Diagnosis of Pre-perimetric Glaucoma using Optical ... - KSOS

March 2008 Saikumar et al. - OCT in Pre-permetric Glaucoma 39
Diagnosis of Pre-perimetric Glaucoma
using Optical Coherence Tomography
Dr. S J. Saikumar MS, Dr. Saphy Jose, Dr. Savita Bhat MS, Dr. Mahesh G. MS, FRCS, Dr. A. Giridhar MS
Abstract
Introduction
Objective: To study the efficacy of Optical Coherence Tomography in pre perimetric
glaucoma.
Methods: 76 glaucoma suspects with normal or borderline white on white visual fields
underwent RNFL analysis with Optical Coherence Tomography (Stratus OCT version 4).
Outcome measure: Borderline or definite RNFL thinning in the inferior or superior
quadrants was taken as the main outcome measure.
Results: Six out of seventy six glaucoma suspects showed RNFL changes in OCT suggestive
of glaucoma giving the test a specificity of 92 %. All six patients had cup disc ratio of 0.6 or
more and five out of six patients had IOP of 18 or more and positive family history of glaucoma.
Conclusion: Optical Coherence Tomography is an useful tool for diagnosis of pre perimetry
glaucoma especially in the presence of other risk factors like raised IOP, enlarged cup and
family history of glaucoma.
Glaucoma is an optic neuropathy characterized by a
specific and progressive injury to the optic nerve and
retinal nerve fiber layer 1 . Because the injury due to
glaucoma is irreversible, early detection and prevention
of glaucomatous RNFL loss is of vital importance.
Examination of the optic nerve head and its surrounding
nerve fiber layer is considered essential in both
detection and monitoring of glaucoma. Damage to the
RNFL has been shown to precede visual field loss. Upto
30-50 % nerve fibre loss might have occurred before
the first detectable field defect 2 . Hence, objective
Giridhar Eye Institute, Ponneth Temple Road, Kadavanthra, Cochin 682 020
E-mail: girieye@vsnl.com
ORIGINAL
ARTICLE
methods of measuring these structures will aid
ophthalmologists in making an accurate diagnosis.
Optical Coherence Tomography (OCT) which was first
described in 1991, is a high resolution cross sectional
imaging technique that allows accurate measurement
of the retinal nerve fiber layer 3 . With the ability to
quantify the thickness of the RNFL with a resolution of
8 to 10 microns, clinicians potentially have a more objective
tool in helping to diagnose glaucoma much earlier than
visual fields. However, white on white perimetry is still
considered the gold standard for diagnosis of glaucoma.
AAO Preferred Practice Patterns still mentions that the
diagnosis of glaucoma is based on appearance of the
optic disc and standard achromatic perimetry 4 . In this
current study glaucoma suspects who had normal or

40 Kerala Journal of Ophthalmology Vol. XX, No. 1
borderline visual fields were subjected to RNFL analysis
using Optical Coherence Tomography.
Materials and Method
The sudy was designed as a retrospective observational
case series which included glaucoma suspects attending
a tertiary care glaucoma centre.
Study Population: 103 glaucoma suspects who
underwent RNFL analysis on Optical Coherence
Tomography were initially enrolled, out of which 76
eyes of 76 patients fulfilled all criteria and were finally
included in the study. Only one eye per person was
included in the study. If one eye had abnormal fields
and the other eye normal, the normal eye was included
in the study. If both eyes were normal or both were
borderline, the eye with the better PSD value on HFA
was selected and assigned to the study.
Complete ophthalmic examination including visual
acuity, intraocular pressure, gonioscopy and optic disc
evaluation was performed. All patients initially
underwent either 30-2 full threshold or SITA - standard
white on white perimetry. The time gap between
perimetry and OCT was not more than two weeks.
Patients with spherical refractive errors of more than
6D, astigmatism more than 3 Dioptres, visual acuity
worse than 6/12 were excluded from the study. Other
exclusion criteria were secondary causes of raised IOP,
abnormal disc appearance such as tilted discs and
suspected neurological diseases which are likely to
affect the field testing. Those patients with extensive
peripapillary atrophy were also excluded from the study.
Definition of glaucoma suspect: For the purpose
of this study a glaucoma suspect was defined as the
presence of an abnormal disc appearance consistent
with glaucoma as determined by an experienced
clinician. Disc asymmetry of 0.2 or more was also
included in the definition of glaucoma suspect.
Observation procedures: All selected patients had
a reliable visual field on Humphrey Visual Field
Analyzer. Reliable fields were defined as fixation loss
rate of less than 33 % and false positive and false negative
error rates of less than 20 %. Normal and borderline
definitions were based on the glaucoma hemi field test.
OCT measurements: The test was performed after
dilation of the pupil to at least 5 millimetre. Three
measurements were performed for each eye. Only
measurements with signal strengths of six or more were
accepted as reliable for this study.
Outcome Measures: Definite RNFL thinning (shaded
as red) or borderline RNFL thinning (shaded as yellow)
in either the inferior or superior portion of the disc
was taken as the main outcome measure. Charts with
only temporal or nasal thinning were excluded from
the study.
Statistical Analysis: The Fisher exact test was used to
assess the statistical significance of glaucomatous
changes in OCT in the presence of other risk factors
like raised IOP, family history of glaucoma and enlarged
cup-disc ratio. Odds ratio was also calculated for the
above mentioned risk factors.
Results
After all exclusions, 76 eyes of 76 patients were enrolled
in the study, of which 51 were males and 25 were
females. The age group distribution is shown in Figure1.
Fig. 1. Age group distribution of the study population
A total of 6 patients had abnormal OCT among the
76 patients enrolled in the study.15 patients had a
positive family history of glaucoma in either their first
degree or second-degree relative and out of these 5
had abnormal OCT. Only one person with abnormal
OCT had no family history of glaucoma. The difference
between the positive family history group and the
negative family history group was statistically
significant (p value 0.001, Fisher exact test). The odds
of having an abnormal OCT was 36 times in persons
having a positive family history of glaucoma.
A total of 47 persons had a CD ratio of 0.6 or more, out
of which 17 had CDR of more than 0.8 (Figure 2).
5 out of 6 OCT positive persons had a CDR of 0.8 or
more, and one had a CDR of 0.7. When a CDR of 0.6
was taken as the cut-off, the chance for having an

March 2008 Saikumar et al. - OCT in Pre-permetric Glaucoma 41
abnormal OCT was not statistically significant (p value
0.0768, Fisher exact test). But when CDR of 0.8 was
taken as the cut-off, the chances of having an abnormal
OCT was statistically significant (p value 0.0017, Fisher
exact test). Persons with a CDR of 0.8 or more are
22 times more likely to have an abnormal OCT,
compared to those having a CDR of 0.7 or less.
The mean IOP of the 76 eyes enrolled in the study was
16.29. 26 patients had an IOP of 18 or more, out of
which only 7 eyes had an IOP of 22 mm Hg or more
(Figure 3). 5 out of the 6 patients who had an abnormal
OCT had IOP more than 18 mm Hg. With 18 mm Hg as
the cut-off, the chance of having an abnormal OCT was
statistically significant (p value 0.0161, Fisher exact
Fig. 2. Distribution of cup disc ratio in the study population
test). The odds of having an abnormal OCT was 11
times more in persons with an IOP of more than 18
when compared to those with IOP of 17 or less.
OCT in glaucoma is a very effective tool in identifying
the true negatives. It shows that 70 out of 76 eyes was
proven as not having glaucomatous damage. This gives
the test a specificity of 92 %.
Fig. 3. Distribution of IOP in the study population
4 eyes had inferior thinning and 2 had superior thinning.
No biarcuate thinning was seen in any of the six cases.
5 eyes out of 6 had definite thinning of RNFL (shaded as
red) and I had borderline thinning (shaded as yellow).
In the 70 persons with normal OCT, mean RNFL
thickness was 119.3 and 124 in the superior and inferior
quadrants respectively. Compared to this, the same
Table 1 showing mean superior and inferior RNFL
thickness in patients with normal and abnormal OCT
values were 79 and 75.33 respectively in the 6 patients
with abnormal OCT. (Table 1)
Discussion
Mean superior Mean inferior
RNFL thickness RNFL thickness
(in microns) (in microns)
Patients with 119.3 124
normal OCT
Patients with 79 75.33
abnormal OCT
We have studied 76 eyes of 76 patients who were
clinically found to have some suspicion of Glaucoma.
The numbers were slightly smaller compared to a few
other studies 5, 6 . Ours was an observational study and
there was no control group, which were used in other
studies 5, 6 . In the study by Kanamori et al 6 normal
population, glaucoma suspects, ocular Hypertensives
and glaucoma patients were included in the study and
compared. We were only studying the ability of the
OCT in picking up Pre perimetric glaucoma in suspected
cases.
The role of family history has been highlighted in many
studies 7,8,9 although the incidence of MYOC mutation
among Indian primary open angle glaucoma patients
has been found to be lower compared to certain other
parts of the world 10 . In our study, in glaucoma suspects
with normal fields, those with positive family history
of glaucoma are 36 times more likely to have an
abnormality in OCT when compared to those with no
family history of glaucoma.
Cup – disc ratio has been used to define glaucoma
suspects in many other studies 11 . Lalezary et al 11 have

42 Kerala Journal of Ophthalmology Vol. XX, No. 1
used stereo photographs to classify the study
population into normal and glaucoma suspects. In our
study the classification has been done by an experienced
glaucoma specialist by using 78 D lens biomicroscopy.
In our study, the specificity was a healthy 92 %, which
means the OCT is a good tool to rule out disease.
Sensitivity was not calculated in our study since this
requires a normal age-matched control group. Budenz
et al showed a sensitivity of 84 % and a specificity of
98 % in their study on perimetric glaucomas 12 .
As expected the mean RNFL thickness in the inferior
and superior quadrant was significantly lower in the
abnormal OCT group compared to the normal OCT group.
Kanamori et al have studied the temporal and nasal
thickness also along with the superior and inferior 6 .
We felt that many errors may crop up if the nasal and
temporal thickness was included. Also the inferior and
superior poles were the first affected in early glaucoma.
The normal OCT showed the characteristic double-hump
pattern which is in agreement with other human 6 and
histologic studies 13 .
Self assessment of this study – STARD
guidelines
Standards for Reporting of Diagnostic Accuracy
(STARD) is an internationally accepted method of
assessing a study conducted on a diagnostic equipment.
A recent report on the quality of reporting of diagnostic
accuracy was conducted with 30 published articles. The
STARD guideline consists of 25 points which are to be
fulfilled for a good diagnostic study 14 . In this meta
analysis only 26 % of the papers reported more than
half of the STARD items. Our study has reported
11 out of the 25 STARD items, and this compares well
with many published articles on diagnostic accuracy of
OCT in diagnosis of early glaucoma.
Conclusion
Optical Coherence Tomography is a useful tool for pre
perimetric diagnosis of glaucoma. The usefulness of
this tool increases in the presence of other risk factors
like family history of glaucoma, large cup disc ratio
and high intra ocular pressure. The specificity of this
tool in our study was 92 % which makes it a good tool
to rule out those who do not have glaucoma.
Comparative studies with the other imaging tools like
HRT and GDx are needed in our population to
determine which is the best tool for diagnosis of early
glaucoma.
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