Chapter 27. Ophthalmology

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.

Visual Acuity Testing

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).

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 Testing

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.

Retracting Eyelids

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.

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.

Ophthalmoscope

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

Improvised Ophthalmoscope

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).

1. Cut a 15-cm piece of pipe; then cut one end so that it has a 45-degree angle "beveled edge" (B).

2. 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.)

3. 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).

4. 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.

5. Cover one side of the flat PVC disc (A) with aluminum foil and drill a small hole through its center (D).

6. 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.

7. Attach the oval disc (A) to the beveled end of the PVC pipe (B) with glue.

8. 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

Heating PVC Pipe

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.

Indirect Ophthalmoscopy

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

Glaucoma

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.

Ultrasound

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.)

Eyeglasses

Fitting for Eyeglasses

Commonly, donated or stock prescription glasses are available. Most clinicians are clueless about how to examine a patient for proper refraction, even if an optician is available to make the lenses. One option is to have the patient try on glasses until she can see objects clearly when they are held 15 inches (40 cm) from the eyes. That works for most patients.

Replacing Eyeglass/Surgical Loupe Hinges

Eyeglasses and surgical loupes (which provide magnification for both outpatient and operating room [OR] procedures) often break at their hinges. If the miniscule screw holding a hinge together is lost, the loss of eyewear can render a person incapable of functioning.

A simple temporary (or not-so-temporary) fix exists: while holding the hinge in position, pass a very small needle and 4-0 (or smaller) nylon suture through the hole for the screw. Depending on the hole's size, several passes may be made with the suture before it is tied in place. Experience proves that this works well.10

If the hinge joint has a larger screw hole, use a paperclip, safety pin, or similar small wire to hold it in place, at least temporarily. Of course, in a pinch, duct tape also works.

Nose Pads for Eyeglasses

Eyeglasses become almost nonfunctional without their nose pads—those little discs that allow the glasses to rest, more or less comfortably, on the nose. One successful method of replacing them is to sew small shirt buttons onto the metal posts coming out from the eyeglass rims.11 For a balanced feel, both nose pads will probably need to be replaced if one is missing.

Improvised Glasses

Eyeglasses generally are improvised for two reasons—to see more clearly and to protect the eyes from damage caused by glare off snow, ice, or water.

To see more clearly, apply the same principle as for pinhole visual acuity testing: if a person looks through a small hole, only the rays passing straight through to the fovea are seen. This is, theoretically, the person's best vision. For temporary eyeglasses, punch multiple holes in a cardboard eye mask over both visual axes (Fig. 27-7, right). The person can wear the mask by attaching two paper clips or safety pins and connecting them with a rubber band. This works, but limits vision to a small area directly in front of the person.

Similar "glasses" can be made to protect the eyes from glare. To improve peripheral vision, make slits rather than holes in the eye mask (Fig. 27-7, left). An alternative is to stick wide black tape to itself (sticky side to sticky side) and punch holes or slits in it. Tie or tape it around the head. To make slits in eyeglasses, cover most of the lenses with black tape. Use additional tape to block the glare around the lenses and on the sides, since that can also cause eye damage. Innovative (or desperate) people have also used leaves, palm fronds, or other materials as sun-blocking glasses.

Eye Irrigation

In resource-poor situations, Morgan lenses for irrigating the eyes after chemical exposure are generally unavailable. An alternative is to use a standard nasal prong cannula attached to a saline bag. Place the patient supine with towels or other material to collect the water. Position the nasal prongs at the bridge of the nose pointing downward. Put a piece of tape over the connector between the two prongs to hold it in place. Attach the IV tubing to the end of the nasal cannula tubing and open the "IV" all the way. This irrigates both eyes. To irrigate just one, clamp one "prong" or just use the end of the IV tubing at the medial side of the affected eye. (Joe Lex, MD, FACEP, FAAEM. Personal oral communication, May 25, 2007.)

Analgesia

Most eye pain resolves with normal analgesics.

