Refractive Surgery Techniques Refractive Surgery Techniques and Technology 101and Technology 101

Clay Falknor, M.D.Clay Falknor, M.D.

Presbyterian Hospital of DallasPresbyterian Hospital of Dallas

August 9, 2005August 9, 2005

Case ExampleCase Example

A 26 yo CM fourth-year medical student A 26 yo CM fourth-year medical student presents with best corrected vision of –4.50 presents with best corrected vision of –4.50 OD and –5.00 OS, now with c/o wanting to OD and –5.00 OS, now with c/o wanting to get rid of his contacts, and wanting to see get rid of his contacts, and wanting to see the alarm clock in the morning so he won’t the alarm clock in the morning so he won’t be late for rounds. He presents to a cornea be late for rounds. He presents to a cornea fellow at a certain prestigious medical fellow at a certain prestigious medical school for refractive surgery consultation school for refractive surgery consultation holding a discount coupon he got by email.holding a discount coupon he got by email.

Basics of OpticsBasics of Optics

[1]

[1]

Basics of OpticsBasics of Optics

P = Power

np = nodal point

f,f’ = primary and secondary focal points

n,n’ = refractive indices Refraction is measured in diopters (D) = reciprocal

of focal length in meters

[1]

• Refractive Refractive media of media of eye eye

• TranspareTransparent mediant media

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AccommodationAccommodation

• Amplitude of accommodation is the Amplitude of accommodation is the number of diopters the eye can number of diopters the eye can accommodateaccommodate

• Accomplished by the variable optical Accomplished by the variable optical power of the crystalline lenspower of the crystalline lens

[3]

Vision Correction BasicsVision Correction Basics

• Far point:Far point: the point at which an object the point at which an object must be placed along the visual axis for must be placed along the visual axis for light rays to be focused on the retina light rays to be focused on the retina when the eye is not accommodating.when the eye is not accommodating.

• Near point:Near point: the point at which an object the point at which an object will be in focus on the retina when the will be in focus on the retina when the eye is fully accommodating. Any object eye is fully accommodating. Any object closer than the near point will not be in closer than the near point will not be in focus.focus.

EmmetropiaEmmetropia

• The far point for the emmetropic eye is at The far point for the emmetropic eye is at infinity.infinity.

• Nearer objects brought into focus on retina with Nearer objects brought into focus on retina with accommodative power of the lens.accommodative power of the lens.

[4]

Myopia (Near-sightedness)Myopia (Near-sightedness)

• The far point for the myopic eye is between the cornea and infinityThe far point for the myopic eye is between the cornea and infinity• Refractive myopia: too much refractive power due to steep corneal Refractive myopia: too much refractive power due to steep corneal

curvature or high lens powercurvature or high lens power• Axial myopia: elongated globe (each 1mm axial elongation = 3D Axial myopia: elongated globe (each 1mm axial elongation = 3D

myopia)myopia)• Overall, the cornea and lens are too “strong” for the length of the globe.Overall, the cornea and lens are too “strong” for the length of the globe.• Distant objects unclear, but near objects within focal point of the eye Distant objects unclear, but near objects within focal point of the eye

seen clearly.seen clearly.• Correct with minus lensCorrect with minus lens

[4]

Hyperopia (Far-sightedness)Hyperopia (Far-sightedness)

• The far point for the hyperopic eye is beyond infinityThe far point for the hyperopic eye is beyond infinity• The cornea and lens are too “weak” for the length of the The cornea and lens are too “weak” for the length of the

globe. globe. • Distant objects focused on the retina with Distant objects focused on the retina with

accommodation, but clear near vision is difficult) accommodation, but clear near vision is difficult) • Correct with plus lensCorrect with plus lens

[4]

AstigmatismAstigmatism• Very common, up to 95% of eyes w/ detectable Very common, up to 95% of eyes w/ detectable

astigmatism, and 10-20% >1D.astigmatism, and 10-20% >1D.• Can be naturally occurring or surgically Can be naturally occurring or surgically

induced. induced. • Most often caused by a toric cornea, and less Most often caused by a toric cornea, and less

commonly by astigmatic effects of the lenscommonly by astigmatic effects of the lens• Refractive power of the eye different in various Refractive power of the eye different in various

meridians. Light can never be brought into meridians. Light can never be brought into focus on a single point regardless of distance.focus on a single point regardless of distance.

• May occur with either myopia or hyperopia.May occur with either myopia or hyperopia.• Regular astigmatism termed “with the rule” Regular astigmatism termed “with the rule”

when steepest corneal meridian close to 90when steepest corneal meridian close to 90°, °, and “against the rule” when close to 180°.and “against the rule” when close to 180°.

• When astigmatism regular but not close to 90° When astigmatism regular but not close to 90° or 180°, termed oblique.or 180°, termed oblique. [1]

AstigmatismAstigmatism

[1]

AstigmatismAstigmatism

• Astigmatism creates two focal lines, one closer to the cornea Astigmatism creates two focal lines, one closer to the cornea formed by the more powerful corneal meridian, and the formed by the more powerful corneal meridian, and the second further from the cornea formed by the less powerful second further from the cornea formed by the less powerful meridian. meridian.

