[Impact of intracameral pressure on donor cut angles in nonmechanical Er:YAG laser trephination for penetrating keratoplasty].
OBJECTIVE
Congruent cut surfaces are a predisposition for good apposition of donor and recipient during penetrating keratoplasty (PK). The purpose of this study was to assess the impact of the intracameral pressure during nonmechanical donor trephination from the epithelial side on the cut angles for experimental human PK.


METHODS
With a Q-switched 2.94 micro m Er : YAG laser a 6 mm sized corneal donor trephination was performed subtotally in 30 human corneas using an artificial anterior chamber device allowing different intracameral pressures (10, 20, and 40 mm Hg). The cut angles were measured immediately after the trephination by ultrasound biomicroscopy (UBM) at 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 degrees /113.5 degrees /126.6 degrees (A1-UBM), 88.4 degrees /93.5 degrees /101.8 degrees (A2-UBM) and 120.4 degrees /125.1 degrees /119.3 degrees (A1-histology) with 10/20/40 mm Hg, respectively. The A2-UBM showed a significant increase of divergence with increasing intracameral pressure (p < 0.03). For A1-UBM cut angles with 10 and 20 mm Hg were significantly smaller compared to those with 40 mm Hg (p < 0.002), but there was no difference of divergence between 10 and 20 mm Hg. The A1-histology cut angle showed no correlation with intracameral pressure (p > 0.09).


CONCLUSIONS
Increasing intracameral pressure using an artificial anterior chamber during donor trephination from the epithelial side for nonmechanical PK using Er : YAG laser results in increasing divergence of cut angles. This may disturb the congruence of the cut angles in donor-recipient apposition. To achieve standardised cut angles for a good donor recipient apposition, similar normotonic intracameral pressures for donor and recipient trephination should be attempted. The UBM has the potential to analyse the cut angle immediately after subtotal trephination preserving the attempted intracameral pressure in the artificial anterior chamber. Histological analysis of the cut angles seems to lack methodological validity.
Sauer
Renate
R
Augenklinik mit Poliklinik der Friedrich-Alexander-Universität Erlangen-Nuremberg, Erlangen.
Seitz
Berthold
B
Mardin
Christian
C
Langenbucher
Achim
A
Hofmann-Rummelt
Carmen
C
Viestenz
Anja
A
Küchle
Michael
M
Naumann
Gottfried O H
GO
D000867:Anterior Chamber / Q000473:pathology / Q000503:physiopathology*; D003315:Cornea / Q000473:pathology; D019573:Epithelium, Corneal / Q000473:pathology; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D015948:Keratoplasty, Penetrating / Q000295:instrumentation*; D012016:Reference Values; D014019:Tissue Donors