the dimmest stimulus (the threshold) that can be seen at a number of predetermined test locations. Traditional threshold testing uses a staircase bracketing procedure in which stimuli of increasing intensity are projected at a test location until it is detected and then stimuli of decreasing intensity are projected until the patient fails to respond. Newer test strategies use forecasting or adaptive strategies. These strategies are able to provide threshold estimations that are similar to staircase procedures but are performed in a fraction of the time [2–4]. They include the Swedish interactive threshold algorithm (SITA), zippy estimation by sequential testing (ZEST), tendency oriented perimetry (TOP), and the German adaptive threshold estimation (GATE).

15.1.3  Program Tests: Humphrey Field

Analyzer vs. Octopus

Test procedures to evaluate the macular region, the central 30° radius, and the far peripheral visual field beyond 30° are available [1]. Each brand of machine has different names for these programs. A variety of target sizes, durations, and test presentation patterns can be selected [1]. On the HFA, the 30-2 program tests 76 points over the central 30° radius with an equidistant grid of points located 6° apart. The 24-2 program has 54 test points covering the central 24° radius, except nasally where it extends to 30°. The size III stimulus is most commonly used with these two programs. The 10-2 program has a pattern of 68 points 2° apart in the central 10° field. (The -2 refers to a Humphrey protocol in which points are tested on either side of the vertical and horizontal axes as opposed to on these axes, which would be a -1 test).

The Octopus glaucoma examination programs are called G1 and G2. They both test a 30° radius field with 59 test locations, while G2 additionally tests 14 points from 30to 60°, and in the macular region the resolution is greater at 2.8°. Octopus program 32 tests 76 locations in an equidistant grid with 6° spacing between locations, similar to the Humphrey 30-2 program. Program C08 is similar to the 10-2 HFA program and covers the central 10° with a total of 56 test points located 2° apart [5].

15.1.4  Testing of Different Mechanisms

of the Visual System

Standard achromatic automated perimetry (SAP), or white-on-white testing, is most widely used for assessing and monitoring visual field loss in glaucoma. It uses a dim white light stimulus on a dim white light background. Specific mechanisms of the visual system that are damaged in glaucoma can be evaluated with other tests. These other tests attempt to identify glaucomatous damage earlier in the process than does SAP. Isolation of blue cone function utilizing a yellow background and a blue size V stimulus is performed with short wave automated perimetry (SWAP) [6, 7]. Spatial visual field properties are tested with high pass resolution perimetry (HRP) and rarebit perimetry (RBP) [8, 9]. Temporal properties are tested with flicker perimetry, edge perimetry, flicker-defined form perimetry, and motion perimetry [10–12]. Spatiotemporal properties can be tested with frequency doubling technology (FDT) perimetry and FDT Matrix [13, 14].

Summary for the Clinician

››Many options exist today for testing visual field function/sensitivity.

››Automated visual field tests are more commonly used but kinetic tests can provide useful information in certain patients.

››Threshold estimation strategies include the time-consuming staircase bracketing strategy and newer strategies (SITA, ZEST, TOP, GATE) that mathematically predict the sensitivity of adjacent points to shorten the test.

››Test grids come in different geometric patterns with a different number of tested points located either equidistantly or at varying distances from each other.

››Newer visual field tests isolate different cell types and visual functions, including color, spatial, and temporal properties of the visual system.

15.2  What are the Theoretical Advantages of Different Test Strategies (SAP, SITA,

FDT SWAP, etc)?

SAP is now the preferred method for performing visual field testing, and it has undergone the greatest amount of evaluation. In this view, SAP represents the clinical standard of care for visual field evaluation of glaucoma and other ocular and neurologic disorders, and it provides a means of information transfer among eye care practitioners. As outlined in Sect. 15.1, SITA and other forecasting test strategies (ZEST, TOP, GATE) are able to provide information that is essentially equivalent to the results found with previous test procedures with the advantage that they provide it in a fraction of the time and with slightly lower test-retest variability [2­ –4]. FDT, SWAP, and other test procedures are able to evaluate the integrity of subsets of neural visual elements, thereby providing a more specific and detailed description of damage produced by glaucoma or other ocular or neurologic disorders [2–4, 6–14]. It should be noted that the methods extending beyond SAP are not intended to be a replacement for SAP, but rather to be supplements to SAP for cases in which their results may provide insights as to severity of the disease, damage to specific mechanisms, and efficacy of treatment. The utility of their use is thus patient-specific and dependent upon the suspected pathophysiology.

