As with most medical areas, ophthalmology generally divides into diagnosis and treatment, although these frequently overlap. For clarity, that is how this chapter is divided.
DIAGNOSTIC EXAMINATION AND EQUIPMENT
Testing visual acuity is, by far, the most important diagnostic test on the eyes; yet, it is frequently overlooked. Even with penetrating or apparently corneal-occluding injuries (e.g., alkali burns), test visual acuity in this order: light perception, movement, counting fingers, and reading/identifying at distance. Testing takes only a short time—just seconds if stopped at counting fingers—but provides invaluable information to a consulting ophthalmologist.
To test whether a nonverbal or uncooperative patient can see, elicit optokinetic nystagmus. (See Chapter 29 for improvising optokinetic test equipment.) This test works in children as young as 4 to 6 months old. The presence of nystagmus with an optokinetic stimulus confirms cortical vision and the integrity of the frontal and parietal lobes and visual fields. An even simpler visual acuity test for a nonverbal or an uncooperative child is to offer him or her various toys and see how he or she reaches for and plays with them.1
If an eye chart is not available, use a newspaper or magazine. Begin with the fine print. Stop if the patient can read it. If not, work up to the largest print the patient can read. That gives a rough gauge of the patient’s visual acuity.
Standard eye charts are easy to manufacture. Download copies from multiple internet sites, including the US National Eye Institute (www.nei.nih.gov/photo/visual-acuity-testing), or smart phone apps. If copies are available, even in miniature, local printers can enlarge them to produce standard Snellen visual acuity charts, as well as “illiterate” eye charts (Landolt ring chart and “E” chart), on heavy paper and cardboard. Mount these on a heavier board and, if possible, laminate or cover charts with a plastic sheet for protection.
For patients who present without their corrective lenses or for those who have never gotten lenses but should have, there are two ways to test visual acuity: an ophthalmoscope or a pinhole device.
To test visual acuity using an ophthalmoscope, have patients cover one eye while looking at the eye chart through the ophthalmoscope. Have the patient hold the instrument as would a practitioner; the examiner should adjust the lenses to find the optimal one for the patient. If the visual acuity examination is done after an ophthalmoscope examination, start with the lens setting with which the patient’s disc is best seen. If only a wall-mounted ophthalmoscope is available, use a pocket eye chart to position the patient at the proper distance from the chart (generally 14 to 16 inches for a pocket chart and 20 feet for a standard chart). For supine patients, such as those suffering trauma, get a helper to ...