2. Customized LASIK & PRK will dominate in next few years
Customized Corneal Ablation
Customized LASIK & PRK will dominate in
next few years
Speedy recovery, good quality of vision
satisfactory outcome
Disadvantage of conventional refractive
surgery in some patients:
* Increase in HOA
* Reduction in visual quality ٤٩

3. Wavefront Customized Visual Correction Ocular wavefront sensing:
Will be increasingly employed
Will become routine in vision
assessment
Wavefront customization is employed to
optimize any refractive surgery
procedure ٥١

4. Wavefront Customized Visual Correction (cont)
Future wavefront customized refractive
procedures
Implantation of optimized IOL’s e.g
Technis aspheric lens
Customized IOL’s preinsersion,
customized phakic IOL’s

6. Types of customization
Two main methods are available in refractive surgery:
Topography guided ablation
Wavefront guided ablation

7. According to recent statistics, approximately 55% of North American refractive surgeons have wavefront analyzers in their practice and routinely perform wavefront-guided ablations.

8. Definition of Wavefront

16. Wavefront-Guided (Customized) Excimer Laser Refractive Surgery
Definition: Wavefront-guided custom ablation is used to correct higher-order aberrations, in addition to spherocylindrical correction.

17. Incidence in General population
10-15% have significant higher-order aberration

19. Hard contact lenses
Corrects higher order aberrations resulting from the cornea.

21. How to measure the higher order optical aberration?
By using a Wavefront analysis system called aberrometry

22. Pupil and Wavefront
Larger diameter leads to a larger Wavefront error

25. Evaluation of vision quality
Compromised more at dim light during night and represented by:
a) Double vision
b) Ghosting
c) Glare
d) Halos
e) Starbursts
d) Reduced contrast sensitivity

26. Quantification of magnitude of the aberration
1)Usually by RMS wavefront error
2)It gives a rough estimate

27. Types of aberrations
Low Order Aberration (LOA) : 1st & 2nd order aberration
High Order Aberration (HOA) : 3rd to 6th or 10th

28. How to evaluate the quantity of optical system
Root Mean Square ( RMS )
The RMS is SD of height (depth) of wavefront relative to the reference at all the point in the wavefront. RMS is very useful measure of optical quality.
Peak-To-Valley (PV)
Distance from the highest to lowest point on the deformed wavefront relative to the reference wavefront.

29. RMS1 is qualitative presentation of 1st order aberration, RMS2 is due to 2nd order and etc.
RMSh represents the total RMS of HOA (including 3rd to 6th OA)
RMSg represents the total RMS of HOA and LOA
Total RMS increases with aging
LASIK increases RMS especially in subjects with larger pupils
RMSh > 0.3 and > 20% of total RMS is clinically significant and indicative for customized ablation

30. Wavefront measuring devices
Hartmann-shack style devices are the most common used

32. Hartmann-shack style
1)A narrow beam of light is projected on to the retina and the light reflected from the fovea passes through the lens and the cornea and exists the eye

33. Customization can be based on corneal topography or wavefront measurements.
Corneal topography guided ablation has been attempted on patients with regular and irregular astigmatism, decentered ablations, and central islands. The irregular astigmatism group is more challenging and may benefit most from corneal topography guided ablation as the systems become more refined.

35. Hartmann-shack aberrometer
A low intensity laser beam is directed to retinal surface
Light rays from this laser spot are reflected back to the front of the eye

37. Laser spot on retinal surface
light rays are reflected back to the front of the eye
Lens arrey
focuses these
light rays
Photodetector (charged coupled device,CCD)
Dots of light

41. Considering refractive lens at corneal surface
Real eye with Aberrations
Considering refractive lens at corneal surface
Excimer etching by customized ablation
Converting wavefront to flat wavefront
Perfect focus on fovea
Ideal eye ١٢

49. Zero order (no order)=axial symmetry, flat
Zernike’s Polynomials
Zero order (no order)=axial symmetry, flat
wavefront
First order = linear aberration, tilting around a
horizontal (x) or vertical axis (y)
Second order = focus shift,
spherical defocus or astigmatism
Third order = corresponding to
coma, triangular astigmatism
Fourth order = spherical
aberration, complex patterns
Fifth-10th order = Irregular aberrations,
important when pupil is wide dilated.
10/14/2007 ٧
XVth Congress of Iranian Society of Ophthalmology
October 2005

60. Wavefront guided customization Goals
Spherocylinder correction
To correct the aberration that are induced by conventional laser vision correction and pre-existing aberration.

61. Requirment for wavefront
Efficient eye tracking
Good registeration system for eye
Small size laser spot
Sufficient corneal bed thickness

62. Challenges to wavefront
Tear film abnormalities
Miotic pupil : If severe may be difficult to measure and provide information beyond the 3mm optical zone and therefore require pharmacological dilation.