Summary for the Clinician

››SAP (white-on-white perimetry) testing is the clinical standard of care.

››Forecasting test strategies – SITA, ZEST, TOP, GATE – provide equivalent information to older threshold staircase strategies in less time and with less patient variability.

››Different tests of the visual system – FDT, SWAP, HRP, RBP, etc – evaluate subsets of neural visual elements. They are not meant to replace SAP but can supplement SAP results.

15.3  Is There a Visual Field Program of Choice at This Point in Time?

As indicated in Sects. 15.1 and 15.2, many options are available for obtaining visual field information. Most eye care practitioners use a forecasting threshold estimation test strategy that evaluates the central visual field, for example, the Humphrey 24-2 SITA Standard test procedure, or an equivalent test on a different automated perimeter (i.e., Octopus G2 TOP). For patients with limited attention spans or other special circumstances, it may be necessary to use a faster and/or less rigorous test procedure (for example, Humphrey 24-2 SITA Fast). If assessments of the far peripheral visual field, the macular region, or other specific areas of the visual field are necessary for clinical diagnostic purposes, then different test programs should be utilized as listed in Sect. 15.1. Finally, specialized visual field testing for evaluation of color vision mechanisms, spatial characteristics or temporal properties may also be important for a thorough clinical evaluation.

Summary for the Clinician

››No one test is ideal for every patient.

››Forecasting threshold estimation strategies (HFA 24-2 SITA Standard or Octopus G2 TOP) are most often used because they save time without sacrificing reliability of test results.

››Other tests may be chosen depending on an individual patient’s needs.

15.4  What Visual Field Program

is Best for Use in a Glaucoma

Subspecialty Clinic?

The most common visual field test procedure that is used for glaucoma patients and glaucoma suspects is a 24-2 test pattern using the SITA Standard threshold estimation procedure [2]. This provides good general coverage of the central (24° radius) visual field and will detect and evaluate most glaucomatous visual field deficits.

Additionally, it is able to provide nearly all of the information that can be determined using the Full Threshold staircase procedures at a fraction (50–80%) of the time. Some practitioners are interested in further reducing the visual field testing time and they use the SITA Fast procedure­ [15]. It should be noted, however, that SITA Fast produces greater patient response variability [16]. Comparable techniques are also available on other automated devices [2–4]. In some instances, specific glaucomatous visual field defects (temporal wedges, subtle nasal steps) will be missed by the 24-2 procedure, and some glaucomatous defects (e.g., arcuate defects) may be difficult to distinguish from artifactual test results (e.g., trial lens rim artifacts), and in these instances a 30-2 test procedure may be more useful. Infrequently, the initial glaucomatous defect may occur in the far periphery beyond the 30° radius, making it necessary to perform testing of the far peripheral visual field. There are also some cases in which other aspects of the eye examination provide a strong suspicion of glaucomatous damage, but conventional visual field testing is within normal limits. In these cases, specialized testing such as FDT perimetry [13, 14], short wavelength automated perimetry (SWAP) [6, 7], high-pass resolution perimetry (HPRP) [8], or RBP [9] may be a useful adjunct to other tests. Finally, for patients with limited cooperation and attention skills, there are other procedures that can be used, as outlined in Sect. 15.7 below.

Summary for the Clinician

››For a glaucoma clinic, a 24-2 SITA Standard threshold estimation procedure (or equivalent) is the most commonly used as it will detect most glaucomatous visual field defects.

››SITA Fast procedures take less time but result in more variable patient responses.

››The 30-2 test pattern takes a little more time to complete but may detect defects missed by a 24-2 test pattern, such as temporal wedge defects and subtle nasal steps, and it may distinguish some artifactual test results from true defects.

