Visual Fields: Fluctuation and Progression

Core Messages

››Intertest visual field fluctuation, which is seen both in normal and glaucoma patients, can confound the assessment of progression.

››True progression is likely if consecutive tests show reproducible defects in the same location.

››More frequent visual field testing is recommended in the first years of follow-up to help establish a consistent baseline and to assess whether or not disease is progressing.

››Deepening or enlargement of previous defects is a common form of progression. New defects usually are associated with worsening of previous defects.

››Automated progression analysis programs, such as the guided progression analysis and visual field index, have been developed to help determine the presence and rate of progression.

16.1  How Do I Distinguish Between Fluctuation and True Progressive Change on Visual Field Printouts?

The primary obstacle in detecting whether or not a glaucoma patient’s visual field loss is progressing is to separate true progression from changes due to variability or

F. A. Medeiros ( )

Hamilton Glaucoma Center, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0946, USA e-mail: fmedeiros@eyecenter.ucsd.edu

fluctuation between tests. Fluctuation is defined as the variability in the response to the same stimulus that is not related to true disease progression. As visual field testing is a subjective examination, variable responses may be obtained each time the test is performed (longterm fluctuation) or even during the same test (shortterm fluctuation). This variability has been the biggest drawback of visual field assessment, as variability can greatly confound interpretation of change. Fluctuation varies among patients and among sectors in the same visual field, and usually it increases with severity of disease. To detect true progression, we need to evaluate whether the observed change exceeds the expected fluctuation for a particular area. Many strategies have been developed to deal with this issue and will be reviewed in this chapter.

16.1.1  Usual Pattern of Visual Field

Progression in Glaucoma

Visual field progression in glaucoma may be seen as

(1) the development of a new defect, (2) deepening or enlargement of a preexisting defect, and (3) less commonly, as diffuse loss of sensitivity. Most frequently, progression is identified as a deepening of a preexisting scotoma (as shown by various research studies), along with enlargement of the scotoma. In one study evaluating visual field progression in glaucoma, most cases showed deepening (86%) or enlargement (23%) of a previous scotoma, while none of the eyes developed new visual field defects in previously normal areas [1]. This highlights the importance of evaluating areas adjacent to existing scotomas when searching for visual field progression. However, these adjacent areas are also known to exhibit larger degrees of fluctuation,

which makes identification of true progression more difficult. Diffuse sensitivity loss may also represent glaucoma progression, although it is usually accompanied by new defects or worsening of previous focal defects. Progressive diffuse loss that is isolated should always raise the suspicion of cataract progression (or other media opacities).

among consecutive tests, whereas a true defect reflecting further loss of ganglion cells will be repeatable. One cannot stress enough the value of confirming new visual field defects. Data from several clinical trials have suggested that change needs to be repeatable, with a defect of the same type in the same general location, on three consecutive examinations before progression can be confirmed [2–5].

16.1.2  Visual Field Defects Need

to be Repeatable

Before concluding that a change in the visual field is a sign of progression, it is important to demonstrate that the defect is repeatable on subsequent visual fields. This is one of the most important aspects of evaluating visual field progression in glaucoma. On any given visual field of a nonprogressing patient, it is common to find a few scattered points with significant depression compared with old fields. Variable responses that do not reflect true progression will vary in location and pattern

16.1.3  Results of Visual Field Tests

Should Be Correlated with Other

Clinical Data

New or enlarged visual field defects should also be concordant with other clinical findings, such as those seen in the optic disc and retinal nerve fiber layer. To this end, several studies have used maps that correlate areas of the visual field with the corresponding optic disc sectors (Fig. 16.1) [6, 7]. Although visual field progression may be seen without detectable optic disc deterioration,