Thomas R. Friberg
INTRODUCTION
The essentials of the clinical examination techniques used to evaluate the ocular fundus have changed little over the past decade. While additional ancillary testing and methods have been developed, a thorough funduscopic examination remains a mainstay of clinical practice. Excellent and efficient retinal examination skills are critical to virtually all ophthalmologists, and this chapter explains the principles of this evaluation.
A thorough examination of the ocular fundus requires excellent powers of observation and clinical experience with ophthalmoscopy and biomicroscopy. Some individuals have almost a natural ability to use these specialized instruments to discover and document subtle retinal abnormalities. Most have considerably more difficulty, however. For instance, a novice might struggle and then fially see scattered retinal hemorrhages in the fundus of a patient's eye but then fail to note the location of the hemorrhages with respect to retinal landmarks. With practice, proper use of the instrumentation can be learned by almost anyone. Unfortunately, some clinicians never become good observers and remain unaware of the important distinction between seeing an abnormality and observing it.[1] Observation is a high-level activity, requiring mental processing and categorization of what is seen.
One method of improving observational skills is to use an examination routine whereby different regions of the fundus are evaluated in a specific sequence. For instance, an ophthalmologist might begin by examining the optic nerve; move on to the temporal vascular arcades, macula, and nasal retina; and fiish by evaluating the equatorial and peripheral retina. By using an organized system of fundus evaluation, diagnostic oversights will be minimized.
PUPILLARY DILATATION
Examination of the fundus and especially the retinal periphery is greatly facilitated by a well-dilated pupil. Suggested mydriatic agents include 1% tropicamide (Mydriacyl) and 2.5% phenylephrine hydrochloride drops (Mydfrin), one drop of each in both eyes. Instillation of a topical anesthetic, such as 0.5% proparacaine hydrochloride, before instilling the dilating drops promotes more rapid mydriasis, as the anesthetic prevents reflex tearing and subsequent dilution of the mydriatic agent. Most patients' pupils dilate adequately after 20-30 min using this regimen. However, darkly pigmented irises dilate more slowly and remain dilated longer than do lightly colored irises, probably because the mydriatic agents are bound to the iris melanin and are released gradually.[2] After the examination, mydriasis can be reversed more quickly by medications designed for this purpose such as 0.5% dapiprazole hydrochloride (Rev-Eyes, Storz Ophthalmics).
DIRECT OPHTHALMOSCOPE
To examine the ocular fundus, specialized instruments are necessary. The simplest is the direct ophthalmoscope, which is in essence a miniature flashlight held very close to the patient's eye and shined through the pupil (Fig. 127.1). The fundus is viewed monocularly through a small peephole located just above the illumination source of the instrument, producing an upright virtual image that magnifies the area of interest ?15 times.[3] This ophthalmoscope also has a dial containing neutralizing lenses, which is rotated to achieve the clearest retinal image.
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FIGURE 127.1 The direct ophthalmoscope is used like a flashlight to illuminate the patient's eye while the examiner looks through a small peephole. The left eye of the examiner is used to study the fundus of the patient's left eye. Conversely, the right eye is used to examine the patient's right eye. |
Although magnification and resolution are quite good with the direct ophthalmoscope, difficulties inherent with its use include lack of stereopsis, inadequate illumination in the presence of media opacities, the necessity of placing the examiner's face in close proximity to the patient's face, a retinal image covering only ?8° of the fundus,[3] and severe degradation of the image when significant lens opacities are present.[4,5] It may be impossible to adequately examine eyes with a high degree of astigmatism or spherical ametropia using this instrument. Furthermore, the direct ophthalmoscope does not allow an undistorted view of the peripheral retina, limiting its use to visualizing the posterior retina only.
Largely because of its portability and simplicity, the direct ophthalmoscope is a useful screening device for the general practitioner who may wish to rule out papilledema, macular degeneration, or hypertensive or diabetic retinopathy. Many ophthalmologists have become facile with binocular slit-lamp biomicroscopes and specialized contact and noncontact fundus examination lenses, however, and observation of the ocular fundus with the direct ophthalmoscope is often redundant and unnecessary in the office setting.
