Normal Optic Disc

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Figure 10-74 Photograph of the retinas of the right (A) and left (B) eyes.

Careful assessment of the optic fundus is important for several reasons. The optic fundus is the only area where the blood vessels can be seen in vivo;it can provide an excellent picture of the state of the vasculature of other organs. In addition, the optic fundus is frequently involved with manifestations of systemic disease such as AIDS, infective endocarditis, hypertension, and diabetes; a thorough evaluation of the fundus can provide valuable clues to their diagnosis. Finally, because the eye is an extension of the central nervous system, evaluation of the optic fundus can provide information about many neurologic disorders.

The optic fundus must be assessed methodically, starting at the optic disc, tracing the retinal vessels emerging from it, inspecting the macula, and evaluating the rest of the retina.

Inspect the Optic Disc

The most conspicuous landmark of the retina is the optic disc (Fig. 10-75). The optic disc is the intraocular portion of the optic nerve and is seen with the ophthalmoscope. Its margins, color, and cup-disc ratio should be determined. The disc should be round or slightly oval with the long axis usually vertical and with sharp borders. The nasal border is normally slightly blurred. The disc is pinkish in light-skinned individuals and yellowish-orange in darker-skinned individuals. The relative pallor of the optic disc is caused by the reflection of light from the myelin sheaths of the optic nerve. In the center of the normal optic disc, there is a funnel-shaped depression known as physiologic cupping. The cup is the portion of the disc that is central, lighter in color, and penetrated by the retinal vessels. The normal ratio of the cup diameter to disc diameter varies from 0.1 to 0.5. The examiner should check the cup-disc ratio in both eyes for symmetry.

The benign condition myelinated, or medullated, nerve fibers is seen in 0.3% to 0.6% of all individuals. In this condition, the nerve fiber layer continues to myelinate into the retina beyond the lamina cribrosa. The fibers appear as white patches with feathery borders that radiate from the optic disc and obscure the retinal vessels over which they pass. The condition is present at birth, does not change, and usually causes no visual impairment. Figure 10-76 shows the retina of a patient with myelinated nerve fibers. Another dramatic example of myelinated nerve fibers at the disc is shown in Figure 10-77. Figure 10-78 shows myelinated nerve fibers in the peripheral retina.

An optic pit is a congenital anomaly of the optic disc. It is a small depression, located temporally in 75% of cases, in the optic nerve and is usually gray or yellow. In 85% of cases, it is unilateral. Figure 10-79A shows an optic pit. Retinal tears and detachment can occur in 50% of patients with an optic pit, as shown in Figure 10-79B; that patient has an optic pit and a retinal tear involving the macula of the left eye.

Inspect the Retinal Vessels

The retinal vessels are evaluated as they arborize over the retina. The central retinal artery enters the globe through the physiologic cup. It divides within the cup and again on the surface, giving rise to four main branches that supply the superior and inferior temporal and nasal quadrants of the optic fundus. The arteries are two-thirds to four-fifths the diameter of the veins and have a prominent light reflex. This light reflex is a reflection of the

Normal Optic Disc
Figure 10-75 Normal optic disc, left eye.

ophthalmoscope's light on the arterial wall and is normally about one-fourth the diameter of the column of blood. The veins exhibit spontaneous pulsations in 85% of patients. This can best be demonstrated as the retinal vein enters the optic nerve, where it can be seen on end.

As all the vessels course away from the disc, they appear to narrow. The crossing of the arteries and veins occurs within two disc diameters from the disc.

Myelinated Optic Nerve
Figure 10-77 Myelinated nerve fibers at optic disc.

The normal vessel wall is invisible, with its thin light reflex. In hypertension, the vessel may have focal or generalized areas of narrowing or spasm, causing the light reflex to be narrowed. With time, the vessel wall becomes thickened and sclerotic, and there is a widening of the light reflex to greater than half of the diameter of the column of blood. The light reflex develops an orange metallic appearance called copper wiring (Fig. 10-80). When such an artery crosses over a vein, there appears to be a discontinuity of the venous column as a result of the widened, but invisible, arterial wall. This is termed arteriovenous nicking.

Follow the vessels in all four directions: superior temporal, superior nasal, inferior nasal, and inferior temporal. Remember to move your head and the ophthalmoscope as one unit.

Inspect the Macula

When the ophthalmoscope is kept level with the disc and moved temporally approximately 1.5 to 2 disc diameters, the macula is seen. This appears as an avascular area with a pinpoint reflective center, the fovea. If the examiner has difficulty in seeing the macula, the patient can be instructed to look directly into the light;the fovea is then visible. The red-free filter is also helpful in locating the macula. Figure 10-81 shows a normal macula of the right eye.

Figure 10-82 shows a patient with a macular hole of the left eye; notice the punched-out appearance at the macula. Macular holes are seen in patients with high myopia.

Describe Any Retinal Lesions

When a lesion is seen, its color and shape are important in determining its cause. Is it red, black, gray, or whitish? Red lesions are usually hemorrhages. They can be located best by using the green contrast filter of the ophthalmoscope. Linear, or flame-shaped, hemorrhages occur in the nerve fiber layer of the retina (Fig. 10-83), whereas round hemorrhages are located in deeper intraretinal layers. Are the borders of the lesions sharp or blurred?

