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LASEK Treatment & Management

  • Author: Brad Feldman, MD; Chief Editor: Hampton Roy, Sr, MD  more...
 
Updated: Mar 31, 2014
 

Preoperative Details

Preoperative testing and workup for laser assisted subepithelial keratectomy (LASEK) include the following:

  • Uncorrected visual acuity (UCVA)
  • Best spectacle-corrected visual acuity (BSCVA)
  • Manifest and cycloplegic refraction
  • Tonometry
  • Slit lamp examination
  • Dilated fundus examination
  • Ultrasound corneal pachymetry

Corneal topography

This test, completed by approximately 93% of surgeons performing refractive procedures, is used to assess the shape and the curvature of the corneal surface.

Several types of topography are noted (see the image below).

Example of corneal topography. This image depicts Example of corneal topography. This image depicts a large inferior cone (or bulging of the cornea) along the contour of the cornea, as illustrated through the inferior red portion, which shows the steepest area of the curvature, against the blue portion, which shows the flattest portion of the curvature. Retrieved from www.opt.indiana.edu, July 22, 2006.

In placido-based topography, a series of light rings is projected onto the eye, outlining the cornea. By measuring the distance between these rings at various points, the unit creates a color-coded map that illustrates the contour of the corneal surface. Irregularities in this contour may be secondary to keratoconus or history of contact lens use.

Corneal tomography

This test, using either scanning slit-beam or Scheimpflug technology, gives information about corneal thickness and posterior corneal curvature, in addition to the anterior corneal curvature information that is presented on standard corneal topographic maps. There is some evidence that this information may help in screening for keratoconus or forme fruste keratoconus.[2]

Corneal optical coherence tomography

Although not commonly performed, literature suggests that epithelial thickness profiles can help in the diagnosis of keratoconus.[22] Anterior segment optic coherence tomography (OCT) is an instrument that can produce such maps.

Infrared pupillometry

This test, performed by approximately 44% of surgeons, allows for an accurate and reproducible measurement of pupil size. The correlation between pupil size and postrefractive symptoms of glare, halos, or night vision problems is now controversial.[3]

Wavefront analysis

The majority of ophthalmologists who perform refractive surgery use this preoperative measurement, often as part of their planning for wavefront-optimized or wavefront-guided surgical treatments.

This analysis attempts to depict optical aberration of the corneal surface in an effort to find irregular astigmatism and refractive error. The technology analyzes the interaction of light within the optical system in the eye. By specifically focusing on oscillations of light waves within the optical path to depict the exiting locus of light points as they relate to the pupillary plane, the technology may detect corneal and lenticular imperfection.

The analysis results in a 2-dimensional wavefront map, wherein a green color indicates minimal wavefront distortion, a blue color indicates myopia, and a red color indicates hyperopia.

Schirmer test

This screening test, performed by approximately 35% surgeons preoperatively, may help quantify the severity of dry eye, which is an important factor when considering any refractive surgery.

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Intraoperative Details

Several LASEK techniques are noted, and some of these techniques are described below. Each technique focuses on creating an epithelial flap under which an excimer laser is used to sculpt the corneal tissue. Camellin developed the first of these techniques, and it serves as the most widely used form of LASEK. Common to all procedures, topical anesthetic is applied prior to surgery, typically a combination of 0.05% proparacaine and 4% tetracaine. The eye is then prepped and draped in a sterile fashion with a lid speculum placed to maximize exposure.

Standard Camellin technique

The first step in this procedure involves creating a sharp, partial-thickness incision using a trephine blade to circumscribe the flap area. This blade is a finer tool than the microkeratome used in laser assisted in situ keratomileusis (LASIK) so that it enables the surgeon to cut through the outer corneal epithelium without penetrating deeper corneal layers, specifically the Bowman layer, which promotes scar tissue formation. Using the trephine, the surgeon applies constant downward pressure upon the cornea to create a 270-degree incision with a hinge.

