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II. BASIC OPHTHALMOLOGIC EXAMINATION

The purpose of the ophthalmologic physical examination is to evaluate both the function and the anatomy of the two eyes. Function includes vision and nonvisual functions, such as eye movements and alignment. Anatomically, ocular problems can be subdivided into three areas: those of the adnexa (lids and periocular tissue), the globe, and the orbit.

VISION

Just as assessment of vital signs is a part of every physical examination, any ocular examination must include assessment of vision, regardless of whether vision is mentioned as part of the chief complaint. Good vision results from a combination of an intact neurologic visual pathway, a structurally healthy eye, and proper focus of the eye. An analogy might be made to a video camera, requiring a functioning cable connection to the monitor, a mechanically intact camera body, and a proper focus setting. In general, measurement of visual acuity is subjective rather than objective, since it requires responses on the part of the patient.

Refraction

The unaided distant focal point of the eye varies among normal individuals depending on the shape of the globe and the cornea (Figure 2-1). An emmetropic eye is naturally in optimal focus for distance vision. An ametropic eye (ie, one with myopia, hyperopia, or astigmatism) needs corrective lenses to be in proper focus for distance. This optical requirement is called refractive error. Refraction is the procedure by which this natural optical error is characterized and quantified (Figure 2-2) (see Chapter 20).

Refraction is often necessary to distinguish between blurred vision caused by refractive (ie, optical) error or by medical abnormalities of the visual system. Thus, in addition to being the basis for prescription of corrective glasses or contact lenses, refraction serves a diagnostic function.

Testing Central Vision

Vision can be divided into central vision and peripheral vision. Central visual acuity is measured with a display of different-sized targets shown at a standard distance from the eye. For example, the familiar "Snellen chart" is composed of a series of progressively smaller rows of random letters used to test distance vision. Each row is designated by a number corresponding to the distance, in feet or meters, from which a normal eye can read all the letters of the row. For example, the letters in the "40" row are large enough for the normal eye to see from 40 feet away.

By convention, vision can be measured either at a distance at 20 feet (6 meters) or at near, 14 inches away. For diagnostic purposes, distance acuity is the standard for comparison and is always tested separately for each eye. Acuity is scored as a set of two numbers (eg, "20/40"). The first number represents the testing distance in feet between the chart and the patient, and the second number represents the smallest row of letters that the patient's eye can read from the testing distance. 20/20 vision is normal; 20/60 vision indicates that the patient's eye can only read from 20 feet letters large enough for a normal eye to read from 60 feet.

Charts containing numerals can be used for patients not familiar with the English alphabet. The "illiterate E" chart is used to test small children or if there is a language barrier. "E" figures are randomly rotated in each of four different orientations throughout the chart. For each target, the patient is asked to point in the same direction as the three "bars" of the E (Figure 2-3). Most children can be tested in this manner beginning at about age 31/2.

Uncorrected visual acuity is measured without glasses or contact lenses. Corrected acuity means that these aids were worn. Since poor uncorrected distance acuity may simply be due to refractive (ie, focusing) error, corrected visual acuity is a more relevant assessment of ocular health.

Pinhole Test

If the patient needs glasses or if they are unavailable, the corrected acuity can be estimated by testing vision through a "pinhole." Refractive blur (eg, myopia, hyperopia, astigmatism) is caused by multiple misfocused rays entering through the pupil and reaching the retina. This prevents formation of a sharply focused image.

Viewing the Snellen chart through a placard of multiple tiny pinhole-sized openings prevents most of the misfocused rays from entering the eye. Only a few centrally aligned focused rays will reach the retina, resulting in a sharper image. In this manner, the patient may be able to read within one or two lines of what would be possible if proper corrective glasses were being used.

Testing Poor Vision

The patient unable to read the largest letter on the chart (eg, the "20/200" letter) should be moved closer to the chart until that letter can be read. The distance from the chart is then recorded as the first number. Visual acuity of "5/200" means that the patient can just make out the largest letter from a distance of 5 feet. An eye unable to read any letters is tested by the ability to count fingers. A notation on the chart that reads "CF at 2 ft" indicates that the eye was able to count fingers held 2 feet away but not farther away.

