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Nandor Bekesi, Pablo Pérez-Merino, Lucía Ibares-Frías, Carmen Martinez-Garcia, Irene E Kochevar, Susana Marcos; Corneal deformation imaging of Rose Bengal-green light cross-linked rabbit corneas: in vivo vs ex vivo treatments and measurements. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1135. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
(1) To assess biomechanical changes induced in rabbit corneas by Rose Bengal green light collagen cross-linking (RB-G-CXL), (2) To compare corneal deformation following ex vivo and in vivo treatments and measurements.
The effects of RB-G-CXL on air puff corneal deformation were studied on a total of 20 rabbit eyes. New Zealand white female rabbits were monolaterally treated with RB-G-CXL in vivo, with the contralateral eyes as controls. Treatment consisted of de-epithelization, application of Rose Bengal photosensitizer (0.1% w/v) for 2 min, 300 s of green light irradiation, 30 s staining and 300 s of irradiation. The light source was a solid-state laser (532 nm, 0.25 W/cm2, Gaussian beam profile FWHM=10 mm). The limbus was masked during the treatment. Corneal deformation was evaluated in vivo 28 days post-treatment in CXL and control eyes. Measurements were repeated ex vivo following euthanasia at constant intraocular pressure (IOP=15 mmHg). Three untreated (contralateral control) eyes and 14 additional virgin ex vivo eyes were treated ex vivo 24-hours post-mortem, following an identical protocol, and measured immediately after CXL. Corneal air-puff dynamic deformation was measured by a Scheimpflug-imaging Corvis ST (Oculus, Germany) device. Deformation amplitude was taken as a metric for corneal stiffness.
Average deformation amplitude was 1.55 ± 0.26 mm in control eyes and 1.56 ± 0.21 mm in CXL eyes in vivo (p=0.9); 1.31 ± 0.05 mm in control eyes and 1.13 ± 0.03 mm in vivo-treated CXL eyes (p=0.005) that were measured ex vivo with constant IOP; 1.40 ± 0.19 mm in control eyes before and 1.30 ± 0.25 mm after ex-vivo CXL (p=0.2), 24-hours post mortem. Statistical differences (p<0.03) were also found between deformation amplitude measured in vivo and ex vivo.
Decreased corneal deformation amplitude following CXL is consistent with increased corneal stiffness, although statistical differences were only found for ex vivo measurements under constant IOP. The absence of significant differences measured in vivo, consistent with clinical findings in patients following other CXL protocols, suggests a major masking role of IOP. Rose Bengal green-light CXL appears to be a suitable method to increase corneal stiffness. However IOP should be incorporated in corneal biomechanical metrics based on air-puff corneal deformation.
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