BINOCULAR INDIRECT OPHTHALMOSCOPE
The binocular indirect ophthalmoscope, in conjunction with a high-quality aspherical hand-held lens, has become the indispensable standard for the proper examination of the fundus, especially when evaluating areas located outside the posterior pole (Fig. 127.2). Introduced by Schepens,[6] binocular indirect ophthalmoscopy offers a typical field of view of 25° or more and excellent resolution of fundus details.[5] Stereopsis is enhanced, allowing the examiner to detect nuances of elevation and excavation of the retinal contour. The device is portable, permits evaluation of the retina with the patient in either the sitting or the supine position, and quickly gives a view of relatively large retinal areas. Furthermore, binocular indirect ophthalmoscopy has been incorporated into laser delivery systems, providing an important alternative to slit-lamp photocoagulation systems.[7]
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FIGURE 127.2 (a) An example of a binocular indirect ophthalmoscope. The coronal and sagittal headbands and the interpupillary distance are adjustable. A transformer provides power for illumination. (b) With the indirect ophthalmoscope adjusted and in place on the head, the examiner holds a lens over the patient's eye to form a retinal image. |
Although an examination of the posterior fundus using the direct ophthalmoscope can be performed after a minimum of instruction, effective use of the indirect ophthalmoscope requires several hours of practice. The image formed by the indirect ophthalmoscope is physically located above the plane of the lens and, as with all real images, is inverted (Fig. 127.3). This inversion creates considerable problems for the novice, especially when he or she tries to draw the observed abnormalities. In addition, the alignment of the indirect ophthalmoscope's illumination beam, the hand-held lens, the patient's pupil, and the ophthalmoscope oculars is crucial to obtaining a sharp image. Hence, before examining patients, it is beneficial to examine a model eye (Mira, Waltham, MA) manufactured for the purpose of practicing indirect ophthalmoscopy (Fig. 127.4). Another aid to learning this important skill is a specially designed interactive computer program contained on a compact disk (CD-ROM) ('Indirect Ophthalmoscopy and Fundus Drawing', © 1996 by The New York Eye and Ear Infirmary).
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FIGURE 127.3 With indirect ophthalmoscopy, a real, inverted image of the patient's fundus is formed in a plane located just above the hand-held lens. |
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FIGURE 127.4 Pliable model eyes with realistic fundus details are valuable when learning binocular indirect ophthalmoscopy. They can also be indented to simulate scleral depression. |
EXAMINATION TECHNIQUE WITH THE INDIRECT OPHTHALMOSCOPE
To use the indirect ophthalmoscope, the examiner first adjusts the headbands so that the scope fits comfortably. A lightweight instrument is preferred. The illumination beam is turned on, and the interpupillary distance of the eyepieces is adjusted so that both eyes can see the examiner's outstretched hand simultaneously. Next, the knob on the headset that controls the location of the illumination beam is rotated until the 'footprint' of the light illuminates the superior portion of the outstretched hand. The head and body of the examiner should be positioned so that her or his viewing axis is in a line with the center of the patient's dilated pupil. When this is done, a bright red reflex should appear through the oculars of the indirect ophthalmoscope.
Once a red reflex is visualized, the indirect hand-held lens is interposed along the imaginary line drawn between the examiner's pupil and the patient's pupil. The indirect lens should be held between the thumb and the forefiger of either hand and positioned a few centimeters from the patient's eye. The lens surface is oriented almost perpendicular to the illumination beam. To minimize problems with light reflections, the lens should be tilted very slightly, with the most convex side of the indirect lens facing the examiner (Fig. 127.5).
