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Assessment of the condition of the optic nerve and layer of nerve fibers
Last reviewed: 11.04.2020
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Glaucoma - a common cause of blindness in all countries, can develop in any age group, but especially often after 40 years. Increased intraocular pressure is the most important causative risk factor for glaucoma, but high intraocular pressure is not necessary for the development of glaucomatous lesions. The physical effect of glaucomatous optic neuropathy lies in the irreversible loss of ganglion cells of the retina, which is clinically manifested in an increase in the excavation of the optic nerve disc and the appearance of local or diffuse defects in the retinal nerve fiber layer. Since glaucomatous lesions are irreversible, but mostly can be prevented, it is very important to establish a diagnosis early and accurately.
Functional tests
Evaluation of the condition of the optic nerve and the layer of nerve fibers consists in examinations that analyze their structure and functions. Glaucomatous loss of ganglion cells of the retina leads to structural changes in the form of defects in the layer of nerve fibers and the optic nerve, and functionally - to changes in the fields of vision, which are estimated from the results of automatic perimetry and electrophysiological studies. Glaucomatous visual field defects include local paracentral scotomas, arcuate defects, nasal stents, and less frequent temporal defects. Most often, visual field defects in glaucoma are encountered in an area commonly called the Bjerrum zone, which extends arched from the blind spot to the medial suture.
Automatic perimetry
Using automatic perimeters, the field of view is examined by presenting static stimuli. These stimuli, of the same size and different light intensity, are presented in certain localizations for a short period of time with simultaneous recording of the patient's responses to each light stimulus. Humphrey Field Analyzer (HFA) in a standard achromatic full threshold study (Humphrey Systems, Dublin, CA) applies white stimuli with white background illumination; Similar programs are also available on other automatic perimeters. Standard achromatic automatic perimetry with clinical examination is the "gold standard" for the management of a patient with glaucoma. But initially an automated test strategy takes a long time, often leading to patient fatigue and its errors in the study. Recent improvements in automatic perimetry have been developed in order to reduce the time of the test and create a strategy for earlier detection of visual disturbances in glaucoma. The study of half the field of view in glaucoma is a strategy that compares certain areas of the visual fields over the horizontal median line and below it. Such a test is available in the software of most automatic perimeters.
[10], [11], [12], [13], [14], [15], [16], [17], [18], [19]
Swedish interactive threshold algorithms
SITA (Humphrey Systems, Dublin, CA) is a family of test algorithms designed to significantly reduce the test time without reducing the quality of the data.
How do Swedish interactive threshold algorithms work?
SITA applies the information collected by the program to determine the threshold strategy for adjacent points, measures the response time of each patient, and uses this information to set the test speed. SITA-strategies are fast enough, they carry out the same or better quality test as a full threshold program. On average, the study time is approximately 5 to 7 minutes per eye with SITA Standard. There is also a SITA Fast strategy, which requires approximately 50% less time than SITA Standard, but because of the decrease in testing time, the sensitivity of the method changes significantly.
When using Swedish interactive threshold algorithms
SITA is becoming the "gold standard" for the clinical management of patients with glaucoma.