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Liliane Ventura, Victor A. Lincoln, Marcio M. Mello, Daniela Sampaio, Sidney J. Faria e Sousa; Spectroscopic Measurements on Cadaveric Cornea During the Cross-Linking Procedure. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1516.
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© ARVO (1962-2015); The Authors (2016-present)
Study of the UVA transmission through the eye during the collagen cross linking procedure (CCP) and corneal dehydration influence on the method.
The 31 human corneas preserved in Optisol-GS (average of 5 days post-mortem and 571μm thickness) were washed with saline, deepithelized and cross-linked with the currently used protocol. Riboflavin solution (0.1% and 400 mOsm) was applied prior to and during exposure. The UV beam - 365nm at 3mW/cm2 - was focused directly onto the corneal stroma. Two groups were tested: G1 - 10 corneas - the optical fiber (probe from the USB2000 Ocean Optics Spectrophotometer) was placed immediately after the endothelium; G2 - 21 corneas - probe was placed 10mm away from the endothelium (crystalline lens position) and the transmission of the UVA light was measured every 4 minutes after each instillation.
The measured average transmittance of the cornea without Riboflavin was 64.1% ± 5.1% for G1; and 63.2% ± 7.5% for G2. Preceding the irradiation but after 6 applications of Riboflavin at 5min intervals (total of 30min) transmittance decreased to 21.1% ± 3.1% for G1; and 33.0% ± 8.4% for G2. The 30min of irradiation were then accompanied by an additional 6 applications of Riboflavin at 5min intervals, resulting in a further decrease in transmittance to 12.2% ± 5.1% for G1; and 21.5% ± 8.2% for G2. Three additional corneas were evaluated with the probe 1.5mm away from the endothelium, but without going under the CCP or Riboflavin instillation. Measurements of the UVA transmission were collected for 60min, every 1min, in order to study the influence of the dehydration of the cornea. An average of 3% of the transmitted UVA light was detected.
The average energy reaching the endothelium during irradiation fluctuated from 0.59 to 0.38mW/cm2, which is beyond the limits established by literature. The dehydration of the cornea that occurs during our performed measurements has no influence on the measurements. The results suggest that the endothelium safe limit for humans might be higher than established on literature, since no endothelial damage has been observed on the patients submitted to CCP. Also, concentration of UVA radiation reaching the crystalline lenses should be considered, since the cornea focus the beam on the lens, due to its high refractive power and may cause early cataract.
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