For an alternative, or to supplement the medicine, use warm moist soaks. One method is to have the patient wrap a cloth around a spoon, dip it in very hot water, and bring it as close as possible to the eye. Do not use this method in a child. The other option is to put a cloth in hot water, such as from the faucet, wring it out, and cover the eye. Put a piece of plastic over the cloth to retain the heat and moisture. Leave the cloth on until it cools; repeat as often as needed for comfort.

Using Eye Drops

No one likes drops placed directly in their eyes. Children squirm and many attempts and hands are needed to accomplish the task; adults grit their teeth and bear it. Often, trying to put in eye drops (e.g., antibiotics, pilocarpine, or other medication) at home leads patients to abandon the treatment. Ease the process by always instilling eye drops at the medial canthus. This also avoids having to get the dropper close to the eyelashes; touching them contaminates the dropper.

Tell patients who need eye drops to tilt their heads back, with the affected eye up. Instruct adults and older children to close their eyes first; infants will do this automatically. Hold the medication container well above the face and instill two drops of medication into the medial canthus. Keep patients in this position until their eye opens, even a little, and the medication will enter—without effort. At home, have adults use this technique on themselves; parents should also use this technique with their children.

Ophthalmic Antibiotics

For most ophthalmic conditions, antibiotic drops are not needed, even though they may be prescribed. The most common example of this is most cases of conjunctivitis. Save resources by not using antibiotics unnecessarily.

If you need antibiotics, chloramphenicol, which is still widely available around the world, works well. Dissolve two 250 mg capsules in 100 mL sterile water. Filter the solution into sterile 10 mL dropper bottles. Screw the caps loosely onto the bottles and put them in a hot water bath at 100°C for 30 minutes without letting the water splash over the bottles' necks. After removing them from the water, tighten the tops and check them again when cool, as the glass may contract, causing the tops to loosen. Refrigerate them at 2°C to 8°C for up to 2 months. Chloramphenicol, since it penetrates the eye when given systemically, is also useful for more severe eye infections.12

When using ophthalmic ointment, Dr. Joseph Miller says the easiest method is to place a dab on a clean cotton swab and transfer it to the inside of the retracted lower eyelid. (Personal written communication, received September 8, 2008.)

Eye Shield

A protective eye shield can be made from a small paper cup by cutting off the top half or top three-fourths of the cup. Put tape around the cut edges so that they don't irritate the patient's face. Tape the cup to the face, so that the bottom and sides protect the eye.

Alternatively, make a protective cone by cutting a 6-cm circle in a piece of x-ray film or lightweight cardboard, then making one cut to the center of the circle. Overlap the cut ends to form a cone. Tape the film in that form and then tape the cone over the eye.13

Corneal Foreign Body Removal

Rather than using an eye burr to remove a corneal foreign body, use a TB or insulin needle with the syringe attached as a handle. Try to do the procedure under magnification—the needle will look enormous. Alternatively, use the sterile plastic 20- or 22-gauge catheter from an IV.

Corneal Ulcer

Corneal ulcers, a common problem among malnourished children in the tropics, usually respond to aggressive therapy. However, children tend to remove bandages and rub their eyes, which often results in a secondary infection and can cause blindness. So, how do you keep an uncooperative child's hands away from the eye while it is healing?

One solution is to use a splint made from an empty disposable plastic container, such as a 0.5- or 1-L bottle of bleach or irrigation solution. Cut off the top and bottom to form a uniform diameter cylinder. Then cut the container in half lengthwise and smooth the rough edges by covering them with a piece of plaster or duct tape. After padding the inside with soft cloth, fit the plastic bottle around the child's elbow and fix it in place with a plaster sheath and an elastic bandage. The child can still bend his arms slightly (for comfort), but cannot remove the eye dressings, thus preserving his vision.14

