LASIK Myopia 

  • Author: Michael Taravella, MD; Chief Editor: Hampton Roy Sr, MD   more...
 
Updated: May 11, 2009
 

Background

One of the most promising and exciting developments in the world of refractive surgery has been the advent of laser in situ keratomileusis (LASIK). The surgical technique involves the creation of a hinged lamellar corneal flap, after which an excimer laser is used to make a refractive cut on the underlying stromal bed. LASIK is a fusion of old and new technologies, with its roots in keratomileusis and automated lamellar keratectomy (ALK). However, as currently practiced, it is perhaps best thought of as photorefractive keratectomy (PRK) performed under a flap instead of on the corneal surface. About 9 million procedures have been performed in the United States since the approval of the excimer laser for refractive surgery in late 1995. About 1.4 million procedures were performed in 2007 alone (Marketscope).

Spherical aberration: a schematic diagram for the Spherical aberration: a schematic diagram for the human eye.
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History of the Procedure

The era of keratomileusis began in 1966 with Pureskin, who demonstrated that refractive changes could be achieved by creating a corneal flap and removing central tissue in a lamellar fashion under the flap. He found that the smaller the diameter of the resected disc, the greater the refractive change.

Jose Barraquer developed the idea of resecting a corneal disc and freezing it, followed by shaping the disc with a cryolathe. However, the technique was limited by complexity of the equipment and tissue damage to the resected corneal disc caused by freezing. Ruiz and Barraquer performed keratomileusis in situ in the late 1980s. Using principles developed by Krumeich, this technique involved first removing a corneal disc with a microkeratome. Refractive change was accomplished by performing a second plano cut with the microkeratome. The thickness and diameter of this second disc of tissue determined the end refractive result; then, the first disc was sutured back onto the cornea. Problems included complexity, poor predictability, and irregular astigmatism.

Burratto and Pallikaris were the first to combine the use of the excimer laser and microkeratome technology. Burratto's original work involved performing a corrective excimer laser ablation on the back of a resected disc of corneal tissue. This disc was replaced and sutured onto the cornea. Pallikaris developed the technique of performing the excimer laser corrective ablation in the corneal stromal bed under a hinged flap. He first studied the procedure in rabbits, followed by blind human eyes in 1989, and then sighted eyes in 1991.

In 1993, Steve Slade added the refinement of using an automated microkeratome to create the flap and was one of the first US surgeons to perform LASIK.

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Indications

As of December 2008, LASIK has been approved by the Food and Drug Administration (FDA) for several different laser platforms, including the VISX STAR S4, Allegretto Wavelight, Alcon LADARVision 4000, and Technolas and NIDEK lasers. The approved range for myopic, hyperopic, and custom treatments varies slightly between platforms.

Table 1 summarizes these devices and their FDA status.

Table 1. Device Summary and FDA Status (Open Table in a new window)

Myopia (MRSE) -Conventional LASIKWavefront ParametersHyperopia LASIKPRK (Myopia)
LADARVision 4000 (Alcon) Small diameter beam; infrared pupil tracker. Dilation required.< -9.0 D sph;-0.50 D to -3.0 D cyl≤ -7.0 D sph with ≤ -4.0 D cylUp to +6.0 D with ≤ -6.0 D cyl-1. 0 D to -10.0 D with ≤ 4.0 D cyl
NIDEK EC-5000-1.0 D to -14.0 D sph; ≤ 4.0 D cylN/AN/A-0.75 D to -13.0 D sph; -1.0 D to -8.0 D sph with -0.5 to 4.0 D cyl
VISX Star S4(S2, S3) < -14.0 D sph;-0.50 D to -5.0 D cyl≤ -6.0 D sph with ≤ 3.0 D cyl+0.50 D to +5.0 D sph; ≤ +3.0 D cyl≤ -12.0 D sph with ≤ -4.0 D cyl
Technolas 217 (B&L)< -11.0 D sph with ≤ -3.0 D cy(217z): <-7.0 D sph with ≤ -3.0 D cyl+1.0 D to +4.0 D sph; ≤ 2.0 D cylN/A
Wavelight Allegretto Wave®< -12.0 D sph with < -6.0 D cyl< -7.0 D sph with < -3.0 D cylN/A
Source: http://www.fda.gov/cdrh/LASIK/lasers.htm 12/27/05.
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Relevant Anatomy

The cornea is a thin layer of transparent tissue that protects the intraocular contents and refracts light. Average central corneal thickness is about 550 µm, increasing to about 700 µm in the periphery. The cornea has a diameter (from the front surface) of about 11 mm vertically and 12 mm horizontally. The air-tear interface is the first refractive surface that light encounters and accounts for about 80% of the eye's total refractive power; the average corneal curvature (K readings) in the adult cornea is approximately 44.00 diopters (D).

