Visual Acuity

Visual acuity is a measurement of the individual’s capacity for visual discrimination of fine details of high contrast. Best corrected visual acuity should be tested for each eye separately with the other eye covered by a tissue, hand, or occluding device ( Fig. 2.1A ). Distance vision is most commonly evaluated with a standard Snellen chart ( Fig. 2.2A ) or with a computer monitor that displays the black optotypes on a white background. Near vision can be tested with a hand-held card ( Fig. 2.2B ). Ideally, best corrected vision should be assessed using current corrective lenses or manifest refraction. If these are unavailable, a pinhole will improve most mild to moderate refractive errors in cooperative patients ( Fig. 2.1B ). Patients with subnormal acuity despite best refracted correction should also be tested with pinholes, which may further resolve some refractive errors (irregular astigmatism) and media opacities (cataract). When acuity cannot be corrected by a pinhole, nonrefractive causes of visual loss (see later discussion) should be considered.

A . Occluder for testing vision one eye at a time. By convention the right eye is tested first. B . Occluder with pinholes. If the visual acuity is subnormal but can be improved with pinholes, refractive error or media opacities should be suspected.

Visual acuity charts. A . Snellen eye chart for testing visual acuity. The largest letter at the top is the 20/200 E, while the letters at the bottom represent the 20/10 line. B . Near card with pupil gauge. Note that near visual acuity is often recorded using the Jaeger notation, as in “Jaeger 2” or “J2,” to indicate 20/30 near acuity. C . Early Treatment in Diabetic Retinopathy Study (ETDRS)–type chart.

Acuity is most often recorded as a fraction (e.g., 20/40), where the numerator refers to the distance (in feet) from which the patient sees the letters and the denominator refers to the distance from which a patient with normal vision sees the same letters. The normal eye can resolve a figure that subtends a visual angle of 5 minutes at a distance of 20 feet. At the distance at which a normal patient can see a line of letters on a Snellen eye chart, the widths of the lines on each letter subtend a visual angle of 1 minute, or one-fifth of the entire letter. A fraction of 20/20−2 indicates the patient saw all the letters on the 20/20 line except two, while 20/20+2 means the patient was able to see the 20/20 letters plus two letters on the next (20/15) line. Usually up to two mistakes on a line or two extra letters on the next line are allowed in this notation. Most normal adults younger than 40 years have best corrected visual acuities of 20/20 or better in each eye.

Visual acuity at distance can also be recorded using the metric or decimal systems. When the testing is at 6 meters (close to 20 feet), the normal visual acuity is recorded as 6/6. The decimal system uses the numeric equivalent of the fractional notation: 20/20 or 6/6 is a visual acuity of 1.0. A visual acuity of 20/100 would be recorded as an acuity of 0.2.

If a patient is unable to read the largest Snellen letters (20/200 or 20/400), the acuity should be recorded by moving a 200-size letter towards the patient until it is seen ( Fig. 2.3 ). That distance is recorded as the numerator. For example, an acuity of 4/200 means the patient was able to see the 200-size letter at 4 feet. Alternatively, the degree of vision can be recorded using the phrases “count fingers” (CF) (and at what distance), “detect hand motions” (HM), and “have light perception” (LP). An eye that is blind has “no light perception” (NLP). Criteria are used by different agencies to determine a level of vision loss that qualifies for disability or benefits (i.e., “legal blindness”) based on a best corrected acuity worse than 20/200 in the better seeing eye or binocular visual field constriction to less than 20 degrees.

Determination of visual acuity using 200-size letters in an eye with worse than 20/200 but better than hand motions vision. The distance at which the patient can see the 20/200 E is determined. If this distance is 3 feet, then the visual acuity is recorded as “3/200.”

Unfortunately Snellen charts have several deficiencies, the most important of which is the nonlinear variation in the sizes of the letters from line to line. Thus, if one patient’s visual acuity decreases by 20/100 to 20/200 using the chart in Fig. 2.2A , and another from 20/80 to 20/100, both are considered to have a decrease in visual acuity by one line. However, in the first instance the difference in letter size is 100%, but in the second it is only 25%. Furthermore, a typical Snellen chart has a different number of letters on each line. The largest letters have the fewest, while the smallest letters have the most in each line. Therefore, more letters must be identified to complete smaller lines in contrast to larger lines. In addition, some letters, such as the “E,” are harder to identify than the “A” or “L,” for example.