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FIGURE 127.5 The most convex side of the hand-held lens is placed so that it faces the examiner. By tilting the lens very slightly, the bright light reflexes produced by the lens surfaces (left) do not enter the examiner's eye. |
To steady the lens, the fourth and fifth digits of the hand holding the lens should rest on the patient's face during the examination. The distance between the patient's eye and the lens should otherwise be as great as possible. To optimize the view, the lens is slowly moved toward or away from the patient's eye. When the lens is properly positioned, the image of the patient's fundus fills the lens and is in sharp focus. To examine different areas of the fundus, the viewing axis of the indirect ophthalmoscope, the center of the hand-held lens, and the patient's pupil must remain in alignment. A useful aid is to envision a solid rod representing the viewing axis of the indirect scope to which the center of the hand-held lens is fixed. This imaginary rod pivots at the center of the patient's pupil when the entire extent of the retina is examined (Fig. 127.6). Indirect ophthalmoscopy is facilitated by having the patient in the supine position with the examiner standing, as this allows easy access to all retinal regions.
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FIGURE 127.6 To view different regions of the fundus, the examiner moves his or her head and the hand-held lens as if there were an imaginary rod connecting the center of the patient's pupil, the center of the lens, and a point midway between the eyepieces of the indirect ophthalmoscope. The examiner then pivots around the central pupil to view the complete fundus. |
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Key Features |
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Many patients, especially those with light complexions, are photophobic when examined with bright light. Hence, the illumination level of the ophthalmoscope must be low enough to allow examination of the fundus without causing patient discomfort and resultant squeezing of the eyelids. Conversely, the light must be sufficiently bright to allow observation of retinal details. For patient comfort, it is best to start with a dimmer light and increase its intensity as necessary.
The patient's eyelids should be held open with the examiner's figers or a lid speculum during indirect ophthalmoscopy. Either the hand holding the lens or the free hand can be used for this purpose, depending on whether scleral depression is being performed. Although use of a lid speculum potentially frees up one of the examiner's hands, an irrigating balanced salt solution (BSS) must be periodically instilled to prevent corneal drying when a speculum is used.
CHOICE OF HAND-HELD LENS
Numerous lenses are available for binocular indirect ophthalmoscopy. When selecting a lens, recall that angular magnification of fundus details is inversely proportional to the power of the hand-held lens. For example, a 20-D lens will magnify the fundus details of an emmetropic eye ?2.3 times, whereas a 30-D lens magnifies it ?1.5 times.[8] A high-quality 20-D aspherical lens is widely used because it offers a good compromise between field of view and magnification. However, when viewing eyes with small pupils or eyes with hazy media, a 30- or 28-D lens is often a better choice for the beginner. The field of view of the lens is generally directly proportional to the lens power, with a 20-D aspherical lens providing about a 35° field.[3] Field of view is also a function of the diameter of the lens, with a larger field offered by a larger diameter lens. A comparison of field of view obtained when using a direct ophthalmoscope versus an indirect ophthalmoscope is shown in Figure 127.7.
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FIGURE 127.7 The field of view of the indirect ophthalmoscope using a 20-D lens (outer circle) is much larger than that provided by the direct ophthalmoscope (inner circle). However, the size of a given retinal lesion obtained using the direct ophthalmoscope appears commensurately bigger. |
SMALL-PUPIL INDIRECT OPHTHALMOSCOPES
Many indirect ophthalmoscopes incorporate a small pupil feature which facilitates the examination of eyes when the pupils dilate poorly or eyes that harbor focal media opacities. Typically, a small lever located under the eye pieces is moved in position to engage this feature. The lever physically places the illumination and visualization pathways closer together by moving a triangular prism. Such a feature is extremely useful and makes the instrument more versatile.
SCLERAL DEPRESSION
To view the total extent of the peripheral fundus of the emmetropic eye, the wall of the eye must be depressed inward toward the visual axis. This examination technique, called scleral depression, should not be attempted until one is first accomplished at obtaining a sharp image of the posterior pole. If one cannot reliably image the posterior segment, attempting to view the retinal periphery with scleral depression is usually futile as well as uncomfortable for the patient.
