Ординатура / Офтальмология / Английские материалы / Neuro-Ophthalmology_Kidd, Newman, Biousse_2008

The Neuro-Ophthalmologic Examination

In this section, we review the components of the neuro-ophthalmologic examination and the techniques necessary to assess the patient’s vision, pupillary function, ocular motility, and funduscopic findings.

VISUAL ACUITY

The neuro-ophthalmologic examination should begin with an assessment of visual acuity. The standard method of testing visual acuity at distance uses the Snellen chart placed at 20 feet (6 meters).23 The patient is asked to cover one eye either by using a tissue or an occluding device. The patient should be wearing glasses or contact lenses because the examiner is most interested in the best corrected acuity. It is not uncommon for meaningless, subnormal acuities to be recorded while the patient’s glasses lie in a pocket or in a drawer. If the patient’s glasses are unavailable or subnormal acuity is obtained despite glasses, a pinhole test should be performed (Fig. 1–14). A pinhole device focuses a small point of light on the retina permitting a window of near optimal refraction. Most Snellen lines end with the numbers to let the examiner know what line is being tested. For example, the 20/30 line ends with a 3 and the 20/25 line ends with numbers 2–5. Acuity is recorded for the right eye first. The numerator represents the testing distance, which is 20 feet. The denominator denotes the size of the letter seen or denotes the distance at which an eye with normal vision sees the same letter. The 20/40 line contains letters twice the size of the 20/20 line. However, the ability to read the 20/40 line correlates with approximately 85% of normal visual function. If the patient cannot read the 20/400 E, then a 200 size E can be slowly brought toward the patient (Fig. 1–15). For instance, if the patient sees the E at 5 feet from their eye, vision is recorded as 5/200 E. More severe acuity loss may be recorded as count fingers, hand motion, light perception, or no light perception. Abnormal visual acuity may be the result of the following:

1.Refractive error (cornea, lens, vitreous)

2.Optic nerve or chiasmal disease and rarely from a bilateral cortical lesion

3.Macular dysfunction

4.Amblyopia

5.Functional visual loss

Figure 1–14 A pinhole device will focus a point of light on the retina correcting most refractive errors.

Figure 1–15 When the patient sees less than 20/200, but better than hand motions, a 200 sized E can be brought toward the patient. If the patient is able to see the E at 4 feet from the eye, visual acuity is recorded as “4/200.”

Once again, the importance of the pinhole examination cannot be overemphasized in this differential diagnosis because it will correct most refractive errors. If acuity cannot be corrected by a pinhole device, then optic nerve disease, macular dysfunction, or amblyopia may be present. These entities are further distinguished by visual field, pupillary, and funduscopic examination. Amblyopic patients usually have a long-standing history of visual loss in one eye resulting from strabismus, asymmetric refractive error, or a media opacity.

NEAR VISION

Despite the accuracy of a Snellen acuity, it is often necessary to assess acuity at near. Near vision may be tested using the Rosenbaum hand held card (Fig. 1–16). Because the test card has been designed to be held at 14 inches (3 5 cm) from the patient, any deviation of the testing distance profoundly affects the acuity equivalent seen. It is for this reason that most ophthalmologists prefer to use the Jaeger numbers. Thus, a near acuity of 20/25 may be written as J1 at 14 inches. Reading cards are also available and they provide an added benefit by testing for alexia. Once again, it must be emphasized that an uncorrected near acuity is virtually useless.

Figure 1–16 The Rosenbaum near card. Note near acuity is often recorded using the Jaeger numbers. For instance, “J1” is equivalent to a 20/25 near acuity.

