Transcript Slide 1

A Prospective Trial Comparing Pneumotonometry of Cornea and Sclera
Usiwoma Abugo BS1 , Sara Duke MD2 , Shuchi Patel, MD2
1Loyola University Chicago, Stritch School of Medicine, Maywood IL
2Department of Ophthalmology, Loyola Medicine, Stritch School of Medicine, Maywood, IL
ABSTRACT
Purpose: Current devices in use to estimate intraocular
pressure (IOP) perform the measurements on the cornea.
However this is not practical or possible in some patients,
such as those with a keratoprosthesis or other corneal
pathology. Therefore scleral IOP measurements have been
attempted but studies have shown that the Tonopen does not
provide accurate readings with scleral measurements. The
purpose of this study is to determine if scleral
pneumotonometry (PT) will provide an accurate and reliable
assessment of IOP. Also, if scleral tonometry is not accurate
but is reliable, perhaps a predictable relationship exists and
thus IOP can be extrapolated from scleral measurement.
Methods: A prospective non-randomized trial of
individuals 18 years of age and older. Each had his/her IOP
measured with the Goldmann applanation tonometer (GAT)
as the gold standard. Then corneal PT and scleral PT on the
temporal sclera were performed.
Results: 108 eyes have been examined to date. The
average GAT IOP was found to be 15.03 mmHg while the
average corneal PT was 18.5 mmHg. The difference between
GAT and corneal PT measurements was 3.4 with a mode of
the differences at 2.0 and 57 of the 108 eyes being over 3
mmHg higher with corneal PT. The average scleral PT was
29.4 with an average difference between GAT and scleral PT
measurements of 14.3 and a mode of 14 with 53 of the 108
eyes above 15 mmHg higher with scleral PT.
Conclusion: Thus far scleral PT has shown consistently
higher IOP measurements than the corneal IOP
measurements in the majority of patients. Yet, there seems to
be a predictable correlation with the IOP being 14 points
higher when measured on the sclera as compared to the gold
standard. With further data collection and analysis we
anticipate that a predictable relationship, that may or may not
be linear, between scleral PT and both corneal PT and GAT
can be established.
MATERIALS AND
METHODS
This was a prospective non-randomized trial
evaluating the accuracy and reliability of scleral PT.
The study was performed at the ophthalmology clinic
of the Loyola Hospital Outpatient Center, Maywood
IL. Patients were recruited and consented in clinic by
a member of the investigative team. Patients were
selected based on the following inclusion criteria:
>18 years of age, male or female, ability to
understand study procedures and to comply with
them for the entire length of the study. Patients were
excluded if they were <18 years of age, had
unwillingness or inability of individual or legal
guardian/representative to give written informed
consent. Patient’s demographic information (age,
gender), ocular history, refractive error, current
medications, PT, GAT and central corneal thickness
readings were collected. Adherence was defined as
at
least
80%
participation
in
tonometry
measurements at the study visit. Values from
patients who did not meet the adherence guideline
were not included in the analysis of the study results.
RESULTS
RESULTS
1.
The average GAT IOP was found to be 15.0mmHg while the average
corneal PT was 18.5mmHg.
2.
The difference between GAT and corneal PT measurements was
3.4mmHg with a mode of the differences at 2.0mmHg and 57 of the
108 eyes being over 3mmHg higher with corneal PT.
3.
The average scleral PT was 29.4mmHg with an average difference
between GAT and scleral PT measurements of 14.3mmHg and a mode
of 14mmHg with 53 of the 108 eyes above 15mmHg higher with scleral
PT.
DISCUSSION
Comparison of Average GAT-C(mmHg), PTC(mmHg), PT-Scl(mmHg). GAT-C was found to be
15.0mmHg ± 3.3mmHg. PT-C was found to be
18.5mmHg ± 3.9mmHg. PT-Scl was found to be
29.4mmHg ± 9.4mmHg.
1.
In our study scleral PT was consistently higher than GAT or corneal
PT for the majority of the patients in the study.
2.
Of the 13 patients whose scleral PT was lower there was no unique
eye pathology distinguishing those eyes from the rest of the
population.
3.
Even with the consistent elevation in scleral IOP preliminary analysis
shows great variability in measurements obtained with the
pneumatonometer.
4.
This observation itself does not rule out the use for scleral
pneumotonometry in the future but points to the need for elimination
of variability in the instrument itself or the measurement taking.
FUTURE DIRECTIONS
Further studies analyzing other factors that may affect the
relationship between GAT and scleral PT such as pachymetry and
age should be conducted to better establish such a relationship and
to eliminate some of the variability. In the future a conversion table
may be established to provide better IOP readings in patients that
cannot have corneal tonometry and are being monitored with finger
tonometry alone.
At the initial visit IOP measurements from both
eyes were obtained. The first measurement was
taken on the central cornea with a Goldmann
Applanation Tonometer AT 900®D (Haag-Streit
International). Then corneal IOP was measured with
a Model 30 Classic Pneumatonometer (Reichert
Ophthalmic Instruments). Scleral IOP was measured
2mm temporally from the limbus. Corneal
Pachymeter was then measured with the DGH
Model 555 PACHETTE 3(DGH Technology Inc.).
REFERENCES
http://www.calcoastophthalmic.com/images/reichert_pneuma.jpg
Comparison of the Differences between
pneumotonometry of the Sclera and
Applanation(PTC-TA), pneumotonometry of the
Sclera and Applanation(PTS-TA), and
pneumotonometry of the Sclera and
pneumotonometry of the Cornea(PTS-PTC).
PTC-TA was found to be 3.379 ± 2.301mmHg.
PTS-TA was found to be 14.3 ± 9.4mmHg. PTSPTC was found to be 10.6 ± 9.2mmHg.
http://pages.glaucoma-association.com/cache/cfx_imagecr3/5381dc677c652311eb5d0d4663eed09b.jpg
http://accessmedicine.net/loadBinary.aspx?name=tint&filename=tint_c636f028t.jpg
1.
Barraza RA, Sit AJ. Investigation to determine a relationship between scleral and corneal tonometry.
ARVO poster presentation; May 02, 2010.
2.
Eisenberg DL, Sherman BG, McKeown CA, Schuman JS. Tonometery in adults and children: a
manometric evaluation of pneumotonometry, applanation and TonoPen in vitro and in vivo.
Ophthalmology: vol 105; 1173-1181.
3.
Erlich JR, Haseltine S, Shimmyo M, Radcliffe NM. Evaluation of agreements between intraocular
pressure measurements using GAT and Goldmann correlated intraocular pressure by Reichert’s ocular
response analyzer. Eye: 2010; 1555-1560.
4.
Shen CC, Downs J, Mansberger SL. Assessment of intraocular pressure along the limbus and sclera
using contact and indentation tonometry. ARVO poster presentation; May 02,
ACKNOWLEDGEMENTS:
This work was supported by The Richard A. Perritt Charitable Foundation and
The Illinois Society for the Prevention of Blindness.