• The The Circle of Least Confusion Circle of Least Confusion is the smallest cross-sectional is the smallest cross-sectional area between the two focal lines, a circular cross-section of area between the two focal lines, a circular cross-section of the conoid of Sturm. the conoid of Sturm.

• The goal of refractive correction is to place the circle of least The goal of refractive correction is to place the circle of least confusion on the retina.confusion on the retina.

[1]

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PresbyopiaPresbyopia• As the crystalline lens hardens with age, it is As the crystalline lens hardens with age, it is

no longer able to attain the more spherical no longer able to attain the more spherical form, leading to decreased accommodation.form, leading to decreased accommodation.

• Net Effect: A lessening of the Net Effect: A lessening of the accommodative amplitude and a increase in accommodative amplitude and a increase in the near point of the eye.the near point of the eye.

• Usually has onset in 5Usually has onset in 5thth or 6 or 6thth decade. decade.• Presbyopia is not correctable with laser Presbyopia is not correctable with laser

surgery, and in fact, the surgery may hasten surgery, and in fact, the surgery may hasten its noticeable developmentits noticeable development

• Solution: Reading glassesSolution: Reading glasses

More vision correction More vision correction basicsbasics

• A lens with the focal point coincident A lens with the focal point coincident with the far point of the eye allows with the far point of the eye allows parallel light rays from infinity to be parallel light rays from infinity to be focused on the retinafocused on the retina

Spectacles and Contact LensesSpectacles and Contact Lenses

• Correct both sphere and cylindrical refractive errors. Correct both sphere and cylindrical refractive errors.

• Prescription read as spherical error, then cylindrical Prescription read as spherical error, then cylindrical error, then axis of astigmatism.error, then axis of astigmatism.

• Myopia treated with concave lenses with minus Myopia treated with concave lenses with minus power (divergent) to focus light on the retina.power (divergent) to focus light on the retina.

• Hyperopia treated with convex lenses with plus Hyperopia treated with convex lenses with plus power (convergent).power (convergent).

• Astigmatism corrected with cylindrical lenses.Astigmatism corrected with cylindrical lenses.• Ex. of myopic Rx w/ astigmatism: -3.50 + 1.50 x 090Ex. of myopic Rx w/ astigmatism: -3.50 + 1.50 x 090• Ex. of hyperopic Rx w/ astigmatism: +4.00 – 2.00 x Ex. of hyperopic Rx w/ astigmatism: +4.00 – 2.00 x

180180[1]

Spectacles and Contact LensesSpectacles and Contact Lenses

• Aberrations induced by thick lensesAberrations induced by thick lenses1.1. Spherical aberration: light at periphery of lens Spherical aberration: light at periphery of lens

refracted more than at center, causing night myopia refracted more than at center, causing night myopia due to larger pupil at night.due to larger pupil at night.

2.2. Coma: A comet-shaped blur when object and image Coma: A comet-shaped blur when object and image are off the optical axis.are off the optical axis.

3.3. Astigmatism of oblique incidence: When a spherical Astigmatism of oblique incidence: When a spherical lens is tilted, it gains a small astigmatic effect causing lens is tilted, it gains a small astigmatic effect causing curvature of the field. Helpful since matches curvature of the field. Helpful since matches curvature of the retina.curvature of the retina.

4.4. Chromatic aberration: Shorter wavelengths bent more.Chromatic aberration: Shorter wavelengths bent more.5.5. Distortion: Greater magnification in periphery. A high Distortion: Greater magnification in periphery. A high

plus lens produces pincushion effects, and high minus plus lens produces pincushion effects, and high minus produces barrel distortion.produces barrel distortion. [1]

Refractive Surgery Refractive Surgery TechniquesTechniques

• Radial Keratotomy (RK)Radial Keratotomy (RK)• Freeze keratomileusisFreeze keratomileusis• Photorefractive Keratectomy (PRK)Photorefractive Keratectomy (PRK)• Laser Epithelial Keratomileusis (LASEK)Laser Epithelial Keratomileusis (LASEK)• Laser-assisted in-situ Keratomileusis (LASIK)Laser-assisted in-situ Keratomileusis (LASIK)• Others:Others:

– Astigmatic Keratotomy (AK)Astigmatic Keratotomy (AK)– Intracorneal ring segments (Intacs)Intracorneal ring segments (Intacs)– Phakic Intraocular Lens ImplantsPhakic Intraocular Lens Implants– Refractive lensectomyRefractive lensectomy

Radial KeratotomyRadial Keratotomy• First used in U.S in 1978.First used in U.S in 1978.• Treats low to mod myopia in Treats low to mod myopia in

outpt setting using topical outpt setting using topical anesthetics.anesthetics.

• RK reduces myopia by RK reduces myopia by steepening the cornea steepening the cornea peripherally, which secondarily peripherally, which secondarily flattens the cornea centrally.flattens the cornea centrally.

