Download Optic Cup in Normal and Glaucomatous Eyes

Volume 9
Number 6
Symposium 425
nographies, carried out at the time of maximal drug effect, showed no reduction in
resistance. Fifty per cent of the patients
studied showed a tachycardia with associated palpitations or weakness following
prolonged use of the drug. It was concluded that isoproterenol produces a re-
duction in intraocular pressure in man,
unaccompanied by an improvement in
facility of outflow. Direct measurements
of aqueous production seem to be necessary
to establish the pharmacologic effects of
the beta stimulator isoproterenol on
aqueous dynamics in man.
Optic cup in normal and glaucomatous eyes
M. F. Armaly
Enlargement of the optic cup occurs early in the clinical course of open-angle glaucoma and
results in inequality of this ratio in the 2 eyes. The enlargement, in general, parallels the
magnitude of field defect. It is suggested that involvement of the visual field in eyes with
ocular hypertension is related to the cup disc ratio (C/D), being more frequent in eyes with
genetically large cups
T,
he ratio of the horizontal diameter of
the optic cup to that of the optic disc
(C/D), estimated to the nearest tenth by
ophthalmoscopic examination, was shown
to exhibit marked individual variation
which was independent of age and sex. It
was found to be genetically determined
and separately related to two genetically
determined measures, applanation pressure (PA) and tonographic estimate of
aqueous outflow facility (C). This relationship exhibited significant interaction,
such that the highest frequency of large
ratios, i.e., C/D > 0.3, occurred in eyes
with high PA readings and low C values,
whereas in eyes with large C values this
frequency did not vary with PA-1"3
In eyes with established glaucomatous
From the Department of Ophthalmology, University Hospitals, Iowa City, Iowa.
This investigation was supported in part by
research grant CD-00017 from the National
Center for Health Services Research and Development Health Services and Mental Health,
and NB-07328 from the National Institute of
Neurological Diseases and Blindness, United
States Public Health Service, Bethesda, Md.
field defect, marked variation in this ratio
was encountered, such that it could not be
used to predict the presence of field defect.4 These studies emphasized the difference between an acquired enlargement
of the optic cup in glaucoma and the
genetically large cup in the normal eye
and indicated that a significant clue in
this regard is that in the normal, the ratio
is equal in the 2 eyes, and a difference >
0.2 occurs in less than 1 per cent of the
normal samples.
This report will be concerned with the
C/D ratio in individuals, free of ocular
complaints, who were discovered to have
glaucomatous field defect as they participated in studies involving the normal
population. Such individuals constitute the
earliest clinical stage of glaucoma. Findings in these subject indicate that enlargement of the optic cup is already evident
at this stage of involvement and can be
suspected by comparison of the 2 eyes.
Ophthalmoscopic examination is important
in this regard. Involvement of the visual
field in eyes with high applanation pressure may be significantly related to the
genetically determined size of the optic
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426 Armaly
Investigative Ophthalmology
June 1970
cup and occurs more frequently in eyes
with large C/D ratios.
The sample
The sample consisted of 83 subjects
who had been discovered, through their
participation in population studies, to have
a PA level of 20 mm. Hg or higher, a
50
Affected eye
40
§
glaucomatous defect of the visual field,
and open angles on gonioscopy. They had
experienced no significant ocular symptoms and had, to the best of their knowledge, normal eyes. Field defects that were
considered glaucomatous were demonstrated with the stimulus of 1-2-e or larger
on the Goldmann perimeter and consisted
•Normal control
30
20
10
0.0-0.1
0.2-0.3 0.4-0.5 0.6-0.7
CUP/DISC, Ratio
0.8-0.9
Fig. 1. The C/D ratio in the affected eye of patients with unilateral field defect. C/D ratio
of the affected eye is represented in stippled bars and that of the normal control in light
gray bars.
50
Unaffected eye
40
rNormal control
30
20
10
0
0.0-0.1
-mm
0.2-0.3 0.4-0.5 0.6-0.7
CUP/DISC Ratio
0.8-0.9
Fig. 2. C/D ratios in the unaffected eye of patients with unilateral field defect. C/D ratio
of the unaffected eye is represented by stippled bars and that of the normal control in light
gray bars.
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Volume 9
Number 6
Symposium 427
of the following: (1) arcuate scotoma
continuous with the blind spot and greater
than 45 degrees, (2) paracentral scotoma
larger than 5 degrees in diameter, and
(3) nasal step greater than 10 degrees.
In 52 subjects the defects existed in one
eye only, the other having normal visual
field. Both eyes were affected in 31 subjects.
Results
In order to compare the C/D ratio in
this sample with an appropriate control,
the frequency distribution of C/D ratio in
individuals with normal visual fields in
both eyes and a pressure of 20 mm. Hg
or higher was used as a reference or control. In this group, the frequency of C/D
> 0.3 was greater (27 per cent) than that
in normal eyes with PA less than 20 mm.
Hg (15.5 per cent).
The results of the first group of unilateral involvement appear in Figs. 1 and
2. The distribution of C/D ratios in the
affected eye differs markedly from that of
the control. In the affected eye, the frequency increases with larger cup/disc
ratios, being greatest for C/D of 0.8 to
0.9, whereas in the control, the frequency
is highest for C/D values between 0.0 and
0.3 and decreases markedly and progressively for larger C/D values so that the
least frequent is 0.8 to 0.9. In the unaffected eye, the frequency distribution of
C/D ratio is also different from the control group. Frequency of C/D of 0.0 to
0.1 is very small compared to the control,
whereas that of values greater than 0.3 is
comparatively greater. These differences
in frequency are statistically significant at
the 1 per cent level of confidence.
