Head-To-Toe Assessment J. Cranial Nerve II (optic nerve)
The optic nerve is assessed by testing for visual acuity and peripheral vision.
Visual acuity is tested using a snellen chart, for those who are illiterate and unfamiliar with the western alphabet, the illiterate E chart, in which the letter E faces in different directions, maybe used. The chart has a standardized number at the end of each line of letters; these numbers indicates the degree of visual acuity when measured at a distance of 20 feet.
The numerator 20 is the distance in feet between the chart and the client, or the standard testing distance. The denominator 20 is the distance from which the normal eye can read the lettering, which correspond to the number at the end of each letter line; therefore the larger the denominator the poorer the version.
Measurement of 20/20 vision is an indication of either refractive error or some other optic disorder.
In testing for visual acuity you may refer to the following:
1. The room used for this test should be well lighted.
2. A person who wears corrective lenses should be tested with and without them to check fro the adequacy of correction.
3. Only one eye should be tested at a time; the other eye should be covered by an opaque card or eye cover, not with client’s finger.
4. Make the client read the chart by pointing at a letter randomly at each line; maybe started from largest to smallest or vice versa.
5. A person who can read the largest letter on the chart (20/200) should be checked if they can perceive hand movement about 12 inches from their eyes, or if they can perceive the light of the penlight directed to their yes.
Peripheral Vision or visual fields
The assessment of visual acuity is indicative of the functioning of the macular area, the area of central vision. However, it does not test the sensitivity of the other areas of the retina which perceive the more peripheral stimuli. The Visual field confrontation test, provide a rather gross measurement of peripheral vision.
The performance of this test assumes that the examiner has normal visual fields, since that client’s visual fields are to be compared with the examiners.
Follow the steps on conducting the test:
1. The examiner and the client sit or stand opposite each other, with the eyes at the same, horizontal level with the distance of 1.5 – 2 feet apart.
2. The client covers the eye with opaque card, and the examiner covers the eye that is opposite to the client covered eye.
3. Instruct the client to stare directly at the examiner’s eye, while the examiner stares at the client’s open eye. Neither looks out at the object approaching from the periphery.
4. The examiner hold an object such as pencil or penlight, in his hand and gradually moves it in from the periphery of both directions horizontally and from above and below.
5. Normally the client should see the same time the examiners sees it. The normal visual field is 180 degress.