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[page 34] [Eye Reports 2011; 1:e11]

The use of ocular coherence
tomography in evaluating optic
nerve health in eyes with large
disc size
Guy A. Weiss,1 Gadi Wollstein,2
Lilly Naveh,3 Maya Landoy-Kalev,3
Dan Ga’aton,4 Zvia Burgansky-Eliash3
1Department of Medicine, University at
Buffalo, Buffalo, NY; 2University of
Pittsburgh Medical Center Eye Center,
Eye and Ear Institute, Ophthalmology
and Visual Science Research Center,
Department of Ophthalmology,
University of Pittsburgh School of
Medicine, Pittsburgh, Pennsylvania, USA;
3Edith Wolfson Medical Center; 4Rabin
Center, Department of Ophthalmology,
Sackler Faculty of Medicine, Tel Aviv
University, Tel Aviv, Israel 

Abstract 

Large discs are often associated with large
cups; in order to exclude glaucomatous cupping
a good objective tool is needed. The purpose of
this study is to evaluate ocular coherence
tomography (OCT) optic nerve head (ONH)
parameters as indicators of ocular health in
subjects with large discs. Eighty-one eyes of 53
healthy patients were evaluated; 46 eyes had
large discs (disc area ≥2.6 mm2) and 35 eyes
had regular size discs (disc area <2.6 mm2). All
subjects underwent OCT. All ONH parameters
were documented, including vertical integrated
rim area (VIRA), horizontal integrated rim
width (HIRW), rim area, cup area, cup-to-disc
(CD) area ratio, horizontal cup to disc ratio
(HCDR), vertical cup to disc ratio (VCDR), cup
area topography, and cup volume. In addition,
OCT retinal nerve fiber layer (RNFL) global
mean thickness and four quadrants mean thick-
nesses were analyzed. All cup parameters were
significantly higher in the large disc group com-
pared to the normal disc group. The parameters
estimating the rim varied between the groups:
in the large disc group VIRA was significantly
lower while HIRW was significantly higher,
compared to the control group. Rim area was
the only parameter with similar values in both
groups (1.52±0.24 mm2 and 1.6±0.3 mm2 in the
large and regular disc groups, respectively).
Correlation analysis revealed significant posi-
tive association between disc area and cup
parameters in the large disc group. In contrast,
in the regular disc group, disc area was positive-
ly associated with rim parameters. Rim area
might serve as an indicator for ocular health in
large discs with large cups. 

Introduction

Ocular coherence tomography (OCT) is a
reliable tool for diagnosing and following
patients with glaucoma.1-3 Glaucoma is charac-
terized by a gradual loss of retinal ganglion
cells and thinning of the retinal nerve fiber
layer4,5 leading to a typical increase in the cup-
to-disc (CD) ratio. Peripapillary circumferen-
tial retinal nerve fiber layer (RNFL) scans and
radial optic nerve head (ONH) scans have sim-
ilar accuracy for glaucoma detection. The best
ONH parameters for discriminating between
healthy and glaucomatous discs in different
studies were: rim area,3 vertical cup to disc
ratio (VCDR),1 and CD area ratio (please see
Appendix for definitions of cup and disc meas-
urement terminology).2 Unfortunately, there is
no available normative database for the ONH
scans in the commonly used StratusOCT
instrument (Carl Zeiss Meditec, Inc. Dublin,
CA, USA); therefore it is not possible to assess
individual patients’ values.
Large discs might have large cups and

increased CD area ratio without an accompa-
nying thinning in RNFL. Moreover, histological
studies in primates and humans demonstrated
an increase in the number of nerve fibers with
the increase in disc area.6,7 Yet in humans, the
larger disc size was associated with a decrease
in nerve fiber density per disc area, since the
fibers have a larger area through which to
cross.7

