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Heralded as "a quantum leap forward in
the evolution of lens design for the condition" of keratoconus, the Rose
K lens has become the world's most frequently prescribed gas permeable
contact lens for keratoconus.
Unlike traditional contact lenses,
the complex geometry built into every Rose K contact lens closely mimics
the cone-like shape of the cornea for every stage of the condition.
The result is a more comfortable fitting lens for patients and
better sight (visual acuity).
The Rose K lenses' complex geometry
has only become possible since computer-controlled contact lens lathes
were developed to cut sophisticated oxygen permeable polymers to the
right shape.
The Rose K lens has a number of features that make
it ideal for keratoconus:
• Its complex geometry can be
customized to suit each eye and can correct all of the myopia and
astigmatism associated with keratoconus.
• They are easy to
insert, remove and clean.
• They provide excellent health to the
eye, because they allow the cornea to "breathe" oxygen directly through
the lens.
• Practitioners have the Rose K trial set fitting
system which achieves a first fit success in over 80% of patients
internationally.
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Standard lens designs
with fixed optical zones (OZ) do not ideally fit the cone shape
of keratoconus patients. Figure 1 shows a standard lens that
will yield unwanted pooling at the base of the cone and
peripheral bearing that can seal off and cause corneal problems. |
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This illustration
demonstrates the benefits of a smaller optical zone to fit the
cone contour. The design results in little tear pooling at the
base of the cone and shows an even distribution of tears under
the lens.
The Rose K system has set optical zones to
maximize vision while maintaining good corneal health. |
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Rose K2 Lens
The
Rose K lens was further refined to take into account the unusual corneal
shapes of keratoconus patients, which require abnormal curves on the
back of the lens to fit the cornea optimally. This new lens is known as
the Rose K2 lens.
With normal corneas the shape does not change
dramatically from the center out, but tends to change evenly in
predictable amounts, and therefore with normal corneas the back surface
of the lens can be designed with small incremental changes (e.g.
eccentricity) over most of the lens with a peripheral curve at the edge.
Usually, this will achieve reasonable alignment with the cornea and a
good fit.
However, to achieve optimum alignment with the cornea
in keratoconus patients, many curves are required on the back surface of
the lens, and adjacent curves are often very different. Particularly in
steeper cones, several curves are often required within the patient's
pupil zone to achieve a good fit over the central area of the lens.
Unfortunately, each one of these curves gives rise to a slightly
different focal point at the back of the eye. This causes the patient to
experience ghosting around the object that they are viewing (like a TV
with poor reception) and this is worse the bigger the pupil is because
more curves on the back surface of the lens come within the patient's
pupil zone. Therefore night driving where the pupil is larger is very
difficult for keratoconus patients. These multiple focuses are called
aberrations.
The Rose K2 lens minimizes these aberrations by
applying very small changes to the curves on both the front and back of
the lens in an attempt to bring the light passing through the lens
within the pupil zone to a single point.
Following extensive
trials, the best combination of aberration control curves have been
developed for computerized digital lathes to cut these very complex
curves for the Rose K2 lens to give the best focus.
Rose
K Post Graft Lens
The Rose K Post Graft Lens is for
patients who have undergone penetrating keratoplasty. This lens is
designed for postoperative recovery and improvement in vision.
ACT (Asymmetric Corneal Technology)
ACT is
quadrant specific and allows the steepening of the inferior quadrant
onlyBy nature, the keratoconic cornea is asymmetric, where the inferior
quandrant is frequently significantly steeper than the superior portion,
causing the GP lens to lift off at 6 o'clock (see illustration E).
Rose K lenses incorporating ACT are designed to accommodate this
asymmetry. The inferior quandrant of the lens is steeper than the
superior quadrants, providing a more accurate fit at 6 o'clock, which
makes the lens more comfortable and stable and often provides superior
vision. |
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