Ординатура / Офтальмология / Английские материалы / Visual Fields Examination and Interpretation_Walsh_2011
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Figure 3-20. Localized scotoma. This patient has primary open-angle glaucoma with a superior nasal step. The surrounding uninvolved field is slightly supranormal. When these values are “normalized,” the pattern deviation plot becomes slightly more significant than the total deviation plot. The supranormal uninvolved field, combined with the small size of the scotoma, contributes to only slight decrease in mean deviation. The pattern standard deviation is highly abnormal (99.5%), as is the Glaucoma Hemifield Test.
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Figure 3-21. Moderate to severe glaucomatous field loss. This patient has primary open-angle glaucoma with a dense inferior arcuate defect ending in a nasal step. Both the mean deviation and the pattern standard deviation are highly abnormal.
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3-6-1 Grid Size. The Humphrey Visual Field Analyzer 30-2 algorithm samples 76 locations with a uniform 6° grid within 30° from fixation (Figure 3-22). All Humphrey programs ending in -2 (e.g., 30-2, 24-2, 10-2) are offset from the central horizontal and vertical meridians. Programs 30-2 and 24-2, which use 6° spacing, are thus offset by 3° from the central meridians. Before invention of the SITA algorithms, approximately 550 questions would have been asked in a typical full threshold test, which may have taken about 15 minutes per eye. As the distance from fixation increases, the normal threshold values decrease, with a corresponding increase in the test variability, providing diminishing quality of the test. One of the initial approaches to shortening the test was to delete the outer row of locations. Program 24-2 does that by testing only out to 21° except for preservation of the important nasal extent of the 30-2 program (see Figure 3-22). The resulting test contains 54 locations, a 29% reduction compared with the Program 30-2 grid, considerably shortening the test duration. This represents a valuable tradeoff in patients who would be tired with additional testing.
3-6-4 FASTPAC. The FASTPAC algorithm uses an entirely different testing strategy. Instead of the standard 24-2 strategy with a double crossing of threshold, FASTPAC adjusts the stimulus intensity by 3-dB increments until the threshold is crossed once. FASTPAC saves the most time in normal or near-normal fields and provides little time advantage in patients with larger amounts of field abnormality. In comparisons to full threshold strategies, FASTPAC shortens the test time by 35% to 40%. FASTPAC may be suitable for observing ocular hypertensive patients
Figure 3-22. Comparison of the grid pattern, right eye, in Programs 24-2 and 30-2. Both programs test a uniform 6° grid offset 3° from the vertical and horizontal meridians. Program 24-2 tests (excludes outer outlined locations) 54 locations extending to 21° superiorly, inferiorly, and temporally and tests to 27° nasally. Program 30-2 tests an additional 22 locations extending the grid to 27° in all four directions.
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or early glaucoma patients, although little longitudinal data are available on its use in these populations and the effect on LTF is presently unknown. One potential advantage of FASTPAC is the ability to use size V stimulus for central 10° testing, which is not available with current SITA algorithms.
3-6-5 Programs 30-1 and 24-1. Programs 30-1 and 24-1 are not used for clinical testing, because they are not offset from the horizontal and vertical meridians. Because scotomas centered on the meridians are difficult to classify (superior versus inferior, nasal versus temporal), these locations have less diagnostic localizing value.
3-6-6 Program 10-2 and Macula Test. Program 10-2 provides a high-resolution test of the central 10° with a tight 2° grid, offset 1° from the meridians. A total of 68 locations are used (Figure 3-23). Central tests are useful in carefully defining central or paracentral scotomas.34 In patients with advanced damage and small remaining central islands of vision, Program 10-2 can be performed with stimulus size V if the FASTPAC algorithm is used. This strategy provides the advantage of testing more areas with measurable thresholds and seems to increase patient cooperation and reduce patient fatigue.
An even more localized test is the macula test, which thresholds 16 locations within the central 5° with 2° spacing. Each location is tested three times to provide better estimates of local STF (Figure 3-24).
Figure 3-23. Program 10-2 tests 68 locations with a 2° grid extending to 9° from fixation. In this example, only a small central island of vision remains.
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Figure 3-24. The macula test thresholds the central 16 locations of the Program 10-2 grid. Each location is tested three times to better assess local short-term fluctuation.
3-6-7 Peripheral 60 and 60-4 Program. These programs allow additional exploration of the peripheral visual field (beyond 30°). Peripheral 60 points of this program extend the test out to 60° with a uniform grid testing 60 additional locations.
3-6-8 Nasal Step Program. Patients with possible nasal steps can be further explored with the nasal step program, which tests 12 locations up to 50° nasally. Two additional locations in the temporal visual field are also included to reduce the predictability of the questions.
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3-6-9 Stimulus Size Option. Most programs are performed with stimulus size III, which subtends a diameter of 0.43° in visual space. This size is derived from the 4 mm2 size III used by the Goldmann perimeter. Testing with size III allows the application of the STATPAC statistical analysis. In fields where the majority of test locations are markedly reduced, it is often preferable to increase the stimulus size to V (1.72° in diameter). This larger size is often preferred by the patient and may reduce fluctuation, although the option of using the glaucoma change analysis is not available.
3-7 FOLLOW-UP PRINTOUT
When evaluating a series of automated fields performed over time, the clinician may find the integration of the massive amount of data overwhelming. The Humphrey instrument allows the creation of several serial printouts to minimize confusion and allow the performance of change-over-time statistical analysis.
