Clinical use of multifocal visual-evoked potentials in a glaucoma practice: a prospective study

Abstract

Purpose: To test a framework that describes how the multifocal visual-evoked potential (mfVEP) technique is used in a particular glaucoma practice.

Methods: In this prospective, descriptive study, glaucoma suspects, ocular hypertensives and glaucoma patients were referred for mfVEP testing by a single glaucoma specialist over a 2-year period. All patients underwent standard automated perimetry (SAP) and mfVEP testing within 3 months. Two hundred and ten patients (420 eyes) were referred for mfVEP testing for the following reasons: (1) normal SAP tests suspected of early functional loss (ocular hypertensives, n = 43; and glaucoma suspects on the basis of suspicious optic disks, n = 52); (2) normal-tension glaucoma patients with suspected central SAP defects (n = 33); and (3) SAP abnormalities needing confirmation (n = 82).

Results: All the glaucoma suspects with normal SAP and mfVEP results remained untreated. Of those with abnormal mfVEP results, 68 % (15/22) were treated because the abnormal regions on the mfVEP were consistent with the abnormal regions seen during clinical examination of the optic disk. The mfVEP was abnormal in 86 % (69/80) of eyes with glaucomatous optic neuropathy and SAP damage, even though it did not result in an altered treatment regimen. In NTG patients, the mfVEP showed central defects in 44 % (12 of 27) of the eyes with apparently normal central fields and confirmed central scotomata in 92 % (36 of 39), leading to more rigorous surveillance of these patients.

Conclusions: In a clinical practice, the mfVEP was used when clinical examination and subjective visual fields provided insufficient or conflicting information. This information influenced clinical management.

Fig. 1

a Flow chart based on our initial impression of how the mfVEP technique could be used in cases of normal or unreliable standard automated perimetry (SAP) tests. In order to be included, patients either had to have glaucomatous optic neuropathy (GON) or intraocular pressure (IOP)>22 mmHg. b A modified flow chart after testing our initial framework in a. GON glaucomatous optic neuropathy, IOP intraocular pressure, SAP standard automated perimetry, GS glaucoma suspect, OHT ocular hypertension, NTG normal-tension glaucoma, mfVEP multifocal visual-evoked potential technique

Fig. 2

Examples of mfVEP probability plots of a patient with glaucoma. The diameter of the display subtended 44.5°. The sectors, and the checks, are scaled to be of approximately equal effectiveness, based upon cortical magnification factors. For example, the inner-most sectors are about 1.2° in width while the outer-most sectors exceed 7° in width. a Interocular probability plot. b monocular probability plots. A colored square indicates that the mfVEP response was significantly smaller in the right (blue) or left (red) eye at either the 5 % (desaturated color) or 1 % level (saturated color)

Fig. 3

a Standard automated perimetry (SAP) and B mfVEP results from a suspect glaucoma eye. The disk photograph c revealed inferior neuroretinal rim loss (arrow). Despite presenting a SAP test within normal limits, the mfVEP showed a superior defect that could be interpreted as an early damage (red dashed oval)

Fig. 4

Example of mfVEP of a normal-tension glaucoma patient. Note that the central scotoma (a, red dashed squares) was confirmed by the mfVEP in both eyes (b, red dashed oval)

Fig. 5

Example of patient in whom the mfVEP (red arrows) was used to confirm an abnormal standard automated perimetry (SAP) test (pink rectangle). Optic disk photography showing significant thinning of both the superior and inferior rim (a, black arrows)