mechanical compression, ischemia, and inflammation. Optic disc and retinal vascular changes can also accompany optic disc edema (Fig 3-4). Regardless of cause, the following clinical features of optic disc edema may be observed:

elevation of the nerve head with variable filling in of the physiologic cup; retinal vessels may appear to drape over the elevated disc margin

blurring of the disc margins

peripapillary NFL opacification; the NFL becomes grayish white and opalescent with feathered margins, obscuring portions of the retinal vessels that course within this level of the retina hyperemia and dilation of the disc surface capillary net

retinal venous dilation and tortuosity

peripapillary hemorrhages, exudates, or cotton-wool spots retinal or choroidal folds or macular edema

Figure 3-4 Papilledema. A, Right eye. B, Left eye. The disc margins are blurred, with grayish white, opalescent thickening of the peripapillary nerve fiber layer (arrows), cotton-wool spots, and flame hemorrhages. The retinal vessels are partially obscured at the disc margin and within the peripapillary retina. (Courtesy of Sophia M. Chung, MD.)

Visual Field Evaluation

Evaluation of the visual field helps localize a lesion along the afferent visual pathway, defines patterns of vision loss, and quantifies the defect, enabling measurement of change over time. The choice of technique depends on the degree of detail required and the patient’s ability to cooperate. Patterns of visual field loss are discussed in detail in Chapter 4.

Confrontation testing

Confrontation testing, easily performed at the bedside or in the clinic, should take place during every ophthalmic examination. It is a screening test only and does not replace formal perimetry.

The examiner sits 1 m from the patient. The patient covers 1 eye and fixates on the examiner’s nose. The examiner asks the patient if specific portions of his face cannot be seen; such information often identifies central or altitudinal visual field defects. Next, the examiner asks the patient to identify a target of 1, 2, or 5 fingers presented at the midpoint of each of the 4 quadrants. Children and nonverbal adults may be asked to mimic the examiner’s finger target. The examiner then presents targets in opposing quadrants (ie, double simultaneous stimulation) and asks the patient to add the total number of fingers. By using an asymmetric number of fingers in the opposite quadrants, the examiner can identify the abnormal visual field. Consistently missed responses in a quadrant or hemifield may indicate a subtle visual field defect or extinction. Extinction is the inability to see a target in an affected hemifield only during simultaneous stimulation of both hemifields. A target presented in the affected hemifield alone can be seen. This finding is characteristic of parietal lobe lesions. If the patient cannot identify fingers, the examiner presents progressively stronger stimuli such as hand movement or light perception in each quadrant. Accurate saccadic movement to an eccentric target is also evidence of some preservation of the peripheral visual field.

Subjective comparisons may detect subtle visual sensitivity defects. With an eye occluded, the patient compares the clarity of the examiner’s hands presented in opposing hemifields, the less clear hand indicating a relative impairment. The examiner can also present identical small red targets, such as buttons or bottle tops from mydriatic eyedrops, in each hemifield. Color may appear altered, washed out, or absent in a damaged hemifield; with slow movement of the target, the patient may identify a change precisely as it crosses the vertical midline. Such a result suggests damage to the chiasmal or retrochiasmal pathway. Alternatively, comparison of the central with the peripheral visual field in an eye may identify similar impairment centrally, suggesting a central scotoma.

Amsler grid testing

Amsler grid testing rapidly screens the central 20° of the visual field (10° from fixation). The patient, optically corrected for near vision, holds the Amsler grid at one-third of a meter, covers 1 eye, and looks at a fixation point in the center of the grid. The patient describes any areas of distortion (ie, metamorphopsia); any such areas suggest macular rather than optic nerve disease. Peripheral “bending” of the grid may represent optical aberration from spectacles and should be disregarded. The patient can also identify any scotomata, but doing so does not replace formal perimetry. It is important to ensure that the patient fixates on the central point rather than scans. Although Amsler grid testing is rapid and simple, its sensitivity is low.

