Optic Disc Measurements Research Articles

Inter-observer agreement in clinical optic disc measurement using a modified 60 D lens.

To assess the inter-observer agreement of the measurement of optic disc dimensions by two observers using a modified 60 dioptre (D) fundus examination lens. The vertical disc and cup diameters of 29 eyes were measured by two independent observers using a 60 D lens modified by incorporation of a 0.1 millimetre scale graticule. The vertical cup/disc ratio was calculated. Inter-observer agreement was assessed by calculation of the inter-observer differences and by the weighted kappa statistic. The two observers showed good agreement for the measurement of disc diameter (mean difference -0.04; range -0.04, 0.2) and for cup diameter (mean difference -0.03; range 0.3, 0.2). Closer agreement for the vertical cup/disc ratio was achieved (mean kappa 0.96; 95% confidence limits 0.90, 1.0). The 95% confidence limit for the mean inter-observer difference in cup/disc ratio was 0.11, suggesting that a change of > 0.1 in the assessment of the cup/disc ratio by this technique is significant at the 5% level. High inter-observer agreement of optic disc measurement can be achieved with this technique. The method has the potential to improve the clinical evaluation of the optic disc and the precision and accuracy of the clinical measurement of other fundal structures.

Mapping Structural Damage of the Optic Disk to Visual Field Defect in Glaucoma

To evaluate the relation between the location of focal visual field defects and optic disk damage in eyes with glaucoma by short-wavelength automated perimetery and confocal scanning laser ophthalmoscopy. In 14 patients (14 eyes) with open-angle glaucoma, focal optic disk damage, and focal visual field loss, we obtain visual fields with short-wave-length automated perimetry. The short-wavelength automated perimetry visual field was divided into 21 zones, representing retinal nerve fiber layer arcuate bundles. Test points were compared with a normative database. The optic disk was assessed with a confocal scanning laser ophthalmoscope. Optic disk measurements were calculated in 10-degree sectors and compared with a normative database using a new measure, the rim area ratio, which adjusts for individual differences in disk size. The mean number (+/-SD) of damaged visual field zones was 3.9 (+/-1.9), and the mean number of damaged rim sectors was 5.0 (+/-2.9). Focal defects on the optic disk and on short-wavelength automated perimetry were topographically related with specific damaged visual field zones corresponding to specific damaged rim sectors. In patients with open-angle glaucoma with focal optic disk damage and focal visual field loss, defects in optic disk and short-wavelength automated perimetry are topographically related. The rim area ratio can be used to identify focal optic nerve defects.

Comparison Between Tomographic Scanning Evaluation and Photographic Measurement of the Neuroretinal Rim

To compare laser tomographic scanning evaluation with photographic measurement of size and shape of the neuroretinal rim. For 25 normal eyes and 32 glaucomatous eyes, the optic disks were examined with the Heidelberg Retina Tomograph (software version 1.11) for confocal laser tomographic scanning evaluation, and color stereoscopic optic disk photographs for planimetric measurements. Area and width of the neuroretinal rim were determined as percentages of the disk area and diameter, respectively. For the normal and glaucomatous eyes, the tomographic results compared with the photographic measurements disclosed significantly larger values for the relative width and relative area of the neuroretinal rim. The differences between both methods were most marked in the nasal part of the optic disk and least marked in the temporal disk region. The relative differences increased significantly (P < .05) with increasing degree of glaucomatous optic nerve damage. In normal and glaucomatous eyes, the Heidelberg Retina Tomograph determines the neuroretinal rim, expressed as percentage of optic disk measurements, to be significantly larger than when the rim is evaluated on optic disk photographs. Because parts of the central retinal vessel trunk are defined as neuroretinal rim in the algorithm of the Heidelberg Retina Tomograph, the differences between Heidelberg Retina Tomograph measurements and photographic determinations of the rim are largest in the nasal disk region and smallest in the temporal disk area. The neuroretinal rim shape and neuroretinal rim area differ appreciably between the two methods. These differences increase with increasing degree of glaucomatous optic nerve damage.

Repeatability and Reproducibility of Optic Disc Measurement with the Zeiss 4-mirror Contact Lens

A simple clinical quantitative method of optic disc diameter measurement using a 4-mirror gonioscope contact lens has been described recently. Intraobserver and interobserver variations are assessed on 77 eyes of 41 patients. Of these eyes, 63 had refractive errors within 3 diopters of emmetropia. The disc was measured by projecting a slit beam of known height onto the disc. Intraobserver variation: the coefficient of variation was 3.04% for observer 1 (experienced) and 4.76% for observer 2 (novice). The mean of the three measurements by the two observers was not significantly different (P=0.2318). For observer 1, the mean variance of the eyes with higher refractive errors did not differ significantly from the eyes with lower refractive errors. Interobserver variation: the coefficient of variation was 4.52%. The measurements for the novice were slightly larger the smallest discs and slightly smaller for the largest discs (regression analysis P=0.0209). Repeatability and reproducibility for this method are comparable with other methods of measurement. Until experienced with the technique, the authors recommend that the mean of three readings is used.