Anatomically, the cornea consists of 5 layers: epithelium, Bowman layer, stroma, Descemet membrane, and endothelium.

Three types of cells are present in the epithelium: (1) basal columnar cells attached to the epithelial basement membrane via hemidesmosomes, (2) wing cells noted for thin winglike projections, and (3) surface cells joined by connecting bridges and covered by microvilli. Mucin is attached strongly to the surface. Usually, 5-7 layers of cells are present. Unlike stratified squamous epithelium in other areas of the body, the epithelium in the eye has an exceptionally smooth and regular surface, contributing to the transparency and light transmission characteristics of the cornea.

The Bowman layer is not a membrane, but rather an acellular structure consisting of collagen and representing the most superficial layer of the stroma.

The stroma makes up about 90% of the corneal thickness and consists of regularly arrayed flattened bundles of collagen called lamellae. Approximately 200-250 lamellae are present in the human cornea. Each bundle extends the width of the cornea and is about 2 µm thick and up to 260 µm wide. The parallel arrangement of these bundles together with the uniform spacing between collagen fibrils helps explain corneal transparency. Although relatively acellular, stromal fibroblasts called keratocytes can be found scattered throughout the stroma between lamellae, and they are responsible for collagen production and wound healing.

The Descemet membrane is composed of a fine latticework of collagen fibers. It represents a true basement membrane, and it is produced by the corneal endothelium.

The endothelium is a single layer of hexagonal cells whose sole purpose is to act as a barrier to the influx of fluid into the cornea and to pump fluid out of the cornea keeping it deturgesced and clear. These cells are incapable of regeneration.

The cornea is richly innervated; myelin sheaths are present on the nerves as they traverse the superficial layers of the cornea. The nerve endings lose their sheath as they penetrate the epithelium. In terms of density, more nerve endings are present in the corneal epithelium than anywhere else in the human body.[1, 2]

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Contraindications

Contraindications include unstable refractive error, active collagen vascular disease (especially in the presence of iritis or scleritis), pregnancy, presence of a pacemaker, any ongoing active inflammation of the external eye (eg, conjunctivitis, severe dry eye), and a refractive error outside the range of laser correction (it is common to have patients treated slightly outside the approved range, but they must understand that it is an off-label use of the excimer laser).

Other contraindications include leaving less than a calculated residual bed of 250 µm of untouched cornea, as well as signs, symptoms, or topographic findings consistent with keratoconus.

Patients who are on Accutane (isotretinoin), Cordarone (amiodarone hydrochloride), and Imitrex (sumatriptan) should be treated with caution, and patient counseling should be provided because these medications may adversely affect corneal wound healing.

A history of herpetic keratitis is a relative contraindication. Although patients have been treated safely with a history of herpes simplex keratitis and the appropriate use of prophylactic antivirals, reactivation of the virus following treatment remains a concern.

Patients who cannot cooperate with procedures under a topical anesthetic and cannot accurately fixate or lay flat without difficulty are poor candidates for refractive surgery.

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Contributor Information and Disclosures
Author

Michael Taravella, MD  Director of Cornea and Refractive Surgery, Rocky Mountain Lions Eye Institute; Professor, Department of Ophthalmology, University of Colorado School of Medicine

Michael Taravella, MD is a member of the following medical societies: American Academy of Ophthalmology, American Medical Association, American Society of Cataract and Refractive Surgery, Contact Lens Association of Ophthalmologists, and Eye Bank Association of America

Disclosure: Nothing to disclose.

Coauthor(s)

Timothy A Perozek, MD  Consulting Ophthalmologist, Private Practice, Perozek Professional Corporation

Disclosure: Nothing to disclose.

Scott A Thomas MD  Staff Physician, Department of Ophthalmology, University of Colorado, Rocky Mountains Lions Eye Institute

Scott A Thomas MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Ophthalmology

Disclosure: Nothing to disclose.

