Ultrasound of the Month - Retinal detachment

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THE CASE…

The patient is an elderly male with a history of diabetes mellitus who presents to the emergency department (ED) with worsening vision in his right eye. He states that his vision has been decreasing since the day before presentation, when he woke up and could not see much in the lower half of his visual field. This continued to worsen throughout the day of presentation. He had no pain in the eye, flashers, or significant trauma to the eye. On evaluation, visual acuity in the left eye was 20/20, right eye was 20/800 in the upper visual fields and had complete vision loss in his lower fields. His intra-ocular pressures were normal with briskly reactive pupils. Ocular ultrasound was performed in the ED.

And now for the ultrasound images…

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What do you see on ultrasound?

There is a hyperechoic line on the temporal side of the retina (left side of the screen) that does not pass over the optic nerve. The line is uniformly thick and sways with ocular movements.

Ultrasound Pearls

Ultrasound has been used by our ophthalmology colleagues for decades starting in the 1950's2. Up to 2-3% of all ED visits are due to ocular symptoms, providing freqeuent opporunities for the use of point of care ultrasound (POCUS) to help differentiate between emergent pathologies3.

The probe used in ocular scanning protocols is a high frequency linear probe2,3. Appropriate settings for an ocular preset include a thermal index (TI) of less than 1 and an mechanical index (MI) of less than 0.23, doing this minimizes the risk of any theoretical thermal or mechanical damage imparted to the small and delicate tissue structures of the eye 6. An important point is to use a lot of gel to help prevent applying significant pressure to the patient’s eye5. To do this, it is best to place a Tegaderm or other non-toxic adhesive covering over the eyelid to keep the gel out of the patient’s eye, although this can degrade image quality. Alternatively, you may use sterile gel (3 packets of sterile lube per eye works quite nicely) and cover the thoroughly cleaned probe with a tegaderm prior to scanning. The eye is a unique structure since the patient can move it independently, thus dynamic scanning can play an important role in ocular ultrasound. In dynamic scanning the provider will hold the probe steady while the patient moves their eye as directed by the provider which can help elucidate pathology.

According to the Amercian College of Emergency Physicians (ACEP),ultrasound can help expedite the diagnosis of several ocular emergencies, including retinal detachment, lens subluxation, vitreous hemorrhage, and intraocular foreign body4. Of note, if there is clinical suspicion for a penetrating globe injury, ocular ultrasound should not be performed due to the risk of increasing intra-ocular pressure.

Retinal Detachment (RD): a hyperechoic line that DOES NOT cross the optic nerve. Compared to a vitreous detachment it is more echogenic and uniformly thick1,4,5

Posterior Vitreous Detachment (PVD): a hyperechoic line that DOES cross the optic nerve, it typically has varying degrees of thickness due to associated hemorrhage or inflammation1,5

Vitreous hemorrhage: Due to the varying appearance of blood as it ages the fluid has variable echogenicity in the posterior chamber3,4

Elevated Intracranial Pressure (ICP): It can be difficult to evaluate for papilledema on fundoscopy in the emergency department due to patient condition and time constraints. POCUS has been offered as a surrogate for elevated ICP. A normal optic nerve sheath is 5 mm in diameter. The diameter is best measured 3 mm behind the globe where the results are most reproducible4,5

Before beginning scanning it is important to know the structures that will help differentiate pathology. The key to differentiating between retinal detachment and vitreous pathology is identifying the optic nerve1. There have been multiple studies evaluating how well emergency physicians can differentiate between RD and PVD. In 2018, it was found that emergency physicians can identify normal ocular ultrasounds 94.9% of the time and had an accuracy of 74.6% and 85.7% in diagnosing RD and PVD, respectively1. A recent publication in 2019 demonstrated a sensitivity of 96.9% for emergency physicians diagnosing retinal detachment with POCUS3. In this study the specificity for diagnosing PVD of 96% but a poor sensitivity of only 42.5%. Overall these data suggests that emergency physicians are likely able to detect these ocular emergencies but POCUS is not able to replace our ophthalmology colleagues.

Case Resolution

The patient was evaluated by ophthalmology in the ED after the above images were obtained. Their examination found a retinal tear that spanned from 10 to 2 o’clock involving the fundus. Since the fundus was involved there was no need for emergent surgery. The patient followed up with a retinal specialist for surgery a few days later.

AUTHORED BY: JESSICA KOEHLER, MD

Dr. Koehler is a PGY-3 in the emergency medicine residency program at the University of Cincinnati, planning to pursue an ultrasound fellowship.

FACULTY REVIEWED BY: PATRICK MINGES, MD

Dr. Minges is an an assistant professor of emergency medicine at the University of Cincinnati and is fellowship trained in Ultrasound.

References

  1. Baker N, Amini R, Situ-LaCasse EH, et al. Can emergency physicians accurately distinguish retinal detachment from posterior vitreous detachment with point-of-care ocular ultrasound? Am J Emerg Med. 2018;36:774-776.

  2. Kim DJ, Francispragasam M, Docherty G, et al. Test characteristics of point-of-care ultrasound for the diagnosis of retinal detachment in the emergency department. Acad Emerg Med. 2018;26(1):16-22

  3. Lahham S, Shniter I, Thompson M, et al. Point-of-care ultrasonography in the diagnosis of retinal detachment, vitreous hemorrhage, and vitreous detachment in the emergency department. JAMA Netw Open. 2019;2(4):e192162.

  4. Adhikari SR. Ultrasound guide for emergency physicians: Small parts-ocular ultrasound. https://www.acep.org/sonoguide/smparts_ocular.html, accessed on 8/4/19.

  5. Mallin M, Dawson M. Introduction to Bedside Ultrasound: Volume 2. 2013.  

  6. The British Ultrasound Medical Society. Guidelines for the safe use of diagnostic ultrasound equipment. 2009. https://www.bmus.org/static/uploads/resources/BMUS-Safety-Guidelines-2009-revision- FINAL-Nov-2009.pdf