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.

Procedure

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.

Findings

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).⁷

Differentiation From Other Ocular Pathology

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.

Discussion

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.

References

1. D’Amico DJ. Clinical practice. Primary retinal detachment. N Engl J Med. 2008;359(22):2346-54.
2. Byer NE. Natural history of posterior vitreous detachment with early management as the premier line of defense against retinal detachment. Ophthalmology. 1994;101(9):1503-13; discussion 1513-4.
3. Gariano RF, Kim C. Evaluation and management of suspected retinal detachment. Am Fam Physician. 2004;69(7):1691-8.
4. Blaivas M, Theodoro D, Sierzenski PR. A study of bedside ocular ultrasonography in the emergency department. Acad Emerg Med. 2002;9(8): 791-9.
5. Elia J, Borger R. Diagnosis of retinal detachment in the ED with ultrasonography. J Emerg Med. 2008. (Article in Press) Available at: www.ncbi.nlm.nih.gov/pubmed/18547771
6. Winter K, Baker T. Images in emergency medicine. Retinal detachment. Ann Emerg Med. 2007;50(1):89, 95.
7. DiBernardo CW, Greenberg, EF. Ophthalmic Ultrasound: A Diagnostic Atlas. 2nd ed. Thieme Medical Publishers; 2007.
8. Lorenzo-Carrero J, Perez-Flores I, Cid-Galano M, et al. B-scan ultrasonography to screen for retinal tears in acute symptomatic age-related posterior vitreous detachment. Ophthalmology. 2009;116(1):94-9.