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General Information ⬇

In PRK, the corneal epithelium is removed and the corneal stroma is ablated using an argon-fluoride excimer laser (193 nm, ultraviolet) to correct a refractive error. In laser subepithelial keratomileusis (LASEK), the epithelium is chemically separated from the Bowman layer, moved to the side before laser ablation of the stroma, and then repositioned centrally. In epithelial laser in situ keratomileusis (epi-LASIK), the epithelium is mechanically separated from the Bowman layer, moved to the side before laser ablation of the stroma, and then repositioned centrally or discarded (see Table 4.29.1).

4-29.1 Refractive Surgery Characteristics

PRKLASEKEpi-LASIKLASIKSMILE
Epithelial flap or method of stromal exposureNo flap. Epithelium removed by blade, spatula, brush, excimer laser, or dilute absolute alcohol.Epithelial flap created by 20% absolute alcohol concentrated on epithelium by marker well.Epithelial flap created by a blunt blade epi-keratome. Epithelial flap may be replaced (epi-on) or discarded (epi-off).Epithelial and stromal flap created by sharp microkeratome or femtosecond laser.No flap. Thin disc of stroma created by femtosecond laser and then mechanically extracted through small incision.
Depth of exposureBowman membraneBowman membraneBowman membraneAnterior stroma (sub-Bowman keratomileusis provides more superficial stromal exposure)Anterior stroma
Typical refractive limitationsSpherical range: −8.0D to +3.0D, cylinder range up to 3.0DSpherical range: −8.0D to +3.0D, cylinder range up to 3.0DSpherical range: −8.0D to +3.0D, cylinder range up to 3.0DSpherical range: −10.0D to +3.0D, cylinder range up to 3.0DSpherical range: −10.0D to −1.0D, cylinder range up to 3.0D
AdvantagesUseful in thin corneas, epithelial pathology. No stromal flap healing issues.Useful in thin corneas, epithelial pathology. No stromal flap healing issues.Useful in thin corneas, epithelial pathology. No stromal flap healing issues.Minimal pain, rapid visual recovery, minimal stromal haze.Minimal pain, rapid visual recovery. No flap complications. Possibly less dry eye than LASIK.
DisadvantagesPostoperative pain, slower visual recovery, higher risk of subepithelial haze.Postoperative pain, slower visual recovery, higher risk of subepithelial haze.Postoperative pain, slower visual recovery, higher risk of subepithelial haze. Not ideal with significant glaucoma or anterior corneal scarring.Not ideal for thin corneas, epithelial dystrophies, severe dry eyes, significant glaucoma. Presence of flap with possible complications (see text).Currently only for myopia or myopic astigmatism in the US. Not ideal for thin corneas or in corneas with epithelial pathology. Removal of stromal lenticule can be technically difficult. SMILE enhancements complex; reoperations often done with PRK.

Symptoms ⬆ ⬇

Early (1 to 14 Days)

Decreasing visual acuity and increased pain.

NOTE:

The induced epithelial defect at surgery, which usually takes a few days to heal, normally will cause postoperative pain. A bandage soft contact lens is used to minimize this discomfort.

Later (2 Weeks to Several Months)

Decreasing visual acuity, severe glare, and monocular diplopia.

Signs ⬆ ⬇

Corneal infiltrate and central corneal scar.

Etiology ⬆ ⬇

Early

Later

  • Undercorrection or overcorrection.
  • Corneal haze (scarring) noted in anterior corneal stroma.
  • Irregular astigmatism (e.g., central island, decentered ablation).
  • Regression or progression of refractive error.
  • Steroid-induced glaucoma or ocular hypertension (see 9.9, STEROID-RESPONSE GLAUCOMA).

Work Up ⬆ ⬇

Workup

  1. Complete ophthalmic examination, including IOP measurement by Tonopen and applanation. IOP may be underestimated given decreased corneal thickness.
  2. Refraction if change in refractive error suspected. Hard contact lens overrefraction corrects irregular astigmatism.
  3. Corneal topography and/or tomography if irregular astigmatism is suspected.

Treatment ⬆

Treatment and Follow Up

  1. Epithelial defect (see 3.2, CORNEAL ABRASION).
  2. Infectious keratitis (see 4.15, HERPES SIMPLEX KERATITIS and 4.11, BACTERIAL KERATITIS).
  3. Corneal haze: Increase steroid drop frequency. Follow up in 1 to 2 weeks. Cases of severe haze may respond to excimer laser PTK with mitomycin C.
  4. Refractive error or irregular astigmatism: Consider surface ablation enhancement. If irregular astigmatism present, topography-guided surface ablation, excimer laser PTK, or hard contact lens may be needed.
  5. Steroid-induced glaucoma. See 9.9, STEROID-RESPONSE GLAUCOMA.