Acute retinal detachment is a sight-threatening condition requiring urgent diagnosis and treatment.
Explore This IssueACEP News: Vol 28 – No 05 – May 2009
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.
- 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.
- 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).
- 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).
- 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).7