To eliminate these issues and when consistency is desired among testing locations, as in multicenter clinical trials, for instance, standardized Early Treatment in Diabetic Retinopathy Study (ETDRS) charts have become the gold standard ( Fig. 2.2C ). Each line contains five letters, the spacing between the letters and lines is proportional to the letter sizes, the sizes of the letters decrease geometrically, and the recognizability of each letter is approximately the same. Using ETDRS charts, a linear scale for visual acuity can be created by calculating the base 10 logarithm of (1/Snellen decimal notation) in what is termed the logarithm of the minimal angle of resolution (logMAR). Each line on the ETDRS chart is therefore separated by 0.1 logMAR units. So in the previous examples, the logMAR score for the first patient would worsen from 0.7 to 1.0, while the second would worsen from 0.6 to 0.7, more accurately reflecting the greater decrease in visual acuity for the first patient.

Visual acuity with the near card is often recorded using the Snellen fraction or the standard Jaeger notation (J1, J3, etc.). When near visual acuity is tested, presbyopic patients older than 40 years of age should wear their reading glasses or bifocals. Near acuities are not as accurate as those obtained at distance, especially when the card is not held at the requisite distance specified on the card.

For illiterate individuals or children unable to read letters, acuity can be tested with tumbling Es ( Fig. 2.4 ), Allen or Lea figures ( Fig. 2.5A ), or HOTV letters ( Fig. 2.5B, C ). In younger preverbal patients, assessment of fixing on and following a light or toy by each eye separately in most instances is sufficient. Caution should be used when examining small infants, since visual fixation normally may be inconsistent or absent until 8–16 weeks of age. When quantification of visual acuities is required in very young children (for serial examinations, for instance), preferential looking tests (Teller acuities ) may be used ( Fig. 2.6 ). These tests are based on the principle that a child would rather look at objects with a pattern stimulus (alternating black and white lines of specific widths) than at a homogeneous field. The frequency of the smallest pattern that the child seems to prefer is termed the grating acuity, which can be converted to Snellen equivalents if the test distance is known. Visual acuity in a newborn is roughly 20/400 to 20/600; it improves to approximately 20/60 by 12 months of age and reaches the 20/20 level by 3–5 years of age.

“Tumbling Es” for assessment of visual acuity in illiterate adults or children. The patient can be asked to indicate in which direction the E points (right, left, down, up). The sizes of the Es correlate with the size of the letters on Snellen chart.

Lea and HOTV visual acuity testing in preliterate children. In both tests the child points to one of four choices to match the figure or letter he or she sees on the computer monitor or chart in the distance. The figure or letter sizes on the computer monitor or chart are varied until the best visual acuity is determined. A . Lea figure testing in a young child. The child matches the presented figure. B,C . HOTV acuity testing. In slightly older children Snellen-like H, O, T, or V letters ( B ) can be presented. C . As in Lea figure testing the child is asked to match the indicated letter on the chart with a hand-held card displaying the HOTV letters.

Teller acuity testing. In very young children, preferential looking tests may be used. These tests are based upon the principle that a child would rather look at objects with a pattern stimulus (alternating black and white lines of specific widths) than at a homogeneous field. The smallest pattern that the child seems to prefer is an indicator of best visual acuity (“grating acuity”). A . The stimuli are presented on one side of a series of rectangular hand-held cards with gray backgrounds. Visual acuity is determined by decreasing the thicknesses of the black and white stripes and presenting them to the left or right until the child no longer preferentially looks at them against the gray background on the rectangular card. The frequency difference between the stimuli on each successive card is approximately 0.5 octaves. B . Results are compared with age-based normal controls. The grating acuity can be converted to Snellen equivalents when the test distance is known.

Ocular causes of reduced visual acuity include refractive error, amblyopia, macular lesion, or media opacity such as cataract, vitreous hemorrhage, vitritis, or corneal opacities or irregularities. Neuro-ophthalmic processes that can decrease visual acuity are those that affect the optic nerve or chiasm. Disturbances that are posterior to the chiasm (retrochiasmal, i.e., tract, optic radiations, and occipital lobe) affect visual acuity only if they are bilateral. Functional visual loss should always be considered when visual acuity is decreased without any obvious abnormality of the eye or visual pathways.