• The surgeon makes deep radial The surgeon makes deep radial incisions with a diamond blade in incisions with a diamond blade in a spoke-like pattern, leaving a a spoke-like pattern, leaving a clear optical zone in the center.clear optical zone in the center.

• Refractive effect determined by Refractive effect determined by the number, length, and depth of the number, length, and depth of the incisions, as well as the size the incisions, as well as the size of the spared central optical of the spared central optical zone.zone.

• The smaller the optical zone, the The smaller the optical zone, the greater the central corneal greater the central corneal flattening (reduction in myopia), flattening (reduction in myopia), but greater risk of side-effects.but greater risk of side-effects.

[5]

RKRK

• 8 incision RK shown above with uniform central optical zone8 incision RK shown above with uniform central optical zone• American (centrifugal with angled blade), Russian (centripetal with American (centrifugal with angled blade), Russian (centripetal with

vertical blade), and combined techniquesvertical blade), and combined techniques• Russian technique allows for deeper incisions and more refractive Russian technique allows for deeper incisions and more refractive

effect, but greater risk of entering optical zone.effect, but greater risk of entering optical zone.• Standardized nomograms based on analysis of previous cases Standardized nomograms based on analysis of previous cases

determine the number of incisions and size of optical zone to determine the number of incisions and size of optical zone to create a given refractive effect. Typically 4 incisions for low create a given refractive effect. Typically 4 incisions for low myopia, 8 for moderate.myopia, 8 for moderate.

[6]

RKRK

• Infected RK incision shown above leftInfected RK incision shown above left• 16 incision RK w/ hypertrophic scarring & irregular optical zone 16 incision RK w/ hypertrophic scarring & irregular optical zone

above rightabove right• Advantage: RK patients have excellent uncorrected vision on POD1.Advantage: RK patients have excellent uncorrected vision on POD1.• Disadvantage: As with other surgical procedures, incisions leave Disadvantage: As with other surgical procedures, incisions leave

permanent changes to the cornea, as contrasted with contact permanent changes to the cornea, as contrasted with contact lenses or spectacles. The cornea may be left weakened.lenses or spectacles. The cornea may be left weakened.

• Complications include: glare, diurnal fluctuation in refraction, Complications include: glare, diurnal fluctuation in refraction, hyperopic shift, corneal perforation, infection.hyperopic shift, corneal perforation, infection.

[6][1]

RK EvidenceRK Evidence

• Prospective Evaluation of Radial Keratotomy Prospective Evaluation of Radial Keratotomy (PERK)(PERK)– 60% of RK treated eyes were w/in 1D of emmetropia up 60% of RK treated eyes were w/in 1D of emmetropia up

to 10 years post-op.to 10 years post-op.– After 10 years, 53% at least 20/20 uncorrected, and After 10 years, 53% at least 20/20 uncorrected, and

85% at least 20/40.85% at least 20/40.– 43% eyes w/ progressive shift toward hyperopia 43% eyes w/ progressive shift toward hyperopia ≥ 1D ≥ 1D

after 10 years, and worse for eyes w/ optical zone after 10 years, and worse for eyes w/ optical zone <3mm diam.<3mm diam.

– Only 3% pts lost 2 or more lines of best corrected Only 3% pts lost 2 or more lines of best corrected acuity, and all 20/30 or better best-corrected.acuity, and all 20/30 or better best-corrected.

– <1% c/o severe glare or starburst during night.<1% c/o severe glare or starburst during night.– 2% with corneal perforation, none req’d suturing.2% with corneal perforation, none req’d suturing.– Best results for low myopia group (-2.00 to -3.00D)Best results for low myopia group (-2.00 to -3.00D)

[1]

Laser technologyLaser technology

• ExcimerExcimer laser: laser: EXCEXCited dited dIMERIMER• AKA “cool laser beam” because little thermal damage AKA “cool laser beam” because little thermal damage

to adjacent tissues.to adjacent tissues.• 193nm wavelength ultraviolet laser with sufficient 193nm wavelength ultraviolet laser with sufficient

energy to disrupt intermolecular bonds within the energy to disrupt intermolecular bonds within the corneal stromal tissue (photoablative decomposition).corneal stromal tissue (photoablative decomposition).

• First excimer lasers FDA approved in 1995, with First excimer lasers FDA approved in 1995, with beam width 4-5mm, now available less than 100 beam width 4-5mm, now available less than 100 microns.microns.

• Each laser pulse removes a given volume of stromaEach laser pulse removes a given volume of stroma• Three types of laser application: wide-area ablation, Three types of laser application: wide-area ablation,

scanning slit, and flying spot lasers.scanning slit, and flying spot lasers.

[1,4,5]

Laser technologyLaser technology

• In myopia, laser flattens central cornea to In myopia, laser flattens central cornea to decrease its focusing power to bring secondary decrease its focusing power to bring secondary focal point back to retina.focal point back to retina.

• In hyperopia, the laser removes peripheral In hyperopia, the laser removes peripheral corneal tissue thereby secondarily steepening the corneal tissue thereby secondarily steepening the central cornea, increasing the focusing power of central cornea, increasing the focusing power of the cornea.the cornea.