Relationship between optic nerve head parameters of Heidelberg Retina Tomograph and visual field defects in primary open-angle glaucoma.

To investigate the correlation between optic nerve head configuration and visual field defects, optic nerve head analysis using confocal scanning laser tomography (Heidelberg Retina Tomograph, HRT) and automated static threshold perimetry using a Humphrey Field Analyzer (program C30-2) were performed on 81 eyes of 44 primary open-angle glaucoma (POAG) patients. The optic nerve head parameters-rim area, rim volume, mean retinal nerve fiber layer thickness, height variation contour, and third moment in contour were measured by HRT and were analyzed for correlation with visual field indices-mean deviation, and corrected pattern standard deviation. All optic nerve head parameters except HVC correlated significantly with the visual field indices; the highest correlation was between rim area and mean deviation (r = 0.6172, p < 0.00001). The rim area of the superior and inferior quadrants correlated significantly with the visual field defects in corresponding sectors. Structural optic disc measurements by HRT correlated significantly with functional optic nerve head damage in POAG.

Clinical Assessment, Optic Disk Measurements, and Visual-Evoked Potential in Optic Nerve Hypoplasia

Because there is a broad spectrum of visual dysfunction in eyes with optic nerve hypoplasia, we determined whether any clinical observations, including optic disk measurements, could predict visual outcome in eyes with hypoplastic optic nerves. We prospectively studied the eyes of 19 children (eight consecutive and 11 randomly selected), ages 7 to 92 months, in whom a diagnosis of optic nerve hypoplasia was made by an ophthalmologist. Clinical assessment included visual acuity, pupillary responses, and nystagmus. The ratio of the horizontal disk diameter to the disk-macula distance was calculated from fundus photographs. The amplitude and latency of the flash visual-evoked potential as well as the threshold response to pattern reversal checks were recorded. Visual acuity was associated with pupil reactivity, nystagmus, the ratio of the horizontal disk diameter to the disk-macula distance, pattern visual-evoked potential threshold, and flash visual-evoked potential amplitude (P < .001 for all parameters). All eyes with a ratio of the horizontal disk diameter to the disk-macula distance greater than .30 had good visual acuity, and all eyes with a ratio of the horizontal disk diameter to the disk-macula distance less than .30 had poor visual acuity. No eye with a ratio of the horizontal disk diameter to the disk-macula distance less than or equal to .15 had visual acuity better than light perception. Visual-evoked potential and photogrammetric measurement of relative disk size can be used to approximate visual acuity in eyes with optic nerve hypoplasia. This finding could lead to a diagnostic criterion or a severity classification for optic nerve hypoplasia.

Correlation of visual field with scanning confocal laser optic disc measurements in glaucoma.

To evaluate the correlation between structural optic disc measurements that were obtained with a scanning confocal laser tomograph and functional measurements that were obtained with automated static threshold perimetry. Cross-sectional study. An American school of medicine. Forty-six patients (mean +/- SD age, 63 +/- 10 years) with early to moderate glaucoma (average mean deviation +/- SD, -4.8 +/- 6.2 dB). Automated static threshold perimetry (performed with either the Octopus G1 program, Interzeag, Schlieren, Switzerland, or the Humphrey 24-2 program, Allergan Humphrey, San Leandro, Calif) and confocal optic disc tomography (performed with the Heidelberg Retina Tomograph, Heidelberg [Germany] Engineering GmbH) were performed on one randomly selected eye per patient. The correlation between the visual field indexes, namely, the mean deviation and corrected pattern SD, and the topographic measurements for the optic disc and nerve fiber layer. A statistically significant correlation was found between the third central moment of the frequency distribution of the depth values for the optic disc structures and the visual field indexes. Pearson correlation coefficients were r = -.65 (P < .0001) and r = .55 (P < .0001) for the mean deviation and corrected pattern SD, respectively. The third central moment of the depth distribution for the optic disc measurements is strongly related to the overall shape of the optic disc cup and is a robust indicator of the degree of glaucomatous optic nerve damage.

