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110 Cards in this Set
- Front
- Back
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What is the MOA of YAG laser?
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Photodisruption
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What is the MOA of Argon laser?
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Photocoagulation
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What is the MOA of Excimer laser?
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Photoablation
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What is the MOA of Krypton laser?
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A krypton laser is an ion laser. It is a type of gas laser using krypton ions as a gain medium, pumped by electric discharge.
Krypton lasers are also used in scientific research, for manufacture of security holograms, and numerous other purposes. |
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Krypton lasers emit at several wavelengths through what spectrum?
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visible: 406-676 nm.
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What gas does the ARGON laser use as the active medium?
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noble gas
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What wavelegnths/spectrum does the ARGON laser emit at?
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the visible and ultraviolet spectrum: 351-528.7nm.
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What are the two types of YAG lasers?
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Nd:YAG Lasers
Neodymium-doped yttrium aluminum garnet Neodymium crystal is used as a lasing medium for SOLID STATE lasers Er:YAG Lasers Erbium-doped yttrium aluminum garnet. Unlike Nd:YAG lasers, the frequency of Er:YAG lasers is strongly absorbed by water. This limits its use in surgery and many other laser applications where water is present. |
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What is the MOA of Nd YAG lasers?
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Neodymium crystal is used as a lasing medium for SOLID STATE lasers
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What is the MOA of Er YAG lasers?
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Er:YAG Lasers
Erbium-doped yttrium aluminum garnet. Unlike Nd:YAG lasers, the frequency of Er:YAG lasers is strongly absorbed by WATER. This limits its use in surgery and many other laser applications where water is present. |
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What does LASER stand for?
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Light
Amplification by the Stimulated Emission Radiation |
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When was the first ophthalmic laser built?
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1986
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When was the first PRK done?
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1987 – First PRK done on a sighted eye by Marguerite McDonald – that patient is still reported to have 20/20 UCVA
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What year was the excimer laser invented?
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1976
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Who published no collateral tissue damage in 1983?
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1983 - Published no collateral tissue damage – Trokel and Scrinivasan
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Wen was the first trial/effect on corneal tissue?
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1981- Taboada, et. Al
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What is the excimer laser derived from?
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The Excimer is a gas laser
GAS and VOLTS of electricity Derived from Excited Dimer Gas elements are excited by thousands of volts of electricity within the laser cavity The motors, mirrors and optics of the laser produce a precise final beam |
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How many microns of tissue per pulse do excimer lasers remove?
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Excimers remove 0.25 microns of tissue per pulse
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What is the collateral damage of an excimer laser?
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less than one micron
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How does excimer laser compare to other lasers?
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50-1000 x more precise than other ophthalmic lasers
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What is the plume cloud?
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Photoablatio causes a plume of dust these particles eject from the surface of the cornea at 1000-2000 m/sec forming the “plume” cloud
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What is the relationship of depth of ablation to optical zone?
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Depth of Ablation increases exponentially with increases in optical zone
Small increases in OZ result in big increases in ablation depth Ablation depth can be calculated using the Munnerlyn Formula |
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The Munnerlyn Formula:
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Ablation Depth=
( Refractive error x (OZ²) ) / 3 OZ: Optical Zone: Ablation Diameter Several uses, including patient selection and calculating PTK ablations. Refractive error- Use spherical equivalent |
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What is the size of the most commonly used ablation zone?
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6.5 mm zone is most commonly used
Ablation is blended out to 8 mm |
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What is the typical lasik flap diameter?
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LASIK flap diameter is typically 8.5-9.5mm
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How does a larger OZ effect the result?
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Reduces glare
Reduces risk of regression Increases ablation depth |
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Define Homogenous Ablation:
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Homogeneity. How even the beam is within each pulse will determine if the ablation is smooth, or if it has bumps (cold spots) and pits (hot spots) remaining in the cornea when the ablation is done.
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A FLAT beam =
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A FLAT beam = Homogenous (even)
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A BELL shaped beam =
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A BELL shaped beam = Gaussian
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What does lasik stand for?
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Laser In Situ Keratomileusis
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The flap in lasik is created by using one of two lasers:
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microkeratome or femtosecond laser
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What is the thickness of the flap?
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Flap thickness is 100 microns
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What is the upper limit of lasik for myopia?
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-10.00 D
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What is the upper limit of lasik for hyperopia?
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+3.00 D
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What is the upper limit for astigmatism?
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-5.00 D
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What are the disadvantages of lasik?
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No guarantees of 20/20 vision
Presbyopia Risk of flap complications Dryness Glare and halo’s Corneal thinning procedure Keratectasia |
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What are the advantages of lasik?
