Aug 2016

SPECIALITY CL FORUM BY ALEX PETTY*
ORTHO-KERATOLOGY FOR THE POST-LASIK CORNEA
Before we delve into our next case I should
make it known that shortly after my
last column was published in May I was
summoned to an urgent meeting with the
NZ Optics editorial team. Disturbing reports
had emerged of the readership falling asleep
when perusing the contents of Speciality
Contact Lens Forum. Admittedly, I was shocked
that there were optometrists out there not
captivated by weird rigid lenses like me. I was
issued an ultimatum: inject some personality
into my case reports or be shipped back to the
penal colony across the Tasman as penance for
the crime of dull writing. Jokes aside it is great
to see the energy Lesley and Jai are putting into
the magazine and I’m excited and grateful to
help out in a small way as NZ Optics evolves.
Naturally I apologise in advance for the glut of
‘dad’ jokes and inappropriate puns that I now
have free-reign to include in future missives.
On to the optometry.
We all know that the results of laser refractive
eye surgery are becoming increasingly
impressive. However, the reality is that despite
the success of the initial surgery, zero refractive
error is not a guarantee as the years continue.
One report suggests that in a 2-13 year followup
of LASIK patients only 64.8% of low myopes
and 37.3% of high myopes remained within
±0.50D of their attempted correction 1 . Not
only can a cornea change shape over time but
the onset of presbyopia can humble/anger
the patient that expects the rest of their life
to be devoid of optical aids. Unsurprisingly the
typical post-LASIK patient is highly reluctant to
return to their bespectacled former selves. This
is where contact lenses come in.
Traditionally I have found that even
experienced optometrists are wary to meddle
with a patient’s cornea that has already been
permanently reshaped by our colleagues in
ophthalmology. You wouldn’t re-glaze a cake
created by a top chef would you? There are
concerns about flap dehiscence, the structural
weaknesses of a thinner cornea and perhaps a
reluctance to incur the wrath of the patient’s
eye surgeon should something go wrong,
(“You put WHAT on my perfectly designed
cornea?!”). Perhaps we should proceed with
caution. Research shows that the central
flap interface following LASIK has only 2.4%
of the strength of normal stroma, while the
peripheral margin is 10x stronger at 28% 2 .
However, the general consensus is that the
use of contact lenses in conjunction with
lasered corneae is quite safe, as despite the
histologically weakened interface LASIK flaps
are quite robust. A fantastically designed
study performed LASIK on the eyes of 18
rabbits then ejected them from a fighter jet
cockpit to see what happened. They concluded
that ‘healed LASIK flaps...are stable when
subjected to a rapid vertical ejection at nine
times the force of gravity 3 . I would hazard a
guess that this is more than most eyes endure
with the use of a contact lens.
Fitting standard contact lenses to a
remodelled cornea is not always straight
forward however. Frequently, following
laser eye surgery, the corneal curvature falls
outside the normal limits that off-the-shelf
You wouldn’t reglaze a cake like this! My birthday treat in 2012
soft contact lenses are designed for. By way of
example I should divulge that I had a highly
successful iLASIK surgery to both of my highly
myopic eyes three years ago courtesy of Dr
Trevor Gray and the team at Eye Institute.
My refractive error was eliminated (but not
my long axial lengths sadly, more on this in a
future article) and I see a superb 6/4.8 unaided
now with just a hint of astigmatism in my
right eye. Needless to say I am one of the
optometrists in the pro-LASIK camp. Prior to
my surgery I was the best contact lens wearer
I had ever met, with complaints of discomfort
few and far between. At the launch of one of
the fantastic new daily-disposables recently
I popped a few -0.50D lenses in to test them
out. Within five minutes they were in the bin.
With every blink the vision would blur over, I
had a noticeable foreign body sensation and
the lens quickly dried out rendering it useless.
Turns out my new 35D corneae did not take to
kindly to a one-size-fits-all policy.
