgements
The author would like to thank the Ophthalmic Imaging
Department at Manchester Royal Eye Hospital, Luisa
Simo, Clare O’Donnell and Ken Pullum for their assistance
in the preparation of this article.
References
Barr JT, Zadnik K, Wilson BS et al. (2000) Factors associated with
corneal scarring in the Collaborative Longitudinal Evaluation of

Keratoconus (CLEK) study. Cornea 19, 501–7
Biswas S, Brahma AK, Tromans C et al. (2000) Management of
pellucid marginal degeneration. Eye 14, 629–34
Cooke CA, Cooper C, Dowds E et al. (2003) Keratoconus, myopia, and
personality. Cornea 22, 239–42
Corbett MC, O’Brart D, Rosen ES et al. (1999) Corneal topography:
principles and applications. London: BMJ Books
Davis LJ, Schechtman KB, Begley CG et al. (1998) The CLEK Study
Group. Repeatability of refraction and corrected visual acuity in
keratoconus. Optom Vis Sci 75, 887–96
Doyle SJ, Bullock J, Gray C et al. (1998) Emmetropisation, axial
length and corneal topography in teenagers with Down’s syndrome. Br
J Ophthalmol 82, 793–6
Edrington TB, Barr JT, Zadnik K et al. (1996) Standardized rigid lens
fitting protocol for keratoconus. Optom Vis Sci 73, 369–75
Edrington TB, Szczotka LB, Begleym CG et al. (1998) Repeatability
and agreement of two corneal–curvature assessments in keratoconus:
keratometry and the first definite apical clearance lens (FDACL).
Cornea 17, 267–77
Edwards M, McGhee CNJ, Dean S (2001) The genetics of keratoconus.
Clin Exp Ophthalmol 29, 345–51
Harrison RJ, Klouda PT, Easty DL et al. (1989) Association between
keratoconus and atopy. Br J Ophthalmol 73, 816–22
Kennedy RH, Bourne WM, Dyer JA (1986) A 48-year clinical and
epidemiological study of keratoconus. Am J Ophthalmol 101, 267–73
Kenney MC, Brown DJ, Rajeev B (2000) The elusive causes of
keratoconus: a working hypothesis. CLAO J 26, 10–13
Multiple Choice Questions
1. Which of these statements is most likely to be true?
(a) There is no association between Down’s syndrome
and keratoconus
(b) All patients with keratoconus will have asthma
(c) All patients with keratoconus rub their eyes
(d) There is some association between eczema and
keratoconus
(e) All patients with keratoconus are atopic
2. Which early sign of keratoconus is most likely to be
detected during a routine eye examination?
(a) Hydrops
(b) Apical scarring
(c) Distorted retinoscopy reflex
(d) Munson’s sign
(e) Stromal thinning
3. Which of the following statements about the use of
corneal topography is false?
77
Managing Keratoconus in Optometric Practice
Krachmer JH, Feder RH, Belin MW (1984) Keratoconus and related
noninflammatory corneal thinning disorders. Surv Ophthalmol 28,
293–322
Lass JH, Lembach RG, Park SB et al. (1990) Clinical management of
keratoconus: a multicenter analysis. Ophthalmology 97, 433–45
Lichter H, Loya N, Sagie A et al. (2000) Keratoconus and mitral valve
prolapse. Am J Ophthalmol 129, 667–8
O’Donnell C, Maldonado-Codina C (2004) A hyper-Dk piggyback
contact lens system for keratoconus. Eye Contact Lens 31, 44–8
Pearson AR, Soneji B, Sarvanathan N et al. (2000) Does ethnic origin
influence the incidence or severity of keratoconus? Eye 14, 625–8
Perry HD, Buxton JN, Fine BS (1980) Round and oval cones in
keratoconus. Ophthalmology 87, 905–9
Rabinowitz YS (1998) Keratoconus. Surv Ophthalmol 42, 297–319
Rabinowitz YS, Garbus J, McDonnell PJ (1990) Computer-assisted
corneal topography in family members of patients with keratoconus.
Arch Ophthalmol 108, 365–71
Tan DTH, Pullum KW, Buckley RJ (1995) Medical applications of
scleral contact lenses: 2 Gas permeable scleral contact lenses. Cornea
14, 130–7
Teng CC. (1963) Electron microscopic study of the pathology of
keratoconus: Part I. Am J Ophthalmol 55, 18–47
Zadnik K, Barr JT, Edrington TB et al. (1996) Biomicroscopic signs
and severity of disease in keratoconus. Cornea 15, 139–46
This paper is reference C5333a. Two College credits are available. 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.
(a) A low surface asymmetry index (SAI) indicates
keratoconus
(b) A high surface regularity index (SRI) indicates
keratoconus
(c) It can be used to make a differential diagnosis
between keratoconus and pellucid marginal
degeneration
(d) It can be used to detect keratoconus in
asymptomatic patients
(e) It can be used to detect the location of the cone
4. In which age group is the age of onset of keratoconus
typically reported?
(a) At birth
(b) Up to 15 years
(c) 15–25 years
(d) 30–40 years
(e) 40–50 years

C Tromans
5. Which of the following rigid lens-fitting strategies
would be generally accepted as the preferred option
to avoid apical scarring and optimise vision?
(a) Use a flat-fitting philosophy
(b) Use a polymethyl methacrylate (PMMA) scleral
(c) Use a large-diameter rigid gas-permeable (RGP) lens
(d) Use a multicurve lens with a three-point touch fit
(e) Use a Kerasoft TM lens
6. The main advantage of using an offset lens design is:
(a) It has a large back optic zone diameter (BOZD)
(b) It can have a large axial edge lift
(c) It can be manufactured in any material
(d) It has an elliptical back surface
(e) It can be made with a very steep back optic zone
radius (BOZR)
7. Which of the following management options may be
more appropriate in the early stages of the disease
process?
(a) Penetrating keratoplasty
(b) LASIK
(c) Toric soft contact lens fitting
(d) Daily disposable soft lens fitting
(e) Piggyback lens fitting
8. Which of the following statements about vortex
staining is false?
(a) Refitting is required with a higher-Dk flatter-fitting
lens
(b) It is an indication of corneal hypoxia
(c) It can be caused by wearing a flat-fitting lens
(d) It can lead to the development of apical scarring
(e) Refitting is required with a steeper lens
78
9. Which of the following signs/complications is most
likely to reduce visual acuity?
(a) Fleischer ring
(b) Contact lens-associated papillary conjunctivitis
(CLAPC)
(c) Dimpling
(d) Vogt striae
(e) Nebulae
10. A piggyback sytem ideally consists of:
(a) A daily disposable lens + high-Dk RGP lens
(b) Low-water bandage contact lens + high-Dk RGP lens
(c) High-water bandage contact lens + low-Dk RGP lens
(d) Silicone hydrogel lens + low-Dk RGP lens
(e) Silicone hydrogel lens + high-Dk RGP lens
11. Which of the following statements has been shown to
be false?
(a) Keratoconus may be inherited
(b) Keratoconus may be caused by eye rubbing
(c) Keratoconus may be associated with mitral valve
prolapse
(d) Keratoconus is associated with a personality disorder
(e) Keratoconus has been shown to have a higher
prevalence in Asian eyes
12. Which of the following complications / signs is least
likely to cause discomfort in an RGP wearer?
(a) Hydrops
(b) Stromal thinning
(c) CLPC
(d) Dimpling
(e) Nebulae