Contrast Sensitivity and Low-Contrast Letter Acuity

Contrast sensitivity testing with sine-wave or square-wave gratings may be a useful adjunct in the evaluation of vision loss. Conventional visual acuity measures spatial resolution at high contrast, while contrast sensitivity testing assesses spatial resolution when contrast varies. In one variation of the test, the patient is asked to identify in which direction the gratings, which span a spectrum of spatial and temporal frequencies and are arranged in increasing difficulty, are oriented. Another version, the Pelli–Robson test, is depicted in Fig. 2.7A . Contrast sensitivity testing should never replace acuity assessment, as its role seems limited to those situations where acuity is normal or near normal and further evaluation is desired. Optic neuropathies, media opacities, and macular disease may reduce contrast sensitivity.

Contrast sensitivity tests. A . In the Pelli–Robson test, each eye is evaluated separately, and the patient is asked to identify the letters across each row, starting at the top of the chart. The level of contrast sensitivity, recorded in log units, is determined when the patient reaches a group of three letters he or she cannot identify. B . Low-contrast Sloan letter acuity chart (Precision Vision, LaSalle, IL). Visual acuity may be specified by the Snellen notation for descriptive purposes (i.e., 20/20), by number of letters identified correctly, or by logMAR units. This photograph shows the 25% contrast level for purposes of illustrating format; the actual contrast levels used in clinical trials, 2.5% and 1.25%, have substantially lighter gray letters. The charts can be presented on hand-held cards or retroilluminated cabinets.

Low-contrast Sloan letter acuity testing captures the minimum size at which individuals can perceive letters of a particular contrast level (shade of gray on white background). Used primarily for research at this time, Sloan charts present gray letters in ETDRS format ( Fig. 2.7B ). The testing evaluates other aspects of visual dysfunction beyond high-contrast visual acuity loss in multiple sclerosis and other neurologic disorders.

Color Perception

Color vision can be tested with standard pseudoisochromatic Ishihara or Hardy–Rand–Rittler plates, both of which contain numbers or geometric shapes that the patient is asked to identify among different colored dots ( Fig. 2.8 ). Like visual acuity, color vision should be tested for each eye separately. The result is recorded as a fraction of the color plates correctly identified (“8/10” or “8 out of 10,” for instance); defective color vision is termed dyschromatopsia, while absence of color vision is called achromatopsia. Their wide availability, ease of administration, and relatively low cost make pseudoisochromatic plates a popular tool for detecting dyschromatopsias of all types, although they were originally designed to screen for congenital dyschromatopsias. Ishihara color plates (see Fig. 2.8A ) may be used, but Hardy–Rand–Rittler plates (see Fig. 2.8B ), which contain blue and purple figures that screen for tritan defects (see later discussion), may be more helpful in detecting acquired dyschromatopsia due to dominant optic neuropathy.

Pseudoisochromatic color plates. Each eye is tested separately. A . In standard pseudoisochromatic color plate testing, the patient is asked to identify the number seen within the colored dots. B . Hardy–Rand–Rittler color plate. In this test, the patient is asked to identify the shape or symbol seen within the dots.

For a more qualitative assessment, comparing the appearance of the color test plates or of a red bottle top, for example, with each eye can test for more subtle intereye differences in color perception. A patient with monocular “red desaturation” may state that with the affected eye the red bottle top appears “washed out,” “pink,” or “orange.”

Congenital dyschromatopsias are characterized by confusion between reds and greens (protan and deutan types) and blues and yellows (tritan type). Binocular, present at birth, and stable over time, they result from relative deficiencies in the red, green, and blue cone retinal photoreceptor pigments. The most common inherited dyschromatopsia is an X-linked red–green defect, occurring in approximately 8–10% of males and 0.4–0.5% of females. The Farnsworth D-15 (dichotomous) panel test ( Fig. 2.9 ) or the larger Farnsworth–Munsell 100-hue test can be used to separate the various types. In both of these tests, patients are asked to arrange colored caps in linear sequence relative to reference caps. The D-15 is shorter and less cumbersome than the 100-hue test and can be performed quickly in the office under proper lighting conditions.

