Part 3 of a 3-part series. Part 1. Part 2.

Common Emergency Department Application

Structure: Vitreous Humor/Body

Evaluate for: Vitreous hemorrhage, vitreous detachment

The vitreous humor, which goes by several names, is a transparent gelatinous mass that occupies 80 percent of the volume of the eye, filling the space between the lens and the retina. The vitreous is more fluid-like centrally and more gelatinous on its peripheral edges. This vitreous body is surrounded by a collagenous membrane that is in contact with the retina. Because its composition is 99 percent water, a normal vitreous will appear anechoic on ultrasound, giving the posterior chamber a completely black appearance. In the case of vitreous hemorrhage, one will note echogenic material in the posterior chamber (see Figure 1). This increased echogenicity may be obvious or subtle. Woo et al found that the sensitivity of ED physicians utilizing POCUS for vitreous hemorrhage was only 43 percent, but the specificity was 94 percent.¹

Figure 1: In vitreous hemorrhage, echogenic material is visible in the posterior chamber.

Figure 2: Vitreous detachment may appear similar to a retinal detachment but is more globular and not tethered by any specific structural attachments.

Vitreous detachment is another pathological condition encountered in the emergency department. It occurs when the vitreous membrane separates from the retina and is most often atraumatic. On ultrasound, this may appear similar to a retinal detachment, but a vitreous detachment is more globular and not likely to appear undulating or move along with patient eye movements (see Figure 2). In contrast to the retina, a detached vitreous will not be tethered by any specific structural attachments.

Tips & Tricks: When suspicion is high, increase the ultrasound gain to pick up subtler vitreous hemorrhages.

Ocular ultrasound is easy to learn and can rapidly assess ocular emergencies. With practice, you can easily incorporate POCUS into your diagnostic algorithm and rule in or out important ocular pathology. 

Ultrasound Technique

1. Explain this bedside procedure to your patient prior to starting. As this is a dynamic
   

   Figure 2: Place a Tegaderm film dressing over the patient’s closed eye, gently press out any pockets of air, and apply a copious amount of gel directly over the Tegaderm.

   scan, the patient will have to move his or her eyes side to side and up and down to allow complete visualization of the posterior segment.

2. The orbit is a superficial structure. Therefore, a high-frequency linear transducer should be used.
3. For comfort and to prevent a mess, place a Tegaderm film dressing over the patient’s closed eye and gently press out any pockets of air. Remember, air is the enemy of ultrasound.
4. When performing ocular ultrasound, a copious amount of gel should be used, which will prevent contact of the transducer with the eyelid and minimize direct pressure. The gel can be applied directly over the Tegaderm (see Figure 2).
5. 

   Figure 3: Transverse visualization of the orbit.

   Visualize the orbit in both transverse (see Figure 3) and longitudinal planes. After scanning through, the patient should be asked to move his or her eye right to left and up and down. A combination of still images and dynamic scanning clips will best document your exam.

6. Repeat these steps on the unaffected eye.
7. Contraindications to the exam include high suspicion of globe rupture.
8. Always supplement your ocular POCUS exam with a visual acuity and intraocular pressure measurement for a well-rounded emergency eye exam.

Tips & Tricks

Figure 5: Stabilize your scanning hand by placing your pinky finger on the bridge of the patient’s nose.

Stabilize your scanning hand by placing your thumb or pinky finger (whichever is medial) on the bridge of the patient’s nose (see Figure 5). This will also prevent you from applying too much pressure

References

1. Woo MY, Hecht N, Hurley B, et al. Test characteristics of point-of-care ultrasonography for the diagnosis of acute posterior ocular pathology. Can J Ophthalmol. 2016;51(5):336-341.