The prevalence of microcystic macular changes on optical coherence tomography of the macular region in optic nerve atrophy of non-neuritis origin: a prospective study

Microcystic Macular Edema Caused by Non-Glaucomatous Optic Atrophy: A Single-Center, Retrospective, Cohort Study in France

Optic Atrophy (OA) can be associated with the development of microcystic macular edema (MME) in the perifoveal retinal inner nuclear layer (INL). We aimed here to retrospectively determine the prevalence of MME in patients with non-glaucomatous OA in our tertiary ophthalmology department between 2015 and 2020. We then examined how MME affected the thicknesses of the different retinal layers and the differences in demographic and clinical characteristics between those patients who developed MME and those who did not. A total of 643 eyes (429 patients) were included (mean age 45.9 ± 17.8 years, 52% female). MME developed in 95 (15%) eyes and across all etiologies of OA except for toxic/nutritional causes, but the prevalence of MME varied between the different etiologies. The development of MME was associated with thinning of the ganglion cell layer (11.0 vs. 9.6 μm; p = 0.001) and the retinal nerve fiber layer (10.1 vs. 9.15 μm; p = 0.024), with INL thickening in the 3- and 6-mm diameter areas of the central fovea. Patients developing MME had significantly worse distance best-corrected visual acuity than those not developing MME (0.62 vs. 0.38 logMAR; p = 0.002). Overall, the presence of MME in OA cannot be used to guide the diagnostic work-up of OA.

Differentiating glaucoma from chiasmal compression using optical coherence tomography: the macular naso-temporal ratio

BACKGROUND/AIMS

The analysis of visual field loss patterns is clinically useful to guide differential diagnosis of visual pathway pathology. This study investigates whether a novel index of macular atrophy patterns can discriminate between chiasmal compression and glaucoma.

METHODS

A retrospective series of patients with preoperative chiasmal compression, primary open-angle glaucoma (POAG) and healthy controls. Macular optical coherence tomography (OCT) images were analysed for the macular ganglion cell and inner plexiform layer (mGCIPL) thickness. The nasal hemi-macula was compared with the temporal hemi-macula to derive the macular naso-temporal ratio (mNTR). Differences between groups and diagnostic accuracy were explored with multivariable linear regression and the area under the receiver operating characteristic curve (AUC).

RESULTS

We included 111 individuals (31 with chiasmal compression, 30 with POAG and 50 healthy controls). Compared with healthy controls, the mNTR was significantly greater in POAG cases (β=0.07, 95% CI 0.03 to 0.11, p=0.001) and lower in chiasmal compression cases (β=-0.12, 95% CI -0.16 to -0.09, p<0.001), even though overall mGCIPL thickness did not discriminate between these pathologies (p=0.36). The mNTR distinguished POAG from chiasmal compression with an AUC of 95.3% (95% CI 90% to 100%). The AUCs when comparing healthy controls to POAG and chiasmal compression were 79.0% (95% CI 68% to 90%) and 89.0% (95% CI 80% to 98%), respectively.

CONCLUSIONS

The mNTR can distinguish between chiasmal compression and POAG with high discrimination. This ratio may provide utility over-and-above previously reported sectoral thinning metrics. Incorporation of mNTR into the output of OCT instruments may aid earlier diagnosis of chiasmal compression.

Peripapillary fluid: Obvious and not so obvious!

Intraretinal or subretinal fluid in the peripapillary area can be clinically visualized in conditions such as peripapillary choroidal neovascularization, optic disc pit maculopathy, and optic nerve head tumors and granulomas. Optical coherence tomography (OCT) helps to visualize peripapillary fluid in many other chorioretinal conditions such as peripapillary pachychoroid syndrome, posterior uveitis, central retinal vein occlusion, malignant hypertension, hypotonic maculopathy as well as neuro-ophthalmological conditions such as glaucoma, microcystic macular edema and disc edema due papilledema, non-arteritic anterior ischemic optic neuropathy, neuroretinitis, and diabetic papillopathy. Often, the differential diagnosis of peripapillary fluid is a bit tricky and may lead to misdiagnosis and improper management. We describe a diagnostic algorithm for peripapillary fluid on OCT and outline the salient features and management of these conditions.