A. Farnsworth D-15 color test. The patient is asked to arrange colored discs in order of color similarity, starting with a reference disc. Each eye is tested separately. B . Each disc is numbered, and the results are recorded by connecting the numbers in the order in which the patient arranged the discs. Protanopes, deutanopes, and tritanopes tend to arrange them in incorrect but characteristic, easily identifiable patterns along one of three axes. A normal response is given on the left, while a protanope’s response is depicted on the right.

Acquired dyschromatopsia may result from macular, retinal, optic nerve, chiasmal, or retrochiasmal lesions. Monocular acuity loss, deficits in color vision, and a relative afferent pupillary defect (see later discussion) are highly characteristic of an ipsilateral optic neuropathy. Acquired optic nerve diseases typically produce a red–green color deficiency, but there are several notable exceptions, such as glaucoma and dominant optic atrophy, as mentioned earlier. Compared with eyes with optic neuropathies, those with amblyopia often have less color vision loss despite the same level of visual acuity deficit. Dyschromatopsias occurring in the setting of retinal disease, such as cone dystrophies, Stargardt disease, and toxic retinopathies, are usually associated with pigment migration or visible disturbances of the retinal pigment epithelium on fundus examination. Color vision loss combined with only mildly reduced acuity would be more suggestive of an optic neuropathy, while color deficits associated with more severe visual acuity loss could be due to optic nerve, macular, or specific conditions (genetic, metabolic) that affect cone photoreceptors. One study demonstrated a visual acuity of worse than 20/100 due solely to visual blur is needed to affect the results of Ishihara color plate testing, and worse than 20/250 is necessary to affect Hardy–Rand–Rittler testing. Retrochiasmal disturbances can produce abnormal color vision in the defective visual field. An inferior occipital lobe lesion involving the lingual and fusiform gyri can cause defective color vision in the contralateral hemifield (see Chapter 9 ).

Confrontation Visual Field Assessment

The patient’s visual fields can be tested at the bedside by finger confrontation methods in all four quadrants of each eye by asking the patient to fix on the examiner’s nose then to “count the fingers” ( Fig. 2.10A ,Video 2.1 ). Because of the overrepresentation of central vision in the nervous system, assessment of each quadrant within the central 10–20 degrees is more important than that of the periphery. One eye at a time is tested while the patient focuses on the examiner’s nose. Sometimes, a visual field defect is best elicited by asking the patient if all parts of the examiner’s face can be seen clearly: “Can you see both of my eyes with equal clarity?” If the patient does not see the nose clearly, a central scotoma should be suspected. Alternatively, the examiner can hold a finger over his or her nose and another finger a few degrees off center. If the patient sees the eccentric finger more clearly than the central one, again a central scotoma should be suspected. Testing of two separate quadrants of one eye enhances the yield of finding a field defect. Moving stimuli are almost always appreciated better than static ones, so the latter are preferable when screening for subtle field defects. Detection of finger wiggling is not as sensitive as finger counting, especially when the patient is asked to count fingers that are presented rapidly.

Methods of confrontation visual field testing. Each eye is tested separately. A . Finger counting. Fingers are presented momentarily in each quadrant within the central 20 degrees, and the patient is asked to count the number of fingers. B . Hand comparison. When checking for subtle hemianopias respecting the vertical meridian, identical targets, either both hands or two red bottle tops, for instance, can be held in front of the patient as shown. The patient is then asked to fixate on the examiner’s nose and state if both hands appear the same. A hand on the side of a relative hemianopia may appear “not as clear,” “blurry,” or “more difficult to see.” Altitudinal hemianopias can be assessed with targets presented one above the other, with each target on the same side of the vertical meridian. C . Saccade to toys. In a child unable to count fingers, this method provides a rough assessment of the integrity of each visual field quadrant. A toy is presented in the upper nasal quadrant of the left eye, and, since the child looked at it, the examiner can presume that vision in that quadrant is grossly intact.

Red top caps can also be used in a similar fashion and enhance the sensitivity of confrontation visual field testing. For example, when testing for a central scotoma, a red top cap 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, again a central scotoma is suspected.

Color or subjective hand comparison is also a useful adjunct to elicit defects respecting the vertical or horizontal meridians ( Fig. 2.10B ). Caution should be applied in patients with visual inattention or neglect, as they may exhibit a field defect during double simultaneous stimulation. However, these patients will exhibit no field defect when stimulated with single targets.