If counting fingers is not possible, the eye may be able to detect a hand moving vertically or horizontally [hand motions (HM) vision]. The next lower level of vision would be the ability to perceive light [light perception (LP)]. An eye that cannot perceive light is considered totally blind [no light perception (NLP)].

Testing Peripheral Vision

Because it is much grosser than central acuity, side vision is harder to test quantitatively. Specialized tests described in the next section are used when peripheral vision measurements are needed, such as for the diagnosis of early glaucoma.

Gross screening of the peripheral field of vision can be quickly performed using confrontation testing. Since the visual fields of the two eyes overlap, each eye must be tested separately. The patient is seated facing the examiner several feet away and begins by covering the left eye while the right eye fixes on the examiner's left eye.

The examiner then briefly shows several fingers of one hand (usually one, two, or four fingers) peripherally in one of the four quadrants. The patient must identify the number of fingers flashed while maintaining straight-ahead fixation. Since patient and examiner are staring eye to eye, any loss of fixation by the patient will be noticed. The upper and lower temporal and the upper and lower nasal quadrants are all tested in this fashion for each eye.

If the examiner closes the right eye while the patient covers the left eye-and if the targets (fingers) are presented at a distance halfway between the patient and the examiner-their respective peripheral fields should be the same. This allows comparison of the patient's field with the examiner's own. Consistent errors indicate gross deficiencies in the quadrant tested, as seen with retinal detachments, optic nerve abnormalities, and ischemic or mass injuries to the intracranial visual pathway. Since dense visual field abnormalities are often asymptomatic, confrontation testing should be included in complete ophthalmologic examinations.

A subtle form of right or left homonymous hemianopia may exist that can only be elicited by simultaneously presenting targets on both sides of the midline-not when targets are presented on one side at a time. To perform simultaneous confrontation testing, the examiner holds both hands out peripherally, one on each side. The patient must signify on which side (right, left, or both) the examiner is intermittently wiggling the fingers. Surprisingly, a patient with a mild left hemianopia may still be able to detect one hand wiggling fingers to the left side and may fail to see them (to the left) only when the examiner is simultaneously wiggling the fingers on both hands. This interesting finding indicates partial or relative inattention to the left side as both sides are being equally-and simultaneously-stimulated.

More sophisticated means of visual field testing are discussed later in this chapter.

PUPILS

Basic Examination

The pupils should appear symmetric, and each one should be examined for size, shape (circular or irregular), and reactivity to both light and accommodation. Pupillary abnormalities may be due to (1) neurologic disease, (2) acute intraocular inflammation causing either spasm or atony of the pupillary sphincter, (3) previous inflammation causing adhesions of the iris, (4) prior surgical alteration, (5) the effect of systemic or eye medications, and (6) benign variations of normal.

To avoid accommodation, the patient is asked to stare in the distance as a penlight is directed toward each eye. Dim lighting conditions help to accentuate the pupillary response and may best demonstrate an abnormally small pupil. Likewise, an abnormally large pupil may be more apparent in brighter background illumination. The direct response to light refers to constriction of the illuminated pupil. The reaction may be graded as either brisk or sluggish. Normally, a consensual constriction will simultaneously occur in the opposite nonilluminated pupil. This is usually a slightly weaker response. The neuroanatomy of the pupillary pathway is discussed in Chapter 14.

Swinging Penlight Test for Marcus Gunn Pupil

As a light is swung back and forth in front of the two pupils, one can compare the direct and consensual reactions of each pupil. Since the direct reaction is usually stronger than the consensual, each pupil as the light falls directly on it should immediately constrict slightly more. Start by shining the light into the right eye, causing consensual constriction of the left pupil. As the light is then swung toward the left eye, the left pupil should constrict slightly more due to the direct light response. The right pupil should behave similarly as the light is swung back toward the right eye.