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Bilateral procedure
Minimal discomfort Low risk of complications Exact results Quick healing |
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What are the signs/symptoms of Keratectasia?
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Corneal Thinning
Loss of BCVA Ghost Imaging Decreased night vision |
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What is the simple rule for corneal thickness required for lasik?
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Simple rule:
Need a pre-operative corneal thickness of 500 microns to do LASIK for -5.00 and lower |
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What are the methods used to remove the flap in PRK surgery?
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Methods to remove the epithelium include:
Brush Laser Scrape Alcohol We prefer alcohol (20%) for 30 seconds |
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PRK is recommend for patients with what anatomical conditions?
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PRK is recommended for patients with:
Thin corneas Patients at risk for keratectasia EBMD Enhancements |
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What is recovery like for PRK?
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Contact lens is applied
Epithelium grows back in 4-5 days Slow visual recovery 2-4 weeks Limits of refractive surgery is same as LASIK |
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What are the advantages of PRK?
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Preserves corneal thickness
Less risk of keratectasia Less dryness to the eye No flaps Vision just as good as LASIK 6 months out |
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What are the disadvantages of PRK?
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Slow visual recovery
Unilateral surgery Higher rate of infection than PRK More discomfort then LASIK Corneal Haze (scarring) Greater risk for high myopia patients >-6.00 High risk for myopia patients >-10.00 |
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What refractive condition does corneal intacts correct for?
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myopia only
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What is the range of myopia that corneal intacts convers?
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Range is -1.00 to -3.50 D
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Intrastromal Corneal Ring Segments are composed of what?
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2 PMMA segments of 150 degree arc length
Inner diameter 6.8mm Outer diameter 8.1mm |
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What choices does the -13.00 diopter myope have?
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Risk with LASIK
Decreased Best Corrected Vision Glare and Halo Keratectasia Risk with PRK Decreased Best Corrected Vision, Night VA Problems What is the risk for PRK and high myopia? Partial Correction? Clear lens exchange Corneal haze patient not happy Phakic Intraocular Lens Patient can't see up close. |
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How does a Phakic Intraocular lenses correct refractive error? What are its uses? What are the two approved FDA lenses?
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IOL implant in anterior chamber
In front of or behind iris Able to correct high degrees of myopia 3 to 20 diopters of myopia No astigmatism correction in US Two lenses FDA approved in USA Visian ICL (Staar Surgical) Verisyse (AMO) |
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What is the Crystallens used for?
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The crystallens is a phakic intraocular lens used to treat high myopia (no astigmatism)
Not FDA approved for hyperopes due to their small anterior chambers. |
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Who is a candidate for phakic intraocular lens implants?
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Between the age of 21-45
Why not older patients? risk of cataracts Myopic patients with low to moderate astigmatism Good Ocular Health Normal Endothelial Cell Count Good Medical Health No History of Past Eye Surgeries |
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What are the two parts of the IOL surgery process?
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Part I - iridotomy
Part II - Lens insertion |
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Versyse Phakic IOL
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FDA approval in September 2004
180,000 procedures performed Range -3.00 to -20.00 >21 years old Iris fixation model Model allows for easy centration 92% 20/40 or better requires a larger incision than other IOLs |
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What is iris enclavation?
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Fixation arms (haptics) of the lens attach to the stroma of the iris
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Staar ICL
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Implantable ICL
Placed behind the iris Treats -3.00 to -15.00 Myopia Lens is vaulted to keep it from rubbing against crystalline lens Inserted through a incision in the cornea: 3mm 55,000 Visian ICLs implanted worldwide. ICL is inserted in a folded state Unfolds inside eye |
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Phakic IOL Advantages?
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Involves inserting a new lens between your real lens and your cornea
Maintains accommodation Treats high amounts of myopia Does not thin or flatten the cornea Reversible Crisp vision Good Contrast Sensitivity Improved BCVA |
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Phakic IOL Disadvantages?
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Complications similar to cataract
surgery Endothelial breakdown Endo cell count before surgery Risk of Retinal Detachment Iritis IOP Spike Risk of cataract formation Glare and halo 6mm zone up to -15.00 with Verisyse 5mm zone >-15.00 Price $4,000-$5,000 an eye |
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Clear Refractive Lens Exchange (CLEX)
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Remove clear crystalline lens and replace with intraocular lens (IOL)
Physicians perform CLEX surgery on patients who have High Myopia (above -11.00) High Hyperopia (above +6.00) Presbyopes seeking presbyopic IOL’s Presbyopes with mild cataracts |
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What are the advantages of CLEX?
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Advantages
Can correct high prescriptions Able to correct astigmatism: Toric IOL Restores near vision in older presbyopic patients Rezoom, Restor, Tecnis, Crystalens |
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What are the disadvantages of CLEX?
