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Impressum
Correction procedures for intraocular pressure in open angle glaucoma with different central corneal thickness
Jünemann A. G. M., Velten I., Wakili N., Dzialach M., Mardin C., Horn F. K.
Department of Ophthalmology, University Erlangen-Nürnberg, Schwabachanlage 6, D-91054 Erlangen
Objective: In the literature different correction factors are
proposed for the intraocular pressure (IOP) depending on the central corneal
thickness (CCT) 1,2. In the present study the effect of different correction
factors on the IOP of patients with glaucoma suspect and open-angle glaucoma
(OAG) was analyzed.
Methods: In 124 normals (N), 229 patients with ocular hypertension
(OHT), 69 preperimetric normal tension glaucoma (preNDG), 167 preperimetric
OAG (preOAG), 84 with NDG, 80 primary OAG (pOAG), and 28 patients with
secondary OAG (sOAG) of the Erlangen Glaucoma Registry the CCT was measured
using the AL-11000-pachymeter (Tomey). The actual IOP was corrected by
0,71mmHg/10µm CCT according to Ehlers1 (E-factor), by 0,5mmHg/10µm
according to Shah2 (Sfactor) and according to the regression analysis
of the present normal group (Rfactor). Statistics: Spearman correlation
coefficient, Mann-Whitney-test, Wilcoxon- Test.
Results: 1) The CCT was significantly different in OHT (584µm,p<0,01)
and NDG (554µm, p<0,01) from the other groups (N: 571µm,
preNDG: 559µm, preOAG: 571µm, pOAG: 568µm, sOAG: 561µm,
p>0,1). 2) In the normal group there was a significantly positive correlation
between CCT and IOP (r=0.32, p<0.001). The Efactor (r=-0.61, p<0.001)
and the S-factor (r=-0.42, p<0,001) caused a significantly negative
correlation. The R-factor caused no significant correlation (r=0.01, p>0.5).
3) In the normal group the maximal correction of IOP was -5,4/+6,5mmHg
for the E-factor, -3,82/+4,58mmHg for the S-Factor, and -1,46/+1,81mmHg
for the Rfactor, respectively. For all factors the correction of IOP was
significant in OHT and NDG (p<0,001). The reclassification of diagnosis
(cut-off for IOP: 21mmHg) was comparable for all three factors (OHT: R/S-factor
4.8%, R-factor 6.1%, NDG: R/Sfactor 2.3%, R-factor 1,2%).
Discussion: The adjustment of IOP for CCT seems to need a correction
factor based on an own normative data base and the techniques used (pachymetry,
Goldmann applanation tonometry). The use of general correction factors
may lead to an overcorrection. A correction of IOP in OHT and NDG might
be helpful (SFB 539).
1) Ehlers N et al. Acta Ophthalmologica 1975; 53: 34-43 2) Shah S. Ophthalmology
2000; 107: 1805-1807