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Impressum
Anterior chamber angle biometry with ultrasound biomicroscopy after diode laser thermal keratoplasty
Stoiber J., Ebner J., Ruckhofer J., Hitzl W., Grabner G.
Landesklinik für Augenheilkunde und Optometrie, St.Johanns Spital, Landeskliniken Salzburg, Österreich
Background: Diode laser thermal keratoplasty is a minimal invasive
procedure to correct hyperopia and hyperopic astigmatism. Using a contact
focusing hand-piece, para-centrally arranged spot coagulation of the corneal
stroma can be accurately achieved. Collagen fibers of the corneal stroma
shorten inducing a structural change that results in a steepening of the
central corneal and an increase in the refractive power. We examined the
effect of the procedure on the geometry of the anterior chamber angle
with ultrasound biomicroscopy.
Methods: In 6 patients (age: 20-58 years) a Rodenstock DTK®
(ProLaser Medical Systems) was used for hyperopia correction (n=3) or
correction of hyperopic astigmatism (n=3). Hyperopic treatment was performed
using a single or double ring pattern, hyperopic astigmatism was treated
with additional spots in each of the flat half meridians. Ultrasound biomicroscopic
measurements of the chamber angle were obtained preoperatively and three
months after surgery using a Humphrey UBM 840 system with a 50-MHz transducer.
Quantitative measurements were performed at three, six, nine and twelve
o'clock position using a standardised method.
Results: More than 90 % of the examined sites displayed a postoperative
enlargement of the chamber angle, compared to the measurements performed
preoperatively. Due to the small number of examined eyes no statistically
significant differences could be obtained.
Conclusion: The results of the ultrasound biomicroscopic measurements
is surprising considering the flattening of the corneal periphery found
by computerized topography, which suggested rather a finding of a narrowing
of the angle. It is possible that the shrinkage of the corneal tissue
results in a traction having an effect on the trabecular meshwork resulting
in a further opening of the chamber angle structures.