As with most medical areas, ophthalmology generally divides into diagnosis and treatment, although these frequently overlap. For clarity, this chapter divides ophthalmology topics into the broad categories of diagnosis and treatment.
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 the ophthalmologist.
Opticokinetic nystagmus can be elicited in children as young as 4 to 6 months old. The presence of nystagmus with an opticokinetic stimulus confirms cortical vision and the integrity of the frontal and parietal lobes and visual fields. A nonverbal or an uncooperative child's visual acuity also can be tested by offering the child various toys and seeing how he reaches for and plays with them.1 (See Chapter 26, Neurology/Neurosurgery, for improvising opticokinetic test equipment.)
If an eye chart is not available, use a newspaper or magazine. Begin with the fine print. Stop if the patient can read that. 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. Copies can be downloaded from multiple internet sites, including the US National Eye Institute (www.nei.nih.gov/photo/keyword.asp?conditions=Eye+Charts). 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. Simultaneously, printers can produce small, pocket-sized charts for clinicians to use.
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: using either 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 exam is done after an ophthalmoscope exam, start with the lens setting with which the patient's disc is best seen. If only a wall-mounted ophthalmoscope is available, a pocket eye chart may be needed to get the patient at the proper distance from the chart (generally 6 feet for a pocket chart and 20 feet for a standard chart). For supine patients, such as those suffering trauma, get a helper to stand on a stool and hold the eye card. Dr. ...