Alternatively, a laser pointer can be used to screen a patient’s visual field. The examiner can stand behind the patient and test the various quadrants using a laser pointer projected on a tangent screen or even on a white wall (Video 3.1 ). This test may be helpful as a screening tool and may detect field defects not observed on confrontation testing.

For a patient who is aphasic, uncooperative, intubated, sedated, or very young, responses such as finger mimicry, pointing to targets presented, looking at the stimulus, or reflex blink to visual threat allow for a gross appraisal of visual field integrity. The stimulus should be silent to ensure the patient is not attending to an auditory stimulus. If the patient saccades to a visual stimulus in a given quadrant, the visual field in that area can be considered relatively intact ( Fig. 2.10C ). However, an absent reflex blink to visual threat, which depends on the intactness of the afferent visual pathway, including the occipital lobe, can be misleading. The reflex may be absent in very young normal infants and patients with Balint syndrome or neglect from right frontal and parietal lesions (see Chapter 9 ). Care should also be taken so that the visual threat, usually a menacing hand gesture, does not move air onto the eye and elicit a corneal blink reflex (see later discussion).

The results of confrontation visual field testing can be recorded in the chart within two circles. By convention, the visual field of the patient’s right eye is drawn within the circle on the right, and the left eye’s visual field in the circle on the left. Furthermore, the visual field of each eye is diagrammed from the patient’s perspective. In Fig. 2.11 , examples of documentation of normal and abnormal confrontation fields are given. Because confrontation techniques produce only a gross assessment of the visual fields, more sensitive testing requires a tangent screen, kinetic perimetry, or automated threshold perimetry. These tests and their interpretation are discussed in detail in Chapter 3 .

Schematic documentation of confrontation visual assessment. The fields are represented from the patient’s point of view with the right eye vision recorded on the right, and the left eye vision on the left. FC, finger counting. A . Normal confrontation visual fields. The patient is able to count fingers in all four quadrants. B . Left lower quadrantanopsia. The defective field is documented by a darkened area, and the patient is able to count fingers in all other quadrants.

The visual field can be altered by lesions anywhere in the afferent visual pathway; the specific patterns of field loss and their relationship to neuroanatomic structures are also discussed in more detail in Chapter 3 .

Amsler Grid Testing

To test central or macular vision, an Amsler grid ( Fig. 2.12 ), which is similar to a piece of graph paper with a central fixation point, can be viewed by the patient at near proximity. The patient fixates on the central dot with near correction and is asked whether all the lines are straight and whether any parts are missing, bent, or blurry.

Amsler grid in a patient with central serous chorioretinopathy involving the macula inferiorly in the left eye. With the right eye covered, a patient was requested to look at the central dot and asked if any of the lines were missing or wavy. She indicated the shaded area was blurry and distorted.

The patient may perceive abnormal areas on the grid that might correspond with visual field deficits. Amsler grid testing is particularly helpful in detecting central and paracentral field defects. Small deficits (affecting only a couple of boxes) point to macular disease and may not be detected on computerized perimetry. Unlike neurologic processes, maculopathies associated with a thickening or surface irregularity of the retina can produce a distortion (bending of the lines) in the grid pattern ( metamorphopsia ). The results of Amsler grid testing can be documented with a convention similar to that of confrontation visual field testing.

Photostress Test

Also not part of the routine neuro-ophthalmic examination, the photostress test can be used to help distinguish retinal (macular) from optic nerve causes of visual loss. After best corrected visual acuity is assessed, a bright light is shone into the affected eye for 10 seconds while the other eye is covered; a penlight, halogen transilluminator, or indirect ophthalmoscope held 2–3 cm from the eye can be used. The test should be performed with undilated pupils. Once the light is removed, acuity in that eye is retested continuously until the patient can read three letters on the Snellen line just larger than the baseline acuity (i.e., 20/25 vs 20/20). The time to recovery is recorded, then the procedure is repeated with the other eye. Photostress recovery time is 27 seconds for normal eyes. Optic neuropathies tend not to produce prolonged photostress recovery times, while macular disorders, such as macular edema, central serous retinopathy, and macular degeneration may be associated with recovery times of several minutes. The photostress recovery time is believed to be related to the amount of photopigment bleached by the light stimulus and the ability of rod and cone photoreceptors to convert photopigment back to the unbleached state. Because the actual recovery time may vary according to technique and age, a more useful clinical measure may be a relative photostress recovery time between the two eyes when one eye is suspected of having visual loss due to either optic nerve or macular disease.