If the afferent conduction of light in the left optic nerve is impaired as a consequence of disease, the left pupil will have a weak direct response but its consensual efferent response will remain unchanged. As the light is swung from the right to the left eye, the left pupil will then paradoxically widen (since its abnormal direct response is weaker than the consensual response initiated by the healthy right optic nerve). This phenomenon is called a Marcus Gunn pupil, or relative afferent pupillary defect, since the paradoxic dilation in response to direct illumination occurs in the eye with the abnormal afferent pathway (ie, optic nerve or retina). Because the Marcus Gunn pupil still reacts and is often of normal size, the swinging flashlight test may be the only means of demonstrating it.

Marcus Gunn pupil is further discussed and illustrated in Chapter 14.

OCULAR MOTILITY

The objective of ocular motility testing is to evaluate the alignment of the eyes and their movements, both individually ("ductions") and in tandem ("versions"). A more complete discussion of motility testing and abnormalities is presented in Chapter 12.

Testing Alignment

Normal patients have binocular vision. Since each eye generates a visual image separate from and independent of that of the other eye, the brain must be able to fuse the two images in order to avoid "double vision." This is achieved by having each eye positioned so that both foveas are simultaneously fixating on the object of regard.

A simple test of binocular alignment is performed by having the patient look toward a penlight held several feet away. A pinpoint light reflection, or "reflex," should appear on each cornea and should be centered over each pupil if the two eyes are straight in their alignment. If the eye positions are convergent, such that one eye points inward ("esotropia"), the light reflex will appear temporal to the pupil in that eye. If the eyes are divergent, such that one eye points outward ("exotropia"), the light reflex will be located more nasally in that eye. This test can be used with infants.

The cover test (see Figure 12-3) is a more accurate method of verifying normal ocular alignment. The test requires good vision in both eyes. The patient is asked to gaze at a distant target with both eyes open. If both eyes are fixating together on the target, covering one eye should not affect the position or continued fixation of the other eye.

To perform the test, the examiner suddenly covers one eye and carefully watches to see that the second eye does not move (indicating that it was fixating on the same target already). If the second eye was not identically aligned but was instead turned abnormally inward or outward, it could not have been simultaneously fixating on the target. Thus, it will have to quickly move to find the target once the previously fixating eye is covered. Fixation of each eye is tested in turn.

An abnormal cover test is expected in patients with diplopia. However, diplopia is not always present in many patients with long-standing ocular malalignment. When the test is abnormal, prism lenses of different power can be used to neutralize the refixation movement of the misaligned eye. In this way, the amount of eye deviation can be quantified based on the amount of prism power needed. A more complete discussion of this test and its variations is presented in Chapter 12.

Testing Extraocular Movements

The patient is asked to follow a target with both eyes as it is moved in each of the four cardinal directions of gaze. The examiner notes the speed, smoothness, range, and symmetry of movements and observes for unsteadiness of fixation (eg, nystagmus).

Impairment of eye movements can be due to neurologic problems (eg, cranial nerve palsy), primary extraocular muscular weakness (eg, myasthenia gravis), or mechanical constraints within the orbit limiting rotation of the globe (eg, orbital floor fracture with entrapment of the inferior rectus muscle). If the amount of deviation of ocular alignment is the same in all directions of gaze, is called "comitant." It is "incomitant" if the amount of deviation varies with the direction of gaze.

EXTERNAL EXAMINATION

Before studying the eye under magnification, a general external examination of the ocular adnexa (eyelids and periocular area) is performed. Skin lesions, growths, and inflammatory signs such as swelling, erythema, warmth, and tenderness are evaluated by gross inspection and palpation.

The positions of the eyelids are checked for abnormalities such as ptosis or lid retraction. Asymmetry can be quantified by measuring the central width (in millimeters) of the "palpebral fissure"-the space between the upper and lower lid margins. Abnormal motor function of the lids, such as impairment of upper lid elevation or forceful lid closure, may be due to either neurologic or primary muscular abnormalities.

Gross malposition of the globe, such as proptosis, may be seen with certain orbital diseases. Palpation of the bony orbital rim and periocular soft tissue should always be done in instances of suspected orbital trauma, infection, or neoplasm. The general facial examination may contribute other pertinent information as well. Depending on the circumstances, checking for enlarged preauricular lymph nodes, sinus tenderness, temporal artery prominence, or skin or mucous membrane abnormalities may be diagnostically relevant.