Specialty Editor Board

Daniel S Durrie, MD  Director, Department of Ophthalmology, Division of Refractive Surgery, University of Kansas Medical Center

Daniel S Durrie, MD is a member of the following medical societies: American Academy of Ophthalmology and Association for Research in Vision and Ophthalmology

Disclosure: Alcon Labs Grant/research funds Independent contractor; Abbott Medical Optics Grant/research funds Independent contractor; Acufocus Ownership interest Consulting; WaveTec Ownership interest Consulting; Topcon Grant/research funds Independent contractor; Avedro Grant/research funds Independent contractor; ReVitalVision Independent contractor

Simon K Law, MD, PharmD  Associate Professor of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, David Geffen School of Medicine

Simon K Law, MD, PharmD is a member of the following medical societies: American Academy of Ophthalmology, American Glaucoma Society, and Association for Research in Vision and Ophthalmology

Disclosure: Nothing to disclose.

Louis E Probst, MD  Medical Director of Refractive Surgery, Chicago, Madison, Milwaukee, and Windsor Centers, TLC the Laser Eye Centers

Louis E Probst, MD is a member of the following medical societies: American Academy of Ophthalmology, American Society of Cataract and Refractive Surgery, and International Society of Refractive Surgery

Disclosure: Nothing to disclose.

Lance L Brown, OD, MD  Ophthalmologist, Affiliated With Freeman Hospital and St John's Hospital, Regional Eye Center, Joplin, Missouri

Disclosure: Nothing to disclose.

Chief Editor

Hampton Roy Sr, MD  Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences

Hampton Roy Sr, MD is a member of the following medical societies: American Academy of Ophthalmology, American College of Surgeons, and Pan-American Association of Ophthalmology

Disclosure: Nothing to disclose.

