Purchase this article with an account.
Sean McCafferty, Jim Schwiegerling; Laser thermal load induces characteristic changes in the corneal surface including asphericity. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3716.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Examine excimer laser thermal load as the elusive etiology for corneal asphericity.
Cadaveric porcine eyes were pressurized and stabilized for processing and imaging. Both a scanning excimer laser and a CO2 laser were used to delivered a uniform disk of radiant energy to the exposed corneal stromal surface. Thermal load was determined by measuring corneal surface temperature during irradiation. Corneal profilometry was measured with broad-band optical interferometry before and after laser irradiation. Photomicrographs of the stromal surface were taken before and after irradiation and the images were superimposed to examine changes in positional marks examining mechanical alterations in the stromal surface.
Uniform scanning excimer laser ablation to corneal stroma produces a significant central steepening and peripheral flattening in the central 3mm diameter. Q-values, measuring asphericity in the central 2mm of the cornea, were significantly lower pre-ablation than post ablation (-5.03+/-4.01vs.-52.4+/-18.7,respectively). Surface roughness increased significantly following ablation. The central 2mm of the stromal surface contracted by 2.21%+/-0.80% at a sustained temperature of 5C. Isolated thermal load from uniform CO2 laser irradiation without ablation also produces central corneal steepening and paracentral flattening in the central 3mm diameter. Q-values, measuring asphericity in the central 2mm of the cornea increased significantly and it was correlated with the temperature rise (R2=0.767). Surface roughness increased significantly and was also correlated with temperature rise (R2=0.851). The central stromal surface contracted and underwent characteristic morphologic changes with the applied thermal load which correlated well with the temperature rise (R2=0.818).
: The thermal load created by laser irradiation creates a characteristic spectrum of morphologic changes on the porcine corneal stromal surface which correlates to the temperature rise and is not seen inorganic, isotropic material. The highly similar surface changes seen with both lasers are likely indicative of temperature induced transverse collagen fibril contraction and stress re-distribution. Refractive procedures which produce significant thermal load should be cognizant of these morphological changes. Corneal thermal response:
This PDF is available to Subscribers Only