Feb 2016

CASE STUDY: CORRECTING ASTIGMATISM
WITH ORTHO-K
Many orthokeratology lens designs
suggest that in determining a patient’s
suitability for orthokeratology the
astigmatic component of their prescription
should be no more than half of the spherical
component. With the availability of the modern
topography-based toric ortho-K lens designs,
this no longer holds true. This case shows how
a patient with principally astigmatic refractive
error can be corrected with a non-rotationally
symmetrical orthokeratology lens and get clear
vision throughout the day.
A dentist of 33 years visited my practice,
curious if orthokeratology would be appropriate
for him. He had never worn contact lenses
before, and was motivated as his glasses would
frequently fog up and slip down during his work.
His spectacle prescription was R -0.25/-1.50 x
170 (6/5), L -0.25/-1.75 x 009 (6/5). Unaided
vision was R 6/7.5, N4 (40cm) and L 6/10, N8
(40cm).
Figure 1: Initial astigmatic topographies R+L
Topography shows regular with-the-rule
astigmatism with ΔSimK R -1.80D, L -2.2D
which is only slightly more corneal cylinder
than the spectacle astigmatism present. Given
that the cornea closely matched with his
refraction I proceeded to design a Forge Myopia
Toric orthokeratology lens for each eye using
Eyespace. Trial fitting a spherical lens on eye
will be of little use in this instance as the fit will
need to fit very differently in each meridian to
seal the cornea correctly and mold the cornea
accurately.
Because the spherical component of this
patient’s prescription is almost zero we do
not require much flattening of the cornea
horizontally. As a result the lens has a tear
profile very similar to an alignment fit lens in
this meridian. In the steep meridian however
we need to correct -1.75D of myopia hence
the conventional ortho-K tear profile pattern.
Research suggests that fitting a lens with a
spherical base curve will correct ~50% of the
corneal astigmatism present , however in my
experience this percentage is closer to ~70%. In
this instance we need more than 1.25D of WTR
astigmatism corrected so the steep meridian’s
BC is 0.1 flatter to ensure full astigmatic
correction.
In order to stabilise the lens on the eye the
alignment curve radii match the underlying
corneal topography in the same way as a bitoric
RGP would. In this way a modern orthokeratology
lens can be fully customised with independent
toricity in the base-curve, Z-Zone (reverse curve)
and the alignment curve. The left lens was
designed in the same way, giving lenses with
significant sagittal height difference of ~140µm
between meridians.
Figure 2: Eyespace simulation of each meridian of the
left toric orthokeratology lens showing the almost
alignment fit horizontally and more conventional
ortho-K tear profile vertically
Specialty contact
lenses forum
BY ALEX PETTY
Figure 3: NaFl image of the left lens on eye illustrating
the accuracy of the rotation simulation of Eyespace and
the NaFl pattern in the steep meridian
After a short period of wear to allow full
stability of the refractive change the patient
presented for aftercare with excellent distance
vision of 6/5 R+L. Residual refraction was
R +0.25/-0.25 x 180 and L plano, showing
full correction of the pre-orthokeratology
astigmatism. Axial difference maps of the right
eye shows a characteristic ‘figure 8’ pattern of
astigmatic correction that closely matches the
residual refraction.
Figure 4: Axial difference map showing excellent
astigmatic correction
The patient was very pleased with the results
and was asked to return in three months for
routine review. This report shows how significant
astigmatism can now be successfully corrected
with orthokeratology by using toric alignment and
base curves to control the fit of the lens and the
refractive change respectively.
Much higher prescriptions than this case can
also be well corrected with OK if you are prepared
to get creative! The below image shows a mixed
myopia (steep meridian)/ hyperopia (flat meridian)
custom Ortho-K lens designed with Eyespace that
corrected a patient with a spectacle prescription
of R +0.75/-4.50 x 178, L +0.25/-3.50 x 12 to give
6/6+ vision in each eye with no astigmatism
present in the residual refraction! ▀
Figure 5: Axial difference maps and NaFl photo of a lens
correcting high astigmatism!
A more detailed report of this case can be found
at eyespace.com.au/blog
REFERENCES
1. Mountford J, Pesudovs K. An analysis of the astigmatic
changes induced by accelerated orthokeratology. Clin
Exp Optom. 2002 Sep;85(5):284-93.