A narrative review of neuro-ophthalmologic disease in African Americans and Hispanics with multiple sclerosis

Multiple sclerosis (MS) is the most common non-traumatic cause of disability in young people, with vision loss in the disease representing the second largest contributor to disability. In particular, African-American patients with MS are noted to have lower vision than their Caucasian counterparts. In this review, we examine the disparities in eye diseases in the MS population with our gaps in knowledge and discuss the underlying nature of pathological disparities.

[OCT in Neuroophthalmology]

Optical coherence tomography (OCT) has become the most important innovation in ophthalmology over the last 30 years and is used routinely, especially in the diagnosis of retinal and glaucomatous diseases. It is fast, non-invasive and reproducible. Since the procedures can offer such a high resolution that the individual retinal layers can be visualised and segmented, this examination technique has also found its way into neuroophthalmology. Especially the peripapillary nerve fibre layer (RNFL) and the ganglion cell layer (GCL) provide valuable diagnostic and prognostic information in cases of visual pathway disease and morphologically unexplained visual disorders. OCT is helpful in determining the cause of optic disc swelling and EDI-OCT can reliably detect buried, non-calcified drusen. This article is intended to provide the reader with an overview of current and future applications of OCT in neuroophthalmology and knowledge of possible pitfalls.

Clinical review of retinotopy

Two observations made 29 years apart are the cornerstones of this review on the contributions of Dr Gordon T. Plant to understanding pathology affecting the optic nerve. The first observation laid the anatomical basis in 1990 for the interpretation of optical coherence tomography (OCT) findings in 2009. Retinal OCT offers clinicians detailed in vivo structural imaging of individual retinal layers. This has led to novel observations which were impossible to make using ophthalmoscopy. The technique also helps to re-introduce the anatomically grounded concept of retinotopy to clinical practise. This review employs illustrations of the anatomical basis for retinotopy through detailed translational histological studies and multimodal brain-eye imaging studies. The paths of the prelaminar and postlaminar axons forming the optic nerve and their postsynaptic path from the dorsal lateral geniculate nucleus to the primary visual cortex in humans are described. With the mapped neuroanatomy in mind we use OCT-MRI pairings to discuss the patterns of neurodegeneration in eye and brain that are a consequence of the hard wired retinotopy: anterograde and retrograde axonal degeneration which can, within the visual system, propagate trans-synaptically. The technical advances of OCT and MRI for the first time enable us to trace axonal degeneration through the entire visual system at spectacular resolution. In conclusion, the neuroanatomical insights provided by the combination of OCT and MRI allows us to separate incidental findings from sinister pathology and provides new opportunities to tailor and monitor novel neuroprotective strategies.

RECALCITRANT CYSTOID MACULAR EDEMA? BILATERAL INTRARETINAL HYPOREFLECTIVE SPACES ON SD-OCT AS A PRESENTATION OF A PITUITARY MACROADENOMA

PURPOSE

To report a case of a pituitary macroadenoma that presented with bilateral intraretinal hyporeflective spaces located primarily in the inner nuclear layer on the macular SD-optical coherence tomography.

METHODS

Case report.

RESULTS

Based on the findings of a macular SD-optical coherence tomography, a 53-year-old man was considered as having cystoid macular edema secondary to a retinovascular condition. He was treated with intravitreal vascular endothelial growth factor inhibitors and corticosteroids with no improvement. Confrontation visual fields suggested a bitemporal defect. MRI confirmed the presence of a nonsecreting pituitary macroadenoma compressing the optic chiasm.

CONCLUSION

Not all intraretinal hyporeflective spaces in the optical coherence tomography are secondary to a retinal vascular condition. Hyporeflective spaces in the inner nuclear layer on optical coherence tomography imaging that do not leak on fluorescein angiography may be secondary to optic atrophy from chiasmal compression.

Posterior segment spectral domain oct in the differential diagnosis of bilateral temporal optic neuropathy and its correlation with visual acuity

PURPOSE

To identify the underlying etiologies and to evaluate the differential diagnostic value of posterior segment spectral domain OCT measurements and their correlation with best-corrected visual acuity (BCVA) in a group of patients with OCT documented bilateral optic neuropathy limited to the temporal quadrants.

METHODS

Retrospective study.

