For all eyes - included in both studies - 15° colour optic disc photographs had been taken with a telecentric Zeiss fundus camera. The slides were projected in a scale of 1 to 15. The outlines of the optic disc, cup, Elschnig’s ring, and the parapapillary zones alpha and beta were plotted on a paper. The plotted „structures were digitised and analysed with the software which was recently developed by the „Erlangen workgroup". This sophisticated software can correct the ocular and photographic magnification using the Littmann method (7,8). The software is able to calculate many parameters of the optic disc but for practical reasons in this study only the following measurements were included: the surface, the maximal and minimal diameter of the optic disc, the surface, the maximal and minimal diameter of the optic cup, the surface of the neuroretinal rim in four sectors according to Jonas (9): nasal, temporal, temporal superior, temporal inferior, and the surface of the parapapillary zones the alpha- and the betazones.

During the course of the first examination slides were taken of the optic nerve heads of ten eyes (n = 7 primary open angle glaucoma (POAG), n = 3 ocular hypertension (OHT )) of ten patients (6 women , 3 men) with a mean +- SD age of 50 +- 15 years. Criteria for the diagnosis of ocular hypertension were: intraocular pressure readings repeatedly measured to be higher than 21 Hgmm, and normal visual field. From each optic disc three slides were taken, which were evaluated by the same examiner on different days using two-dimensional computer assisted planimetry. (3 x 10 slides for one observer)

During the course of the second examination slides were taken of the optic nerve heads of 27 eyes (n = 19 POAG, 8 OHT) of 27 patients (15 women 12 men) with a mean +- SD age of 52+-13 years. 3 different examiners on separate days performed planimetric measurements from the same slides. (27 slides x 3 observers). After both examinations the variances of the measurements were calculated.

The results of the interphotographic - intraobserver examination is presented in Table 1.

Table 1 Interphotographic - intraobserver examination - Results

Examined structure             Error of measurement (%)     +-SD
Surface of the optic disc:              1,5                  0,7
Maximal diameter of the optic disc:     0,7                  0,3
Minimal diameter of the optic disc:     1,4                  0,5
Surface of the excavation:              6,6                  2,4
Maximal diameter of the excavation:     3,8                  0,3
Minimal diameter of the excavation:     3,7                  0,5
Neuroretinal rim area in 4 sectors
Nasal                                   8,1                  4,5
Temporal:                               4,9                  3,1
Temporal inferior:                      4,7                  1,7
Temporal superior:                      6,9                  3,2
Surface of the parapapillary zones:
alpha:                                 46,5                 40,3
beta:                                  22,5                 30,4

Table 2 Interobserver examination - Results

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Examined structure             Error of measurement (%)         +-SD
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Surface of the optic disc:              2.0                     0.9
Maximal diameter of the optic disc:     1.6                     0.6
Minimal diameter of the optic disc:     1.2                     0.6
Surface of the excavation:              7.8                     4.2
Maximal diameter of the excavation:     4.2                     2.6
Minimal diameter of the excavation:     4.8                     2.5
Neuroretinal rim area in 4 sectors
Nasal:                                 10.6                     5.9
Temporal:                               5.3                     2.9
Temporal inferior:                      7.3                     3.8
Temporal superior:                      7.7                     3.5
Surface of the parapapillary zones:		
      alpha:                           63.9                    44.4
       beta:                           30.0                    43.5

Planimetry is a possible method for quantitative two dimensional evaluation of the structures of the optic disc and the parapapillary region. In the present study the examiners wanted to test the intraobserver - interphotographic and interobserver reproducibility of this method.

The intraobserver and interobserver examinations showed very similar tendencies, and the interobserver examinations showed larger variances. As it was expected the best reproducible structures were the surface and the diameters of the optic discs. The parameters of the optic cup - which has a strong correlation with the neuroretinal rim areas - showed larger but acceptable variances. Hendrickson (10) reported larger interobserver variances when 27 experts analysed one single photograph. The evaluation of the cup can be difficult in some particular cases, e.g. if the excavation is shallow, or the photo is focused on the lamina cribrosa. Especially in this cases its very useful to define the cup with the help of stereoscopic photographs. In this study only some of the slides had its stereo pairs. If the definition of the same cup is different by the observers this may result in differences in the measurements of the neuroretinal rim parameters. Examining the measurements of the neuroretinal rim areas we can suggest that the less reproducible area was the nasal sector, (intraobserver examination variance : 8.1 % +- SD 4.5 %, interobserver - interphotographic examination: 10.6 % +- SD 5.9 %). The probable explanation for this tendency can be the definition of the exit of the central retinal vessel trunk some of the observers defined it as the part of the neuororetinal rim and not as a part of the optic cup. The reproducibility of the other sectors of the neuroretinal rim were acceptable. The variance of measurements of the areas of the parapapillary zones were extremely large. There can be several reasons of it, but the most important factors are - as we think - is the quality of the pictures, or the slight disturbances of the retinal pigment epithelium. It is obvious that if the photo is focused on the lamina cribrosa, the nerve fiber layer will be fuzzy, and under such conditions its impossible to define this fine structures. As a conclusion we can note that except of the parapapillary zones planimetry is a good reproducible method for two dimensional measurements of the optic disc.

1. Airaksinen PJ, Drance SM, Schultzer M (1985): Neuroretinal rim areas in early glaucoma. Am J Ophthalmol 99:1-4.

2. Balazsi AG, Drance SM, Schulzer M, Douglas GR (1984): Neuroretinal rim area in suspected glaucoma and early chronic open angle glaucoma. Arch Ophthalmol 102:1011-1014.

3. Varma R, Steinmann WC, Scott IU (1992): Expert agreement in evaluating the optic disc for glaucoma. Ophthalmology 99:215-21.

4. American Academy of Ophthalmology (1996): Primary Open-Angle Glaucoma. Preferred practice pattern. American Academy of Ophthalmology, San Francisco

5. Betz P, Camps F, Collignon - Brach C, Lavergne G, Weekers R (1982): Biometric study of the disc cup in open - angle glaucoma. Graefe’s Arch Clin Exp Ophthalmol 218:70-74.

6. Jonas JB, Gusek GC, Naumann GOH (1988): Optic disc morphometry in chronic primary open- angle glaucoma. I. Morphometric intrapapillary characteristics. Graefe’s Arch Clin Exp Ophthalmol 226:522-30.

7. Littmann H (1982): Zur Bestimmung der wahren Grösse eines Objektes auf dem Hintergrund des lebenden Auges. Klin Monatsbl Augenheilkd 180:286-289.

8. Littmann H (1988): Zur Bestimmung der wahren Grösse eines Objektes auf dem Hintergrund des lebenden Auges. Klin Monatsbl Augenheilkd 192:66-67.

9. Jonas JB, Fernandez MC, Naumann GOH (1992): Glaucomatous parapapillary atrophy. Occurence and correlations. Arch Ophthalmol 110:214-222.

10. Hendrickson PH (1992): Über Fehlerquellen bei der Planimetrie des Sehnerven. Klin Monatsbl Augenheilk 200:489-493.