Ocular Examination Techniques and Diagnostic Tests
Pedram Hamrah
Deborah Pavan-Langston
I. General Principles
Physical examination and evaluation of the ocular system are greatly facilitated by a detailed history and a number of techniques that are performed in the office using equipment readily available through any optical or medical supply house. However, a specialist in a hospital setting must perform some of the more complicated techniques. These techniques are discussed with a view to (a) their indications, (b) how they are performed, so that the referring examiner can explain to a patient what might be expected, and (c) the necessary information to aid the examiner in management of the patient.
Order of examination. Examination of the eye and its surrounding tissues with and without special aids may yield valuable information for the diagnosis and treatment of ocular disease. After acquiring the ophthalmic history, a systematic routine should be adopted for the examination, with particular attention paid to the patient’s chief complaint. Additional tests may be required after the initial exam. Individual chapters should be referred to for related details.
The typical order for nonemergency examination is as follows:
History. Chief complaint; present and past ocular problems; family history of eye problems; present and past general illnesses; previous surgeries; ocular and general medications; allergies; social history. Depending on the patient’s particular problem, the history may be brief or extensive.
Visual acuity. Distant and near without and with glasses, if used, and with pinhole if a vision of less than 20/30 is obtained.
Extraocular motility and alignment testing. Range of action in all fields of gaze, stereopsis testing, and screening for strabismus and diplopia.
Pupillary examination.
Color vision testing.
Visual field testing.
External examination (face, periocular tissues).
Anterior segment examination under magnification, if possible (loupes or slitlamp), with and without dyes.
Intraocular pressures (IOPs).
Ophthalmoscopy of the fundi.
Other tests as indicated by history and prior examination:
Tear film adequacy and drainage.
Corneal sensation.
Transillumination.
Exophthalmometry.
Gonioscopy.
Keratometry.
Keratoscopy.
Corneal topography.
Wavefront analysis.
Schleimpflug camera.
Corneal pachymetry.
Specular microscopy.
Confocal slit-scanning microscopy.
Fluorescein and indocyanine green angiography.
Anterior segment fluorescein angiography.
Electroretinography (ERG) and electrooculography (EOG).
Ultrasonography.
Optical coherence tomography (OCT).
Scanning laser ophthalmoscopy.
Scanning laser polarimetry.
Retinal thickness analyzer.
Radiology, tomography, magnetic imaging.
Paracentesis.
Procedures e–w are done by eyecare specialists, and referral should be made if such testing is indicated.
II. Routine Office Examination
History. The main goals of taking history are to obtain a likely or differential diagnosis and to aid with the selection of treatment or referral to the appropriate specialist.
Chief complaint. The patient’s main complaints are recorded in the patient’s own words in order to document the patient’s subjective view of the problem(s). Symptoms, rather than, diagnosis are recorded. All complaints, whether major or minor, are listed.
History of present illness. It is important to document any additional information and details about the chief complaints. This information will allow the forming of a differential diagnosis. The time of onset, severity, temporal variations, influencing factors, and laterality are documented. It is imperative to ask for visual disturbances, ocular discomfort and pain, photophobia, ocular secretions, abnormal external appearance noted by the patient or family members, and trauma.
Past ocular history. Ask the patient for any prior ocular problems. These can include, but are not limited to, past ocular medications, ocular trauma, ocular surgery, glasses, contact lens wear, and history of strabismus or amblyopia.
Ocular medications. Current ocular medications are recorded. It is important to document the duration of the current therapy and the response to current and past therapies. Patients are asked about over-the-counter medications. Occasionally, patients will not remember names of their medication. When this is the case, it is useful to ask for the color of the bottle caps, as these are color coded for eye drops.
Systemic medications. Systemic medication may be important in regards to ocular problems or surgical management. Particular attention is given to anticoagulants and oral medication used for ocular problems. Further, the medications taken by the patient will give clues about the patient’s specific medical problems.
Past medical and surgical history. The present and past medical history is documented. Many ocular problems are secondary to systemic diseases. In addition, the general health of the patient is important for the preoperative evaluation. A detailed review of systems is further recorded. Date of onset and surgical treatments are documented. Of special importance are diabetes, cardiac and renal status, and autoimmune collagen vascular diseases.
Allergies. The patient’s history of allergies is recorded. The specific reactions are documented because most patients are not able to differentiate the nature of a reaction. In addition to inquiring about allergies to medications, inquire about allergies to shellfish, latex, dyes etc.
Family history. The family history is important for genetically transmitted disease. Patients are asked about a family history of glaucoma, retinal diseases and detachments, corneal problems, cataracts, diabetes, malignancies, or any other ocular and systemic diseases.