Perimetry

Perimetry provides more detailed evaluation of the visual field. Static and kinetic techniques are both important. In static testing, stimuli turn on and off at designated points within the region of the visual field to be tested. In kinetic testing, a stimulus moves from a nonseeing to a seeing area of the visual field to determine the location at which it is consistently detected by the patient. In kinetic testing, all points of equal sensitivity for a specific stimulus are connected to form an isopter, which represents the outer limit of visibility for that stimulus. Analysis of several isopters (plotted with different stimuli) produces a “contour map” of the island of vision. In both static and kinetic techniques, the visual field is analyzed for areas of decreased sensitivity, in location and degree.

Tangent screen In this type of evaluation, the patient is seated 1 m from a black screen and, while fixating on a central white target, is asked to identify targets moving in from the peripheral, nonseeing

field to the central field along each radial meridian. A black wand with various-sized targets attached to the tip is used to map 1 or 2 isopters kinetically. Static visual fields can be mapped by rotating the target to present the opposite black side. Other stimuli include using a focal light source such as a handheld laser pointer to screen for visual field loss.

Goldmann perimetry Goldmann perimetry uses kinetic and static techniques and offers the advantage of evaluating the entire visual field. Stimuli of varying sizes and intensities are presented along each radial meridian from a peripheral to central location. Typically, 2 or 3 isopters are plotted, because relative defects that are undetected using larger or brighter stimuli may become apparent using smaller or dimmer ones. The examiner performs static testing within each isopter to identify scotomata. Varying the stimulus size, intensity, and location can delineate the depths and borders of such defects. Goldmann perimetry requires a skilled and knowledgeable perimetrist who can interact with patients to elicit optimal cooperation. Unfortunately, perimetrists may tire with repetitive examination and also experience operator bias.

Automated static perimetry Automated static perimetry became the standard for many clinicians in the 1990s. Although this method is particularly difficult to use with older or inattentive patients, it possesses numerous advantages over manual kinetic perimetry techniques:

standardized testing conditions, which improve serial and inter-institutional comparisons of results

less technician dependence improved sensitivity

numerical data amenable to statistical analysis for comparisons and clinical studies results amenable to electronic data storage

Most automated perimeters use static stimuli similar in size to the standard Goldmann size III stimulus. The perimeter randomly presents stimuli at predetermined locations within a specified region of the visual field. Because nearly 80% of the visual cortex correlates to the central visual field, testing the central 24° or 30° of visual field is typically adequate for detecting most visual defects (Fig 3-5).

Figure 3-5 Diagrammatic representation of the extent of the visual field evaluated by Goldmann perimetry vs the 30° central program in automated static perimetry. The largest isopter in Goldmann testing extends 90° temporally and 60° in other quadrants; typical automated static perimetry evaluates only the central 30°. (Courtesy of Anthony C. Arnold, MD.)

The stimuli vary in brightness, and patient responses determine the minimum visible stimulus at each location—the sensitivity threshold. This threshold is defined as the dimmest target identified 50% of the time at a given location. For each region tested, the printout displays the threshold value in decibels (on a logarithmic scale of intensity, measuring attenuation from the maximum stimulus of the perimeter); a higher value at a certain point indicates that the patient is able to see a dimmer stimulus, reflecting greater visual sensitivity at that point. The measured values are not absolute numbers and do not have equivalence among perimeters because the machines have different maximum intensities, backgrounds, and durations of presentation.

A symbolic representation of the threshold values, the grayscale map, depicts an overall topographic impression of the visual field data by using dark symbols for low-sensitivity points and lighter symbols for high-sensitivity points. The computer program interpolates between tested points to provide a user-friendly picture (Fig 3-6). For clinical interpretation, the perimeter calculates the statistical probability for each value that the value falls outside the normal range as compared with age-matched control subjects; the results are placed in a total-deviation plot. Optic neuropathy may cause substantial total deviation depression with few or no pattern deviation abnormalities. Because ocular media abnormalities (eg, refractive error, cataract) may depress the sensitivity of the entire

visual field, the pattern-deviation plot determines the sensitivity values for all points shifted (by the seventh-highest point) and reanalyzes them based on age-expected values. This reanalysis compensates for the overall sensitivity depression, allowing recognition of abnormal patterns (eg, scotomata, arcuate defects, homonymous defects) that might have been otherwise masked. Abnormal values are depicted topographically according to statistical probability: dark squares represent higher probability and lighter squares represent lower probability.