utilizing topolyzer vario & oculyzer ii for accurate refractive

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Utilizing TopolyzerVario & Oculyzer II for accurate refractive outcomes

Michael Mrochen, PhD

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Content

• What essential data are required by your ex500?• What is different between WFO and T-CAT?• A limiting factor: the subjective refraction• Accuracy of the TopolyzerVario• Accuracy of the Oculyzer II• A small pocket guide on: What to use when?

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What essential data are required by your ex500?

• Ablation profile– A map of required tissue removal at each point of the

cornea – It’s based on difference between the pre- and to post-

operative cornea anterior surface– Derived from either modelled or measured anterior

cornea data

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What essential data are required by your ex500?

• How to calculate an ablation profile?– Assume a preoperative cornea shape (R,Q, Cyl,…)– Calculate the postoperative corneal shape based on the

attempted refractive power change– Define to optical zone– Calculate the change in corneal height maps within the

optical zone– Define a transition zone

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Preoperative

Postoperative

Optical zone

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What is different between WFO and T-CAT?

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Ex500Algorithm

WFO Wavefront Optimized for sphere and cylinder

Manifest Refraction

Optical zone

WFOAblation profile

- Refractive predictability- Maintain visual performance

Ex500Algorithm

T-CAT Topography guided for sphere, cylinder and corneal irregularities

Manifest Refraction

Optical zoneT-CAT

Ablation profile

- Refractive predictability- Improve visual performanceHeight maps from

Topolyzer / Oculyzer

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A limiting factor: the subjective refraction

Thomas W. Raasch1, Kenneth B. Schechtman2, Larry J. Davis3, Karla Zadnik1 Repeatability of subjective refraction in myopic and keratoconic subjects: results ofvector analysis. Ophthal. Physiol. Opt. Vol. 21, No. 5, pp. 376±383, 2001

Error of refraction (normal eyes)

60% [43% to 75%] ±0.2592% [80% to 98%] ±0.5100% [91% to 100%] ±1.0

Error of refraction (irregular cornea)

25% [18% to 33%] ±0.2550% [41% to 58%] ±0.580% [72% to 86%] ±1.0

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Accuracy of the TopolyzerVario

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44Edges

Edge Detection

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Accuracy of the TopolyzerVario

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Eye lashes, lid & nose Corneal irregularities

Pupil detection Corneal surface / tear film

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Degree of light scattering is of clinical relevance

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Accuracy of the Oculyzer II

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Accuracy of the Oculyzer II

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Segmented measurement Motion compensation

Light scattering

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Consequences of accuracy

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Uncertainty of topography ~ 2 - 5 microns @ 8 mm

2 micrometer will result in an uncertainty of approximately 0.14 D for an optical zone of 6.5 mm

2 micrometer will result in an uncertainty of approximately 0.98 D for an optical zone of 2.5 mm

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A small pocket guide on: What to use when?

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Manifest Refraction

How much can I trust the Rx?

TopolyzerVarioMeasurement

Oculyzer IIMeasurement

Mires of rings well detected?

Scheimpflug images well detected?

Yes

Successful Topolyzer or

Oculyzer measurement?

Noex500

Yes

NoOther treatment

options

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Summary

• TopolyzerVario and Oculyzer II are accurate measurement devices as demonstrated by experimental measurements and clinical studies.

• Measurements of each device can be affected differently by the condition of the patient’s eye.

• Raw data checks are required to assure accurate measurements.

• Consequences can be irregular ablations or poor refractive predictability

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