Motion perception deficit may persist after optic neuritis attack
MedWire News: Long-term visual disturbances reported by patients who have recovered from an optic neuritis (ON) attack may be due to sustained deficits in motion perception, researchers report.
Indeed, when Netta Levin (Hadassah University Hospital, Jerusalem, Israel) and colleagues tested motion perception in patients with an ON, they found this function was impaired for much longer than visual acuity, visual field, and color perception.
Levin and co-investigators, therefore, suggest: "Motion perception should be included in the routine ophthalmologic tests following ON."
The study, published in the journal Neurology, involved 21 first-time patients with an ON, aged 18-41 years, and 21 aged-matched controls. All underwent regular visual testing, including visual acuity, fundoscopy, visual evoked potentials (VEP), and optical coherence tomography, over a 1-year period.
Functional magnetic resonance imaging (fMRI) was also performed on a subgroup of 13 ON patients and 13 aged-matched controls, while each participant viewed a flickering checkerboard, an expanding and contracting array of dots, and static objects. This tested primary visual regions, motion-related higher visual areas, and motion-related recognition areas, respectively.
The findings revealed that within 4 months of the ON attack, routine visual functions - visual acuity, visual fields, and color vision - were restored to 100% of expected values (determined by controls' achieved values). However, VEP latencies remained prolonged, with a median latency of 138 ms compared with the expected value of 103 ms.
Although motion perception showed some improvement over the first 4 months of the study, it remained impaired after 1-year, reaching a median 38% of expected function.
Results from the fMRI studies supported this finding and showed recovery of normal cortical activation during static object recognition, but not in response to motion-perception tasks for which a deficit in cortical activity persisted throughout the entire 1-year follow-up period.
To determine if the deficit in motion perception noted among the patients with an ON was related to contrast sensitivity (CS), Levin and team measured CS in all affected eyes. In doing so, they found that eyes with intact CS had motion perception deficits similar to that of eyes with impaired CS.
"Thus, motion-perception deficit is independent of CS levels," the team surmises.
"We suggest that sustained deficit in motion perception may explain patients' persistent visual complaints, even when standard testing is normal," conclude Levin and colleagues.
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By Lauretta Ihonor