The Science of Vision Correction

Dean Dornic, MD

(Mr. Science)

Laser Eye Center of Carolina

A 60 Year History of LASIK

1949 Columbian Ophthalmologist Barraquer describes a lamellar corneal procedure to correct refractive error

ALK the Predecessor to LASIK

A microkeratome is used to create a flap and to remove a disc of corneal tissue

Birth of LASIK: Introduction of Excimer Laser Results in Name

Change

1983: First journal article describing the use of the Excimer laser to treat refractive error

1989: First patent for the LASIK procedure

Improvements in Technology Have Resulted in Improvements

in Outcomes

Lower risk of complications (decentered ablations, asymmetric ablations, quality of vision issues)

Higher likelihood of spectacle independence

Higher Order Aberrations

Introduction of aberrations reduce visual quality and decrease patient satisfaction

Spherical aberration a result of oblate cornea

Significant Refinements: Ablation

Wider treatment zones

Flying spot

Pupil tracker

Wavefront-guided and optimized treatments

Iris registration

Wavefront Technology

Wavefront-guided procedures utilize a wavefront analyzer to correct higher order aberrations

No analyzer necessary for wavefront-optimized procedures

Wavefront Technology Benefits are More than Just Theoretical

Wavefront-guided procedures have greatest rates of 20/20 or better

WFG procedures have lowest enhancement and night-vision problems

Night Vision Satisfaction after CustomVue

Patient satisfaction with night vision increases after WFG procedures

Ratio of improved vs worsened night vision is 4:1

Important Points for Patients

Wavefront Guided is not equivalent to Wavefront OptimizedWFG Procedures can correct HOAs

WFO Procedures strive to limit new HOAsYou can achieve good results with conventional LASIKWFG need not be reserved for patients with high HOAs

WFG Procedures give the Opportunity for Improved BVAWFG Procedures Give the Best Night VisionWhy would you not want a WFG procedure?

The LASIK Flap

Serves to speed recovery

Lessens likelihood of haze, regression and infection

Most common source of complication

Significant Refinements in Flap Creation/ Improved Safety

Elimination of perforation riskElimination of exposed gears

Elimination of on-eye assemblyVacuum meters/ audible tones

Increased customizationFemtosecond laser flap creation

Sidecuts

Cornea Flap Creation with Microkeratome

Suction ring exposes cornea.

Oscillating blade a set distance below metal plate creates flap

Variability in amount of exposed cornea results in variability of flap parameters

Flap Creation with IntraLase Femtosecond Laser

Cleavage plane created by photodisruption and resultant gas bubbles released a set distance below cornea surface applanated by glass plate

Downside of IntraLase (FS30)

Increased ExpenseIncreased Time

Flaps More Difficult to LiftRisk of Flap Tears

Transient Light Sensitivity Syndrome

Ziemer LDV

PortableFamiliar Technique

FastAble to Create Thin Flaps

Ziemer Complications

Free FlapsSmall Irregular Flaps

Result of Ziemer Complications

Small Irregular Flaps Managed with Immediate PRK

Both Cases Required Enhancements For Quality of Vision Issues

IntraLase FS60

Less OBL DelayFaster Procedure Time

No Free FlapsNo Small Irregular Flaps

Head to Head Comparison of Complications: First 150 Cases

Most Previous Papers Attempt to Compare Complication Rates Utilized Different Surgeons

Same Surgeon

98 cases IntraLase FS30

150 cases Ziemer LDV

52 Cases IntraLase FS60 added to IntraLase Group for Equal Sample Size

Comparison of ComplicationsFirst 150 Cases

IntraLase

1 incomplete flap

1 slipped flap

Ziemer

2 free flaps

2 small irregular flaps

1 slipped flap

My Ziemer Complication Rate vs Pietela et al J Ref Surg

My Results (150 cases)

2 Free Flaps 1.3%

2 Irregular Flaps 1.3%

1 Flap Displacement 0.7%

Pietela (787 cases)