SLITLAMP EXAMINATION

Basic Slitlamp Biomicroscopy

The slitlamp (Figure 2-4) is a table-mounted binocular microscope with a special adjustable illumination source attached. A linear slit beam of incandescent light is projected onto the globe, illuminating an optical cross section of the eye (Figure 2-5). The angle of illumination can be varied along with the width, length, and intensity of the light beam. The magnification can be adjusted as well (normally 10× to 16× power). Since the slitlamp is a binocular microscope, the view is "stereoscopic," or three-dimensional.

The patient is seated while being examined, and the head is stabilized by an adjustable chin rest and forehead strap. Using the slitlamp alone, the anterior half of the globe-the "anterior segment"-can be visualized. Details of the lid margins and lashes, the palpebral and bulbar conjunctival surfaces, the tear film and cornea, the iris, and the aqueous can be studied. Through a dilated pupil, the crystalline lens and the anterior vitreous can be examined as well.

Because the slit beam of light provides an optical cross section of the eye, the precise anteroposterior location of abnormalities can be determined within each of the clear ocular structures (eg, cornea, lens, vitreous body). The highest magnification setting is sufficient to show the abnormal presence of cells within the aqueous, such as red or white blood cells or pigment granules. Aqueous turbidity, called "flare," resulting from increased protein concentration can be detected in the presence of intraocular inflammation. Normal aqueous is optically clear, without cells or flare.

Adjunctive Slitlamp Techniques

The eye examination with the slitlamp is supplemented by the use of various techniques. Tonometry is discussed separately in a subsequent section.

A. Lid Eversion:

Lid eversion to examine the undersurface of the upper lid can be performed either at the slitlamp or without the aid of that instrument. It should always be done if the presence of a foreign body is suspected. A semirigid plate of cartilage called the tarsus gives each lid its contour and shape. In the upper lid, the superior edge of the tarsus lies centrally about 8-9 mm above the lashes. On the undersurface of the lid, it is covered by the tarsal palpebral conjunctiva.

Following topical anesthesia, the patient is positioned at the slitlamp and instructed to look down. The examiner gently grasps the upper lashes with the thumb and index finger of one hand while using the other hand to position an applicator handle just above the superior edge of the tarsus (Figure 2-6). The lid is everted by applying slight downward pressure with the applicator as the lash margin is simultaneously lifted. The patient continues to look down, and the lashes are held pinned to the skin overlying the superior orbital rim, as the applicator is withdrawn. The tarsal conjunctiva is then examined under magnification. To undo eversion the lid margin is gently stroked downward as the patient looks up.

B. Fluorescein Staining:

Fluorescein is a specialized dye that stains the cornea and highlights any irregularities of its epithelial surface. Sterile paper strips containing fluorescein are wetted and touched against the inner surface of the lower lid, instilling the yellowish dye into the tear film. The illuminating light of the slitlamp is made blue with a filter, causing the dye to fluoresce.

A uniform film of dye should cover the normal cornea. If the corneal surface is abnormal, excessive amounts of dye will absorb into or collect within the affected area. Abnormalities can range from tiny punctate dots, such as those resulting from excessive dryness or ultraviolet light damage, to large geographic defects in the epithelium such as those seen in corneal abrasions or infectious ulcers.

C. Special Lenses:

Special examining lenses can expand and further magnify the slitlamp examination of the eye's interior. A goniolens (Figure 2-7) provides visualization of the anterior chamber "angle" formed by the iridocorneal junction. Other lenses placed on or in front of the dilated eye allow slitlamp evaluation of the posterior half of the globe's interior-the "posterior segment." Since the slitlamp is a binocular microscope, these lenses provide a magnified three-dimensional view of the posterior vitreous, the fundus, and the disk. Examples are the Goldmann-style three-mirror lens (Figure 2-7), the Hruby lens, and the Volk-style 90-diopter biconvex lens.

D. Special Attachments:

Special attachments to the slitlamp allow it to be used with a number of techniques requiring microscopic visualization. Special camera bodies can be attached for photographic documentation and for special applications such as corneal endothelial cell studies. Special instruments for study of visual potential require attachment to the slitlamp. Finally, laser sources are attached to a slitlamp to allow microscopic visualization and control of eye treatment.