The effect of large ONH on RNFL thickness
is controversial. It has been suggested that the
peripapillary RNFL thickness is greater closer
to the ONH.8 When measuring RNFL around a
large disc with fixed-diameter OCT protocol,
the RNFL thickness is overestimated and
pathological thinning might be overlooked.
Savini, et al. demonstrated that an increase in
disc size is associated with an increase in
RNFL measurements using a fixed-diameter
OCT protocol scan.9 RNFL thickness decrease
with increasing scan radii was also demon-
strated by Carpineto, et al.10 Another study
using RNFL in a constant distance from the
ONH rim, and not the standard fixed-diameter
scan, found thinner RNFL in larger discs.11

Other studies did not find such a correlation
between the circumpapillary RNFL measure-
ment placement and disc size.12

In this study we aim to evaluate OCT ONH
parameters as indicators of eye health in sub-
jects with large discs.

Materials and Methods

Eighty-one eyes of 54 healthy subjects were
evaluated in this retrospective cross- sectional
study in two separate cohorts. Forty-six eyes of

consecutive eligible subjects with large discs
imaged at the Edith Wolfson Medical Center
(Holon, Israel) were recruited to the large disc
size group. Thirty-five eyes of consecutive eli-
gible subjects with normal disc size imaged at
the University of Pittsburgh Medical Eye
Center (Pittsburgh, PA, USA) were recruited to
the control group. The definition of a large disc
was established by the disc area measurement
obtained by OCT according to previously pub-
lished data in healthy subjects.13-15 All discs
with area larger than 2.6 mm2 (mean area +1
standard deviation) were considered to be
large discs, while the control group had disc
areas under 2.6 mm2 This study was approved
by the Institutional Review Board (IRB) /
Ethics Committee at both institutions and
adhered to the Declaration of Helsinki and
Health Insurance Portability and
Accountability Act (HIPAA) regulations.
Informed consent was obtained from all partic-
ipants.
In both groups, all subjects denied ocular

complaints or diseases, had intraocular pres-
sure of less than 22 mmHg, normal anterior
segments on slit lamp exam, normal discs and
maculae, reliable normal visual fields in both
eyes, and normal mean RNFL thicknesses in
both eyes. Exclusion criteria were refractive
error > ± 6 D (spherical equivalent), peripap-
illary atrophy, and any eye pathology or previ-
ous eye surgery except for uncomplicated
cataract extraction. 
All subjects were scanned after pupillary

dilatation with the time-domain OCT, the
StratusOCT (software version 4.0; Carl Zeiss
Meditec, Inc. Dublin, CA, USA), by experienced
operators. OCT measurements of the ONH
were generated with the fast optic disc acqui-
sition protocol of six total radial scans 6 mm in
length in a spoke pattern configuration cen-

Eye Reports 2011; volume 1:e11

Correspondence: Zvia Burgansky - Eliash,
Department of Ophthalmology, Wolfson Medical
Center, P.O. Box 5, Holon 58100, Israel.
Tel. +972.3.5028469 - Fax: +972.3.5028133.
E-mail: zviaeb@gmail.com

Key words: ocular coherence tomography, optic
nerve head, large discs.

Received for publication: 11 May 2011.
Revision received: 5 October 2011.
Accepted for publication: 18 October 2011.

This work is licensed under a Creative Commons
Attribution NonCommercial 3.0 License (CC BY-
NC 3.0).

©Copyright G.A. Weiss et al., 2011
Licensee PAGEPress, Italy
Eye Reports 2011; 1:e11
doi:10.4081/eye.2011.e11

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[Eye Reports 2011; 1:e11] [page 35]

tered on the ONH, evenly spaced 30 degrees
apart. Each radial scan included 128 A-scans.
Qualified scans had signal strength of at least
6. The OCT defined the ONH margin automat-
ically as the end of the retinal pigment epithe-
lium. The generated image was manually cor-
rected in case the OCT did not recognize accu-
rately the ONH margin. The rate of images that
were manually adjusted was not recorded; pre-
vious studies reported manual adjustment of
disc margin in 50-60% of cases.9,16 All ONH
parameters were documented, including VIRA,
HIRW, rim area, cup area, CD area ratio,
HCDR, VCDR, cup area topography (using an
offset of 150 microns), and cup volume (using
an offset of 150 microns). In addition, OCT
RNFL global mean thickness and four quadrant
mean thicknesses were analyzed.
Statistical analysis was performed to deter-