• Astigmatism treated with elliptical or cylindrical Astigmatism treated with elliptical or cylindrical beams that flatten the steepest corneal meridian.beams that flatten the steepest corneal meridian.

• To minimize glare and halos, optical zone should To minimize glare and halos, optical zone should be larger than the dilated pupil.be larger than the dilated pupil.

Corneal TopographyCorneal Topography

• Computer-based videokeratography used to evaluate the corneal Computer-based videokeratography used to evaluate the corneal curvature. Most systems use a video camera to detect curvature. Most systems use a video camera to detect reflectedreflected images of rings projected onto the cornea, while others use slit beams, images of rings projected onto the cornea, while others use slit beams, which can also measure the corneal thickness.which can also measure the corneal thickness.

• Pre-operative and post-operative topographic maps can be used to Pre-operative and post-operative topographic maps can be used to generate a “difference map” to isolate the procedure-induced generate a “difference map” to isolate the procedure-induced changes.changes.

• Subtle abnormalities, such as early keratoconus or contact lens-Subtle abnormalities, such as early keratoconus or contact lens-induced corneal warping can be picked up.induced corneal warping can be picked up. [1]

Photorefractive Photorefractive KeratectomyKeratectomy• PRK can effectively treat low to PRK can effectively treat low to

mod myopia or hyperopia +/- mod myopia or hyperopia +/- astigmatism.astigmatism.

• Performed as outpt with Performed as outpt with topical anesthesia.topical anesthesia.

• First, the corneal epithelium in First, the corneal epithelium in the area to be ablated is the area to be ablated is removed to expose Bowman’s removed to expose Bowman’s layer and the underlying layer and the underlying corneal stroma (spatula, corneal stroma (spatula, laser).laser).

• Excimer laser then applied as Excimer laser then applied as directed by the corneal directed by the corneal topography-driven computer topography-driven computer program.program.

• Topical antibiotics, steroids, Topical antibiotics, steroids, and NSAIDs applied, along with and NSAIDs applied, along with a bandage contact lens (BCTL)a bandage contact lens (BCTL) [5]

PRKPRK• In the post-op period, pt may experience tearing, In the post-op period, pt may experience tearing,

photophobia, blurred vision, and discomfort due to photophobia, blurred vision, and discomfort due to abrasion of central epithelium.abrasion of central epithelium.

• This can be controlled with topical steroids and This can be controlled with topical steroids and NSAIDs.NSAIDs.

• Pts occ. require systemic analgesia for severe painPts occ. require systemic analgesia for severe pain• BCTL removed once epithelial defect healed (avg BCTL removed once epithelial defect healed (avg

3-4 days).3-4 days).• Abx continued several more days, and steroids for Abx continued several more days, and steroids for

up to 3 months post-op.up to 3 months post-op.• Visual acuity improves once the epithelial defect Visual acuity improves once the epithelial defect

heals, but fluctuates for a few months and finally heals, but fluctuates for a few months and finally stabilizes at ~3 months.stabilizes at ~3 months.

• Glare, halos, and dry eye symptoms common the Glare, halos, and dry eye symptoms common the first month post-op, usually first month post-op, usually diminishing/disappearing by 3-6 months.diminishing/disappearing by 3-6 months.

[4,5]

PRKPRK

• Left: mild stromal haze at 3 monthsLeft: mild stromal haze at 3 months• Center: moderate-to-severe stromal haze at 6 monthsCenter: moderate-to-severe stromal haze at 6 months• Right: light microscope of rabbit cornea showing epithelial Right: light microscope of rabbit cornea showing epithelial

hyperplasia in ablated regionhyperplasia in ablated region• Bottom: fluorescent microscope in rabbit cornea 1 month post PRK Bottom: fluorescent microscope in rabbit cornea 1 month post PRK

showing new connective tissue deposition between stained old showing new connective tissue deposition between stained old stroma and epithelium. stroma and epithelium.

• Post-op corneal haze seen in a minority of patients at 3 months, and Post-op corneal haze seen in a minority of patients at 3 months, and in none at 1 yearin none at 1 year

• Initially following PRK, corneal epithelium hyperplastic, modifying Initially following PRK, corneal epithelium hyperplastic, modifying refraction.refraction.

• Deposition of new collagen and GAGs by activated stromal Deposition of new collagen and GAGs by activated stromal keratocytes, manifesting as stromal haze or subepithelial scarring.keratocytes, manifesting as stromal haze or subepithelial scarring.

