Ocular Ultrasound | Emergency Department Critical Care

If the optic nerve sheath is >5mm at a point 3 mm behind the globe, then there is increased icp (ACAD EMERG MED d April 2003, Vol. 10, No. 4)

Third Study (Annals of Emergency Medicine 2007;49(4):508-514)The sensitivity for the ultrasonography in detecting elevated intracranial pressure was 100% (95% confidence interval [CI] 68% to 100%) and specificity was 63% (95% CI 50% to 76%).

(Inten Care Med 2007;33:1704)

Confirmation with real ICP measurements ((2008) Academic Emergency Medicine 15 (2) , 201–204)

another real time showed nerve sheath but not nerve reflected ICP (Inten Care Med 2008;34:2062)

Reply to Copetti and Cattarossi

Thomas Geeraerts¹, Olivier Bergès², Sybille Merceron¹, Yoann Launey¹, Dan Benhamou¹, Bernard Vigué¹ and Jacques Duranteau¹

(1)	AP-HP, Département d’Anesthésie-Réanimation Chirurgicale, Hôpital Bicêtre, Université Paris-Sud, Centre Hospitalier Universitaire Bicêtre, 94275 Le Kremlin-Bicêtre, France

(2)	Service d’Imagerie Médicale, Unité Ultrasons, Fondation Ophtalmologique Adolphe de Rothschild, 25 rue Manin, 75019 Paris, France

Thomas Geeraerts
Email: thgeeraerts@hotmail.com

Accepted: 28 February 2009 Published online: 15 April 2009

Without Abstract

This reply refers to the comment available at: doi:10.1007/s00134-009-1494-4

We thank Drs. Copetti and Cattarossi for their comments. We however disagree with the assumption that our results [1, 2] are related to artifacts.

Using ocular sonography, the optic nerve sheath diameter (ONSD) can be measured on coronal view (with the probe being vertical) or on axial view (horizontal probe). On axial view, the optic nerve sheath can appear fusiform, but not as a result of an acoustic artifact arising from the lamina cribrosa, but rather from unintended reconstruction when using an outdated ultrasound system, or from a meningeal shadow when the nerve does not run strictly straight. Blehar et al. [3] showed that measurements in the horizontal axis are consistently larger than those in the vertical axis. This could be related to a nonspherical ONSD, but also in some cases to this shadow. This discrepancy could become an issue when performing only one measurement in the horizontal axis, probably as Copetti and Cattarossi did. In both of our studies, this point has been considered. For each eye, we performed two measurements, one in coronal and one in axial view, the average being retained as the ONSD value. Nevertheless, to control this point, we performed an additional analysis of our second study [1]. We have now separated vertical and horizontal axis measurements of ONSD. We found a similar and significant relationship between intracranial pressure (ICP) and ONSD, with r = 0.65 (P < 0.0001) for horizontal ONSD and r = 0.71 (P < 0.0001) for vertical ONSD. Receiver operating characteristic (ROC) curves for the detection of raised ICP (>20 mmHg) show very similar patterns and best ONSD cutoff values for vertical, horizontal, and both averaged ONSD (5.88, 5.86, and 5.86 mm, respectively) (Fig. 1).

Fig. 1 Receiver operating characteristic curves with respect to raised intracranial pressure (>20 mmHg) for optic nerve sheath diameter (ONSD) measured in vertical and horizontal axis, and for averaged horizontal and vertical axis. Curves are not significantly different

Moreover, we also disagree with the assumption that magnetic resonance imaging (MRI) and sonographic ONSD values strongly differ. We recently performed a study in 38 traumatic brain injury patients with invasive ICP monitoring, measuring ONSD with MRI [4]. Interestingly, we found a strong relationship between ICP and ONSD (r = 0.71, P < 0.0001) and a best cutoff value for raised ICP (5.8 mm) very close to the values obtained using ocular sonography.

We do not support the fact that color Doppler imaging of retrobulbar arteries can help in the ONSD measurement. There is no justification in the literature for this statement. Figure 2 is not convincing. The left cursor (mark 1) is 1–2 mm too lateral, resulting in a falsely enlarged ONSD. This could be related to the probe used by Copetti and Cattarossi. The frequency of the probe has to be superior to 7.5 MHz for enough precision [5]. Such a probe was used in our studies, but not in Copetti and Cattarossi’s work. Finally, ONSD values presented in their comments are not in the correct units. ONSD are probably 5.9 and 3.5 mm rather than 59 and 35 mm.

We strongly believe that the method we applied is appropriate. Data appear to be controlled, reproducible, and robust. Larger studies are certainly needed to confirm the accuracy and real-life feasibility of this method. This measure appears, however, to be interesting to rule out raised ICP.

A new study showing accuracy at 5.2 and rapid normalization when ICP is brought down (Neurocritical Care Dec 2009)

Results Ninety-four ONSD measurements were analyzed. 5.2 mm proved to be the optimal ONSD cut-off point to predict raised ICP (>20 mmHg) with 93.1% sensitivity (95% CI: 77.2–99%) and 73.85% specificity (95% CI: 61.5–84%). ONSD–ICP correlation coefficient was 0.7042 (95% CI for r = 0.5850–0.7936). The median interobserver ONSD difference was 0.25 mm. CSF drainage to control elevated ICP caused a rapid and significant reduction of ONSD (from 5.89 ± 0.61 to 5 ± 0.33 mm, P < 0.01).

Conclusion Our investigation confirms the reliability of optic nerve ultrasound as a non-invasive method to detect elevated ICP in intracranial hemorrhage patients. ONSD measurements proved to have a good reproducibility. ONSD changes almost concurrently with CSF pressure variations.

