New Trends and Practices in the Diagnosis and Management of Glaucoma | Eyes On Eyecare

New Trends and Practices in the Diagnosis and Management of Glaucoma

by Murray Fingeret, OD, FAAO, John G. Flanagan, PhD, DSc(hon), FCOptom, FAAO, and David Lam, OD

In this course, review the basic glaucoma test battery and the structure-function relationship in glaucoma; plus, learn the latest innovations in visual field technologies and how they can be integrated into the clinical care of patients with glaucoma.

5.0 (4 ratings)
Updated Aug 16, 2021
30min
1 quiz
What You'll Learn
  • Understand the test battery for glaucoma
  • Describe the structure and function relationship of glaucoma
  • Learn how to systematically analyze a visual field
  • Understand the new 24-2C Test Pattern and compare to 24-2 and 10-2

Introduction and Quiz

This course will review the basic glaucoma test battery and the structure-function relationship in glaucoma. You will also learn how to systematically analyze a visual field. Finally, you will learn the latest innovations in visual field technologies and how they can be integrated into clinical care of patients with glaucoma.

Note: This course is self-directed learning, and is not COPE-approved CE.

New Trends and Practices in the Diagnosis and Management of Glaucoma

10 Questions

Take this quiz to test your knowledge of new trends in glaucoma diagnosis and management.

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Glaucoma Test Battery

Like with any other ocular condition, we always start our exam with a case history. We want to ask if there is a family history of glaucoma, any ocular trauma, or a history of topical corticosteroid use. Of course we need to assess IOP with Goldmann Applanation Tonometry since this is the gold standard for measuring IOP. A good baseline IOP is important since it is the only modifiable risk factor for glaucoma. We need pachymetry since thin central corneal thickness is an independent risk factor for glaucoma. We need gonioscopy in order to classify the type of glaucoma. It is critical to evaluate the optic nerve with a stereoscopic view through a dilated pupil. Next, we need good baseline disc photos. Stereo photos are preferred. The test battery continues with OCT imaging of the Optic Nerve, RNFL, and Macula. Finally, we need to assess Visual Fields. The most common test patterns are 24-2 and 10-2. Now, we have the newest test pattern: 24-2C, which we will discuss more in detail later.


Structure-Function Relationship

On clinical exam, we diagnose glaucoma when there is suspicious or obvious structural damage to the optic nerve head. According to Dr. Weinreb, there is a continuum of glaucomatous progression. He proposes that glaucoma starts out in the undetectable stage with microscopic remodeling and apoptosis of the lamina cribrosa and ganglion cells. This proceeds to asymptomatic disease where there are detectable changes to the RNFL and optic nerve head or mild visual field changes. The last stage is functional impairment. In this stage there is moderate to severe visual field changes, which progresses to blindness as in end stage glaucoma.

figure-1-glaucoma-continuum.png

Figure 1: Glaucoma continuum. When field loss occurs, especially if it is in the better-seeing eye, the functional impairment can affect quality of life. Even mild to moderate visual field loss is associated with falls and difficulty driving.

Significant structural damage necessary before visual field loss occurs

On average, visual field loss occurs when the average RNFL has thinned to around 75 microns. This is already about a 17% loss from normal average thickness.1 This means that substantial structural loss must be necessary before functional loss occurs.

figure-2-rnfl-scatter-plot.png

Figure 2: Scatter plot of healthy (H) and glaucoma (G) values using unlogged (1/l) visual field threshold values. The grey line is a spline fit, and the black line is the two-segment ‘broken stick’ model. RNFL—retinal nerve fiber layer, L—Lambert. (Source: Wollstein et al)

Are Visual Fields Still Relevant?

Will visual fields, a subjective functional test, continue to be performed to manage glaucoma in the future? The answer is yes. There are objective functional tests such as ERG and VEP, which may be an alternative. However, these tests are not ready to be widely accepted yet. Visual fields are still important! The testing algorithms keep getting faster. We know about SITA Standard and SITA Fast. Now there is SITA Faster, which we will discuss more later.

Why do we still perform visual fields? It helps us diagnose glaucoma. Not only that, the staging of glaucoma is still dependent on visual fields. Does the patient have mild, moderate, or severe disease? By staging the glaucoma, we can then determine target IOP and how closely we want to follow the patient. Finally, serial visual fields allow us to detect progression of glaucoma. Knowledge of progression is critical to help us decide when to intervene with changes to treatment.

Visual Field Analysis

Let us walk through step by step how to analyze a visual field. First, we verify that the right test is performed. Which strategy do we want? Do we want SITA Standard, SITA Fast, or SITA Faster? Next is stimulus size. The vast majority of fields are performed with a Test Size III. The next factor is the test pattern. Do we want a 24-2, 30-2, 10-2, or 24-2C? Is the correct eye performed? Is the correct date of birth entered so that the correct normative database is used? Furthermore, we need to make sure that the patient’s pupils are greater than 3mm in order to reduce illumination artifacts. Finally, refractive error needs to be corrected so that the data is accurate.

figure-3-humphrey-vfa-single-field-analysis.png

Figure 3: Humphrey Visual Field Analyzer II-i Single Field Analysis.

Next, we want to look at the reliability indices (Figure 2, 1). There are four that we generally consider. The first is fixation losses. If there are high fixation losses, this means that the patient kept moving his eye to look at a stimulus that was presented in his blind spot. The second reliability index is false positives. If there are high false positives, this means that the patient was “trigger-happy” or anxious. False negatives is the third reliability index. This means that the stimulus was seen initially, then tested again at a brighter level, but the patient did not press the button. In theory, false negatives should measure attention. However, high false negatives can also represent the variability and noise in glaucomatous disease, rather than inattention or unreliability.

The final reliability index is gaze tracking (Figure 2, 11). This is the line at the bottom of the visual field report that tracks if the patient was staring straight at the fixation light or moving his eye around during the test. If the test is unreliable, the test should not be used! Have a talk with the patient and repeat the field.

Assuming the test is fairly reliable, the next step is to review the probability plots (Figure 2, 7,8,9). There are four of these: Mean Deviation (MD), Pattern Standard Deviation (PSD), Visual Field Index (VFI), and Glaucoma Hemifield Test (GHT). MD is a number that represents the average loss for an entire field. It represents global loss of sensitivity. The higher the MD, the more global field loss a patient has. PSD is essentially a standard deviation of all the values. It represents how much all the values deviate from each other. PSD helps us look for local glaucomatous visual field defects. An increasing PSD over time is suggestive of deepening of a local defect. VFI is a single number that is based on Pattern Deviation that ranges from 0 to 100%. 100% represents a normal field, and 0% represents a blind field. GHT looks at clusters of points on either side of the horizontal meridian and gives us one of five responses: within normal limits, outside normal limits, borderline, general reduction in sensitivity, or abnormally high.

Once we review the probability plots, we can describe the pattern of loss. Is there a nasal step, arcuate defect, paracentral defect, or temporal wedge? Is fixation involved?

Finally, we want to reaffirm the diagnosis. Does the visual field defect match up with the structure of glaucomatous damage based on optic nerve exam and OCT?