Post-LASIK dryness can also be a factor when
using a contact lens, even with a customised
daily RGP (which can be an excellent option
to mask corneal irregularities and fit the
unusual bespoke cornea). Fortunately, we
live in a realm of new technologies and their
applications: It may surprise you that many
post-laser refractive surgery patients with
troublesome residual refractive error do very
well when fitted with ortho-Keratology lenses.
Cue the deafening sounds of aghastment.
Fitting an already heathen device to a
previously altered cornea? You must be mad!
Indeed, in the main orthokeratology ‘bible’;
John Mountford’s Orthokeratology: Principles
and Practice published back in 2004, there is
no mention of fitting ortho-K to the post-
LASIK cornea (although John is working on
a new edition which may address this). A
pubmed search shows no articles about
ortho-K on a post-LASIK cornea. Despite this
many experienced ortho-Keratologists around
the world practice ortho-K on the post-LASIK
cornea with excellent results. I personally
believe there is no more harm in fitting ortho-
Keratology lenses to a lasered cornea than to a
virgin example. It is the understanding of most
orthokeratologists that the refractive effect of
ortho-K comes about due to modification of
the epithelial cells of the cornea, although the
jury is still out in some circles. This OCT (Fig 1.)
of a patient of mine using ortho-K lenses for
high myopia illustrates this by showing the
thinned epithelium centrally and thickened
layer para-centrally. The stroma remains
relatively uniform. In contrast all forms of laser
refractive corneal surgery involve permanent
modification to the stroma of the cornea.
The mechanism of refractive change in
these two modalities are mutually exclusive.
In post-LASIK ortho-K the main challenge
comes with designing the back surface of an
orthokeratology lens to firstly fit the paracentral
cornea safely and comfortably, and
secondly remodel the central epithelium in a
way to correct the refractive error. Let’s look at
an example:
A 67-year-old lady saw me due to the sudden
appearance of flashes and floaters the previous
weekend. Dilated exam revealed a benign
posterior vitreous detachment. The woman
had hyperopic LASIK carried out to both eyes six
years before but she was having more trouble
with her distance vision lately. She was also
sick of using reading glasses. Unaided distance
vision was only R 6/10 and L 6/12 and refraction
revealed residual hyperopia of R +0.75/-0.25
x 175 (6/5), L +1.50/-0.50 x 85 (6/5). Her
topography confirmed her hyperopic LASIK with
tangential maps showing a flatter para-central
ring encircling a steeper central cornea (Fig 2.).
Her left cornea was slightly steeper which was
surprising given the higher hyperopic error.
Given the foundations were essentially already
in place hyperopic post-LASIK orthokeratology
was offered to this patient. We chose to further
steepen her cornea in a monovision set up, with
her dominant right eye for distance
and her left for near tasks.
In these complex cases using
topography-based lens design is a nobrainer
for me. To marry the correct
peripheral fit with the appropriate
sagittal height and base curve for the
desired refractive change with a trial
lens would be time-consuming and
inaccurate, even if such a post-LASIK
hyperopic design set existed. Instead
I plugged the patients topography
into rigid lens simulation software
EyeSpace (Innovatus Technology,
Fig 3.) and designed a custom hyperopic
ortho-K lens for each eye. Because the cornea
is reasonably regular we can use a rotationally
symmetrical lens to get a great fit. Of course
with all hyperopic ortho-K the lens base curve
is steeper than the existing corneal curvature to
create additional plus power.
One month later the patient was thrilled
with her vision as she was no longer using
reading glasses and seeing well at distance.
Her right eye was seeing 6/6 N8 with a
modest central steepening. Her left eye was
6/15 N4 with an impressive 4.7D steepening
in a well centred location (Fig 4.). Importantly
she experienced no discomfort and her cornea
was pristine with no trace of corneal insult.