TONOMETRY

The globe can be thought of as an enclosed compartment through which there is a constant circulation of aqueous humor. This fluid maintains the shape and a relatively uniform pressure within the globe. Tonometry is the method of measuring the intraocular fluid pressure using calibrated instruments that indent or flatten the corneal apex. As the eye becomes firmer, a greater force is required to cause the same amount of indentation. Pressures between 10 and 24 mm Hg are considered within the normal range.

Two common types of tonometry are the Schiotz and applanation methods. The Schiotz tonometer measures the amount of corneal indentation produced by a preset weight or force. The softer the eye, the more a given force will be able to indent the cornea. As the eye becomes firmer, less corneal indentation will result from the same amount of force.

In contrast to the Schiotz tonometer, the applanation tonometer can vary and measure the amount of force applied. The ocular pressure is determined by the force required to flatten the cornea by a predetermined standard amount. At lower intraocular pressures, less tonometer force is needed to achieve the standard degree of corneal flattening than at higher intraocular pressures. Since both methods employ devices that touch the patient's cornea, they require topical anesthetic and disinfection of the instrument tip prior to use. (Tonometer disinfection techniques are discussed in Chapter 21.) While retracting the lids with any method of tonometry, care must be taken to avoid pressing on the globe and artificially increasing its pressure.

Schiotz Tonometry

The advantage of this method is that it is simple, requiring only a portable hand-held instrument-the Schiotz tonometer (Figure 2-8). It can be used in any clinic or emergency room setting, at the hospital bedside, or in the operating room. It is a practical device for the nonophthalmologist, who might use it to screen patients for glaucoma or to diagnose acute angle closure glaucoma in an emergency situation.

The three separate components of the tonometer should be cleaned, assembled, and then disassembled with each use. The tonometer body consists of a cylindric hollow plunger barrel fixed to a measuring scale with an indicator needle. The attached handle, which can slide along the outside of the cylindric barrel, supports the weight of the tonometer when it is not resting on the eye. The plunger is a slender blunt-tipped rod that is inserted into the barrel shaft, where it can slide back and forth. One end will touch the cornea, while the other end will deflect the needle of the measuring scale. The 5.5 g weight screwed onto the upper end of the plunger (farthest from the patient) keeps it from falling out of the shaft.

The patient is placed supine, and topical anesthetic is instilled into each eye. As the patient looks straight ahead, the lids are kept gently opened by lightly retracting the skin against the bony orbital rims. The tonometer is lowered with the other hand until the concave "end" of the barrel balances on the cornea (Figure 2-9). With a force determined by the attached weight, the blunt protruding plunger will press into and slightly indent the central cornea. The corneal resistance, which is proportionate to the intraocular pressure, will displace the plunger upward. As the plunger slides upward within the barrel, it will deflect the needle on the scale. The higher the intraocular pressure, the greater the corneal resistance to indentation, the more the plunger will be displaced upward, and the farther the needle will be deflected along the calibrated scale.

A conversion chart is used to translate the reading from the scale into millimeters of mercury. If the eye is firm, additional weights (7.5 g and 10 g) can be added to the plunger to increase the force brought to bear on the cornea. Calibration is checked by placing the tonometer on a "cornea-shaped" metal block that should deflect the needle maximally so that it aligns with the "0" end of the scale.

Applanation Tonometry

The Goldmann applanation tonometer (Figure 2-10) is attached to the slitlamp and measures the amount of force required to flatten the corneal apex by a standard amount. The higher the intraocular pressure, the greater the force required. Since Goldmann applanation tonometer is a more accurate method than Schiotz tonometry, it is preferred by ophthalmologists.

Following topical anesthesia and instillation of fluorescein, the patient is positioned at the slitlamp and the tonometer is swung into place. To visualize the fluorescein, the cobalt blue filter is used with the brightest illumination setting. After grossly aligning the tonometer in front of the cornea, the examiner looks through the slitlamp ocular just as the tip contacts the cornea. A manually controlled counterbalanced spring varies the force applied by the tonometer tip.

