Unilateral or bilateralenophthalmos(recession of theeyeball within the orbital cavity) or exophthalmos (protrusion of the eyeball) are characteristic of many orbital disorders (Table 15.2). These conditions should be distinguished from pseudoexophthalmos due to a long eyeball in severe myopia, and pseudoenophthalmos due to a small eyeball, such as in microphthalmos or phthisis bulbi.
The following list of examination techniques begins with the simple stan-dard techniques and progresses to the difficult, more elaborate methods. As a general rule, orbital disorders require interdisciplinary cooperation between ENT specialists, neurologists, neurosurgeons, neuroradiologists, internists, nuclear medicine specialists, and oncologists.
Visual acuity, the sharpness of near and distance vision, is tested separately for each eye. One eye is covered with a piece of paper or the palm of the hand placed lightly over the eye. The fingers should not be used to cover the eye because the patient will be able to see between them (Fig. 1.4).
The general practitioner or student can perform an approximate test of visual acuity. The patient is first asked to identify certain visual symbols referred to as optotypes (see Fig. 1.2) at a distance of 5 meters or 20 feet (test of distance vision). These visual symbols are designed so that optotypes of a cer-tain size can barely be resolved by the normal eye at a specified distance (this standard distance is specified in meters next to the respective symbol). The eye charts must be clean and well illuminated for the examination. The sharpness of vision measured is expressed as a fraction:
Normal visual acuity is 5/5 (20/20), or 1.0 as a decimal number, where the actual distance equals the standard distance.
An example of diminished visual acuity (see Fig. 1.2): The patient sees only the “4” and none of the smaller symbols on the left eye chart at a distance of 5 meters (20 feet) (actual distance). A normal-sighted person would be able to discern the “4” at a distance of 50 meters or 200 feet (standard distance). Accordingly, the patient has a visual acuity of 5/50 (20/200) or 0.1.
The ophthalmologist tests visual acuity after determining objective refraction using the integral lens system of a Phoroptor, or a box of individual lenses and an image projector that projects the visual symbols at a defined distance in front of the eye. Visual acuity is automatically calculated from the fixed actual distance and is displayed as a decimal value. Plus lenses (convex lenses) are used for farsightedness (hyperopia or hypermetropia), minus lenses (concave lenses) for nearsightedness (myopia), and cylindrical lenses for astigmatism.
If the patient cannot discern the symbols on the eye chart at a distance of 5 meters (20 feet), the examiner shows the patient the chart at a distance of 1 meter or 3 feet (both the ophthalmologist and the general practitioner use eye charts for this examination). If the patient is still unable to discern any symbols, the examiner has the patient count fingers, discern the direction of hand motion, and discern the direction of a point light source.
The pattern of disturbed ocular motility can be asign of thecause of the disorder. Causes may be neurogenic, myogenic, or mechanical.
Retrobulbar processes can press the globeinward. This often produces choroidal folds that are visible upon ophthal-moscopy. Compression of the optic nerve by a tumor may result in optic nerve atrophy or edema. Meningiomas in the sheath of the optic nerve leadto the development of shunt vessels on the optic disk.
TheHertel mirror exophthalmometer(Figs. 15.2aandb)measures the anterior projection of the globe beyond the orbital rim. A change in the position of the globe with respect to the orbital rim is a cardi-nal symptom of many orbital disorders (see Table 15.2).
The difference between the two sides is more important than the abso-lute value. A difference greater than 3 mm between the two eyes is abnormal. Unilateral exophthalmos is recognizable without an exoph-thalmometer. To do so, the examiner stands behind the patient, slightly lifts the patient’s upper eyelids, and looks down over the patient’s fore-head toward the cheek.
This is used to document damage to the optic nerve in orbital disorders.
Two techniques are available for this noninvasive examination.
The B-mode scan (B stands for brightness) provides a two-dimensional image of orbital structures. This examination is indicated in the presence of suspected orbital masses.
The A-mode scan (A stands for amplitude) permits precise measurement of optic nerve and muscle thickness. This examination is indicated as a follow-up study in the presence of Graves’ disease (endocrine orbitopathy).
These studies may also be combined with Doppler scans to evaluate blood flow.
These studies usually only provide information about the nature of bone structures, i.e., whether a fracture is present and where it is located. Smaller fractures often cannot be diagnosed by conventional radiography and require CT scans.
These modern examination modalities can precisely visualize orbital structures in various planes. They are standard methods for diagnosing tumors.
This is indicated in the presence of suspected arteriovenous fistulas.