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Diffuse intralamellar keratitis (day 5).
Bacterial keratitis following LASIK.
Epithelial ingrowth.
Striae.
Thin, perforated flap.
Incomplete flap.
Buttonhole in flap.
Decentered flap and ablation.
Pupil alignment or visual axis alignment for laser ablation.
Spherical aberration: a schematic diagram for the human eye.
Zernike polynomials: pictorial representation.
Spherical aberration post-LASIK. The original refractive error was -10.00 diopters.
Coma in a patient with mild ectasia. This higher order optical aberration is also characteristic of decentered ablation zones and ectasia.
Postoperative ectasia: Orbscan. Note the elevation on anterior and posterior floats and the thinning of the central cornea on the pachymetry map.
Ectasia post-LASIK: Tracey WaveScan. Note the preponderance of higher order aberrations, including spherical aberration and coma. The Orbscan of this same patient appears in the image above.
Table 1. Device Summary and FDA Status
Myopia (MRSE) -Conventional LASIKWavefront ParametersHyperopia LASIKPRK (Myopia)
LADARVision 4000 (Alcon) Small diameter beam; infrared pupil tracker. Dilation required.< -9.0 D sph;-0.50 D to -3.0 D cyl≤ -7.0 D sph with ≤ -4.0 D cylUp to +6.0 D with ≤ -6.0 D cyl-1. 0 D to -10.0 D with ≤ 4.0 D cyl
NIDEK EC-5000-1.0 D to -14.0 D sph; ≤ 4.0 D cylN/AN/A-0.75 D to -13.0 D sph; -1.0 D to -8.0 D sph with -0.5 to 4.0 D cyl
VISX Star S4(S2, S3) < -14.0 D sph;-0.50 D to -5.0 D cyl≤ -6.0 D sph with ≤ 3.0 D cyl+0.50 D to +5.0 D sph; ≤ +3.0 D cyl≤ -12.0 D sph with ≤ -4.0 D cyl
Technolas 217 (B&L)< -11.0 D sph with ≤ -3.0 D cy(217z): <-7.0 D sph with ≤ -3.0 D cyl+1.0 D to +4.0 D sph; ≤ 2.0 D cylN/A
Wavelight Allegretto Wave®< -12.0 D sph with < -6.0 D cyl< -7.0 D sph with < -3.0 D cylN/A
Source: http://www.fda.gov/cdrh/LASIK/lasers.htm 12/27/05.
Table 2. Myopia: Conventional LASIK Outcomes in FDA Trials
Laser (Mfr.) Approval Number and DateTreatment parameters and follow-up period for which all data is calculatedSafety (% loss of ≥ 2 lines BCVA)UCVA 20/20 or betterUCVA 20/40 or betterStability(Change in MRSE by = 1.0 D)MRSE = 0.50 D of intendedUCVA 20/20 or better, low/ moderate myopia (MRSE)UCVA 20/20 or better, high myopia (MRSE)
LADARVision (Alcon)P970043/S5 5/9/00-11.00 D sph with up to -6.0 D cyl 3 months f/u4/327 (1.2%)165/301(54.8%)274/301(91.0%)95%250/327(76.5%)139/240(57.9%) [< 7.0]25/48 (52.1%) [≥ 7.0 D]
EC-5000 (NIDEK)P970053/S2 4/14/00-1.0 to -20.0 D sph with up to-4.0 D cyl 6 months f/u11/752 (1.5%)359/758(47.4%)640/758(84.4%)590/612 (96.4%)455/755(60.3%)197/333(59.2%) [< 6.0 D]162/425(38.1%) [≥ 6.0 D]
VISX Star S2P990010 11/19/99-1.0 to -14.0 D sph with up to 6.0 D cyl 6 months f/u0/850 (0%)437/808 (54.1%)771/808 (95.4%)426/453 (94.0%)765/844 (90.6%) [= 1.0D]332/567 (58.6%) [< 7.0 D]150/241 (43.6%) [≤ 7.0 D]
Technolas 217a (B&L)P990027 2/23/00-1.0 to -7.0 D sph with up to 3.0 D cyl 6 months f/u3/361(0.8%)302/346(87.3%)345/346(99.7%)346/349(99.1%)313/361 (86.7%)302/346 (87.3%) [< 7.0 D]N/A
Technolas 217a (B&L)P990027/S2 5/15/02-7.0 to -12.0 D sph with up to 4.0 D cyl 6 months4/263 (1.5%)138/259 (53.3%)234/259 (90.3%)236/248(95.2%)161/263 (61.2%)N/A138/259 (53.3%) [≥ 7.0 D]
Wavelight Allegretto Wave® PO20050 10/7/03-14.0 sphere up to –6.0 cyl 3 months4/813 (.5%) at 1 year686/813 (84.4%)797/813 (98.0%)793/813 (97.6%)716/813 (84.8%)686/813 (84.4%) [< 7.0 D]77/109 (70.6%) [7-13.0 D]
*: Only includes patients whose preoperative BSCVA was 20/20 or better
Table 3. Myopia: Wavefront-guided LASIK Outcomes in FDA Trials
Laser, (Mfr.) Approval Number and DateTreatment parameters and follow-up period for which all data is calculatedNumber of eyesSafety (% loss of ³ 2 lines BCVA)UCVA 20/20 or betterUCVA 20/40 or betterStability (Change in MRSE by =0.5 0D)MRSE = 0.50D of intendedUCVA 20/20 or better, low (<-3.00D) MRSEUCVA 20/20 or better, mod (-3.0 to -6.0D) MRSEUCVA 20/20 or better, high (> -6.0 D) MRSE
LADARVision 4000 (Alcon)P970043/S10 10/18/02Spherical Myopia: =-7.0D sph with = -0.50D cyl 6 months f/u1390.7% (includes 424 eyes =-7.0D sph with = -4.0D cyl)79.9%98.6%100% between 3 and 6 months. (n=139) (= 1.0D of intended)74.8%50/64 (78.1%)59/71 (83.1%)2/4 (50.0%)
LADARVision 4000 (Alcon)P970043/S15 6/29/04Myopic astigmatism:=-7.0D sph with= -4.0D cyl 6 months f/u2320.0%84.1%97.4%100% between 3 and 6 months. (n=232)(= 1.0D of intended)186/232(80.2%)72/79 * (91.1%)88/106 *(83.0%)33/40 *(82.5%)
VISX StarS4 WavefrontP930016/S16 5/23/03Myopic Astigmatism: = -6.0D sph with = 3.0D cyl 3 months f/u3180.3%88.4%96.2%96.7% between 3 & 6 mos. (n=275)87.1%146/157 (93%)135/161 (83.9%)N/A
Technolas 217z (B&L) P990027/S6 10/10/03Myopic astigmatism:<-8.0 D sph with < 4.0D cyl 6 months f/u3400.6%91.5%99.4%90.9 % between 3 & 6 mos. (n=340)75.9%122/127 (96.1%)161/178 (90.4%)28/35 (80.0%)
Wavelight Allegretto Wave® P020050/S004 7/26/06Myopic astigmatism: <-7.00 D sph with < 3.00 D cyl 6 months f/u1663.6%93.4%99.4%100% between 3 & 6 mos. < 1.0 D (n=156)94.6%81/83 (97.5%)79/84 (94.0)11/13 (84.6%)
*: Only includes patients whose preoperative BSCVA was 20/20 or better
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