Your next patient is a young African-American female with no history of sickle cell disease, ocular conditions, or any other medical problems. She was triaged with a chief complaint of “floaters” in her right eye. She tells you she developed the floaters after coughing very hard the previous night. She thought it would be better this morning, but things have not really changed. She denies any trauma, pain, flashing lights or cobwebs, and states that what she really has is one big floater right in the middle of her vision making it hard to see with that eye.
Physical examination is essentially normal except for a few ocular findings. Inspection of the external eye is normal and pupils are equal and reactive without photophobia. On close inspection, she appears to have a very mild afferent pupillary defect (APD). Fields of vision are full when checked in each eye independently, but visual acuity is worse than 20/200 in the affected eye with best performance being finger counting at 5 feet. On fundoscopic exam, you see the normal retinal red reflex, but despite adjusting the lens of the ophthalmoscope, you cannot get a clear view of the optic nerve or retinal vessels. In the good eye, you are able to visualize a nice, normal retina, optic disc, macula, and retinal vessels.
Prior to calling the ophthalmologist, you decide to scan the eye with your ED ultrasound machine to see if you can pick up any abnormalities. Using the linear array transducer and a generous amount of ultrasound gel over a CLOSED eyelid, you obtain the following image. What do you think it shows?
What does the ultrasound show?
Dx: Ruptured Vessel
The ultrasound image shows a view of the globe with the retina at the bottom of the image. The vitreous humor appears anechoic (black) and the retina echoic (gray). Just in front of the retina is a small echoic area that was not present in the unaffected eye. It does not appear to be connected to the retina, making it a bit atypical in appearance for a retinal detachment. A vitreous detachment could also look like this on ultrasound, but would also be attached at some point to the posterior globe. Examination by ophthalmology with his fancy gadgets and unique skill set revealed that this echoic area seen on ultrasound was a collection of blood from a subhyaloid hemorrhage. The patient ruptured a retinal blood vessel during her hard coughing fits the night before.
Remember that the hyaloid border is basically the outer edge of the vitreous humor. There was also a small amount of vitreous hemorrhage that had occurred, which impaired visualization of the retina with the ED ophthalmoscope. The patient was able to be discharged home with limited activity and recheck with the ophthalmologist in two days. At the time of publication, her vision is still impaired, but gradually recovering.
Pearls & Pitfalls for performing Ocular Ultrasonography
Ocular ultrasound can be used to image the lens, vitreous chamber, retina, optic nerve, and retrobulbar space. It does not require pupillary dilatation to optimize imaging. Ultrasound is especially useful in a patient whose retina may be obscured by blood, edema, cataracts, or opacification of the cornea, and for evaluation of the vitreous chamber in uncooperative patients who won’t keep their eye open for fundoscopic evaluation.
Ultrasound is relatively contraindicated in the presence of a suspected globe rupture. Applying increased pressure will not enhance your image and could theoretically worsen an eye injury. If you are performing an ultrasound on a patient with a potential globe rupture, apply more ultrasound gel to improve your interface and float the transducer on the large layer of gel.1 Do not leave the ultrasound probe in contact with the eyelid for more than 60 seconds. Propagation of heat from the probe can theoretically coagulate the aqueous humor. For some machines there is a special setting for ocular ultrasound – use it.
Higher resolution probes will provide you with better images. 7.5 MHz or 13 MHz linear array transducers are best. Have the patient close the eyelid before applying ultrasound gel and have them keep their eyes closed for the entire scan. Systematically obtain images of all four retinal quadrants by having the patient look up, down, left, and right during the scan. Make sure you get a clear view of the periphery where many occult findings can be missed. Scan the contra-lateral eye for a comparison view. Remember to turn up your gain to improve visualization of subtle tears and vitreous hemorrhage.
04 The Retina
A retinal detachment will appear as a hyperechoic layer in front of the hyperechoic RPE with a black/hypoechoic layer in between. Go to EMresource.org for some examples. A detached retina will often undulate with eye movement. Bear in mind that a posterior vitreous detachment (PVD) may look like a retinal detachment (RD) on ultrasound.
05 The Optic Nerve
The optic nerve can be used to assess for elevated intracranial pressure (ICP), and can be seen immediately posterior to the globe when the ultrasound probe is oriented properly. The normal optic nerve diameter is <5mm wide (<4.5mm for age 1-15 years, <4mm for age <1 year). When swollen to a larger diameter, >5mm, it is usually an earlier sign of increased ICP than papilledema. Measurement of diameter should be taken 3mm behind the optic disc for both eyes and the average value used. Sensitivity is >95%, and specificity is 63% for elevated ICP.2
06 The Orbit
A retrobulbar hematoma may be seen as dark fluid collection just posterior to the globe, near the optic nerve. Consider this diagnosis with orbital pain and trauma or coagulopathy, especially if there is proptosis, decreased acuity or pain with eye motion.
07 Practice, Practice, Practice
The best way to minimize errors is through experience, so scan lots of normal anatomy. The more scans you do, the better you will be able to differentiate abnormal from normal, even when you may not be sure exactly what the abnormality is. An image library of normal and abnormal scans helps immensely, so check out the Soundings archives on www.epmonthly.com
08 Go Mobile
Stay up to date on how you can use bedside ultrasound to enhance your clinical practice. There are many smartphone and tablet apps that can help with training and continuing education.
1. Wu TS; Dommer P; Pearson TC. Images in Emergency Medicine: Woman with right eye pain and swelling. Partial globe rupture. Ann Emerg Med. 2011 57(6):703-708.
2. Dubourg J; Messerer M; Karakitsos D; et al. Individual patient data systematic review and meta-analysis of optic nerve sheath diameter ultrasonography for detecting raised intracranial pressure: protocol of the ONSD research group. Sys Rev. 2013:6(2):62.