Several types of scleral depressors have been designed, and each has its advocates. The working end of most depressors consists of a metal shaft with an enlargement or crosspiece at the tip. Some depressors have a more elaborate construction with moving parts. Alternatively, one can simply use a cotton-tipped applicator pressed against the lids to accomplish the same goal, although the tip is too bulky for many patients.
Pressure is exerted on the globe by pressing gently on the patient's partially opened eyelid until the peripheral retina is brought into view (Fig. 127.8). If excessive pressure is used, the patient will become uncomfortable, squeeze the eyelids shut, and prevent the examination from proceeding. With practice, patient discomfort should be minimal. Typically, scleral depression of the entire 360° of the retinal periphery is easier to accomplish if the patient is in the supine position. The shaft of the depressor, the area of interest in the retinal periphery, and the central cornea should all be kept in the same plane during scleral depression.[9]
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FIGURE 127.8 To perform scleral depression, light pressure is exerted on the globe through the patient's eyelids with the tip of the scleral depressor. The shaft of the depressor, the area of interest in the fundus, and the central cornea should all be in the same plane. |
Scleral depression is not a static process whereby the peripheral retina is merely brought into view and observed. Gentle movement of the depressor in the vicinity of a suspicious area during observation may open up a previously unseen tear or demonstrate areas of vitreoretinal traction. Hence, to detect and diagnose subtle retinal abnormalities, dynamic scleral depression is required.
Topical anesthesia, such as a drop of 0.5% proparacaine hydrochloride, may facilitate the examination with scleral depression. To limit patient discomfort, the complete examination should be performed without placing the depressor directly onto the conjunctival surface (Fig. 127.9). Occasionally, evaluation of some peripheral areas, particularly those at the 3 and 9 o'clock meridians, necessitates placement of the depressor directly on the globe.
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FIGURE 127.9 The scleral depressor is carefully repositioned along the upper and lower eyelids to completely examine all 360° of the retinal periphery. |
DOCUMENTING THE RETINAL FINDINGS
Detailed sketches of the fundus are made on durable drawing paper to document the retinal pathologic condition (Fig. 127.10). The location of a given lesion is drawn in reference to the major retinal veins, the meridional location of the lesion within the eye, and its relative peripheral location. The arteries are not typically drawn. By convention, the 12 o'clock meridian is placed at the top of the retinal drawing because it represents the uppermost part of the clock face. Keep in mind that mapping the retinal surface, which is spherical, on a flat piece of paper necessarily produces inaccuracies of scale in the fiished drawing. For instance, the peripheral retina is disproportionately represented, just as the size of equatorial regions of the world is exaggerated in flat, polar maps generated by gnomonic projection.[10] Hence, a lesion of a given area will appear larger on the retinal drawing paper if it is located in the peripheral fundus than it would if it were located in the macula.
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FIGURE 127.10 Drawing of a retinal detachment on conventional retinal drawing paper. The center of the paper represents the fovea, the inner circle (E) represents the equator, and the outer circle (O) represents the ora serrata. The region defied by the two outermost circles represents the pars plana. On this paper, labeled O.S. for the left eye, the optic nerve is predrawn and located to the left of the fovea. Drawing paper labeled O.D. has the optic nerve drawn to the right of the fovea. Findings located on the drawing correspond to their clock-hour location within the patient's eye, with 12 o'clock representing the superiormost portion of the globe. In this figure, a retinal detachment has been drawn extending from the 9:30 to the 12:30 positions. The retinal tear is drawn at the 11:45 position. |
Because the retinal image is inverted during indirect ophthalmoscopy, beginners often make the mistake of assuming that the pathologic condition seen at the 6 o'clock position in the hand-held lens must be located at the 12 o'clock position in the eye. In fact, since only part of the fundus is imaged at a time, only the small fundus region that is being viewed is inverted (Fig. 127.11).[5] To avoid confusion, one can move the hand-held lens out of the way occasionally to observe which quadrant of the patient's eye the indirect ophthalmoscope is being directed toward.