21 Free Flaps 2.7%

16 Decentered 2.0%

10 Pseudobuttonholes 1.3%

2 Split Flaps 0.3%

3 Flap Displacements 0.4%

IntraLase Flap Creation

3-Dimensional flap

2-steps with side cut added last

Flap creation visible throughout

IntraLase Flap Creation

Diameter and location of flap can be altered before proceeding

Side cut is created last as a seperate stage

IntraLase Control Panel

Allows for perfectly centered flap

True customization

Unlimited flap diameters and flap thicknesses

Last minute adjustments

IntraLase Flap

Flap creation visible throughout procedure

Because surface not affected, flap can still be salvaged if there is interruption

Ziemer Flap Creation

Single Plane “Cut” Similar to Microkeratome

Initial Applanation and Alignment Visible

Creation of Flap Not Visible to Surgeon

Ziemer Flap Creation

Diameter of Ziemer flap dependent on area applanated

Diameter affected by corneal curvature

Sidecut performed simultaneously with the rest of the flap

Loss of Suction with IntraLase

Loss of suction visible. Procedure can be halted and resumed.

Loss of Suction with Ziemer

Loss of full applanation before flap creation is initiated results in a free flap

Loss of full applanation after flap initiation results in smaller, irregular flap

Suction Loss is Not Rare

The Consequences of Suction Loss is Different for 2 Reasons:

1. Surgeon is “Blind” to Flap Creation When the Ziemer Laser is Used: Loss of Full Applanation May not Be Apparent

2. The Side Cut is a Second Seperate Stage When the IntraLase Laser is Used: This Allows for Recovery/Salvage of the Case When Suction is Lost

Prevention of Complications

Proper and Adequate Suction/Applanation

Separate Side-Cut With “Manhole” Configuration Should Reduce Slipped Flaps

Separate Side Cut Allows for Salvage/Resumation When Suction Lost

Full Visualization/Proper Intervention Should Limit Incomplete or Free Flaps

Ziemer Pros and Cons

Pros

Portable

No OBL

Technique Familiar

Fast

Flaps Easy to Lift

Cons

Limited Customization

Diameter Influenced by Corneal Shape

Single Plane Flaps

Unable to Visualize

Interuption of Case Usually Results in Cancellation

Higher Complication Rate

IntraLase Pros and Cons

Pros

Customization

Better “Fine Tuning”

Manhole Configuration

Full Visualization

Free and Irregular Flaps are Rare

Interruption Rarely Results in Cancellation

Cons

More Cumbersome

OBL Can Slow Down Case

Not as Portable

More Uncomfortable For Patient

Higher Rate of Subconjunctival Hemorrhage

Summary

Femtosecond Laser Technology Can Produce Thinner, More Consistent Flaps

The IntraLase Laser Allows for Better Surgeon Control and Is Much Less Likely to Result in Complications, Postponement or Conversion to PRK than the Ziemer LDV Laser

Z-LASIK Flap Architecture

Single plane, exactly as that created by a microkeratome

All complications seen with microkeratome can be seen with Z-LASIK

IntraLase Flap Architecure

Manhole configuration

No free flaps

No Small/ irregular flaps

Second chance possible

More secure

Electron Micrograph Comparison

IntraLase Flap

Z-LASIK Flap

Bonus Advantage

Stromal bed smoother with IntraLase

IntraLase Flap Creation

Monitor View

Conclusion

Safest way to make a flap is IntraLase

Best vision achievable is with CustomVue

Chief advantage of Z-LASIK is cost

Military does not perform Z-LASIK. Statements such as “technology approved by the military” are, at the very least, misleading

All “custom procedures” are not equivalent

All “all-laser” procedures are not equivalent

Need for New Terminology

The precedence for a change in terminology is evidenced by change from ALK to LASIK

There is a need to differentiate iLASIK and similar technologies from LASIK and Z-LASIK

Side effect / complication statistics from earlier technologies are not applicable to iLASIK

Consumers need to be able to compare “apples to apples”