Visual Field Impairments Found in NMOSD Adults With Optic Neuritis
Patients experience a loss of peripheral vision, worse outcomes
Impairments in the visual field — the total area in which objects can be seen in a person’s peripheral vision — were found in adults with optic neuritis (ON) related to neuromyelitis optica spectrum disorder (NMOSD), according to a new study.
NMOSD patients with optic neuritis had more visual field impairments and worse outcomes than those with idiopathic demyelinating optic neuritis — a condition affecting the optic nerve, like NMOSD, but with a different underlying cause that is associated with the neurodegenerative disorder multiple sclerosis (MS).
The researchers studied the effects of an optic neuritis attack on patients over a follow-up period of at least six months, noting that any impairment in the visual field “evolves during the process of acute attack until the inflammation finally stables.”
Their findings showed that the “exact course” of an optic neuritis attack “was the main factor” in determining visual field defects among these patients.
The study, “Comparing evolvement of visual field defect in neuromyelitis optica spectrum disorder-optic neuritis and idiopathic optic neuritis: a prospective study,” was published in the journal BMC Ophthalmology.
Investigating visual field impairments
Most cases of NMOSD are caused by a mistaken immune attack on astrocytes, a cell type that supports nerve cells in the brain. An NMOSD-related immune attack on these cells can cause optic neuritis (NMOSD-ON), or inflammation and damage to the optic nerve, potentially leading to eye pain, blurry vision, or vision loss.
Optic neuritis also can be an early symptom of MS, an autoimmune condition caused by immune damage to myelin, the protective sheath around nerve fibers. These cases are often referred to as idiopathic demyelinating optic neuritis (IDON).
The visual field (VF) test measures how far the eye sees in any direction without moving, as well as vision in different parts of the visual field. However, the visual field in NMOSD-related optic neuritis is not well characterized.
The purpose of this study, by scientists at the Sun Yat-Sen University, in China, was to compare visual field progression in patients with NMOSD-ON and IDON.
According to the researchers, “this is the first longitudinal prospective study [over time] of the VF characteristics of NMOSD-ON during acute attack with a follow-up period at least 6 months after onset.”
The team enrolled 104 patients with an optic neuritis diagnosis who were within 14 days after onset. The participants ranged in age from 18 to 65, and all were followed for at least half a year. Among them, 33 had NMOSD-ON, while 71 had IDON.
Consistent with other reports, the NMOSD-ON group had more females than those with IDON (81.8% vs. 50.7%) and a higher percentage of optic neuritis relapse (51.5% vs. 26.8%). No differences were found between the two groups regarding the age at onset nor involvement in one or both eyes.
At optic neuritis onset, the proportion of eyes that failed the VF exam due to poor visual acuity was similar between the two groups. Among those with VF results, generalized (diffuse) visual impairment was the most common pattern across both groups, followed by nerve fiber abnormalities and impairment in the center of the visual field.
At six months or more of follow-up, the proportion of eyes that failed the VF exam was lower. Among those with VF results, nerve fiber abnormalities were the most common pattern across both groups, followed by diffuse, then central impairment.
Worse damage found for NMOSD-ON patients
The team then followed changes in optic neuritis severity at onset and follow-up by measuring visual acuity, mean defect (MD), the total amount of visual field loss, and pattern standard deviation (PSD), indicating localized vision loss.
At optic neuritis onset, the average MD was similar between the two groups but significantly less in the NMOSD-ON group than IDON throughout follow-up. The PSD in the NMOSD-ON group was significantly higher than in the IDON group at onset and each follow-up. At onset and at six months or more, visual acuity in IDON patients was significantly better than that in the NMOSD-ON group.
In both groups, correlation analysis with visual acuity, MD, and PSD found no relationship between onset and follow-up at more than six months. However, there was a significant positive relationship between higher MD and PSD at one month of follow-up, and three and six or more months of follow-up.
Better visual acuity at one month also was related to better results after six months or more in NMOSD-ON patients, and three months and six months or more in both groups.
Recovery from an optic neuritis episode was most common in one of the four parts, or quadrants, of the visual field in both groups, followed by diffuse recovery, then central recovery.
In a group of patients with data at the first-ever episode of optic neuritis, the percentage of female NMOSD patients was significantly higher than in IDON group (81.3% vs. 47.2%). Although there was no significant difference in MD and PSD between the two groups at onset and each follow-up, visual acuity was worse in the NMOSD-ON group than in the IDON group at onset but not at follow-up points.
In this group, the proportion of eyes that failed the VF exam was higher in NMOSD-ON participants than in IDON patients at onset (65.2% vs. 35.1%) and at six months or more (26.1% vs. 5.4%). Central scotoma, a blind spot in the center of vision, only occurred in the IDON group, while curved or multifocal visual patterns were found more often in the IDON group. However, the difference was not statistically significant.
“The NMOSD-ON patients tended to suffer more severe VF damage, VF irregularity and worse prognosis than that of IDON patients,” the researchers concluded. “Diffuse abnormalities and nerve fiber bundle abnormalities were the two most common types in both groups.”