Examination Methods Visual Acuity see Chapter 1 1221 Examination of the Fundus

Direct ophthalmoscopy (Fig. 12.4a; see also Fig. 1.13): A direct ophthalmoscope is positioned close to the patient's eye. The examiner sees a 16-power magnified image of the fundus.

Advantages. The high magnification permits evaluation of small retinal findings such as diagnosing retinal microaneurysms. The dial of the ophthalmoscope contains various different plus and minus lenses and can be adjusted as necessary. These lenses compensate for refractive errors in both the patient

a Direct ophthalmoscopy: the examiner sees an erect fundus image of the patient. b Indirect ophthalmoscopy: the examiner sees a virtual inverted fundus image. c Position of examiner and patient for indirect ophthalmoscopy.

Ophthalmoscopy.

Ophthalmoscopy.

Light source

Indirect Ophthalmoscope Technique Retianal Ffa Examin

and the examiner. They may also be used to measure the prominence of retinal changes, such as the prominence of the optic disk in papilledema or the prominence of a tumor. The base of the lesion is brought into focus first and then the peak of the lesion. A difference of 3 diopters from base to peak corresponds to a prominence of 1 mm. Direct ophthalmoscopy produces an erect image of the fundus, which is significantly easier to work with than an inverted image, and is therefore a suitable technique even for less experienced examiners.

Disadvantages. The image of the fundus is highly magnified but shows only a small portion of the fundus. Rotating the ophthalmoscope can only partially compensate for this disadvantage. Direct ophthalmoscopy also produces only a two-dimensional image.

Indirect ophthalmoscopy (Figs. 12.4b and c): A condensing lens (+14 to + 30 diopters) is held approximately 13 cm from the patient's eye. The fundus appears in two to six-power magnification; the examiner sees a virtual inverted image of the fundus at the focal point of the loupe. Light sources are available for monocular or binocular examination.

Advantages. This technique provides a good stereoscopic, optimally illuminated overview of the entire fundus in binocular systems.

Disadvantages. Magnification is significantly less than in direct ophthalmos-copy. Indirect ophthalmoscopy requires practice and experience.

Contact lens examination: The fundus may also be examined with a slit lamp when an additional magnifying lens such as a three-mirror lens (see Fig. 12.5) or a 78 to 90 diopter lens is used.

Mirror Fundus

Figs. 12.5a and b Principle of the examination: The lens is placed directly on the eye after application of a topical anesthetic. The various mirrors of Goldmann three-mirror lens visualize different areas of the retina: 1) posterior pole, 2) central part of the peripheral retina, 3) outer peripheral retina (important in diagnosing retinal tears), 4) gonioscopy mirror for examination of the chamber angle.

Figs. 12.5a and b Principle of the examination: The lens is placed directly on the eye after application of a topical anesthetic. The various mirrors of Goldmann three-mirror lens visualize different areas of the retina: 1) posterior pole, 2) central part of the peripheral retina, 3) outer peripheral retina (important in diagnosing retinal tears), 4) gonioscopy mirror for examination of the chamber angle.

Advantages. This technique produces a highly magnified three-dimensional image yet still provides the examiner with a good overview of the entire fundus. The three-mirror lens also visualizes "blind areas" of the eye such as the angle of the anterior chamber. Contact lens examination combines the advantages of direct ophthalmoscopy and indirect ophthalmoscopy and is therefore the gold standard for diagnosing retinal disorders.

Where significant opacification of the optic media (as in a mature cataract) prevents direct visualization of the retina with the techniques mentioned above, the examiner can evaluate the pattern of the retinal vasculature. The sclera is directly illuminated in all four quadrants by moving a light source back and forth directly over the sclera. Patients with intact retinas will be able to perceive the shadow of their own vasculature on the retina (entoptic phenomenon). They will see what looks like "veins of a leaf in autumn". Patients who are able to perceive this phenomenon have potential retinal vision of at least 20/200.

Ultrasonography: Ultrasound studies are indicated where opacification of the optic media such as cataract or vitreous hemorrhage prevent direct inspection of the fundus or where retinal and choroidal findings are inconclusive. Intraocular tissues vary in how they reflect ultrasonic waves. The retina is highly reflective, whereas the vitreous body is normally nearly anechoic. Ultrasound studies can therefore demonstrate retinal detachment and distinguish it from a change in the vitreous body. Optic disk drusen are also highly reflective. Ultrasound is also helpful in diagnosing intraocular tumors with a prominence of at least 1.5 mm. The specific echogenicity of the tissue also helps to evaluate whether a tumor is malignant, for example in distinguishing a choroidal nevus from a malignant melanoma (Fig. 12.6).

Ultrasound studies can demonstrate retinal detachment where the optic media of the eye are opacified (due to causes such as cataract or vitreous hemorrhage). This is because the retina is highly reflective in contrast to the vitreous body. Ultrasound can also be used to confirm the presence of malignant choroidal processes.

Fundus photography: Abnormal changes can be recorded with a single-lens reflex camera. This permits precise documentation of follow-up findings. Photographs obtained with a fundus camera in green light provide high-contrast images of abnormal changes to the innermost layers of the retina such as changes in the layer of optic nerve fibers, bleeding, or microaneurysms.

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