what to use when…

What To Use When…..

Ken Kopp FCLSAParagon Vision Sciences

Paragon CRT CRT Dual Axis

RG-4 (Domestic only)

All are laser marked

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 DataFlat 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

Topography

Apical / Incomplete CRT or RG-4

Limbus-to-limbus -Calculate elevation CRT Dual Axis

Patient Pre-Treatment DataRefractive 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

HVID• 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 mmCRT – 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

Dual Axis CRTSpherical 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

Summary

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

• Spherical CRT trial lens• Proper position• Proper “bull’s eye” pattern• Over-refraction

Summary

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.

Summary

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

YES!!

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

Thank you for your attention Questions??

Send email to; Your authorized CRT laboratory or

consultation@paragonvision.com