In the assessment of the visual field we measure the total area of the binocular visual field by confrontation techniques and the quality of the central visual field either using proper tests, like the Damato Campimeter or by asking about distortion of the straight lines in the Amsler test and about disappearance of letters in the words looked at by the child. The usual Amsler test has such thin lines they may not be seen by the child. In such a case use a page of a regular college block for visually impaired students.
Peripheral visual field
Confrontation visual fields can be measured by using the tester's finger movements as the stimulus or a white or black ball on a thin stick. The object or the fingers are moved forwards from behind the person's head and the person tells when (s)he sees the object or the fingers. A young child turns the eyes as soon as the stimulus is seen in the peripheral visual field.
The approximate place of the stimulus detection is recorded, e.g." 90 degrees to the right, and left, 60 degrees up and down". In a person whose right eye is blind and left eye has slightly constricted visual field the finding could be e.g."30R, 60L, 30U and 45D". A more exact test for measurement of confrontation field by using a standard size white dot on a gray background is also available at VICE VERSA.
Visual field defects can be hemianopias, half field defects in one or both eyes, on the same side (homonymous hemianopias) or on both temporal sides (bitemporal hemianopias) or - rarely - on both nasal sides (binasal hemianopias). They can be quadrantanopias, quarter of the visual field defects, again in one or both eyes. The defect can also be a ring scotoma, loss of visual function in the "midperiphery" of the visual field, i.e. not in the very periphery but around the central visual field.
The functional importance of the child's visual field defect should be carefully assessed. There are two aspects that are not well covered in most medical reports. One is the case of bitemporal visual field loss. If both temporal halves are blind and the nasal halves of the visual fields function, the child has an approximately 120 degree visual field when looking straight ahead. However, when (s)he looks at something close by there is no visual field in a sector in front of that fixation point. That means that when the child looks on something on the desk, (s)he is unaware of a sector of the classroom in front of her/him and the same problem is present in physical education and during games.
Another feature that is not reported because it is not tested, is the presence of motion perception in some "blind" areas. This can be roughly tested with Goldmann visual field apparatus so that the tester moves the stimulus quickly back and forth within a scotoma found by using the normal testing technique. If the child responds to the quickly moving stimulus, the scotoma is not "absolute" even if the child does not respond to the maximum bright stimulus when it does not move. Most young children respond best if you ask them to shift fixation from the central fixation target to the stimulus as soon as it becomes visible somewhere.
The central visual field of only 10-20 degrees can be tested using plain white paper at a distance of 57
centimetres and a dark pen. Draw a cross in the middle of the paper and ask the person to look toward
the centre of the cross all the time, independent of whether the actual crossing point is seen or not.
Move the pen from the side of the paper toward the cross and ask the person to say when the pen
becomes visible at the edge of the tubular field. Measure the extent from the right, left, up, down
and diagonally. Then draw a line through these points and you have the size of the visual field depicted
by that oval area. At 57cm each centimetre on the paper equals one degree of visual angle, so you
can measure the size of the visual field simply by measuring the size of the area in centimetres.
When the visual field is very limited, you may like to use a longer distance, 114cm or 228cm to
make the measurement even more exact. At 114cm 2cm equals to one degree of visual angle and
at 228cm 4cm equals to one degree.