Nov 2016

SPECIALITY CL FORUM BY ALEX PETTY*
HOW NOT TO REVOLUTIONISE CONTACT LENSES DESIGN
In the annals of history there exists a number of
important discoveries that were conceived over
a few beers. Arthur Holmes and his colleagues
developed the theory of continental drift whilst
sipping cocktails in Hawaii. Watson and Crick
unravelled the mysteries of DNA’s double helix in
the now-famous Eagle Tavern in Cambridge. Trivial
Pursuit, the Iron-Man triathlon and even Harry
Potter’s fictional sport Quidditch are all famous
ideas that may not have come to be without the
influence of a chilled alcoholic beverage.
The following innovation is not one of these.
Picture this scenario: on a balmy summer’s evening
last year, a colleague and I decided a quenching ale
was just the ticket after a long Friday of checking
eyeballs. My final appointment of the day was a
scleral contact lens fitting for a chap with advanced
keratoconus. Once I had finished regaling my fellow
optometrist with tales of the complexity of the case
our conversation (rightly) turned to weekend plans.
Given the heat, a swim at the local beach was on
the agenda. “That patient of mine would have a
tough time checking the water for sharks!” I laughed
sympathetically. “Did you not design his sclerals
to see underwater too?” my colleague retorted.
Chuckles simultaneously turned to quiet speculation
as metaphorical light-bulbs switched on above our
heads. What if it could be done ...?
Water-wear
One of the few limitations of day-wear contact
lenses are the difficulties when swimming. In my
younger years I would dive and swim with lids
clenched tight for fear of my soft dailies drifting
away (Fig 1.). Three years ago I had laser refractive
eye surgery and still I get a guilty kick when opening
my eyes underwater to experience the (blurry)
wonders beneath the waves. This freedom is one
of the main reasons I recommend orthokeratology
lenses to patients who enjoy the water. Goggles are
all good, but they have their limitations: fogging
of the lens, water influx, discomfort, field of view,
and those lovely compression marks visible after
removal. Plus, you’d never see a trendy surfer
waiting for the next set with a pair of goggles
strapped on. Wouldn’t it be neat if we could design
a scleral lens swimming goggle that could offer
great vision in and out of the water instead?
Several high-fives later we calmed down, ordered
another round and extra napkins, and got serious.
First things first: would a scleral lens stay in an open
Fig 1. One from the family album: Me as an 11-year-old soft contact lens
wearer demonstrating the clenched-eye diving technique that I had perfected
Fig 2. Is than an RGP lens? Or a pneumatic retinopexy gone wrong? No, this
ladies and gentleman, is a scleral swimming goggle
eye underwater? We decided yes: the large surface
area provides ample surface tension (when was the
last time you were able to pull a scleral or hybrid
lens straight off the eye without a suction tool?
Clue: it’s not easy) and the lids should provide an
additional barrier.
Second: how do we get around the issue of
the vergence changes when a rigid contact lens
is moved from air to water? As most of you will
appreciate when underwater the human eye
becomes severely hyperopic, by approximately 40
diopters, due to the cornea being almost entirely
neutralised. A traditional rigid lens would behave
similarly. Simply adjusting the contact lens front
curvature to focus correctly underwater would
lead to a colossal level of myopia when above the
surface. Not ideal. One solution would to create a
monovision-type set up, with one lens designed for
vision in air and the other for vision underwater.
Again highly impractical.
Eureka!
Then it hit us. Why not make a tiny goggle for each
eye? Create the lens with a completely flat front
and back surface, and insert the lens with an air
gap, rather than filled with solution, so that the air/
cornea refractive interface, and therefore the power
of the eye, remained the same in air and water! In
theory it would work perfectly. We left the bar that
night with a sense of purpose rarely experienced by
slightly-inebriated eye care professionals.
First thing on Monday morning I called Graeme
Curtis at Contact Lens Corporation in Christchurch.
“Was it even possible?” I asked. This lens would have
quite possibly the flattest base curve ever created
on a rigid lens, with essentially a radius of infinity.
It is testament to the technology of modern day
lathes (not to mention Graeme’s patience with
seemingly foolish requests) that his reply was “Sure,
let’s give it a try”. I heavily modified the parameters
of a trial scleral lens using rigid lens design software
Eyespace to match the cocktail napkin diagrams we
had sketched previously. Regrettably ‘infinity’ was
not a BOZR value I could input, so I had to settle on r
= 99999mm. You read that correctly: Our lens had a
100 metre base-curve radius.
Weird science
As I opened the courier parcel from CLC you could
have cut the tension with a knife. As it turned out
the parcel’s contents; possibly the world’s first
scleral swimming goggle, was the weirdest
contact lens I had ever seen. The completely
flat 6mm optic gave the lens a sinister
appearance: It looked more like a part from
a Terminator than something a water-sports
enthusiast would wear. After the initial
excitement subsided, human trials began.
Much like Australian Dr Barry Marshall, who
drank a petri dish filled with the bacterium H.