Next, the surgeon typically uses a holding well to cover the eye with a solution of ethanol in sterile water, balanced salt solution (BSS), or physiologic solution for approximately 20-30 seconds to loosen the epithelial edges. Although the concentration of ethanol varies between surgeons, the current standard practice uses approximately 18-25% ethanol solution. This concentration has been shown to allow sharp wound edges and a clean, smooth Bowman layer. Greater concentrations of ethanol, as well as other chemical agents, such as 0.5% proparacaine, iodine, cocaine, and alkali-n-heptanol, have been associated with inflammatory response with a damaging effect on stromal keratocytes. Also, although mechanical epithelial debridement has also been shown to be effective, this technique often causes defects on the Bowman layer, which can result in corneal haze and irregularity.

Once the surface of the eye has been immersed in the alcohol appropriately, a sponge is used to dry the area and BSS is used to rinse the area. Usually, the area is also irrigated with an antihistamine in an effort to minimize the amount of histamine induced by the alcohol. An epithelial microhoe starts the flap, followed by use of the short end of an epithelial detaching spatula to detach the epithelium from the Bowman layer. Although the initial exposure to alcohol should not exceed 35 seconds, alcohol may be reapplied at this time for as long as an additional 15 seconds if the epithelial flap does not loosen easily secondary to adhesions or other epithelial irregularities.

Once loosened, the flap is folded at the 12-o'clock position to maintain hydration of the epithelium. The longer side of the spatula is then passed over the stromal surface to remove any debris. The flap typically consists of epithelium with its basement membrane attachment intact, which provides support to the epithelium throughout surgical manipulation. The point of detachment after alcohol submersion appears to be within the epithelial basement membrane or between the basement membrane and the Bowman layer.

Ablation with the 193-nm excimer laser is then carried out. The laser is focused and centered onto the pupil, enabling ablation of the tissue at the level of the Bowman layer. This is in contrast to LASIK, in which the ablative energy is transmitted to the midstromal region. During this treatment, the patient must maintain fixation. Modern lasers are typically equipped with a tracking mechanism that allows the laser to follow most small eye movements and to increase the accuracy of the ablations. Within this technique, Camellin proposed a 10% reduction in the attempted correction when treating myopia up to 10 D and a 20% reduction when treating 10-20 D relative to photorefractive keratectomy (PRK) in an effort to prevent overcorrection.

Once laser ablation is complete, another spatula is used to return the epithelial flap to its original position. Intact hemidesmosomal structures in the basal epithelium allow adhesion of the epithelial cells to ablated stroma after repositioning of the flap, a feature necessary to promote proper healing that may be disrupted by ethanol toxicity. Lastly, a soft bandage contact lens is applied, usually for 3 days. See the images below for intraoperative details.

This image depicts the epithelial flap of a porcin This image depicts the epithelial flap of a porcine eye as it is folded along its hinge to reveal the surface for laser ablation. Image courtesy of Ronald R. Krueger, MD, Cole Eye Institute, The Cleveland Clinic Foundation.
This image, taken intraoperatively on a rabbit eye This image, taken intraoperatively on a rabbit eye, depicts the creation of the epithelial flap using the microkeratome. Image courtesy of Ronald R. Krueger, MD, Cole Eye Institute, The Cleveland Clinic Foundation.
Image of corneal haze following refractive surgery Image of corneal haze following refractive surgery, as viewed through a slit lamp. Image courtesy of Ronald R. Krueger, MD, Cole Eye Institute, The Cleveland Clinic Foundation.

Azar flap technique

The Azar flap technique is similar to the standard Camellin technique, as described above, with the soaking of the corneal surface in ethanol, except this technique uses either one arm of a jeweler's forceps or one arm of a modified Vannas scissors to delineate the wound edge rather than a trephine blade. This difference allows customized variations for different corneal types.

The epithelial flap is pushed aside using a dry, nonfragmenting cellulose sponge, after which the excimer laser ablates the tissue appropriately. In this procedure, an anterior chamber cannula is used to hydrate the stroma and to float the epithelial flap back to its original position, after which the area is allowed to dry for 2-5 minutes.

Vinciguerra Butterfly technique

This technique maintains the limbal connection of the epithelial stem cells and the limbal vascular connections in an effort to increase epithelial viability, thereby improving visual recovery time and reducing discomfort.