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FIGURE 127.11 (Left) Some fundus details located along the meridian at the 1:30 position on the clock are outlined by three circular areas, representing three areas to be viewed by indirect ophthalmoscopy. (Center) The individual image fields of the fundus, as seen through the examiner's lens. Each field has been inverted by the optical system. (Right) The salient details of each image field are drawn onto the fundus drawing paper. The paper is oriented with the 12 o'clock meridian directed toward the patient's feet. This allows the examiner to draw what she or he sees within each field as if it were being 'pasted' directly onto the drawing paper. If the drawing paper were not inverted, the examiner would have to mentally invert the images before drawing them. |
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When drawing the fundus, it is helpful to place the drawing paper on a clipboard and have the patient hold or support the clipboard on his or her chest. By orienting the paper so that its 12 o'clock meridian is directed inferiorly toward the patient's feet, the image fields can be visually translated directly onto the paper without having to mentally invert them. Holding a pencil in one hand while holding the lens and the patient's eyelids open with the other hand greatly speeds up the process of generating an accurate retinal drawing (Fig. 127.12).
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FIGURE 127.12 The patient's fundus fidings can be documented rapidly if the examiner holds the lens in one hand while drawing on the paper with a pencil held in the other hand. Again, the paper is purposely inverted. |
As retinal features are color-coded by convention (Table 127.1), color pencils are characteristically used for the retinal drawing.
TABLE 127.1 -- Color Coding for Retinal Drawing
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Color |
Anatomic Feature |
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Red |
Retinal arteries, retinal hemorrhage, attached retina, retinal neovascularization |
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Blue |
Retinal veins, detached retina, retinal edema |
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Green |
Media opacities, vitreous hemorrhage |
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Yellow |
Retinal and choroidal exudates |
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Brown |
Pigmented lesions, choroidal detachments |
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Red lined with blue |
Retinal breaks |
LIMITATIONS OF THE INDIRECT OPHTHALMOSCOPE
Although the indirect ophthalmoscope is an invaluable instrument, it has limitations. A major drawback is that its magnification is insufficient to allow detection of very small retinal abnormalities, particularly subtle macular lesions. For example, retinal microaneurysms, tiny areas of subretinal neovascularization, foveal cysts, and small round retinal breaks may be difficult to resolve with this instrument. For this reason, other ancillary devices are necessary to thoroughly evaluate the fundus.
BIOMICROSCOPY OF THE RETINA
The slit lamp is an essential instrument for fundus examination, particularly when a high degree of magnification is desired. It consists of a movable binocular biomicroscope mounted on a table and an intense illumination beam or slit beam of adjustable width that can be rotated 360° in the vertical plane. Focusing is accomplished by moving a joystick located on the microscope platform. The slit lamp is used in conjunction with a diagnostic contact lens or hand-held lens to provide a high-quality magnified stereoscopic image of the fundus. Slit-lamp biomicroscopy of the fundus is particularly useful in determining whether the location of a hemorrhage is preretinal, intraretinal, or subretinal; in detecting cystoid macular edema; and in diagnosing clinically significant macular thickening.
The slit lamp also provides optical sections of the vitreous body to allow detection of posterior vitreous detachments, abnormal vitreous surfaces, and vitreous floaters. Furthermore, the surface contours of a chorioretinal lesion are more apparent if a narrow beam of light is projected onto the lesion's surface. If an elevation or depression of a chorioretinal lesion is present, the slit beam on the retina will appear curved rather than straight (Fig. 127.13a). In some cases, when there is very little subretinal fluid, illumination of the retinal vessels with the slit beam produces shadows of the vessels at the level of the retinal pigment epithelium (Fig. 127.13b). Such shadows are further proof of retinal elevation.
