‘‘Collaborative Normal-Tension Glaucoma Study (CNTGS),’’ and ocular hypertension –– the ‘‘Ocular Hypertension Study (OHTS)’’ and the ‘‘European Glaucoma Prevention Study (EGPS).’’ Early open-angle glaucoma patients were included in the EMGT trial as well as in the ‘‘Collaborative Initial Glaucoma Treatment Study (CIGTS),’’ whereas advanced glaucoma patients were examined in the ‘‘Advanced Glaucoma Intervention Study (AGIS).’’ In all of these studies, SAP represented a prominent diagnostic tool as well as a primary endpoint of the study. (The Advanced Glaucoma Intervention Study (AGIS): 1, 1994; Gordon and Kass, 1999; Musch et al., 1999; European Glaucoma Prevention Study (EGPS) Group, 2002; Heijl et al., 2002; Miglior et al., 2007).

SAP visual field assessment: interpretation and reliability factors

Fixation losses. The HFA periodically checks the patient’s fixation by presenting stimuli within their blind spot (Heijl–Krakau technique). If the number of fixation losses is greater than 20%, a symbol will appear next to the fixation losses.

False-negative errors. A brighter stimulus is presented at a test point in the field that was earlier seen at a lesser luminance: If the patient does not respond to the brighter stimulus, a falsenegative error is displayed. High false-negative rate might indicate fatigue or inattentive patient, but are frequent in very damaged VFs.

False-positive errors. The patient responds to a stimulus that was not projected by the projector: A false-positive error is displayed.

Short-term fluctuation (SF). SF represents intratest variability in threshold measurements of selected VF locations. Two main reasons rely on an abnormal SF: an inattentive patient or a patient with a damaged visual system. Normal SF values are lesser than 3 dB when the same VF location is tested twice.

On the contrary, long-term fluctuation (LF) is the variability in threshold measurements between two VF sessions. LF represents a physiologic

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measurement variability) or learning effect (Flammer et al., 1984).

Although it is an actual change in differential light sensitivity, LF is not quantified in clinical perimetry. However, its occurrence must be considered when evaluating multiple VFs over time.

Graytone map. It represents both tested points and nontested VF intermediate points, which have been assigned values interpolated from neighboring VF locations. For this reason, the accuracy of this representation is poor.

Total deviation (TD). TD is the difference at each test point between the patient’s measured threshold sensitivity and the median normal value for the patient’s age.

Pattern deviation (PD). PD plot shows localized defects that may not be revealed because of either a generalized depression or an elevation of the hill of vision. To obtain the PD plot, an adjustment for the general height of the hill of vision is made on the basis of the 24-2 pattern: The seventh most sensitive (compared with normal) point, that is, the 85th percentile best point of the 24-2 grid, is adjusted to 0 deviation to represent the overall general height of the hill of vision.

It has been pointed out that ophthalmologists should evaluate both total and PD analyses to make informed decisions on VF progression in glaucoma.

Probability of abnormality. The P-value represents the probability whereto measured threshold values have deviated from the expected normal values. The probability statement is based on the hill of vision distribution observed in the normal population. This P-value is computed from the TD and the PD plots. Po1% means that this deviation happens in less than 1% of the normal population and must be considered highly suspicious.

Global indices

HFA: MD, SF, PSD, CPSD

Mean deviation (MD). The MD is the mean difference in decibels (dB) between the ‘‘normal’’ expected hill of vision and the patient’s hill of

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vision. If the deviation is significantly outside the norms, a P-value will be given. Po0.5% means that less than 0.5% of the normal population showed an MD value larger than the value found for this test. This index is a measure of overall depression, elevation of the field, or significantly deep losses in one part of the field and not in others.

Pattern standard deviation (PSD). This is a measurement of the degree by which the shape of the patient’s measured field or hill of vision departs from the ‘‘normal’’ age-corrected reference field model. The value is expressed in decibels, and any value of 2 dB or greater will have a (P) value next to it, indicating the significance of the deviation.

Short-term fluctuation (SF). It represents an index of the consistency of the patient’s responses during the field testing. This value is obtained when 10 preselected points are tested twice and the difference, in decibels, of the patient’s responses is compared.

Corrected pattern standard deviation (CPSD).

This is a calculated measurement in decibels of how much the total shape of the patient’s hill of vision deviates from the shape of the ‘‘normal’’ hill of vision for the patient’s age, after being corrected for intratest variability. In calculating the CPSD, the STATPAC attempts to determine if the irregularities in the hill of vision are real by removing the SF, which may mask a relative scotoma.

Glaucoma hemifield test

In the glaucoma hemifield test (GHT) (30-2 or 24-2 program; FT or Swedish interactive threshold algorithm [SITA] strategies), five areas in the upper hemifield are compared with five mirroring areas in the lower one. A score is assigned to each zone on the basis of the percentile deviations in the PD plot of the locations in that area. A comparison of each zone is made with the mirroring zone. The difference in scores between the two mirroring areas is then compared with significance limits of a database of normal subjects. GHT produces five possible messages: outside normal limits, borderline, general reduction of sensitivity, abnormal high sensitivity, and within normal limits (Anderson and Patella, 1999).

Octopus indices: MD, SF, CLV

The Octopus perimeter (program G1) provides four equivalent global indices: mean defect, corresponding to HFA MD; loss variance (LV), corresponding to HFA PSD; SF; and corrected loss variance (CLV), corresponding to HFA CPSD. However, they differ in that positive values of MD represent loss of sensitivity, and the indices of localized loss are given as the variance instead of the standard deviation. Nevertheless, they share common significance with HFA indices.

OCTOPUS seven-in-one report (Fig. 2)

The reliability factor (RF) is a percentage value of the positive and negative catch trials. For reliable results, the RF should be under 15%.

Bebie curve. This method allows an easy recognition of diffuse as well as local damage. According to Kaufmann and Flammer (1989), the clinical application of the cumulative defect curve in different diseases allows an easy recognition of diffuse as well as local VF damage. Ranking all defects values from left to right, the Bebie curve shows the actual VF results together with the normal bandwidth. It differentiates overall depression (parallel to the band of normality) from focal defects (steep decline).

Statistical information about uniform (MD) and localized loss (LV) provide an easy assessment of the field. For Octopus perimetry, the MD normal tolerance range is from 2 to +2 dB (Paetzold et al., 2007).

The VF indices attempt to summarize the distribution of differential sensitivity within the VF in a few numeric parameters and to give useful information on the functional loss (Flammer, 1986). VF indices can also be used in staging VF defects in glaucoma. In this case, however, it must be considered that VF indices miss to show any spatial distribution of defects; either threshold fluctuations or a variety of artifacts can influence any classification based on VF indices only. Nevertheless, different studies seem to demonstrate that the MD, considered together with the CPSD (or PSD, CLV, or LV) indices, may be useful in the staging of functional damage in