Before the middle of the nineteenth century, nobody had seen the inside of a living eye and much of the science of medical ophthalmology was unknown. In 1851, Hermann von Helmholtz introduced his ophthalmoscope and it rapidly became used in clinics dealing with ophthalmo-logical problems. The task of von Helmholtz was to devise a way of looking through the black pupil and, at the same time, illuminate the interior of the globe. He solved the problem by arranging to view the fundus of the eye through an angled piece of glass. A light projected from the side was reflected into the eye by total internal reflection. Most modern ophthalmoscopes employ an angled mirror with a small hole in it to achieve the same end. They also incorporate a series of lenses that can be interposed between the eye of the patient and that of the observer, thereby overcoming any refractive problems that might defocus the view. These lenses are positioned by rotating a knurled wheel at the side of the ophthalmoscope. A number on the face of the instrument indicates the strength of the lens. When choosing an ophthalmoscope, it is worth remembering that large ones take larger batteries,which last longer (or, better still, they might have rechargeable batteries); small ophthalmoscopes are handy for the pocket. Some ophthalmoscopes have a wider field of view than others and this is an advantage when learning to use the instrument.
If examining the patient's right eye, it is best to hold the ophthalmoscope in the right hand and view through one's own right eye. A left eye should be viewed with the left eye using the left hand (Figure 3.11). It is best if the patient is seated and the doctor is standing. The first thing to observe is the red reflex, which simply refers to the general reddish colouring seen through the pupil. If viewed from about 30 cm away from the eye, slight and subtle opacities or defects in the optical media can be seen against the background of the red reflex. The patient's eye must always be brought into focus by rotating the lens wheel on the ophthalmoscope.
Having observed the red reflex, the eye can be approached closely and the focus of the
ophthalmoscope adjusted so that fundus detail becomes visible. It is best to look for the optic disc first, remembering its position nasal to the posterior pole and slightly above the horizontal meridian. The patient should be asked to look straight ahead at this point. The important points to note about the disc are the clarity of the margins, the colour, the nature of the central cup, the vessel entry and the presence or absence of haemorrhages. Once the disc has been examined carefully, the vessels from the disc can be followed. For example, the upper temporal branch vessels can be followed out to the periphery and back, then the lower temporal branch vessels, then the upper nasal vessels and then, finally, the lower nasal vessels. Having examined the vessels, ask the patient to look directly at the ophthalmoscope light and the macular region should come into view. At first, this might look unremarkable, like a minute dot of light that follows our own light. More careful examination will reveal that it has a yellowish colour. To obtain a highly magnified view of the macular region, it is usually necessary to examine it with a special contact lens on the slit-lamp microscope, the Goldmann fundus lens. A fundus photograph is also helpful. After viewing the macula, the general fundus background should be observed. The appearance here depends on the complexion of the patient: in a lightly pigmented subject, it is possible to see through the stippled pigment epithelium and obtain an indefinite view of the choroidal vas-culature. In heavily pigmented subjects, the pigment epithelium is uniformly black and prevents any view of the choroid, which lies behind it. Finally, the peripheral fundus can be inspected by asking the patient to look to the extremes of gaze and by refocusing the ophthalmoscope. Examining the peripheral fundus demands some special skill, even with the ordinary ophthalmoscope, but it is best seen using the triple-mirror gonioscope. This is a modified contact lens that has an angled mirror attached to it. A view through this mirror is obtained using the slit-lamp microscope.
There are a number of other methods of examining the fundus. The ophthalmoscope described above is known as the direct ophthalmoscope. The indirect ophthalmoscope was introduced shortly after direct ophthalmoscopy. If one examines an eye with the pupil dilated through a mirror with a hole in it, the patient
being at arm's length from the observer and the mirror being held close to the observer's eye, the red reflex is seen. If a convex lens is placed in the line of sight about 8 cm from the patient's eye, then, rather surprisingly, a clear wide field inverted view of the fundus is obtained. The view can be made binocular, and the binocular indirect ophthalmoscope is an essential tool of the retinal surgeon (Figure 3.12). If we want a highly magnified view of the fundus, the slit-lamp microscope can be used. However, a special lens must be placed in front of the patient's eye. This can be in the form of the triple-mirror contact lens (Figure 3.13). In recent years, it has become a routine practice to examine the fundus with the slit-lamp and strong convex lenses (e.g., VOLK +60, +78 or +90DS aspheric lenses). These high-power
convex lenses provide inverted reversed images like the indirect ophthalmoscope. Another useful way of examining the fundus is by means of fundus photography. The photographs provide a permanent record of the fundus. A special type of fundus photograph, known as a fluorescein angiogram, shows up the retinal vessels, including the capillaries, in great detail. The technique involves taking repeated photographs in rapid succession after the injection of the dye fluorescein into the antecubital vein. The dye in the vessels is selectively photographed by using filters in the camera (Figure 3.14). Indo-cyanine green angiography (ICG) is more useful in assessing the choroidal circulation as ICG-A fluorescence is transmitted through the retinal pigment epithelium (RPE; compared with fluorescein [Figure 3.15]). Video filming is
becoming an important method for observing changing events in the fundus and it is now possible to view a real-time image of the optic fundus on a television screen using the scanning laser ophthalmoscope. This type of equipment will undoubtedly become a routine tool for the ophthalmologist.
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