Retinal Detachment

ACEP News Article By Nate Teismann, M.D. , Sachita Shah, M.D. , and Arun Nagdev, M.D.

Acute retinal detachment is a sight-threatening condition requiring urgent diagnosis and treatment.

The most common type of retinal detachment (RD) is termed "rhegmatogenous" (from the Greek rhegma, meaning "tear"), which refers to a break or tear in the retinal epithelium. The majority of these cases result from age-related vitreous detachment, which can create tiny, horseshoe-shaped holes that allow fluid to pass into and accumulate in the subretinal space.1 In patients who are younger, direct trauma is the most common etiology.2

Less common types of RD include "tractional," in which the vitreous contracts and pulls the neural retina off the underlying pigmented layer but does not cause a break in the epithelium, and "exudative," in which serous fluid accumulates beneath the retina because of inflammatory conditions such as sarcoid uveitis.3

Regardless of the cause, RD must be diagnosed and treated rapidly to prevent monocular vision loss.

Traditionally, diagnosis of RD has relied on direct examination of the retina using an ophthalmoscope. However, a number of factors may make this difficult or impossible, including 1) contraindications to the use of mydriatics such as narrow-angle glaucoma or the need to follow pupillary exams in a head-injured patient; 2) significant periorbital trauma or soft tissue swelling; and 3) inability to visualize the posterior segment of the eye because of hyphema, lens opacification, or vitreous hemorrhage. In such cases, bedside ultrasound is critical to the timely diagnosis of RD.

Already in use for decades by ophthalmologists, ocular ultrasound is a relatively recent addition to emergency ultrasonography. Since 2002, a number of studies have demonstrated that emergency physicians using general-purpose, high-frequency transducers can accurately identify a variety of ocular pathologies, including retinal detachment.4,5,6 Bedside ultrasound is an indispensable tool for evaluating this potentially vision-threatening condition.

Here is a simple mnemonic to help you with each CASE of potential retinal detachment: 1) Close and cover the eye; 2) place the transducer in the axial plane; 3) scan the retina; and 4) evaluate the periphery.

1) Place the ultrasound machine at the head of the bed with the patient supine. Ask the patient to close his or her eyes, and place a liberal amount of gel over the eyelid. A bio-occlusive dressing may be used to shield the eye from the gel.

2) Gently place the high-frequency linear (7.5-10 MHz) transducer over the patient's closed eye. In order to obtain a stable image, the fourth and fifth digits of the examiner's hand should rest against the bridge of the patient's nose. The probe should be placed in a transverse orientation to scan in the axial anatomic plane. The probe marker should face the patient's right side, which will correspond to the marker on the ultrasound screen (see image 1).

3) Carefully scan the eye for evidence of pathology. The normal retina is continuous with the other posterior elements of the globe and is not visible as a distinct structure. With retinal detachment, fluid enters the potential space beneath the retinal epithelium and accumulates, forcing the retina away from the outer surface of the globe. Sonographically, retinal detachment is seen as a thick, undulating, hyperechoic membrane that appears to have been lifted off the posterior surface of the eye (see images 2A and 2B).

4) Make sure to evaluate the entire globe in order to avoid missing a small RD at the periphery of the retina. Because the anterior-most attachment of the retinal epithelium is just lateral to the ciliary bodies, care must be taken to interrogate its entire surface. This may require asking the patient to gaze upward and downward while tilting the transducer accordingly to achieve adequate visualization.

In general, RD will appear as a prominent, continuous linear density rising from the fundus. Depending on the timing and severity of the detachment, the retinal separation may be visible only as a small peripheral convexity or, with an extensive detachment, as a complex array of bright, intersecting lines (see image 3A). Because the retina is fixed firmly to the optic disc, even a complete detachment will often appear tethered to this point, giving a "funnel" appearance (see image 3B).

Other ocular processes may appear similar to RD on sonography, especially posterior vitreous detachment (PVD) and vitreous hemorrhage (VH). PVD may also appear as a hyperechoic linear density that has been lifted off the posterior globe; however, it typically appears as a thinner and smoother structure compared to RD. VH typically appears as nonlayering, low-level echoes within the vitreous body that are unattached to periphery of the globe (see image 4).

Because it can be difficult even for the expert ocular sonographer to differentiate these diagnoses from RD, we recommend prompt follow-up in any case with equivocal findings, especially when clinical features (e.g., photopsia) suggest RD.

Other findings such as retinal breaks or tears--which, as already addressed, are often the inciting event leading to RD--may be seen with ultrasound and are visible as small, echodense tufts elevated off the fundus.8 Given their small size, however, these structures typically require specialized ophthalmologic transducers for visualization. Thus, we do not believe this diagnosis should be considered within the scope of emergency sonography.

Ocular ultrasound is emerging as a promising technique to diagnose RD. Sonography is especially helpful in cases where an adequate eye exam is impossible, or when the emergency physician does not have the luxury of time or expertise to perform a thorough, dilated fundoscopic exam.

If RD is identified, the patient should be referred to an ophthalmologist on an emergent basis, ideally within 24 hours. Because the sensitivity of this technique in the hands of emergency physicians using general-purpose portable ultrasound machines has yet to be determined, we recommend that any cases with high-risk clinical features, such as the presence of flashes of light or vision loss, also be referred on an urgent basis regardless of sonographic findings.

With this simple guide to ocular ultrasound, we hope more physicians will learn and incorporate ultrasound into their evaluation of ocular complaints in the emergency setting. We believe that ocular ultrasound is fast, safe, and easy to teach and learn. We hope you will remember to pick up the ultrasound probe for each CASE of potential retinal detachment you encounter.

Ocular

Retinal Detachment

Learning Objectives