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Ophthalmic Imaging Tools to Detect Glaucoma Progression
Tigran Kostanyan, MD 1 and Gadi Wollstein, MD 2
1. Research Fellow; 2. Associate Professor of Ophthalmology, UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center,
Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Philadelphia, US
Abstract Ocular imaging devices provide objective and reliable structural measurements and estimate structural progression that has important clinical
implications in ocular pathologies such as glaucoma. This review describes the working principles and main methods for detection of glaucoma
progression used in the leading commercially available ocular imaging. This information allows clinicians to better identify eyes that are
suspicious of progression and adjust the clinical management as needed.
Keywords Spectral domain optical coherence tomography (SD-OCT), confocal scanning laser ophthalmoscopy (CSLO), scanning laser polarimetry (SLP),
Disclosures: Tigran Kostanyan, MD, and Gadi Wollstein, MD, have no conflicts of interest to declare. No funding was received in the publication of this article.
Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any noncommercial use, distribution, adaptation,
and reproduction provided the original author(s) and source are given appropriate credit.
Received: August 30, 2014 Accepted: October 10, 2014 Citation: US Ophthalmic Review, 2015;8(1):37–42
Correspondence: Gadi Wollstein, MD, UPMC Eye Center, Eye and Ear Institute, 203 Lothrop St, Pittsburgh, PA 15213, US. E: firstname.lastname@example.org
Glaucoma is a chronic progressive optic neuropathy, which can lead to
irreversible blindness. 1 It is characterized by loss of retinal nerve tissue
that results in visual function deterioration. Structural changes, such as
accelerated loss of retinal ganglion cells (RGCs) and their axons, and a
specific pattern of damage in the optic nerve head (ONH) associated with
visual field (VF) loss, are considered hallmarks of glaucoma. 2
The efficacy of glaucoma management depends mostly on the ability to
reliably detect disease progression as early as possible. Detection of
progression allows the clinician to initiate or modify treatment, which can
slow glaucoma progression and potentially preserve vision.
Even though optic disc stereophotographs are considered the gold
standard for the evaluation of glaucomatous structural damage, the
estimation of structural progression in glaucoma using this tool is
challenging due to its subjective nature. 3 The recent evolution of imaging
tools noticeably improved the objective and quantitative determination
of structural changes and the assessment of progression caused
by glaucoma. 4–6 However, the assessment of structural progression
in glaucoma still comprises several dilemmas due to difficulties in
differentiating between true glaucomatous change and natural age-
related loss of retinal nerve tissue, measurement variability, and a lack of
widely accepted and efficient gold standard criteria for establishing
glaucoma progression. In this review we will summarize the imaging
tools that are currently available, namely scanning laser polarimetry
(SLP), confocal scanning laser ophthalmoscopy (CSLO), and spectral
domain optical coherence tomography (SD-OCT). We will focus
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particularly on their ability to detect glaucoma progression, as well as the
strengths and limitations of each imaging technology.
Detection of Glaucoma Progression
Progression of glaucoma can be estimated by subjective assessment
based on clinical experience and judgment, or by statistical analysis of
quantitative measurements. The statistical methods used to detect
glaucoma progression can be classified as event- or trend-based analysis.
In event-based analysis a series of follow-up measurements are
compared with baseline measurements, and progression is defined
when measurements exceed a predetermined threshold for change
from baseline. This method is highly sensitive to the threshold level, with
a higher threshold resulting in fewer cases identified as progressing
with only a small number of false positive classifications and vice versa
when choosing a lower threshold. The threshold is often selected based
on the physical properties of the imaging device (e.g., measurement
reproducibility), or by population-based data. The main disadvantage of
this method is the effect of erroneous deviating measurements that
might be labeled as progression. A confirmatory second test can resolve
most of the false progression classifications in this method.
Trend-based analysis uses regression analysis or mixed effect regression
analysis to estimate the rate of change in the examined parameters.
Progression is defined either when the rate of change is significantly
different than a no change slope (zero slope), or when the rate is
different than population or individually derived slope. This method