Transcript Corneal Wave Front

Corneal Wave Front-
DOES IT REALLY EXIST ?
Dr Kumar Doctor
Mumbai India
NO FINANCIAL INTEREST
CORNEAL ABBEROMETRY
Purpose
• To Evaluate Corneal Wave Front
treatment
• KERATRON SCOUT
•
•
TOPOGRAPHER
USES A SMALL CONE
AND 28 RINGS ,PLACIDO
DISC PRINCIPLE
CONCEPT OF ARC STEP
RECONSTRUCTION OF
THE CORNEAL SURFACE
PROFILE,VERY
ACCURATE TO A MICRON
CORNEAL ABBEROMETRY
OPTICAL PATH DIFFERENCE(OPD)
• LIGHT RAYS THAT EXIT FROM THE CORNEA TRAVEL FASTER
IN AIR THAN THOSE STILL IN THE CORNEAL SUBSTANCE
DUE TO THE DIFFERENCE IN RI OF AIR AND CORNEA
• EMERGING RAYS FORM A WAVEFRONT WHICH HAS A SHAPE
EQUAL AND OPPOSITE TO THE CORNEAL SURFACE BUT
ABOUT 1/3RD MAGNITUDE
• OPTICAL PATH DIFERANCE IS THE DIFERANCE BETWEEN
THIS NEW WAVEFRONT AND THE IDEAL
OPTICAL PATH DIFFERENCE(OPD)
“Rule of 3”:
Every 3 micron distortion on the Cornea creates
1 micron of Wavefront Error “Corneal Wavefront” is
the component of eye refraction owed to the cornea
(or OPTICAL PATH DIFFERENCE OPD)
Aberrations:
“Ocular” = “Corneal” + “Internal”
(or “Total”)
From WA
From TC
(100%)
(80%)
ADVANTAGES OF USING A CORNEAL
DERIVED WAVEFRONT-WHY NOT JUST USE
A WAVEFRONT ABBEROMETER?
• OPTICAL ZONE IS NOT RESTRICTED BY PUPIL
SIZE.WE CAN DO A 8.5 MM ABLATION
• ABBERATIONS ARE EXCLUSIVELY CORNEAL
AND DO NOT DEPEND ON
ACCOMODATION,LENS, OR PUPIL SIZE
• CORNEA IS RESPONSIBLE FOR OVER 80% OF
THE TOTAL ABBERATIONS OF THE EYE
METHOD - CORNEAL WAVEFRONT
LASIK FOR A DECENTERED CORNEAL
GRAFT
Preop corneal
• PATIENT OPERATED
•
•
FOR PENETRATING
KERATOPLASTY 5
YEARS AGO
BCVA WITH -4 SPH 5CYL,6/12
POST LASIK RESULT
0.5 CYL,6/6
Preop bcva 6/12
Ablation
shotfile
wavefront
RESULT
This is only possible with
corneal wavefront which
breaks down any surface
distortion into a
combination of zernicke
polynomials which can
then be treated with the
software on the schwind
ESIRIS laser
POSTOP TOPOGRAPHY 6/6 UCVA!!
Conclusion
Patient Treated By MEL 70
in 1999
Post op Refraction before Retreatment
OD -0.75 D Sph. 6/6
Patient treated in November 2006
Post Op Corneal WF image
Post op image on 28/10/06
Post op Corneal WF image
Conclusion – CORNEAL WF
WORKS VERY WELL WITH
SCHWIND ESIRIS LASER
• Add –on aspheric Rx to improve night
Quality vision in previously treated eyes
• Works very well in High corneal
Astigmatism