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R. Sauer, B. Seitz, C. Mardin, A. Langenbucher, C. Hofmann-Rummelt, A. Viestenz, M. Küchle, G.O. Naumann; Impact of Intracameral Pressure on Donor Cut Angles in Nonmechanical Er: YAG Laser Trephination for Penetrating Keratoplasty . Invest. Ophthalmol. Vis. Sci. 2003;44(13):669.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To study the impact of different intracameral pressures during nonmechanical donor trephination on the cut angles using Er:YAG laser for experimental human penetrating keratoplasty. Methods: With a Q-switched 2.94 µm Er:YAG laser a 6 mm diameter corneal donor trephination was performed in 30 human corneas using an artificial anterior chamber device allowing different intracameral pressures (10, 20, and 40 mmHg). The cut angles were measured immediately after the trephination by ultrasound biomicroscopy (UBM) in four quadrants: between trephination cut and corneal epithelium (angle 1 = A1-UBM) and between trephination cut and horizontal plane (angle 2 = A2-UBM). The positions of the measures were marked, the corneas were fixed in a buffered 10% paraformaldehyde solution, and the same positions were analyzed by histology. The histological cuts were digitized, the images printed, and the cut angles measured in paper (A1-histology). Results: Mean angles were 111.6° / 113.5° / 126.6° (A1-UBM), 88.4° / 93.5° / 101.8° (A2-UBM) and 120.4° / 125.1° / 119.3° (A1-histology) with 10 / 20 / 40 mmHg, respectively. The A2-UBM showed a significant proportional increase of divergence with increasing intracameral pressure (p<0.03). For A1-UBM cut angles with 10 and 20 mmHg were significantly smaller compared to those with 40 mmHg (p<0.002), but there was no difference of divergence between 10 and 20 mmHg. The A1-histology cut angle showed no correlation with increasing intracameral pressure (p>0.09). Conclusions: Increasing intracameral pressure using an artificial chamber during donor trephination for nonmechanical penetrating keratoplasty using Er:YAG laser results in increasing divergence of cut angles, which may disturb the congruence of donor-recipient apposition. The UBM can determine a real and credible cut angles analysis because the cut angle is measured immediately after trephination preserving the attempted intracameral pressure in the artificial anterior chamber. Histological analysis of cut angles seems to lack methodological validity.
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