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Y. Mandel, D. Zadok, A. Bitman, G. Peleg; Measuring Corneal Cross-Linking by Terahertz Radiation. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4990.
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Corneal cross-linking is an emerging treatment modality used for corneal reinforcement in cases of keratoconus or other ecstatic corneal disorder. Currently, there is no non-destructive method to control or measure treatment effect on corneal tissue. The aim of this study was to measure the effect of corneal cross linking on terahertz transmittance in order to evaluate the feasibility of this method for clinical control of crosslinking effect.
Porcine corneas were treated within 8 hours of enucleation with 0.1% riboflavin in 20% dextran solution and radiated by UV light (365nm) 3.0mW/cm2 for 30 minutes. Control group were treated by the riboflavin without UV radiation. Transmittance tests were performed with a terahertz time domain spectrometer (TR-2000, Picometrix). The terahertz spectrum covered 0.05 to 2 terahertz range. The samples were positioned at a focus of a 10 cm focal length Teflon lens. The transmission was first measured through a circular pinhole as a reference. Then, after mounting the corneas in front of the pinhole, the transmission of each cornea was measured. The terahertz amplitude transmitted through an empty pinhole was 0.55 V. Following the first transmittance test, corneas were dehydrated at a controlled temperature and humidity room (20.60C, 63.3% humidity) and were re-examined at times 90, 180, 1440 minutes.
Transmitted peak amplitude were significantly higher for the treated corneas as compared to control cornea at time 0 [0.029 Vs. 0.013, P<0.001], 90 [0.064 Vs. 0.029, P<0.001], 180 [0.147 Vs. 0.082, P=0.02]. There was a small non-statistically significant difference for the totally de-hydrated corneas [0.414 Vs. 0.832, P=0.07].
Corneal cross linking induced higher terahertz transmittance. The effect was more pronounced in hydrated corneas as compared to dehydrated corneas. The mechanism of this effect might be related to reduced water content in treated corneas as compared to control group or to other effects of cross linking on corneal lamellas.
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