Upon contact, the tonometer tip flattens the central cornea and produces a thin circular outline of fluorescein. A prism in the tip visually splits this circle into two semicircles that appear green while viewed through the slitlamp oculars. The tonometer force is adjusted manually until the two semicircles just overlap, as shown in Figure 2-11. This visual end point indicates that the cornea has been flattened by the set standard amount. The amount of force required to do this is translated by the scale into a pressure reading in millimeters of mercury.

A portable electronic applanation tonometer, the Tono-Pen, has been developed. Although accurate, it requires daily recalibration. It is more expensive than the Schiotz tonometer and therefore is less often found in clinics and emergency departments. The Perkins tonometer is a portable mechanical applanation tonometer with a mechanism similar to the Goldmann tonometer. The pneumatotonometer is another applanation tonometer, particularly useful when the cornea has an irregular surface.

Noncontact Tonometry

The noncontact ("air-puff") tonometer is not as accurate as applanation tonometers. A small puff of air is blown against the cornea. The air rebounding from the corneal surface hits a pressure-sensing membrane in the instrument. This method does not require anesthetic drops, since no instrument touches the eye. Thus, it can be more easily used by technicians and is useful in screening programs.

DIAGNOSTIC MEDICATIONS

Topical Anesthetics

Eye drops such as proparacaine, tetracaine, and benoxinate provide rapid onset, short-acting topical anesthesia of the cornea, and conjunctiva. They are used prior to ocular contact with diagnostic lenses and instruments such as the tonometer. Other diagnostic manipulations utilizing topical anesthetics will be discussed later. These include corneal and conjunctival scrapings, lacrimal canalicular and punctal probing, and scleral depression.

Mydriatic (Dilating) Drops

The pupil can be pharmacologically dilated by either stimulating the iris dilator muscle with a sympathomimetic agent (eg, 2.5% phenylephrine) or by inhibiting the sphincter muscle with an anticholinergic eye drop (eg, 0.5% or 1% tropicamide). Anticholinergic medications also inhibit accommodation, an effect called "cycloplegia." This may aid the process of refraction but causes further inconvenience for the patient. Therefore, drops with the shortest duration of action (usually several hours) are used for diagnostic applications. Combining drops from both pharmacologic classes produces the fastest onset (15-20 minutes) and widest dilation.

Because dilation can cause a small rise in intraocular pressure, tonometry should always be performed before these drops are instilled. There is also a risk of precipitating an attack of acute angle-closure glaucoma if the patient has preexisting narrow anterior chamber angles (between the iris and cornea). Such an eye can be identified using the technique illustrated in Figure Figure 2-4. Finally, excessive instillation of these drops should be avoided because of the systemic absorption that can occur through the nasopharyngeal mucous membranes following lacrimal drainage.

A more complete discussion of diagnostic drops is found in Chapter 3.

DIRECT OPHTHALMOSCOPY

Instrumentation

The hand-held direct ophthalmoscope provides a magnified (15×) monocular image of the ocular media and fundus. Because of its portability and the detailed view of the disk and retinal vasculature it provides, direct ophthalmoscopy is a standard part of the general medical examination as well as the ophthalmologic examination.

Darkening the room usually causes enough natural pupillary dilation to allow evaluation of the central fundus, including the disk, the macula, and the proximal retinal vasculature. Pharmacologically dilating the pupil greatly enhances the view and permits a more extensive examination of the peripheral retina. The fundus examination is also optimized by holding the ophthalmoscope as close to the patient's pupil as possible (approximately 1-2 inches), just as one can see more through a keyhole by getting as close to it as possible. This requires using the examiner's right eye and hand to examine the patient's right eye and the left eye and hand to examine the patient's left eye (Figure 2-12). If the examiner wears spectacles, they can either be left on or off.

The intensity, color, and spot size of the illuminating light can be adjusted as well as the ophthalmoscope's point of focus. The latter is changed using a wheel of progressively higher power lenses that the examiner dials into place. These lenses are sequentially arranged and numbered according to their power in units called "diopters." The descending scale of black numbers designates the (+) converging lenses, whereas the ascending scale of red numbers designates the (-) divergent lenses.