Using a special spatula, a thin paracentral epithelial incision is made from the 8-o'clock position to the 11-o'clock position. Then, 20% alcohol in BSS is placed on the cornea for 5-30 seconds, allowing the epithelium to be separated from the Bowman layer. The spatula is used to further separate the epithelium from its underlying layer, from the center to the periphery in both directions, thereby creating 2 flaps from the original single paracentral line. The surgeon then retracts the sheets of epithelium toward the limbus. While holding these sheets in place using the retractor, the surgeon uses the excimer laser to ablate the tissue. The surface is smoothed with a hyaluronic acid masking solution, and the stretched epithelium is repositioned with overlapping margins.

McDonald gel-assisted technique

This alcohol-free technique uses viscous hydroxypropyl cellulose 0.3% (GenTeal Gel, Novartis Ophthalmics) to allow the separation of the epithelial flap and to prevent dehydration. After applying this gel below the epithelium with a cannula, with fine holes along the side, the cells are stripped using microkeratome suction. Within this procedure, 5% sodium chloride may be used to stiffen the epithelial cells before their manipulation, as the gel does not offer this property.

Once the gel is in position, the cells may be manipulated as the surgeon uses Vannas scissors to cut down the middle of the cornea. Within the gel cushion, the epithelium is pushed to the periphery without compromising cellular viability. After the flap has been created and folded, the gel is removed from the Bowman layer using a wet Weck-cel sponge, after which ablation may be performed. Once laser ablation is complete, the gel is again applied so that the epithelial sheet may be repositioned and a bandage contact lens may be placed.

Amolis cruciform technique

The Amolis cruciform technique is very similar to the standard Camellin technique, except a rotating microbrush is used to cut a cross into the epithelium to allow creation of the flap. Like the Butterfly technique, this method is aimed to protect the epithelial limbal stem cells and vascular connections in an effort to increase epithelial viability.

Epipolis laser in situ keratomileusis or epikeratome laser-assisted keratomileusis

Epipolis laser in situ keratomileusis or epikeratome laser-assisted keratomileusis (epi-LASIK) was developed by Pallikaris as a revision of the traditional LASEK procedure. Within this technique, the use of alcohol to float the flap is replaced with an epikeratome tool, which mechanically cuts and lifts the flap of epithelium. As discussed above, alcohol may cause potentially toxic responses in the cornea. This technique attempts to use the principles of LASEK without the use of alcohol, thereby promoting faster healing and less pain for patients. Additionally, the epikeratome leads to a precise, reproducible separation within the epithelium, thereby further eliminating many of the flap complications associated with LASIK.

Epi-LASEK technique

The theoretical advantage of Epi-LASIK over LASEK is the avoidance of alcohol and its potentially negative effects on flap viability. However, without the use of alcohol, the epithelium in the peripheral flap remains adherent, and flap separation may be difficult. Camellin developed Epi-LASEK, a technique that combines alcohol application with epikeratome use for flap creation.[4]

Sub-Bowman keratomileusis (SBK)

Also known as “thin-flap” LASIK, this technique aims to combine the benefits of surface ablation and LASIK. Instead of creating a epithelial flap, in SBK, a thin anterior flap (90-110 μ m) of epithelium, the Bowman layer, and the stroma is created with a femtosecond laser, which is a tool that provides a level of precision in flap creation previously unattainable with the microkeratome. This technique theoretically maintains both the postoperative comfort and flap viability advantages of LASIK while minimizing the depth of ablation and loss of corneal structural integrity seen in LASIK. Possible disadvantages of SBK compared with LASEK and surface ablative procedures include increased ablation depths and decreased corneal sensitivity. The risk of flap complications may be increased compared with standard LASIK.

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Postoperative Details

In all of the procedures discussed above, a soft bandage contact lens is placed on the cornea at the closing of surgery and remains on the eye for several days to allow complete re-epithelialization. Healing of the corneal surface defect normally takes 3-10 days. This healing time is dependent on numerous factors, including the size of the area treated, the baseline health of the cornea, the patient's immune response, the concentration and the duration of medications applied intraoperatively, and the presence of coexisting medical problems, specifically diabetes. Approximately 78% of patients show complete closure of the defect by day 3 and 98.8% by day 7. If the contact lens is removed before closure is complete, the flap may peel away with the lens. If re-epithelialization remains incomplete at 3 days, the original lens may be replaced by a new lens for 3 additional days.

