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With the multifocal technique, visual evoked potentials (VEPs) can be recorded simultaneously from many regions of the visual field. For the multifocal VEP (mfVEP), the patient views a display that typically contains 60 sectors, each with a checkerboard pattern. The display covers about the same retinal area as the 24-2 Humphrey visual field (HVF). However, due to the scaling of the sectors of the mfVEP display, the fields are sampled differently by the mfVEP and HVF. To assess local defects in the visual field, the mfVEP responses must be compared with normal controls. These comparisons require relatively sophisticated analyses and software. Whereas the mfVEP can be recorded relatively easily with the same equipment used to record multifocal electroretinograms (mfERGs), the software needed to perform the analysis is not yet widely available. The mfVEP is valuable for ruling out non-organic visual loss, diagnosing and following patients with optic neuritis/multiple sclerosis, evaluating patients with unreliable or questionable HVFs, and following disease progression. When combined with the mfERG, diseases of the outer retina (before the retinal ganglion cells) can be distinguished from diseases of the ganglion cells and/or optic nerve. The difficulties encountered in recording and analyzing mfVEP responses are greater than those involved in full-field VEP testing. Thus, in its current form, the mfVEP is best recorded and interpreted by ophthalmologists and electrophysiologists experienced with the technique. However, this technique is developing rapidly; advances in commercial hardware and software are expected in the near future.

The multifocal electroretinogram (mfERG) technique allows local ERG responses to be recorded simultaneously from many regions of the retina. As in the case of the full-field ERG, the ganglion cells contribute relatively little to the response, which originates largely from the outer retina. The mfERG is particularly valuable in cases in which the fundus appears normal, and it is difficult to distinguish between diseases of the outer retina and diseases of the ganglion cells and/or optic nerve. The mfERG can also help to differentiate among outer retinal diseases, to follow the progression of retinal diseases, and, with the addition of the mfVEP, to differentiate between organic and nonorganic causes of visual loss. However, because the difficulties encountered in recording and analyzing mfERG responses are greater than those involved in full-field ERG testing, mfERG testing is best left to centers with an electrophysiologist familiar with the mfERG test. Although this technique is relatively new and standards are still being developed, centers capable of recording reliable mfERG responses can be found in hundreds of locations around the world.

A 90-year-old woman presented with subacute painless left ptosis. Examination of the left eye revealed ptosis with loss of the superior eyelid sulcus, 2 mm of proptosis, mild tenderness with retropulsion, and optic disc edema. Levator function and extraocular movements were normal, and there was no relative afferent pupillary defect. MRI demonstrated thickening of the extraocular muscles in the left orbit with lacrimal gland enlargement and mild enhancement of the optic nerve sheath. Serology revealed a positive enzyme-linked immunosorbent assay for Lyme antibodies and a positive Western blot of Lyme IgG titer. The patient recalled a tick bite 6 months earlier, at which time Lyme serologies were negative. After 3 weeks of intravenous ceftriaxone, she had a significant improvement and a full recovery by 3 months. Lyme disease should be included in the differential diagnosis of orbital inflammation, especially in Lyme-endemic areas.