If we now compare in each individual
the C/D ratio in the affected eye with
that of the uninvolved eye, we see evidence that the C/D ratio in the affected
eye has already become enlarged. Instead
of values falling on the line indicating
equality of the 2 ratios or being distributed randomly above and below it, a systematic effect is evident (Fig. 3): The
C/D ratio of the affected eye is larger
than that of the unaffected eye.
The results of the second group with
bilateral involvement appear in Figs. 4
and 5. They demonstrate the greater frequency of large C/D ratios in these eyes
and the greater enlargement of the cup in
eyes with a greater field defect.
Comments
0.9
•
*
/
0.7
i
6
«i
w
•
0.5
0.3
0.1
0 0.1 0.3 0.5 0.7 0.9
Fig. 3. C/D ratios in subjects with unilateral
glaucomatous field defect. C/D ratio in the eye
with normal field appears on the abscissa and
that in the eye with field defect on the ordinate.
The line representing equality of the 2 ratios is
drawn. Each subject is represented by one point
at the intersection of the 2 coordinates of the
C/D ratios in his 2 eyes.
These findings clearly point out that enlargement of the optic cup in open-angle
glaucoma is not limited to the later stages
of the clinical disease but can be detected
in the earlier stages, long before the individual becomes aware of this condition. As
such, it becomes an important useful tool
in the suspicion and detection of this
otherwise symptomless disease.
In individuals with monocular involvement of the visual field, the C/D ratio
was larger in the affected eye in 36 subjects. Thus, with careful ophthalmoscopic
examination, one could have suspected
glaucoma on the basis of this inequality in
69 per cent and successfully identified the
involved eye in 63 per cent of this group.
Considering the simplicity of this procedure and the high frequency of false posi-
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Investigative Ophthalmology
June 1970
428 Armaly
50
r
40
-Normal control
^
I
30
mm
mm
20
10
0L
0.0-0.1
0.2-0.3 0.4-0.5 0.6-0/?
CUP/DISC Ratio
0.8-0.9
Fig. 4. C/D ratio in patients with bilateral field defects. C/D ratio of affected eyes is
represented in stippled bars and that of the normal control in light gray bars.
0.9 r
0 0.1
Fig. 5. C/D ratios in subjects with bilateral glaucomatous field defects. C/D ratio in the eye with
the lesser defect appears on the abscissa and that
in the eye with the greater defect on the ordinate.
The line indicating equality of the 2 ratios is
drawn. Each subject is represented by one point
at the intersection of the 2 coordinates of C/D
ratios of his 2 eyes.
tive suspicion by tonometry alone, the
clinical usefulness of ophthalmoscopy in
early detection of glaucoma becomes obvious. This is further emphasized by the
innocuous nature of this examination and
the feasibility of including ophthalmoscopy as a part of the general medical
examination of the practicing physician.
This inequality was present also in bilaterally involved eyes. Here, however, the
process of enlargement of the cup has affected both eyes and the difference between them has been masked by this process so that inequality occurred in 52 per
cent. In the two groups combined, inequality was present in 63 per cent of
subjects.
If we consider the C/D ratio in the uninvolved eye in individuals with unilateral
field defects to represent the genetically
determined ratio for that individual, and
compare its distribution with that in ocular hypertensive subjects with normal
visual fields in both eyes, we are led to
conclude that affected individuals were
not randomly selected from among the
ocular hypertensive group to represent all
C/D ratios. Instead, those with large C/D
ratios were selected with a significantly
greater frequency. Thus, from among
ocular hypertensive subjects, those with
large C/D ratios developed a glaucomatous field defect with a significantly
greater frequency than those with small
C/D ratios. Long-term follow-up of individuals with ocular hypertension and varying values of C/D ratio, who have normal
visual fields, is currently in progress in
order to evaluate this conclusion. Those
who have a large C/D ratio are expected
to develop field defects in the future more
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Symposium 429
Volume 9
Number 6
frequently than those with small C/D
ratios.
The results in bilaterally affected individuals suggest that they fall into two
clusters: one with small C/D ratios and
another with large C/D ratios. This could
reflect a distortion in the distribution of
C/D ratio due to the acquired enlargement; on the other hand, it could indicate
that different sets of factors are involved
in the production of the field defect in
these two groups. Systemic factors, vascular, metabolic, or endocrine, have been
shown to influence the vulnerability of the
visual field to the ocular pressure level.
These may play different roles in the two
clusters.
REFERENCES
1. Armaly, M. F.: Genetic determination of
cup/disc ratio of the optic nerve, Arch.
Ophthal. 78: 35, 1967.
2. Armaly, M. F., and Sayegh, R. E.: The
cup/disc ratio—the findings of tonometry and
tonography in the normal eye, Arch. Ophthal.
82: 191, 1969.
3. Armaly, M. F.: The optic cup in the normal
eye. I. Cup width, depth, vessel displacement,
ocular tension and outflow facility, Amer. J.
Ophthal. 68: 401, 1969.
4. Armaly, M. F.: The correlation between
appearance of the optic cup and visual function, Trans. Amer. Acad. Ophthal. Otolaryng.
78: 898, 1969.
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