Field of view - space perceived by the eye with a fixed gaze. The field of view is a function of the peripheral parts of the retina; his condition is largely determined by the ability of a person to freely navigate in space. The approximate boundaries of the field of vision define a control method. For this purpose the subject sits down with his back to the light, his one eye shut light bandage. Exploring sits down against him at a distance of about 1 m and closes his eyes, opposite the closed eye of the patient. The subject commits an open eye investigating. The latter has progressively from the periphery to the centre in various directions finger of his hand and marks the moment when the individual notices finger. By comparing the obtained boundaries of the field of view of the subject and explore, whose field of vision must be normal, and set changes. A more precise study of the field of view is made by means of perimeter (see Perimetry).
Change the field of view caused organic or functional diseases of the visual analyzer: retina, optic nerve, the visual pathways, the Central nervous system. Violations of the field of view, apparent or narrowing of its boundaries, or loss of its individual parts (see Hemianopsia), the emergence of scotomas (see). The narrowing of the field of view is expressed in degrees. The value of livestock determine with the help of special nets (scotomata) and expressed in degrees or linear terms.
Field of view - a set of all points in space, simultaneously perceived motionless, fixing one Central point of the eye. This fixed point is projected on the net shell in the macula (see Eyes, anatomy), the image of all the other places of the field of view of the falls on the peripheral parts of the retina. According to exit the eye, optic nerve, where svetovosprinimayuschie elements of the retina are missing, there is a small physiological defect P. C.- physiological scotoma, blind spot.
For research of P. C. there are different methods, the simplest of them is the so-called test. The doctor sits directly against studied at a distance of 1 m from it. Investigational must accurately record his right eye left eye doctor, which in turn secures the right eye investigated. Second both eyes closed. The doctor slowly promotes the right hand in all directions from the point of fixation, trying to hand were all the time at equal distance between him and investigated, and determines when elongated fingers will disappear from sight under him and investigated. If the doctor and have studied normal P. C., the fingers will be hidden from view both simultaneously. If the investigational ceases to see the fingers before the doctor, this suggests that the investigated P. C. right eyes narrowed. Similarly explore the field of view of the second eye. The control method of research of P. C. very inaccurate and is indicative only.
The field of vision.
More precise data on the size and configuration of borders P. C., and the presence of partial defects in sight - the so-called cattle (see) - get in the study of special devices (see Perimetry). To determine the precise boundaries of cattle, located in pericentral areas P. C. (for example, in the area of the blind spot), is used the method of campimetria (see). To identify the Central scotomas there are special devices - scotomata.
Peripheral border normal P. C. (Fig) depend on the specific structure of the eyeball and eyelid, and the bones of the orbit. So, top, P. C. the eye is limited to the upper eyelid and the exposed ridges, inside the nose. Therefore, normal P. C. bounded from above to 55 degrees from the point of fixation, from the inside and bottom - up to 60 degrees outside and from below-from the outside extends to 90 degrees. However, these boundaries taken over the standard, are only average
the norm, and can vary depending on the configuration of the orbit.
When assessing the boundaries of the field of view should be taken into account that full visual acuity normal eye is only in the centre, and further to the periphery of the retina visual acuity decreases. Therefore presented in figure borders P. C. the color white is correct only for large white objects with a diameter of not less than 5 mm, demonstrated at a distance of 33 cm from the eye to the point of fixation. In the study of P. C. small objects - 2 or 1 mm in diameter - the bounds of its defined narrower, because the visual acuity is the most peripheral parts of the retina is so low that small objects from a distance of 33 cm normal eye can no longer be perceived.
The normal field of vision in the study colored objects is significantly narrower than in the study of white objects. This is due to the inability of peripheral parts of retina perceive color.
In clinical practice, research P. C. is very important to clarify the diagnosis of a number of eye and common diseases. Especially important is the nature of the detected violations P. C. for topical diagnosis of Central nervous system lesions, mainly to clarify localization basal tumors, bronchial inflammation or bleeding. When the location of a lesion in the field of the Turkish saddle occurs most often a loss of temporal half P. C. in both eyes bitemporal hemianopsia (see). When certain processes (mainly vascular nature)that is located on the same level, there may be a loss of internal halves P. C. in both eyes binasarana hemianopsia. The loss of the same name halves P. C. both eyes, both right-wing or both left - gomonimnaja hemianopsia - indicates the location of the source behind the Turkish saddle. If you saved the Central plot P. C. in both eyes, one can think of the defeat of the occipital region of the cerebral cortex or zone optic lights. If the lesion is located in the area of traktorov, together with the corresponding half P. C. falls and its Central area. Concentric narrowing of the field of view combined with a Central scotoma is a characteristic symptom of retro-bulbar neuritis. However, the survey P. C. has the greater value as the eye patients may long remain normal and only later develops a picture of the primary atrophy of the optic nerve papilla.
Often expressed human P. C. seen in conjunction with the development of inflammatory processes in the retina - when retinity, retinal haemorrhage, exudates. In these cases detected visual field defects are generally correspond to the configuration of Ophthalmoscope changes of the bottom of the eye. Quite typical changes P. C. glaucoma (see). Sharp concentric contraction P. C., until tube, found in pigmentary retinal degeneration. Sometimes this symptom occurs when hysteria.
Expressed hemianopsia defects P. C. or abrupt its concentric contraction can be an obstacle for the implementation of a number of labour processes in the production, for the driver or the driver.