RESULTS

We included 61 patients: 35 presented with presumed "classic" acquired mitochondrial optic neuropathy (MON) (18 nutritional, 11 toxic, 6 mixed toxic-nutritional) and 2 with suspected hereditary MON. Nine patients were identified as 'MON mimickers' (especially multiple sclerosis), and 4 were found to have a mixed mechanism, while 11 remained undiagnosed. Across all etiologies, the strongest positive relationship between BCVA and tested OCT parameters was with macular GCL (ganglion cell layer) and GCIPL (combined ganglion cell and inner plexiform layer) volumes rather than peripapillary retinal nerve fiber layer (RNFL) thicknesses (all statistically significant). There was an inverse relationship between BCVA and inner nuclear layer (INL) volumes, with significant differences for BCVA and all tested OCT parameters between eyes with and without INL microcystoid lesions. OCT (absolute values and intereye differences) was not helpful in distinguishing between presumed acquired mitochondrial disease and patients with multiple sclerosis without optic neuritis. However, significantly greater intereye differences in global RNFL and inner plexiform layer and GCIPL volumes were found in patients with a previous history of unilateral optic neuritis.

CONCLUSIONS

The strongest positive relationship with BCVA was found for macular GCL and GCIPL volumes. OCT could not differentiate between acquired mitochondrial disease and multiple sclerosis without optic neuritis.

Diagnostic ability of confocal near-infrared reflectance fundus imaging to detect retrograde microcystic maculopathy from chiasm compression. A comparative study with OCT findings

PURPOSE

To evaluate the ability of confocal near-infrared reflectance (NIR) to diagnose retrograde microcystic maculopathy (RMM) in eyes with temporal visual field (VF) loss and optic atrophy from chiasmal compression. To compare NIR findings with optical coherence tomography (OCT) findings in the same group of patients.

METHODS

Thirty-four eyes (26 patients) with temporal VF loss from chiasmal compression and 41 healthy eyes (22 controls) underwent NIR fundus photography, and macular OCT scanning. VF loss was estimated and retinal layers thickness were measured on OCT. Two examiners blinded to the diagnosis randomly examined NIR images for the presence of hyporeflective abnormality (HA) and OCT scans for the presence of microcystic macular abnormalities (MMA). The total average and hemi-macular HA area and number of microcysts were determined. The groups were compared and the level of agreement was estimated.

RESULTS

The OCT-measured macular retinal nerve fiber and ganglion cell layers were thinner and the inner nuclear layer was thicker in patients compared to controls. HA and MMA were detected in 22 and 12 patient eyes, respectively, and in 0 controls (p<0.001, both comparisons). HA was significantly more frequent than MMA in patients with optic atrophy, and agreement between HA and MMA (both total and hemi-macular) was fair (kappa range: 0.24-0.29). The mean HA area was significantly greater in the nasal than temporal hemi-macula. A re-analysis of the 14 eyes with discrepant findings allowed to confirm RMM in 20 eyes (20/34) indicating that OCT detected RMM in 12 and missed it in 8 eyes. On the other hand, NIR correctly detected 18 out of 20 eyes, overcalled 4 and missed 2.

CONCLUSIONS

RMM is a frequent finding in eyes with severe VF loss from long-standing chiasmal compression. NIR photography appears to be more sensitive than OCT for detecting RMM and may be useful as screening method for its presence.

Evaluation of non-exudative microcystoid macular abnormalities secondary to retinal vein occlusion

Purpose

We aimed to investigate non-exudative microcystoid macular abnormalities for visual and anatomical outcome in patients with retinal vein occlusion (RVO) with and without glaucomatous optic neuropathy (GON).

Methods

Medical records of 124 eyes (105 patients) with RVO were reviewed and analyzed. Eyes demonstrating microcystoid macular abnormalities were divided into 2 groups, those with evidence of glaucoma (group A) and those without glaucoma (group B). Best-corrected visual acuity (BCVA), the prevalence and number of microcystoid macular abnormalities, and number of intravitreal anti-vascular endothelial growth factor (anti-VEGF) injections were compared at baseline and follow-up.

Results

Seventy-one out of 105 eyes (67.6%) with RVO displayed microcystoid macular abnormalities. Thirty-eight out of 71 eyes (53.5%) presented with concomitant glaucoma (group A), while the remaining 33 eyes (42.6%) had no history of glaucoma (group B). At the end of the follow-up period, mean BCVA was worse in group A versus group B (20/80 versus 20/40, respectively; p = .003). The mean number of anti-VEGF injections was 10.1 ± 9.2 in group A versus 5.9 ± 6.9 in group B (p = .03).

