Optic Disc Size in Glaucoma Patients Attending a Tertiary Institution in Nigeria.

Background: Assessment of optic disc size is an important component of optic nerve head examination which is often overlooked in the diagnostic evaluation for glaucoma. Measured values of optic disc size vary with the measurement technique utilized. The actual disc size varies with race and possibly other demographic characteristics. Disc size is also associated with variation of specific anatomical structures of the optic nerve head and the retinal nerve fiber layer. These disc size-dependent variations are risk factors for glaucoma or affect the likelihood of glaucoma diagnosis [1]. Aim: To report the clinical (measured by biomicroscopy) disc diameters of small, average and large optic discs and produce data on the disc sizes of Nigerian patients who have been diagnosed with glaucoma and are currently undergoing treatment. Materials and Methods: One hundred eyes of 100 glaucoma subjects were studied. Disc diameter was measured using stereo biomicroscopy (78 D). Discs were classified into small (<1.3 mm2), average (1.3-1.75 mm2) and large (>1.75 mm2) using the European Glaucoma Society Guidelines [2,3]. The relationship between disc size and age, sex and type of Glaucoma was also assessed. Results: One hundred eyes of 100 individuals were studied comprising 64 (64.0%) males and 36 (36.0%) females. Age range was 20- 80 years with a mean age of 50±13.66. Mean disc size was 1.99±0.239. Eighty-two percent of discs were large size (>1.75 mm2). Males (61%) had larger discs than females (21%) (p=0.001). There was no correlation between disc size and age (p=0.87) or clinical types of glaucoma (p=0.59). Conclusion: Majority had large optic discs in our study (82%). Large discs have large cup: Disc ratio. These differences must be considered while evaluating the optic disc to prevent over diagnosis of glaucoma and its attendant economic burden on the patient.

The Ability of Disc-to-Fovea Distance to Disc-Diameter Ratio to Estimate Optic Disc Size

PURPOSE: To investigate the usefulness of the measurement of disc-to-fovea distance to disc-diameter ratio (DF/DD ratio) in detecting large and small discs. METHODS: A total of 300 randomly selected subjects were included in the present study. All patients underwent stereoscopic disc photography and DF/DD ratio, which is the shortest distance between disc margin and fovea divided by mean disc diameter was determined by planimetry. The diagnostic accuracy of DF/DD ratio was evaluated using areas under the receiver operating characteristics curves (AUCs), sensitivity, and specificity. RESULTS: No significant differences in disc-to-fovea distance were observed among small and large disc groups. The DF/DD ratio was significantly lower in subjects with large discs (1.74 +/- 0.27) compared with subjects with small discs (2.70 +/- 0.15). AUCs of the DF/DD ratio were 0.942 and 0.947 in detecting large and small discs, respectively. In detecting disc size by a fixed DF/DD ratio of 2.0, sensitivity was 100% for both large and small discs, and specificity was 70.1% and 40.9% for the large and small discs, respectively. CONCLUSIONS: The DF/DD ratio may be a simple and useful clinical aid in detecting large and small discs. The 2.0 fixed DF/DD ratio, showed 100% sensitivity in detecting both large and small discs, although medium discs may be misdiagnosed as small discs more often than as large discs.

Correlation Between Disc Size and Retinal Nerve Fiber Layer Thickness in Normal Tension Glaucoma

PURPOSE: To investigate the correlation between optic disc size and retinal nerve fiber layer (RNFL) thickness in healthy subjects and patients with normal tension glaucoma (NTG). METHODS: Optical coherence tomography was performed on 50 eyes of 50 healthy subjects and on 50 eyes of 50 NTG patients. RESULTS: The optic disc size showed a significant correlation with the RNFL thickness in healthy subjects and in patients with NTG. Significant correlations were observed between the optic disc size and the ratio of superior-to-total RNFL thickness (r=-0.283, p=0.049) and the ratio of nasal to total RNFL thickness (r=0.403, p=0.004) in healthy subjects. In patients with NTG, significant correlations were observed between the optic disc size and the ratio of superior to total RNFL thickness (r=-0.314, p=0.029) and the ratio of inferior to total RNFL thickness (r=-0.302, p=0.034). CONCLUSIONS: RNFL thickness increased significantly with an increase in optic disc size in both healthy subjects and NTG patients. The correlation between optic disc size and the ratios of each quadrant to the total RNFL thickness showed a different pattern between healthy subjects and NTG patients.

