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Abstract #18518 Published in IGR 3-3
Masked primary open angle glaucoma in cornea plana by wrongly too low applanation tonometry: a case report
Hafner A; Seitz BKlinische Monatsblätter für Augenheilkunde 2001; 218: 621-625
BACKGROUND: Cornea plana is a rare syndrome which leads to a flat corneal curvature due to a reduced sclerocorneal angle. Depending on the regularity of the corneal astigmatism, the frequently resulting hyperopia may be difficult to compensate for. Because of the flatness of the cornea, the anterior chamber is also flat, the anterior chamber angle can be restricted, and the applanatory intraocular pressure (IOPs) are measured too low. Primary open-angle glaucoma (POAG) is therefore not diagnosed for a long time, until changes in the optic nerve head occur. PATIENT AND METHOD: The authors report on a 66-year-old male with cornea plana. Although his IOP, measured with an applanation tonometer (Goldmann), had always been normal (<21 mmHg), he suffered from increasing glaucomatous atrophy of the optic disc. A complete ophthalmological investigation was carried out, including keratometry and corneal topography analysis (TMS-1, Tomey). Furthermore, visual field was determined (G1, Octopus) and the optic nerve heads were documented and analyzed by papillometry. A 48-hour tension profile was calculated for both eyes, including applanation and Schiötz tonometry. RESULTS: The central refractive power of the cornea was 31 diopters and the cornea seemed to be flattened on slit-lamp evaluation. The glaucomatous atrophy of the optic disc was more pronounced in the OD than in the OS (OD = neuroretinal rim loss in the upper part, at the bottom, and in the lateral part of the optic disc; OS = laterally distinct neuroretinal rim loss). While the anterior parts of the eye were shortened (depth of the anterior chamber was OD/OS = 1.9 mm), a macrophthalmus posterior was stated (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. The applanatory IOP values were converted according to the flat corneal power, as described in the 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. CONCLUSIONS: In patients with cornea plana, applanatory IOPs are measured too low. Therefore, in the case of very flat corneas, mathematical correction of the applanatory IOP should be carried out, in order to diagnosis POAG in time. LA: German
Dr A. Hafner, Augenklinik mit Poliklinik der Universität Erlangen-Nürnberg, Schwabachanlage 6, 91054 Erlangen, Germany
Classification:
2.2 Cornea (Part of: 2 Anatomical structures in glaucoma)
