■ First, locate the optic disc. Look for the round yellowish orange structure described above. If you do not see it at first, follow a blood vessel centrally until you do. You can tell which direction is central by noting the angles at which vessels branch—the vessel size becomes progressively larger at each junction as you approach the disc.
■ Now, bring the optic disc into sharp focus by adjusting the lens of your ophthalmoscope. If both you and the patient have no refractive errors, the retina should be in focus at 0 diopters. (A diopter is a unit that measures the power of a lens to converge or diverge light.) If structures are blurred, rotate the lens disc until you find the sharpest focus.
For example, if the patient is myopic (nearsighted), rotate the lens disc counterclockwise to the minus diopters; in a hyperopic (farsighted) patient, move the disc clockwise to the plus diopters. You can correct your own refractive error in the same way.
■ Inspect the optic disc. Note the following features:
- The sharpness or clarity of the disc outline. The nasal portion of the disc margin may be somewhat blurred, a normal finding.
- The color of the disc, normally yellowish orange to creamy pink. White or pigmented crescents may ring the disc, a normal finding.
- The size of the central physiologic cup, if present. It is usually yellowish white. The horizontal diameter is usually less than half the horizontal diameter of the disc.
In a refractive error, light rays from a distance do not focus on the retina. In myopia, they focus anterior to it; in hyperopia, posterior to it. Retinal structures in a myopic eye look larger than normal.
See Table 5-11, Normal Variations of the Optic Disc (p. 183), and Table 5-12, Abnormalities of the Optic Disc (p. 184).
An enlarged cup suggests chronic open-angle glaucoma.
- The presence of venous pulsations. In a normal person, pulsations in the retinal veins as they emerge from the central portion of the disc may or may not be present.
- The comparative symmetry of the eyes and findings in the fundi
■ Inspect the retina, including arteries and veins as they extend to the periphery, arteriovenous crossings, the fovea, and the macula. Distinguish arteries from veins based on the features listed below.
Light Reflex (reflection)
Smaller (% to % the diameter of veins) Bright
Dark red Larger
Loss of venous pulsations in pathologic conditions like head trauma, meningitis, or mass lesions may be an early sign of elevated intracranial pressure.
Follow the vessels peripherally in each of four directions, noting their relative sizes and the character of the arteriovenous crossings. Identify any lesions of the surrounding retina and note their size, shape, color, and distribution. As you search the retina, move your head and instrument as a unit, using the patient's pupil as an imaginary fulcrum. At first, you may repeatedly lose your view of the retina because your light falls out of the pupil. You will improve with practice.
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