Positive Findings (Patient Has This)

Finding Increased Disease Probability (Positive Likelihood Ratio)
POCUS for Retinal Pathology
Symptoms: Visual reduction 5 (95% CI 3.1-8.1)
Symptoms: >10 new floaters 8-36
Signs: Vitreous hemorrhage 10. (95% CI 5.1-20)
Signs: Vitreous pigment 44. (95% CI 2.3-852)

Negative Findings (Patient Doesn't Have This)

Finding Decreased Disease Probability (Negative Likelihood Ratio)
POCUS for Retinal Pathology
Signs: Vitreous pigment 0.23

Source: Hollands H, Johnson D, Brox AC, Almeida D, Simel DL, Sharma S. Acute-onset floaters and flashes: is this patient at risk for retinal detachment? JAMA. 2009;302:2243-9.

Study Population: 2496 patients referred to ophthalmologists for evaluation of acute onset floaters and flashes of suspected ophthalmologic origin and/or diagnosed posterior vitreous detachment

Narrative: Posterior vitreous detachment (PVD) or separation of the posterior vitreous from the retina, is usually due to degeneration and age. PVD may present with floaters and/or flashes or may be asymptomatic for years.1 The incidence of PVD increases with age, from 25% in those 50-59 years to 87% in those 80-89 years.2 This condition sets the stage for further ophthalmologic pathologies, including a retinal tear.3, 4 Thus, previously diagnosed PVD is an important component of the history in a patient with an ophthalmologic complaint. A feared complication of PVD and retinal tear is retinal detachment. Retinal detachment occurs in 33-46% of patients with retinal tear and affects 0.8-1.8 per 10,000 persons per year,3, 4with a population prevalence of 0.3%.5, 6 Rapid diagnosis and treatment of retinal detachment can reduce visual loss and may even restore vision.7

This review included studies evaluating elements of the history and physical examination in patients with acute floaters and flashes of suspected ophthalmologic origin and suspected or diagnosed PVD.8 The systematic review and meta-analysis assessed the symptoms or clinical findings that could predict retinal tear in patients with acute onset floaters and/or flashes and a diagnosis of PVD established by the ophthalmologist.8

The authors of the meta-analysis identified 12 relevant studies (n = 2496 patients). All 12 were performed in ophthalmology clinics, with patients referred from primary care, optometry, or general ophthalmology. All patients had floaters and/or flashes of suspected ophthalmologic origin and suspected or diagnosed PVD. The prevalence of retinal tear was 14%. Only one study evaluated subjective vision reduction, finding that this increased likelihood of retinal tear (LR+: 5.0, 95% CI 3.1-8.1).1 Normal visual acuity decreased the likelihood of retinal tear (LR+: 0.60, 95% CI 0.5-0.7). Twelve studies evaluated slit lamp examination findings, showing vitreous hemorrhage and vitreous pigment increased the likelihood of retinal tear (LR+: 10, 95% CI 5.1-20 and 44, 95% CI 2.3-852, respectively).

Caveats: While certain features on history and examination increase the likelihood of retinal tear in the presence of flashes and floaters and/or PVD, several findings depended upon a thorough fundoscopic and slit lamp examination. Thus, ED provider experience and equipment for fundoscopic and slit lamp examination play an important role in evaluation for retinal tear.9 Importantly, slit lamp examination does not evaluate the posterior chamber of the eye. In order to appropriately visualize the posterior chamber, fundoscopy, typically with full eye dilation, is needed. While point-of-care ocular ultrasound can be diagnostic of several ophthalmologic conditions, this modality was not evaluated in this meta-analysis.10 The prevalence of retinal tear in patients presenting to the ED with visual symptoms such as vision loss and flashes/floaters is likely lower than found in this meta-analysis, suggesting spectrum bias, and in fact, most patients enrolled in the trials were diagnosed with PVD first or were suspected to have PVD, making this a highly select group likely to be different from patients with these complaints in the emergency department (ED). Regardless, this information might help ED physicians suspect retinal tear early and refer the patients to an ophthalmologist as soon as possible, as retinal tear leads to retinal detachment in 33-46% of patients.3, 4

Lastly, many of the likelihood ratios generated by the meta-analysis had wide confidence intervals, with lower limits approaching 1.0, most likely resulting from the small sample size. Larger studies are needed to generate better precision.

Based on the existing data, new onset floaters and/or flashes, subjective vision loss, and vitreous pigment or hemorrhage on ophthalmologic examination are associated with increased risk of retinal tear among patients with suspected or known PVD. In most studies included in the meta-analysis, PVD was often established by the ophthalmologist during initial encounter, suggesting further data are needed to determine whether these findings remain consistent among patients in acute care settings such as ED. Nonetheless, in the absence of other relevant data, this review suggests that findings outlined here may be useful in the evaluation of acute floaters/flashes. Newer data also suggest point-of-care ultrasound may be a useful indicator of retinal detachment.10 Future studies should determine how ultrasound may be used in combination with the above findings to risk stratify patients with new vision changes in non-ophthalmology settings.

The original manuscript was published in Academic Emergency Medicine as part of the partnership between TheNNT.com and AEM.

Author: Brit Long, MD; Alex Koyfman, MD; Michael Gottlieb, MD, RDMS
Supervising Editor: Shahriar Zehtabchi, MD

Published/Updated: June 14, 2019

LR, pretest probability and posttest (or posterior) probability are daunting terms that describe simple concepts that we all intuitively understand.

Let's start with pretest probability: that's just a fancy term for my initial impression, before we perform whatever test it is that we're going to use.

For example, a patient with prior stents comes in sweating and clutching his chest in agony, I have a pretty high suspicion that he's having an MI – let's say, 60%. That is my pretest probability.

He immediately gets an ECG (known here as the "test") showing an obvious STEMI.

Now, I know there are some STEMI mimics, so I'm not quite 100%, but based on my experience I'm 99.5% sure that he's having an MI right now. This is my posttest probability - the new impression I have that the patient has the disease after we did our test.

And likelihood ration? That's just the name for the statistical tool that converted the pretest probability to the posttest probability - it's just a mathematical description of the strength of that test.

Using an online calculator, that means the LR+ that got me from 60% to 99.5% is 145, which is about as high an LR you can get (and the actual LR for an emergency physician who thinks an ECG shows an obvious STEMI).

(Thank you to Seth Trueger, MD for this explanation!)