Social history. For ocular conditions, the social history is not always relevant. Nevertheless, questions about drug abuse, tobacco, alcohol use, sexual history, and HIV are important. No causal relationship, however, should be inferred by the physician.
Visual acuity. Determination of visual acuity is a test of macular function and should be part of any eye examination, regardless of symptomatology or lack thereof. It refers to an angular measurement that relates distance to the minimal object size resolvable at that distance.
Distant visual acuity. Visual acuity is examined one eye at a time, the other eye being occluded. By convention, the right eye is tested first. Pressure on the occluded eye should be avoided so that there will be no distortion of the image when that eye is subsequently tested. On the initial exam, the test should be made both with and without corrected lenses (if used) and recorded as “uncorrected” and “corrected” (sc or cc). On subsequent visits, glasses are worn for the test.
The chart most commonly used for distance vision with literate patients is the Snellen chart, which is situated 20 ft (6 m) away from the patient and diffusely illuminated without glare. At this distance, the rays of light from the object in view are almost parallel, and no effort of accommodation (focusing) is necessary for the normal eye to see the subject clearly. The Snellen chart is composed of letters of graduated sizes; the distance at which each size subtends an angle of 5 minutes of arc is indicated along the side of the chart. The farther one is from an object, the smaller the retinal image. By combining the two factors of size and distance, it is possible to determine the minimum visual angle (i.e., the smallest retinal image that can be seen by a given eye). A normal visual system can identify an entire letter subtending an angle of 5 minutes of arc and any components of the letter subtending 1 minute of arc at a distance of 20 ft. Some patients, however, may resolve letters subtending even smaller visual angles. The vision is recorded as a fraction. The number in the numerator position is the equivalent of the testing distance from the eye to the chart in feet or meters. The number in the denominator position is the distance at which a subject with normal vision can read the same figure. The vision of a normal eye is therefore recorded as 20/20, or 6/6 in metric measurement. If the patient is able to read down only to the 20/30 line, the vision is recorded as 20/30. If the patient is unable to read even the large E at the top, which subtends an arc of 400 degrees, he or she may be moved closer so that the distance measurement is changed. The visual acuity may then be recorded as 10/400, for instance, if the patient is able to read this letter at 10 ft from the chart.
Pinhole vision is tested if the patient is unable to read the 20/30 line. A pinhole aperture is placed in front of the eye to ascertain any improvement in acuity. The pinhole admits only central rays of light that do not require refraction by the cornea or lenses. This will allow the patient to resolve finer detail without the use of glasses. The eye not being tested is occluded, and the patient holds the pinhole occluder in front of the eye being tested. Through the pinhole, a patient’s visual acuity should improve two or more lines, if a refractive error is present. However, if the pinhole fails to improve the patient’s visual acuity score, the examiner must suspect another cause for the reduced vision, such as cataracts, macular or optic nerve disease. The visual acuity obtained is recorded with a preceding abbreviation of PH to note a pinhole was used.
Preschool children or patients who are unable to read are shown the tumbling E or Landolt ring (C) chart, which are made up entirely of the letter E or C facing in different directions. Patients are instructed to point their finger in the same direction of the bars of the E or circle opening of the C. Children as young as 3 years of age may be able to cooperate in this testing. Another form of testing is with the Allen picture chart, which may result in overestimating of visual acuity; at a distance of 20 ft, a visual acuity of 20/30 may be tested. If the patient is unable to identify the pictures at that distance, the distance at which the picture is identified is recorded (e.g., 10/30, 5/30, etc.). The type of chart used is always recorded together with the visual acuity. Abbreviations such as central (C), steady (S), maintain (M), or fix and follow (F/F) are occasionally used in nonverbal children when no other method has been successful. An estimated visual function can be made based on the child’s ability to fixate
an object, follow the object, and maintain steady fixation. Teller acuity charts can be used to obtain a more detailed measurement in infants. These are large plates with line gratings printed on one side and a central pinhole to determine the baby’s direction of gaze. The baby will look preferentially toward the side of gratings, as long as he or she can identify the image. Once the visual acuity is surpassed, the baby will look in random directions. This test can be used up to an age of 1 year. Alternatively, optokinetic nystagmus (OKN) can be induced with a regular striped object or a commercially available OKN drum. The stripes are passed slowly in front of the infant’s eye, with the observer examining the eye movements. A fine nystagmus, with the slow phase going in the direction of the stripes rotation, will indicate the infant’s ability to discriminate the stripes. A horizontal OKN can be used before 3 months of age, whereas a vertical OKN should not be used before 6 months of age.
