A Scotoma Is an alteration that is characterized by the experimentation of a zone of blindness in the visual field of the person.
The condition causes partial blindness, as it does not limit vision altogether, and can be both temporary and permanent.
Example of vision with scotoma.
On the other hand, it is necessary to take into account that scotoma can result in a normal situation in people, or a pathological condition. When it comes to this second case, the alteration is usually caused by an injury to the retina of the optic nerve.
In this sense, today two main types of scotoma have been described: the negative scotoma that is not perceived by the subject and the positive scotoma that is perceived by the person.
Likewise, these alterations can also be divided according to the visual field affected, and depending on the causes that originate the visual disturbance.
This article reviews the main features of the scotomas, and explains the types and pathologies that can cause them.
Scotoma Features
The scotoma is an alteration of vision that creates blind spots or"dark holes"in the person's visual field.
This alteration is characterized by affecting only specific regions of the visual field. Thus, although they cause complete blindness at certain points in the visual field, they do not motivate a total loss of vision.
The most common is that a person with scotoma can see with relative normality, but visualize black spots in their field of vision, which limits their ability to visualize the environment.
This alteration can be both temporary and permanent. That is, it can appear for certain periods of time or spread chronically. However, the most common is that it is a temporary condition.
On the other hand, the scotomas are characterized by being both a normal condition and a pathological condition. That is, they can be experienced by a person without any type of pathological process and can suffer from a subject due to a certain disease.
In most cases, scotomas are caused by an injury to the retina of the optic nerve. This lesion prevents the reception of visual stimuli in specific regions of the retina, so visual information transmitted to the brain has black spots in some areas of the visual field.
However, the scotoma may also be caused by an injury to the visual areas of the brain. In this case, the retina works properly but when the brain processes the captured information, it generates black spots in certain parts of the visual field.
Finally, this condition may also be due to vascular alteration. The most typical case of scotoma due to vascular alteration is usually seen during migraine attacks.
Types of scotoma
In general, the scotomas can be classified into two large groups. Negative scotomas and positive scotomas.
The negative scotoma is characterized by not being perceived by the subject. That is, the person who suffers from this alteration does not detect any conditions of blindness or visualize black spots in his field of vision.
Positive scotoma, on the other hand, constitutes a totally contrary alteration. In this case, the person does perceive alterations in the visual field and is able to detect the elements referring to the scotoma that have been previously commented.
Although these are the two main classifications of scotoma, at present several types of this condition have been described that allow a greater delimitation of its properties.
In this sense, the types of scotoma are elaborated according to several criteria such as the location of blindness in the visual field, the anatomical regions injured or the pathologies that directly cause the suffering of the visual disorder. The main types of scotoma that have been described today are:
1- Blind spot
The blind spot is a physiological and absolute scotoma, so it is usually encompassed within negative scotomas that are not perceived by the person.
This alteration corresponds to the projection of the papilla (region of the retina that does not contain photoreceptors) in the visual field.
The blind spot usually measures about seven degrees vertically and about five degrees horizontally and is usually located about fifteen degrees to temporal and one degree below the mid-horizontal raphe.
Seidel's scotoma
This alteration constitutes a visual deformation of the blind man. It is usually caused by a slightly curved early arcuate defect.
Paracentral scotomas
These conditions include a small group of isolated scotomas occurring in the circular area between the ten and twenty degrees surrounding the point of fixation of the retina. It is usual for these scotomas to appear in the upper sector and as the pathology progresses, a superior arched scotoma forms.
4- Central scotomas
These visual disturbances affect the fixation and the surrounding field. They are one of the types of papillomacular scans and are characterized by being the most common and those that produce a greater decrease of the vision.
Centrocecal scotomas
They correspond to a type of cecal scotoma that affects the area of normal blind macha. In this case, the alteration extends to the fixation area and appears to affect the papillomacular bundle.
6- Bjerrum's scotoma
The Bjerrum scotoma occurs in the arcuata area, due to the union of paracentral scotomas. They usually start at the upper pole and affect the central area of the visual field.
7- Nasal step
The nasal step occurs due to an injury to the bundle of arched nerve fibers in the retina. This alteration can generate asymmetries in the upper and lower poles, as well as along the raphe.
Causes
Visual affections can be caused by a great variety of pathologies and situations, so scotomas have a very varied etiology.
The most common is that these alterations occur as direct or indirect effect of a particular pathology. For this reason, scotomas are considered to be a group of symptoms belonging to a great variety of both visual pathologies and non-vision related conditions.
Specifically the main diseases that are related to these visual alterations are:
Presbyopia
Presbyopia is a condition that causes a noticeable reduction in the ability to focus on objects. It is a disorder highly linked to the age that usually occurs among people over 40 years. It constitutes a degenerative pathology and, in some cases, can motivate the appearance of scotomas.
2- Cataratas
Cataract is a pathology that generates partial or total opacity of the lens, a fact that causes light to disperse into the eye and can not be focused on the retina, thus producing diffuse visual images.
This condition presents several causes although it is usually strongly attributed to age and can be treated by surgery.
3- Glaucoma
Glaucoma is one of the main pathologies of sight. It is characterized by generating a pressure inside the eye that causes defective vision at night. It also provokes blind spots and loss of vision on either side of the field of vision.
Diabetic retinopathy
Diabetic retinopathy is a complication of diabetes And one of the leading causes of blindness worldwide. This condition appears due to damage of the small blood vessels of the retina. It can cause bleeding in this region of the visual system and usually causes both scotomas and total blindness.
5- Macular Degeneration
Macular degeneration is an ocular disorder in which the central and acute vision is slowly and progressively destroyed, a fact that makes the specific vision of the person difficult.
It is the most common visual pathology among people over 60 years and can generate blurred vision, distorted vision, faded perception of colors and scotomas.
7- Infection
Another important cause of scotomas is the infectious or inflammatory processes of the retina, as well as ocular injury.
In these cases, the condition may be temporary and disappear when the infectious process causing the visual disturbance is stopped.
8- Flying flies
Flying flies are small particles that float through the eye. They usually last little and are harmless in nature but, in some cases, they may be a sign of retinal detachment.
9- Retinal detachment
Retinal detachment is an alteration produced by a separation of the light-sensitive membrane (the retina) from its supporting layers located at the back of the eye.
This condition usually causes blurred vision, flashes of bright light, flies in the eye and blindness in a part of the visual field of an eye.
10- Optic Neuritis
Optic neuritis forms an inflammation of the optic nerve due to infection or the direct effect of multiple sclerosis. It often causes eye pain and blindness in certain regions of the visual field.
References
1. Blanskby D.C. (1992). Visual evaluation and programming: VAP-CAP manual. Victoria, Australia: Royal Institute for the Blind (translated into Spanish by the Spanish National Organization of the Blind for internal use).
2. Fletcher, Donald C.; Schuchard, Ronald A.; Renninger, Laura W. (2012-09-01). "Patient awareness of binocular central scotoma in age-related macular degeneration". Optometry and Vision Science: Official Publication of the American Academy of Optometry. 89 (9): 1395-1398.
3. Langley, B. (1990). Potential Assessment of visual efficiency. Louisville, Kentucky: American Printing House for the Blind.
4. The role of axoplasmic transport in the pathogenesis of retinal cotton-wool spots, D. McLeod, J. Marshall, E. M. Kohner, and A. C. Bird, Br J Ophthalmol (1977), 61 (3), pages 177-191.