Topical steroids and antibiotics should be used until the defect is healed to limit inflammation and prevent infection. Steroids are typically continued for 3 weeks or longer, up to several months.

Typically, approximately 50% of patients experience mild-to-moderate postoperative pain, lasting 1-2 days postoperatively. This percentage may be lower compared with PRK but is definitely higher as compared with LASIK.

Functional vision recovery follows a pattern similar to re-epithelialization, also taking 3-10 days. This period is similar to PRK but exceeds the less than 24-hour recovery associated with LASIK.

In addition, the most commonly encountered adverse effect is light sensitivity with halo effect. This occurrence is similar to that seen in LASIK and PRK.

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Complications

Although laser assisted subepithelial keratectomy (LASEK) avoids many of the flap-associated complications of laser assisted in situ keratomileusis (LASIK), including free caps, incomplete pass of the microkeratome, flap wrinkles, epithelial ingrowth, flap melt, interface debris, corneal ectasia, and diffuse lamellar keratitis, LASEK has its own disadvantages.

Complications associated with LASEK include the following:

  • Conversion of procedure into photorefractive keratectomy (PRK) - 10%
    • The 50-µm thin epithelial flap may not be strong enough to be repositioned and may instead need to be removed, thus converting the procedure into PRK.
    • Although most patients who undergo LASEK are within the parameters of PRK and are not likely to suffer adverse effects of this complication, those patients who are high myopes may have a greater likelihood of corneal haze associated with PRK.
  • Pain (greater than LASIK in 80% of patients)
  • Epithelial defects
  • Corneal scarring/haze (< 1-2%)
    • Although LASEK may carry a decreased rate of corneal haze relative to PRK, it may still develop secondary to an inflammatory response to the surgical manipulation of the corneal surface.
    • The inflammation leads to the formation of an opacified cellular layer that appears as a white haze and restricts light from transmitting to the back of the eye, thus causing a defect in vision (see the image below).
      Image of corneal haze following refractive surgery Image of corneal haze following refractive surgery, as viewed through a slit lamp. Image courtesy of Ronald R. Krueger, MD, Cole Eye Institute, The Cleveland Clinic Foundation.
    • The risk of scar formation increases with increasing ablation depth, and scars are common when treating more than 8 D of myopia.
  • Keratitis (0.5-1%)
    • The risk of keratitis is theoretically less than that of PRK, as the retained epithelial flap should act as a protective barrier. Postoperative infection is more likely when epithelial coverage is incomplete or when the surgical duration is longer than average.
    • Additionally, contact lenses may serve as a source of infection, as they are known to often be contaminated with microorganisms. Likely, because contact lenses are not used postoperatively in LASIK, LASIK has a lower incidence of keratitis (about 0.2%).
    • The occurrence of causative organisms of LASEK-associated keratitis is as follows:
      • Gram-positive bacteria (55.6%)
      • Atypical mycobacteria (19.4%)
      • Gram-negative bacteria (13.9%)
      • Fungal (< 1%)
      • Viral (< 1%)
  • Dry eye syndrome associated with recurrent erosions
    • This complication is secondary to decreased corneal sensation due to corneal denervation. It may last from a few weeks to 1 year, although, on average, it lasts 1-4 weeks.
    • Although this complication occur in LASEK and LASIK, it is more likely to be associated with a longer duration in LASIK.
  • Overcorrection (1%, incidence similar to LASIK and PRK)
  • Undercorrection (10-15%, incidence similar to LASIK and PRK)
  • Macular cyst formation (< 0.1%)
  • Irregular astigmatism (< 1%): This complication is secondary to decentration of the laser optical zone or uneven healing, leading typically to a wavy corneal surface.
  • Regression
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Outcome and Prognosis

The United States Army WRESP Survey (2000-2003) concluded that photorefractive keratectomy (PRK), laser assisted in situ keratomileusis (LASIK), and laser assisted subepithelial keratectomy (LASEK) achieved comparable postoperative outcomes.[5] LASEK, specifically, has been found to be an effective procedure, with 76% efficacy in attaining 20/20 uncorrected visual acuity (UCVA) and 99% efficacy in attaining 20/40 UCVA. In a study of 421 eyes, an efficacy index comparing preoperative best spectacle-corrected visual acuity (BSCVA) to postoperative UCVA found improvement in 94.7% of patients after LASEK.