mine the differences in mean values of ONH
parameters between the two groups, using the
general linear model (GLM). The number of
eyes was included in the linear model in order
to control for the use of both eyes in some
patients. In each model, diagnosis and sex
were included as fixed factors. Correlation
analysis was used to determine the association
between rim and cup parameters to disc area,
in both groups. Significance was set as a P
value of less than 0.05.

Results

The study population characteristics are
summarized in Table 1. There were no age dif-
ferences between the two study groups. All
subjects were Caucasians. There were more
female subjects in the large disc group than in
the control group (P=0.03). The average disc
area in the large disc group was 3.01 mm2

(range 2.6-3.7) while the average disc area in
the control group was 2.05 mm2 (range 1.5-2.5,
P<0.01). 
The various average ONH parameters pro-

vided by the OCT in the two groups are shown
in Table 2. All cup parameters were significant-
ly higher in the large disc group compared to
the control group. The parameters estimating
the rim varied between the groups: in the large
disc group, VIRA was significantly lower while
HIRW was significantly higher, compared to
the control group. The only parameter that did
not vary between the groups was the rim area,
with a value of 1.52 ± 0.24 mm2 in the large
disc group and 1.6 ± 0.3 mm2 in the control
group (P=0.15).
In the large disc group, a significant correla-

tion was demonstrated between all cup param-
eters and disc area (cup area: r=0.75, P<0.01,
CD area ratio: r=0.48, P=0.001, HCDR: r=0.34,
P=0.02, VCDR: r=0.495, P<0.01, cup area
topography: r=0.56, P<0.01, and cup volume:

r=0.36, P=0.001, Figure 1). On the other hand,
in this group, no significant correlation was
demonstrated between any of the rim parame-
ters and the disc area (Figure 2). 
In the regular disc size group, a significant

association with disc area was evident only in
cup area (r=0.34, P=0.04) and cup volume
(r=0.35, P=0.04) but not in the other cup
parameters (Figure 3). In this group, 2 of 3 rim
parameters were significantly correlated with
disc area: HIRW (r=0.57, P<0.01) and rim area
r=0.54, P=0.001 (Figure 4).
We found a trend of correlation (P=0.07,

r=0.3) between the disc area and the mean
RNFL in the control group but not in the large
disc group or the two groups combined. The
quadrant RNFL data did not correlate to the
disc area in any of the groups.

Discussion

Disc size varies significantly in healthy sub-
jects with ophthalmoscopically-measured disc
area ranging between 0.8 and 6 mm2.17

Subjects with large discs and large cups are
often referred to glaucoma clinics with sus-
pected glaucoma by optic nerve appearance. It
is known that in a large disc, a large cup is also
expected.6,18 Nevertheless, a good objective tool

is needed to differentiate between physiologi-
cal large cups in large discs and glaucomatous
large optic nerves. Measuring circumferential
RNFL with fixed-diameter OCT protocol may be
misleading in these cases because of closer
approximation to the ONH edge, which gives
artificially higher values.8 In this study we
found that while all ONH parameters varied
between subjects with regular disc size and
those with large disc and large cups, rim area
had similar values in both groups.
There are three different rim parameters

derived from the ONH scan: VIRA, HIRW and
rim area, each behaved differently when the
two study groups were compared. VIRA esti-
mates the total volume of rim tissue, as
defined previously. In this study we found a
significantly lower value in the large disc
group, suggesting the discs in this group were
shallower. HIRW estimates the total area of rim
tissue, as defined previously. Interestingly, the
value of HIRW was significantly higher in the
large disc group compared to the controls,
implying that the rim in this group is thicker,
as was found in histology studies.7,18 In con-
trast to the VIRA and HIRW, the rim area
parameter, as defined previously, had similar
values in both groups. We did find that in the
large discs, all 6 parameters describing the cup
and CD area ratio are larger, as described by
previous histology studies that found larger

Article

Table 2. Optic nerve head mean parameters.