Pylori to prove the cause of stomach ulcers,
in the name of science I bravely inserted the
dry scleral lens onto my left eye.
Initial impressions were positive. For those
of you who have not worn a well-fitting
scleral lens they are surprisingly comfortable.
I could feel this lens a little more than usual
due to the abrupt junction at the optic zone
edge but it was not irritating. And I could see!
I could happily make out the 6/6 line on the
chart due to my plano unaided refraction.
Topography over the lens confirmed a front
surface power equalling zero diopters;
the lens was as flat as a pancake. OCT
and anterior photography highlighted
the unusual shape of the lens (Fig 3.) and
confirmed ~250μm of central clearance -
important when the lens is 35D flatter than
alignment.
However, things did not stay hunky-dory
for long. After a few minutes my vision
started to blur; I was struggling to see 6/12.
Under the slit-lamp the rear surface of the
lens was misting up like a bathroom mirror.
We removed the lens and added a lubricant
drop to the lens bowl prior to insertion. This
helped for about five more minutes but the
blur slowly returned. Only this time the lens
was starting to become quite uncomfortable.
Fig 3 & 4. OCT and slit lamp appearance of the flat scleral lens profile on eye
Fig 4.
Inspection showed the lens was fitting well in the
peripheral area and still had adequate clearance. I
managed to keep the lens in the eye for a further
ten minutes, before the pain and significant blur
necessitated removal.
We created a monster
Rather than relief, my first emotion was concern:
the vision in my left eye was still very hazy: I was
only reading 6/36 in my guinea-pig eye! The cornea
was clear and uninflamed however instillation
of sodium fluorescein revealed a subtle patchy
negative staining of the central epithelium. Further
investigation with corneal topography showed
very irregular central mires (Fig 5.). Realisation
dawned: we had created a corneal exposure
scenario mimicking the pathophysiology of
patients with conditions like Bell’s Palsy, thyroid
orbitopathy, restrictive eyelid disease and nocturnal
lagophthalmos. Even a healthy eye with excellent
tear film function will experience significant visual
problems and discomfort when the lids are not
regularly smoothing and spreading fresh tears over
our fragile corneal surface.
A case of one of my colleagues highlights this
concept in a similar way. At routine aftercare a
happy keratoconic patient noted that from time
to time his lenses would be very painful and
irritable for the duration of the day. The lens was
fitting beautifully and in the chair his eyes looked
pristine. The patient was asked to return wearing
his lens if the irritation arose. A few weeks later
the patient returned with a very red eye. One look
explained his troubles - poor insertion technique
had trapped a bubble of air under his lens (Fig 6.).
As the bubble was for the most part off the optic
axis he was unaware of it. Following removal,
a kidney-shaped depression was evident at the
site of the bubble, with dense epithelial staining
within its confines (Fig 7.). Needless to say it is
important to educate scleral lens patients to check
for bubbles after insertion with the aid of a mirror
and sometimes a penlight. Like a stone trapped
in a shoe, even a small pocket of air will gradually
cause problems.
In the end it took roughly an hour for my vision
to return to normal. Despite my scare I gamely
tried the scleral lens one further time, except with
a soft bandage lens worn beneath. The discomfort
was not noticeable but vision became equally poor
as the soft lens surface desiccated slowly. It was to
be the last time that the scleral goggle would ever
be worn.
Reinventing the wheel
The novel concept of using an air gap under the
lens had ultimately proven the design’s downfall.
So disappointing (and not to mention traumatic)
Fig 5. The exposure keratopathy induced by the air-filled scleral lens.
Note the distorted mires seen on topography
Fig 6 & 7. Epitheliopathy and inflammation caused by a trapped bubble
under a well-fitting scleral lens. Images: Lachlan Scott-Hoy
Fig 7.
was the outcome that the lens was never even
tested underwater. With our luck it would have
just floated off anyway!
It may seem like a waste of time to publish an
account of this fruitless escapade. However, I think
failures in science can also be viewed as learning
opportunities. Rome wasn’t built in a day after all.
I discovered:
Contact lens technology is progressing at an
incredible rate and more and more is possible
when designing rigid lenses.
A healthy lid-wiper should not be
underestimated in patients with irritation and
dryness symptoms. Neither should the absence of
obvious clinical problems preclude patients from
a diagnosis of dry eye. As I personally found out
symptoms can far exceed signs.
We are not born with two eyes as a handy
surplus should one be blinded through
irresponsible self-experimentation.
And perhaps the most important life lesson we
glean from this tale, the grander a pub idea is, the
more miserably it will fail!
On that sour note thank you for your support
this year. Have a safe and happy holiday period. I
look forward to entertaining with further specialty
contact lens reports in 2017. ▀
ABOUT THE AUTHOR
*Alex Petty is a New Zealand
optometrist based in
Tauranga with a particular
interest and knowledge in
speciality contact lenses,
ortho-k and myopia control.
16 NEW ZEALAND OPTICS November 2016