June 2013
Volume 54, Issue 15
Free
ARVO Annual Meeting Abstract  |   June 2013
Laser thermal load induces characteristic changes in the corneal surface including asphericity
Author Affiliations & Notes
  • Sean McCafferty
    Arizona Eye Consultants, Tucson, AZ
  • Jim Schwiegerling
    Arizona Eye Consultants, Tucson, AZ
  • Footnotes
    Commercial Relationships Sean McCafferty, None; Jim Schwiegerling, Alcon Laboratories (F), Wavetec (F), Visioneering (C)
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2013, Vol.54, 3716. doi:
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      Sean McCafferty, Jim Schwiegerling; Laser thermal load induces characteristic changes in the corneal surface including asphericity. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3716.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract
 
Purpose
 

Examine excimer laser thermal load as the elusive etiology for corneal asphericity.

 
Methods
 

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.

 
Results
 

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).

 
Conclusions
 

: 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:

     
Keywords: 678 refractive surgery • 681 refractive surgery: corneal topography • 684 refractive surgery: optical quality  
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