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Impressum
Masked primary open angle glaucoma in extreme cornea plana
Hafner A., Seitz B., Naumann G. O. H.
Augenklinik mit Poliklinik der Universität Erlangen-Nürnberg, Schwabachanlage 6,D-91054 Erlangen
Objective: Cornea plana is a rare syndrome, which leads to a flat
corneal curvature due to a reduced sclero-corneal angel. Because of the
flatness of the cornea the anterior chamber is also flat, the anterior
chamber angel can be restricted, and the applanatory intraocular pressures
(IOPs) are measured too low. A primary open angel glaucoma can therefore
not be diagnosed for a long time, until changes of the optic nerve head
occur.
Methods: We report on a 66-year old male with cornea plana. Although
his intraocular pressure (IOP), measured with an applanation tonometer
(Goldmann), had always been normal (< 21 mmHg), he suffered from an
increasing glaucomatous atrophy of the optic disc. The investigations
included keratometry and corneal topography analysis (TMS-1, Tomey). Furthermore,
visual fields were determined (G1, Octopus) and the optic nerve heads
were documented and analysed by papillometry. A fourtyeight- hour-tension-profile
included applanation and Schiötz tonometry.
Results: The central refractive power of the cornea was 31 diopters
and the cornea seemed to be very flattened on slit lamp evaluation. The
glaucomatous atrophy of the optic disc was more pronounced in the OD than
in the OS. While the anterior parts of the eye were shortened (depth of
the anterior chamber was OD/OS = 1.9 mm), the patient had a macrophthalmus
posterior (axial length OD = 25.78 mm, OS = 25.72 mm). However, the IOPs
were measured below 21 mmHg by applanation during the entire tension analysis.
Comparable values measured with the Schiötz tonometer showed values
above 21 mmHg. We converted the applanatory IOP values according to the
flat corneal power, as described in literature (addition of 1 mmHg to
the applanatory values per 3 diopters decreased corneal power). The tension
analysis now showed increased values, as expected after observation of
the glaucomatous excavated optic nerve head.
Conclusion: In patients with extreme cornea plana applanatory IOPs
are measured too low. Therefore in case of very flat corneas a mathematical
correction of the applanatory IOP should be carried out, in order to diagnose
a primary open angel glaucoma early enough.