Definition:A scotoma (Greek: darkness; plural: “scotomas” or “scotomata”) is an area or island of loss or impairment of visual acuity surrounded by a field of normal or relatively well-preserved vision.
Every normal mammalian eye has a scotoma in its field of vision, usually termed its blind spot. This is a location with no photoreceptors, where the retinal ganglion cell axons that comprise the optic nerve exit the retina. This location is called the optic disc. The blindspot does not intrude into consciousness because the corresponding visual field locations of the optic discs in the two eyes differ: The visual signals that are absent in one eye are sent to the cortex by signals from the other eye.
The presence of the scotoma can be demonstrated subjectively by covering one eye, carefully holding fixation with the open eye, and placing an object (such as your thumb) in the lateral and horizontal visual field, about 15 degrees from fixation (see the blind spot article). The size of the monocular scotoma is surprisingly large – 5×7 deg of visual angle.
It is a common type of vision loss post stroke or traumatic brain injury, a scotoma is an island of visual field loss (blindness) or impaired vision surrounded by relatively normal vision. The eyes of mammals naturally have a small scotoma (blind spot) that we normally don’t detect. However, a wide range of diseases and injuries can cause a pathological scotoma. For example, a scotoma can be a sign of optic nerve damage sustained during a stroke or brain injury. Previously considered untreatable, new research has led to exciting developments in treating scotoma.
Types of Scotoma: After a stroke or brain injury, a scotoma may occur in any shape or size, and it may affect any portion of the visual field. In some cases, a scotoma will include and enlarge the blind spot occurring naturally in a person’s eye. The main types of scotomas include:
* Central scotoma: an area of decreased or lost vision that interferes with central vision (likely to affect daily life)...CLICK & SEE
* Hemianopic scotoma: an area of decreased or lost vision that affects half of the central visual field….CLICK & SEE
* Peripheral scotoma: an area of decreased or lost vision toward the edge of the visual field (less likely to affect daily life)...CLICK & SEE
Symptoms: The main symptom of scotoma is one or more dark, light, or blurred areas in the field of vision. Those affected by visual field loss may also experience a need for greater illumination and contrast when reading, and may have difficulty perceiving certain colors.
Symptom-producing or pathological scotomata may be due to a wide range of disease processes, affecting either the retina (in particular its most sensitive portion, the macula) or the optic nerve itself. A pathological scotoma may involve any part of the visual field and may be of any shape or size. A scotoma may include and enlarge the normal blind spot. Even a small scotoma that happens to affect central or macular vision will produce a severe visual handicap, whereas a large scotoma in the more peripheral part of a visual field may go unnoticed by the bearer due to the normal reduced visual resolution in the peripheral visual field.
Causes:Common causes of scotomata include demyelinating disease such as multiple sclerosis (retrobulbar neuritis), toxic substances such as methyl alcohol, ethambutol and quinine, nutritional deficiencies, and vascular blockages either in the retina or in the optic nerve. Scintillating scotoma is a common visual aura in migraine. Less common, but important because sometimes reversible or curable by surgery, are scotomata due to tumors such as those arising from the pituitary gland, which may compress the optic nerve or interfere with its blood supply.
Rarely, scotomata are bilateral. One important variety of bilateral scotoma may occur when a pituitary tumour begins to compress the optic chiasm (as distinct from a single optic nerve) and produces a bi-temporal hemicentral scotomatous hemianopia. This type of visual field defect tends to be very eloquent symptom-wise but often evades early objective diagnosis, as it is more difficult to detect by cursory clinical examination than the classical or text-book bi-temporal peripheral hemianopia and may even elude sophisticated electronic modes of visual field assessment.
In a pregnant woman, scotomata can present as a symptom of severe preeclampsia, a form of pregnancy-induced hypertension.
Click To learn about Detection:->
* Amsler grid…..CLICK & SEE
* Perimetry……..CLICK & SEE
* Visual field test….CLICK & SEE
Treatment: There is no treatment for scotomas.
When they are in the peripheral areas and are not large, they usually do not cause severe problems in general visual functioning. If the scotomas are large or numerous, mobility may be affected.
Central scotomas are another situation entirely. Functional acuity is severely affected and educational adjustments are indicated. Magnification or large print may be indicated. Higher levels of illumination and good contrast in reading materials may also be useful. Color perception may be affected.
Vision loss post stroke or brain injury, which may include scotoma, hemianopia / quadrantanopia, and diffuse field defect / low vision, can drastically impact a person’s quality of life. In the past, these vision defects were considered untreatable. However, cutting-edge research into neuroplasticity, the brain’s ability to grow and heal throughout adulthood, has led to effective methods of vision rehabilitation.
Developed by NovaVision, one such method of vision rehab, called Vision Restoration Therapy, works by stimulating the brain in precise, consistent ways. Studies show that 70 percent of patients who complete Vision Restoration Therapy experience significant improvements in their vision, which improves their quality of life. Today, the therapy is available at premier institutions and medical centers across the United States.
Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose
Resources:
http://www.helpforvisionloss.com/vision-loss/scotoma/#types
http://en.wikipedia.org/wiki/Scotoma
http://www.spedex.com/resource/documents/veb/scotoma.html
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