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

146 Visual Fields

C

Figure 4-9. (Continued)

4-5-1 Baseline Establishment. Several caveats regarding the establishment of a baseline field are worth mentioning. A major confounding variable to establishing an accurate baseline field is the learning effect. If the first field is poorly performed, the baseline may be artificially depressed and may reduce the sensitivity to detect subsequent deterioration. With a patient inexperienced in perimetry, baseline testing should be repeated up to three times over several weeks or months until an apparent plateau of field improvement has occurred. The two or three most suitable fields can then be selected and averaged for a sensitive baseline (master) field against which future tests can be compared. Occasionally, patients have sufficiently high LTF during the establishment of the baseline that particular fields may be inappropriate for inclusion. In that event, the two fields that appear to be least damaged should be included if the reliability indices demonstrate a lack of false-positive responses and fixation losses.

Patients who show significant glaucoma progression should usually undergo more aggressive ocular hypotensive therapy or surgical intervention. Once the

TABLE 4-3. Staging of Glaucomatous Visual Field Loss (Program 30-2)

Early Defect

Mean deviation (MD) is < – 6 dB

Pattern deviation plot: <25%(18) of points are depressed below 5% and <10 points are depressed below 1%

No point in central 5° has sensitivity of <15 dB

Moderate Defect

MD is < – 12 dB

Pattern deviation plot: <50% (37) of points are depressed below 5% and <20 points are depressed below 1%

No point in central 5° has sensitivity of 0 dB

Only one hemifield may have a point with sensitivity of <15 dB within 5° of fixation

Severe Defect

MD is > – 12 dB

Pattern deviation plot: >50% (37) of points are depressed below 5% and >20 points are depressed below 1%

Any point in central 5° has sensitivity of 0 dB

Both hemifields have points in central 5° with sensitivity of <15 dB

Reprinted with permission from Hodapp EA, Parrish RK II, Anderson DR: Clinical Decisions in Glaucoma. St Louis: Mosby–Year Book; 1993:chap 2.

intraocular pressure is lowered, it is often helpful to reestablish new baseline fields for future comparison so that further progression is not hidden by prior statistically significant loss. This reestablishment is usually not as time-consuming as establishing the initial baseline because the learning effect is less significant.

4-5-2 Nature of Progression. Several different perimetric characteristics of glaucoma progression can generally be applied to other causes of field abnormality. Most commonly, a mild to moderately dense scotoma deepens as the disease worsens. Scotomas may also enlarge and new scotomas may develop in previously uninvolved locations. Whenever a series of fields appears to indicate disease progression, the clinician must consider a possible increase in other factors, such as a shift in refractive error, an increase in ptosis, or the initiation of miotic therapy. Also, the onset or worsening of confounding non-glaucomatous disease (e.g., cataractous, corneal, retinal, or neurologic conditions) must be considered (Figures 4-13 through 4-15).

4-5-3 Artifacts. Various artifacts that can influence the performance of a single field are described in Chapter 3. These artifacts may develop or increase over time and give a false impression of glaucomatous field loss or progressive glaucoma (Figure 4-16). Properly trained technicians and a thorough knowledge of the influences of artifact will help provide a high specificity in detecting progressive glaucoma.

154 Visual Fields

C (cont.)

Figure 4-13. (Continued)

4-5-4 Long-Term Fluctuation. Although the printouts allow a convenient presentation of data with sophisticated, comparative, statistical analyses, the variability of LTF in the individual patient remains problematic. Quantification of this fluctuation is suggested by the pattern of the MD slope regression analysis, but this is a single index largely influenced by the homogeneous component of LTF. Wide fluctuation in the size and shape of scotomas, which is more a function of heterogeneous LTF, remains the single most difficult problem in interpreting a series of fields for subtle progression over time. In a study involving six experienced observers reviewing serial visual fields from 30 patients, only half the patients had at least five-observer agreement.26

Frequent determination of visual field status, particularly in patients with borderline intraocular pressure control or an advanced scotoma close to fixation,

C (cont.)

Figure 4-13. (Continued)

is presently the best way to detect subtle progression. Some studies have suggested that four or five fields may be necessary over a short period of time to detect extremely subtle progression.27 When progression is more dramatic, either because the disease is worsening rapidly or because the time interval between tests is long, performing such extensive confirmatory studies may not be necessary.

4-5-5 Criteria for Progression. Anderson28 published guidelines for recognizing progression and stresses that they should usually be confirmed with subsequent testing (Table 4-4). In a previously normal region of the field, on two or more reliable tests, the existence of a new isolated defect could be taken as evidence for progression. Criteria for a new defect include a cluster of three points worsening by 5 dB each, one of which has worsened by 10 dB.

A previously abnormal region may be concluded to have deepened if two or three points have deteriorated by 10 dB with results confirmed on a second test. A defect may be deemed to have widened if two or more new contiguous points are involved. This scheme was found to be overly sensitive and nonspecific when used in the Normal-Tension Glaucoma Study.27 The specificity was greatly improved when two cycles of confirmatory fields are performed 3 months apart; each cycle consists