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FIGURE 127.13 (a) A slit beam has been directed over a questionably elevated choroidal lesion. Bending of the beam is observed, indicating that the lesion is indeed elevated. (b) To detect a subtle elevation of the sensory retina, the area of suspicion is illuminated by the slit beam. Shadows of the retinal vessels are seen at the pigment epithelial level, indicating the presence of subretinal fluid and a shallow serous detachment of the sensory retina. |
If the slit beam of the biomicroscope is placed across an elevated retinal lesion, the behavior of the scattered light also provides important diagnostic clues. Often the borders of a small serous retinal or pigment epithelial detachment can be made to glow by positioning the slit beam across the elevation, making the lesion easier to demarcate. This technique is very useful in evaluating the posterior pole for the presence of a macular hole or for detecting cystic spaces within the fovea.
Slit-lamp examination methods can be separated into two major categories: (1) contact methods requiring the placement of a specialized contact lens onto the corneal surface to neutralize its power and (2) noncontact methods, which use the refractive power of the cornea and a special lens to form a fundus image. Noncontact fundus examinations are generally performed more rapidly, particularly if only the posterior pole requires evaluation. However, the patient may squeeze the eyelids shut during noncontact fundus evaluations. With diagnostic contact lenses, the eyelids cannot be closed, but corneal irritation may result if the examination is not performed gently. Furthermore, excessive pressure exerted on the eye during a contact lens evaluation may induce vasovagal reactions such as fainting and nausea. These side effects rarely occur if the examiner is experienced.
NONCONTACT METHODS OF BIOMICROSCOPIC RETINAL EXAMINATION
PLANOCONCAVE LENSES
A planoconcave lens of high negative optical power, such as a Hruby lens, is incorporated into some slit-lamp biomicroscopes. To use this lens, a broad vertical slit beam is first rotated to illuminate the fundus from virtually a straight-on direction until the red reflex is clearly seen through the oculars. The lens is centered over the patient's cornea, positioned a few centimeters from the patient's eye, and focused via a lever until the fundus comes into view (Fig. 127.14). Some systems focus the lens more or less automatically. The image formed is upright and vertical, but the image quality is not uniformly good, especially near the edges of the field of view. This lens is used almost exclusively to view the posterior pole, as distortion seriously degrades the image if the fundus is viewed along any axis other than the approximate optical axis of the patient's eye.[11]
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FIGURE 127.14 A high-power minus lens placed in front of the cornea forms a virtual image of the fundus. Moving a lever on the lens holder focuses the image, which is observed through the slit-lamp binoculars. |
ASPHERICAL LENSES (60 D, 78 D, 90 D) AND SLIT-LAMP INDIRECT OPHTHALMOSCOPY
A real image of the fundus is formed at the slit lamp several centimeters in front of the patient's eye when a high-powered plus lens is positioned in front of the cornea. This aerial image of the fundus is magnified by the slit-lamp optics. The resultant image is real, inverted, and of high quality if a superior high-power aspherical lens made for this purpose is used. Typically, indirect biomicroscopic lenses are positioned farther from the patient's eye than is the Hruby-type lens. With a lens of lower power or longer focal length, the image is produced at a location farther in front of the patient's eye than with a higher-power lens. Because some slit-lamp focusing tracks are limited in travel away from the patient, it may be impossible to obtain a clear fundus image with certain low-power indirect lenses.
Indirect ophthalmoscopy at the slit lamp is performed by placing the lens between the thumb and the forefiger, with the elbow supported by the slit-lamp table (Fig. 127.15). Because these lenses are of relatively high power, any movement of the examiner's hand induces sizable prism shift movements of the image. Some examiners prefer, therefore, to have the lens mounted on a small jointed holder affixed to the slit lamp (Volk Optical, Mentor, OH). As with indirect ophthalmoscopy, higher-power lenses provide wider fields of view at the expense of magnification.
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FIGURE 127.15 (a) Binocular indirect ophthalmoscopy at the slit lamp is accomplished by holding a high-power plus lens in front of the cornea and focusing the slit lamp on the aerial image that forms anterior to the lens. (b) Lenses of various powers provide the examiner with an array of magnification and field of view options. |
Although noncontact lenses are suitable for viewing the posterior pole, they do not by themselves provide an adequate view of the retinal periphery. Scleral depression can be attempted while viewing the fundus through these lenses, but this technique requires considerable practice and is technically difficult.
