Three “Red Lines” for Pattern Recognition-Based Differential Diagnosis Using Optical Coherence Tomography in Clinical Practice

Abstract

Background: Optical coherence tomography (OCT) devices for imaging of the eye are broadly available. The test is non-invasive, rapid and well tolerated by patients. This creates a large number of OCT images and patient referrals. Interpretation of OCT findings at the interface between neurological and ophthalmological conditions has become a key skill in the neuro-ophthalmology service. Similar to the interpretation of visual fields a vertical and horizontal median are helpful. A third red line is added which will be reviewed here.Evidence: Levels 1a to 5 evidence.Acquisition: Literature research.Results: There is level 1a evidence that neurodegeneration of the brain is associated with inner retinal layer atrophy. Predominantly this is driven by retrograde (trans-synaptic) axonal degeneration from the brain to the eye. This process typically stops at level of the inner nuclear layer (INL). Anterograde (Wallerian) axonal degeneration from the eye to the brain can trespass the INL. The geography of atrophy and swelling of individual macular retinal layers distinguishes pre-from post-chiasmal pathology. The emerging patterns are a Front-Back "red line" at the INL; a vertical "red line" through the macula for chiasmal / postchiasmal pathology; a horizontal "red line" through the macular for pathology pointing to the optic disc. This is summarized by illustrative cases vignettes. Conclusion:The interpretation of patterns of individual retinal layer atrophy (three "red lines") needs to be combined with recognition of localized layer thickening (edema, structural) at the macula. Certain macular patterns point to pathology at the level of the optic disc. This requires revision of the optic disc OCT and will guide need for further investigations. The three "red lines" proposed here may be found useful in clinical practice and the related mnemonics ("half moon", "sunset", "rainbow") for teaching.

Diagnosis and classification of optic neuritis

“…Nasal pRNFL atrophy is more frequent in optic neuritis associated with anti-MOG antibodies than in optic neuritis associated with multiple sclerosis, where temporal pRNFL dominates. Sectoral atrophy of the peripapillary retinal nerve fibre layer elsewhere at the optic disc alerts to other differential diagnoses such as ischaemic damage 112 . Nasal pRNFL atrophy is rarer in MS-ON compared to MOG-ON Diffuse atrophy of the retinal nerve fibre layer and macular inner plexiform and ganglion cell layers in the range of about 10-20 µm is common with pathology directly involving the optic nerve, whereas an atrophy of about 2-10 µm can be the results of retrograde-trans-synaptic axonal degeneration from brain pathology 8,55, 113 .…”

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

“… 31 The finding of predominant nasal atrophy has been called the ‘half-moon sign’. 4 Importantly, this pattern can also be detected in patients with POAG who later also develop compression of the chiasm. This study demonstrates that a comprehensive measure of regional retinal atrophy, being the mNTR, can distinguish chiasmal compression, POAG and controls.…”

“… 3 Similar to patterns of visual field defects, patterns of macular atrophy on optical coherence tomography (OCT) likely convey important diagnostic clues, which can be obscured in overall retinal thickness measures. 4 5 …”

Branch Retinal Artery Occlusion Mimicking Optic Neuropathy

“…Branches of the central retinal artery supply the inner twothirds of the retina including ganglion cells and their axons as well as the inner plexiform layer and inner nuclear layer of the retina. 1 Branch retinal vascular occlusions (RVOs) produce arcuate pattern of visual field loss mirroring the path of retinal vessels and simulating visual field defects caused by glaucomatous and nonglaucomatous optic neuropathies.…”

“…All patients with a visual field defect and no evidence of optic neuropathy (optic nerve head pallor and RAPD) should have macular OCT performed which will reveal atrophy of all inner retinal layers in BRAO as compared to selective ganglion cell and nerve fiber layer loss in optic neuropathies. 1…”