[1] [5][6]

[5]

PRK EvidencePRK Evidence• A 2001 prospective study of 72 cases showed with A 2001 prospective study of 72 cases showed with

significance that a larger ablation area (7mm) with significance that a larger ablation area (7mm) with transitional zones has less pronounced corneal transitional zones has less pronounced corneal optical aberration after PRK than with first generation optical aberration after PRK than with first generation (5mm) ablation areas with out transitional zones. [7](5mm) ablation areas with out transitional zones. [7]

• A 1999 multi-center prospective study demonstrated A 1999 multi-center prospective study demonstrated PRK to correct myopia from -1 to -10D +/- PRK to correct myopia from -1 to -10D +/- astigmatism showed refractive stability, excellent astigmatism showed refractive stability, excellent UCVA with no significant loss of BSCVA, and very low UCVA with no significant loss of BSCVA, and very low levels of corneal haze at one year post-op. [8]levels of corneal haze at one year post-op. [8]

• A 2004 British 12-year prospective follow-up study of A 2004 British 12-year prospective follow-up study of PRK patients showed that for mild myopia, refractive PRK patients showed that for mild myopia, refractive stability achieved at 1 year was maintained to 12 stability achieved at 1 year was maintained to 12 years without hyperopic shift, diurnal fluctuation, or years without hyperopic shift, diurnal fluctuation, or late regression in the long term. Night halos late regression in the long term. Night halos remained a significant problem in the subset of pt’s remained a significant problem in the subset of pt’s with small ablation zones. [9]with small ablation zones. [9]

PRK EvidencePRK Evidence• A large 1998 prospective study (3000 cases) in Spain to A large 1998 prospective study (3000 cases) in Spain to

monitor complications of PRK for myopia +/- astigmatism monitor complications of PRK for myopia +/- astigmatism at two years revealed that only 0.7% of eyes lost 2 or at two years revealed that only 0.7% of eyes lost 2 or more Snellen lines for BCVA at one year post-op. more Snellen lines for BCVA at one year post-op. Retreatment for undercorrection was performed in 7% of Retreatment for undercorrection was performed in 7% of the low myopia group and 39% of the high myopia group. the low myopia group and 39% of the high myopia group. There were no cases of progressive hyperopia. Severe There were no cases of progressive hyperopia. Severe corneal haze was only present in 0.5% at one year. Only corneal haze was only present in 0.5% at one year. Only rare occurrences of surgically induced astigmatism rare occurrences of surgically induced astigmatism (0.5%), delayed re-epithelialization, or recurrent corneal (0.5%), delayed re-epithelialization, or recurrent corneal erosion. [10]erosion. [10]

• Results of PRK are comparable to RK for similar Results of PRK are comparable to RK for similar magnitudes of myopia.magnitudes of myopia.– 68% w/in 1D of emmetropia uncorrected (RK 60%)68% w/in 1D of emmetropia uncorrected (RK 60%)– 60% with at least 20/20 uncorrected (RK 53%)60% with at least 20/20 uncorrected (RK 53%)– 90% with at least 20/40 uncorrected (RK 85%)90% with at least 20/40 uncorrected (RK 85%)

• For low to mod myopia (-1.5 to -3.0D), 80% For low to mod myopia (-1.5 to -3.0D), 80% ≥ 20/20 ≥ 20/20 uncorrecteduncorrected

• Hyperopic shift infrequent in PRK compared to RK.Hyperopic shift infrequent in PRK compared to RK.

KeratomileusisKeratomileusis

[5]

Laser Sub-Epithelial Laser Sub-Epithelial KeratomileusisKeratomileusis

• LASEK can treat mild to moderate myopia and LASEK can treat mild to moderate myopia and hyperopia +/- astigmatism.hyperopia +/- astigmatism.

• Can be performed as an outpt with topical anesthesiaCan be performed as an outpt with topical anesthesia• The corneal epithelium is incompletely incised using a The corneal epithelium is incompletely incised using a

microkeratome with a 70 micron deep blade.microkeratome with a 70 micron deep blade.• A hinge is left at the 12 o’clock position.A hinge is left at the 12 o’clock position.• Dilute alcohol (20%) drops are applied to the exposed Dilute alcohol (20%) drops are applied to the exposed

tissue and left for ~30 seconds. The area is then tissue and left for ~30 seconds. The area is then washed with water and allowed to dry. The excimer washed with water and allowed to dry. The excimer laser is applied as in PRK to the sub-epithelial stroma. laser is applied as in PRK to the sub-epithelial stroma.

• The epithelial flap is repositioned afterward.The epithelial flap is repositioned afterward.

[4,5]

LASEK EvidenceLASEK Evidence

• In theory, since the flap is repositioned with the In theory, since the flap is repositioned with the epithelium intact, there is less post-op pain, faster epithelium intact, there is less post-op pain, faster visual recovery, and less incidence of infection.visual recovery, and less incidence of infection.

• A 2004 randomized prospective clinical trial at A 2004 randomized prospective clinical trial at Travis Air Force base compared LASEK with PRK in Travis Air Force base compared LASEK with PRK in different eyes in the same patients (n=30) for subj. different eyes in the same patients (n=30) for subj. pain levels, visual acuity, and corneal healing.pain levels, visual acuity, and corneal healing.– No statistical advantages in pain levels or in visual acuity. No statistical advantages in pain levels or in visual acuity. – There was a statistically significant smaller median There was a statistically significant smaller median

epithelial defect in the LASEK-treated eyes on POD1, but epithelial defect in the LASEK-treated eyes on POD1, but by POD3 the PRK defects were smaller and by POD7, there by POD3 the PRK defects were smaller and by POD7, there were no detectable defects in either group.were no detectable defects in either group.

