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Impressum
Determination of corneal diameter and position of visual axis using the Zeiss IOLMaster
Haigis W., Lege B. A. M.
Augenklinik, Julius-Maximilians-Universität, Josef-Schneider-Str.11, D- 97080 Würzburg
Introduction: In the last 2 years, the IOLMaster of Carl Zeiss
Jena has established itself as an alternative to ultrasound biometry.
Apart from measuring axial length by means of partial coherence interferometry,
anterior chamber depth as well as corneal radii can be determined with
this instrument. Now, with a new software version, it is possible to additionally
measure corneal diameter and the position of the visual axis.
Methods: The new measurement options are based on an analysis of
images from the system camera during fixation. In addition to the position
of the visual axis, those of pupil and iris as well as their diameters
are derived. The respective results for 605 left and 598 right eyes of
605 patients and volunteers were analyzed.
Results: For all n=1203 eyes, a mean horizontal white-to-white(wtw)
diameter of 11.76 ± 0.44 mm (9.87-14.44 mm) was derived. The wtw
diameter increased with increasing axial length (R2=0.1608).
For left eyes, with respect to the iris (pupil) center, the visual axis
was situated in 75.0% (65.5%) of all cases in the upper, in 22.5% (20.5%)
in the lower nasal quadrant. The respective results for right eyes were
74.9% (62.5%) in the upper and 20.9% (24.4%) in the lower quadrant. The
mean distance between iris (pupil) center and visual axis was found to
be 0.49 ± 0.22 (0.33 ± 0.20) mm on the right side and 0.52
± 0.21 (0.36 ± 0.20) mm left. In 292 out of 1203 cases (24.3%),
the visual axis was </= 0.2 mm away from the center of the pupil. A
mean inclination of y = 3.7 ± 1.6 ° between optical
and visual axis was derived with y decreasing with increasing axial
length.
Conclusions: The new software options of the IOLMaster allow
easy noncontact measurements of corneal diameter and the position of the
visual axis, thus offering - especially to corneal refractice surgery
- new possibilities for a better centration of the treatment zone. To
our knowledge it was for the first time that the described variables were
derived from such a broad statistical basis.