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What is Keratoconus?
Keratoconus is a disorder of the
anterior surface of the eye (the cornea). In simple terms,
the cornea becomes thinner causing it to bulge from its
normal round shape to a cone shape. This bulging interferes
with a person's vision and can severely affect the way they
see the world, making simple tasks like reading, watching TV
or driving very difficult. The distortion caused by
keratoconus has been compared to viewing a street sign
through your car windshield during a driving rainstorm.
The progression of keratoconus is
unpredictable, but generally the condition progresses slowly
and can cease at any stage. While keratoconus interferes
with the clarity of a person's sight it rarely causes
blindness. In its early stages, keratoconus causes slight
blurring and distortion of vision and increased sensitivity
to glare and light. As the disorder progresses, the degree
of vision obtained through glasses becomes less acceptable
and contact lenses often become the best method of
correcting vision problems. |
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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. |