[15–18]. Large increases in latency are associated with demyelinating diseases such as multiple sclerosis [19] and with compressive tumors [20], while moderate increases suggest retinal disease [21].

Summary for the Clinician

››The mfVEP report should indicate those regions of the field in which the responses are abnormal.

››The presentation of abnormal regions should allow comparison to the patient’s SAP field.

››Abnormal latencies should also be noted, as these may indicate retinal disease, optic tract demyelination and compressive lesions.

21.3  Is the mfVEP a Useful Test in Glaucoma?

21.3.1  The mfVEP Is Not Ready for Routine Screening of Glaucoma Patients

The mfVEP is not yet ready for routine screening in the typical clinical setting. First, the successful recording of mfVEPs requires specialized equipment. Presently, there is no commercially available product that can record and do an adequate job of analysis. Some devices can yield good recordings but they require specialized software, such as the programs we have written for mfVEP analysis [5, 6]. This situation is likely to change in the future as a number of manufacturers now sell equipment capable of mfVEP recording and some are working to improve their analysis programs. Second, trained personnel are needed for both the recording and its interpretation. Currently, mfVEP testing is best performed in centers with the necessary equipment, expertise, and experience.

21.3.2  The mfVEP Can Provide Clinically Useful Information

The empirical and theoretical evidence suggest that the sensitivity and specificity of the mfVEP test are

approximately the same as that of the 24-2 SAP test [5, 22, 23]. However, in some patients the mfVEP can detect damage before it is detected by 24-2 SAP, although in other patients the reverse is true. For example, the mfVEP can outperform the 24-2 SAP in cases of early damage where one eye is healthy and the responses are robust [5, 24]. Figure 21.2 illustrates this point; it shows the results obtained from a patient with an arcuate defect that was detected first with the mfVEP. We have found the mfVEP useful in the clinic under the following conditions discussed in Sects. 21.3.2.1 through 21.3.2.3.

21.3.2.1  Inconclusive SAP Visual Field

and Disc Examinations

The mfVEP can clearly detect glaucomatous damage in some patients with normal 24-2 SAP fields [5, 7, 9, 13, 23, 24]. In our experience, the single most important clinical use involves patients with ambiguous SAP and disc examinations. For example, in patients with a normal 24-2 SAP visual field, questionable disc examinations, and an abnormal FDT and/or SWAP examination, the mfVEP can aid the clinician. If the mfVEP confirms the abnormal FDT or SWAP, then the clinician may initiate treatment. Another example is the case of a normal 24-2 SAP field that may have a single abnormal point that is located in an arcuate region. Again, if the mfVEP confirms a defect in this region, it provides an argument in favor of treatment.

21.3.2.2  Unreliable Visual Fields

Many patients are unable to produce reliable and consistent SAP visual fields as indicated by excessive fixation, false positive, and/or false negative errors. In most cases, the mfVEP test provides information that is equivalent to visual field information [5].

21.3.2.3  Inconsistent Visual Fields

Some patients produce reliable and reproducible SAP visual fields, but these fields are inconsistent with other clinical findings. A typical example involves a patient with a fairly poor SAP field with normal reliability indices whose optic disc appears “too good” for the degree of visual field loss. The mfVEP is often much better than standard perimetry in this type of patient