The Funduscopic Examination

Excerpt

Funduscopic examination is a routine part of every doctor's examination of the eye, not just the ophthalmologist's. It consists exclusively of inspection. One looks through the ophthalmoscope (Figure 117.1), which is simply a light with various optical modifications, including lenses. The ophthalmoscope illuminates the retina through the normal iris defect that is the pupil. Light rays forming the image of the retina re-emerge through the pupil. The viewing aperture (window) of the ophthalmoscope contains a lens that modifies light rays to assist the user. In the procedure, one looks at structures lying in the innermost aspect of the globe, collectively known as the eyegrounds: retina, retinal blood vessels, optic nerve head (disk), and to a limited degree, subjacent choroid. The pupil is frequently dilated pharmacologically to render retinal inspection easier, and for examination of the macula. One paralyzes the pupilloconstrictor muscle of the iris with nonabsorbable, short-acting topical parasympatholytic drugs, resulting in a larger pupillary aperture. In comparison to the ophthalmologist, the internist, neurologist, or pediatrician concentrates particularly on funduscopic manifestations of systemic disease and less on local ocular disease. Synonyms for funduscopic examination include funduscopy, ophthalmoscopy, and direct ophthalmoscopy. Only ophthalmologists perform retinoscopy and indirect ophthalmoscopy, which require other equipment and provide different information.

The term temporal is used in describing ophthalmoscopic landmarks and findings, rather than "lateral"; and nasal replaces "medial." The optic nerve head or disk is seen when one looks through the pupil from an angle about 15 degrees temporal to the optical axis (the patient's line of sight, "straight ahead"). The disk is a yellow-pink color that stands out from the redder, browner, or more orange retina proper (see Figure 117.4D). The disk is sharply demarcated temporally and to a lesser degree nasally from the background retina, which is all the retina that is not disk, vessels, or macula. Frequently, a narrow crescent of stippled pigment adjoins the sides of the disk, especially the temporal side (house staff have called the author to see "lesions" that turned out to be this normal feature). The disk is slightly taller than wide. The central part of the disk is paler, and is called the optic cup or physiologic excavation; normally this occupies less than one-third the diameter of the disk. In glaucoma and in high myopia the cup is enlarged. The transverse diameter of the disk is a standard yardstick in fundal description, so that, for example, a lesion may be characterized as "one-half disk diameter out at two o"clock, and extending two disk diameters superiorly therefrom." Although some examiners realize that the disk is 1.5 mm wide, nobody describes a lesion as 3 mm across. Near mid-disk, the central retinal artery and vein emerge from the optic nerve, with which they have run forward into the orbit. Each soon bifurcates into superior and inferior branches, which run "flat," that is, parallel with the retinal surface. Beyond one disk diameter out, they are called arterioles and venules. With all retinal vessels, the artery/arteriole appears slightly smaller, and distinctly lighter, more orange-red and less purple than the vein/venule. The color difference reflects the contained blood column that is visualized: the vascular walls are transparent, and deoxygenated venous blood is darker than arterial blood. Before it crosses the disk edge, each large vessel divides into a nasal and a temporal branch. Thus the principal arteries, veins, and quadrants of any retina are the superior temporal, inferior temporal, inferior nasal, and superior nasal. The avascular, dusky area two disk diameters due temporal to the disk is the macula. This is the area of greatest visual acuity. Apart from this zone, the background retinal color will parallel the patient's skin and hair pigmentation, from pale in light-skinned blondes to an umber shade in the darkest black people.

Normally, the largest veins pulsate slightly and the arteries do not, the reverse of the situation elsewhere in the body. No hemorrhage is seen in normal fundi. Any yellow, yellow-white, gray, or black interruptions of the background retinal color pattern suggest pathologic exudate, edema, or scar. No wrinkling of the retina should be seen. Chalky whiteness or erythema of the disk is abnormal, as are indistinct disk margins. Any sharp change in elevation that renders one area out of focus with the ophthalmoscope, while the remainder of the retina remains in focus, is abnormal. Tortuous blood vessels usually bespeak pathology.