If a verbal patient is unable to identify any letter on the chart at any distance, visual acuity is recorded as counting fingers (CF) at whatever distance in feet the patient is able to perform this function (e.g., CF 3). Vision less than CF is recorded as hand motion (HM) or light perception (LP). If an eye is unable to perceive light, the examiner should record no light perception (NLP) rather than the misleading term blind.
Tests of light projection may demonstrate normal retinal function when vision is extremely poor and the examiner is unable to see the retina, as in the presence of a mature cataract or severe corneal scarring. This test is done by covering the other eye completely and holding a light source in four different quadrants in front of the eye in question. The patient is asked to identify the direction from which the light is approaching the eye. Additionally, a red lens can be held in front of the light and the patient is asked to differentiate the red from the white light. If all answers are correct, one can assume a reasonably degree of retinal function. It is important to note that good retinal and macular function may be present despite abnormal LP due to unusually dense anterior segment disease, which prevents sufficient light from reaching the retina for proper stimulation.
The potential acuity meter (PAM) is a reasonably accurate device for differentiating between visual loss from anterior segment (e.g., corneal scarring, cataract) and macular disease. The PAM attaches easily to a standard slitlamp and projects a Snellen acuity chart into the eye using a 1.5-mm-diameter pinhole aperture. It allows a preoperative prediction for what the potential postoperative vision might be. For example, if the vision is 20/400 by routine testing but 20/40 with PAM, one can, in most cases, assume good macular function and good correction of vision once the anterior segment defect has been corrected. Conversely, if the vision is 20/400 both by regular and PAM testing, one can assume that almost all of the visual loss is due to macular disease and that anterior segment surgery or medical therapy will be to no avail. In cases in which the cornea is clear but cataract obstructs vision, the patient is tested at different points on the cornea in an attempt to project through clearer areas in the lens and allow the best possible reading.
Photostress recovery test. Very early macular dysfunction, whether from spontaneous or toxic degeneration, may be detected by the macular photostress recovery test. This test works only with a visual acuity of 20/80 or better. The patient looks at a flashlight held 2 cm from the eye for 10 seconds. The time it takes for visual recovery to one line less than the visual acuity determined prior to this test is measured. Normal time is about 45 to 60 seconds and is maintained in cases with optic neuropathy. Recovery taking longer than this (90 to 180 seconds) indicates macular dysfunction, even though the area may appear anatomically normal.
Macular function may be tested in the presence of opaque media by gently massaging the globe through closed lids with the lighted end of a small flashlight. If the macula is functioning normally, the patient will usually see a red
central area surrounded by retinal blood vessels. If macular function is abnormal, the central area will be dark rather than red and no blood vessels will be seen.
Legal blindness. Visual acuity correctable by glasses or contact lenses to 20/200 or less in both eyes or visual fields in both eyes of less than 10 degrees centrally constitutes legal blindness in the United States. Its presence requires that the patient be reported to the Commission for the Blind in the patient’s home state. Report forms are short and readily available from the commission.
Near visual acuity is usually measured using a multipurpose reading card, such as the Rosenbaum Pocket Vision Screener or the Lebensohn chart. The patient holds the chart approximately 16 inches (40 cm) from the eye and, separately with each eye with and without glasses, reads the smallest print he or she is able to identify. This may then be recorded directly from the chart as 20/30, 20/25, or as Jaeger equivalents J-2, J-1. In patients older than their late 30s, the examiner should suspect uncorrected presbyopia if the patient is unable to read a normal visual acuity at 40 cm but is able to read it completely or at least better if the card is held farther away. Abnormally low close vision in an elderly patient without reading glasses is meaningless per se, except for comparative purposes in serial examinations of the severely ill. Near visual acuity can be tested in children with Allen picture cards, Lighthouse picture cards, Lea figure set, or HOTV equivalent cards.
Extraocular motility and alignment testing. The movement of the eyes in all fields of gaze should be examined (see Chapter 12, Sections I and XI for details).
Alignment testing. Several methods can be used to assess the patient’s alignment. These include the Brückner or red reflex test, corneal light reflex with either Hirschberg or Krimsky test, and the cover tests.
Brückner test (red reflex test). This is the most rapid test for detection of strabismus and therefore good for screening purposes. A direct ophthalmoscope is used with white light and the lenses are placed to zero. The patient is asked to look directly into the light. The goal is to obtain a red reflex simultaneously in both eyes. In patients with strabismus, the deviated eye will have a brighter and lighter reflex than the nondeviated eye.