Conclusion

Eyes with RVO and concomitant glaucoma exhibited a significantly higher number of microcystoid macular abnormalities and worse BCVA versus eyes with RVO without glaucoma.

Microcystic macular degeneration in autosomal hereditary optic neuropathies: A cross-sectional retrospective study

OBJECTIVE

Patients with autosomal optic neuropathies (AON) may develop microcystic macular degeneration (MMD), observed on retinal optical coherence tomography (OCT) examination. This study aimed to report the prevalence of MMD in AON patients and to assess the consequences of MMD on retinal architecture.

METHODS

Retrospective single-center study conducted between 2001 and 2018. Patients affected by AON secondary to OPA1 or WFS1 gene mutations were included. The following data were collected: visual acuity, macular volume, vitreomacular interface and presence or absence of MMD.

RESULTS

Forty-two subjects (34 OPA1, 8 WFS1) were included. MMD was found in 12 (29%) patients, i.e. 6 of the 8 WFS1 patients (75%) and 6 of the 34 OPA1 patients (17%). In cases with MMD, total retinal volume was greater (P=0.02) in accordance with thickening of the inner nuclear layer (P<0.001). WFS1 subjects had the highest total retinal volume (P=0.01), in relation to a thickening of the inner plexiform layer (P=0.02), inner nuclear layer (P<0.001) and outer plexiform layer (P=0.002). MMD was significantly associated with the WFS1 mutation (P<0.001). No significant association was found between the presence of vitreomacular adhesion and MMD.

CONCLUSION

MMD was found in 29% of patients affected by AON and was more frequent in cases with a WFS1 gene mutation. MMD appears to be related to primary ganglion cell degeneration and Müller cell dysfunction. The vitreomacular interface does not appear to play a role in the occurrence of MMD.

Optical coherence tomography (OCT) in neuro-ophthalmology

Optical coherence tomography (OCT) is a non-invasive medical imaging technology that is playing an increasing role in the routine assessment and management of patients with neuro-ophthalmic conditions. Its ability to characterise the optic nerve head, peripapillary retinal nerve fibre layer and cellular layers of the macula including the ganglion cell layer enables qualitative and quantitative assessment of optic nerve disease. In this review, we discuss technical features of OCT and OCT-based imaging techniques in the neuro-ophthalmic context, potential pitfalls to be aware of, and specific applications in more common neuro-ophthalmic conditions including demyelinating, inflammatory, ischaemic and compressive optic neuropathies, optic disc drusen and raised intracranial pressure. We also review emerging applications of OCT angiography within neuro-ophthalmology.

Neuro-ophthalmologic manifestations of multiple sclerosis other than acute optic neuritis

Acute optic neuritis is the most common neuro-opthalmologic manifestation of multiple sclerosis (MS). Treatment with high-dose intravenous corticosteroids accelerates visual recovery, although it has no long-term visual benefit. MS has several others, less common, neuro-ophthalmological manifestations, where corticotherapy may not be the best treatment option. Neuro-ophthalmologic manifestations of MS other than optic neuritis can be divided in afferent and efferent visual pathways, acute and chronic and may be associated with drugs that are employed in MS. The authors propose is to review the neuro-ophthalmologic manifestations of multiple sclerosis other than optic neuritis. Recognition of these leads to a more targeted treatment and may prevent visual deterioration.

