Other Tests Available in an Eye Department

Several special tests are available to measure the ability of the eyes to work together. A department known as the orthoptic department is usually set aside within the eye clinic for making these tests. When there is a defect of the ocular movements, this can be monitored by means of the Hess chart (see Chapter 14). The ability to use the eyes together is measured on the synop-tophore, and any tendency of one eye to turn out or in can be measured with the Maddox rod and Maddox wing test (Figure 3.16). The use of contact lenses and also of intraocular implants has demanded more accurate measurements of the cornea and of the length of the eye. A ker-atometer is an instrument for measuring the curvature of the cornea, and the length of the eye can now be accurately measured by ultrasound. If one eye appears to protrude forwards and one wishes to monitor the position of the globes relative to the orbital margin, an exoph-thalmometer is used (Figure 3.17). X-rays of the eye and orbit are still used. An X-ray is essential if an intraocular foreign body is suspected and it is useful for detecting bony abnormalities in

Figure 3.16. The Maddox wing. I

Figure 3.17. The exophthalmometer.CQ

the walls of the orbit caused by tumours. Computed tomography (CT) scanning has become an important diagnostic technique, especially for lesions in the orbit (Figure 3.18), particularly those involving bony tissues. This specialised X-ray has surpassed plain X-rays for most ophthalmic purposes. Magnetic resonance imaging (MRI) is more useful in assessing soft tissues of the orbit and cranium. Ultrasonogra-phy is a technique for measuring the length of the eye (which is a prerequisite for all cataract surgery); it can also be used to depict tissue planes within the eye, showing, for example, the size of intraocular tumours or the presence of vitreous membranes. It can be used to determine the presence or absence of retinal diseases, especially in eyes with opaque media (e.g., cataract or vitreous haemorrhage). Electro-retinography provides a measure of the electri

Figure 3.18. Computed tomography (CT) scan of eyes and orbit (normal).CQ

Figure 3.16. The Maddox wing. I

Figure 3.18. Computed tomography (CT) scan of eyes and orbit (normal).CQ

Figure 3.19. The Heidelberg retina tomograph.

Mocrfields regression classification: within normal limits

Figure 3.19. The Heidelberg retina tomograph.

cal changes that take place in the retina when the eye is exposed to light. It can indicate retinal function in the same way that the electrocardiogram indicates cardiac function. The visually evoked potential is a measure of minute electrical changes over the back of the scalp, which occur when the eyes are stimulated with a flashing light. This test has been shown to be useful in detecting previous damage to the optic nerve in patients with suspected multiple sclerosis.

Technological advances have led to increasing dependence on imaging devices, such as digital fundus cameras for retinal screening in patients with diabetes. In addition, recent laser technologies, such as the Heidelberg retina tomograph, allow for a quick and easy way of scanning the optic nerve head in three dimensions (Figure 3.19) and the retinal nerve fibre layer. This is especially helpful in evaluating changes in patients with glaucoma.

0 0

Post a comment