Unfortunately, not all post-LASIK refractive
error is regular. Post-LASIK ectasia can be
highly debilitating and severely limit the
corrective options available. In some cases,
highly customised ortho-K lenses can be
used to remodel the irregularity and improve
vision. A patient of mine in his mid-50’s had
myopic LASIK done over a decade before but
had developed severe post-LASIK ectasia in his
right eye and moderate ectasia in his left eye
since then. The better left eye had a variation
of 7D of axial power along the 150 meridian
leading to unaided acuity of 6/12 and a
refraction of -1.00DS (6/6 with aberrations).
This gentleman was very keen to explore his
ortho-K options and we settled on fitting only
the left eye with a custom myopic ortho-K
lens. This had an aspheric back optic zone with
a diameter to match the treatment zone of his
myopic LASIK (Fig 5.).
In these cases, interpreting the axial
difference map can require some thought.
Rather than creating a uniform degree of
refractive change in the form of a ‘bulls-eye’
that we are used to with simple myopic
ortho-K, instead we are trying to create a
post-ortho-K cornea that is more regular.
This will decrease the aberrations in the
optical system. You will see in the axial
difference map (Fig 6.) that the ortho-K lens
has succeeded in steepening the flat section
of the cornea at axis 150 and flattening
the steep section opposite this. The patient
was seeing 6/6 unaided with only a quarter
diopter of residual cylinder when using his
lens. He commented that the halos around
streetlights were much reduced, although
not completely eliminated. His main gripe
was that we couldn’t do the same treatment
on his severely ectatic right cornea due to
its ‘munted’ irregularity! Patients with other
forms of irregular corneae such as forme
fruste keratoconus can also be treated with
ortho-K lens in a similar way (often with an
inferior ‘tuck’ quadrant specific design) as
long as the practitioner is mindful to monitor
the cornea at each aftercare for signs of
progression or insult.
These cases highlight how versatile the
practice of orthokeratology is these days. No
longer is it reserved for simple myopia and
it can be a great problem-solver for those
particular patients that are determined to be
spectacle-free! It is encouraging to know that
when my LASIK goes kaput (as it is bound to,
given my eyes’ record to date) I will have ortho-K
up my sleeve to restore my super-vision.
Tune in next time as I regale you with a story
about the night we invented a revolutionary
contact lens at the pub, and how it did not turn
out to be quite as ingenious as we expected... ▀
1. Dirani M, Couper T, Yau J, Ang EK, Islam FM,
Snibson GR, Vajpayee RB, Baird PN. Long-term
refractive outcomes and stability after excimer laser
surgery for myopia. J Cataract Refract Surg. 2010
Oct;36(10):1709-17.
2. Schmack I, Dawson DG, McCarey BE, Waring GO 3rd,
Grossniklaus HE, Edelhauser HF. Cohesive tensile
strength of human LASIK wounds with histologic,
ultrastructural, and clinical correlations.J Refract
Surg. 2005 Sep-Oct;21(5):433-45.
3. Goodman RL, Johnson DA, Dillon H, Edelhauser HF,
Waller SG. Laser in situ keratomileusis flap stability
during simulated aircraft ejection in a rabbit model.
Cornea. 2003 Mar;22(2):142-5.
Fig 1. Anterior OCT showing the thickness profile of the corneal epithelium in myopic
orthokeratology. Note this well-fitted lens does not touch the cornea within the
treatment zone.
Fig 2. Our patient’s post hyperopic LASIK corneal topography showing the relatively
steep central cornea R+L respectively.
Fig 3. EyeSpace simulation, post-lens tear profile and the real lens on the left eye.
Note the slightly irregular central tear profile due to the LASIK result.
Fig 4. Axial difference map of the left eye showing the well-centred +4.7D
topographical change.
Fig 5. Our second patient’s EyeSpace simulation of his customised myopic ortho-K lens
over his irregular post-LASIK left cornea.
Fig 6. Axial difference maps showing our second patient’s irregular post-LASIK corneal
topography in Exam A, the more regular post-ortho-K cornea in exam B and the
unusual difference map showing how this patient’s cornea has been modified to
decrease the aberrations due to his ectasia.
* 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.
8 NEW ZEALAND OPTICS August 2016.indd