Colour Shape Sixe Normal MaculaNerve Macule Ligament
exudates in the nerve fiber layer. Figure 10-81 Normal macula, right eye.
Colour Shape Sixe Normal Macula

Figure 10-82 Macular hole. -

Figure 10-83 Flame-shaped hemorrhages and a cotton-wool spot in a patient with hypertension.

Figure 10-82 Macular hole. -

Figure 10-83 Flame-shaped hemorrhages and a cotton-wool spot in a patient with hypertension.

A common benign retinal finding is congenital hypertrophy of the retinal pigment epithelium (RPE). This appears as a round, dramatically dark pigmented lesion, often one to several disc diameters in size. The surface is flat, and the edges are very sharp. Several small, punched-out holes are commonly present within. The retinal vessels appear normal. This is an asymptomatic lesion and is usually unilateral;it may occur in any position in the retina. Its recognition is important and should not be misdiagnosed as a malignant melanoma. Figure 10-84 shows a retina with congenital hypertrophy of the RPE.

Black lesions that are shaped like bone spicules are associated with retinitis pigmentosa. In this condition, melanin tends to unsheathe the retinal vessels (see Fig. 10-142 and a discussion of this condition at the end of this chapter). A doughnut-shaped lesion is often found in chronic inactive toxoplasmosis chorioretinitis (see Figs. 10-127 and 10-128). A pigmented, raised, disc-shaped lesion is suggestive of a melanoma (see Fig. 10-139). Diffuse spotting of the retina is often a degenerative state. Flat, gray lesions are usually benign choroidal nevi (see Fig. 10-138).

White lesions may appear as soft, cotton-wool spots or may be dense. Soft, cotton-wool spots or exudations are caused by infarctions of the nerve fiber layer of the retina (see Figs. 10-80 and 10-83). White lesions are common and are frequently associated with hypertension or diabetes. The differentiation of white lesions of the retina is summarized in Table 10-8.

White Lesions Fundus

Table 10-8 Differentiation of Whitish Lesions of the Fundus

Feature Cotton-Wool Spots* Fatty Exudates{ Drusen{ Chorioretinitis4

Cause}

Border

Shape Patterns

Comments

Hypertension Diabetic retinopathy Acquired immunodeficiency syndrome Lupus erythematosus Dermatomyositis Papilledema

Fuzzy

Irregular Variable

Caused by an ischemic infarct of the nerve fiber layer of the retina; obscures retinal blood vessels; usually several in number

Diabetes mellitus Retinal venous occlusion Hypertensive retinotherapy

Well defined

Small, irregular

Often clustered in circles or stars

In deep retinal layer

Can be normal with aging Age-related macular degeneration

Well defined, nonpigmented

Round, well circumscribed

Variable; symmetrical in both eyes

Often confused with fatty exudates; deep to retinal blood vessels

Toxoplasmosis

Sarcoidosis

Cytomegalovirus

Often large with ragged edge, heavily pigmented

Very variable

Variable

Acute with white exudate; healed lesion with pigmented scar (toxoplasmosis)

*See Figures 10-80 and 10-83.

{Also known as edema residues. See Figures 10-104 and 10-105. {Also known as colloid bodies. See Figure 10-121. §See Figures 10-125 to 10-135.

}The diseases noted do not constitute a complete etiologic list. Only the most common causes are indicated.

Difficulties in Using the Ophthalmoscope

Frequently, difficulties arise in the use of the ophthalmoscope. These include the following:

A small pupil

# Extraneous light

Improper use of the ophthalmoscope

Myopia in the patient

# Cataract in the patient

The use of mydriatic drops to visualize the retina better is important. Many medical students fear that these drops will precipitate an attack of narrow-angle glaucoma. It is clear from the data that more retinal findings are missed by not dilating the pupils than when the drops precipitate such an attack, which occurs in less than 0.1% of patients. If this reaction occurs, the patients are in the best possible facility for treatment.

The examiner should use one drop of tropicamide 1.0% in each eye. Care should be taken to place the drop on the inside of the lower lid and not on the cornea. The patient should be told that the drop will sting slightly and will cause photophobia in sunshine. The duration of the mydriatic action depends primarily on the patient's sensitivity to the medication: a more heavily pigmented iris requires more time to achieve mydriasis. The cycloplegic* action lasts for about 6 hours. These drops can be used in patients wearing contact lenses. Atropine should be avoided because its effect lasts for up to 2 weeks. The large aperture of the ophthalmoscope is used when the pupil is dilated. Record in the chart that the patient's pupil or pupils were dilated and which medications were used.

The room should be darkened as much as possible for the easiest evaluation of the retina. Another common problem is corneal reflection. Often, light is reflected from the cornea, which makes the examination more difficult. Use of the small aperture or a polarizing filter, which many ophthalmoscopes include, may be helpful.

Patients with myopia provide the most problems for the novice examiner. In myopic eyes, the retinal image is enlarged, making it difficult sometimes to visualize the retina adequately.

*Producing paralysis of accommodation.

If the patient is severely myopic, it may be necessary for the patient to wear corrective lenses while being examined.

A cataract does not allow adequate visualization of the retina, especially if the cataract is central.

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  • drogo
    What is a normal optic disc examination?
    6 months ago

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