Large disc Regular disc P*
(mean ± SD) (mean ± SD)

Vertical integrated rim area (VIRA, mm3) 0.25±0.01 0.41±0.18 <0.0001 
Horizontal integrated rim width (HIRW, mm2) 1.76±0.16 1.64±0.19 0.003 
Rim area (mm2) 1.52±0.24 1.60±0.30 0.15 
Cup area (mm2) 1.49±0.37 0.45±0.27 <0.0001 
CD area ratio 0.49±0.01 0.21±0.12 <0.0001 
Horizontal CD ratio (HCDR) 0.72±0.008 0.46±0.14 <0.0001 
Vertical CD ratio (VCDR) 0.66±0.01 0.43±0.13 <0.0001 
Cup area topography (mm2) 1.32±0.37 0.76±0.62 <0.0001 
Cup volume (mm3) 0.33±0.14 0.009±0.01 <0.0001 
The mean value of the ONH parameters in each group and the P value of comparison. ONH, optic nerve head; CD, cup to disc; *Independent-
sample two-tailed t-test.

Table 1. Demographic and clinical characteristics of the study population.

Large disc Regular disc P

N eyes (pts) 46 (25) 35 (28)
Age (yrs) 55.1±12.6 54.4±19.4 0.86*
Female / Male 31/15 15/20 0.03°
Disc area (mm2) 3.02±0.26 2.05±0.26 <0.0001*
RNFL (µm) 99.09±9.1 96.24±9.73 0.18*
Superior RNFL (mm) 121±11.8 117±17.3 0.26*
Nasal RNFL (mm) 80±13.2 79±14.5 0.89*
Inferior RNFL (mm) 126±16.8 120±16.1 0.11*
Temporal RNFL (mm) 70±12.3 69±11.5 0.62*
A comparison of patients’ characteristics between the study groups. RNFL, retinal nerve fiber layer; *Independent-sample two-tailed t-test;
°Chi-square tests.

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[page 36] [Eye Reports 2011; 1:e11]

cup area in larger discs.6,18

Moreover, in large discs, we found a positive
correlation between the cup parameters and
disc area, while such association was not
found with rim parameters. Thus, when pass-
ing a certain threshold of disc size, further
enlargement of the disc directly influences the
cup size while rim magnitude does not
increase. On the other hand, in disc area range
under 2.6 mm2, as the disc is getting bigger,
rim size increases while most cup dimensions
are not influenced. Indeed, a recent large scale
study with subjects who had a wide range of
disc sizes (average 2.27 mm2) found correla-
tions between disc area and the same parame-
ters as seen in the regular disc group in our
study.14

Rim area was found to be similar in the
entire cohort of healthy discs in our study,
whether large or normal in size (1.52±0.24
mm2 and 1.6±0.3 mm2, respectively) as was
previously demonstrated using the Heidelberg
retinal tomography, HRT (Heidelberg
Engineering, Inc., Carlsbad, CA, USA).19 This
parameter was also found to be a reliable indi-
cator of glaucomatous optic neuropathy. The
area under the receiver operating curve
(AROC) for discrimination between healthy
and glaucomatous eye in different publications
was 0.92 to 0.97 with average values of
0.84±0.31 mm2 in Wollstein, et al.3 and
0.89±0.34 mm2 in Naithani, et al.13 in the glau-
comatous population. This data from the liter-
ature further supports the role of rim area
parameter as an important indicator for disc
health. 
The lack of correlation between RNFL meas-

urements and disc size in the large disc group
may have resulted from inhomogeneity of the
discs characteristics. Two possible and contra-
dicting factors may influence the RNFL thick-
ness measurement with a fixed-diameter scan
circle in large discs. The first factor is the
shorter distance from the ONH rim which
increases the thickness,9,10 and the second fac-
tor is the thinner overall RNFL thickness in
these discs.7,11 As these factors are opposed,
the net correlation in a group may vary.
One potential limitation of this study is the

