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. Joseph Miller, a professor of ophthalmology at the University of Arizona, says that another option is to borrow someone's reading glasses and test the patient's vision with and without the glasses. (Personal written communication, received September 8, 2008.)
A pinhole device can also be used to determine a patient's optimal visual acuity. Make this device by cutting a 5-cm circular piece of opaque x-ray film and attaching it to a handle. Puncture the center of the film to produce a hole about the size of the head of a pin. Putting in more holes may improve the chance of some patients finding a hole to look through. Alternatively, use a paper cup with holes punched in the bottom rather than x-ray film (Fig. 27-1).
Pinhole device improvised from paper cup.
An even easier method is to remove the top from a salt shaker and use that as the pinhole device. While it may be little messy, a soda (e.g., Saltine) cracker with holes may also be used. Many elderly patients use cracker holes to read the menu in restaurants, so we know it works.
Color vision testing probably won't be important in austere circumstances. But, if it becomes necessary, the only method is to ask the patient if he (nearly always a "he") can tell you the color of various objects in the room. Choose red, green, violet, and pink objects, since red-green color blindness is most common. The only caveats are (a) be certain that you have good color vision yourself to get a baseline and (b) be aware that there is a spectrum of "normal" color vision.
Eyelids may need to be manually opened for examination or treatment, particularly in patients with periorbital swelling due to trauma or infection or to look under the lids for foreign bodies. Perform this exam as early as possible after the patient presents; the swelling may progress enough that it may be nearly impossible to examine the eye later without surgery. Opening massively swollen eyes may reveal the most surprising result—a normal eye with normal vision. Without the exam, however, you won't know that.
The best way to open swollen eyelids is to use lid retractors. If the patient is conscious, drop in some topical anesthetic. Open a paperclip so that the small (inside the clip) and large (outer part of the clip) pieces are in the same plane (i.e., flat) (Fig. 27-2). Use a clamp to hold one end and bend it 180 degrees. (With some paperclips, this can also be done by hand, although that's not recommended.) Bend the larger side for use in adults; the smaller side is best for children. Clean the paperclip and use it as a lid retractor. Use two if both the upper and lower lids must simultaneously be retracted, which is usually the case (Fig. 27-3). These can be sterilized and reused.
Eyelid retractors from paperclip.
Using eyelid retractor made from a paperclip.
In the operating room, tie a suture to the paperclip and secure that to the drape. If you have a sterile rubber band, secure that to the paper clip: it provides additional laxity, if you need it. Occasionally, a 7-0 (or smaller) silk or nylon suture is used for lid retraction. Pass it through the lid just above the lash line and pass it back through so it is just on the other side of the lashes. Do not penetrate the palpebral conjunctiva.
For a better view of the sclera and cornea during the examination, use an ophthalmoscope or put a (an additional) pair of reading glasses or a handheld magnifying lens between your eye and the patient's.
Focusing with an Ophthalmoscope
In truth, many clinicians no longer routinely use an ophthalmoscope. So, using the ophthalmoscope may be challenging. This method helps you get a clear view of the fundus if you are unable to focus when using the diopter lenses. Wear your glasses and have the patient put on his eyeglasses. Flip the ophthalmoscope lenses until the fundus comes into focus. Then both of you remove your glasses so you can take a closer look.2,3
A method of constructing an improvised ophthalmoscope uses a flashlight, a 2-cm-diameter piece of black polyvinylchloride (PVC) pipe, aluminum foil, glue, a drill, a small saw, and an oven (Fig. 27-4).
Cut a 15-cm piece of pipe; then cut one end so that it has a 45-degree angle "beveled edge" (B).
Cut another 10-cm piece of pipe and split it lengthwise; heat it to obtain a flat piece of PVC. (See "Heating PVC Pipe" that follows.)
Cut this flat piece into two discs: one disc (C) is the same diameter as the glass at the front of the flashlight, which it will replace. (If you have a small [mini-] mag light, that may provide a better view.) Drill a 2-cm hole in its center. Cut the other disc (A) so that it fits over the beveled end of the long pipe (B).
Cover the inside of the pipe (B) with aluminum foil, except for the tip at the beveled end. The bright side of the aluminum foil should face the center of the pipe to increase illumination.
Cover one side of the flat PVC disc (A) with aluminum foil and drill a small hole through its center (D).
