Ординатура / Офтальмология / Английские материалы / Practical Ophthalmology A Manual for the Beginning Ophthalmology Residents 4th edition_Wilson_1996

308 Chapter 13: Posterior Segment Examination

Headset Adjustment

for penetrating through hazy ocular media and for examining the peripheral fundus.

Limiting the duration of indirect ophthalmoscopy helps to minimize the subjective discomfort felt by the patient. An examination prolonged beyond 15 minutes per eye should use a reduced power setting of the headset light and a condensing lens with an ultraviolet filter or yellow coating. Any risk of phototoxicity caused by indirect ophthalmoscopy is also minimized if the examiner avoids repeatedly shining the light onto the fovea.

Choosing and Positioning the Condensing Lens

The lens usually used for a general posterior segment examination with an indirect ophthalmoscope is the +20 D lens. The +30 D and +28 D aspheric lenses have less magnification but are sometimes preferred when a wider field is helpful (eg, with large or diffuse retinal abnormalities), when the pupil does not dilate well, and when viewing the peripheral fundus through an oblique pupil. Lower-power lenses (eg, + 14 D) provide more magnification but a narrower field of view and are reserved for examining the optic nerve and individual lesions. Lenses must be kept spotless and free of dust and finger smudges.

Grasp the edge of the indirect lens between the thumb and index finger, with the more convex side toward you (white ring facing the patient). You should hold the lens in your nondominant hand, reserving the dominant hand for scleral depression and drawing the fundus record (see "Scleral Depression" and "The Fundus Record" later in this chapter). The middle finger of the hand holding the lens is used to open the upper or lower eyelid, and the thumb of the opposite hand can be used to hold the other eyelid open (Figure 13.8). Depending on where the examiner is standing, the hand holding the lens can be braced against the patient's upper or lower orbital rim to maintain the proper focal distance and to keep the image centered. Figure 1 3.9 provides instruction and practice in centering an image in a condensing

310 Chapter 13: Posterior Segment Examination

Figure 13.8 Techniques for holding the condensing lens during indirect ophthalmoscopy while holding the patient's eyelids open. (A) Elevating upper eyelid with third finger of the hand holding the lens while retracting the lower eyelid with the free hand's thumb. (B) Elevating the upper eyelid with the free hand's thumb while retracting the lower eyelid with the third finger of the hand holding the lens.

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A B C D

Figure 13.9 Practice and instruction in focusing the condensing lens for indirect ophthalmoscopy. (A) A small square, such as this, is the target over which you should hold the lens. (B) Center the square in the lens and move the lens toward or away from the page to make the entire image uniformly fill the lens, as in this example. (C) If the image in the lens looks like this, you are too far from or too close to the square. (D) If the image in the lens looks like this, you are too far sideways.

lens. A +20 D condensing lens gives a 2-inch working distance for an emmetropic eve. Clinical Protocol 13.1 summarizes how to obtain a fundus image with the headset and lens.

Two distracting light reflections corresponding to the images of the ophthalmoscope's bulb on the front and back surfaces of the condensing lens are seen when the lens is held exactly perpendicular to the line of sight, lilt the lens to spread these reflections apart. Some lenses have an antireflective coating to reduce these bothersome reflections.

Figure 13.10 For indirect ophthalmoscopy, the examiner maintains a fixed axis with the fulcrum at the patient's pupil when viewing adjacent parts of the fundus. (Redrawn from: The technique of binocular indirect ophthalmoscopy, courtesy of Benjamin F. Boyd, MD,

Highlights ofOphthalmology, 1966; 9:179-257.)

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Changing Position to View Different Fundus Areas

Alignment

During indirect ophthalmoscopy, the examiner maintains a viewing axis through the condensing lens while pivoting around the patient's pupil to examine different portions of the fundus (Figure 13.10). Move your head and tilt the lens while using your rigid third finger as a fulcrum. Rather than having the patient look in different directions, it is preferable to move your torso and to approach the patient from different directions and angles. Keeping the pupil centered in the condensing lens will maintain alignment of the light beam and the view returning to both of the examiner's eyes (Figure 13.11). Examination of the equatorial and peripheral fundus may require changing the direction of the light beam, switching to a different condensing lens, or tilting the head (Figure 13.12).