Corneal light reflex test. In the primary position of gaze (i.e., straight ahead), the straightness, or orthophoria, of the eyes may be ascertained by observing the reflection of light on the central corneas. In normally aligned eyes, the reflections should be symmetric and central on both corneas. In some patients, the light reflex will be slightly inside or outside of the central cornea due to a normal difference between the visual axis and the anatomic axis between the central cornea and the fovea. This angle is referred to as the angle kappa and is positive if the eye appears to be deviating outward and negative if the eye appears to be deviating inward. No ocular movement will occur on cover–uncover testing if the apparent deviation is due to angle kappa alone (see Chapter 12, Section III.B).
Hirschberg test. The patient is asked to look directly at a flashlight held 2 ft in front of the eyes. The asymmetric positioning of a light reflex in one eye indicates deviation of that eye. Location of the reflex on the nasal side of the central cornea indicates that the eye is aimed outward, or is exotropic; location of the reflex temporal to the central cornea indicates that the eye is deviated inward, or is esotropic. Each millimeter of deviation is equivalent to 7 degrees or 15 prism diopters (PD) of turn. A light reflex at the pupillary margin is equivalent to 2 mm or 15 degrees and corresponds to 30 PD of deviation. A light reflex at the limbus is equivalent to 45 degrees or 90 PD. Vertical deviation may be determined by noting the location of a light reflex above or below the central cornea.
Krimsky test. This method is more accurate than the Hirschberg test. Similar to the Hirschberg test, a flashlight or penlight is held 2 ft away from the patient and the patient is asked to look at the light. However,
instead of estimating the amount of deviation, prisms with increasing or decreasing power are held in front of the fixating eye until the corneal reflex in the deviating eye is centered. The apex (narrow end) of the prism should be pointed toward the deviation. The strength of the final prism used should be recorded.
Cardinal positions of gaze. A small object or finger is held 12 inches to 14 inches in front of the patient. The patient is asked to follow the target as it is moved in the six cardinal positions of gaze (i.e., left, right, up and right, up and left, down and right, and down and left). The upper lid should be elevated with a finger to observe the down gaze. Congruity (parallelism) of gaze between the two eyes should be noted as well as the extent of the excursion. The examiner should check for restriction of gaze in any direction or for double vision in any field of gaze due to restriction of one eye. Occasionally, involuntary movement may occur in normal patients at the extremes of gaze; this movement is referred to as end-gaze or physiologic nystagmus. Nystagmus is a short-excursion, back-and-forward movement of the eye that may be fine or coarse, slow or rapid. Occasionally, fine rotational nystagmus may also be observed. Except in end-gaze nystagmus, this rotational nystagmus may bear further investigation (see Chapter 12, Fig. 12.2, Sections XI and XIII).
The near point of conversion (NPC) is the point closest to the patient at which both eyes converge on an object as it is brought toward the eyes. This point is normally between 6 cm and 10 cm in front of the eye. The moment one eye begins to deviate outward or the image doubles, the limit of conversion has been reached. A NPC greater than 10 cm is considered abnormal and may result in excessive tiring of the eyes on close work such as reading or sewing.
Stereopsis is tested grossly by having the patient touch the end of one finger to the tip of the examiner’s finger coming in horizontally end to end. Past pointing may indicate lack of depth perception in the absence of central nervous system (CNS) disease. More refined testing is done using the Titmus fly test, circle, and animal figures with three-dimensional (3-D) polarized glasses. Stereopsis may be graded from the equivalent of 20/400 (large fly) to 20/20 (nine-circle depth perception) using this commercially available test. Another test is the Worth four-dot test, also commercially available. Simultaneous perception of four lights (one red, two green and one white light) while wearing glasses with a red lens over one eye (eye sees only red) and a green lens over the other (eye sees only green) indicates a more gross but significant form of fusion. If less than four lights are seen, one eye is suppressed. If more than four lights are seen, diplopia is present.
Pupillary examination. The pupil size, shape, location, and reaction to light, can be altered by numerous pathologic disorders (see Chapter 13, Section III for details). The examiner begins with observation of the pupil. The pupillary reflexes are tested with the light-reflex test, the swinging flashlight test, and the near-reflex test.
Pupillary observation and light-reflex test. The patient should be asked to fixate a distant target to minimize accommodation and miosis. In a semidark room, a flashlight is held from below the nose to illuminate the pupil. The pupil size should be measured with a ruler or near vision chart. A difference in pupil size between both eyes (anisocoria), as well as the shape and location, should be noted. Further, the direct pupillary response to the light in terms of briskness should be graded separately for each eye from 0 for no response to 4+ for brisk response. In addition, the consensual response should be evaluated by observing the pupillary response of the nonilluminated eye.