ABOUT THE AUTHOR
* Alex Petty is a Kiwi optometrist
who graduated from the
University of Auckland in 2010.
He has an interest in specialty
contact lenses, ortho-K and
myopia control.
New CEO for Auckland Eye
Auckland Eye has appointed e-health
management consultant Deb Boyd as their
new chief executive.
Previous to her recent consultancy experience,
Boyd was general manager at Australia’s first
fully-integrated digital hospital, St Stephens in
Hervey Bay, a coastal city in southern Queensland.
St Stephens opened in October 2014 and
achieved HIMSS Level 6 in November 2014. HIMSS
(Healthcare Information and Management Systems
Society) is a global, not-for-profit organisation
focused on optimising care outcomes and
improving information management in hospitals
through its Electronic Medical Record Adoption
Model (EMRAM), which has 7 levels in total.
“This was a thrilling project to be part of and to
experience such incredible technology with a fully
functioning EMR (Electronic Medical Record) and
closed loop medication management system. It was
a privilege to see first-hand the patients and staff
experiences as they transitioned from old ways of
doing things to successfully using new technology.”
A self-confessed technophile and passionate
advocate for the value technology can bring to
organisations and customer care, Boyd says her key
strengths are in operational management, change
management, systems improvement, healthcare
innovation, digital integration and developing
teams. “I use transformational leadership to bring
teams together and find creative solutions for
success,” she says in her LinkedIn biography.
Boyd’s previous roles in New Zealand include
hospital manager at Southern Cross Hospital
in Wellington; ward and day stay manager at
Southern Cross Hospital in Christchurch; and
business manager and child health services and
community services manager for the Canterbury
TearLab goes it alone
in ANZ
TearLab’s George Koukides at RANZCO 2015 in Wellington
TearLab has commenced direct distribution
of its ground-breaking Osmolarity System,
through its manufacturing partner MiniFAB
based in Scoresby, Victoria, Australia.
The Osmolarity System is believed to be the
first objective and quantitative point-of-care test
enabling eyecare professionals to easily measure the
osmolarity of human tears to diagnose and manage
patients suspected of having dry eye disease.
Osmolarity is a key test as recognised by the first
DEWS (Dry Eye Workshop) report and previously
was only able to be tested in the laboratory.
Manager George Koukides, who was appointed
to set up and run TearLab Australia last year, says
MiniFAB wanted to get closer to the market for
research and development purposes so it made
sense for them to take over the distribution of the
System in their own area and TearLab, based in
San Diego, agreed.
TearLab has been out on its own in Australia
since April last year, but its first real foray into
New Zealand was at RANZCO’s 2015 Scientific
Auckland Eye’s new CEO Deb Boyd. (Fraser Coast Chronicle)
District Health Board. According to her LinkedIn
biog. she was also the owner-operator of a
Brumby’s bakery franchise in Christchurch, during
the time of the quakes.
Her governance experience includes time on the
inaugural board of Partnership Health PHO and
she is a current member of the board of Health
Informatics New Zealand (HiNZ).
Auckland Eye’s board chair Dr Stephen Best says,
“We’re delighted to have Deb at Auckland Eye and
feel her vast experience in hospital management
and health infomatics will be invaluable to our
organisation.” ▀
Congress in Wellington in November last year.
“That was the start for New Zealand,” said
Koukides, who expects to be visiting New Zealand
on a quarterly basis from now on.
Currently the TearLab system is being employed
on a regular basis in New Zealand by just a
handful of practitioners, he says. These include
Associate Professor Jennifer Craig, who leads the
Ocular Surface Laboratory at Auckland University
and is the vice-chair of the Tear Film & Ocular
Society’s second dry eye workshop (DEWS II); the
Auckland-based Eye Institute; and Fendalton Eye
Clinic in Christchurch.
The TearLab system has a better predictive value
for dry eye than any other test, claims Koukides,
and is particularly useful for ophthalmologists
in the pre-surgical workup as it identifies
hyperosmolarity which can significantly affect
visual acuity and K-readings and thus affects
lens choice.
TearLab’s system was previously distributed in
New Zealand by Designs for Vision. ▀
8 NEW ZEALAND OPTICS Feb 2016