Using the 16-lens trial set of CRT Dual Axis
®
lenses,
follow these procedures:
1. Aer evaluating the suggested spherical lens from the Paragon CRT® Initial Lens
Selector (example: 8.60/550/-33), place the dual axis lens having the nearest BCR,
but same RZD, and LZA. e RZD for the deeper meridian will be 50 microns
greater (8.90/550 & 600/-33). A RZD with a 75 micron dierence would be for a
cornea with more corneal astigmatism than normal.
2. Observe the lens on eye for the criteria for an ideal t:
a. A minimum of 4 mm treatment zone that is round in appearance
b. Lens centered within 0.5 mm of pupil center
c. Circumferential bearing under the landing zone (complete/uniform “bulls eye”
pattern)
d. Edge clearance between 0.2 and 0.5 mm
3. If the edge clearance is signicantly dierent 90 degrees apart, consider a dual axis
LZA (33 & 34) dierence where the angle is increased by one degree for every 0.2
mm required decrease in the edge clearance in the respective meridian (8.90/550 &
600/-33 & -34).
4. Over-refract for the appropriate BCR and order the nal Paragon CRT Dual Axis®
lens. It is of critical importance that the desired meridian is identied relative to the
shallow and deep RZD meridians. In some cases you may need to deepen the LZA
in the same meridian that is already made deeper by the RZD increase.
Prescribing Paragon CRT Dual Axis
®
Lenses in the
Absence of Topographic Elevation Map Options
e Dual Axis feature can be successfully used in the absence of elevation data by
careful identication of corneal astigmatism on the AXIAL topography map as well
as careful observation of the uorescein pattern of the initial Paragon CRT® lens
parameter suggested from the at K and spherical refraction. e following
are the indicators for a dual axis design:
• Limbus-to-limbus corneal astigmatism greater than 1.00 D
(pre treatment axial map)
• Oval versus the round treatment zone observation in a best-t Paragon CRT®
spherical diagnostic lens
• Signicant dierence in edge clearance 90 degrees apart with a best-t
spherical Paragon CRT® diagnostic lens
• Flexure as measured by keratometry or topography over a best-t Paragon
CRT® lens
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