As one dials this focusing wheel counterclockwise from high plus (+) lenses down to zero and on through increasingly minus (-) lenses, the focus is shifted progressively farther away from the ophthalmoscope toward the patient. By starting with a higher (+) lens and dialing in this direction, the examiner will eventually bring the cornea and iris into focus, followed several steps later by the retina. The refractive error (ie, "prescriptions") of the patient's and the examiner's eyes will determine the lens power needed to bring the fundus into optimal focus.

Fundus Examination

The primary value of the direct ophthalmoscope is in examination of the fundus (Figure 2-13). The view may be impaired by cloudy ocular media, such as a cataract, or by insufficient pupillary dilation. As the patient fixates on a distant target with the opposite eye, the examiner first brings retinal details into sharp focus. Since the retinal vessels all arise from the disk, the latter is located by following any major vascular branch back to this common origin. At this point, the ophthalmoscope beam will be aimed slightly nasal to the patient's line of vision, or "visual axis." One should study the shape, size, and color of the disk, the distinctness of its margins, and the size of the pale central "physiologic cup." The ratio of cup size to disk size is of diagnostic importance in glaucoma (Figures 2-14 and 2-15).

The macular area (Figure 2-13) is located approximately two "disk diameters" temporal to the edge of the disk. A small pinpoint white reflection or "reflex" marks the central fovea. This is surrounded by a more darkly pigmented and poorly circumscribed area called the macula. The retinal vascular branches approach from all sides but stop short of the fovea. Thus, its location can be confirmed by the focal absence of retinal vessels or by asking the patient to stare directly into the light.

The major retinal vessels are then examined and followed as far distally as possible in each of the four quadrants (superior, inferior, temporal, and nasal). The veins are darker and wider than their paired arteries. The vessels are examined for color, tortuosity, and caliber as well as for associated abnormalities such as aneurysms, hemorrhages, or exudates. Sizes and distances within the fundus are often measured in "disk diameters (DD)." (The typical optic disk is generally 1.5-2 mm in diameter.) Thus, one might describe a "1 DD area of hemorrhage located 2.5 DD inferotemporal to the fovea."

Dilating the pupil pharmacologically enables more of the periphery to be visualized. The patient is asked to look in the direction of the quadrant one wishes to examine. Thus, the temporal retina of the right eye is seen when the patient looks temporally to the right, while the superior retina is seen when the patient looks up. This principle works because as the globe rotates about a point in the center of the eye, the retina and the cornea move in opposite directions. As the patient looks up, the superior retina rotates downward into the examiner's line of vision.

The spot size and color of the illuminating light can be varied. If the pupil is well dilated, the large spot size of light affords the widest area of illumination. With a smaller pupil, however, much of this light would be reflected back toward the examiner's eye by the patient's iris, interfering with the view. For this reason, the smaller spot size of light is selected for undilated pupils. The green "red-free" filter assists in the examination of the retinal vasculature and the subtle striations of the nerve fiber layer as they course toward the disk (see Figure 14-6).

Anterior Segment Examination

As discussed earlier, the direct ophthalmoscope can be focused more anteriorly so as to provide a magnified view of the conjunctiva, cornea, and iris. The slitlamp allows a far superior and more magnified examination of these areas, but it is not portable and may be unavailable.

Red Reflex Examination

If the illuminating light is aligned directly along the visual axis of a dilated pupil, the pupillary space will appear as a homogeneous bright reddish-orange color. This so-called red reflex is a reflection of the fundus color (actually the combined color of the choroidal vasculature and pigmentation) back through clear ocular media-the vitreous, lens, aqueous, and cornea. The red reflex is best observed by holding the ophthalmoscope at arm's length from the patient as he looks toward the illuminating light. By dialing the lens wheel, the bright red reflex will appear when the ophthalmoscope is focused on the plane of the pupil.

Any opacity located along this central optical pathway will block all or part of this bright reflex and appear as a dark spot or shadow. If a small opacity is seen, have the patient look momentarily away and then back toward the light. If the opacity is still moving or floating, it is located within the vitreous (eg, small hemorrhage). If it is stationary, it is probably in the lens (eg, focal cataract) or on the cornea (eg, scar). Less red reflex is visible with a small pupil, limiting the usefulness of this test.

