Ever feel frustrated with your eye exam? Confused by the slit lamp and even more distressed at the thought of doing funduscopy? Point-of-care ultrasound (POCUS) is taking over emergency medicine and can definitely help improve your eye evaluation. The eye is an ideal structure for viewing with ultrasound since it is a superficial structure that is conveniently filled with fluid. However, the spherical three-dimensional structure of the ocular globe can be confusing when trying to view it using a two-dimensional ultrasound image. This POCUS post offers an introduction to ocular ultrasound and some tips to make sure you capture every detail.
Ocular Ultrasound Applications
Ocular ultrasound has a range of clinical applications:
- painless vision loss (e.g. retinal detachment, posterior vitreous detachment)
- painful vision loss (e.g. globe rupture)
- vascular phenomena (e.g. central retinal artery occlusion)
- raised intracranial pressure (e.g. papilledema)
- examination of the orbital bones.1
The most common use, and the one we will focus on, is painless vision loss in particular assessing for retinal detachment (RD) and posterior vitreous detachment (PVD).
Basic Ocular Scanning Technique
Before diving into the details of RD and PVD lets review the standard instructions for carrying out ocular ultrasound. Most resources1–4 offer advice that can be summed up as:
- Scan the eye in the transverse plane
- Ask the patient to look up and down.
- Scan the eye in the sagittal plane.
- Ask the patient to look side to side.
This approach is not wrong but it glosses over some important details that can dramatically improve your ocular ultrasound technique. In particular:
- when looking for retinal pathology you want to LOOK UP / SCAN UP and LOOK DOWN / SCAN DOWN
- when looking for vitreous pathology you want to use a DYNAMIC VIEW (aka. oculokinetic echography)
Improved Ocular Scanning Technique: Retinal Sweep
Let’s start with retinal pathology and see how the standard technique falls short. We often think of the retina as a posterior structure but it actually covers 65% of the interior surface of the eye. The anterior part of the retina attaches to an area called the ora serrata [Figure 1] that is often neglected during funduscopy and ocular ultrasound. Like any attachment point, the ora serrata is an area where retinal detachments can originate and needs to be included in a complete ocular scan.
Figure 1: Oro-Serrata
A common mistake when assessing for retinal detachment is having patients look directly forward and sweeping the posterior part of the eye. This technique only assesses a small portion of the retina [Figure 2] and does not assess the anterior limits of the retina where it forms the ora serrata [Figure 3]. To properly capture the remaining retina we need to follow this rule: “SWEEP UP and LOOK UP” or conversely “SWEEP DOWN and LOOK DOWN”. When we sweep the probe upwards the orbital bones and curved surface of the eye limit how much of the retina is seen [Figure 4] however at this point we can scan the reminder of the retina by having the patient move their eye upwards and thus bring the remainder of the retina into view [Figure 5]. The scan is repeated in the sagittal view where the same rule can be rephrased as “SWEEP LEFT and LOOK LEFT” and “SWEEP RIGHT and LOOK RIGHT”
Figure 2: Partial Sweep.
A common mistake is to conduct a partial sweep of the retina, with the patient looking directly ahead, that only captures the retina under the arc in light blue.
Figure 3: The extent of the retina missed by the sweep in Figure 2 is represented by bright red semi-circles. The actual retina tissue is the yellow layer below that thins out and terminates at the ora-serrata.
Figure 4: Common limits of the retina scan. Sweeping the probe at steeper angles is usually limited by the facial bones / soft tissue or the probe loses contact with the curved surface of the eye. Blue arc represents the portion of the retina already scanned. The red arcs represent portions of the retina that have not been scanned.
Figure 5: Look-up-sweep-up. The patient’s gaze is directed upward and following the rule that you need to “LOOK UP and SWEEP UP” the lateral extremes of the retina (identified as red semi-circle) up to the ora serrata now come into view.
CASE 1: Incomplete Retinal Sweep
Let’s look at a case that emphasizes the importance of scanning the entire retina all the way to the lateral edges at the ora serrata. A clip [Clip 1] shows the usual approach of scanning the eye with the patient looking directly forward. Do you see a bright posterior structure indicating a retinal detachment? No? Neither did we. Scanning the same eye again with the patient looking up reveals a very different result [Clip 2]. Now this peripheral retinal detachment is much more obvious.
Clip 1: Failure to scan to the peripheral edges.
Clip 2: Complete scanning to the peripheral edges.
Improved Ocular Scanning Technique: Oculokinetic Echography
When seeking out vitreous pathology the rules are different. As opposed to a retinal detachment, a vitreous detachment is more subtle and more mobile. We can take advantage of these features to identify a PVD by examining the vitreous using a DYNAMIC PROCESS (aka. “Oculokinetic echography”).
[bg_faq_start]CASE 2: Dynamic View of the Vitreous
As before let’s use a real case to illustrate the value of static vs dynamic views of the vitreous. In the first clip [Clip 3] can you confidently see any echogenic material floating freely? Maybe? If you look very closely, there is a faint trace of white material towards the back of the eye but it is by no means convincing. Repeating the same scan with dynamic eye movements [Clip 4] yields a much more convincing diagnosis of PVD.
Clip 3: No clear evidence of PVD without motion.
Clip 4: The PVD is much more obvious with the eye in motion.
Summary
When looking for retinal pathology:
Start in transverse:
- Sweep UP … then patient looks UP
- Sweep DOWN … then patient looks DOWN
Rotate to longitudinal:
- Sweep LEFT … then patient looks LEFT
- Sweep RIGHT … then patient looks RIGHT
When looking for posterior vitreous detachments:
Start in transverse
- DYNAMICALLY look left / right
Rotate to longitudinal
- DYNAMICALLY look up / down
This post was originally published on the POCUS Toronto blog on October 14th, 2016. It was copyedited by Dat Nguyen-Dinh (@dat_nd) and reviewed Sean Nugent (@sfnugent), prior to republication on CanadiEM.1234
References
Reviewing with the Staff
Puneet does a great job going over the details to help improve the sensitivity of ocular scans for retinal detachments and posterior vitreous detachments.
LOOK UP, SWEEP UP, LOOK DOWN, SWEEP DOWN, LOOK RIGHT, SWEEP RIGHT and LOOK LEFT, SWEEP LEFT should be used to help pick up those rare, but important, retinal detachments in the ora serrata.
Ultrasound has been a game changer for my practice, in terms of ruling in or out critical ophthalmological diagnoses, such as retinal detachments. It’s as important to me as visual acuity in those patients with flashers and floaters. I also use the scans to help triage ophthalmologist referrals and, from the consultation letters I receive back, it’s well received in my centre.
In terms of actually performing the scan, you can place the gel directly on the closed eye lid of a patient if they are able to keep their eye lids shut for a period of time. This will help save a few minutes trying to find that tegaderm that isn’t nearby. That said, if there is any hesitancy that they will open their eye during the scan, I use a tegaderm or some other adherent skin film.
Now, some may think that this will add too much extra time to the already lengthy visual exam, however, once someone becomes more experienced performing the scan, it literally adds 30 seconds to one minute per eye – pretty good bang for your buck, if you ask me.
Puneet Kapur
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