– Overall, no clinical advantage was seen in LASEK over Overall, no clinical advantage was seen in LASEK over PRK. [11]PRK. [11]

LASEK EvidenceLASEK Evidence

• A 2002 non-randomized, retrospective study of 58 A 2002 non-randomized, retrospective study of 58 LASEK-treated eyes with myopia +/- astigmatism LASEK-treated eyes with myopia +/- astigmatism resulted in 45% with 20/40 or better UCVA at resulted in 45% with 20/40 or better UCVA at POD1, and 89% at 1 month, and 97% at 6 POD1, and 89% at 1 month, and 97% at 6 months, with 73% with UCVA 20/20 or better. 7% months, with 73% with UCVA 20/20 or better. 7% of eyes had visually significant corneal haze at 6 of eyes had visually significant corneal haze at 6 months, and no eyes lost 2 or more lines of months, and no eyes lost 2 or more lines of BSCVA. [12]BSCVA. [12]

• Similar results found in a 2002 South Korean Similar results found in a 2002 South Korean study with 6 month follow-up of LASEK treated study with 6 month follow-up of LASEK treated eyes for low to moderate myopia (-3.25 to -eyes for low to moderate myopia (-3.25 to -7.00D). [13]7.00D). [13]

Laser-assisted in-situ Laser-assisted in-situ KeratomileusisKeratomileusis• LASIK can treat mild, moderate, and high LASIK can treat mild, moderate, and high

myopia and hyperopia +/- astigmatism.myopia and hyperopia +/- astigmatism.• Can also be performed as an outpt with Can also be performed as an outpt with

topical anesthesiatopical anesthesia• LASIK is now the most commonly LASIK is now the most commonly

performed refractive surgery in the world.performed refractive surgery in the world.• A suction ring is applied to the A suction ring is applied to the

anesthetized cornea and a microkeratome anesthetized cornea and a microkeratome is used to raise a corneal flap of is used to raise a corneal flap of ~160microns thickness (25-30% of the ~160microns thickness (25-30% of the corneal thickness), hinged at the 12 corneal thickness), hinged at the 12 o’clock position.o’clock position.

• The suction is turned off and the flap is The suction is turned off and the flap is lifted aside, exposing stromal tissuelifted aside, exposing stromal tissue

• The excimer laser is applied as with PRK The excimer laser is applied as with PRK and LASEK, controlled by the topography-and LASEK, controlled by the topography-driven computer software, to reshape the driven computer software, to reshape the cornea.cornea.

• The flap is replaced on the stromal bed The flap is replaced on the stromal bed without sutures or a BCTL, as the without sutures or a BCTL, as the endothelial pumps create a driving force to endothelial pumps create a driving force to keep the flap in position.keep the flap in position. [5]

LASIKLASIK

• The use of the suction ring helps hold the cornea The use of the suction ring helps hold the cornea steady and provides for a uniform cut by the steady and provides for a uniform cut by the microkeratome. microkeratome.

• Flaps can be formed by an automated process Flaps can be formed by an automated process involving a blade guide on the suction ring to guide involving a blade guide on the suction ring to guide a turbine-driven microkeratome, producing a very a turbine-driven microkeratome, producing a very smooth, regular cutsmooth, regular cut

• Patients usually sent home on topical antibiotics, Patients usually sent home on topical antibiotics, steroids, and NSAID drops. Pt is usually seen steroids, and NSAID drops. Pt is usually seen ~POD 1, and 7, then at 1, 3 and 6 months.~POD 1, and 7, then at 1, 3 and 6 months.

• Benefits include little pain, quick recovery of vision, Benefits include little pain, quick recovery of vision, and potential to treat higher levels of myopia. and potential to treat higher levels of myopia. LASIK enhancements are also easily performed.LASIK enhancements are also easily performed.

[1]

LASIK EvidenceLASIK Evidence• A 1996 Saudi Arabian retrospective study looked at the efficacy A 1996 Saudi Arabian retrospective study looked at the efficacy

of LASIK to correct myopia from -2 to -20D, and showed of LASIK to correct myopia from -2 to -20D, and showed promising results in the entire range of refractive error. [14]promising results in the entire range of refractive error. [14]

• A 2001 cohort study by McDonald A 2001 cohort study by McDonald et alet al also showed refractive also showed refractive efficacy and stability, good UCVA outcomes, no significant loss efficacy and stability, good UCVA outcomes, no significant loss of BCVA, and accurate correction of astigmatism in the range of BCVA, and accurate correction of astigmatism in the range of -1 to -11D with up to -5D of astigmatism. [15]of -1 to -11D with up to -5D of astigmatism. [15]

• At six months, for spherical myopes, At six months, for spherical myopes, – UCVA 20/20 or better in 61%UCVA 20/20 or better in 61%– 20/40 or better UCVA in 94%20/40 or better UCVA in 94%– 0.6% lost 2 lines of BSCVA, and none > 2 lines0.6% lost 2 lines of BSCVA, and none > 2 lines

• At six months for astigmatic myopes,At six months for astigmatic myopes,– UCVA 20/20 or better in 52%UCVA 20/20 or better in 52%– 20/40 or better UCVA in 94%20/40 or better UCVA in 94%– 0.9% lost 2 lines of BSCVA, and none > 2 lines0.9% lost 2 lines of BSCVA, and none > 2 lines

• A refractive stability was achieved between 1 and 3 months in A refractive stability was achieved between 1 and 3 months in 98% of spherical and 99% of astigmatic myopes, and 100% 98% of spherical and 99% of astigmatic myopes, and 100% between 3-6 months for both groups.between 3-6 months for both groups.

