When we come to deal with the fundus we are called upon to study the details of a picture presented as it were at the back of a room into which we can see only through a keyhole. We cannot see the whole of the picture at any one time, but must carry in our minds what we have seen in one part while we are looking at another, and join all the parts together mentally to form a whole. Each picture varies from every other in certain details, just as faces differ in their features, and sometimes there is nothing in a detail itself to tell us whether what we see is a physiological or a pathological deviation. Gross departures from the normal are perceived readily to be such, yet it is not always easy to determine their nature or even their exact site, regarding which our judgment has to be guided by a consideration of all of the details presented, together with the history and the effects which are produced on the vision and the fields for white and colors, while minute variations furnish opportunities for the judgments of experts to differ widely. Before we attempt to solve the puzzles furnished by pictures of the abnormal fundus it is essential that we should become familiar with those presented by the normal, at least in their main outlines, that we may recognize the principal physiological variations, and gradually learn by experience to differentiate minor ones from pathological changes.<Callout type="important" title="Important">The size of the papilla seems to vary with the refraction of the eye, so that its upright image appears to be larger in myopia than in hypermetropia, but in reality it varies very little, and therefore its diameter forms a convenient unit of measurement for other objects, as well as a center from which we are able to compute distances, and to indicate directions.</Callout> The diameter of the papilla is 1.5 mm., and we may say that a certain lesion is one half of a papillary diameter, that is three fourths of a millimeter across, and that it is located 14 p. d., or 2.25 mm., from the lower border of the optic disk.<Callout type="warning" title="Warning">Any anteroposterior curvature, except at the point where the vessels turn to plunge into the nerve, is to be looked upon as a pathological symptom.</Callout> The papilla is round, though commonly it seems to be ellipsoidal with its long axis vertical, less often horizontal or oblique. This elongated appearance is to be ascribed in most cases to astigmatism, but it is occasionally due to a foreshortening.<Callout type="tip" title="Tip">The true color of the papilla can only be seen under daylight conditions.</Callout> The margin of the papilla should be visible, except where it is covered by blood vessels. This is a distinction that is hard to make on paper, though it can be appreciated quickly when we compare the margin of a normal disk with that of one which has undergone simple atrophy; in the former we see it clearly through the transparent nerve fibers, but in the latter it stands out with an added degree of sharpness. The temporal margin is more distinct than the nasal, but any obscuration of any portion of the margin must be due to one of three things, a refractive error, a pathological condition of the nerve head itself or of the immediately adjacent retina, or a projection of the sclera, choroid, and retina over the nasal margin, called by some a supertraction, which is met with only in the conus and posterior staphyloma of high myopia.<Callout type="risk" title="Risk">A distinctly white, gray, or blue color, or a great redness of the papilla is perceived readily and recognized to be a pathological symptom.</Callout> The vessels of the papilla and retina vary a great deal, largely because minute differences in the sites of their branching produce marked effects on the appearance. The central artery and vein divide each into two branches, one of which runs upward, the other downward, to form the superior and inferior artery and vein. Usually this bifurcation takes place just before, or as the central vessels reach the surface, when we see one artery running up, and another running down on the surface of the disk, each accompanied by a vein, from a place in the physiological excavation about the center of the nerve head, where they are separated by a small interspace, or seem to fuse. Each of these vessels divides into two branches, the superior temporal and nasal, and the inferior temporal and nasal arteries and veins, either before or after it has left the disk to enter the retina.<Callout type="gear" title="Gear">Microscopes with high magnification are essential for detailed fundus examination.</Callout> These divide and subdivide into continually smaller branches that spread through the retina, but the subdivision is by no means regular and symmetrical. Less often the central vessels divide farther back in the nerve, when the superior and inferior branches emerge from the nerve tissue separated by a much wider interval, or we may see three or four arterial and venous trunks come to the surface in widely separated parts of the nerve head, when a subdivision of these branches has already taken place. In still other cases short portions of the central vessels are visible before they divide.<Callout type="important" title="Important">Arteries and veins cross each other frequently, sometimes with one, sometimes with the other in front, but an artery never crosses an artery, and a vein never crosses a vein; if an exception to this rule exists it must be one that is very rare.</Callout> Both arteries and veins tend to be tortuous, the veins the more so, as a rule. At times the large vessels may be seen to be twisted about each other, the artery taking its natural course and the vein winding about it in most cases, or one of them may form a twisted loop, which occasionally projects into the vitreous, where it is liable to be mistaken for the remains of a hyaloid artery. The tortuosity of the vessels is much greater in some persons than in others, and as tortuosity often is a pathological symptom we need to know when it is physiological. It is only in rare cases that a physiological tortuosity is not present and of a similar character in both eyes.<Callout type="warning" title="Warning">Any anteroposterior curvature, except at the point where the vessels turn to plunge into the nerve, is to be looked upon as a pathological symptom.</Callout> The vessels are largest where they bend to enter the nerve, but occasionally they appear to taper at this place. In the case of an artery we refer this appearance to a foreshortening caused by an oblique course, or to the presence of a certain amount of connective tissue, but if a vein seems to taper at this point we think at once of an increased intraocular tension.<Callout type="tip" title="Tip">The one exception to this statement, as regards the normal eye, is that occasionally we can make out very narrow, pale yellow, or whitish lines along the sides of the blood columns on the
Key Takeaways
- Familiarize yourself with normal fundus appearances to differentiate minor variations from pathological changes.
- Use a microscope for detailed fundus examinations.
- Pay attention to the color, size, and shape of the papilla for diagnostic purposes.
- Recognize physiological vs. pathological excavations in the papilla.
Practical Tips
- Use high-magnification microscopes for accurate fundus examination.
- Compare findings between both eyes to identify asymmetrical changes.
- Be aware of physiological variations and their impact on diagnosis.
Warnings & Risks
- Pathological symptoms like white, gray, or blue papilla colors can indicate serious conditions.
- Anteroposterior curvature in vessels is a sign of pathology.
- Tortuosity of vessels may be physiological but could also indicate increased intraocular tension.
Modern Application
While the techniques described in this chapter are rooted in historical practices, they still provide valuable insights for modern survival preparedness. Understanding fundus examination can help in triage situations where immediate medical attention is critical. The use of high-magnification microscopes and careful observation remain essential tools even today.
Frequently Asked Questions
Q: How does the size of the papilla vary with eye refraction?
The size of the papilla appears larger in myopia than in hypermetropia, but its actual diameter varies very little. This makes it a useful unit for measuring other objects and computing distances.
Q: What are some signs that indicate pathological changes in the fundus?
Pathological changes can be indicated by white, gray, or blue papilla colors, anteroposterior curvature of vessels (except at the point where they enter the nerve), and tortuosity of vessels. These symptoms should be carefully noted as they may indicate serious conditions.
Q: How do you differentiate between physiological and pathological excavations in the papilla?
Physiological excavations are marked by a pinkish zone around a white spot, while pathological excavations like atrophy or glaucoma show differently colored disks with specific vessel patterns. Glaucomatous cups have precipitous walls that reach to the margin of a discolored papilla.