Higher Cortical Visual Function

Examination of visual attention, object recognition, and reading ability are important in patients with visual complaints unexplained by acuity or field loss. These functions and their neuroanatomic localization are discussed in greater detail in Chapter 9 .

It is often difficult to separate a dense left hemianopia from dense neglect in a patient with a large right parietal lesion. When the deficits are more subtle, the examiner can screen for visual inattention by presenting visual stimuli, such as fingers, separately in each hemifield, then together on both sides of the midline (double simultaneous visual stimulation—similar to hand comparison (see Fig. 2.10B )). Individuals with subtle visual inattention but intact fields will see both stimuli when they are presented separately but may not see one of them when they are shown simultaneously. Other bedside tests include letter cancellation, in which the patient is asked to find a specific letter or shape within a random array. Patients with left visual neglect may find the specified letter only when it appears on the right side of the page ( Fig. 2.13 ). The line cancellation test, in which the individual is asked to cross lines drawn in various locations at different angles throughout the page, is similar. When patients with left neglect are asked to bisect a horizontal line, they may tend to “bisect” the lines to the right of the true center.

Letter cancellation. Patients are asked to identify the A’s within the random array. This patient with severe left neglect may find only those A’s along the very right hand side of the page.

Reproduced from Liu GT, Bolton AK, Price BH, et al. Dissociated perceptual-sensory and exploratory-motor neglect. J Neurol Neurosurg Psychiatr 1992;55:701–726.

In patients suspected of visual agnosias, informal tests of visual recognition can be performed at the bedside using common objects such as a pen, cup, or book and asking the patient to name them. An inability to recognize faces ( prosopagnosia ) can be tested with magazine or newspaper photographs containing famous faces. Standardized facial and object recognition tasks are available during more formal neuropsychologic testing. An inability to interpret complex scenes ( simultanagnosia ) can be tested with magazine pictures containing several elements or with a letter made up of smaller elements (Navon figure) ( Fig. 2.14 ). Simultanagnosia may be evident when the patient is tested with Ishihara color plates and is able to recognize the colors and trace the digits but is unable to recognize the number represented among the dots.

Simultanagnosia tested by a Navon figure. The letter H is drawn by arranging multiple A’s. A patient with simultanagnosia might be able to identify the A’s but will not realize that the smaller elements together make an H.

Central achromatopsia, or difficulty perceiving colors because of a cortical lesion, may be detected using the Hardy–Rand–Rittler color plates or Farnsworth D-15 tests (mentioned previously), which may demonstrate complete lack of color vision. When the deficit is incomplete, as in cerebral dyschromatopsia, a tritan (blue–yellow) defect may be demonstrated.

Errors in figure or clock drawing or copying are often nonspecific. However, these tasks sometimes can provide useful information about visuospatial abilities, especially in patients with hemifield loss or hemineglect. For instance, such patients can be asked to copy a cube, house, flower, or Rey–Osterrieth complex figure ( Fig. 2.15 ). An individual with left hemineglect may duplicate only half of a figure ( Fig. 2.16 ), whereas one with a right parietal lesion may show evidence of visuospatial difficulty. In a more difficult task, when a patient with a right parietal lesion is asked to draw a clock face, visuospatial abnormalities may be more pronounced. Errors include placing all the numbers on the right side ( Fig. 2.17 ) and reversing the order of the numbers. In a cautionary note, a normally drawn clock face does not exclude left unilateral spatial neglect. The task can be performed with or without a predrawn circle, but if a circle is provided, the examiner should make sure it is large enough (2–3 inches in diameter) to make the test a useful one for evaluating visuospatial function. When asked to draw the clock and the circle, patients with right brain lesions may draw small clocks. Interested readers are referred to the informative, detailed analysis of clock drawing by Freedman et al.

Rey–Osterrieth complex figure used for visuospatial and visual memory tasks. Patients can be asked to copy it or study the figure then redraw it from memory.

Copying a drawing. A figure of a house was drawn by the examiner ( left ), and a patient with left-sided neglect was asked to copy it. The patient’s drawing ( right ) missed elements from the left side of the figure.

Clock drawing in a patient with a right parietal lesion. A large circle was drawn, and the patient was asked to draw in the numbers of a clock. The patient’s response reflects the left-sided neglect and visuospatial difficulties.