Swinging flashlight test. This test determines the presence or absence of a relative afferent pupillary defect (RAPD). Similar to the light-reflex test, the handheld flashlight is used to illuminate the pupils. The constriction of the pupils is observed. The light is then moved immediately over the patient’s nose to the other eye, and the pupillary response is noted. In a normal patient, the pupil will slightly constrict or stay unchanged. However, if the pupil dilates, a RAPD is present, indicating optic nerve or severe retinal damage. The light is then moved back swiftly to the other eye and the response noted. This process should be performed several
times, spending equal amount of time illuminating each eye. The presence or absence of a RAPD and the location should be noted.
Near-reflex test. This test is based on the fact that looking at a near target is associated with convergence, accommodation, and miosis (near synkinesis). These three processes occur simultaneously. The patient is initially instructed to look at a distant target. A target or a finger is than held in the patient’s line of vision, and the patient is asked to shift fixation to the near target. The pupillary response is observed. Normally both pupils constrict simultaneously. The test may need to be repeated several times to obtain best results. Under normal conditions, if the pupil reacts to light, it will react to accommodation, as well. The Argyll Robertson pupil is a condition due to CNS lues and occasionally to herpes zoster in which there is a failure of direct and consensual light response but a normal reaction to accommodation. The Adie’s tonic pupil responds to either stimulation but does so abnormally slowly (see Chapter 13).
Color vision testing
Purpose. Demonstration of adequate color vision complements evaluation of visual acuity and is mandatory for certain jobs in a number of states and for obtaining a driver’s license. Jobs affected are armed services trainees, transportation workers, and others whose occupations require accurate color perception. Color vision, particularly red perception, may be disturbed in early macular disease, whether toxic or idiopathic degenerative, and in optic nerve, chiasmal, or bilateral occipital lobe disease. In optic nerve disease, the degree of color vision loss or dyschromatopsia is greater than the loss in visual acuity. In macular disease, both decline correspondingly. Some of the earliest and reversible drug toxicities, such as that from chloroquine and avitaminosis A, are detected by repeated color vision testing; regression and progression may also be documented. These tests are designed for:
Screening defective color vision from normal.
Qualitative classification as to type of defect. Protans and deutans are red-green deficient and are found in 4% of all males and 0.4% of all females; tritans and tetartans are very rare and are blue-yellow deficient.
Quantitative analysis of degree of deficiency: mild, medium, or marked.
Technique. The progressively more subtle and difficult pseudoisochromatic plates of Ishihara, Stilling, or Hardy-Rand-Ritter are made up of dots of primary colors printed on a background of similar dots in a confusion of colors or grays. These dots are set in patterns, shapes, numbers, or letters that would be recognized by a normal individual but not perceived by those with color perception defects. Patients are shown a series of plates, the number of correct answers is totaled in various color test areas, and the type and severity of any deficiency are thus defined. Lanthony tritan plates may be used specifically to detect blue-yellow color defects, but are less commonly available. For more detailed color testing, the Farnsworth Panel D-15 test or the Farnsworth-Munsell 100-hue test detect earlier, more subtle changes. The patient has to arrange colors in a specific sequence. To a normal patient, the sequence is obvious. A color-deficient patient, however, arranges color chips differently.
Visual field testing.
The purpose of visual field testing is to determine both the outer limits of visual perception by the peripheral retina and the varying qualities of vision within that area. The visual field is an inverted and reversed map of the corresponding retinal location. Visual field interpretation is important for diagnosing disease, localizing it in the visual pathway between the retina and the occipital cortex in the brain, and noting its progress, stability, or remission. As a result, repeated tests of the visual field are important both diagnostically and in ascertaining the effects of therapy. Each eye is tested separately with one or more tests. With one eye fixing on a given test object, the sensitivity of various areas of the visual field may be tested with varying size and color of test objects moved throughout that field. The greatest sensitivity, of course, is at the fovea and represents the highest visual acuity of central fixation. This visual acuity decreases rapidly as the test objects
are moved away from central fixation. Therefore, an object may be too small to be detected by peripheral retinal receptors but quite effective in mapping out central visual field within 10 to 15 degrees of foveal fixation.
Techniques. Visual fields are examined most frequently by four methods: Amsler grid, confrontation, perimetry, and tangent screen.
Amsler grids for qualitative vision evaluation make it possible to analyze the earliest maculopathies and their progression, as well as to detect any scotomatous defects encroaching on the central 10 to 20 degrees of vision.