LASIK EvidenceLASIK Evidence

• A 2001 retrospective study by A 2001 retrospective study by Tabbara Tabbara et alet al showed efficacy in showed efficacy in LASIK refractive correction of LASIK refractive correction of hyperopia from +0.5 to +11.5D at hyperopia from +0.5 to +11.5D at six months follow-up [16]:six months follow-up [16]:– 44% with UCVA of 20/20 or better44% with UCVA of 20/20 or better– 98% with UCVA of 20/40 or better98% with UCVA of 20/40 or better

LASIK EvidenceLASIK Evidence• Even though simultaneous bilateral LASIK has been shown Even though simultaneous bilateral LASIK has been shown

to be safe (Gimbel et al, 1999 [17]), Chiang to be safe (Gimbel et al, 1999 [17]), Chiang et al et al in 1999 in 1999 showed that the refractive predictability between a person’s showed that the refractive predictability between a person’s two eyes after LASIK is correlated, and therefore that using two eyes after LASIK is correlated, and therefore that using a correction gained from the first eye to customize the a correction gained from the first eye to customize the procedure for the second eye has better outcomes, esp. in procedure for the second eye has better outcomes, esp. in mild myopes. [18]mild myopes. [18]

• A prospective 2001 study at Bascom Palmer and a A prospective 2001 study at Bascom Palmer and a retrospective study at Univ. of Washington showed that retrospective study at Univ. of Washington showed that irritation, or “dry eye” symptoms are due to sensory irritation, or “dry eye” symptoms are due to sensory denervation of the ocular surface following bilateral LASIK denervation of the ocular surface following bilateral LASIK (neurotrophic epitheliopathy), and resolve by 6 months (neurotrophic epitheliopathy), and resolve by 6 months post-op. [19], [20]post-op. [19], [20]

• A 2003 Ohio State retrospective study examined risk factors A 2003 Ohio State retrospective study examined risk factors for decreased patient satisfaction and showed that most are for decreased patient satisfaction and showed that most are satisfied with their vision after LASIK, but that increasing satisfied with their vision after LASIK, but that increasing age, flatter pre-operative minimum corneal curvature, and age, flatter pre-operative minimum corneal curvature, and surgical enhancement were significant factors for decreased surgical enhancement were significant factors for decreased satisfaction and increased night vision symptoms. [21]satisfaction and increased night vision symptoms. [21]

ComparisonsComparisons• PRK vs. LASIK PRK vs. LASIK

– 1998 prospective study Hersh 1998 prospective study Hersh et alet al) [22] showed similar ) [22] showed similar refractive outcomes, though faster results in LASIK, and refractive outcomes, though faster results in LASIK, and undercorrection more likely in LASIK than PRKundercorrection more likely in LASIK than PRK

– 2000 control-matched study also showed equal refractive 2000 control-matched study also showed equal refractive outcomes between LASIK and PRK up to -9D, but LASIK 2x outcomes between LASIK and PRK up to -9D, but LASIK 2x more likely to cause halos [23].more likely to cause halos [23].

– 1999 El-Maghraby 1999 El-Maghraby et alet al showed LASIK significantly lowers showed LASIK significantly lowers post-operative pain and hastened recovery of vision, but did post-operative pain and hastened recovery of vision, but did not alter refractive outcomes [24].not alter refractive outcomes [24].

• LASEK vs. LASIKLASEK vs. LASIK– LASEK with thinner flap, corneal ectasia less likelyLASEK with thinner flap, corneal ectasia less likely– LASIK needs more complicated equipment with higher risk of LASIK needs more complicated equipment with higher risk of

intraoperative flap complications.intraoperative flap complications.– LASEK lowers risk of DLKLASEK lowers risk of DLK– Lost LASEK flap less risky than a lost LASIK flap.Lost LASEK flap less risky than a lost LASIK flap.– LASEK can cause stromal haze similar to PRKLASEK can cause stromal haze similar to PRK– More studies neededMore studies needed

Wavefront-guided LASIKWavefront-guided LASIK

• Wavefront testing allows for the measurement of not Wavefront testing allows for the measurement of not only myopia, hyperopia, and regular astigmatism, but only myopia, hyperopia, and regular astigmatism, but also higher-order aberrations (irregular astigmatism).also higher-order aberrations (irregular astigmatism).