LASEK is also relatively predictable, with 83% achievement within 0.5 D of the target refraction and 98.4% within 1 D at the 6-month follow-up visit in 152 patients. At 4 years out, approximately 7% of patients need secondary surgical correction, predominantly because of the initial undercorrection in those with a high preoperative refractive error. The image below shows a more detailed table comparing the refractive techniques.

Relative differences of laser assisted in situ ker Relative differences of laser assisted in situ keratomileusis (LASIK), laser assisted subepithelial keratectomy (LASEK), and photorefractive keratectomy (PRK). Adapted from Taneri S, et al: Evolution, techniques, clinical outcomes, and pathophysiology of LASEK: review of the literature. Surv Ophthalmol 2004 Nov-Dec; 49(6): 576-602.

Although controversy surrounds the relative benefit of LASEK compared with PRK or EpiLASIK, a meta-analysis revealed no significant difference between LASEK outcomes and PRK outcomes over time.[6] Both procedures are equally acceptable and likely have similar outcomes to EpiLASIK.

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Future and Controversies

Many refractive surgeons view laser assisted subepithelial keratectomy (LASEK) as the answer for patients who desire laser correction but who are not ideal candidates for laser assisted in situ keratomileusis (LASIK), most commonly secondary to corneal thinning or irregularities. However, these patients must be educated that many of the risk factors associated with LASIK apply to LASEK as well.

Although LASEK avoids many of the flap-associated complications of LASIK, such as free caps, incomplete pass of the microkeratome, flap wrinkles, epithelial ingrowth, and flap melt, it continues to have its own disadvantages, specifically postoperative discomfort and prolonged visual recovery as the patient awaits complete epithelial closure. Additionally, although probably lower than in photorefractive keratectomy (PRK), the risk of corneal haze continues.

Furthermore, like LASIK and PRK, LASEK is a relatively new procedure, developed within the past decade. Although the use of the excimer laser is FDA approved for LASIK, it is accepted as only an off-label use for LASEK. No studies have been conducted on the long-term effects of these procedures on the cornea, so their final effects, stability, and prognosis may only be theorized.

Of the choices, no one procedure has been established as ideal for all patients. Therefore, each surgeon must determine which refractive technique is appropriate on an individual basis.

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Contributor Information and Disclosures
Author

Brad Feldman, MD Cornea, Cataract, and Refractive Surgeon, Philadelphia Eye Associates

Brad Feldman, MD is a member of the following medical societies: American Academy of Ophthalmology, American Society of Cataract and Refractive Surgery, Association for Research in Vision and Ophthalmology

Disclosure: Nothing to disclose.

Coauthor(s)

Reecha Sachdeva, MD Resident Physician, Cole Eye Institute, Cleveland Clinic

Reecha Sachdeva, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Ophthalmology, American Medical Student Association/Foundation

Disclosure: Nothing to disclose.

Sanjeev Grewal, MD, FRCSC Associate Professor of Ophthalmology, Chief, Cornea and Refractive Surgery, Residency Program Director, Department of Ophthalmology, Medical Faculty Associates, George Washington University

Sanjeev Grewal, MD, FRCSC is a member of the following medical societies: American Academy of Ophthalmology, Association for Research in Vision and Ophthalmology, College of Physicians and Surgeons of Ontario, Royal College of Physicians and Surgeons of Canada

Disclosure: Nothing to disclose.