Working distance

The ophthalmoscopic examination is performed at arm's length, normally with about 40-50 cm between the examiner's headset and the patient's eye. Difficulty seeing through a small pupil can be partially overcome by withdrawing to a greater examination distance or bv using a higher-power lens.

The working distance between the examiner and the lens does not have to be fixed. The distance can be shortened (lens brought closer to examiner) for greater magnification of fundus details, although the field then becomes narrower and binocularity can be lost more easily. The examiner can shift the lens to grossly estimate the relative height of a lesion. Each 1 cm of up or down displacement needed to focus on the lesion's apex or pit is equivalent to about 1 mm of lesion elevation or excavation, respectively.

Sequence of the Complete Examination

For patients who are about to undergo any type of fundus examination, avoid using any ointment or doing anything that could cause corneal haze, such as instilling certain topical anesthetics or applying diagnostic contact lenses. Ensure that the patient's pupils are completely dilated, and instruct the patient to keep both eyes open. Warn the patient what to expect by explaining that a very bright light will be used that will not be harmful. Having the patient lie down in a relaxed position with the plane of the head exactly horizontal is helpful to begin the examination. This avoids having to hold the lens out in front of you in a fatiguing position and facilitates movement around the patient's head to get optimal views. By convention, the right eye is examined first.

Many examiners begin indirect ophthalmoscopy without the condensing lens by quickly shining the light of the indirect ophthalmoscope into the patient's eye to get a red reflex in order to discern any changes in the anterior eye or media. The condensing lens is then brought into position (see Clinical Protocol 13.1, "Obtaining a Fundus Image in Indirect Ophthalmoscopy"). With experience, the examiner automatically finds the proper spot for the lens. The beginner should hold the condensing lens close to the patient's eye, then withdraw it slowly until a focused image is seen. Keep in mind that the fundus image that the examiner sees is completely inverted; that is, it is upside down and reversed as regards to right and left.

The examiner begins the examination of the fundus by identifying the optic disc, then shifting the viewing axis from one part of the fundus to another, keeping the axis centered at the patient's pupil. Rather than having the patient look in one direction and then observing this view of the fundus, the examiner should follow each meridian from the posterior pole to the periphery by changing the viewing axis. This enables each meridian to be examined completely, following retinal vessels from the optic disc to the equator. Smooth body-lens coordination will help obtain a continuous, sweeping picture of an entire meridian of the fundus, from the optic disc to the periphery. The

Figure 13.13 Instruments for scleral depression (top to bottom): thimble scleral depressor; pencil-type depressor; cotton-tipped applicator.

iner does not use careful and responsive movements. Patient cooperation can be encouraged by gradual advancement to the limit of the patient's tolerance. Be especially careful to avoid the depressor tip slipping off the eyelids and onto the cornea.

Sequence of scleral depression

Because the ora serrata is most easily visualized superonasally, this area is often examined first in a circumferential sequence. To begin scleral depression, the examiner stands to the right of the patient. The right hand grasps the scleral depressor. The patient is asked to look inferotemporally. The depressor is applied at the upper tarsal margin of the inner portion of the upper eyelid. The patient is then asked to look straight ahead. As the upper eyelid moves up, the instrument's tip is slid along the globe. The examiner then tilts his or her head to direct the headset's light beam into the patient's pupil and the left hand brings the condensing lens into position, enabling the examiner to observe the superonasal equatorial fundus. Gentle pressure is then exerted with the scleral depressor. The indented fundus should be seen, and the condensing lens is brought slightly closer to the examiner to focus on this mound. The patient is then instructed to look superonasally, and the examiner's fingers help keep the patients eyelids open. The instrument's tip is then slid anteriorly until the superonasal ora serrata is seen.

The entire sequence described above is repeated in all principal meridians, always keeping the examiner's visual axis and the scleral depressor in alignment. This entails moving around the patient's head, and instructing the patient to look in the appropriate direction each