title: Noncontact laser photothermal keratoplasty. II: Refractive effects and treatment parameters in cadaver eyes.
abstract: BACKGROUND
  Noncontact laser photothermal keratoplasty may provide a new alternative for the treatment of myopia, hyperopia, and astigmatism. The purpose of this article is to study the refractive effect that laser photoablation keratoplasty is capable of producing on a normal human cadaver cornea, including the relationship between the keratometric changes and laser treatment parameters.
  
  
  METHODS
  The human cadaver eyes were treated with a holmium laser (pulsed Ho:YAG, 2.10 microns, 250 microseconds) coupled to a maskable, polyprismatic delivery system mounted on either an optical bench or a slit-lamp microscope. Using a topographic videokeratography system, we first investigated the refractive effect that noncontact laser photothermal keratoplasty would produce on a normal cadaver cornea. We then studied the keratometric changes produced by different radiant exposure levels at a fixed treatment pattern, as well as by different treatment patterns at a fixed radiant exposure level. Finally, we studied the possible therapeutic application of laser photothermal keratoplasty for correcting high postoperative astigmatism on a cadaver eye model.
  
  
  RESULTS
  For the single-pulse 3-millimeter ring of eight-spot treatment, the keratometric power of the cornea initially increased with the radiant exposure and peaked at 26 J/cm2. The refractive effect was increased by projecting an additional set of eight spots equidistant between the first eight spots on the same diameter ring. Eighteen J/cm2 was the minimal radiant exposure required to produce consistent and predictable keratometric changes. The corneas were flattened using treatment patterns smaller than or equal to 3 mm in diameter and steepened using treatment patterns larger than or equal to 5 mm in diameter. A transition zone between 4 and 5 mm was observed in which minimal and unpredictable keratometric changes of the central cornea occurred. The surgically-induced astigmatism (> 10.00 D) was corrected by progressive laser photothermal keratoplasty treatments.
  
  
  CONCLUSIONS
  Laser photothermal keratoplasty can acutely steepen and flatten the cornea in human cadaver eyes.
authors.affiliation: Department of Ophthalmology, University of California, Irvine, CA 92715.
authors.forename: G
authors.initials: G
authors.lastname: Simon
authors.forename: Q
authors.initials: Q
authors.lastname: Ren
authors.forename: J M
authors.initials: JM
authors.lastname: Parel
mesh_terms: D001251:Astigmatism / Q000601:surgery; D002102:Cadaver; D016039:Corneal Transplantation; D006801:Humans; D066298:In Vitro Techniques; D053685:Laser Therapy; D012029:Refraction, Ocular; D016896:Treatment Outcome