Moran CORE

Open source ophthalmology education for students, residents, fellows, healthcare workers, and clinicians. Produced by the Moran Eye Center in partnership with the Eccles Library

Search Moran CORE

Red Flag Symptoms of Unilateral Vision Loss

Home / Basic Ophthalmology Review / Visual Acuity and Vision Loss

 Title: Red Flag Symptoms of Unilateral Vision Loss

Author: Troy Teeples, 4th year medical student, University of Utah School of Medicine; Griffin Jardine, MD

Photographer: James Gilman, CRA, FOPS

Date: 8/7/2018

Keywords/Main Subjects: Unilateral vision loss, monocular vision loss, red flags, headache, painful eye, pain with eye movement, floaters, flashes, atherosclerosis, central retinal artery occlusion, central retinal vein occlusion, giant cell arteritis, acute angle closure glaucoma, optic neuritis, keratitis, retinal detachment, vitreous hemorrhage, amaurosis fugax


Acute, monocular vision loss is a frightening experience for patients and may have long-term consequences depending on the etiology. The key to providing efficient, effective care is a careful history, a focused physical exam and knowing when to seek help from an ophthalmologist. The goal of this section is to help identify red flag signs and symptoms during a work up of unilateral vision loss in order to able to 1) efficiently narrow a differential diagnosis and 2) know when to urgently consult ophthalmology.

Red Flags from History and Physical Exam

There are key elements that need to be addressed when working up a patient with unilateral vision loss. Providers should look for the following associated symptoms and signs in order to guide the decision-making process.


When a patient over the age of 60 complains of a headache and unilateral vision loss, Giant Cell Arteritis (GCA) should be immediately considered given the potential for permanent vision loss. Ask the patient about a history of polymyalgia rheumatica, scalp tenderness, jaw claudication and other constitutional symptoms such as fever, malaise, weight loss or anorexia. If GCA is suspected, order an ESR, CRP and CBC looking for an elevated platelet count.  If there is a high enough suspicion for GCA, don’t wait for the lab results to initiate high-dose systemic corticosteroids. An ophthalmologist should be consulted to evaluate the cause of the vision loss, specifically looking for a central retinal artery occlusion. The patient should then be schedule for a diagnostic temporal artery biopsy within the next week as an outpatient.

Red, Painful Eye

There are several causes of monocular vision loss accompanied by a red, painful eye.  After inquiring about recent trauma and ruling out a ruptured globe, check the patient’s intraocular pressure (IOP) with a Tono-pen® to evaluate for Acute Angle Closure Glaucoma, as this may lead to permanent vision loss if not treated appropriately. Patients will present with a red, painful eye as well as a headache, and nausea/vomiting. They may also complain of halos around lights. Physical exam will reveal a steamy (hazy) cornea, a dilated pupil that is not reactive to light, and an IOP greater than 40 typically. Consult an ophthalmologist if suspected.

Keratitis or corneal ulcers may also present with a red, painful eye and unilateral decreased or blurry vision. Patients may complain of excessive tears or discharge, and photophobia. Ask about contact lens wear, autoimmune conditions such as rheumatoid arthritis and look for corneal whitening or loss of corneal clarity and consult an ophthalmologist if concerned.

Pain with eye movement

Optic neuritis will present with acute vision loss, typically over the course of < 1 week. The majority of these patients will have pain with eye movement and decreased color vision. They may have a history of demyelinating symptoms or a known diagnosis of multiple sclerosis. On exam, a relative afferent pupillary defect (APD) will be seen during a swinging flashlight test.

Floaters and flashes

Another combination of concerning symptoms are flashes and floaters in combination with monocular vision loss. Flashes and floaters of acute onset are concerning for a retinal detachment. Patients are commonly myopic (short-sighted) and may additionally complain of vision loss as a “curtain drawn” over their vision. A retinal detachment is painless but a surgical emergency and a vitreoretinal specialist should be consulted.

A vitreous hemorrhage may also present as painless monocular vision loss associated with floaters. Patients should be questioned regarding a history of trauma, ocular surgery, diabetes, sickle cell anemia, leukemia and high myopia, all of which may precipitate a vitreous hemorrhage.

Atherosclerosis Risk Factors

If a patient presents with painless, temporary monocular vision loss with subsequent restoration of sight, then amaurosis fugax should be high on the differential. A thorough history should include atherosclerotic risk factors such as diabetes mellitus, smoking, CAD, and HTN. Fundoscopy may reveal Hollenhorst plaques (cholesterol emboli).

Central Retinal Artery Occlusion (CRAO) and Central Retinal Vein Occlusion (CRVO) are nearly impossible to distinguish by history alone. Patients will present with acute, painless monocular vision loss without other associated symptoms. These diagnoses are made with fundoscopy revealing a “blood and thunder” appearance in CRVO along with diffuse hemorrhages and cotton wool spots (figure 1). No emergent treatment is particularly effective in reversing the changes, but there are several long-term sequelae and corresponding treatments so these patients should be referred to an ophthalmologist for close follow-up.

CRAO, on the other hand, does have a few emergent treatment options and is an ophthalmologic emergency. It can by recognized on fundoscopy by diffuse ischemic retinal whitening and a cherry red fovea along with boxcar segmentation of blood in the retinal veins (figure 2). Consult an ophthalmologist immediately if suspected and within the first several hours of the vision loss.

Images or video:

Figure 1: A color fundus photo of the left eye with diffuse retinal hemorrhages in all four quadrants (“blood and thunder”) and optic nerve edema, consistent with a central retinal vein occlusion.

Figure 2: A color fundus photo of the right eye demonstrating diffuse, ischemic retinal whitening; arterial attenuation and a “cherry red spot” at the fovea—pathognomonic in the context of retinal whitening and sudden, painless vision loss for a central retinal artery occlusion.



  1. Farris W, Waymack JR. Central Retinal Artery Occlusion. [Updated 2017 Dec 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2018 Jan-. Available from: Accessed 6/19/2018.
  2. Khazaeni B, Khazaeni L. Glaucoma, Acute Closed Angle. [Updated 2017 Apr 9]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2018 Jan-. Available from: Accessed 6/20/2018.
  3. Ness T, Bley TA, Schmidt WA, Lamprecht P. The diagnosis and treatment of giant cell arteritis. Dtsch Arztebl Int 110: 376-385, 2013.
  4. Patel A, Nguyen C, Lu S. Central Retinal Vein Occlusion: A Review of Current Evidence-based Treatment Options. Middle East Afr J Ophthalmol. 2016 Jan-Mar;23(1):44-8. PubMed PMID: 26957838.

Faculty Approval by: Griffin Jardine, MD


Copyright statement: Copyright Troy Teeples, ©2018. For further information regarding the rights to this collection, please visit: