The purpose of this study was to compare Intraocular Pressure (IOP) measurements obtained with the Diaton Tonometer (DT) and Non Contact Pneumotonometer (PT) in normal eyes. The effect of central corneal thickness (CCT) on IOP measurement using both the tonometers was also evaluated.

1. 260 AIOC 2008 PROCEEDINGS
Comparison of Diaton Tonometry and Non Contact Tonometry
in Indian Subjects
Dr. Shaun Maria Dacosta, Dr. Babu Rajendran, Dr. Janakiraman P.
(Presenting Author: Dr. Shaun Maria Dacosta)
I ntraocular pressure is an important risk informed consent, the intraocular pressure was
factor for the development of any form of measured first with the Non contact
glaucoma. Measurement of intraocular pneumotonometer (CT-60 Computerized
pressure has come a long way, since the use of Tonometer Topcon) and after an interval of 10
digital palpation of the upper lid, the earliest mins with the Diaton tonometer (BiCOM Inc.).
method employed to approximately estimate Central corneal thickness (CCT) was measured
the intraocular pressure. Currently, there are using Specular Microscope (SP-2000P
several noncontact and contact tonometers Topcon).The average of three readings were
available for intraocular measurement. With taken for the measurements obtained with
the recent introduction of the Diaton Non contact pneumotonometer and Specular
tonometer, intraocular pressure measurement Microscope. Left eyes were randomly chosen
has come one full circle. However, the for the analysis. All patients who met the
Goldman applanation tonometer is still inclusion criteria described below were
considered the gold standard, despite the enrolled in this study.
sources of error which significantly influence Each study participant underwent complete
its readings1. ophthalmic examination including a medical
Diaton tonometer is a non-contact (no contact history review, best corrected visual acuity
with cornea), pen like, hand held, portable (Snellen’s visual acuity), slit lamp examination
tonometer. It has the advantages of requiring and dilated fundus examination.
no anaesthesia, avoids spread of infection and
INCLUSION CRITERIA
can be used in children2.
To be included in the study, the subjects had
The purpose of this study was to compare to have a refraction within ± 5.0 dioptres of
Intraocular Pressure (IOP) measurements spherical equivalent, intraocular pressure d”
obtained with the Diaton Tonometer (DT) and 21mmHg, no family history of glaucoma, no
Non Contact Pneumotonometer (PT) in systemic illnesses, no history of lasers or
normal eyes. The effect of central corneal ocular surgery and no anterior or posterior
thickness (CCT) on IOP measurement using segment pathology.
both the tonometers was also evaluated.
DIATON TONOMETRY
Materials and Methods The patient was placed in the supine position
This study included 100 eyes of 100 normal and instructed to look a little downwards. The
subjects selected randomly from the patient’s upper lid was stretched (without
outpatients who attended our hospital. With pulling it or pressing the eyeball) so as to

2. GLAUCOMA SESSION- II 261
ensure that the edge of the upperlid coincided among the CCT groups. A value of less than
with the superior limbus. After initialization 0.05 was considered to be statistically
of the rod, the tonometer’s tip was placed significant. Bland-Altman plot was used to
vertically on the cartilaginous part of the lid evaluate the agreement between IOP
margin and parallel to it. The vertical position measurements obtained with PT and DT.
of the tonometer was indicated by the lack of
Results
the sound signal, at which instance, the
This study comprised of 48 males and 52
tonometer’s body was gently moved down
females with a mean age of 42.58 ± 13.83 years.
until the rod fell on the eyelid, which was
The summary statistics are shown in Table 1.
accompanied by a short sound signal. The
The CCT was stratified into various groups
measurements were repeated six times with an
and the IOP measurements with both
interval not more than 30secs, at the end of
tonometers were analysed for the different
which a single long signal or two long signals
groups (Table 2). The Bland-Altman plot used
were heard. The operation button was then
for comparison of 2 methods (DT and PT) of
pressed and the mean IOP value was displayed
measurement of the same variable (IOP) is
in nonflickering mode which indicated a
shown in Figure 2.
reliable result.
STATISTICAL ANALYSIS Table-1: Summary statistics (N=100)
Descriptive analysis including mean values Parameter Mean±Standard
and standard deviation (SD) of the various Deviation Range
parameters were performed. Paired t-test was Age 42.58±13.83 20-74
done to compare IOP measurements between PT IOP 17.72 ± 2.65 10-23
the two tonometers. One-way ANOVA was
DT IOP 16.39 ± 4.84 6-25
performed for the comparison of means
PT-DT IOP 1.35 ± 5.40 -10-15
CCT 518 ± 35 425-604
PT IOP = Pneumotonometry intraocular pressure;
DT IOP =Diaton tonometry intraocular pressure;
PT-DT IOP =difference between PT and DT
Fig-1: Diaton Tonometer
tonometry IOP; CCT = central corneal thickness.
Discussion
Currently, there are several instruments
available for the measurement of intraocular
pressure. Studies have shown that the
intraocular pressure measurement obtained
with most of these instruments is influenced
by central corneal thickness by varying
degrees 3. Diaton tonometer is a newly
developed transpalpebral tonometer in which
the ballistic principle of tonometry based on
measuring the elastic reaction of the eye
during the momentary influence of a free
falling object with a definite weight is used.
Fig-2: Bland—Altman plot of the agreement This study was conducted to compare the
between Non Contact Pneumatonometry (PT) intraocular pressure measurements by the
intraocular pressure measurements and Diaton
Diaton tonometer and the Non contact
Tonometry (DT) intraocular pressure
pneumotonometer and to evaluate the
measurements. The difference between the
influence of central corneal thickness on
measurements is plotted against the average of
intraocular pressure measurements with these
the measurements. Dashed lines represent 95%
limits of agreement. instruments.