Race-, Age-, Gender-, and Refractive Error—Related Differences in the Normal Optic Disc

To determine race-, age-, gender-, and refractive error-related differences in the size and topography of the optic disc in healthy Americans. Population-based study. Eastern and southeastern health districts of Baltimore, Md. A population-based sample of 4877 non-institutionalized black and white individuals aged 40 years or older without evidence of optic nerve disease. Race-, age-, gender-, and refractive error-related differences in optic disc measurements: disc area, neural rim area, cup area, cup-to-disc ratio, and neural rim area-to-disc area ratio. We analyzed simultaneous stereoscopic optic disc photographs from 3387 (1534 black and 1853 white) of the 4877 healthy individuals using an image analyzer (Topcon Image Analyzer, Topcon Instrument Corporation, Paramus, NJ). A total of 1490 individuals were excluded owing to the absence of good-quality images from either eye. The image analyzer defined the cup margin 150 microns below the surface of the disc margin. On average, blacks had significantly larger disc areas (blacks, 2.94 mm2; whites, 2.63 mm2), larger cup areas (blacks, 1.04 mm2; whites, 0.71 mm2), larger cup-to-disc ratios (blacks, 0.56; whites, 0.49), similar neural rim areas (blacks, 1.90 mm2; whites, 1.92 mm2), and smaller neural rim area-to-disc area ratios (blacks, 0.66; whites, 0.74) compared with whites. There were no age-related differences in any of the disc measurements. Male subjects had 2% to 3% larger optic discs compared with female subjects. No association between refractive error and any of the optic disc measurements studied was detected. Racial differences in the normal optic disc are present among urban Americans, and these differences must be considered in evaluation of the optic disc for glaucoma and other optic neuropathies. Among the individuals in our study, all of whom were 40 years of age or older, no progressive age-related decline in neural rim area was detectable. Neither gender nor refractive error were associated with any significant differences in the size and topography of the normal optic disc.

Covariation of optic disc measurements and ocular parameters in the healthy eye

To understand the variations in optic disc topography that may affect the local susceptibility of nerve fibers to glaucomatous damage, we evaluated the correlations between optic disc topography and selected ocular parameters in 210 normal eyes of healthy Japanese. In the total study group, eyes with a longer axial length had a longer distance between the disc and foveola, a larger index of ovalness and a larger disc (P < 0.01). A longer disc-foveola distance correlated with a larger index of ovalness (P < 0.01). The optic discs of severely myopic eyes had a considerably different structure from other eyes. Eyes with a tilted optic disc were unique in that the area of the optic disc was not large despite a positive correlation with long axial length (P < 0.01) a long disc-foveola distance (P < 0.01), and a large index of ovalness (P < 0.01). Eyes with a rotated optic disc were another special case. This eye type correlated in a contradictory fashion with two parameters: a large axial length (P < 0.01) and a short disc-foveola distance (P < 0.01). These findings suggest that changes in optic disc topography or susceptibility to glaucomatous damage correlate with selected ocular parameters but are not completely parallel.

Growth of the Human Optic Disk and Nerve During Gestation, Childhood, and Early Adulthood

We measured vertical and horizontal diameters of the optic disk and retrobulbar optic nerve in eyes from 95 patients on whom autopsies were performed at the UCLA Medical Center over a 20-year period. Ages at death ranged from 4.8 months' gestation to 21.9 years. Optic disk surface area and nerve cross-sectional area were calculated for each subject by using the formula for an ellipse. Approximately 50% of the growth of the optic disk and nerve occurs by 20 weeks' gestation, and 75% by birth; 95% of the growth occurs before the age of 1 year. All optic disk and nerve measurements correlate strongly (correlations > .67; P < .0001) with subject height and globe anteroposterior diameter. We applied our results to the current understanding of optic disk and nerve development, and compared them to previous clinical and pathologic studies of optic nerve dimensions in adults and older children.

Progression of disc and field damage in early glaucoma.

To assess the temporal relationship between visual field progression and optic disc deterioration in early glaucoma, we studied 15 patients with unilateral visual field loss from primary open angle glaucoma. Planimetric optic disc measurements were compared with automated static threshold perimetry during a mean follow-up of 6.1 years. Eight (53%) of 15 eyes with an initially normal visual field showed progression of the disc; six of these eyes did not develop field abnormalities. The mean rates of rim-area loss were 1.7%/y in eyes with initially normal fields and 2.1%/y in eyes with initial field loss. The mean rate of visual field deterioration (change in corrected loss variance) was lower in the eyes with an initially normal field (0.3 dB2/y) than in eyes with initial field loss (3.6 dB2/y; P = .016). This longitudinal study documents progressive disc damage prior to field loss in early glaucoma.