COLOR VISION

Color vision may be assessed using the Ishihara or the Hardy-Rand-Rittler (HRR) color plates series (Fig. 1–17). We prefer the latter because it is designed to test both acquired and congenital color blindness (includes yellow-blue plates). The Ishihara series only tests for congenital color blindness (red-green plates only). The major utility of color plate testing is to detect the difference in color perception between the two eyes. Most color plates contain numbers or geometric shapes created by a series of colored dots. The examiner should record the number of plates correctly identified by each eye. Nearly 9% of males and 1% of females are congenitally color blind.21 When color plates are unavailable, difference in color perception between the two eyes may be identified using a color pen or bottle top (Fig. 1–18). Even with normal color plates testing, the patient may readily recognize a color difference in a red bottle top alternately presented to each eye. The patient may tell the examiner that one eye sees the bottle top as pink or orange. The patient may also be able to give the examiner

Figure 1–17 Pseudo-isochromatic color plates. A, In the Ishihara color series, the patient is asked to identify the number among the colored dots. B, In the Hardy Rand Rittler series, the patient is asked to identify the geometric shapes.

Figure 1–18 When color plates are unavailable, the examiner may use a color bottle top to detect a color difference between the two eyes.

a percentage of this desaturation. On occasion, green or blue bottle tops may detect a color difference not appreciated when the red tops were used. More extensive color vision testing can be carried out using the color sorting tests known as the Farnsworth-Munsell 100 hue test or the Farnsworth D-15 panel test.24

Acquired dyschromatopsia usually results from retinal or optic nerve lesions. In general, dyschromatopsia is more common with optic nerve lesions even if the visual acuity loss is mild. Dyschromatopsia secondary to retinal disease is typically associated with funduscopic abnormalities such as large macular scarring or diffuse pigmentary disturbances.

CONTRAST SENSITIVITY AND LOW-CONTRAST LETTER ACUITY

Eye charts have been designed for maximal contrast (i.e., dark black letters on a white background). Contrast sensitivity testing uses shades of gray to better assess visual resolution problems. In some contrast sensitivity tests, the distance between the bars (thickness) can be altered to give various spatial frequencies; other types of contrast sensitivity testing capture minimum level of contrast perception using large sized letters (Pelli-Robson chart, as used in the Optic Neuritis Treatment Trial, has letters that correspond to 20/680 Snellen equivalent). However, patients with neurologic disorders may have selective losses of contrast vision at small letter sizes ( 20/25 or 20/20 Snellen equivalent); low-contrast letter acuity charts (Sloan charts, Fig. 1–19) may have even greater sensitivity for capturing visual dysfunction in neuro-ophthalmologic patients. In addition to optic neuropathies, macular disease and media opacities such as cataracts may be associated with impaired contrast sensitivity and low-contrast acuity. Contrast sensitivity is only one measure of visual function and should not be substituted for all other measures.25

Figure 1–20 The Amsler grid resembles graph paper and may be used to assess macula function or the central ten degrees of the visual field.

AMSLER GRID TESTING

The Amsler grid, which resembles graph paper, is an extremely useful test to detect macular abnormalities as a cause for central acuity loss (Fig. 1–20). Each eye is tested separately. The patient should fixate on the central dot and determine whether all the lines on the paper are straight and whether all lines are present. The patient with a maculopathy will often see the straight lines as curved (metamorphopsia). Patients may also detect abnormal areas of the Amsler grid that correspond with their visual field loss. For documentation, the patient may draw the perceived field defect on the Amsler grid paper.

VISUAL FIELD TESTING

The field of each eye is tested individually. The first step is to have the patient examine the examiner’s face. One should ask them to fixate on the examiner’s nose. If the nose is not clear to the patient, this implies a central scotoma. One should have the patient compare the examiner’s eyes and upper and lower face for any difference. Altitudinal or hemianopic defects may be readily detected by this method. The next step is to have the patient count fingers in the four quadrants (Fig. 1–21). Simultaneous presentations of fingers in two separate quadrants increase the yield of finding a field defect. The examiner should hold up both hands on each side of the vertical or horizontal meridian and have the patient compare them for clarity (Fig. 1–22). If a field defect is found, the hand is moved from the defective field to the normal one to establish the boundaries of the defect. Red bottle tops can also be used in a similar fashion. For example, when testing for a central scotoma, a red bottle top is placed in front of the examiner’s nose and another cap is held slightly off the midline. If the patient sees the cap held in the periphery as a better red, a central scotoma is suggested. Visual fields are recorded from the patient’s perspective (Fig. 1–23).