What is the difference between hemianopia and quadrantanopia?

In the world of medicine, eye health plays a great role in human life. Having good eyesight and a clear one is certainly what everyone wants for their life. While you may be familiar with eye vision problems such as blurry vision, there are actually conditions such as hemianopia and quadrantanopia that can occur. These two conditions can also affect eye vision causing a person having trouble to see well. We will learn more about these conditions in this article.

Before we learn more, you might want to know more about the way we humans see. When light that travels through the opening of the eye known as pupil hits the retina located at the back of the eye, the cells on the retina layers convert the light into electrical signals. These electrical signals will then travel through the optic nerve to the brain. It is the brain that converts such signals to images you are able to see and identify. This is only the general way images are produced. In understanding how hemianopia and quadrantanopia affect a person, we will have to go through what is known as the visual pathway.

When we talk about the visual pathway, we will start at the visual processing in the retina. As the electrical signal travels through the optic nerve, the optic nerve of each eye meets the other at the optic chiasm. This optic nerve goes through the bony orbit known as the optic canal. At the optic chiasm, fibres from the nasal aspect of the retina cross over to the contralateral optic tract whereas the fibres from temporal retina remain on its site. This is how the left-sided post-chiasmal fibres give images to the right side of the visual and vice versa. The electrical impulses further travel to the visual cortex of the brain. Visual cortex contains calcarine sulcus where images from both eyes are combined before the final image is formed. Ironically, the image is inverted and the brain will re-invert the image in accordance to the orientation in space.

Hemianopia is a condition where the visual field is lost by one half.  Homonymous hemianopia refers to visual field loss in both eyes on the same side of the visual field. In  other words, a person is unable to see left or right from the centre of the field of vision. For example, left homonymous hemianopia will cause a person unable to see the left side as it will be missing. The missing area represents loss of the left half of the visual field in both eyes. Lesions that affect the vision could be from the optic nerve, optic chiasmal or behind chiasm such as the visual cortex. Hemianopia is often the result of traumatic brain injury, stroke or brain tumour. Apart from homonymous hemianopia, there is actually bitemporal hemianopia. Bitemporal hemianopia causes a person to have missing outer half of both right and left visual field. It is often caused by tumour or lesion pinching the optic chiasm.

Quadrantanopia is a condition where a quarter of the visual field is missing or lost. The common kind of quadrantanopia is known as homonymous superior quadrantanopia. This condition is also known as “pie in the sky” which causes missing vision to the upper field of both eyes on the same side. The visual field affected is often both sides of the eyes and involves lesions behind the chiasm such as lesion to the temporal lobe of the brain. Common causes for this condition are stroke and brain tumours. When it affects the temporal lobe, hallucination and aphasia can be found in patients. Another kind of quadrantanopia is homonymous inferior quadrantanopia. This visual defect causes missing vision to the lower field of both eyes on the same side, also known as “pie on the floor”. This kind of quadrantanopia often resulted from damages to the left parietal lobe. Patients may be found with conditions such as confusion between right-left, agraphia (loss or previous ability to write) and acalculia (inability to process numbers and perform calculations).

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It can be concluded that the eye sight is more than what just is clear to be seen. Visual pathways show that when there is something wrong along the path, it can cause symptoms such as hemianopia or quadrantanopia. Stroke and brain tumour are the common causes for this visual field loss. Loss of visual field can cause reading problems and even mobility problems. These visual field problems may put patients at risk for accidents or injury in their life. Patients who are diagnosed with any of the visual field loss should seek support and advice from their health professional on how to cope with their life. Support from family, friends and caregivers can provide the best quality of life for patients. It is important to get the utmost support both emotionally and physically as patients who have visual field loss already have diseases such as stroke or tumour that makes their life already a bit more difficult than normal.