Neuro-ophthalmic pathologies

Pubblicato il

Thursday, 23 May 2024

Argomento

Retina

Characteristics and prevalence of neuro-ophthalmic pathologies and novelties in the most advanced diagnostic imaging.

Neuro-ophthalmic diseases are not very common, but they generally have serious symptoms, including in terms of ocular disorders, and in some cases may entail the risk of permanent impairment of visual function. In particular, diseases affecting the optic nerve are often regarded as prodromes of blindness.

Neuro-ophthalmic diseases include optic neuritis and retinal atrophy with different aetiologies, papilledema, malignant tumours of the optic nerve and a heterogeneous range of neuropathies. In addition, proptosis or exophthalmos - i.e. protrusion or protuberance of one or both eyes - can be a manifestation of malignant tumours affecting the optic nerve and meninges.

Ocular motor nerve palsies are, among other things, among the aetiological factors contributing to the development of strabismus (see Correction of strabismus in adults - Oculista Italiano) and diplopia (double vision)

In many studies, neuro-ophthalmic diseases have been described individually, with reference to a specific related pathology, and limited data are still available on their overall profile, incidence and prevalence.

Neuro-ophthalmology is, in fact, a 'young' branch that combines Neuroscience and Ophthalmology, focusing on the study of neurological disorders that manifest themselves as visual dysfunctions. It was recognised as a medical specialisation in the 1960s and has since undergone lively development.

I vision pathwaywhich connect the retina to the visual cortex, and the oculomotor system, which connects the ocular muscles to the cortical centres, have direct connections with a significant portion of the central nervous system. The neuro-ophthalmologist is, therefore, called upon to assess the integrity of these connections and can, therefore, make assessments on the severity and localisation of related visual problems.

Neuro-ophthalmic patients may experience ocular symptoms of varying severity, such as reduced visual acuity, temporary low vision or blindness, double vision, atypical eye movements, abnormal eyelid function, irregularities in pupil size, and sometimes perceptual distortions.

Neuro-ophthalmological pathologies can affect two different anatomo-functional areas of visual function: the afferent visual systemcausing different types of visual dysfunction, and the efferent visual systemleading to oculo-motor pathologies, cranial oculo-motor neuropathies, gaze instability, pupillary pathologies.

Alterations in the sensory and motor pathways can arise from a variety of causes, including: autoimmune, infectious, inflammatory, ischaemic, hereditary, degenerative diseases or traumatic or compressive events.

It is not uncommon for neuro-ophthalmic dysfunctions, such as inflammatory optic neuropathy, to be an early marker of underlying neurological diseases, such as multiple sclerosis.

Numerous studies have been conducted in different countries to determine the incidence of specific neuro-ophthalmic diseases. For example, a study conducted in the United States reported an incidence of non-arteritic anterior ischaemic optic neuropathy (NAION) in individuals over 50 years of age of as many as 10 cases per 100,000 people in Olmsted County, Minnesota.
In a study conducted in France, optic neuropathies were found to be the most frequent cause of neuro-ophthalmic diseases.

The role of imaging in diagnosis

The role of modern imaging techniques in the diagnosis of neuro-ophthalmic pathologies is constantly evolving, as extensively illustrated in the review Imaging in Neuro-ophthalmology : CONTINUUM: Lifelong Learning in Neurology (lww.com). In particular, future development will be aimed at the precise clinical-anatomical localisation of lesions that cause alterations in afferent and efferent visual functions.

Technological advances in CT, MRI and OCT methods have dramatically changed the way neuro-ophthalmological diseases are now diagnosed and monitored over time.

The Magnetic resonance imaging is today the preferred imaging modality for the diagnosis of afferent and efferent ocular pathway disorders, with the exception of acute haemorrhage and abnormalities in bone tissue, for which CT scans are preferable. MRI has many advantages over CT, as it provides superior contrast between pathological lesions and healthy tissue. Secondly, it allows multiplanar imaging without repositioning the patient and, finally, being unaffected by beam hardening graphic artefacts allows better visualisation of posterior cranial fossa structures

L'Magnetic resonance angiography (MRA)) serves, specifically, to examine vascular anatomy and any abnormalities and lesions, including aneurysms, arterial stenosis and vascular malformations. With its introduction, it was possible to drastically reduce the use of catheter angiography, which is an invasive examination, as a method of examining vascular structures.

Extensive use continues to be made in ophthalmic practice of theFluorescein angiography (FAG) to examine retinal vascular conditions in real time and to distinguish cases of actual optic disc oedema from cases of pseudopapilledema. FAG is an invasive technique using a contrast agent, fluorescein, which can cause allergic reactions in some individuals.

OCT

OCT (Optical Coherence Tomography) is a non-invasive imaging method for examining the optic nerve and retinal anatomy. OCT uses the principles of low coherence interferometry to acquire 'in vivo' high-resolution images, from 3 μm to 6 μm, of retinal structures.

Recent technological developments in retinal segmentation have made it possible to quantify the thickness of individual retinal layers through the spectral domain OCT.

This diagnostic finding facilitates indirect quantification of axonal loss, measured as thinning of the retinal nerve fibre layer, and neuronal damage, measured as thinning of the inner plexiform layer of macular cells, as an outcome of lesions involving the optic nerves, chiasm and optic fibres. These OCT findings correlate closely with functional outcomes across the spectrum of optic neuropathies, including glaucoma, optic neuritis, ischaemic optic neuropathy, hereditary disorders, toxic optic nerve injury, gliomas and papilledema.

OCT is particularly useful in distinguishing mild forms of retinal suffering from severe optic nerve disease. In parallel, high-resolution imaging of the macula can be useful for ruling out retinal pathologies in cases of sudden vision loss that present themselves to neurologists and neuro-ophthalmologists.

The increasing role of neuro-imaging does not, however, reduce the importance of the clinical-anatomical localisation of lesions. On the contrary, imaging techniques should be conceived as complementary to a process that starts with a detailed history, followed by a thorough and complete physical examination of the patient.