The Correlation between Aquaporin-4 Antibody and the Visual Function of Patients with Demyelinating Optic Neuritis at Onset

Aquaporin 4 beyond a water channel; participation in motor, sensory, cognitive and psychological performances, a comprehensive review

Aquaporin 4 (AQP4) is a protein highly expressed in the central nervous system (CNS) and peripheral nervous system (PNS) as well as various other organs, whose different sites of action indicate its importance in various functions. AQP4 has a variety of essential roles beyond water homeostasis. In this article, we have for the first time summarized different roles of AQP4 in motor and sensory functions, besides cognitive and psychological performances, and most importantly, possible physiological mechanisms by which AQP4 can exert its effects. Furthermore, we demonstrated that AQP4 participates in pathology of different neurological disorders, various effects depending on the disease type. Since neurological diseases involve a spectrum of dysfunctions and due to the difficulty of obtaining a treatment that can simultaneously affect these deficits, it is therefore suggested that future studies consider the role of this protein in different functional impairments related to neurological disorders simultaneously or separately by targeting AQP4 expression and/or polarity modulation.

Current understanding of the epidemiologic and clinical characteristics of optic neuritis

Optic neuritis is an ocular disorder whose pathogenesis has not been fully determined, although autoimmune mechanisms have been suggested to be involved in its development. In recent years, anti-aquaporin-4 antibody (AQP4-Ab) and anti-myelin oligodendrocyte glycoprotein antibody (MOG-Ab) have been shown to play major roles in the development of optic neuritis. Because these two antibodies target different tissues, optic neuritis can be classified by the type of antibody. AQP4-Ab-positive optic neuritis responds poorly to steroid therapy and has a poor prognosis in terms of visual acuity. On the other hand, MOG-Ab-positive optic neuritis responds favorably to steroid therapy but is likely to recur when the dosage of steroids is reduced or discontinued. We first present the high incidence of idiopathic optic neuritis and discuss these relatively newer disease concepts of AQP4-Ab-positive optic neuritis and MOG-Ab-positive optic neuritis.

A prospective case-control study comparing optical coherence tomography characteristics in neuromyelitis optica spectrum disorder- optic neuritis and idiopathic optic neuritis

Background

Neuromyelitis optica spectrum disorder-optic neuritis (NMOSD-ON) can now be distinguished from other types of ON as a specific disease by the Aquaporin-4 antibody (AQP4-Ab) test. NMOSD-ON can cause severe retinal nerve fiber layer (RNFL) damage. The optical coherence tomography (OCT) characteristics between NMOSD- ON and idiopathic optic neuritis (IDON) were seldom studied in Asians.

Methods

This prospective case-control study involved 152 eyes from 143 optic neuritis (ON) patients. All the patients were divided into either the NMOSD-ON group or the IDON group based on the AQP4-Ab test. The retinal nerve fiber layer thickness (RNFLT), retinal thickness (RT), and choroidal thickness (CT) were measured by spectral-domain OCT and compared to the 60 age- and gender-matched healthy controls. The association between RNFLT and best corrected visual acuity (BCVA) was examined.

Results

The RNFLT was significantly thinner in all ON patients than in healthy controls, while NMOSD-ON eyes were significantly more affected than IDON eyes in all quadrants (p < 0.01). NMOSD-ON patients had stronger visual function impairment than IDON patients (p < 0.01). RNFLT was related to BCVA in both the NMOSD-ON and IDON groups. Microcystic macular edema (MME) was identified in 28 patients (19.58%) and in 29 of 152 eyes (19.08%), including 20 of 40 eyes (50%) previously affected by ON. MME was more common in patients with NMOSD-ON (32.2%) than in those with IDON (10.75%) (p = 0.001).

Conclusions

The NMOSD-ON group had more pronounced RNFLT thinning and visual function impairment than the IDON group. MME prevalence was higher in NMOSD-ON and was associated with higher frequency of clinical relapses.

Visual function and inner retinal structure correlations in aquaporin-4 antibody-positive optic neuritis

PURPOSE

To investigate the correlation between visual function and thinning of the retinal nerve fiber layer (RNFL) and the macular ganglion cell-inner plexiform layer (GCIPL) as measured by optical coherence tomography (OCT) in eyes with aquaporin-4 IgG-positive optic neuritis (AQP4-IgG-positive ON).

STUDY DESIGN

Prospective study.

METHODS

Patients with a history of ON were categorized into 2 groups: the AQP4-IgG-positive group and the AQP4-IgG-negative group. Patients with multiple sclerosis were excluded. All patients underwent ophthalmologic examination and OCT imaging at least 6 months after the last episode of acute ON. Visual function and inner retinal structure correlations were analyzed using Pearson correlation and regression analyses.

RESULTS

Thirty-one previous ON eyes of 17 AQP4-IgG-positive patients and 21 previous ON eyes of 15 AQP4-IgG-negative patients were registered. Visual function, especially the visual field, was better correlated with RNFL than with macular GCIPL. The best correlation between visual function and RNFL was the linear model, whereas the best correlation between visual function and GCIPL was the nonlinear model (inverse regression). Regression models revealed worse visual function in AQP4-IgG-positive ON than in AQP4-IgG-negative ON, whereas no differences in RNFL and GCIPL were found between the 2 groups.

CONCLUSIONS

RNFL measured by OCT can be a useful retinal structure for estimating and monitoring visual field loss in AQP4-IgG-positive ON patients, particularly in patients whose visual field cannot be quantitated. The correlation between visual function and the inner retinal structure of eyes with AQP4-IgG is unique and differs from that of eyes without AQP4-IgG.