CONTACT LENS METHODS OF BIOMICROSCOPIC RETINAL EXAMINATION
Before placing the diagnostic contact lens on the patient's cornea, a drop of a mild anesthetic agent such as 0.5% proparacaine hydrochloride is instilled. A viscous, clear liquid such as methylcellulose or hydroxypropyl methylcellulose (Goniosol) is placed in the concave portion of the lens to optically couple the lens to the cornea. With the patient looking up, the lids are held open and the lens is placed gently on the patient's cornea (Fig. 127.16). Small air bubbles are eliminated by exerting gentle pressure on the lens. When fundus photography is scheduled directly after removal of the diagnostic contact lens, any residual interface solutions remaining on the cornea can degrade the retinal image. Hence, many examiners prefer to use low-viscosity BSSs rather than thicker, more tenacious interface liquids. Unfortunately, BSSs are of such low viscosity that they spill out of the fundus contact lens unless the lens is placed on the cornea in a smooth, rapid motion while the patient gazes ahead.
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FIGURE 127.16 (a) A diagnostic fundus contact lens containing an optical coupling fluid is placed on the anesthetized cornea by holding the lids open while the patient looks up. (b) The patient then gazes straight ahead to center the lens, which is held in place with very light pressure. |
GOLDMANN THREE-MIRROR LENS
The three-mirror lens has a clear central portion for viewing the posterior pole, surrounded by three radially arranged mirrors (Fig. 127.17, left). Each mirror has a different inclination between its surface and the axis of the lens. Through the central posterior pole portion, the field of view is ?30° for an emmetropic eye. The smallest mirror is used to view the anterior chamber angle and occasionally the far periphery of the fundus. The middle-sized mirror is configured to allow viewing of the retinal periphery anterior to the equator, and the largest mirror is chosen when the area of interest is within the equatorial and posterior equatorial regions of the fundus (Fig. 127.18).[12]
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FIGURE 127.17 Specialized fundus contact examination lenses. (Left) Goldmann three-mirror contact lens. (Center) Mainster biomicroscopic lens. (Right) Rodenstock panfunduscopic lens. Each lens has specific attributes and shortcomings. |
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FIGURE 127.18 (Left) The Goldmann three-mirror lens has a clear central zone (D) for examination of the posterior pole. The adjacent mirrors (A, B, C) are each inclined at different angles to the optical axis of the lens, providing visual access to different regions of the fundus, as depicted at right. |
The beam of the slit lamp should be projected along the radial axis of the mirror being used. This is achieved by rotating a collar or knob on the slit lamp, which, in turn, rotates the slit beam. With the patient gazing straight ahead, the best image is obtained when the front surface of the lens is kept perpendicular to the viewing axis of the slit lamp. By rotating the examination mirror and readjusting the slit beam, all meridians of the retina can be evaluated.
Redirection of the patient's gaze facilitates viewing of more anteriorly or posteriorly located retinal regions positioned within a given mirror. If the patient moves her or his eye toward the mirror, a more posteriorly located portion of the fundus comes into view. If the eye is moved away from the mirror, more peripheral areas of the fundus are seen (Fig. 127.19). This change in image field with a change in the patient's gaze is especially important to note when photocoagulating a patient's eye through a mirror. The fovea may inadvertently appear within the treatment mirror of the lens on extreme gaze. Failure to recognize the fovea in this situation can lead to its destruction by photocoagulation.
