Low-contrast Vision Test May Better Detect Past Optic Neuritis Episodes

Marta Figueiredo, PhD avatar

by Marta Figueiredo, PhD |

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A vision test using a 2.5%-contrast letter chart is more effective than the conventional 100%-contrast chart at detecting previous episodes of optic neuritis, an eye condition that is often the first symptom of neuromyelitis optica spectrum disorder (NMOSD), a study shows.

Results, drawn from responses in unaffected people and those with NMOSD and multiple sclerosis (MS), also highlighted that combining both low- and high-contrast vision tests leads to higher detection rates of previous optic neuritis.

These findings support the use of low-contrast visual acuity test, alone or in combination with the standard high-contrast test, to better detect optic neuritis-induced visual impairment, the researchers noted.

The study, “Low Contrast Visual Acuity Might Help to Detect Previous Optic Neuritis,” was published in the journal Frontiers in Neurology.

Optic neuritis is an inflammation of the optic nerve that, if left untreated, can lead to vision loss. It often occurs in association or as the first symptom of NMOSD and MS, two autoimmune diseases that affect the central nervous system (the brain and spinal cord).

As such, optic neuritis is increasingly being considered an important early marker of these autoimmune conditions, making its detection critical for their early diagnosis and treatment.

Importantly, people with MS and NMOSD can have asymptomatic or subclinical optic neuritis, episodes that may be missed by conventional vision tests, such as the high-contrast visual acuity test.

This type of test assesses visual function using a chart with letters of different sizes with high (100%) contrast between the letters and the white background. Low-contrast visual acuity tests — which use letters of different shades of gray, instead of black — have been shown to be more effective than conventional high-contrast tests at capturing vision problems in MS patients.

Both low- and high-contrast vision tests take about 5 to 10 minutes, making them good candidates for the detection of visual impairment caused by optic neuritis in the clinical setting.

Researchers in South Korea evaluated whether two low-contrast vision tests (with 1.25% and 2.5% of contrast) were superior to the standard high-contrast test at detecting evidence of a previous optic neuritis episode in NMOSD and MS patients.

The three tests were conducted in both eyes of 73 people with NMOSD, 35 MS patients, and 35 healthy individuals used as control. Among patients, a total of 137 eyes (100 from NMOSD patients and 37 from people with MS) had a history of optic neuritis (ON group), while 79 did not (non-ON group).

To limit the analysis to eyes with already stabilized visual function after optic nerve inflammation, the study included only patients with no episode within the past three months.

Researchers analyzed the specificity (percentage of unaffected cases being correctly ruled out) and sensitivity (percentage of optic neuritis cases being correctly identified) of each test in detecting evidence of prior optic neuritis.

Eyes with a known history of optic neuritis were found to score significantly worse in all three tests, compared both with non-ON and control groups. No significant differences were observed between the latter groups.

The 2.5%-contrast visual acuity test was the most effective of the three at distinguishing eyes with previous optic neuritis from those with no such history (non-ON and control groups).

In turn, the 1.25%-contrast test showed the poorest results, as its very faint grey letters were difficult for even healthy eyes to distinguish, the researchers noted.

Particularly, when comparing between ON and non-On patients, the 2.5%-contrast test showed both higher specificity (88.6% vs. 71.4%) and sensitivity (71.5% vs. 64.2%) in detecting earlier optic neuritis than did the conventional 100%-contrast test.

Combining the 2.5%- and 100%-contrast tests also resulted in significantly higher specificity and sensitivity than were achieved with either individual test.

These findings indicate that the 2.5%-contrast visual acuity test “can better detect the visual disturbance in ON [optic neuritis] than [the high-contrast test] in NMOSD as well as MS,” the researchers wrote.

As such, this low-contrast test might be “the most useful, feasible, and rapid method to detect evidence of ON and could be used as a potential additive diagnostic tool of ON,” the team added.

In addition, using both high- and low-contrast letter charts “may yield more powerful result for ON detection in clinical practice,” the researchers wrote.

Future studies are needed to determine the best cutoff values of the 2.5%-contrast test for optic neuritis detection and its potential in helping to diagnose NMOSD or MS, as well as to assess the test’s utility in detecting ongoing or acute optic neuritis episodes.