>Shining a light on acute vision loss: PoCUS for the retina

Shining a light on acute vision loss: PoCUS for retinal pathology

Resident Clinical Pearl (RCP) August 2019

Dr. Devon Webster – PGY2 FMEM Dalhousie University, Saint John NB

Reviewed by Dr. Kavish Chandra

 

It’s a quiet night in RAZ and you pick up your next chart- a 68 year old Ms. Iris Snellen has come in with new onset, painless, monocular vision loss. You pick up the ophthalmoscope to perform fundoscopy, and despite your best attempts, like many ED physicians before you, you see nothing helpful. So instead you pick up your investigative tool of choice, the ultrasound probe, and begin your ocular POCUS exam…


Anatomy and pathophysiology

The retina is composed of multiple layers of neurons that allow for the human eye to convert light energy (photons) into images within the occipital brain. The retina sits on top of the vascular choroid which provides blood flow.

Fundoscopy allows for visualization of the following structures:

  • Optic disc
  • The macula (central, high-resolution, color vision)
  • The fovea (sits centrally in the macula and provides sharp, central vision)
  • The retinal artery and vein

https://stanfordmedicine25.stanford.edu/the25/fundoscopic.html

 

PoCUS is adjunctive test to assess for vision-threatening and common conditions impacting the eye such as retinal detachment (RD), posterior vitreous detachment (VD) and vitreous hemorrhage (VH).

A normal eye should allow you to visualize the following structures:

https://www.nuemblog.com/ocular

In retinal detachment, the retina is separated from the choroid either through formation of a hole in the retina, peeling away from the choroid if attached to the vitreous humour or through edematous infiltration between the two layers. Separation results in rapid ischemia and death of photoreceptors with subsequent vision-loss.

Posterior vitreous detachment is common and occurs secondary liquification of the gel-like vitreous body.

Vitreous hemorrhage can occur secondary trauma, spontaneous retinal tears or vitreous detachment or any cause of retinal neovasculiarzation such as in diabetes.

 


Retinal detachment and the DDx

When assessing your pt, a retinal detachment should be at the top of your list of diagnoses to rule out given that prompt recognition and referral to ophthalmology may be a vision-saving intervention.

On history she may describe the following features of RD:

  • Floaters: may appear as spiderwebs, a large spot that comes and goes that may ‘look like a big fly’ or a showering of many small black dots.
  • Painless monocular vision loss: may present as a ‘curtain descending’ across her vision and/or visual field loss.
  • Flashes: may be easier to see at night or in a dark room (consider turning off the lights in the exam room)

Assess for risk factors for retinal detachment:

  • Myopia (near-sightedness): Major risk factor!
  • Cataract surgery
  • Family history of retinal detachment
  • Diabetes
  • Glaucoma
  • Old age
  • History of posterior vitreous detachment

Physical exam:

  • Assess for changes in visual acuity
  • Assess for loss of visual fields
  • Fundoscopy may reveal advanced detachments however, early detachments are often not visible with direct fundoscopy. Advanced detachments may reveal absence of a red reflex and a billowing retinal flap.
  • Ultrasound!

Your DDx may include:

  • Posterior vitreous detachment
  • Vitreous hemorrhage
  • Ocular migraine
  • CRAO/CRVO
  • Amaurosis fugax

(see below for distinguishing features of the DDx)

 


The PoCUS assessment

Most ED physicians feel more comfortable with their ultrasonography skills over their fundoscopy skills. PoCUS is a fast, portable and radiation-free approach to assessing patients for potential vision-threatening pathology such as retinal detachment. While ultrasonography should not replace ophthalmologic assessment and fundoscopy, it can be used as an additional tool to support your primary diagnosis.

Most recently, Lanham, et al., published a prospective diagnostic study involving 225 patients and 75 ED providers that found POCUS was 96.9% sensitive and 88.1% specific for the diagnosis of retinal detachment1. While studies have varied in whether sensitivity was better than specificity or vice versa, ultimately each study has shown that when trained, emergency providers are quite good at identifying RD by US2,3. In addition to RD, Lanham, et al further found ED providers did well at identifying vitreous hemorrhage (sens 81.9%, sp 82.3%) and vitreous detachment (sens 42.5%, sp 96%).

Get the PoCUS Scan:

  • Place a tegaderm over the eye to protect it from US gel which may be painful. You may consider using topical freezing drops to limit irritation.
  • Use the linear probe and scan through the eye until you are able to visualize the optic nerve, the hypoechoic structure at the back of the eye
  • Have the patient look side to side/up and down as this will accentuate movement of retinal or vitreous pathology.
    1. Retinal detachment: Bright echogenic line that appears to have separated from the posterior eye/choroid and remains tethered to the optic nerve.
    2. Posterior vitreous detachment: Bright echogenic line separated from posterior eye/choroid that is detached from the optic nerve.
    3. Posterior vitreous hemorrhage: Vitreous shows fluid collection with variable echogenicity and ‘washing machine’ appearance.

Jacobsen et al. (2016). WestJEM. 17(2)

 

Differential of painless visual loss

 

Resources:

  1. Lahham S, et al. Point-of-Care Ultrasonography in the Diagnosis of Retinal Detachment, Vitreous Hemorrhage, and Vitreous Detachment in the Emergency Department. JAMA Netw Open. Published online April 12, 20192(4):e192162. doi:10.1001/jamanetworkopen.2019.2162
  2. Kim, D., et al. Test Characteristics of Point-of-care Ultrasound for the Diagnosis of Retinal Detachment in the Emergency Department. Academic Emergency Medicine. 2019;26[1]:16; http://bit.ly/2TEFutH
  3. Vrablik ME, et al. The diagnostic accuracy of bedside ocular ultrasonography for the diagnosis of retinal detachment: a systematic review and meta‐analysis. Ann Emerg Med 2015; 65( 199–203): e1.
  4. Mason, J. (Host). (2019 Jan). C3-Vision Loss-Retinal Detachment [Audio podast]. Retrieved from EMRAP: https://www.emrap.org/episode/c3visionloss/c3visionloss1 .
  5. Arroyo, J. (Jan 2018). Retinal Detachment. Retrieved from Uptodate: https://www.uptodate.com/contents/retinal-detachment
  6. Givre, S., et al. (Feb 2019). Amaurosis fugax (transient monocular or binocular visual loss). Retrieved from Uptodate: https://www.uptodate.com/contents/amaurosis-fugax-transient-monocular-or-binocular-visual-loss?search=painless%20monocular%20vision%20loss&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1
  7. Porfiris, G. (2015). ABCs of Emergency Medicine, 14th Edition, Chapter 23: Eye Emergencies.

 

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