exclusive inclusion of Caucasian subjects.
Subjects from African ancestry present higher
prevalence of large discs, when compared with
Caucasian patients,14 therefore further investi-
gation is warranted in this population. Another
possible limitation results from a higher preva-
lence of female participants in the large disc
group, although we controlled for sex bias in
the statistical analysis we conducted. We did
not perform sample size calculations, thus the
lack of difference in rim area could result from
insufficient study cohort, although differences
in other ONH parameters were highly signifi-
cant. Another limitation is the lack of axial
length comparison between the groups,

Article

Figure 1. Correlation of cup parameters with disc area in the large disc group. In the large disc
group, a significant correlation was demonstrated between all cup parameters and disc area.

Figure 2. Correlation of rim parameters with disc area in the large disc group. In the large
disc group, no significant correlation was demonstrated between any of the rim parame-
ters and the disc area.

Figure 3. Correlation of cup parameters with disc area in the control group. In the regu-
lar disc group, a significant association with disc area was not evident in most cup param-
eters except for the cup area and cup volume.

Figure 4. Correlation of rim parameters with disc area in the control group. In the regu-
lar disc group, 2 of 3 rim parameters were significantly correlated with disc area (HIRW
and rim area).

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[Eye Reports 2011; 1:e11] [page 37]

despite exclusion of subjects with high refrac-
tive errors. The axial length was found to be
inversely correlated to the disc size20 and
should be included in future studies. A possi-
ble bias is a selection bias of large cups among
the large disc cohort, since these subjects were
referred to the clinic with suspicious discs, yet
this served to answer the clinical question.
Our findings may have significant implica-

tions on the clinical use of OCT. Rim area
might serve as an indicator for disc health in
large discs. These findings need to be further
explored in subjects with large discs who have
glaucoma.

Appendix

The StratusOCT provides several calculated
values. The vertical integrated rim area (VIRA)
is a measure of the total volume of the retinal
nerve fiber layer within the rim that is calcu-
lated by the StratusOCT using the product of
the disc circumference and average of 6 indi-
vidually-calculated sectional rim areas (in
each of the 6 spokes). The horizontal integrat-
ed rim width (HIRW) is a measure of the total
rim area that is calculated by the StratusOCT
using the product of the disc circumference
and average of 6 individually-calculated sec-
tional rim widths (in each of the 6 spokes)
rather than rim areas. The rim area is the area
of the cup subtracted from the area of the disc,
calculated from a flattened planimetric image
of the disc in axis with the pupil. The cup area
also is calculated from a flattened planimetric
image of the disc in axis with the pupil. The
horizontal cup to disc ratio (HCDR) is the ratio
of longest horizontal line across the flattened
planimetric ring image of the cup calculated
from cross-sectional 3-dimentional data along
6 axes (in each of the 6 spokes) to the longest
horizontal line across the flattened planimetric
image of the disc calculated from cross-sec-
tional 3-dimentional data along 6 axes (in each
of the 6 spokes), whether or not these two hor-
izontal lines overlap. The vertical cup to disc
ratio (VCDR) is the ratio of longest vertical
line across the flattened planimetric image of
the cup calculated from cross-sectional 3-
dimentional data along 6 axes (in each of the
6 spokes) to the longest vertical line across the
flattened planimetric image of the disc calcu-
lated from cross-sectional 3-dimentional data
along 6 axes (in each of the 6 spokes), whether
or not these two vertical lines overlap. The cup

area topography is the calculated cup area
based on the 3-dimentional topography of the
cup obtained along 6 axes (in each of the 6
spokes) using a fixed standard offset which is
often 150 microns. The cup volume is the cal-
culated cup area based on the 3-dimentional
topography of the cup obtained along 6 axes
(in each of the 6 spokes) using a fixed stan-
dard offset, which is often 150 microns. 

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