• When examining patients, start with a plus 8 (black number); you see an orange blur.
• Turn the lens selector wheel counterclockwise using progressively weaker plus lenses until the surface of the disc is sharply defined. Note the magnification (eg, + 4).
• Look at the patient's fundus again beside the disc and keep decreasing the plus lens until retinal details come into focus (eg, +1).
The difference in these two readings is the amount of papilledema in diopters, that is, 3. (We cannot use a lens of less than 1 diopter. A difference between the nerve head and surrounding retina of less than 1 diopter is too subjective to be meaningful.)
About 3 diopters are equal to 1 mm of change. The target to be seen clearly is usually the smallest vessel you can see. You do not need a patient with papilledema to learn this; one of your classmates has a normal physiological cup. You can see the bottom of it with great clarity using a (for example) -2 (red number) in your ophthalmoscope. He has a fine artery in the retina to one side of the disc. You will see this vessel with great clarity by using a +1 (black number), that is, 3 diopters, or three clicks on the scope; the retinal vessel is about 1 mm closer to you than the bottom of the cup.
Remember, the higher the plus lens you use, the shorter the focal length and the more anterior is the part of the patient's eye you can clearly see, for example, with a +20 lens in the window of the ophthalmoscope you will focus on his cornea. The more negative the lens, the longer the length and the farther back in the patient's eye is the point of focus; for example, -50 to -10 enables you to focus on the retina of the myopic patient with the long oval eye.
Do not look at the fundus with a zero lens in the ophthalmoscope and plan to increase the plus lenses as you concentrate on the elevated disc, thinking it will become clear while the surrounding retinal details blur. Your own accommodation will not allow it, and you will miss the papilledema.
2. Diminish the lens strength (by a counterclockwise turn on the lens selector wheel).
3. Stop when the disc is clearly seen.
4. Note the lens number.
5. Aim beside the disc at the retina.
6. Diminish the lens strength.
7. Stop when retinal details are clearly seen.
8. Note the lens number (the difference is the amount of papilledema).
The normal eye is shown in cross-section in Figure 3-1A, and the disc area is shown in more detail in Figure 3-1B. The disc is 1.5 mm in diameter and, seen with the ophthalmoscope, looks like those in Figures 1-3 and 1-4.
The disc edges are of different elevations at various points on the circumference of the nerve head. The physiological cup is a true depression in the nerve head. There is no retina overlying the nerve head, hence the normal blind spot.
The optic nerve is surrounded by a sheath space continuous with the sub-arachnoid space surrounding the brain (Figure 3-1B). This space, which contains spinal fluid, may be filled with blood, inflammatory products, or spinal fluid under increased pressure in various disease states.
Figure 3-2A and B shows cross-sections of a papilledematous eye. The nerve is swollen, bulging forward, and expanded. Notice in Figure 3-2B how the retina is pushed laterally by the bulging nerve head.
Examine both eyes, because the amount of papilledema is frequently different in the two eyes. Look in both eyes and judge them independently.
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