Technique. With the Amsler grid held at 30 cm from the patient’s eye, the distance between lined square grids correspond to a visual angle of 1 degree. The patient stares at the central spot of the grid with one eye at a time. Alterations in perception of the regular patterns, including missing or distorted lines, indicate various field defects.
Purpose. The examiner may find central scotomas (focal area of decreased or lost retinal sensitivity) as in macular scarring, cecocentral scotomas as in toxic amblyopias, paracentral scotomas as in chorioretinitis, and metamorphopsia (distortion of vision) as in very early maculopathies. The edge of a glaucomatous Bjerrum scotoma, a peripheral field defect secondary to CNS or peripheral retinal disease encroaching on the central 10 degrees of vision, will also be detected.
The monocular confrontation field test. No special instruments are required for this screening test, which provides a rough estimate of the patient’s visual field by comparing it with the examiner’s visual field. It is assumed that the examiner’s visual field is normal. This technique is highly recommended for use in the emergency room and is the technique of choice in the bedridden and in children.
Technique. The patient and examiner face each other at a distance of 1 m. With the left eye covered, the patient is instructed to look with the right eye at the left eye of the examiner, whose own right eye is covered. A small object, such as a pencil or pin, or a larger one, such as a wiggling finger, may be used as a target. The examiner places his or her hand midway between the patient and him- or herself and initially beyond the limits of field of vision of either in a given meridian (e.g., far temporal to both patient and examiner). As the test object is moved slowly toward the line of vision between patient and examiner, the patient is asked to respond as soon as he or she is able to see the target. The physician compares this to the time when he or she is able to perceive the target. This is repeated at 8 to 10 equally spaced meridians at approximately 360 degrees. The visual field is considered normal if the patient sees the target 90 degrees temporally, 50 degrees nasally, 50 degrees upward, and 65 degrees downward. The test is then repeated on the other eye. With careful testing, the blind spot and focal scotomas can be detected. To evaluate the central 20 degrees, a red pin (5 mm or 10 mm) can be used. If in one spot the red appears pale or hazy, a relative scotoma is present. The central scotoma in optic neuritis is rapidly detected this way.
Purpose. This test may also detect gross alterations in field defects due to ocular disease, such as chorioretinitis or advanced glaucoma, or intracranial disease, such as brain tumor or hemorrhage (see also Chapter 10, Section II.E, Fig. 10.2 [glaucoma]; and Chapter 13, Figs. 13.3,13.4,13.5 [neuroophthalmic fields]).
Perimetry is done to obtain accurate examination of the peripheral extent of the visual field. Perimetry may be done as manual kinetic (moving target from nonseeing to seeing areas of vision) using a Goldmann-type bowl perimeter or static (nonmoving target flashed at different locations in visual field) by automated Humphrey visual field analyzer or the Octopus. In addition to varying target size, perimeters vary target brightness, presenting them at threshold (the dimmest spot detected during testing) or suprathreshold levels. Size I is 0.25 mm2 and size V is 64 mm2 with gradations in between.
Luminance varies from 32 to 1,000 apostilbs with 10 gradations in between. With the Goldmann perimeter, at least two isopters should be charted: the first to a large well-visualized spot to aid in training the patient, and the second to the smallest dimmest target he or she can reliably see to permit detection of early defects. Recording several isopters also ensures that all regions of the field are tested in addition to helping to define the slope of the borders of a defect. Steep slopes (isopters crowded together) usually indicate that the defect is caused by an acute lesion (frequently vascular); gradual slopes are indicative of a progressive lesion (tumor). Most automated perimeters provide normal values and compare the patient to normal in the printout of the results. The Humphrey analyzer will also give a probability that any test location is not normal dependent on patient age and location in the visual field. The standard glaucoma field is 30-2, with follow-up fields either 30-2 or 24-2.
In addition to automated static perimetry, short-wavelength automated perimetry (SWAP), which appears to detect visual field defects earlier than automated static perimetry, and frequency doubling technology (FDT) perimetry, which is a 1-minute screening test that is very good in detecting moderate to advanced glaucoma, are available. Unlike static perimetry, FDT uses a stimulus that is a sinusoidal contrast sensitivity grading. This stimulus is presented at multiple retinal locations to map out a visual field while undergoing a rapid counterphase flicker. The disadvantage is that the FDT introduces additional sources for abnormal test results. Therefore, while it is abnormal in patients with true visual field defects, it may also be abnormal in eyes with a normal visual field but impaired contrast sensitivity.
The Octopus detects threshold sensitivity to a light stimulus at 72 points in the visual field. The intensity of the stimulus is carried to below threshold and worked up to suprathreshold. Its advantages are that the Octopus picks up the earliest, most subtle field defects, the results are reproducible, and progression of subtle or gross defects can easily be documented. The disadvantages of all automated perimeters are subjective patient fatigue, the expense of the machines, and the need for trained personnel to run them.
