Macular sparing is

visual field loss The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a point ...

that preserves vision in the center of the visual field, otherwise known as the

macula The macula (/ˈmakjʊlə/) or macula lutea is an oval-shaped pigmented area in the center of the retina of the human eye and in other animals. The macula in humans has a diameter of around and is subdivided into the umbo, foveola, foveal avas ...

. It appears in people with damage to one hemisphere of their

visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...

, and occurs simultaneously with bilateral

homonymous hemianopia Hemianopsia, or hemianopia, is a visual field loss on the left or right side of the vertical midline. It can affect one eye but usually affects both eyes. Homonymous hemianopsia (or homonymous hemianopia) is hemianopic visual field loss on the sa ...

or homonymous

quadrantanopia Quadrantanopia, quadrantanopsia, refers to an anopia (loss of vision) affecting a quarter of the visual field. It can be associated with a lesion of an optic radiation. While quadrantanopia can be caused by lesions in the temporal and parieta ...

. The exact mechanism behind this phenomenon is still uncertain.Whishaw, I. Q., & Kolb, B. (2015). Fundamentals of Human Neuropsychology (7th ed.). New York, NY: Worth Custom Publishing. The opposing effect, where vision in half of the center of the visual field is lost, is known as macular splitting.Windsor, R. L. (n.d.). Visual Fields in Brain Injury - Hemianopsia.net Everything you need to know about Hemianopsia. Retrieved from http://www.hemianopsia.net/visual-fields-in-brain-injury/

Causes

The favored explanation for why the center visual field is preserved after large hemispheric lesions is that the macular regions of the cortex have a double vascular supply from the

middle cerebral artery The middle cerebral artery (MCA) is one of the three major paired cerebral artery, cerebral arteries that supply blood to the cerebrum. The MCA arises from the internal carotid artery and continues into the lateral sulcus where it then branches an ...

(MCA) and the

posterior cerebral artery The posterior cerebral artery (PCA) is one of a pair of cerebral arteries that supply oxygenated blood to the occipital lobe, part of the back of the human brain. The two arteries originate from the distal end of the basilar artery, where it bifur ...

(PCA). If there is damage to one vascular pathway, like in the case of a MCA or PCA stroke, there is still another blood supply that the macular portions of the visual cortex can rely on. Vision in the center of the visual field is then preserved whereas vision in peripheral areas is lost due to the resulting infarct. Another possible reason is that the maculae project to both hemispheres, so in the event of a lesion in one hemisphere, the other intact hemisphere will still receive and process visual information from the maculae in both eyes.

Diagnoses

Macular sparing can be determined with

visual field testing A visual field test is an eye examination that can detect dysfunction in central and peripheral vision which may be caused by various medical conditions such as glaucoma, stroke, pituitary disease, brain tumours or other neurological deficits. ...

. The macula is defined as an area of approximately + 8 degrees around the center of the visual field.Carroll, J. N., & Johnson, C. A. (2013, August 22). Visual Field Testing: From One Medical Student to Another. Retrieved from http://eyerounds.org/tutorials/VF-testing/ During examination, vision in an area of greater than 3 degrees must be preserved for a patient to be considered to have macular sparing because there is involuntary eye movement within 1 to 2 degrees.Remington, L.A. (2012). Clinical Anatomy and Physiology of the Visual System (3rd ed.). Oxford: Elsevier Butterworth-Heinemann.

Implications

Macular sparing is usually a product of unilateral visual cortex lesions, not optic tract or lateral geniculate nucleus lesions in the thalamus. This can help diagnose whether a patient’s visual field loss is due to cortical damage, or optic tract or thalamic damage. Note that macular sparing does not always occur in patients with visual cortex damage. Patients with macular sparing often retain their ability to perform high resolution visual acuity tasks.Schiller, J., Dietrich, T.J., Lorch, L., Skalej, M., Braun, C., Schiefer, U. (1998/1999). Homonymous Visual Field Defects Perimetric findings and corresponding neuro-imaging results. The Hague, the Netherlands: Kugler Publications. For example, they can read fairly well because they can process the entirety of a word presented to their center field of vision like a person with normal vision. Patients with macular splitting fare much more poorly on such tasks, particularly if they lose vision in their right visual field. This is because the right visual field projects to the left hemisphere, where most people are language dominant. People with macular sparing may experience difficulty with moving around, especially in crowds, because they might unintentionally bump into people or objects in their periphery where they cannot see.Zhang, X., Kedar, S., Lynn, M., Newman, N., & Biousse, V. (2006). Homonymous hemianopias: Clinical-anatomic correlations in 904 cases. American Journal of Ophthalmology, 142 (2), 365-366. doi:10.1016/j.ajo.2006.06.022

References

{{Reflist Visual disturbances and blindness Ophthalmology Vision Visual system

Causes

Diagnoses

Implications

See also

References