3-7-1 Overview Printout. The overview printout simply presents a sequential listing of condensed single field printouts chronologically (Figure 3-25). For each test session, four plots are displayed (from left to right): Threshold Graytone plot, Threshold (numeric) dB plot, Total Deviation P value plot, and Pattern Deviation P value plot. Above these four plots are the GHT results, reliability data, pupil size, and Snellen acuity. Below the plots are listed foveal sensitivity and global indices. The examiner familiar with the single field analysis printout will have no difficulty understanding all these terms.
3-7-2 Change Analysis Printout. The change analysis printout represents each field as a box plot depicted graphically over time (Figure 3-26). To create this plot, deviation values at each location are ranked from least to most depressed. As can be seen from the legend at the left side of the printout, each box contains the 15th to 85th percentile deviation values from this ranking, with a central triple line representing the median value. The tails extending from the box cover the full range of deviation throughout the field. In general, a small box with long tails suggests a clumping of values with a few outliers. If a box is small and near 0 dB, most of the field is normal. If the box changes in location over time with a stable size, a generalized change is likely occurring. A change in box dimension usually indicates a more localized process.
The change analysis printout also plots the global indices over time, including threshold levels for statistical significance, with STF and PTSD plots being empty, if SITA algorithm was used. If the MD values plot is not demonstrating progressive change, it is likely that the field is not worsening, although a stable MD with an increasing PSD may indicate early progression of a localized scotoma. If the MD value is declining, the other indices and actual fields should be evaluated closely to discern confounding developments such as cataract formation. When five or more fields are available, linear regression analysis of the MD slope over time will be
Figure 3-25. Overview printout. The overview printout displays chronological series of tests. These include the Graytone, numeric dB, Total Deviation, and Pattern Deviation plots from each test session. Above the plots are the test date and the Glaucoma Hemifield Test (GHT) results. Below the plots are the global and reliability indices, along with foveal sensitivity. Three tests performed over a 15-month period are displayed. Note that the probability symbols displayed in the total deviation and pattern deviation plots compare each location’s threshold with age-matched normal values. Similarly, the probability values next to the global indices are significance values compared with normal data.
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Figure 3-26. Change analysis printout. The glaucoma change analysis printout displays each field in box plot form as well as displaying the global indices graphically over time. The legend for the box plot is located to the left. The box plot is created by ranking total deviation values from most depressed (0%) to least depressed (100%). The box itself encompasses the central 70% of the field (between 15th and 85th percentile). The median rank value is displayed as a dark triple stripe inside the box. If the box is elongated toward the bottom of the plot, as in this example, then a large dense scotoma is present.
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calculated, which describes the slope in decibels per year and assigns a significance level, producing one of the two messages: “MD SLOPE SIGNIFICANT” or “MD SLOPE NOT SIGNIFICANT.” The MD plot and slope calculations are also included in the Glaucoma Progression Analysis printout. Studies suggest that a PSD could be used to monitor glaucoma progression in patients with glaucoma and cataract using SITA Standard to differentiate generalized worsening (cataract) from localized progression (glaucoma).35
3-7-3 Glaucoma Progression Analysis Printout. The Glaucoma Progression Analysis is an optional module in the STATPAC intended to assist with detection of glaucoma progression. At the time this chapter was written, the analysis was available for SITA Standard and SITA Fast algorithms but not for SITA-SWAP tests. Tests using Full Threshold algorithm could be used as baseline. Two initial fields are averaged into a baseline measurement, and then a point-by-point statistical comparison of each subsequent field is performed, indicating the presence or absence of a clinically significant change (Figure 3-27) and demonstrating each point’s change in decibels.
The printout first displays the two baseline fields in Graytone and in Total Deviation plots. At the bottom of the page, following these two fields is a plot of Mean Deviation over time (MD Slope), identical to the one seen on Change Analysis Printout. Each follow-up field is displayed on the following pages labeled Follow-up on the top of the page.
The follow-up portion of the Glaucoma Progression Analysis printout (Figure 3-28) differs from the Overview printout by replacing the Total Deviation and Pattern Deviation plots at the right with a point-by-point analysis of Deviation From Baseline plot in decibels from the baseline plot and the Progression Analysis probability plot. This latter plot identifies points that have progressively changed on consecutive fields, where crosses indicate changes outside of calculable statistical range. The analysis was found to have high specificity and sensitivity and be a useful test to assist in the detection of glaucomatous progression.36
3-7-4 GPA - Guided Progression Analysis. A new Guided Progression Analysis (GPA)37 may be a somewhat confusing term (see the previously described Glaucoma Progression Analysis). The GPA presents the results of a baseline examination, Visual Field Index Plot, Glaucoma Change Probability Map, and the GPA Alert, indicating “Possible Progression,” “Likely Progression,” or “No Progression Detected” on one page.
3-8 VISUAL FUNCTION SPECIFIC PERIMETRIC TECHNOLOGIES
Visual function can also be evaluated by selectively testing specific retinal ganglion cells, potentially allowing for earlier detection of glaucoma. However, no technology has been shown to be superior due to significant variations of visual function in early glaucoma.38
Figure 3-27. Glaucoma progression analysis printout. Baseline: |
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two fields are averaged and the results are considered a baseline |
fiel d. Each |
subsequent field undergoes a point-by-point change from the b aseline comparison, displayed with decibel values and accompanying pro bability symbols. The mean deviation (MD) change probability com are the MD of each follow-up field to the baseline MD with associated P val es. A lin ar regression of the MD values over time is displayed next to the b aselinne fields and, in this case, the resulting MD slope is not significant at a 95 % co nfide ce level. In this case, note the same level of significance over time, indicating stability, despite preexisting significant loss of sensitivity
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