The new scanning laser ophthalmoscope microperimetry makes it possible to test the retinal sensitivity while directly observing and evaluating the fundus. This machine allows the examiner to observe the retinal image illuminated by a 790-nm infrared laser light source while stimuli created by a 633-nm HeNe laser are superimposed on the retina. These superimposed stimuli are used to provide static perimetry with fixation targets of adjustable sizes, shapes, and intensities.
Visual field examination is indicated when the physician detects or suspects a disorder that has constricted the side, paracentral, or central vision. In uncooperative patients, the results of this test are unreliable.
Technique. The patient is seated at the perimeter with one eye covered and the chin on the chin rest. The patient must fix his or her vision on the central target of the perimeter, and a test target, static or kinetic as just described, is presented at some location in the field. The patient is asked to signal immediately when the target is in view. By the end of the test, the entire 360 degrees of field have been mapped.
Purpose. The examiner may accurately map defects in the peripheral vision all the way from the far extent of the field into central or foveal fixation. The smaller the test target used, the greater the possibility of discovering scotomas in the field.
The tangent screen is a black felt screen on which radial lines and 5-degree concentric circles are inconspicuously marked. It is used to examine the central field within 30 degrees from the fixation point and to determine the size of the blind spot. By increasing the distance of the patient from the screen, the size of the field defect increases and allows evaluation in detail. The hysterical constricted field characteristically remains the same size when charted at different distances. Screens are therefore made for use at 1 m or 2 m. A 1-m
screen can be accommodated on the wall of most consulting rooms and evenly illuminated. It is not as sensitive in picking up early defects as the Goldmann and automated perimeters.
Technique. The patient is seated 1 m from the tangent screen. One eye is tested at a time. A 3- to 50-mm white test object is brought in from the periphery, exploring 8 to 10 meridians from periphery to central fixation, as in perimetry. The patient must indicate immediately when the object appears and disappears so that the examiner can map areas of decreased or absent vision. The blind spot should be outlined carefully and early in the examination to show the patient the nature of scotoma mapping. The findings, including the size and color of the test object and the distance from the screen, are recorded on a simple chart stamped in one corner of the large perimeter field chart to facilitate quick comparison and filing. Color fields with red and blue test objects are most useful in the central 10 to 15 degrees of vision and may be the test that picks up early toxic retinopathy soonest.
External examination. A stepwise approach that includes inspection, palpation, and auscultation, helps ensure that no details are overlooked. This process occurs automatically with increased experience.
Inspection. The inspection should take place in a well lighted room. The patient’s actions and appearance should be observed for clues as to the overall health of the patient, including signs for mental, neurological, medical, and dermatological diseases. Extremities, for example, can give clues to systemic diseases, such as rheumatoid arthritis, gout, or tuberous sclerosis. The head and face should be inspected for any masses or lesions, and these should be measured and drawn if present. The face is assessed for symmetry, signs of prior trauma, and motility of facial muscles. If a neurosensory deficit is suspected, the facial nerve function is assessed by asking the patient to close eyes forcefully, to smile and show teeth, and to lift the forehead, while muscle function is also assessed. The facial nerve sensation is then tested by comparing corresponding areas of both sides of the face with fingertips or cotton wisp, testing all three trigeminal dermatomes.
The facial skin is evaluated for color, moisture, tone, texture, and vascular changes. The mouth and nose are then examined with a penlight for changes. The orbits can be evaluated for their anatomic relationship. In addition, if abnormalities are suspected, the intercanthal distance and interpupillary distance are measured with a ruler. The average pupillary distance is 61 mm. Any apparent signs of proptosis (exophthalmos) or enophthalmos should be noted and measured with an exophthalmometer, as detailed below. Further, the relative position and symmetry of the eyebrows are evaluated. Old photographs are an invaluable tool when abnormalities are detected to determine longstanding asymmetry and lesions. It is also important that the examiner take pictures when new findings or changes are noted.
Palpation. Tactile, temperature, and proprioceptive senses are important when feeling for abnormalities. However, the examiner should be gentle and inform the patient about the process. In general, the thumb and index fingers are used to open the eyelids. The middle fingers are used to examine the preauricular lymph nodes. Masses are recorded for shape, size, tenderness, composition, and mobility.
