An Overview of laser vision correction

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An Overview of laser vision correction

• Michael J. Taravella MD
• Department of Ophthalmology
• University of Colorado
• Medical Director Clear Vision Laser Centers

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Refractive Errors

• Myopia Nearsighted
• HyperopiaFarsighted
• Astigmatism
• DIOPTER
• inverse of focal length
• Example 10 D 1/10 meter focal length

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Simple Myopia

• Inherited trait
• becomes evident at 8-12 years of age
• Eyeglasses may need to be changed frequently
  during adolescence
• Tends to stabilize after 20 years of age
• MYOPIANEARSIGHTED

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Myopia
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Low to Moderate Myopia

• 1-6diopters considered low
• 6-9 moderate
• 10 considered high

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High Myopia

• 10 diopters or more
• Can be associated with pathologic retinal changes
• retinal holes and tears
• retinal detachment
• macular changes
• Vision can be distorted by high power minus
  glasses

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Farsighted

• Hyperopia
• Able to see at distance better than near
• optical system of eye too weak
• Light rays focused behind retina

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Hyperopia
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ASTIGMATISM

• Refractive term describing different powers in
  different meridians of cornea
• Toric surface football, doughnut
• Can be corrected by both incisional and laser
  techniques

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Refractive Surgery

• Incisions made with a diamondknife
• Radial Keratotomy, Astigmatic Keratotomy
• Laser vision correction
• PRK (Photorefractive Keratectomy)
• LASIK
• OTHER
• Intracorneal ring (ICR)
• Intraocular contact lens (ICL)

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How does refractive surgery work?

• All procedures either alter the shape of the
  cornea or enhance the internal lens of the eye
• FOR NEARSIGHTEDNESS
• All CORNEAL procedures result in a decreased
  corneal power (Flatter cornea)

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Definitions RK

• RADIAL KERATOTOMY
• Radial (spoke-like) cuts in cornea which result
  in corneal flattening
• 4,6, or 8 cuts
• 16,32 no longer performed

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How does RK work

• Deep cuts (90 depth) alter normal structural
  forces acting on cornea
• Intraocular pressure deforms cornea
• Central cornea flattens
• peripheral cornea steepens
• RESULT Less myopia

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How RK works
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Factors affecting surgical outcome

• Depth of cut
• No. of incisions
• 1st 4 80
• Age
• Older more effect , Elasticity of cornea?

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Complications of RK

• Under/overcorrections
• Glare, starburst
• Microperforations
• Inablility to wear contact
• Progressive effect (stability)
• some patients 10-40 shift towards being
  farsighted!!
• Enhancement rate 20-30

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Rare complications

• Macroperforations
• Infection
• early, late
• Cataract
• Loss of BCVA
• Irregular astigmatism
• Endopthalmitis
• Endothelial cell loss

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PRK

• Photorefractive keratectomy
• Utilizes high energy photons to ablate and
  reshape corneal surface

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Definitions

• LASER
• Light
• Amplification by
• Stimulated
• Emission of
• Radiation

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EXCIMER

• Excited Dimer
• Rare Gas (Argon) combined with Halide (Flourine)
• Electrical Discharge creates high energy
  state--return to more stable energy level
  associated with the release of a photon
• UV--193nm

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How does PRK work?

• Each laser pulse removes .25 microns
• Allows precise remodeling of corneal surface
  (flattening)
• 1/2 wavelength of light
• Current technoloy wide field ablation
• Beam is shaped by enlarging mechanical diaphragm

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How the laser light is shaped by a diaphragm
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Precision of the excimer laser
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An excimer laser
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Summit U.S. Results_at_ 1 year

• 20/20 --80.5
• 20/25--89.0
• 20/40--98.8
• 51 /- .50D
• 85.3 /- 1.0D
• From FDA study

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Who can have PRK?

