Getting the Markings Right
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Transcript of Getting the Markings Right
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Why is Marking Important?
For every degree of rotation 3.3% of the effect is lost
With 30 degree rotation all effect of the Toric lens is lost
Beyond that you start adding to the astigmatism
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Why is Marking Important?
Higher the Toric correction greater the chances of errors
e.g. For a 5 degree misalignmentIn a 6 D Toric – error is 1 DIn a 1.5 D Toric – error is 0.25 D
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So let’s get the marking spot on ! Two issues in marking
Making sure our 0 – 180 meridian is ‘true’ horizontal
Making sure that the marks bisect the cornea through the optical centre
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Current Markers
Hand held markersWith spirit level to ensure horizontality
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Current Markers
Do not ensure that the marks pass through the centre of the cornea
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Are you bisecting the cornea?
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Current Markers
You also need a second intra-op mark if the placement axis is not 0 – 180
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Current Markers
Come in only one size But the corneas are not of the
same size or shape!
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Issues
Still does not solve the problem of bisecting the cornea through the optical centre
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A New Approach
A slit lamp based system Uses gravity to define horizontal Uses Purkinje images to ensure
centring on the cornea
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3 Simple Steps
1. Set the slit lamp beam to the desired placement axis
2. Align the beam to pass through the corneal centre (described later)
3. Mark the cornea
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Step 1 – Setting the Angle The slit beam can be set to the axis
of placement No need for reference marking
Clamp device to chin rest of slit lamp
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Setting the Angle
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Step 2
Unclamp the calibrator device Place the patient’s head normally
on the slit lamp
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Centring on the Cornea
Patient looks at the light with the other eye closed
Move the slit beam across the cornea until you get a bright Purkinje image
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Centring on the Cornea
Images bordered in red show the correct positioning of the slit beam
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How do we know it is accurate?
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Planiware 2.0
This is a IOL planimetry software designed for measuringCentration of IOL, rhexis, pupilMeasurement of rhexis / pupil areas
and diametersAngular measurements of Toric IOLs
Planiware can be downloaded from www.suryodaya.in/planiware
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Verifying your markings
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