15.5  What Program is Best for Use in a General Clinic to Screen for Glaucoma?

When performing a screening test, for glaucoma or any other ocular or neurologic condition, there is always a trade-off between accuracy and efficiency. The large number of screening procedures that are available for automated perimetry produces a large series of choices for the eye care practitioner. On the one hand, it is possible to select a procedure that has high specificity (minimizes the number of times that an individual with normal visual function is incorrectly classified as having glaucomatous damage) at the cost of reducing sensitivity­ (incorrectly classifying a person with glaucomatous damage as having normal visual function). On the other hand, one can select a procedure that has high sensitivity at the cost of reducing specificity. Selecting an appropriate­ visual field screening procedure depends on the particular­ needs of the eye care practitioner, the characteristics of his/ her clinic population, and the amount of time available for testing. One procedure that appears to be especially useful to screen for glaucomatous visual field loss is the FDT perimeter. It has two screening procedures, one that is designed to optimize sensitivity and another that is designed to enhance specificity [17]. Additionally, there are decision rules that have been established for evaluation of FDT visual field screening results [18]. To date, it has been determined that good performance for screening can be achieved with this device using a test that takes between 30 and 90 s per eye to perform [19].

Summary for the Clinician

››The FDT perimeter has been found to be useful to screen general populations for glaucomatous visual field defects.

15.6  How Can I Convert from One Visual Field Strategy to Another to Help Me Interpret and Compare Tests?

Most eye care practitioners have found that it is often a straightforward matter to qualitatively convert from one visual field strategy to another, but it gets very complicated to do so, on a quantitative basis. One of the major advances afforded by automated perimetric testing has been the ability to immediately compare a patient’s test results with the distribution of values obtained from a normal population (adjusting for typical aging effects, visual field location differences, and related issues). This allows comparisons to be made from one procedure to another in a straightforward manner, although it should be kept in mind that each normative database will be slightly different. Additionally, the use of probability levels and percentiles provides a means of evaluating visual field data in a manner that is less dependent on specific test conditions and measurement values. For progression, the availability of a database containing repeated testing of patients with varying levels of damage (usually with glaucomatous visual field loss) can also be helpful. Finally, many practitioners have found that the best method of switching from one procedure to another is to test the patient with the older procedure and to then begin a new series of testing with the new procedure at the same visit. In this manner, it is possible to establish a new baseline with the latest test procedure.

Summary for the Clinician

››Qualitatively it is straightforward to convert from one visual field strategy to another.

››Comparing probability levels and percentiles between different test types can be useful, although the normative databases may not be equivalent.

››If a switch of test procedures is planned, at the same visit test the patient on the old and new visual field procedure in order to establish a new baseline.

15.7  What Can be Done to Obtain Visual Field Information in a Patient who Consistently Tests Unreliably?

Fortunately, most glaucoma patients are able to perform­ automated static threshold perimetry in a consistent and reliable manner, provided that proper test procedures are conducted [1–3]. In the Ocular Hypertension Treatment Study (OHTS), the Optic Neuritis Treatment Trial (ONTT) and other multicenter clinical trials, enrolled patients were able to perform consistent, reliable visual fields approximately 95% of the time [20­ –22]. However, there are some populations that are not able to perform reliable automated static perimetry tests. In these instances, kinetic testing (using the Goldmann perimeter, tangent screen, or Octopus semiautomated perimeter) may be helpful in providing appropriate visual field information because these procedures are more flexible and interactive. For large visual field deficits, confrontation visual field testing can also be performed, using a variety of techniques [23]. Procedures­ such as FDT perimetry are able to perform rapid and reliable visual field screening, and this is useful in populations that are difficult to test, such as children and patients with limited attention and cooperation skills [24]. There have been recent developments in more “objective” forms of visual field testing that impose fewer demands on the cooperation of the patient. These new techniques include pupil perimetry [25], multifocal electroretinograms (mfERG), and multifocal visual evoked potentials (mfVEPs) [26] (see Chap. 21 for explanation of test of VEP and mfERG). Pupil perimetry records pupillary responses to light stimuli presented at different visual field loci; it has limited sensitivity since the stimulus must be large and bright to elicit a response. Finally, if none of these procedures is able to provide reliable, clinically relevant visual field information, then diagnosis and monitoring of the patient must be obtained using other clinical methods (intraocular pressure, optic disc evaluation, comprehensive eye examination, review of medical and social history, treatment regimen and response, etc.).