• 21 years of age
• Stable refraction
• Approved for -1.5 to -12.0 D correction with less
  than 4.0 D astigmatism
• VISX Laser can now correct up to -15 diopters of
  myopia and about 7 diopters of astigmatism

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Contraindications

• Dry eye
• Blepharitis
• Active inflammation
• Autoimmune disease (Rheumatoid arthritis),
  antimetobolites
• Herpetic eye infections
• Pregnancy
• Previous RK

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Advantages of PRK

• No structural weakening of cornea
• true for LASIK too
• Enhancement rate much lower
• Much less surgeon dependent
• Accuracy for low myopia about same as RK, better
  for higher degress of myopia
• ABOVE -6.00 CONSIDER LASIK

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Complications _at_ 1 year

• Loss BCVA --1.2 lost 2 or more lines
• all were correctable to 20/20
• Glare --2.4
• Halo-- 2.4
• Haze -- 43.9 trace
• None had marked haze
• Decentration -- 1.5or less

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PRK ablation contour
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LASIK

• LASER In-situ keratomilieusis
• Flap and Zap
• Combination of ALK and Excimer Laser
• Refractive laser cut made after corneal flap
• Technique for making corneal flap has been
  constantly improved and modified for over 30 years

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Advantages of LASIK

• Less healing response
• Appears more predictable in higher myopia
• Quick visual recovery
• No sutures required
• less pain than PRK
• easy to enhance (lift flap at 3 months)
• BILATERAL SURGERY

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Disadvantages

• Not FDA approved (investigational)
• Nomograms not worked out entirely
• Newer procedure
• Keratome cut can be too thick or too thin
• Laser related complications same as PRK

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Pre-op screening

• Vision with and without glasses
• Refraction
• Check against old glasses
• Corneal topography
• keratoconus, contact lens warping
• Slit lamp exam, Retinal exam
• cataracts, retinal holes or tears
• pressure check, pachymetry

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Corneal Topography

• Quantitative method of measuring power over
  corneal surface
• Image of reflected rings captured digitally and
  analyzed
• Color map produced which gives a qualitative
  impression of corneal surface
• KERATOCONUS
• Contact lens warpage

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Keratoconus
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Contact Lens Wear

• RGP (hard) lens must be stopped 2 weeks before
  exam and refraction should be checked until
  stable
• Not unusual to see 3 diopter or more change
• Soft contact lens wear should be stopped few days
  before screening

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LASIK Creating a flap
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LASIK Laser under the flap
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LASIK Replacing the Flap
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The Microkeratome
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The microkeratome a close-up view
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PRK versus LASIK

• Low surgical skill
• Slower visual recovery
• Cuts across visual axis
• Haze, scarring
• More pain
• Harder to enhance
• does not weaken cornea

• Moderate skill
• Fast visual recovery
• Cuts across visual axis
• Flap complications
• Less pain
• EASY to enhance
• does not weaken cornea

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Laser vision correcton vs. RK

• PRK and LASIK results are laser dependent
• RK results are surgeon dependent
• Predictability for low myopia about same
• RK weakens cornea
• Altitude affects RK
• Not good for higher degrees of myopia

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So why does it cost so much?

• LASER--500,000
• Maintenance--500,000 over 5 years
• Ar-Fl gas expensive
• UV light hard on Optics
• PILLAR POINT!!! 250 dollars per eye
• Laser and microkeratome technician
• (50,000 dollars for microkeratome)
• 50 dollars per blade

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Long term Side Effects??

• U.S. approval in 1995
• Worldwide, late 1980s
• No laboratory studies to suggest mutagenic or
  teratogenic effects of this wavelength of light

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Special Issues in LASIK

• Not FDA approved
• off label
• Bilateral surgery?
• How high of a refractive error can LASIK correct
• Thickness of cornea, optical problems

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Alternatives to Refractive Surgery

• Contacts
• safe and effective--not without complications
• infection, abrasion, GPC
• GLASSES!!!!