The ability to read should be tested along with all the other main components of language function (see Mental Status Evaluation ). An individual who can see well but not read and is able to write ( alexia without agraphia ) likely has a lesion in the left occipital lobe and splenium of the corpus callosum. Pseudoalexias may be caused by hemianopias.

Pupils

Although pupillary dysfunction often reflects a lesion in the efferent parasympathetic pupillary pathway, abnormal pupillary reactivity also may be a sign of disorders affecting the afferent visual pathway. Some pupillary abnormalities are mentioned here in the context of the pupillary examination, but each, along with its differential diagnosis, is discussed in more detail in Chapter 13 .

At a minimum, pupillary size and reactivity to light (direct responses and consensual responses during the swinging flashlight test) should be evaluated. Pupillary shape should be documented if it is not round; slit-lamp evaluation is helpful in these instances.

Many health professionals were taught to use the acronym “PERRLA” in the chart to document that the “ p upils were e qual, r ound, and r eactive to l ight and a ccommodation.” Acronyms are easier to write if one is in a rush but, as in the case of PERRLA, do not always reflect exactly what was tested. We prefer a less generic, more descriptive sentence such as “The pupils were equal in size in ambient light and reacted briskly to light without a relative afferent pupillary defect (RAPD).” This can also be shortened as “Pupils: equal and reactive. No RAPD.” The roundness of the pupils is implied, and, because the pupils reacted briskly to light, it was not necessary to test their reaction while viewing a near stimulus. Alternatively, one could record the size of each pupil and its reactivity. One scale for pupil reactivity is as follows: 3+, normal brisk reaction; 2+, slightly sluggish; and 1+, sluggish. Qualitative descriptions such as “brisk,” “sluggish,” or “unreactive” also can be used to describe the speed of the pupillary constriction to light.

Pupillary Size. The most practical method of measuring pupillary size uses the pupil gauge available on most near-acuity cards (see Fig. 2.2B ). Usually, the two pupils are equal in size, and each is located slightly nasal and inferior to the center of the cornea. Transient fluctuations in pupillary diameter are normal and are termed hippus. In infancy the pupils are often small, but they widen as the child grows older and achieve their largest sizes in adolescence. In adulthood they then become progressively more miotic.

The term anisocoria refers to asymmetric pupillary sizes; in cases of anisocoria the amount of pupillary inequality in ambient light and dark should be compared. In the most common type of anisocoria, physiologic or essential, pupillary function is normal and the relative inequality is the same in light and dark (although in some instances it can be slightly worse in the dark and better in the light because of the mechanical limitations of the pupil when it is small). Long-standing pupillary inequality can be confirmed by viewing old photographs with the magnification of a slit lamp or 20-diopter lens or by enlarging digital images.

Pathologic anisocoria suggests dysfunction in the efferent part of the pupillary pathway. Afferent pupillary dysfunction, due to optic nerve disease, for instance, does not produce anisocoria. In general, anisocoria that is greater in light implies the larger pupil has a parasympathetic abnormality, while anisocoria more prominent in the dark suggests the smaller pupil has oculosympathetic dysfunction (Horner syndrome). In the latter situation, the pupil may redilate slowly (dilation lag) compared with the other pupil when the lights are turned down. To assess dilation lag, the examiner shines a dim light from below the patient’s nose to provide minimal illumination before turning the room lights off. The size and speed of dilation are assessed for the first 2–4 seconds after the patient is placed in the dark. During this time, dilation lag should be maximal. Often the sympathetically denervated pupils will begin to catch up in size over the next 10 seconds of observation.

Light Reactivity: Direct and Consensual. Pupillary light reactivity (constriction) should be tested with a bright light such as a halogen transilluminator or indirect ophthalmoscope while the patient views a distant target (to prevent near viewing-induced miosis) ( Fig. 2.18 ) in a dimly lit room. Fixation may be difficult in smaller children or uncooperative adults who may not hold still. With the light shining in one eye, the ipsilateral pupillary light reflex is the direct response, while that of the contralateral eye is the consensual response. Because light from one eye will reach both Edinger–Westphal nuclei symmetrically, normally both pupils react briskly when light is shone into just one eye (i.e., the direct and consensual responses are equal) ( Fig. 2.19A ).

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