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What To Use When…. Ken Kopp FCLSA Paragon Vision Sciences. Paragon CRT CRT Dual Axis. All are laser marked. RG-4. (Domestic only). Paragon CRT. Patented design using Proximity Control Technology Certification necessary/up to -6.00 with up to -1.75 D of astig.

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What To Use When…..

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What To Use When…..

Ken Kopp FCLSA

Paragon Vision Sciences

Paragon CRT CRT Dual Axis

All are laser marked


(Domestic only)

Paragon CRT

  • Patented design using Proximity Control Technology

  • Certification necessary/up to -6.00 with up to -1.75 D of astig.

  • Calculated from flat K and spherical manifest

  • 10.5 mm diameter is most often used/range from 10.0-12.0 mm

  • LZA has no radius of curvature

  • 100 lens DDS or SureFit options (domestic)

Paragon CRT Dual Axis

  • This design mimics the shape of the astigmatic cornea by RZD and/or LZA manipulation without changing the BC (Proximity Control).

  • Based on the average elevation difference between the flat and steep meridian

  • FDA approval indication remains the same as the spherical product. Up to -6.00 D with or without up to -1.75 D of astigmatism

  • No certification necessary

  • Diagnostic sets of 16, 40 or 80 lenses

When Do I Use Which Design?

The CRT DDS should be the “go-to” tool for all reshaping candidates. It will be the design of choice to trial for proper centration, tear patterns, and correct BC selection.

When Do I Use Which Design?

The pre-treatment data is a “clue” as to what option choices you may need.

  • Flat K and spherical manifest

  • Pre-treatment topography

  • Refractive vs. Corneal astigmatism

  • HVID

  • Fissure and/or abnormal pupil size

Patient Pre-treatment Data

Flat K and Spherical Manifest

  • Flatter (<42.00 D) and steeper (>45.00) corneas can be more difficult to achieve proper centration and complete treatment.

    Options – RG-4 or CRT

  • Higher myopes (>5.00 D) most often take longer to achieve stable VA and may need to treat in two steps.

    Options – CRT or CRT Dual Axis depending on elevation differences

Patient Pre-Treatment Data


Limbus-to-limbus -

Calculate elevation

CRT Dual Axis

Apical / Incomplete

CRT or RG-4

Patient Pre-Treatment Data

Refractive vs. Corneal Astigmatism

  • More refractive than corneal = uncorrected astigmatism (ROL)

  • More astigmatic correction than spherical component - not a desirable candidate

  • Corneal astigmatism approaching 2.00D will require a deeper sag (RZD/Mean K) choice initially. CRT DA/CRT/RG-4

Patient Pre-treatment Data


  • Average HVID is 11.8 mm

  • Larger diameters than 10.5 mm may be required to improve centration or aid patient comfort

  • Smaller diameters may be necessary for HVID of <10.8 mm

    CRT – 10.0 to 12.0mm, CRT DA – 10.5 & 11.0 mm, RG-4 = 10.0 to 12.4

Patient Pre-treatment Data

Fissure and Pupil Size

  • Asian fissure size and lid structure can determine diameter choice

  • Larger pupil size (> 6mm ) in normal illumination can result in flare/glare issues

  • Insertion/removal difficulties can determine design choice

    CRT/CRT DA/RG-4 have fixed 6 mm OZ

Design Choices

CRT – Spherical

  • With DDS, trial for all reshaping candidates.

  • Make necessary parameter adjustments for

    proper positioning or edge lift appearance

  • Over-refract to determine the proper BC

  • If the desired position, “bull’s eye” pattern, edge lift and ROL are satisfactory – dispense and follow-up.

Design Choices

If the spherical CRT trial shows an incomplete “bulls eye” pattern or does not center properly…consider CRT Dual Axis

Spherical CRT

CRT Dual Axis

Incomplete/Apical Elevation Difference

Spherical CRT

Dual Axis CRT

CRT Dual Axis

Elevation difference

  • RZD difference depends on the calculated average elevation difference between the flat and steep meridian (pre-treatment)

  • RZD difference can range from 25 to 75 microns

  • LZA can also be altered in either meridian to adjust edge lift

    appearance – 2 degree maximum

  • If elevation data is not available, a default of 50 micron RZD difference with single LZA is chosen.

  • Observe trial lens or order with calculated/default RZD

Design Choices

Without DDS trial option

  • Order CRT with *SureFit or normal warranty depending on pre-treatment criteria

  • If the Flat K is below 42.00 D or above 45.00 D and the spherical manifest is below -5.00 D, consider RG-4 first.

    * SureFit has limited parameter specifications and only available in the US


The decision to choose a specific design is best derived from;

  • Spherical CRT trial lens

    • Proper position

    • Proper “bull’s eye” pattern

    • Over-refraction


If the CRT Trial lens does not display proper centration or incomplete “bull’s eye” pattern;

  • Consider Dual Axis design based on elevation differences of the flat vs. steep meridian (from elevation/height map)

  • Consider RG-4 for flatter corneas (<42.00 D) or steeper corneas (>45.00 D) or when the CRT design is no longer manageable.


Can either the CRT, Dual Axis , or the RG-4 lens be the initial lens choice and ordered empirically?


If you are not sure…contact your authorized Paragon CRT laboratory

Thank you for your attention


Send email to;

Your authorized CRT laboratory or consultation@paragonvision.com

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