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FIGURE 127.19 The patient's direction of gaze will influence the field being observed through each mirror of the Goldmann lens. If the patient looks toward the particular mirror being used for viewing, a more posterior region of the fundus will be seen. |
THREE-MIRROR LENS EXAMINATION COUPLED WITH SCLERAL DEPRESSION
A highly magnified view of the ora serrata and the most peripheral retina can be achieved by performing scleral depression during the three-mirror lens examination. This magnified examination of the retinal periphery is often easier to accomplish if the Goldmann lens is placed in a specialized conical holder, which, in turn, has a small depressor located along its circumference (Fig. 127.20). The middle-sized or smallest mirror should be inserted into the position opposite the depressor location. The lens holder is then held gently but firmly against the patient's eye, producing the desired scleral indentation. One type of lens holder incorporates an adjustable depressor that can be moved more posteriorly along the sclera in any meridian.[13] Unfortunately, many patients fid these scleral depression devices very uncomfortable, especially in inexperienced hands.
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FIGURE 127.20 Placement of the Goldmann lens into a conical holder containing a scleral depressor at its periphery allows the examiner to perform scleral depression while using the slit-lamp biomicroscope. Two of these devices are illustrated. |
GOLDMANN POSTERIOR FUNDUS CONTACT LENS
If the examiner is primarily interested in studying the posterior retina, a small lightweight lens incorporating a peripheral flange at the point at which it touches the eyelids is often preferred over a larger, bulkier lens. The flange and smaller contact diameter make this lens more difficult to dislodge if the patient squeezes the eyelids.
PANFUNDUSCOPIC LENS
The panfunduscopic lens (Rodenstock, Munich, Germany) (see Fig. 127.17, right) consists of a meniscus lens coupled with a spherical lens located within the same lens holder housing. When the meniscus lens is placed on the cornea, the resultant image of the fundus is inverted, real, minified, and located well forward of the anterior lens surface. Magnification provided by the slit lamp counteracts the minification produced by the lens configuration. A wide-angle view of the fundus in an emmetropic eye, extending from the fovea to the equatorial region, is produced by such a panfunduscopic lens.[14] This device also facilitates the examination of the fundus through a poorly dilated pupil. However, panfunduscopic lenses are used more often during laser photocoagulation than for diagnostic purposes, primarily because the image of the retina is small and the view through the peripheral portions of this lens is not excellent.
MAINSTER LENS
The Mainster lens (Ocular Instruments, Bellevue, WA) (see Fig. 127.17, center) provides a somewhat reduced field of view (45°) compared with the panfunduscopic lens but also produces less minification.[15] Resolution with this lens is sufficient to detect retinal thickening from macular edema. The image size is comparable with that provided by the Goldmann lens, making the Mainster lens versatile for diagnostic as well as therapeutic purposes. The image plane is located quite anterior to the lens surface, however, making it difficult to view the fundi of patients with hyperopia or exophthalmos when using slit lamps with limited forward travel.
SPECIALIZED RETINAL EXAMINATION TECHNIQUES
If a fiber optic probe or other suitable light source is placed against the sclera in a darkened room, the retina can be visualized using indirect ophthalmoscopy with the illuminating scope light turned off. This examination technique (transillumination ophthalmoscopy) requires that light be transmitted through the sclera and choroid. If an eye contains a solid pigmented mass, transillumination is useful in that the tumor will appear dark, whereas other choroidal lesions, such as a choroidal detachment, will be much more brightly illuminated.
Alternately, a transillumination light can be placed on the cornea so that it shines through the pupil. The examiner then observes the surface of the sclera, which should glow a uniformly orange color. A pigmented tumor or foreign body within the choroid will prevent the transillumination light from illuminating the sclera beneath it, and a dark shadow will be present within the affected scleral quadrant. In eyes that are lightly pigmented, a bright transilluminator may be applied directly to the sclera to achieve a similar effect (Fig. 127.21).
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FIGURE 127.21 Transillumination. The globe is illuminated, through the sclera in this illustration, via a fiberoptic light source placed on the globe externally or on the cornea. In a darkened room, the sclera is observed, glowing yellow-orange. A dark choroidal lesion will block the transmission of light through the eye wall and will appear as a dark shadow surrounded by the red glow of the remainder of the sclera. |
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