Ronald R Krueger, MD Medical Director, Department of Refractive Surgery, Division of Ophthalmology, Cole Eye Institute, Cleveland Clinic Foundation

Ronald R Krueger, MD is a member of the following medical societies: American Academy of Ophthalmology, American Medical Association, American Society of Cataract and Refractive Surgery, Association for Research in Vision and Ophthalmology, International Society of Refractive Surgery, SPIE

Disclosure: Nothing to disclose.

Specialty Editor Board

Simon K Law, MD, PharmD Clinical Professor of Health Sciences, Department 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, Association for Research in Vision and Ophthalmology, American Glaucoma Society

Disclosure: Nothing to disclose.

Louis E Probst, MD, MD Medical Director, TLC Laser Eye Centers

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

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, Pan-American Association of Ophthalmology

Disclosure: Nothing to disclose.

Additional Contributors

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, Association for Research in Vision and Ophthalmology

Disclosure: Received grant/research funds from Alcon Labs for independent contractor; Received grant/research funds from Abbott Medical Optics for independent contractor; Received ownership interest from Acufocus for consulting; Received ownership interest from WaveTec for consulting; Received grant/research funds from Topcon for independent contractor; Received grant/research funds from Avedro for independent contractor; Received grant/research funds from ReVitalVision for independent contractor.

References
  1. Scerrati E. Laser in situ keratomileusis vs. laser epithelial keratomileusis (LASIK vs. LASEK). J Refract Surg. 2001 Mar-Apr. 17(2 Suppl):S219-21. [Medline].

  2. Wolf A, Abdallat W, Kollias A, Frohlich SJ, Grueterich M, Lackerbauer CA. Mild topographic abnormalities that become more suspicious on Scheimpflug imaging. Eur J Ophthalmol. 2009 Jan-Feb. 19(1):10-7. [Medline].

  3. Schmidt GW, Yoon M, McGwin G, Lee PP, McLeod SD. Evaluation of the relationship between ablation diameter, pupil size, and visual function with vision-specific quality-of-life measures after laser in situ keratomileusis. Arch Ophthalmol. 2007 Aug. 125(8):1037-42. [Medline].

  4. Camellin M, Wyler D. Epi-LASIK versus epi-LASEK. J Refract Surg. 2008 Jan. 24(1):S57-63. [Medline].

  5. Hammond MD, Madigan WP Jr, Bower KS. Refractive surgery in the United States Army, 2000-2003. Ophthalmology. 2005 Feb. 112(2):184-90. [Medline].

  6. Zhao LQ, Wei RL, Cheng JW, Li Y, Cai JP, Ma XY. Meta-analysis: clinical outcomes of laser-assisted subepithelial keratectomy and photorefractive keratectomy in myopia. Ophthalmology. 2010 Oct. 117(10):1912-22. [Medline].

  7. Adams GW, Hubbard AD. Kennerley Bankes Clinical Ophthalmology: A Text and Color Atlas. 4th ed. 1999.

  8. [Guideline] American Academy of Ophthalmology Refractive Management/Intervention Panel. Refractive errors & refractive surgery. San Francisco (CA): American Academy of Ophthalmology; 2007. [Full Text].

  9. Aydin B, Cagil N, Erdogan S, Erdurmus M, Hasiripi H. Effectiveness of laser-assisted subepithelial keratectomy without mitomycin-C for the treatment of high myopia. J Cataract Refract Surg. 2008 Aug. 34(8):1280-7. [Medline].

  10. Brown MC, Schallhorn SC, Hettinger KA, Malady SE. Satisfaction of 13,655 patients with laser vision correction at 1 month after surgery. J Refract Surg. 2009 Jul. 25(7 Suppl):S642-6. [Medline].

  11. Chen KH, Hsu WM, Lee SM, Lai JY, Li YS. Laser-assisted subepithelial keratectomy for dry eye associated with soft contact lenses. J Cataract Refract Surg. 2005 Dec. 31(12):2299-305. [Medline].

