the Keratoconus Challenge
contact lens alternatives for keratoconus patients.
eye was post PKP and fit with an intra-limbal design, resulting in poor centration
same eye was fit with a Jupiter Mini-Scleral. Note the improved centration, as well
as the fenestration at eight o'clock.
is something that we are familiar with and see routinely in our offices. It can
be very challenging to fit these patients successfully, but by the same token, very
The typical therapeutic
sequence for the treatment of these patients is to correct them with spectacles
until they can no longer provide satisfactory vision. Soft/toric contact lenses
are sometimes used next but usually with limited success, because soft lenses tend
simply to drape over the cornea, transferring the corneal irregularities to the
anterior surface of the soft lens. Eyecare practitioners then turn to GP lenses;
in fact 75% of diagnosed keratoconus patients are best corrected with GP lenses.
They have several therapeutic advantages over the other non-surgical options.
Evaluating the GP option
They allow for
a uniform refracting surface and eliminate most astigmatic error; resulting in increased
visual acuity. They can, however, be difficult to fit. Patients have to "build-up"
their wearing time. The lenses may cause punc
keratopathy and epithelial defects which can ultimately lead to further corneal
scarring. Standard curve GP lenses are often implemented first and used until the
keratoconus progresses so far that standard curves are no longer able to provide
an adequate fit.
GP lenses are ultimately used. These are by far the most successful non-surgical
means of treating keratoconus. These GP lenses have a high Dk value and steep central
curves to avoid excess bearing on the apex of the cone. The peripheral curves then
flatten disproportionately to avoid tight lens syndrome.
first generation hybrid lens was
the piggyback lens design. This was simply a rigid lens fitted over a hydrogel lens.
Although the soft lens improved comfort and wearing time while the GP improved vision,
persistent decentration, handling difficulties, and expense prevented this from
being a widely- used treatment.
Newer hybrid lens
designs fused a GP lens to a soft lens skirt. Again the GP center provided better
vision and the soft skirt increased comfort and wearing time for the patient. The
fusing of the GP and the soft lens in one overcame the centration problems encountered
in earlier designs. Although still widely used today, these lenses present some
problems as well. In addition to poor movement and limited tear exchange, the GP
center has a relatively low Dk of 14, further starving an already sick cornea of
oxygen. Problems with breakage and tearing of the RGP/soft lens junction limit the
average life of this lens to six months to a year. An additional disadvantage is
These lenses often cost twice that
of a keratoconus design GP lens.
The soft lens/GP lens interface of a
of these lenses both at the GP center and at the soft lens/GP junction limit durability.
Rizzuti's sign is appreciated when a
slit lamp beam is focused on the nasal aspect of the limbus. When viewed temporally,
the apex of the cone is illuminated.
lenses are the latest option for this population of previously underserved patients.
Keratoconus-design hydrogel lenses have recently come on the market. Innovations
In Sight has created a lens called the Super Nova HydroKone, and it was recently
put to use in our clinic. It's a glycerol methacrylate lens with 59% water content
and a Dk of 21.0. It uses a steep aspheric central curve, flatter para-central curve,
with a center thickness of 0.35mm (low minus) to provide stability.
base curve range of 4.1-9.3mm
and total diameters of 12.0-17.0mm are available in powers from +50.00 to -75.00.
A wonderful feature of these lenses is that once the trial lens is fit, a sphero-cylindrical
over refraction is performed and a lens is made-to-order, including the residual
Sight has another lens to treat these patients the Jupiter Mini-Scleral GP.
A new spin on an old idea, the Jupiter lens is a large-diameter (14.4mm - 18.6mm)
GP lens made of Boston XO or Equalens 2 with a 100 Dk and 85 Dk values respectively.
It vaults the entire cornea, creating a large tear lens between the cornea and the
posterior surface of the lens to neutralize surface corneal irregularities. The
lens actually rests
outside the limbus on the less sensitive sclera and can use a fenestration for added
tear exchange. It's a very interesting alternative for keratoconic patients as well
as patients suffering from other corneal irregularities.
Technologies is developing a new generation hybrid lens, the SynergEyes KC, which
holds a great deal of promise in overcoming problems encountered with earlier generations
of this type of lens. It has a central GP made of Paragon HDS (100 Dk) and a surrounding
soft skirt (31% water). It's been reported that the soft lens-GP interface is more
than 10 times stronger than previous lenses of similar design. Additionally, the
lens is slated to be less expensive than previous hybrid lenses. Another exciting
aspect of is the use of wavefront-guided lens design, offering a made-to-order
lens with rotation stabilized by proprietary thin zones.
Provide more answers
We've used all
of these lenses in our clinic with mixed success. None of them will provide increased
comfort or improved vision for all specialty contact lens patients. However, they
do offer new options in treatment modalities for these challenging patients. While
GP lenses currently remain the primary modality to treat keratoconus, we have a
host of alternative lenses at our disposal for GP-intolerant patients, as well as
exciting new lenses on the horizon.
available on request.
HOLT IS IN GROUP PRACTICE AT THE MOUNT OGDEN EYE
CENTER AND BOUNTIFUL HILLS EYE CENTER IN UTAH. HE
COMPLETED A RESIDENCY AT THE UNIVERSITY OF UTAH
MORAN EYE CENTER AND VETERANS HOSPITAL.
Optometric Management, Issue: July 2005