3. 262 AIOC 2008 PROCEEDINGS
Table-2: Comparison of Non Contact Pneumotonometry (PT), Diaton Tonometry (DT) and
difference between PT and DT intraocular pressure measurements among Central Corneal
Thickness Groups
Pa value
CCT Groups < 500 501-550 551-600 >600
PT (mm Hg)
Mean (SD) 16.97 (2.82) 17.64 (2.33) 19.33 (2.35) 22.50 (0.71) 0.002
Median (range) 17 (10-23) 17 (12-22) 20 914-220 22.50 (22-23)
DT (mm Hg)
Mean (SD) 16.12 (4.85) 16.64 (4.84) 15.83 (5.41) 17.50 (3.54) 0.919
Median (range) 15 (8-25) 17 (6-25) 17.50 (6-22) 17.50 (15-20)
PT-DT
Mean (SD) 0.85 (5.64) 1.04 (5.29) 3.50 (5.33) 5.00 (2.83) 0.355
Median (range) 1 (-9 to 11) 0.00 (-10 to 15) 3 (-5 to 15) 1 (-10 to 15)
PT IOP = Pneumotonometry intraocular pressure; DT IOP = Diaton tonometry IOP;
PT-DT IOP = difference between PT and DT tonometry IOP; CCT = central corneal thickness.
a
One wa y ANOVA for comparison of means within the groups was done.
Table 3: Results of multiple regression analysis of the association between intraocular
pressure measurements with age and CCT
Parameter PT IOP DT IOP
Coefficient (Standard Error) P value Coefficient (Standard Error) P value
Age 0.045 (0.018) 0.012 -0.008 (0.036) 0.823
CCT 0.028 (0.007) 0.000 0.007 (0.014) 0.638
PT IOP = Pneumotonometry IOP; DT IOP = Diaton tonometry IOP
difference in the DT IOP’s (p = 0.919).In the
We found the mean IOP by the Diaton
present study, PT IOP measurements were
tonometer (16.39±4.84 mm Hg) to be
influenced significantly by CCT and age as
statistically lower compared with the Non
predicted by other studies6. However DT IOP
contact pneumotonometer (17.72 ± 2.65mm
measurements were not influenced
Hg) (p = 0.01). However, studies have shown
significantly by CCT and age.
that the transpalpebral method of measuring
IOP with the Diaton tonometer correlates well The Bland-Altman plot showed excellent
with Goldmann Applanation and Tonopen 4,5. agreement between the DT and PT tonometers
as indicated by the mean difference being near
The mean CCT in our study was 518 ± 35. The
zero and location of very few points outside the
DT and PT IOP’s were highest for thicker
upper and lower boundary limits (Figure 2).
corneas (> 600µ). The difference between the 2
measurements was greatest in subjects with In conclusion, Diaton tonometer may be a
thick corneas, gradually lessening as CCT clinically useful device for measuring IOP in
decreased. Although there was a significant routine eye exams especially in patients after
difference in the PT IOP’s among the various refractive surgery or with corneal pathology
CCT groups (p = 0.002) there was no significant since Diaton does not applanate the cornea.
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