INDIRECT OPHTHALMOSCOPY

Instrumentation

The binocular indirect ophthalmoscope (Figure 2-16) complements and supplements the direct ophthalmoscopic examination. Since it requires wide pupillary dilation and is difficult to learn, this technique is used primarily by ophthalmologists. The patient can be examined while seated, but the supine position is preferable.

The indirect ophthalmoscope is worn on the examiner's head and allows binocular viewing through a set of lenses of fixed power. A bright adjustable light source attached to the headband is directed toward the patient's eye. As with direct ophthalmoscopy, the patient is told to look in the direction of the quadrant being examined. A convex lens is hand-held several inches from the patient's eye in precise orientation so as to simultaneously focus light onto the retina and an image of the retina in midair between the patient and the examiner. Using the preset head-mounted ophthalmoscope lenses, the examiner can then "focus on" and visualize this midair image of the retina.

Comparison of Indirect & Direct Ophthalmoscopy

Indirect ophthalmoscopy is so called because one is viewing an "image" of the retina formed by a hand-held "condensing lens." In contrast, direct ophthalmoscopy allows one to focus on the retina itself. Compared with the direct ophthalmoscope (15× magnification), indirect ophthalmoscopy provides a much wider field of view (Figure 2-17) with less overall magnification (approximately 3.5× using a standard 20-diopter hand-held condensing lens). Thus, it presents a wide panoramic fundus view from which specific areas can be selectively studied under higher magnification using either the direct ophthalmoscope or the slitlamp with special auxiliary lenses.

Indirect ophthalmoscopy has three distinct advantages over direct ophthalmoscopy. One is the brighter light source that permits much better visualization through cloudy media. A second advantage is that by using both eyes, the examiner enjoys a stereoscopic view, allowing visualization of elevated masses or retinal detachment in three dimensions. Finally, indirect ophthalmoscopy can be used to examine the entire retina even out to its extreme periphery, the ora serrata. This is possible for two reasons. Optical distortions caused by looking through the peripheral lens and cornea interfere very little with the indirect ophthalmoscopic examination, compared with the direct ophthalmoscope. In addition, the adjunct technique of scleral depression can be used.

Scleral depression (Figure 2-18) is performed as the peripheral retina is being examined with the indirect ophthalmoscope. A smooth, thin metal probe is used to gently indent the globe externally through the lids at a point just behind the corneoscleral junction (limbus). As this is done, the ora serrata and peripheral retina are pushed internally into the examiner's line of view. By depressing around the entire circumference, the peripheral retina can be viewed in its entirety.

Because of all of these advantages, indirect ophthalmoscopy is used preoperatively and intraoperatively in the evaluation and surgical repair of retinal detachments. A minor disadvantage of indirect ophthalmoscopy is that it provides an inverted image of the fundus, which requires a mental adjustment on the examiner's part. Its brighter light source can also be more uncomfortable for the patient.

EYE EXAMINATION BY THE NONOPHTHALMOLOGIST

The preceding sequence of tests would comprise a complete routine or diagnostic ophthalmologic evaluation. A general medical examination would often include many of these same testing techniques.

Assessment of pupils, extraocular movements, and confrontation visual fields is part of any complete neurologic assessment. Direct ophthalmoscopy should always be performed to assess the appearance of the disk and retinal vessels. Separately testing the visual acuity of each eye (particularly with children) may uncover either a refractive or a medical cause of decreased vision. Finally, screening tonometry measurements using the Schiotz tonometer may detect the asymptomatic elevated intraocular pressure of glaucoma, a prevalent condition among the elderly.

The three most common preventable causes of permanent visual loss in developed nations are amblyopia, diabetic retinopathy, and glaucoma. All can remain asymptomatic while the opportunity for preventive measures is gradually lost. During this time, the pediatrician or general medical practitioner may be the only physician the patient visits.

By testing children for visual acuity in each eye, examining and referring diabetics for regular dilated fundus ophthalmoscopy, and referring patients with suspicious discs or tonometry readings to the ophthalmologist, the nonophthalmologist may indeed be the one who truly "saves" that patient's eyesight. This represents both an important opportunity and responsibility for every primary care physician.

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