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Disadvantages
Same risk as cataract surgery Retinal detachments, CME, IOP spikes, endopthalmitis Loss of accommodation with monofocal and toric IOL’s |
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Ways to correct astigmatism:
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Toric IOL
Surgical incisions induce astigmatism Limbal Relaxing Incisions Astigmatism correction is more variable LASIK or PRK to correct astigmatism |
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How does the Crystalens move in the eye?
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Lens moves forwards and backwards
Once in the capsular bag the haptics push the lens optic back against the posterior capsule |
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What is the MOA of the Crystalens in the eye?
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With accommodation, the ciliary muscle enlarges within the vitreous cavity.
The pressure in the vitreous rises relative to the pressure in the anterior chamber, pushing the vitreous forward and forcing the lens to move forward as well Lens moves and it also arches forward |
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What are the benefits and drawbacks of the Crystalens?
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Benefits of Crystalens:
Contrast sensitivity is better then multifocal IOL’s Maintain depth perception Good distance acuity Better night VA then multifocal IOL’s Drawbacks Near is not great Risks of Surgery Cost |
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Patient Selection for the Crystalens?
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Bilateral surgery does better then monocular
Hyperopes tend to be more pleased then myopes CrystaLens provides 1-2 Diopters of Accommodation Not good for small details Most patients still need glasses for small print CrystaLens is labeled for cataract patients only Clear lens exchange is off label |
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What is the cost of CLEX vs. cataract surgery?
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$4000 - $5000 an eye for a clear lens exchange
$2300 - $2700 an eye for premium lens upgrade with cataract When insurance pays part |
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What are the three multifocal IOL lenses?
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Multifocal IOL Lenses
AMO ReZoom Alcon AcrySof ReSTOR Tecnis: AMO |
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ReSTOR
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Multifocal lens
Diffractive lens Two types of lens 4.0~ 3.2 diopter add 3.0~ 2.5 diopter add Requires Neuroadaptation Halos at night |
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Tecnis Multifocal
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Aspheric design to lessen spherical aberration
Posterior surface of diffractive rings to provide near and distance vision Similar to Restor lens |
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What is Conductive Keratoplasty used for?
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FDA Hyperopia approval April 2002:
For the temporary reduction of: +0.75 D TO +3.00 D Less than or equal to 0.75 D of astigmatism. FDA Presbyopia approval March 2004: Regulatory approval for the temporary improvement of near vision in emmetropic presbyopes and hyperopic presbyopes. Performed on one eye to provide monovision or “blended vision” |
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How does conductive keratoplasty work?
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Heat is distributed in an even pattern throughout the cornea (8,16, 24 or 32 spots)
The radio frequency energy is placed in multiple spots outside the visual axis |
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Radial Keratotomy
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Some patients did receive good results
However, some patients ended up hyperopic with astigmatism Difficult to correct with enhancement surgery |
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Radial Keratotomy / Astigmatic Keratotomy –
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Oldest of elective refractive procedures
Popular during 1980’s, with some resurgence just before Excimer Lasers were approved Problems: Weakens Globe Many side effects – long term fluctuation of vision, halo’s, glare, Limited Application – low to moderate myopia and astigmatism Not very precise |
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Standard Laser Ablation
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Patients Rx is programmed into the laser
Each patient receives the same laser ablation Diameter of laser ablation can be adjusted to fit the patients need For myopia 6.0 mm optical zone 6.5 mm optical zone 8.0 mm blend Hyperopic laser ablations have a 9.0mm diameter No iris registration |
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Problems with standard laser ablation.
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Treatment was not customized to visual system
High order aberrations are not corrected Treatment zone was smaller Night Vision Problems Glare and Halo Irregular ablations (dishomogenous ablations) What would an irregular ablation do to the vision? |
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Advantages of Custum Wavefront Ablations:
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Custom Wavefront ablations were introduced in 2004
Wavefront ablations customized to patients RX Increases the chance of 20/20 vision Better contrast sensitivity Better chance of improving BCVA Lessens the chance of visual side effects Glare Halo Diplopia Ghost Images |
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Why is Custom Wavefront Better?
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Custom Wavefront ablations
Treatment is customized to each patient with wavefront mapping Larger ablation zones Iris registration Pupil tracking Flying spot lasers Leaves cornea more prolate |
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Wavefront Analyzer
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Captures an image of the visual system
Uses this information to determine a programmable ablation pattern |
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Hartmann Shack Wavefront Data
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Cornea must be healthy before image is taken
Poor Tear Film distorts the image Each dot represents a lenslet that measures the visual system Cataracts, PVD, Corneal Scar Accommodation during testing can also be a problem |
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Custom WavePrint
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% of Aberrations
Shows what percentage of the prescription is high order aberrations: LOW Rx: Greater % High Rx: Lower % |
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Acuity Map RMS Error
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Acuity Map RMS Error
Total of all aberrations (Low order and High Order) |
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RMS Error
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RMS Error
Amount of high order aberrations (High Order Only) <0.5 is significant |
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Zernike Coefficient Table
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Zernike Coefficient Table
Quantifies individual aberrations |
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Coma is associated with what visual symptoms?
