Approach to acute vision loss: Clinical sciences

Acute vision loss is a relatively sudden worsening of visual perception. The underlying pathology could be anywhere along the visual pathway, including the eyes, optic nerves, optic chiasm, optic tracts, optic radiations, and the visual cortex.

Now, vision loss associated with eye pain is common for conditions like infectious keratitis, glaucoma, and optic neuritis. However, painless vision loss is found with stroke, mass compression of the optic chiasm, retinal detachment, as well as central retinal artery or venous occlusion, or ischemic optic neuropathy.

If your patient presents with acute vision loss, first obtain a focused history and physical exam, as well as a fundoscopic exam. Patients typically report a sudden vision loss, while the physical exam demonstrates decreased visual acuity and possibly impaired visual fields. Don’t forget to perform the swinging flashlight test. This test is used to assess the pupillary reflex pathway, which involves the optic nerve as the sensory afferent limb, and the oculomotor nerve as the motor efferent limb.

During the swinging flashlight test, you shine a light, such as with a penlight, back and forth between the two eyes. Normally, regardless of which eye the light is shining into, the sensory afferent limb of the optic nerve will send a signal to the Edinger-Westphal nucleus in the midbrain. From here, the signal will be sent back via the oculomotor nerves and the ciliary ganglia to the pupillary sphincter muscles in both eyes, causing both pupils to constrict.

However, if there’s a lesion of the afferent pathway, when you swing the light from the normal eye to the affected eye, the stimulus will not reach the Edinger-Westphal nucleus. In other words, efferent signals will not reach pupillary sphincter muscles, so the patient’s pupils will not constrict, instead, they will dilate. This is known as a relative afferent pupillary defect or Marcus Gunn pupil. Finally, in some individuals with acute vision loss, the fundoscopic exam might reveal optic disc edema. With these findings, you can diagnose acute vision loss, so your next step is to assess for eye pain.

If there is pain associated with vision loss, examine the patient for conjunctival injection, meaning redness of the conjunctiva. The presence of conjunctival injection suggests ophthalmologic causes of vision loss, such as infectious keratitis and acute angle closure glaucoma.

Let’s start with infectious keratitis. These patients typically report tearing of the eye. They might also have a history of unhygienic contact lens use, such as swimming with their contact lenses in. When it comes to the physical exam, it reveals corneal opacification, sometimes with corneal ulcers or mucopurulent drainage.

At this point, you should consider infectious keratitis, so obtain scrapings of the cornea and send samples for gram stain, culture, and PCR. If gram stain or cultures detect bacteria or fungus, or PCR results come back positive for HSV or adenovirus, diagnose infectious keratitis.

Here’s a couple of clinical pearls to keep in mind! HSV keratitis commonly presents with dendritic ulcers, which have a branching appearance that look like dendrites. These dendrites can be detected with a fluorescein stain exam. If you see them, start a topical or oral antiviral agent. Now, while keratitis is inflammation of the cornea, other parts of the eye can also become inflamed and cause painful vision loss. For example, inflammation of the eyelash follicles or Meibomian glands of the eyelid is known as blepharitis and causes similar symptoms in addition to eyelid swelling.

Next, your patient might present with inflammation of the conjunctiva, also known as conjunctivitis, which can occur due to bacteria, viruses, or allergies. Some other common examples include periorbital and orbital cellulitis, uveitis, and dacryocystitis.

Okay, let’s move on to acute angle closure glaucoma, which is the closure of the anterior chamber angle where aqueous humor is drained. In addition to painful vision loss, these patients might report headache, nausea, or vomiting. They may also tell you that their symptoms were precipitated by entering a dark room. This happens due to pupillary dilatation in the dark, which further narrows the anterior chamber angle, making it even more difficult for aqueous humor to drain.

On physical exam, you will find a fixed and dilated pupil. With these findings, consider acute angle closure glaucoma, Next, perform tonometry and gonioscopy. If tonometry reveals elevated intraocular pressure, and gonioscopy confirms a closed anterior chamber angle, you are dealing with acute angle closure glaucoma.

Now let’s go back and take a look at patients with no conjunctival injection. In this case, consider optic neuritis. Optic neuritis can be caused by various conditions, including infectious, autoimmune, and granulomatous conditions. The most common ones are demyelinating disorders. Your next step is to obtain an MRI of the brain and orbits. If it reveals optic nerve enhancement and edema, possibly with enhancing white matter lesions, diagnose optic neuritis.

Time for a clinical pearl! If your patient is a young, biological female with a first-time presentation of optic neuritis, suspect multiple sclerosis. Another condition to consider is neuromyelitis optica spectrum disorder, which tends to be more severe with poorer recovery.

Patients with optic neuritis often report painful eye movements, as well as colors not appearing as bright as usual. This can be tested on exam by asking patients to look at a red object with each eye individually. To the affected eye, the red color may appear lighter or washed out, known as red desaturation.