Drill another, slightly larger, hole (E) directly opposite to where the disc's hole will be, at the end of the long piece of PVC pipe (B). This (hole E on pipe B) is the viewing port.
Attach the oval disc (A) to the beveled end of the PVC pipe (B) with glue.
Glue the "non-viewing" end of the long pipe (B) to the round piece with the 2-cm hole (C). Both PVC glue and cyanoacrylate work. Remove the flashlight's glass and replace it with the flat end of the device. The ophthalmoscope is ready for use. This device provides enough light to observe an upright image of the optic disc without needing to dilate the eye. For refraction, use either a lens-correcting set (such as optometrists use) or various eyeglass lenses.4
Ophthalmoscope improvised from PVC pipe and a flashlight.
To flatten pieces of PVC pipe, they must be heated. Since PVC pipe emits dioxins and other toxic, potentially cancer-causing gasses, heat it in a well-ventilated area, preferably outside, while wearing a good protective mask. If possible, work on a large flat piece of wood since it acts as a good insulator, allowing the pipe to stay warmer longer. Wear gloves to protect your fingers and slowly heat the PVC with one of the following: (a) a propane torch (keep enough distance to not burn the pipe); (b) a heat gun, which will not burn the pipe; (c) very hot or boiling water (dip the piece into the water until it heats completely through and repeat as necessary); (d) an ordinary heat lamp; or (e) another heat source, such as a kerosene heater. Keep testing the pipe with a gloved finger until it becomes flexible, like rubber. Put a flat, fireproof object (like metal) on it. Once the PVC pipe is flat, cool it by spraying it with or dunking it in cool water.
Ophthalmologists who want to do indirect ophthalmoscopy, but who don't have the standard equipment, may succeed in the unconscious patient with fixed, dilated pupils. Hold a ≥2-inch-diameter handheld magnifier positioned at arm's length, about 4 cm from the patient's eye. Use a direct ophthalmoscope as a light source (preferred), a transilluminator (second choice), or a Mini-Maglight (focused to the smallest possible spot, a distant third choice as it can be quite tricky). You can get a nice, wide-field view of the retina and optic nerve. It is the best way to see hemorrhages and so forth. With good-quality 4X and 5X magnifiers (corresponding to about 20-diopter lenses), it works well. However, the cheapest handheld magnifiers (3X magnification, costing about 30 cents) produce too poor an image to use. If using the direct ophthalmoscope, set it so you can see the magnifying glass clearly and in focus. An aerial image of the retina forms about 3 inches in front of the lens. This wonderful trick does not require the fancy headlamp that ophthalmologists routinely use. (Joseph Miller, MD, PhD. Personal written communication, received September 8, 2008.)
Non-Traumatic Eye Conditions
Non-traumatic eye complaints are common. Table 27-1 provides a method of differentiating among them. Some, such as an external hordeolum (sty), are usually minor problems; a corneal ulcer can be a serious, and potentially sight-threatening, condition.5
Table 27-1 Differential Diagnostic Features of Non-traumatic Eye Complaints |Favorite Table|Download (.pdf)
Table 27-1 Differential Diagnostic Features of Non-traumatic Eye Complaints
|Symptoms and Signs||External Hordeolum (Sty)||Internal Hordeolum||Chalazion||Conjunctivitis||Anterior Uveitis||Corneal Ulcer|
|Eye pain||Sensation of foreign body||Sensation of foreign body possible||Sensation of foreign body possible. After a few days, signs and symptoms resolve||Itching or burning||Moderate to severe dull ache||Moderate to severe|
|Photophobia||Possible||Absent||Absent||Absent to moderate||Present||Present|
|Discharge||Lacrimation||Absent||Absent||Present (purulent or watery)||Absent||Purulent|
|Redness/inflammation||Usually localized, but may be diffuse||Localized|
Grayish-red, freely moveable mass in lid.
