NONCONTACT LASER PHOTOTHERMAL KERATOPLASTY .2. REFRACTIVE EFFECTS ANDTREATMENT PARAMETERS IN CADAVER EYES

BACKGROUND: Noncontact laser photothermal keratoplasty may provide a n ew alternative for the treatment of myopia, hyperopia, and astigmatism . The purpose of this article is to study the refractive effect that l aser photoablation keratoplasty is capable of producing on a normal hu man cadaver cornea, including the relationship between the keratometri c changes and laser treatment parameters. METHODS: The human cadaver e yes were treated with a holmium laser (pulsed Ho:YAG, 2.10 mum, 250 mu s) coupled to a maskable, polyprismatic delivery system mounted on eit her an optical bench or a slit-lamp microscope. Using a topographic vi deokeratography system, we first investigated the refractive effect th at noncontact laser photothermal keratoplasty would produce on a norma l cadaver cornea. We then studied the keratometric changes produced by different radiant exposure levels at a fixed treatment pattern, as we ll as by different treatment patterns at a fixed radiant exposure leve l. Finally, we studied the possible therapeutic application of laser p hotothermal keratoplasty for correcting high postoperative astigmatism on a cadaver eye model. RESULTS: For the single-pulse 3-millimeter ri ng of eight-spot treatment, the keratometric power of the cornea initi ally increased with the radiant exposure and peaked at 26 J/cm2. The r efractive effect was increased by projecting an additional set of eigh t spots equidistant between the first eight spots on the same diameter ring. Eighteen J/cm2 was the minimal radiant exposure required to pro duce consistent and predictable keratometric changes. The corneas were flattened using treatment patterns smaller than or equal to 3 mm in d iameter and steepened using treatment patterns larger than or equal to 5 mm in diameter. A transition zone between 4 and 5 mm was observed i n which minimal and unpredictable keratometric changes of the central cornea occurred. The surgically-induced astigmatism (> 10.00 D) was co rrected by progressive laser photothermal keratoplasty treatments. CON CLUSIONS: Laser photothermal keratoplasty can acutely steepen and flat ten the cornea in human cadaver eyes.