Ординатура / Офтальмология / Английские материалы / Visual Fields Examination and Interpretation_Walsh_2011

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Figure 4-14. (Continued)

of two positive tests of a possible three performed 1 to 4 weeks apart. Although, in general, confirming progression with subsequent tests is recommended, it may not be necessary if other clinical features, such as optic disc cupping or retinal nerve fiber layer loss, are worsening.

Other published guidelines stress the concept that initially normal values are not likely to fluctuate as much as moderately depressed values, which can fluctuate widely without true progression occurring (Table 4-5)29 By definition, absolute defects (threshold = 0 dB) at baseline cannot worsen, as the machine is already generating a maximal stimulus. In addition, analysis of pairs or clusters of locations may help minimize heterogeneous LTF. 30

4-5-6 Glaucoma Progression Analysis. The latest versions of HVF software offer automated glaucoma progression analysis (Guided Progression Analysis [GPA]). The GPA software presents analyzed data in a user-friendly report in an attempt to more accurately compare and quantify data between visual fields. Two baseline exams are selected, either automatically or manually, and used as a comparison against changes on future tests. Disease progression is defined by the Early Manifest Glaucoma Trial (EMGT) criteria as a statistically significant loss of sensitivity at three or more test points in the same location on three consecutive visual field evaluations. Deviations from baseline are presented numerically as well as symbolically, with an open triangle demonstrating progression on one field, a half-dark triangle indicating progression on two fields, and a fully dark triangle signifying progression on three consecutive fields. GPA software has the additional advantage of adjusting for alterations in general sensitivity from ocular changes such as cataracts, but it is not available for 10-2 programs (Figure 4-17A, B, and C).

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Figure 4-15. (Continued)

4-5-7 Trend Analysis. The PROGRESSOR software analysis for HVF was created at Moorfields Eye Hospital and the University College, London. The PROGRESSOR program uses trend analysis to evaluate changes at individual points in the visual field to determine a slope or rate of change, helping clinicians assess the risk of the development of glaucomatous vision loss in the future (Figure 4-18).

The schemes outlined here are only guidelines; the clinician’s index for determining progression should be influenced by multiple individual patient factors such as the patient’s subjective assessment of his or her vision, age, intraocular pressure control, optic disc appearance, and nerve fiber layer status.

4-5-8 Follow-up of Central Abnormalities. An additional approach to minimizing the effect of LTF is to follow up defects that are present within the central 10° with Program 10-2. This program appears to be considerably more sensitive in detecting the subtle progression of scotomas located in this region compared with programs with a larger grid size.31 This increased sensitivity may occur for two reasons. First, the relatively high sensitivity in the normal central field is less prone to LTF than the less-sensitive midperipheral regions (see Figure 3-10). Second, the high-resolution sampling provided by a 2° grid makes any subtle enlargement of the steep edge of dense scotomas more apparent. An overview plot can be created with serial tests of Program 10-2. In addition, the overview printout demonstrates the mean sensitivity of each field over time and can perform a mean sensitivity slope calculation with a P value interpretation. Because sensitivity is displayed as opposed to deviation, there may be a slight gradual reduction in sensitivity over many years in a clinically stable patient.

TABLE 4-4. Guidelines for Recognizing Progression

New defect in previously normal region: cluster of 3 points worsening by 5 dB each, 1 of which has worsened by 10 dB

Previously abnormal region has deepened if: 3 or more points have deteriorated by 10 dB each

Previously abnormal region has widened if: 2 or more new contiguous points are involved

Note: This scheme requires reliable fields.In general, progression should be confirmed on a subsequent field or fields. See text. Adapted with permission from Anderson DR: Automated Static Perimetry. St Louis: Masby–Year Book;1992:208–211.

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TABLE 4-5. Guidelines for Evaluating Change From One Test to Another in Single Test Location and in Adjacent Pair of Test Locations

Consider as Progression If Change (dB) Exceeds

*Values may fluctuate between 0 and normal.

†A single test location drop to 9 dB may be due to fluctuation.

Reprinted with permission from Zulauf M, Caprioli J: What constitutes progression of glaucomatous visual field defects? Sem Ophthalmol 1992;7:130–146.

4-6 FUTURE OF AUTOMATED PERIMETRY

Automated perimetry remains an evolving field. Recent developments can be broadly classified into those that alter the nature of the presented stimulus, those that present a standard white-on-white stimulus in an altered strategy, and those that aid in the interpretation of results. Among the altered stimulus technologies are the selective functional tests that are designed to isolate one visual receptor system, such as the parvocellular, magnocellular, or koniocellular ganglion cells. Isolating one visual processing system seems to enable earlier detection by reducing redundancy that can mask damage. In addition, some types of ganglion cells may be more susceptible to glaucomatous damage.32, 33

4-6-1 Altered Stimuli

4-6-1-1 SWAP. Short-wavelength automated perimetry (SWAP), also known as blue-on-yellow or color perimetry, alters the typical white-on-white stimulus to a size V blue stimulus on a yellow background. Several longitudinal studies have shown earlier identification of abnormality and progressive glaucoma using SWAP.34–36 The physiologic theory behind SWAP is to isolate the koniocellular, blue cone system. The lens-density effect, specifically nuclear sclerotic cataracts, diffusely may reduce a patient’s ability to perform the test and alter the field result.

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Figure 4-18. PROGRESSOR trend analysis evaluates changes at individual points in the visual field to determine a rate of change (slope).

Techniques that analyze patterns within the field such as the pattern deviation plot or GHT may provide adequate specificity without the need for time-consuming density measurements.37 SWAP is available on later models of HVF analyzers and can be performed with full threshold and SITA algorithms (Figures 4-19 and 4-20).

4-6-1-2 FDT. Frequency doubling perimetry/frequency doubling technology (FDP/FDT) uses spatial frequency grating patterns that are contrast modulated at high rates to induce an optical illusion of flickering. The magnocellular ganglion cells that are selectively stimulated may be more susceptible to glaucomatous damage.38 FDT has the additional advantages of short test times, limited influence by visual acuity and refractive error, and lower need for standardized background lighting, which make it a useful screening tool outside of the controlled office setting. FDT is available in a large grid, screening-type program that tests 17 points, as well as a 30-2 and 24-2 Matrix program that tests 69 and 56 points, respectively (Figure 4-21), Multiple studies have demonstrated reasonable sensitivity and specificity for disease detection by FDT.39–41 While FDT has been shown to be useful to detect glaucomatous defects earlier than standard white-on-white perimetry and its testing point resolution has improved, small and early defects may be missed, so standard perimetry should be used to help confirm disease and monitor for progression.42–44

4-6-1-3 Flicker Perimetry. Temporal-modulation/flicker discrimination is also believed to selectively stimulate magnocellular ganglion cells and flicker discrimination is reduced in glaucoma.45 Perimeters that present a flickering white- on-white stimulus are available on later Octopus perimeters. While increasing numbers of studies are evaluating flicker perimetry, its use is not widespread and more robust data are needed to determine its role in glaucoma detection and monitoring. (Nomoto).46–48