Peripheral Vision

Peripheral fields of vision reflect the function of the retina (the nonmacu-lar part) and the visual pathways connected to the nonmacular retina. When testing acuity, letters and parts of letters and numbers of different size that subtend a portion of an arc are used. When testing peripheral fields, the stimulus is movement.

To test visual fields by confrontation, seat the patient facing you with his glasses off. Ask him to cover his right eye with his hand and to stare at your right eye with his left eye. Hold your arms out to either side so that your fingers are at the edges of his visual fields, as in Figure 1-6A. If the examiner has his right hand at A in Figure 6A, he will get no responses from the patient, as the test object (his moving finger) is behind the patient's field and the patient cannot see it, let alone say whether or not it is moving. If the examiner's right hand is at B, then the test object is inside the field, not on the edge, and a substantial crescent of blindness could be present in the patient's left temporal field and yet be missed because the test is being done incor-

rectly. Keep the examining fingers on the edges of the fields. Start with your hands behind the patient's vision at A and Al. Bring your hands forward, one at a time, while wiggling your fingers until the patient can see them. You have thus discovered the edges of the fields and are ready to start testing.

It is important to have the patient continue staring at your right eye with his left. Ask him to tell you on which side he sees fingers moving, that is, right, left, or both. Some patients cannot or will not say "right" or "left." They sometimes mean their right and sometimes your right, and doctor and patient can both become confused. You may ask the patient to point to the side that moves and say "both" if both move. Alter the moving side randomly, sometimes right, sometimes left, and sometimes both. Test in both the upper and lower portions of the visual fields.

Do not test with your fingers on the equatorial line of the fields or on the midsagittal meridian.

With a test object as big as your moving finger, you will not know whether you are in the upper or lower half of the field. These halves are anatomically distinct. Test the upper halves well up in the field and the lower halves well down in the field. If movement in any area is being ignored, move the hand toward the midline until it is seen to be moving. Keep the movement small, that is, only a portion of one finger, and slow. Coarse, fast movements are much easier to see than fine, slow ones.

Always move both right and left fingers simultaneously at least twice in the upper portion of the fields and again in the lower portion.

Simultaneous right and left stimulation is valuable. A patient may be able to see all the movements along the left edge and all the movements along the right edge when the two sides are examined individually. However, when the two sides are stimulated simultaneously, the competitive effect of the two simultaneous stimuli may bring out a consistent visual field defect. This kind of field defect is not an absolute defect, but is known as an inattention field defect.

Figure 1-6. A. Testing the field of vision of the patient's left eye by confrontation. Points A and A1 are behind the edges of the field, point B is well inside the field, and the examiner's fingers are correctly placed on the edges of the field. B. Visual field assessment of the patient who cannot or will not fix. Ask him to quickly point to the center of the string. If his hand is at A, his lateral fields are approximately full; if at B, he has a left hemianopia (see text for using the string test).

Blind spot

Figure 1-7. Record the patient's visual fields with his right eye field on your right. Mark his right field with Rt. and his left field with Lt. Indicate central vision with a plus sign. Add the visual acuity (corrected or uncorrected), date, and shade the blind areas.

Blind spot

Figure 1-7. Record the patient's visual fields with his right eye field on your right. Mark his right field with Rt. and his left field with Lt. Indicate central vision with a plus sign. Add the visual acuity (corrected or uncorrected), date, and shade the blind areas.

Sometimes you cannot get the patient's cooperation, and field testing by confrontation will not work. Try the string test as shown in Figure 1-6B. Hold a piece of string with your hands about 24 in apart. Without a lot of instruction or warning, ask the patient to quickly point to the center of the string. If his fields are full (from side to side), he will point to the approximate center. If he has a field defect on his left, he will point to the right of center. This can be used to detect altitudinal defects as well if you hold the string vertically.

Finally, in uncooperative patients whose disease is clearly in the hemi-sphere(s), it is often impossible to test one eye alone. Such patients cannot or will not keep one eye closed. Therefore, you may have to examine the fields with both eyes open, and if the lesion is retrochiasmal, this is good enough.

Visual fields may also be tested by perimeter. This creates a permanent record of visual field loss.

A Bjerrum's screen is used for the formal examination of the central, as opposed to the peripheral, visual fields.

When making notes about visual fields, draw the patterns in the patient's history as though they were your own fields (Figure 1-7), that is, the right eye field on your right and the left eye field on your left. Include the visual acuity and date.

Although visual fields are not really round and they overlap on the nasal side, they are usually drawn this way. The plus sign in the center represents

Figure 1-8. Various field defects. A. Scotomas: 1—cecocentral, 2—central, 3—arcuate, 4—paracentral. B. Bitemporal central scotomas. C. Bitemporal complete heml-anopla with sparing of central vision. D. Left complete homonymous hemlanopla with splitting of central vision. E. Right upper quadrantanopla. F. Altltudlnal or horizontal field defect (upper). G. Incomplete congruous right homonymous hemlanopla. H. Incomplete asymmetrical congruous right homonymous hemlanopla.

Figure 1-8. Various field defects. A. Scotomas: 1—cecocentral, 2—central, 3—arcuate, 4—paracentral. B. Bitemporal central scotomas. C. Bitemporal complete heml-anopla with sparing of central vision. D. Left complete homonymous hemlanopla with splitting of central vision. E. Right upper quadrantanopla. F. Altltudlnal or horizontal field defect (upper). G. Incomplete congruous right homonymous hemlanopla. H. Incomplete asymmetrical congruous right homonymous hemlanopla.

central vision. The shaded oval area, lateral to the center and partially astride the equatorial line, is the normal blind spot. This is an absolute scotoma representing the optic nerve head, or disc, which has no retinal function.

You need to be familiar with the types of field defects shown in Figure 1-8 and their significance. (The blind areas are shaded.) In testing visual fields by confrontation, remember:

• The patient must fix his gaze on your eye and keep this eye still.

• No one can detect color or definition in his peripheral fields of vision—the stimulus is movement.

• Keep your testing fingers on the edge of his fields.

• Test in both the upper and lower quadrants of each eye.

• Always make the right half fields compete against the left half fields by offering simultaneous right and left stimulation.

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