Hemianopsia: causes and features of this visual deficiency

Dr Catalano proposes an in-depth study on hemianopsia, its causes and characteristics

Our editorial team is pleased to host Dr Catalano: ophthalmologist surgeon, graduate in Medicine and Surgery at the University of Studies "Magna Graecia" of Catanzaro and expert in the diagnosis and treatment of retinal diseases, cornea, and glaucoma. Dr Catalano provides an in-depth study on hemianopsia: causes and characteristics, as to shed light on this peculiar visual deficit.

Function and components of the optical pathways

This kind of visual impairment is caused by partial damage to the middle of the visual field and can be unilateral or bilateral, involving one eye or both. Any damage from the cerebral cortex to the retina can cause damage to the visual field.

The optical pathways consist of three functional components:

• Retinocortical: from the retina to the primary visual cortex.
• Retinocorticale:dalla retina alla corteccia visiva primaria.
• Integrative: from the primary visual cortex to the parietal and temporal cortex related to vision.

The optical component carries the light signal to the retina. In the retino-cortical section, the signal reaches the photoreceptors that transform the light signal into an electrical signal, which is then transmitted to the visual cortex for elementary encoding.

In the integrative portion, the occipitoparietal path integrates the information of movement and depth in spatial perception. The occipitotemporal path integrates the information of shape and colours into recognizable symbols.

Homonymous hemianopsia: where does it start?

Generally, the homonymous hemianopsia has a chiasmatic or post-chiasmatic origin, that is, a lesion present in the section where the nerve fibres from the optic nerve cross or have already divided and passed into the opposite hemisphere. In these areas, nerve fibres are coming from both externally, from the temporal hemiretina, not decussa (45%), while internally, from the nasal hemiretina decussa (55%).

Hemianopsia: causes

Generally, the causes that can lead to this visual deficit are:

• Partial temporal lesion of the optic nerve (unilateral nasal nerve).
• Retinal ischemic phenomena that can give an upper or lower (unilateral) hemianopsia.
• Partial medial lesion of the optic nerve (unilateral temporal).
• Retinal (unilateral) trauma.
• Lesion of the optic chiasma (bitemporal).
• Damage to the optic tract (homonymous right or left).

What are the origins of the lesions that give rise to this symptomatology?

The types of lesions that may result in loss of field of view may have the following origin:

• Ischemic
• Traumatic
• Compressive
• Toxic

In all the above cases, neuronal damage occurs leading to blindness in the affected area.

What tests can be used?

A very useful examination in the event of an injury to the optics is the computerized view field. It is a subjective examination because the patient must recognize a light stimulus and report it to the machine that will later translate the answers in a graphic reconstruction explanatory in addition to all the parameters useful to the ophthalmologist and the neurologist for the follow-up of the pathology.

Instead, objective examinations are electro functional ones, in which the retina is exposed to a light stimulus, and through electrodes, the amplitude and latency of the response are studied.

A new hope coming from neuro-functional rehabilitation

These injuries can lead to a major disability, limiting the lifestyle, work, and social activity of those affected, with a significant impact on the emotional state and, consequently, the general state of health of the patient. To read more about it check out our article "The problems of hemianopsia"

While a visual rehabilitation of such injuries was once considered unnecessary, the evolution of rehabilitation techniques today has given hope to many patients. Neuro-functional rehabilitation aims to strengthen healthy areas so that they can make up for the disability caused by damaged areas.

We thank Dr Catalano for giving us this insight into hemianopsia: causes and characteristics of what is very peculiar symptomatology.