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MANAGING OPEN ANGLE GLAUCOMA

Progression is usually identified clinically as a loss of tissue on structural assessment or a decrease in visual
function on psychophysical testing. Both structural objective imaging devices (such as optical coherence to-
mography or scanning laser ophthalmoscopy) and visual function testing instruments (usually standard auto-
mated perimetry) have the capability to monitor for progression once reliable baseline data has been acquired.
There are two types of progression analysis in common use: event-based analysis and trend-based analysis. In
order to maximize the ability to detect progression it is important to use the same visual field testing strategy
(ie. 24-2 SITA-Standard) and imaging instrument to acquire baseline and follow-up data.

Event-based analysis is the type of analysis used in the landmark glaucoma studies to confirm the presence a pro-
gression endpoint. It describes a statistically significant change in structure or function from baseline, such as the
deepening or enlargement of an existing defect or the development of a new defect. 14,15,153,208,293 Event-based analysis
is better for detecting slowly progressive change and localized change. It has the advantage of providing early de-
tection of change, and fewer tests are required to detect and confirm change. However, event-based analysis can be
more variable, and does not provide a rate of change. 267,287,294,295
Trend-based analysis identifies the rate of change over time using linear regression analysis. It is better at
differentiating fast progressors from slow progressors, and allows extrapolation to predict clinically signifi-
cant change over time. 287,295,296 Quantifying the rate of change is imperative to making informed management
and follow-up decisions. The main disadvantage of trend-based analysis is that it takes more tests and longer
follow-up to generate the rate of change. It is also less sensitive to focal changes at specific loci and diffuse
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loss across the entire visual field.
MONITORING FOR PROGRESSION ON VISUAL FIELD ANALYSIS
Functional progression is best monitored using both event-based and trend-based analysis in standard automated
perimetry. Both the Humphrey and Octopus instruments include software to identify progression against an age-
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matched normative database, and change from baseline. It is advisable to utilize the software available to generate
both event-based and trend-based analysis. 295
Event-based analysis requires at least 3 reliable visual fields before the analysis will be generated. The in-
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strument will look for change that exceeds the variability of stable glaucoma in a cluster of adjacent points
and flag the defects when the change becomes statistically significant. 267,298 Trend-based analysis requires at
least 5 reliable visual fields to calculate a predicted rate of change. The Humphrey Field Analyzer plots the
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Visual Field Index (VFI, a center-weighted percentage representation of residual visual field) and generates a
linear regression analysis to estimate rate of progression over a 5-year period (see Figure 14 for an example of
using both trend- and event-based analysis in monitoring glaucoma progression). 299,300 The VFI appears to give
a similar rate of change to linear regression of mean deviation but may be less susceptible to the influence of
cataracts. The Octopus perimeter has customizable progression analysis and can generate rate of progression
using different variables to view mean deviation change per year or localized defect change per year. Rate of
change for various speeds of progression using mean deviation and VFI change per year are: 57,267,299

• -0.2dB MD or 1% VFI per year for mild rate of change
• -0.5dB MD or 2% VFI per year for moderate rate of change
• -1.0 to -2.0dB MD or 6 to 8% VFI per year for rapid (potentially catastrophic) rate of change

CANADIAN JOURNAL of OPTOMETRY | REVUE CANADIENNE D’OPTOMÉTRIE VOL. 79 SUPPLEMENT 1, 2017 43