size (Eisner et al., 2006), and a flaw-normative database that did not rule out, at least, the cases with a major learning effect. SITA SWAP, a novel program included in the latest version of the HFA II-i, has a shorter duration (between 3 and 6 min) and may at least partially reduce the impact of such limitations (Bengtsson and Heijl, 2003, 2006) and improve the performances of this perimetry.

Clinical data comparing FDT and SWAP

The studies comparing the diagnostic efficacy of FDT and SWAP are the most pertinent to the purpose of this review, but, to the best of our knowledge, only 10 have been published. Ideally, each study should answer to two questions: ‘‘Is it worth testing patients with glaucoma or glaucoma suspect with unconventional perimetries?’’ and

‘‘Which one, among FDT and SWAP, is preferable?’’ The first question implies a longitudinal design to verify whether unconventional perimetries are more effective than SAP in detecting conversion to the disease or progression. As funding allocation is common for all perimetries, in the case of their validation, unconventional perimetries would be performed at the expense of SAP. This hypothetical superiority over SAP should therefore be demonstrated using an independent ‘‘gold standard’’ for diagnosis (ONH or RNFL appearance). Unfortunately, as shown in Table 3, no studies fulfilled all these features, and therefore any conclusion on the efficacy of unconventional perimetries over SAP must be considered with great caution.

Landers conducted a study over 62 OH patients (normal ONH and SAP) to verify whether FDT and SWAP could detect underlying earlier visual field loss (Landers et al., 2003). Patients underwent SAP, SWAP, and FDT every year for a 3-year follow-up. At the end of the study, nine subjects had abnormal SWAP and 10 abnormal FDT. Field loss at SAP developed in five subjects, all of whom had pre-existing abnormal SWAP and FDT results; no SAP defects developed in patients with normal SWAP or FDT. This study suggested that both FDT and SWAP are useful tools to predict the development of SAP loss in OH patients.

A number of cross-sectional studies obtained similar results, thus suggesting that FDT and SWAP were equally effective in diagnosing pre-perimetric glaucoma cases (Bayer and Erb,

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2002; Bayer et al., 2002; Leeprechanon et al., 2007), with a sensitivity ranging from 20 (Ferreras et al., 2007) to 72% (Leeprechanon et al, 2007) for FDT, and from 20 (Ferreras et al., 2007) to 54% (Leeprechanon et al., 2007) for SWAP; specificity was similar for the two techniques (53% for FDT vs. 44% for SWAP) (Leeprechanon et al., 2007).

Other studies suggested that FDT may achieve better diagnostic performances than SWAP (Bowd et al., 2001; Soliman et al., 2002). An interesting study compared the diagnostic ability of several morphological and functional tests in diagnosing early glaucoma (Bowd et al., 2001). Two different definitions were adopted, based on ONH appearance and SAP. The area under the curve (AUC) was calculated for each test; overall, FDT had better diagnostic power than SWAP (AUCs of 0.87 and 0.88 compared to 0.76 and 0.78 for SWAP).

Another relevant piece of information from this study was that, when specificity was set at 90%, the two techniques obtained a poor diagnostic agreement. This means that, at the initial stage of the disease, no single perimetric test was always affected, whereas the other remained normal, a fact that has been recently confirmed (Sample et al., 2006).

On the other hand, performing a battery of SWAP and FDT is a good strategy for identifying the largest number of early glaucoma cases as possible (Ferreras et al., 2007; Horn et al., 2007).

Detection of early glaucoma cases can be further maximized in both screening (To´th et al., 2007)

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and specialistic (Horn et al., 2003; Bagga et al., 2006) settings if a combination of functional and morphological examinations is obtained. It has been shown that adding FDT perimetry to each of

Table 4. Items that are required to improve the clinical applicability of unconventional perimetries

1.Provide high-quality scientific evidence of the importance of increasing the frequency and the regularity of visual test repetitions (with both conventional and, eventually, unconventional techniques) in order to obtain a more generous resource allocation for perimetry in glaucoma management

2.Provide high-quality scientific evidence of the superiority, if any, of unconventional perimetries in the early diagnosis of glaucoma:

-Prospective, longitudinal studies

-Possibly multicentric studies

-Morphological ‘‘gold standard’’

-Comparative data between conventional and unconventional techniques

-Large sample size to provide a reasonably high number of progressing cases

3.Unify and validate the diagnostic criteria for FDT and SWAP

4.As for SAP, generate software to evaluate FDT and SWAP progression

5.Validate the new SITA SWAP program

the best structural parameters led to a significant increase in sensitivity without a significant change in specificity compared with structural parameters alone, whereas adding SWAP to each of the best structural parameters led to a significant increase in sensitivity and a significant decrease in specificity compared with each structural parameter alone (Shah et al., 2007).

Conclusions

FDT and SWAP are two relatively novel perimetric techniques that can provide additional or confirmatory evidence in glaucoma patients. Furthermore, other perimetric techniques (MAP and HPRP) may have a role in the management of the disease, but due to their poor diffusion their use is still limited to experimental settings.

Some functional features of the RGCs, such as segregation (Kaplan, 2004; Callaway, 2005), isolation (Sample et al., 1996), and redundancy (Johnson, 1994; Haymes et al., 2005), have been only recently clarified; these aspects provided confirmation that both SWAP and FDT, thanks

to their selective evaluation of subgroups of RGCs with low number and redundancy, actually investigate functions that are impaired in the early stages of the disease (Johnson et al., 1993a, b; Trible et al., 2000; Landers et al., 2003).

Clinical studies on SWAP and FDT are growing in number, and they seem to confirm the ability of both techniques in detecting abnormalities in early

glaucoma cases otherwise judged as normal on the basis of SAP results (the so-called ‘‘pre-perimetric’’ glaucomas) (Johnson et al., 1993a, b; Johnson and Samuels, 1997). Overall, FDT shows a slightly better diagnostic power, a more solid database (with lower intraand inter-individual variability), and more reliable results than SWAP (Soliman et al., 2002; Zangwil et al., 2006).

On the other side, the clinical applicability of both procedures is still limited by a number of factors. Serious doubts on the validity of the full-threshold SWAP database have been raised (high intraand intertest variability; presence of a learning effect also in patients already experienced with SAP) (Bengtsson and Heijl, 2003; Rossetti et al., 2006), whereas no data derived from clinical settings are currently available for the novel SITA SWAP program.

The testing strategy for SWAP is very similar to SAP, and therefore the same diagnostic criteria

could be used to detect glaucoma changes (although some authors raised skepticism on the validity of SAP criteria for SWAP) (Johnson et al., 2002). On the other side, several criteria to define FDT abnormality have been proposed (Delgado et al., 2002), but no criterion has been clearly validated and accepted. As for all physical measurements, also for first-generation FDT, it has been shown that the loosest criterion (i.e., abnormality defined in the presence of at least one location with Po5%) obtains the highest sensitivity but it

invariably causes an increase of the false-positive rate. The novel Matrix FDT uses a testing program that is more similar to SAP; this could also probably allow the introduction of more uniform criteria for abnormality for this technique.

The large part of the literature on SWAP and FDT is composed of cross-sectional studies; very

few prospective data are available, and they were conducted on small groups of patients. Many studies had a selection bias, since only patients with normal SAP were recruited; as a consequence, the diagnostic power of SAP may be underestimated, a fact that has been confirmed by the recent studies considering the appearance of ONH

as the ‘‘gold standard’’ for diagnosis (Bagga et al., 2006; Sample et al., 2006). Finally, very scanty data are available on the efficacy of SWAP and FDT in detecting the progression of glaucoma.

Being resource allocation common to all perimetries, in routine clinical practice the use of unconventional perimetries is strictly related to a reduction in the number of SAP tests. Unfortunately, the number of SAP examinations already

falls substantially below published recommendations for maintaining minimum practice standards in the majority of clinical settings (Friedman et al., 2005). Based on the actual knowledge of unconventional perimetry, a further reduction seems inappropriate, above all in consideration that SAP provides the only parameters having a direct relevance to quality-of-life measures (Gutierrez et al., 1997; Parrish et al., 1997; Sherwood et al.,