Ocular pathology is a topic that is often underappreciated in wilderness medicine education, despite vision being one of the major sensory inputs required for almost every task. Even seemingly benign issues such as a corneal abrasion, in a technical environment, can lead to debilitating pain and incapacitation. Impaired vision, even in one eye, can lead to decreased depth perception that can impact safe travel in difficult terrain, such as scree fields or ski touring. Consequently, the ability to diagnose and properly treat ophthalmologic issues in the backcountry is imperative. In part 1, we will cover all of the components of the complete eye exam. Depending on level of training, this may seem a little technical, but hang with me.
The Eye Exam
In a hospital or clinic environment, there are several aspects to the complete eye exam. Visual acuity and intraocular pressure are considered the “vital signs” of the eye. Extra-ocular muscle function, pupil size, shape, and response to light, and the examination of lids, lashes, and peri-orbital soft tissues make up the external part of the exam. Visual fields should also be assessed. Fundoscopy to evaluate the posterior chamber and retina, and a slit lamp exam to evaluate the cornea, anterior chamber, and lens are more advanced parts of the eye exam that take time and practice to develop proficiency. The response to topical anesthetic gives important information, as an improvement in pain generally guarantees that the pathology is external. Lastly, fluorescein staining to evaluate for any corneal defects such as abrasions or ulcerations finishes out the complete eye exam.
Outside of the hospital environment, the exam is more limited, however the components of the exam are still the same, even with a basic kit. A Snellen chart isn’t required for visual acuity – anything with print can be used to grossly estimate vision, with progression to finger counting, hand movement, and light and dark differentiation just like in the hospital. Acuity should be assessed with corrective lenses, but if the lenses are damaged or not available, a pin-hole can be easily improvised and provide an accurate exam. Increased intra-ocular pressure can be grossly assessed by pressing gently on the globes, feeling for asymmetry, firmness, or resistance to normal retropulsion. Extra-ocular muscle function, pupil exam, and evaluation of the external structures are no different from in a clinic, as long as a light source such as a flashlight or headlamp is available. Defects in pupil size and shape are usually obvious, but it is important to be able to know and look for a relative afferent pupillary defect. There are several causes, and almost all of them are vision threatening. A link to a video reviewing the exam can be found here. Fundoscopy is limited to those who choose to carry a direct ophthalmoscope in their kit, which isn’t unreasonable as there are lightweight options designed for austere environments. The slit lamp exam is impossible in the out of hospital arena, although there are small handheld potable devices available. Cutting a small slit in a thick piece of paper or tape does allow for a narrow beam of light that can be used to grossly assess anterior chamber angle and to look for corneal opacities. A topical anesthetic such as tetracaine should be part of a medical kit, although, just as with all medications, attention to environmental stability should be considered. Fluorescein staining is limited by the availability of either a UV light or a cobalt blue filter, however filters manufactured specifically for penlights are easily obtainable and there are several phone apps that have a cobalt blue screen light. One of the major limitations to performing an eye exam in the austere environment is getting out of the light into a dark enough area to be able to perform the exam, however going into a tent or covering up with a tarp or jacket can help to create a dark environment.
One final topic to discuss is ocular ultrasonography, which can be great adjunct to the eye exam. As ultrasounds platforms become smaller and more packable, it is much more feasible to bring one into the prehospital environment. Ocular ultrasound can give an immense amount of information, allowing for differentiation of some of the causes of acute vision loss, examining for glaucoma, penetrating foreign body, retrobulbar hematoma, increased intracranial pressure, and even pupillary response and extra ocular movements in a patient with extensive peri orbital edema. There are several great online resources regarding ocular ultrasound, which can be found here, here, and here. If available, ultrasound can help distinguish between the need to "call in the helicopter" versus having someone walk out or even stay on the expedition.
A thorough eye exam is essential in establishing a differential diagnosis for eye pathology, which can determine whether basic treatment is sufficient or if evacuation is required. Not all parts of the exam are required in every situation, but knowing how to perform an eye exam is crucial. If ultrasound is something that is available, it can be very useful. In part 2, we will get more into the meat with a discussion on the approach to the eye complaint and management of different common conditions seen in the wilderness environment.
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