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diplopia & ghost images
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Coma
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radial asymmetry
3rd order |
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Treefoil
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symmetry
3rd order |
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Spherical aberration
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radial asymmetry
4th order |
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If the wavefront refraction does not match the manifest refraction...
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cannot do custom wavefront
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Iris registration
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prevents cyclorotation
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Alegretto Lasers
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Correct low order aberrations
Myopia -12.00 Hyperopia +6.00 Astigmatism -5.00 400 KHz Pulse Rate Very quick laser ablation Wavefront Optimized laser ablation Leaves cornea more prolate Less spherical aberration Avoids inducing aberrations, especially spherical aberration, by adding energy to the periphery of the ablation Does not correct higher order aberrations |
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thin corneas =
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higher risk for developing keratoectasia.
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D/C RGPs for how long b4 surgery?
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Rigid Gas Permeable
Six Weeks Or 4 weeks + 1 week for every decade of wear |
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PMMA Lenses & CRT lenses
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PMMA Lenses & CRT lenses
8 weeks or until RX stable |
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D/C Soft DW, Toric or EW how many weeks b4 surgery?
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2 weeks
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VISX S4 limitations
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Conventional treatment
+6.00 to -15.00 with up to 6.00 cylinder Custom Wavefront Treatment +3.00-11.00 diopters 5.0 diopters of cyl with mixed astigmatism 3.75 diopters of cyl with myopic cylinder |
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Absolute contraindication
for lasik |
Pregnant and nursing patients
Sjorgen’s Syndrome Uncontrolled diabetes, high blood pressure, and heart disease Pacemakers Electromagnetic waves Auto-immune diseases Rheumatoid Arthritis Ankylosis spondylitis Higher risk for? Herpes Simplex/ Zoster keratitis Why? Monocular patients: Amblyopia worse then 20/40 Keratoconus Corneal Transplants Optic Neuropathy Glaucoma with moderate to severe ONH loss |
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Health considerations
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Depression
Multiple Sclerosis: Hx of Optic Neuritis HIV positive Diabetes Fibromyalgia Keloid formers Scarring with PRK OK for LASIK Dry eye Retinal holes/tears: History of retinal detachment with scleral buckle EBMD/ Recurrent erosion |
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Medication concerns for lasik:
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MAACI
Methotrexate Accutane Aralen Imitrex Amiodarone |
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Microkeratome
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Increased IOP for 20-30 Sec
IOP reaches 122 mmHg |
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Intralase Flap
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Increased IOP 40-50 sec
IOP reaches 89 mmHg |
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Example - How flat will the cornea be post surgery?
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-4.50-1.00X 180 myope with
keratometry measurements of 41.50 42.50 @90 Average K? Spherical Equiv RX? Change in corneal curvature -5.00 · 0.8 = 4.0 change in K’s You started with 42.00 42.00 – 4.0 = 38.0 |
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Appropriate corneal curvature for hyperope:
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Post-Op > 50.00 is a concern
1 Diopter change in corneal curvature for 1 diopter hyperopia correction |
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Appropriate corneal curvature for myopia:
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Myopia – Flatter
Post-Op <35.00 is a concern Expect~ 0.8 Diopter (K) change on the corneal map per 1.0 Diopter spherical equivalent correction. |
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Variables of lasik surgery that are not easily measured affecting vision:
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hydration of cornea
density of cornea cell migration |
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Risk factors for night vision problems: glare & halo
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high rx
high astigmatism large pupils small optical zones standard laser ablation |
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Treatment for night vision problems induced by lasik:
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Time - lasts about 6 mos
Mitotics - alphagan 1 gtt 1 hour before driving Custum wavefront enhancement: Correct spherical aberration |
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What causes dry eye after surgery?
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Microkeratome high pressure can damage conjunctival goblet cells
Severed corneal nerves - reduced corneal sensation, reduced blink rate, decreased reflexive tear production. Neural feedback to lacrimal gland |
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Which patient will be dryer hyperopes or myopes following surgery?
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hyperopes
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Which patient will be dryer after surgery high myopia or low myopia?
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High myopia
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Which patient will be dryer the patient corrected with microkeratome laser or intralase?
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intralase
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