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Refractive Corneal Surgery
Aka: Refractive Corneal Surgery, Refractive Surgery, Laser Thermal Keratoplasty, Intrastromal corneal ring, Intacs, Phakic Intraocular Lens
- See Also
- Refractive Error
- Epidemiology
- Incidence: 600,000 procedures per year in U.S. (peaked at 1.4 Million in 2006)
- Age: 30-40 years old most typical
- Indications
- Refractive Error Correction
- Contraindications
- See Laser In-Situ Keratomileusis (LASIK)
- Background: Refractive Surgery reshapes Cornea
- Myopia (Near-sightedness)
- Eye globe is too long, and light rays focus in front of Retina
- Surgery flattens Cornea to focus light further back
- Hyperopia (Far-sightedness)
- Eye globe is too short, and light rays focus behind Retina
- Surgery steepens Cornea to focus light closer
- Astigmatism
- Cornea is non-spherical with uneven surface
- Surgery evens out Cornea, directs light at Retina
- Background
- See Cornea for anatomy
- Cornea undergoes computer-aided reshaping with multiple different techniques
- For Myopia, Corneal curvature decreased by removing central Corneal tissue
- For Hyperopia, Corneal curvature increased by removing peripheral Corneal tissue (less predictable)
- For Astigmatism, Corneal surface is smoothed
- Refractive Surgery mechanism
- Pulsatile laser (excimer laser) is used to a pre-programmed section of Corneal Stroma
- Techniques
- Laser In-Situ Keratomileusis (LASIK)
- Contact Lens sized flap is made into the Corneal Epithelium (via femtosecond/cutting laser or microtome)
- Cornea epithelial flap is folded over, allowing laser access to the underlying Corneal Stroma
- Corneal Stroma is removed via pulsatile (excimer) laser
- Corneal flap is folded back into place and spontaneously re-adheres
- Variant methods use Lenticule (lens-shaped) extraction: FLEx, SMILE
- Photorefractive Keratectomy (PRK)
- Epithelial surface is scraped away allowing access to Corneal Stroma (but causing a large Corneal Abrasion)
- As with LASIK, Corneal Stroma is removed via pulsatile (excimer) laser
- Replaced by LASIK for most patients
- LASEK
- Variant of PRK, in which the epithelial layer is removed with Alcohol
- Radial Keratotomy (RK)
- Replaced by LASIK
- Laser Thermal Keratoplasty (LTK)
- YAG laser mediated radial spot placement
- Heats Cornea and shrinks stromal collagen
- Modifies anterior Corneal curvature
- Corrects presbyopic patient with <4 D Refraction
- Intrastromal corneal ring (ICR or Intacs)
- Polymethylmethacrylate (PMMA) ring implanted
- Flattens central Cornea
- Corrects low Myopia (<3 D)
- Surgery easily adjustable
- No risk of central Corneal scarring
- Phakic Intraocular Lens
- Plastic intraocular lens
- Placed anterior to natural crystalline lens
- Corrects high Myopia and Hyperopia
- References
- Bower (2001) Am Fam Physician 64(7):1183-90 [PubMed]
- Sanders (1998) J Cataract Refract Surg 24:607 [PubMed]
- Schanzlin (1997) Ophthalmology 104:1067 [PubMed]
- Wilkinson (2017) Am Fam Physician 95(10): 637-44 [PubMed]
- (1999) Med Lett Drugs Ther 41(1068):121-3 [PubMed]