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David
Thomas Contact Lenses now offer a solution to fitting
the Irregular
Cornea successfully - the Rose K2 IC lens
With increased practitioner interest and the availability
of modern instrument technology such as corneal topographers,
the irregular cornea is no longer the difficult challenge
it used to be. David Thomas Contact Lenses have now helped
bring
the fitting of irregular cornea with specialist lenses into
the hands of any contact lens practitioner. Through investment
in the latest lathing and oscillating tool technology and
now the introduction of the Rose K2 IC lens design, David |
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Thomas
Contact Lenses can offer the practitioner a solution to
fitting even the most difficult cases with a high degree
of success. |
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| Rose
K2 IC Indications |
The
Rose K2 IC contact lens for irregular corneas is a large
diameter GP lens which opens up an extended range
of applications such as Pellucid marginal Degeneration (PMD),
Keratoglobus, Post Graft, and LASIK Induced
Ecstasia with secondary applications for Nipple and Oval
cones. |
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| Pellucid Marginal Degeneration (PMD) |
PMD
is a bilateral corneal disorder hallmarked by a thinning
of the inferior peripheral cornea
typically
1 to 2mm above the inferior limbus (figure
1). It is usually restricted to the 4-8 o’clock region.
The cornea will exhibit a flat area just
inside this region before steepening rapidly as the cornea
thins and is characterised by large degrees
of central against the rule astigmatism (figure 2). Topography
maps often show a pattern ‘likened
to two birds kissing’.
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Figure
1 -
Pellucid
Marginal Degeneration (Courtesy of Pat Caroline)
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Figure 2 - PMD with high ATR astigmatism (Courtesy of
Pat Caroline) |
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| Keratoglobus |
In instances of globus
cones where a large area of the cornea is affected of which
up to 75% is below the visual
axis, then Munson's sign is usually present. This is where
there is forward displacement of the lower
lid by the cone on downward gaze. |
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| Post Graft |
Where
patients have undergone penetrating keratoplasty or a
corneal graft, then the Rose
K2 IC lens is useful
to aid postoperative recovery and improve vision. In these
cases a large diameter lens is preferable
to bridge the graft and host/donor junction. Expect
to
see significant toricity in most grafts. |
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| LASIK induced ecstasia |
Lasik procedure can occasionally
lead to complications such as Lasik Induced Ecstasia. This
causes an outward
bulging of the cornea resulting in irregular astigmatism
and poor vision and usually happens when the cornea is not
thick enough to leave an adequate stromal
bed following Lasik treatment. |
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Rose
K2 IC Fitting Guidelines |
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| Initial Base Curve Selection |
If the patient is already
wearing RGP lens then select a base curve similar to the
present lens. If the patient is
not wearing an RGP lens then take the K readings and select
a trial lens 0.2mm steeper than the average
of the two K readings. If using topography then start with
a trial lens close to the measurement at
the temporal 4-5mm position. This is only an initial indication
as to what trial lens to first select. |
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| Central Fit |
Allow the lens to settle
for a few minutes and ignore the peripheral fit at this
stage. Evaluate the lens
fit immediately after a blink when the lens
is centred. A light central touch is the goal. A slightly
flatter fit is more desirable then a steeper
fit as the central touch is spread over a larger area and
the cornea does not erode as much in normal
keratoconus. With Lasik cases some central pooling over the
ablation area will be present because of
the significant flattening. Even with reverse geometry lenses
this central pooling often has to be accepted. |
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| Peripheral Fit |
Once a good central fit
has been achieved then assess the peripheral fit. The ideal
fluorescein band width at
the edge of lens will be 0.5mm to 0.7mm. This may not be uniform
around the whole diameter of the lens, but
it should not display excessive lift off or excessive sealing
in any one area. By ordering increased or
decreased edge lift the optimal fluorescein band width can
be achieved. For asymmetric edge lift differences
a toric periphery can be ordered. For significant edge lift
stand off usually inferiorly, an ACT (Asymmetric
Cornea Technology) lens can be ordered. |
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| Diameter |
The standard diameter is 11.4mm.
Selecting the correct diameter will help lens location.
Increasing the overall
diameter will nearly always help improve lens location, however,
ensure that the lens is not too large to
impinge on the upper sclera. |
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| Power Evaluation |
Perform
over refraction in a well illuminated room. Over refract
using ±1.00D
steps initially and then refine with 0.50D and 0.25D steps.
Include evaluation of residual
astigmatism. |
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| Fitting Pearl |
Lens location is the biggest
issue with the irregular cornea. Poor, usually inferior
location can be remedied by
using a combination of diameter and edge lift changes. These
are your greatest tools in solving this
common problem. |
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| Rose
K2 IC Design Information |
The
Rose K2 IC lens design is manufactured with a larger posterior
optical zone than
standard lenses. It has
an aspheric posterior surface incorporating aberration controlled
optics and reverse geometry paracental
fitting curves. The Rose K IC lens has a standard diameter
of 11.4mm
and can be supplied up to 12.0mm diameter. |
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| Rose
K2 IC Availability |
It
is recommended that the Rose K2 IC lens design be fitted
from a diagnostic trial
lens set only. This is supplied
as a twenty lens diagnostic trial set in Boston ES non-uv
material to aid accurate fluorescein assessment.
The diagnostic trial set is supplied in an 11.4mm diameter
and standard edge lift with a base curve
range from 6.0mm to 6.8mm in 0.2mm steps, 6.9mm to 8.0mm
in 0.1mm steps and 8.0mm, 8.4mm and 8.6mm. |
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| Rose
K2 IC Parameter Range |
Base Curve: 6.0mm in 9.0mm in 0.1mm steps
Diameter: 9.4mm to 12.0mm in 0.1mm steps
Power: +30.0D to -30.0D in 0.25 steps |
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| Rose
K2 IC Material |
It
is important that with all large diameter lenses oxygen
permeability is not compromised and the
Rose K2 IC lens is only available in Boston XO material
in either blue, green or violet tints. |
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| Also
Available: |
Rose
K2 IC with warranty (allows up to two exchanges within 90
days from invoice date)
Rose K2 IC Diagnostic Trial Set (20 lenses).
Rose K2 IC trial lens. |
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To
receive a Rose K2 IC Price list and brochure please use
the contact details below. |
David Thomas Contact Lenses Ltd
Gatelodge Close
Round Spinney
Northampton NN3 8RJ
Tel: +44 (0)1604 646216
Fax: +44 (0)1604 790366
Email: enquiries@davidthomas.com
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