• A beam of light is shone onto the eye, reflected off the A beam of light is shone onto the eye, reflected off the back of the eye and refracted on its way back out. The back of the eye and refracted on its way back out. The light then enters a micro-lens array to produce a spot light then enters a micro-lens array to produce a spot image array of reflected light.image array of reflected light.

• Computer analysis determines the relative displacement Computer analysis determines the relative displacement of each spot image. The images are then processed to of each spot image. The images are then processed to give the local slope and character of the wavefront light.give the local slope and character of the wavefront light.

• A 2004 Israeli prospective, non-randomized comparative A 2004 Israeli prospective, non-randomized comparative clinical study showed that WFG LASIK patients have clinical study showed that WFG LASIK patients have significantly improved contrast sensitivity compared to significantly improved contrast sensitivity compared to the standard LASIK patients at one month post-op, even the standard LASIK patients at one month post-op, even though visual acuities were not different with though visual acuities were not different with significance between the groups. [25]significance between the groups. [25]

LASIK ComplicationsLASIK Complications• Potential complications:Potential complications:

– Intra-operative flap complicationsIntra-operative flap complications: A 2000 UCLA retrospective : A 2000 UCLA retrospective study of ~4000 eyes found a microkeratome complication study of ~4000 eyes found a microkeratome complication rate of 0.7%, but a higher rate with surgeon inexperience rate of 0.7%, but a higher rate with surgeon inexperience (1.3% in surgeons first 1000 eyes). [26](1.3% in surgeons first 1000 eyes). [26]

– Post-operative flap complicationsPost-operative flap complications– Flap-bed interface epithelializationFlap-bed interface epithelialization: Walker : Walker et al et al in 2000 in 2000

showed that epithelial growth at the interface could showed that epithelial growth at the interface could significantly be reduced by irrigating the stromal surfaces and significantly be reduced by irrigating the stromal surfaces and using a BCTL for one day. [27]using a BCTL for one day. [27]

– Irregular astigmatismIrregular astigmatism– InfectionInfection::– Diffuse lamellar keratitis (DLK):Diffuse lamellar keratitis (DLK): (AKA Sands of Sahara (AKA Sands of Sahara

syndrome) Wavy inflammatory reaction at LASIK flap interface syndrome) Wavy inflammatory reaction at LASIK flap interface 1-3 days post-op of unknown cause. Treatment involved high-1-3 days post-op of unknown cause. Treatment involved high-dose topical steroids or lifting the flap to irrigating the dose topical steroids or lifting the flap to irrigating the interface.interface.

– Progressive corneal ectasiaProgressive corneal ectasia: progressive corneal thinning and : progressive corneal thinning and steepening with worsening irreg. astigmatism thought to steepening with worsening irreg. astigmatism thought to result from too thin a stromal bed after LASIK. Most believe result from too thin a stromal bed after LASIK. Most believe stromal bed thickness should be at least 250 microns.stromal bed thickness should be at least 250 microns.

LASIK ComplicationsLASIK Complications

• A 1998 Canadian retrospective study A 1998 Canadian retrospective study showed that even with early techniques, showed that even with early techniques, there was no significant loss of BCVA. 1.9% there was no significant loss of BCVA. 1.9% of procedures involved microkeratome-of procedures involved microkeratome-related complications, and 1.3% involved related complications, and 1.3% involved complications with the suctioning device. complications with the suctioning device. Only 1.8% involved post-op complications Only 1.8% involved post-op complications requiring repositioning of shifted or wrinkled requiring repositioning of shifted or wrinkled flaps. [28]flaps. [28]

Poor LASIK CandidatesPoor LASIK Candidates

• Thin corneaThin cornea

• Irregular astigmatismIrregular astigmatism

• KeratoconusKeratoconus

• Anterior basement membrane dystrophyAnterior basement membrane dystrophy

• Herpes keratitisHerpes keratitis

• Unstable refractionUnstable refraction

• Pregnant or nursing (unstable refraction)Pregnant or nursing (unstable refraction)

• History of dry eyesHistory of dry eyes

[1]

Good LASIK CandidatesGood LASIK Candidates

• Proper expectation of outcomeProper expectation of outcome• >18 years old>18 years old• Stable refraction for at least 1 year (<1D change)Stable refraction for at least 1 year (<1D change)• Sufficient corneal thicknessSufficient corneal thickness• Good wound healing potential (no Good wound healing potential (no

immunosuppresing conditions or medications or immunosuppresing conditions or medications or autoimmune conditions).autoimmune conditions).

• Mild to moderate refractive error (though high Mild to moderate refractive error (though high myopes and hyperopes, as well as higher-order myopes and hyperopes, as well as higher-order aberrant eyes are relatively good candidates)aberrant eyes are relatively good candidates)

[5]

Other options…Other options…

• Astigmatic keratotomy (AK)Astigmatic keratotomy (AK)

• Phakic intraocular lens implantsPhakic intraocular lens implants

• Refractive lensectomyRefractive lensectomy

• Intracorneal ringsIntracorneal rings

[1]

[6]

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