64. Optical effects of tear film disruption

65. Wavefront map with cycloplegic or mydriatic
1) Has significant difference in pre-op refractive error compared to subjective refraction

66. (Ablation profile algorithm)
1) After good aberration maps, Ablation profile algorithm is needed 2) Should be designed to make the post-op higher order aberrations as minimal as possible 3) Not only correcting the pre-op higher order aberration but also preventing the induction of new higher order aberrations.

67. Conversion to Ablation Profile:
Ablation profile is fundamentally inverse of wavefront
error map
Goal: Correction of refractive error and higher-order
aberrations
Pupil diameter at least 0.5mm
larger than scotopic
Limbal marking for cyclotorsion
detection
Wavefront measurement + corneal curvature +
biomechanics ablation profile complex ٣٥

69. Emphasis on Registration

70. Registration
Registration refers to the method by which a customized ablation pattern based on preoperative wavefront analysis from the aberrometer is superimposed in the same position on the eye during the laser treatment.

71. LADARWave and LADARVision systems:
Centration is established by the surgeon when the patient fixates on the target light. The instrument captures a video image of the eye, and the surgeon defines the pupillary ring (red) and limbus ring (yellow). These will be used by the LADARVision tracker to follow the eye during application of the customized ablation pattern.

72. Torsional alignment
Torsional alignment refers to the need to compensate for the cyclotorsion of the eye that occurs when the patient lies down.
The eye usually rotates less than 5 degrees, but in some patients, postural cyclotorsion can be as much as 10 to 12 degrees.

73. Misalignment
A small misalignment in in the axis can have significant impact on the results of procedure
A 5-7 degrees of cyclotorsion when changing from sitting position to supine position. 50% of the visual benefit of HOA is lost.

75. Bausch and lomb zyolptix system has
Diagnostic
Treatment components for wavefront customized corneal ablation

76. Diagnostic part of zioptix systems (2172 laser)
In zy wave aberometer and ORBscan both machine are integrated in one workstation. It has Hartmann-shack sensor that measures up to 5th order zernike term. It measures sphere from +6.0 D to -12. D and 0 to 5 D of cylender with pupil diameter from 2.5 to 8.6 mm.

77. Pupil during exam Orbscan must be performed with an undilatd pupil
Wavefront meaurements are taken with a dilated pupil.

79. Types of beam
Has a truncated gaussion 3 beam to achieve the benefits of both beam types. 1 2 3

80. Laser beam sizes in Tech217z
The 2mm beam treat the majority of the refractive errors.
The 1mm beam used for more specific ablation pattern on the transition zone

82. Eye tracker
The system has 120 Hz active eye tracker with a passive automatic shut-off system corrects for intraoperative eye movement in every dimention including cyclotortion and pupil shift

83. FDA investigation for outcomes for wavefront guided lasik in myopia for 3 separate laser platforms
LADAR vision
Technolus 217 z for low to moderate myopia
visx
Conventional
Wave front guided
72% ………….20/20
89% ……..20/20

84. Environmental Conditions
Control of environmental conditions during treatments is important. In previous U.S. FDA Multi-Center Clinical Trials, the room conditions were:
Temperature ranged from 68ºF to 72ºF (20ºC to 22.2ºC)
Relative humidity ranged from 40% to 45%
Treatments performed at >24ºC were associated with less accurate outcomes
Stability of temperature and humidity is important

85. Future of Customized Corneal
Ablation
LASIK vs surface ablation
Each microkeratome induces specific “flap
only” aberration
(flap size, thickness)
Considering “flap aberrations” in total
treatment calculations ٤٢

86. Show promising results with use of
Future of Customized Corneal Ablation …
cont.
Surface Ablations:
Show promising results with use of
immunomodulating agents
Better control of cellular and biochemical
reactions
Introduction of new drugs to better regulate
wound healing and refractive outcome
Gene therapy for better control of post laser
keratocyte activation and wound healing ٤٣

88. Presbyopia: Customized multifocal ablation
Aberrations may be induced when creating
multifocality
Potential loss of contrast sensitivity and quality
of visual function
Future results will be improved:
* Wavefront mapping, sophisticated eye
trackers and corneal registration
* Preoperative simulation of postop condition ٤٤

89. Correction of HOA needs smaller spot delivery
Laser Delivery Refinements
Correction of HOA needs
smaller spot delivery
requires mm spot size
>5th order
Smaller spot size needs faster and better eye
trackers
Smaller ablation depth per pulse provides
ideal correction profile for higher orders ٤٥

90. The Human Hair (125 microns) Etched with an excimer laser
Courtesy of IBM

91. Effects of Laser Ablation
Thermal
Non-thermal
YAG
CO2
Excimer

94. Wavefront measurement devices and consequently wavefront correction
Conclusion
Wavefront measurement devices and
consequently wavefront correction
procedures are still in process of
evolution
Achievement of “supervision”: with
advancement in current procedures
will not be a dream in near future ٥٤

96. Thanks for your attention