Variability in perimetry and optical coherence tomography: its importance in glaucoma detection, diagnosis and management
Date
2017
Authors
Pearce, John Graham
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Abstract
The detection, diagnosis and monitoring of glaucoma requires
numerous investigative techniques and strategies in order to
provide definitive diagnosis and management of glaucoma. Two
investigative techniques used extensively for this purpose today
are standard automated perimetry (SAP) and spectral domain
optical coherence tomography (SD-OCT).
The presence of test-retest variability (TRV) for repeat measures
in these instruments can impact on our ability to differentiate
TRV from true progressive change. In this thesis, we examine two
popular devices which, at present, have little or no published
TRV criteria available. The instruments under consideration are
the Medmont M700 automated perimeter and the Topcon 3D OCT-2000
SD-OCT. The purpose of this study is to quantify TRV for both
instruments in both healthy and glaucoma patients, and identify
any modifiable external components of TRV.
Chapters 1 and 2 determine the test-retest variability (TRV) of
both instruments in glaucoma patients. We were able to develop
event based progression criteria which could be easily applied by
clinicians using these instruments. We also established that TRV
for several summary measures, structural and functional, was
dependent on the level of glaucomatous damage.
We reported that for the Medmont, retest variance did not
increase with eccentricity when comparing points of equal decibel
value in the central 10° of the 30-2 test with points of equal
decibel value in the outer 20° of the same test. This finding
had not been reported previously, and was counter to that of
other studies (involving healthy eyes) which had reported that
variability increased with eccentricity.
There are few published studies which have examined diurnal
variations in SAP and SD-OCT summary measures, and none that had
investigated diurnal variations in TRV in either instrument. In
Chapter 3, we therefore investigated whether diurnal variation
existed in either summary measures or TRV.
Whilst we found no detectable changes to mean summary measures
over the course of a normal working day, we were able to detect
statistically significant diurnal variations in TRV for several
SAP and SD-OCT summary measures. This was now evidence to suggest
that reduced TRV, and therefore enhanced progression detection,
might be available by testing subjects on both instruments at
consistent and specified times of day.
In Appendices 1 and 2, we investigated whether any circadian
variations in SAP and SD-OCT summary measures were detectable
over a 24 hour period. We were unable to discern any significant
differences in SAP or SD-OCT summary measures, nor were we able
to discern any consistent cycles in any summary measures. We were
able to detect statistically significant circadian variation in
the peripapillary retinal nerve fibre layer using SD-OCT, and we
were able to achieve the first recorded 24 hour test session
results for both SAP and SD-OCT.
The final part of our study, Appendix 3, involved generating TRV
values for healthy subjects on the Topcon, which could be used
clinically to differentiate true progression from TRV.
We hope that the overall results generated from our studies have
enhanced disease and progression detection for possibly millions
of patients worldwide, and that we have stimulated the
development of future studies to further investigate some of the
preliminary findings from this study.
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glaucoma, test-retest variability, visual fields, spectral domain optical coherence tomography, Medmont M700, Topcon 3D OCT-2000, diurnal variations in test-retest variability
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