Patterns of retrograde axonal degeneration in the visual system

Conclusive evidence for existence of acquired retrograde axonal degeneration that is truly trans-synaptic (RTD) has not yet been provided for the human visual system. Convincing data rely on experimental data of lesions to the posterior visual pathways. This study aimed to overcome the limitations of previous human studies, namely pathology to the anterior visual pathways and neurodegenerative co-morbidity. In this prospective, longitudinal cohort retinal optical coherence tomography scans were acquired before and after elective partial temporal lobe resection in 25 patients for intractable epilepsy. Newly developed region of interest-specific, retinotopic areas substantially improved on conventional reported early treatment diabetic retinopathy study (ETDRS) grid-based optical coherence tomography data. Significant inner retinal layer atrophy separated patients with normal visual fields from those who developed a visual field defect. Acquired RTD affected the retinal nerve fibre layer, ganglion cell and inner plexiform layer and stopped at the level of the inner nuclear layer. There were significant correlations between the resected brain tissue volume and the ganglion cell layer region of interest (R = -0.78, P < 0.0001) and ganglion cell inner plexiform layer region of interest (R = -0.65, P = 0.0007). In one patient, damage to the anterior visual pathway resulted in occurrence of microcystic macular oedema as recognized from experimental data. In the remaining 24 patients with true RTD, atrophy rates in the first 3 months were strongly correlated with time from surgery for the ganglion cell layer region of interest (R = -0.74, P < 0.0001) and the ganglion cell inner plexiform layer region of interest (R = -0.51, P < 0.0001). The different time course of atrophy rates observed relate to brain tissue volume resection and suggest that three distinct patterns of retrograde axonal degeneration exist: (i) direct retrograde axonal degeneration; (ii) rapid and self-terminating RTD; and (iii) prolonged RTD representing a 'penumbra', which slowly succumbs to molecularly governed spatial cellular stoichiometric relationships. We speculate that the latter could be a promising target for neuroprotection.

OPTICAL COHERENCE TOMOGRAPHY ANALYSIS OF OUTER RETINAL TUBULATIONS: Sequential Evolution and Pathophysiological Insights

PURPOSE

To describe the sequential evolution of outer retinal tubulations (ORTs) in patients diagnosed with choroidal neovascularization and/or retinal pigment epithelium atrophy.

METHODS

Retrospective evaluation of spectral domain optical coherence tomography of a consecutive cohort of patients with various retinal conditions.

RESULTS

We reviewed the clinical findings of 238 eyes of 119 consecutive patients (54 men and 65 women) with a mean age of 76.2 ± 14.2 years (range: 57-90) and a mean follow-up of 3 ± 1.6 years (range 1-7). Over the follow-up period, ORTs were diagnosed in 67 of 238 eyes (28.1%), 9 of which were imaged with sequential, eye-tracked spectral domain optical coherence tomography dating from the beginning of ORT formation. The presence of geographic atrophy and subretinal hyperreflective material at baseline were found to be risk factors for ORT development (P < 0.001 and P < 0.001, respectively). Outer retinal tubulations were divided into forming versus formed morphologies. The latter was comprised open and closed ORTs of which the open subtype was the most common. The formation of ORTs was significantly associated with microcystic macular lesions in the inner nuclear layer and the downward displacement of the outer plexiform layer, referred to as the outer plexiform layer subsidence sign (P < 0.001).

CONCLUSION

Outer retinal tubulation is a frequent optical coherence tomography finding in eyes with choroidal neovascularization and geographic atrophy. Open ORTs with progressive scrolled edges and shortened diameter were significantly associated with microcystic macular lesions in the inner nuclear layer and the outer plexiform layer subsidence sign.

Microcystic macular oedema in optic neuropathy: case series and literature review

Cavitations in the inner nuclear layer associated with severe optic atrophy and loss of retinal ganglion cells have clinically been termed microcystic macular oedema (MME). We describe a case series of MME in patients of all ages but predominantly younger patients with a wide range of optic atrophies ranging from acute onset optic disc drusen associated ischemic optic neuropathy to slowly progressive disease as glaucoma. There were no physical distinctions between MME in different causes of optic atrophy suggesting a common causative mechanism. We reviewed the literature on MME and it appears that MME is associated with more severe visual loss, and is more common in hereditary optic neuropathies and neuromyelitis optica spectrum disease rather than in patients with optic atrophy secondary to multiple sclerosis and glaucoma. Three main causative mechanisms have been proposed, including increased vitreal traction on the macular as the ganglion cells are lost. Others have suggested that trans-synaptic loss of cells in the inner nuclear layer causes formation of empty spaces or cavities. Finally, some have hypothesized a disturbance in the fluid homeostasis of the inner retina as Müller cells are lost or their function is impaired. There are no known treatments of MME. In conclusion, MME seems to be a marker of severe optic nerve atrophy irrespective of the underlying cause.

Microcystoid Macular Changes in Association With Idiopathic Epiretinal Membranes in Eyes With and Without Glaucoma: Clinical Insights

PURPOSE

To describe the clinical and surgical significance of microcystoid macular changes in the inner nuclear layer in patients with idiopathic epiretinal membranes, with and without glaucomatous optic neuropathy.