Clinical Disc Biometry in Early Glaucoma

To assess the potential of a clinical method of optic disc measurement in the detection of early neuroretinal rim loss in glaucoma. A method of disc biometry based on indirect ophthalmoscopy was used to estimate disc and neuroretinal rim areas in 81 ocular hypertensive eyes of 43 patients and in 28 fellow eyes with normal visual fields of patients with unilateral visual field loss from primary open-angle glaucoma. The results were compared with those from age-matched visually normal patients. Neuroretinal rim area was significantly smaller in both hypertensive and fellow eye groups compared with controls (P < 0.0001; P = 0.0009). Disc area also was smaller in both groups (P = 0.0034; P = 0.046); however, this was inadequate to explain the differences in rim area, which, when corrected for disc size, were still highly significant (P < 0.0001; P = 0.0001). The differences in neuroretinal rim area observed are likely to indicate that a proportion of the eyes studied had suffered a reduction of neuroretinal rim area, which was measurable by this method at a stage before the development of demonstrable visual field loss.

Importance of standardized photos for planimetry

In a series of 30 patients we compared the optic disc measurements. Disc photographs were either taken centric or excentric. Pictures with excentric discs showed significantly smaller measurements. However, the C/D-ratio demonstrated a good correlation (r = 0.95). For follow-up studies even not standardized photos can be useful, especially if the same examinator makes all the measurements.

Disc and field damage in patients with unilateral visual field loss from primary open-angle glaucoma.

To assess the temporal relationship between field and disc change in early glaucoma, 24 patients with unilateral visual field loss from primary open angle glaucoma were identified for planimetric optic disc measurements. Cross-sectional analysis of disc rim area was performed and compared to 25 age-matched normal controls. The mean (+/- SD) disc rim area in eyes with normal visual fields (1.10 +/- 0.31 mm2) was slightly larger than that of eyes with visual field loss (0.90 +/- 0.33 mm2). The mean disc rim area in the control group (1.49 +/- 0.19 mm2) was significantly different from both sets of eyes in the asymmetric primary open angle glaucoma patients (p = 0.000). These findings support the hypothesis that loss of the optic disc rim can be detected before perimetric abnormalities develop in patients with glaucoma.

Regional and Long-term Variability of Fundus Measurements Made With Computer-Image Analysis

We studied the variability of optic disk and peripapillary nerve fiber layer surface contour measurements made by use of computer-image analysis. Six hundred twenty-five measurements of surface contour were made on each eye by use of simultaneous stereoscopic videography. Regional differences in short-term measurement variability were studied in 12 eyes (six normal and six glaucomatous), each imaged nine times over several days. The widths of the 95% confidence interval for the measurements averaged 82 microns for the juxta-papillary surface and 132 microns for the disk surface. Measurements of peripapillary surface contour were significantly less variable than were measurements of the disk surface (P = .000). The greatest variability was detected along large blood vessels and at steep contours. Long-term variability was studied in a separate group of 30 clinically stable patients with glaucoma, each imaged three to six times over a period of more than one year. The widths of the 95% confidence intervals were 132 microns for the peripapillary surface and 217 microns for the disk surface. The long-term variability was significantly greater than the short-term variability (P = .000). The peripapillary nerve fiber layer surface, located away from the margins of large vessels, may provide the most dependable measurements of contour. These estimates of long-term variability of optic disk and peripapillary contour measurements provide clinically relevant confidence intervals with which to detect progressive glaucomatous nerve fiber damage.

Retinal nerve fiber layer abnormalities and high‐pass resolution perimetry

The purpose of this study was to compare high-pass resolution perimetry (HRP) test results with clinical optic disc measurements and semi-quantitative retinal nerve fiber layer (RNFL) estimates. HRP reflects the separation of functional ganglion cells in the retina, and estimates a 'Functional Channel Fraction (FCF)' index that expresses the number of functional ganglion cells relative to average normal. FCF was statistically highly significantly correlated both with the overall and diffuse RNFL score (r = -0.63, P less than 0.0001) and with the neuroretinal rim area (r = 0.44; P less than 0.001). This suggests that HRP is a useful psychophysical test to assess optic nerve integrity in glaucoma.

Optic disc rim area is related to disc size in normal subjects.

Measurements of optic disc rim area are used to quantitatively evaluate the optic nerve head in open angle glaucoma. It has been suggested that disc rim area (neuroretinal rim area) is independent of disc size, unlike measurements of cup-disc ratio that co-vary with measurements of disc size. To test the relationships between topographic optic disc measurements and disc size, we used computerized image analysis (Rodenstock analyzer) of the optic nerve head to measure total disc area, cup area, disc rim area, and disc cup volume in 38 normal subjects. Magnification-corrected measurements of cup area, disc rim area, and cup volume were positively correlated with measurements of disc area. Measurements of disc rim area were therefore not independent of disc size in this group of normal subjects. A normal range of values for disc rim area can be predicted for an eye depending on the area of its optic disc. Sensitive predictions require further refinement based on the patient's age, race, and sex.