  12. Cleveland Clinic Foundation Health Information Center. LASEK: Overview. 2006. [Full Text].

  13. Gimbel HV, Penno EEA. Trends and Techniques. LASIK Complications. 3E. 184-90.

  14. Horwath-Winter J, Vidic B, Schwantzer G, Schmut O. Early changes in corneal sensation, ocular surface integrity, and tear-film function after laser-assisted subepithelial keratectomy. J Cataract Refract Surg. 2004 Nov. 30(11):2316-21. [Medline].

  15. Kanski, Menon, Boulton. A Systematic Approach. Clinical Ophthalmology. 5th ed. 2003. 56-63.

  16. Laplace O, Bourcier T, Chaumeil C, Cardine S, Nordmann JP. Early bacterial keratitis after laser-assisted subepithelial keratectomy. J Cataract Refract Surg. 2004 Dec. 30(12):2638-40. [Medline].

  17. Lee HK, Lee KS, Kim JK, Kim HC, Seo KR, Kim EK. Epithelial healing and clinical outcomes in excimer laser photorefractive surgery following three epithelial removal techniques: mechanical, alcohol, and excimer laser. Am J Ophthalmol. 2005 Jan. 139(1):56-63. [Medline].

  18. Samalonis LB. LASEK techniques. EyeWorld. 2002. 7(9):31-32.

  19. Sandoval HP, de Castro LE, Vroman DT, Solomon KD. Refractive Surgery Survey 2004. J Cataract Refract Surg. 2005 Jan. 31(1):221-33. [Medline].

  20. Taneri S, Zieske JD, Azar DT. Evolution, techniques, clinical outcomes, and pathophysiology of LASEK: review of the literature. Surv Ophthalmol. 2004 Nov-Dec. 49(6):576-602. [Medline].

  21. Vinciguerra P, Camesasca FI, Torres IM. Transition zone design and smoothing in custom laser-assisted subepithelial keratectomy. J Cataract Refract Surg. 2005 Jan. 31(1):39-47. [Medline].

  22. Li Y1, Tan O, Brass R, Weiss JL, Huang D. Corneal epithelial thickness mapping by Fourier-domain optical coherence tomography in normal and keratoconic eyes. Ophthalmology. Dec 2012. 119 (12):2425-33. [Full Text].

 
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Illustration of myopia.
Illustration of hyperopia.
Illustration of an astigmatic cornea.
Illustration depicting the layers of the human cornea.
Histologic slide of the human cornea identifying its layers: (1) corneal stratified squamous epithelium with underlying Bowman layer, (2) stroma with keratocytes dispersed throughout, (3) Descemet membrane, and (4) single layer of endothelium. Image courtesy of Mission for Vision. Retrieved from http://www.missionforvisionusa.org/anatomy/2005/10/cornea.html.
Example of corneal topography. This image depicts a large inferior cone (or bulging of the cornea) along the contour of the cornea, as illustrated through the inferior red portion, which shows the steepest area of the curvature, against the blue portion, which shows the flattest portion of the curvature. Retrieved from www.opt.indiana.edu, July 22, 2006.
This image depicts the epithelial flap of a porcine eye as it is folded along its hinge to reveal the surface for laser ablation. Image courtesy of Ronald R. Krueger, MD, Cole Eye Institute, The Cleveland Clinic Foundation.
This image, taken intraoperatively on a rabbit eye, depicts the creation of the epithelial flap using the microkeratome. Image courtesy of Ronald R. Krueger, MD, Cole Eye Institute, The Cleveland Clinic Foundation.
This image depicts the epithelial flap created in laser assisted subepithelial keratectomy (LASEK) surgery on a rabbit eye. Image courtesy of Ronald R. Krueger, MD, Cole Eye Institute, The Cleveland Clinic Foundation.
Image of corneal haze following refractive surgery, as viewed through a slit lamp. Image courtesy of Ronald R. Krueger, MD, Cole Eye Institute, The Cleveland Clinic Foundation.
Relative differences of laser assisted in situ keratomileusis (LASIK), laser assisted subepithelial keratectomy (LASEK), and photorefractive keratectomy (PRK). Adapted from Taneri S, et al: Evolution, techniques, clinical outcomes, and pathophysiology of LASEK: review of the literature. Surv Ophthalmol 2004 Nov-Dec; 49(6): 576-602.
 
 
 
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