Interocular comparison of nerve fiber layer thickness and its relation with optic disc size in normal subjects

We conducted an investigation of the relation between RNFL thickness and optic disc size along with an interocular comparison of optic disc size, RNFL thickness, and RNFL density in healthy subjects. A total of 64 normal eyes from 32 Korean volunteers were enrolled in this study. A GDx Nerve Fiber Analyzer with software version 2.0.09 was used to image all subjects. Optic disc size was measured by pi x (horizontal radius) x (vertical radius). The RNFL density of each quadrant was calculated by dividing each quadrant integral by the total integral. Optic disc size was positively correlated with the total RNFL thickness (r = 0.615, p < 0.01). Optic disc size and RNFL density were inversely related in the superior quadrant (r = -0.248, p < 0.05). There was a significant positive correlation between optic disc size and RNFL density in the nasal quadrant (r = 0.439, p < 0.01) and the temporal quadrant to a certain degree. A significant positive correlation was found between the right and left eyes in terms of total RNFL thickness in and that of each quadrant. Interocular RNFL density was positively correlated in both the temporal and nasal quadrants. These findings must be considered when one evaluates and compares RNFL measurements between two eyes as is often the case where both eyes are usually affected in the course of glaucomatous RNFL damage.

Criteria to Determine the Relevance of the Changes of Disc Parameter to the Progress of the Disease

The purpose of this study is to establish the criteria to discriminate whether the difference of the optic disc parameters compared actually reflects the progress of the disease or it is merely caused by the intraexaminer or interexaminer error. Using the confocal scanning laser ophthalmoscope (TopSS), one eye of each of 20 healthy adults were exmained by the same examiner and one eye of each of 10 adults were examined by different examiners for two consecutive days. The results out of these repeated examinations were analysed to obtain 95%confidence intervals by analysis of the change of the 12 optic disc parameters, and to determine whether the results have been influenced by the disc size or the disc tilt. The criteria to differentiate actual progression of disease from potential errors of the test were obtained. In addition, it was confirmed that changes in the parameters were not influenced by the disc size or the contour tilt. In conclusion,the outcomes of this study can be utilized as a guiding criteria when judging the relevance of the parameter changes to the progress of the disease.

The Normal Values of Optic Disc Parameters According to the Optic Disc Size

We analysed the optic nerve head of 151 normal eyes with 8 confocal scanning laser ophthalmoscope (TopSSTM, Laser Diagnostic Technologies, Inc.), and obtained the normal values of each parameters. As the optic disc size increases, the cup shape, effective area, 1/2 depth area, C/D ratio, neuroretinal rim area, volume above, volume below, and 1/2 depth volume also increase. Therefore we obtained the normal values of these parameters according to the optic disc size. The entire subjects were divided into four groups according to the disc area, each group of 1. 5mm2-2.0mm2, 2.0mm2-2.5mm2, 2.5mm2-3.0mm2, and 3.0mm2-3.5mm2`, respectively. The normal values of other parameters such as contour variation, rnean contour depth, average depth, maximum depth, average slope, and maximum slope which are not affected by optic disc size were obtained without grouping. This may minimize the error in evaluating the optic disc parameters and may be useful in the early detection of glaucomatous optic disc changes.

Measurements of the Diameter and Area of the OpticDisc in Enucleated Human eyes

To measure the optic disc diamete and area in enucleated human eyes, thirty-three enucleated human eyes (20 men, 13 women), with a mean age of 44.2+/-17.7 years (+/-standard deviation; range 8 -74 years), were studied. After enucleation, the globes were immediately fixed in a solution of 10% formalin, were bisected through the optic nerve head and specimens were stained with hematoxylin-eosin. The slides were histomorphometerically evaluated with a light microscope. Each disc was measureed vertically and horizontally on a macrophotograph of the whole specimens with an aligned micromete scale. For correction preparation-induced shrinkage factor, one specimen was measured on the unfixed state. Compared to values obtained in unfixed specimens, preparation-induced shrinkage factor was 6.5% Mean maximal and minimal diameters of the optic disc were 2.16+/-0.15mm (range 1.38 -3.25mm) and 1.79+/-0.44mm (range 1.06 -2.90mm), rrespectively. Mean area of the optic disc was 3.20+/-1.58mm2(range 1.15 - 7.40mm2). These practical values of the optic disc diameter and area may be the important standard units to the further quantiative optic nerve studies.

The Effect of Optic Disc Size or Age on Evaluation of Optic Disc Parameters

It has been reported that the number of optic nerve fibers decrease with age, and the C/D ratio increases as the optic disc size increases. Consequently, the normal values of the optic disc parameters measured by an optic disc analyser may change according to the optic disc size or age. We attempted to investigate the effect of individual variations in optic disc size or age on interpretation of optic disc parameters. Topographic disc parameters of 104 normal subjects aged 40 to 69 were measured using a confocal scanning laser ophthalmoscope (TopSSTM , Laser Diagnostic Technologies, Inc.). Fourteen parameters were evaluated according to the optic disc size or age. Statistical analysis was done by regression analysis. With an increase in optic disc size, the increase in cup shape, effective area, 1/2 depth area, C/D ratio, neuroretinal rim area, volume above, volume below, and 1/2 depth volume were statistically significant (p0.1). Age did not show any statistically significant influence on optic disc parameters (p>0.1). In conclusion, optic disc size, but not age, should be considered in the interpretation of optic disc parameters.