Conjunctiva red and elevated
|Entire eye red, more pronounced away from cornea||Pink to red flush around cornea||Entire eye red, darker away from cornea|
|Pupil size||Normal||Normal||Normal||Normal||Constricted||Normal or constricted|
|Pupil shape||Normal||Normal||Normal||Normal||May be irregular||Normal|
|Pupil reaction to light||Normal||Normal||Normal||Normal||Diminished or absent||Normal or diminished|
|Special notes||Small, round, tender area of induration on lid margin||Small elevation or yellow area at site of affected gland, on conjunctival side of lid||If mass is nonmobile, it may be malignant||Rarely a serious condition||Moderately serious condition||Very serious condition|
If a tonometer is not available, a gross screen for glaucoma is to check visual fields. Bilateral loss of lateral vision is common with late glaucoma because of the damage to the optic nerve.
Another option to assess the intraocular pressure by using your fingers is known as digital ocular compression. This method is highly inaccurate. However, left with no other choice, it is worth trying. Ask the patient to close their eyes and try to stare straight ahead. Alternate between depressing and releasing the cornea of one eye using two index fingers placed side by side. Pushing with just one finger or somewhere on the eye other than on the cornea simply tests how easy it is to push the eye back into the orbit. The easiest method to "calibrate" this exam is to do it on a normal subject (not yourself) and immediately do it on the patient. (Joseph Miller, MD, PhD. Personal written communication, received September 8, 2008.)
Another useful tool, which has been the gold standard for more than 50 years, is the Schiøtz indentation tonometer (Fig. 27-5). It is inexpensive and does not require a power source. It measures how far a fixed, weighted plunger can indent the cornea. Although less accurate than applanation tonometers, if used correctly it provides good information about intraocular pressure. To use the Schiøtz tonometer correctly, (a) anesthetize the eye with a topical anesthetic, (b) zero it using the fixed metal piece that comes in its case, (c) open the lids widely, (d) hold it only by the "side rails" (Fig. 27-6), and (e) have the patient hold his ipsilateral thumb in front of him to stare at during the procedure. The mean intraocular pressure (IOP) in normal adults is 15 to 16 mm Hg; the normal range (mean ± 2 SD) is 10 to 21 mm Hg.
Schiøtz indentation tonometer. (Reproduced from Meller and Sweet.6)
Schiøtz indentation tonometer in use.
Ultrasound, available in many remote and austere circumstances (e.g., the International Space Station), provides an excellent diagnostic tool for intraocular abnormalities. Ultrasound may be able to define lesions that cannot be seen due to their being obscured by blood or due to the lack of an ophthalmoscope (or the ability to use one well).
To examine the eye with ultrasound, use a linear array transducer in the 7.5- to 15-MHz frequency, which is the same one used for soft tissue exams, line placement, and musculoskeletal exams. Set the machine on a "small parts" setting if there is one. Have the patient close his eyes and fill the orbit you will examine with a large amount of gel—a really whopping amount. (Put lots and lots of gel into the orbit!) That allows an exam without any discomfort to the patient; the transducer should never touch the eyelid.7
To avoid a shaky image, the examiner should rest his arm on a bony part of the patient's face, such as the ridge of the nose or the eyebrow. The anterior and posterior chambers, the lens, and the optic nerve are easily seen. During the procedure, adjust the gain to avoid artifacts. The transducer should be used not only in the vertical and horizontal positions, but also swept side to side across the eye. The patient, if cooperative, can help by moving the eye in various directions when instructed to do so.7
Common abnormalities that can be evaluated using ultrasound are retrobulbar hematomas; vitreous hemorrhage; globe perforations; foreign bodies; optic nerve abnormalities; lens dislocations; and vitreous, choroidal, and retinal detachments. As with any imaging study, the more experience one has, the better he can define and understand the images.
Disinfecting Ophthalmological Equipment
If disposable covers are not used, applanation tonometers routinely become contaminated. In austere situations, even if tonometers are available, there probably will not be disposable covers. This poses a risk of contaminating patients with a variety of organisms, including those causing epidemic keratoconjunctivitis. Rather than the ineffective practice of wiping them with 70% isopropyl alcohol, which is frequently done, tonometers can be disinfected by immersing them for 10 minutes in 0.05% sodium hypochlorite (1:100 dilution of bleach in water) or a 3% hydrogen peroxide solution. Soaking them in 70% alcohol destroys the tip.8
Most other ophthalmological equipment can be disinfected in the same manner, using 0.05% bleach or 3% hydrogen peroxide. If equipment needs to be sterile, meaning no spores are present, they should be autoclaved.9 (See Chapter 6, Cleaning and Reusing Equipment, for additional information.)