Local Anesthesia for Eye Procedures

If the normal topical anesthetic for the eye is not available, two other commonly available options exist: lidocaine and cocaine. As Boulton wrote, "Lidocaine 4% is a suitable surface analgesic for the cornea which is as efficacious as a topical analgesic as is 2% cocaine; it does not dilate the pupil or the corneal vessels."15

If performing a procedure under or with the aid of topical anesthetic, apply 2 to 3 drops to the cornea and conjunctiva every 5 minutes, starting about 20 to 30 minutes before surgery. Give additional drops, as needed, throughout the procedure.16

Glaucoma Treatment

If acute narrow-angle glaucoma affects someone in an austere setting, several actions can be taken to ameliorate the problem. Atropine 1% can be applied topically six times a day.17 Epinephrine also works, although it irritates the eye and may need to be used in high concentrations or frequently.18,19 Commonly carried and used by high-altitude groups, acetazolamide (250 mg qid) or other carbonic anhydrase inhibitors can be used to decrease aqueous humor production, lowering intraocular pressure. So can beta-blockers, which are generally administered bid. However, these measures only temporize the situation until the patient can be put on a chronic medical regimen or have surgery.17

Improvising Operating Room Instruments

For cataract surgery: "If a formal operating room is not available, any clean room and a body-length table will suffice. A clean water source is necessary."20

A small-gauge surgical hook that can be used intraocularly for ophthalmologic surgery can be fashioned from a 27-gauge needle. Similar to fashioning a skin hook (see Chapter 21, Surgery/Trauma), make it by bending the tip of a 5/8-inch, 27-gauge needle with a needle holder. After sterilization, this can be used alone or connected to a 1-mL syringe as a handle.21

A metal lid plate for eyelid surgery (provides lid support and elevation) can be made from the handle of a stainless steel soup spoon. It has the benefits of being available without alteration, its length makes it easy to handle, and it does not distort the nasal and temporal aspects of the lid.22

Corneoscleral sutures can be made by attaching a bent 30-gauge needle to size 9-0 monofilament nylon (or the fishing line equivalent).23 Swag the suture onto the needle as described in Chapter 21, Surgery/Trauma.

Cataract Surgery

Cryoextractor

Cataracts—especially those that are mature, intumescent, or hypermature—are often extracted by allowing the cold tip of a cryoextractor to form an adhesion with the cataract. A cryoextractor is expensive and often not available. It can, however, be improvised by passing a short length of copper electrical wire into the barrel of a 5-mL syringe (Fig. 27-8).

Most of the wire extruding from the syringe tip (~1 cm) should remain covered with insulation; only remove the insulation from a very small part of the wire at the tip. Also, remove the insulation from about 1 cm of the wire inside the syringe barrel. Invert a container of refrigerant, such as dichlorodifluoromethane (i.e., Freon, Frigen), and hang it from an IV stand. Run 1 to 2 mL of Freon through the tubing on the Freon container, and into the syringe. The evaporation of the Freon immediately freezes the copper wire. Experience shows that the Freon should be refilled in the syringe, if necessary, so that contact with the cataract lasts 10 to 15 seconds before extraction.24,25

Aphakic Surgery Problems

Blindness, both from cataracts and from a lack of eyeglasses post-cataract surgery, is a common problem in areas with scarce resources.26 Anyone doing cataract surgery should understand that the main problem with aphakic surgery (removing the lens for a cataract) is that patients often cannot get or replace their eyeglasses after the surgery. This leaves them essentially no better, or even worse, than prior to the surgery.

One solution is to hold or tape a single magnifying lens over an eye. Even better is to fit two lenses into a makeshift holder to use as a pair of glasses. Instruct the patient to move the makeshift glasses closer to or further from the eyes until the right focal distance is found. For these aphakic individuals, even a pair of reading glasses can produce an in-focus image. However, the patient must hold the glass a very long distance from his eye. This way, the patient gets a reduced field of view but the image is focused. (Joseph Miller, MD, PhD. Personal written communication, received September 8, 2008.)