DESIGN

Retrospective case series.

METHODS

Clinical charts and spectral-domain optical coherence tomography images of 264 eyes of 234 consecutive patients diagnosed with idiopathic epiretinal membranes were reviewed and analyzed. Surgical data were analyzed in a subgroup of eyes with microcystoid macular changes treated with pars plana vitrectomy and epiretinal and internal limiting membrane peel. In surgical cases, postoperative functional and anatomic results at 1 and 6 months were compared between glaucomatous and nonglaucomatous eyes. Associations of microcystoid macular changes with visual acuity and other morphometric parameters were assessed by means of linear or multiple logistic regressions.

RESULTS

Microcystoid macular changes in the inner nuclear layer were diagnosed in 52 out of 264 eyes with epiretinal membranes (19.7%), of which 28 (55.0%) had concomitant glaucoma. The likelihood to develop microcystoid macular changes increased at advanced glaucoma and epiretinal membrane stages. The morphology of microcystoid macular changes was similar between glaucomatous and nonglaucomatous eyes. Forty-four out of 52 eyes (84.6%) with microcystoid macular changes, of which 20 were with glaucoma and 24 without glaucoma, underwent surgery with pars plana vitrectomy and epiretinal and internal limiting membrane peel. At 1 and 6 months after surgery the mean number of microcysts decreased significantly from baseline in nonglaucomatous eyes (P = .003 and P = .002, respectively) and remained unchanged in glaucomatous eyes (P = .400 and P = .700, respectively).

CONCLUSIONS

This study reports a high frequency of microcystoid macular changes in the inner nuclear layer in eyes with concomitant epiretinal membrane and glaucomatous optic neuropathy. In glaucomatous eyes, pars plana vitrectomy with epiretinal and internal limiting membrane peel was ineffective in the treatment of microcystoid macular changes.

The Ocular Manifestations of Drugs Used to Treat Multiple Sclerosis

Recent times have seen an increase in the number of options to treat multiple sclerosis. Ocular manifestations of multiple sclerosis are well known to treating physicians; however, the medications used to treat multiple sclerosis can also have ocular side effects. This review article focuses on the ocular manifestations of corticosteroids and disease-modifying agents such as interferon, fingolomod, natalizumab, alemtuzumab and mitoxantron used to treat the disease. The ocular manifestations of multiple sclerosis treatments can be varied depending on the drug used, and include retinopathy, chronic central serous chorioretinopathy, macular oedema, Graves' ophthalmopathy and cortical blindness. These effects may be specific to the drug or secondary to their immunosuppressive effect. The association of macular oedema with fingolomod is clear and merits ocular screening for toxicity. The immunosuppressive nature of the treatments makes patients prone to acquired infections. Hence, if a patient with multiple sclerosis presents with vision loss, infectious and drug-induced aetiology should be considered alongside relapses of multiple sclerosis itself as a cause.

Complement-independent retinal pathology produced by intravitreal injection of neuromyelitis optica immunoglobulin G

Background

Neuromyelitis optica (NMO), an autoimmune inflammatory disease of the central nervous system, is often associated with retinal abnormalities including thinning of the retinal nerve fiber layer and microcystic changes. Here, we demonstrate that passive transfer of an anti-aquaporin-4 autoantibody (AQP4-IgG) produces primary retinal pathology.

Methods

AQP4-IgG was delivered to adult rat retinas by intravitreal injection. Rat retinas and retinal explant cultures were assessed by immunofluorescence.

Results

Immunofluorescence showed AQP4-IgG deposition on retinal Müller cells, with greatly reduced AQP4 expression and increased glial fibrillary acidic protein by 5 days. There was mild retinal inflammation with microglial activation but little leukocyte infiltration and loss of retinal ganglion cells by 30 days with thinning of the ganglion cell complex. Interestingly, the loss of AQP4 was complement independent as seen in cobra venom factor-treated rats and in normal rats administered a mutated AQP4-IgG lacking complement effector function. Exposure of ex vivo retinal cultures to AQP4-IgG produced a marked reduction in AQP4 expression by 24 h, which was largely prevented by inhibitors of endocytosis or lysosomal acidification.

Conclusions

Passive transfer of AQP4-IgG results in primary, complement-independent retinal pathology, which might contribute to retinal abnormalities seen in NMO patients.