Bony changes of the head and face are noted. Patients with sinusitis might complain of tenderness over the maxillary and frontal sinuses that can be elicited on palpation. In elderly patients, the temporal artery is palpated to reveal tenderness and tortuosity when giant cell arteritis is suspected. Neck vessels are palpated to evaluate the carotid artery pulse and jugular vein hum. Lymph nodes are than palpated to evaluate signs of enlargement or tenderness. Preauricular, submandibular, superficial cervical, jugular, post-sternocleidomastoid, and supra-clavicular lymph nodes should be palpated. When trauma is suspected, the orbital margins are palpated for signs of orbital fracture that include a step-off. The examiner should start laterally and proceed in a clockwise fashion, palpating along the orbital rim. It is, however, important to be certain that no globe rupture is
present before doing so. To evaluate eyelid masses, the closed eyelid is palpated gently by sliding the index fingers over the eyelid skin. Even when a mass cannot be seen, it can be felt. In patients with epiphora, the evaluation of the lacrimal sac involves compression of the sac with the index finger or a cotton-tipped applicator to assess any refluxed material from the puncta. Mucus or mucopurulent material can be expressed and confirm an obstructed nasolacrimal duct. The color of the refluxed material should be noted. It should be noted that pressure on the globe might elicit the oculocardiac reflex with bradycardia.
Auscultation. To assess the orbit for a bruit, the bell of the stethoscope is placed over the closed eyelid while the patient briefly holds his or her breath. Auscultation of the frontal sinus and the temple is performed to listen around the orbit. If an orbital bruit is heard, the presence of a carotid-cavernous fistula or an arteriovenous malformation should be suspected. Compression of the ipsilateral carotid artery or both jugular veins will decrease the bruit. The examiner should listen for a heart murmur and carotid bruit to ensure that these are not transmitted and heard as the orbital bruit.
Anterior segment examination (see frontispiece)
Magnifying loupes. The external examination of the eye itself is greatly facilitated by the use of a bright light source, such as a flashlight or transilluminator, magnifying loupes, and double aspheric 20 D magnifying lenses in conjunction with an indirect ophthalmoscope. Loupes can basically be divided into two categories. Spectacle loupes, which can be mounted on normal prescription glasses, have a magnification from 2× to 5×, and working distances ranging from 20 to 50 cm. The second form of loupe is a headband loupe, which can range in power from 1.75× to 5.25×, with working distances ranging between 20 and 50 cm. Loupes are of great help in evaluating not only local tissue changes and location of corneal abrasions and staining, but also in minor surgical, strabismus, and oculoplastics procedures and the removal of corneal foreign bodies. Handheld magnifiers do not leave both hands free for other purposes.
Slitlamp biomicroscopy of anterior segment and fundus. Biomicroscopy involves examination of the external ocular structures and the front of the eye to a depth of the anterior vitreous using a specially designed microscope and light source that allow for a binocular, stereoscopic view and permit the examiner to perform applanation tonometry. Slitlamps are most commonly stand-mounted, but for bedside exam, handheld lamps are available. Use of a slitlamp is indicated in any condition in which examination is facilitated and made more accurate by a well-illuminated and highly magnified view of the anterior segment of the eye (e.g., corneal ulcerations, iris tumors, cataract evaluation). Patient and examiner are seated on either side of the slitlamp, the patient placing his or her chin on a chin rest and the forehead against a frame while the examiner views the eye through the microscope. By moving the microscope in and out with a hand control, the examiner can adjust the depth of focus so that the object of interest is brought clearly into view. The general order of examination is to start with the lids and then progress to the conjunctiva, cornea, anterior chamber, iris and pupil, lens, and anterior vitreous. The fundi are seen by use of double aspheric 60, 78, 90 D lenses, or digital wide field lens that combines a high magnification with a wide field of view. The examiner holds these lenses in front of the patient’s eye and shines the slit beam straight through the (usually) dilated pupil to focus on the retina, thus obtaining a stereoscopic but inverted view. This is useful for evaluating macular edema, optic nerve lesions, or other posterior pole lesions. It is less useful for the peripheral retina beyond the equator. Other techniques for views of the deeper vitreous, retina, and optic nerve are described below.
Special dyes such as fluorescein to detect ulcerations or rose bengal and lissamine green to detect dead and dying cells on the ocular surface may be used. With fluorescein, a cobalt filter is swung into place to delineate clearly the areas of epithelial absence. A white or green light is used for rose bengal staining. A white light with or without a red filter is used for lissamine green staining.
The slitlamp beam may be widened to a full circle to illuminate the entire front of the eye (diffuse illumination) or narrowed to a tiny slit that will assist the examiner in determining the thickness of various anterior segment structures. The tissue illuminated by the narrow beam is referred to as an optical section
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