Read this tutorial on the use of point of care ultrasonography (POCUS) for pediatric ocular ultrasonography for optic nerve evaluation. Then test your skills on the ALiEMU course page to receive your PEM POCUS badge worth 2 hours of ALiEMU course credit.

 

PATIENT CASE: Child with a Headache

Madeline is a 15-year-old female presenting to the Emergency Department with chief complaint of a headache for 1 week. She has been struggling with headaches for more than a year. The headache has been intermittent and tends to develop close to the end of the day, but it does improve with sleep. She denies photophobia, but has been complaining of blurry vision over the last week for which she is scheduled to see an ophthalmologist. Her medications include ibuprofen as needed for the headache and a daily medication for her acne.

Vital Signs

Exam

Overall she is well appearing. She has a normal cardiac, respiratory, abdominal, and neurological examination including the cranial nerves.

On ocular examination, she has normal extra-ocular movements and a pupillary examination.

• Visual acuity: Right eye 20/30, left eye 20/25
• No visual field deficits
• You attempt to evaluate her optic discs with an ophthalmoscope. Although not confident, you believe she has blurring of the optic disc margins bilaterally.

Given your examination findings, you request an ophthalmology evaluation and consider head imaging. While waiting, you decide to perform an ocular point of care ultrasound (POCUS) examination.

Why perform an ocular POCUS?

Ocular POCUS can be performed for various complaints, and it can provide valuable information. This especially is true in cases where the physical examination is difficult to perform such as from lack of patient cooperation, sensitivity to light, or pain. In resource-limited settings and when access to advanced diagnostic imaging or an ophthalmologist could be delayed or unavailable, ocular POCUS can be easily performed and provide information within minutes. 

Indications to performing ocular POCUS include:

• Visual changes
• Acute loss of vision
• Ocular trauma
• Non-traumatic eye pain
• Evaluation for increased intracranial pressure (ICP)

IMPORTANT NOTE: Ocular POCUS should not be performed when there is a concern for globe rupture to avoid applying pressure on the eye and exacerbating loss of intraocular contents. 

Step-By-Step Technique

• The examination can be performed with the patient in the supine position or with the head of the bed slightly elevated
• A high frequency linear transducer (Figures 1 & 2) should be used, preferably with a smaller footprint
• A copious amount of gel should be applied to a closed eye
  • Different types of gel could be used such as the regular water-soluble ultrasound gel, sterile gel/surgical lube, and commercially available ocular-specific ultrasound gel. All these are safe, easy to clean, and do not irritate the eye.

Pro Tip: A tegaderm placed over a closed eye could be used to keep the gel from going into the eye. A tegaderm placed over a closed eye could be used to keep the gel from going into the eye depending on the patient’s preference.

• Ultrasound Setup: Ideally use the ocular preset. The ocular setting lowers both mechanical and thermal indices, thus decreasing the amount of ocular exposure to the energy released from the transducer. Set the depth at 4-5 cm. This will allow imaging of the globe and the orbit behind the eyeball.

Pro Tip: If your POCUS machine does not have an ocular preset, a musculoskeletal or small parts preset could be used after turning down the dynamic range and mechanical index. Figure 3 is an example of how this could be done on a Mindray TE7 ultrasound machine.

• Provider Positioning: Anchoring is important when performing an ocular examination to avoid applying pressure on the eyeball. Place 2 or 3 fingers on the patient’s forehead, nasal bridge, or temple (Figure 4, left). Please note: Applying high pressure to the eye can induce the oculocardiac reflex leading to bradycardia. It can also stimulate nausea and vomiting.

• Ultrasound Views: The ocular POCUS exam can be performed in transverse and sagittal orientations (Figure 5).
  • Transverse: place the transducer on the closed eyelids with the marker towards the patient’s right. Fan the probe until you identify the optic nerve.
  • Sagittal: with the transducer in transverse, turn it 90 degrees until the marker is pointing to the forehead. Tilt Fan the probe until you identify the optic nerve.

Pro Tip: If the optic nerve cannot be seen, ask the patient to move the eye from one side to another. The optic nerve will move in the opposite direction (opposite to the patient gaze).

Normal Anatomy

Assessment of the Optic Disc

The optic disc is where the optic nerve enters the eyeball. On POCUS, it normally appears smooth and in-line with the retina. Sometimes a small elevation is noted at the optic disc. This is called Optic Disc Elevation (ODE). It can be measured from the base of the optic disc to its peak at the widest area. It normally measures < 1 mm (figure 7). If the ODE is > 1 mm, this indicates papilledema and increased ICP. Of note, normal ranges are still an active area of study, see table in Ocular POCUS: Facts and Literature Review section for more information.

Assessment of the optic nerve sheath diameter (ONSD)

• The optic nerve is covered with the optic nerve sheath that is made up of the 3 layers of meninges surrounding the brain (dura mater, arachnoid mater, and pia mater). Pressure in the subarachnoid space is transmitted to the optic nerve sheath. ONSD (which is the hyperechoic membrane covering the hypoechoic optic nerve) can be measured 3 mm behind the retina (Figures 8 & 9 below). This measurement should done from the outer wall of the optic nerve sheath (hyperechoic sheath) to the outer wall of the sheath on the other side.
  • Do not include the shadow outside the ONSD in the measurement.
  • Identify the trajectory of the optic nerve because this measurement has to be done perpendicular to the nerve’s axis. 
• Although definitive ONSD normal ranges are still an active area of research, a rough guide for a normal ONSD measurement is:
  • Infants less than 1 year: ONSD <4 mm
  • Children older than 1 year: ONSD <4.5 mm

• Use color doppler to identify the central retinal vessels that run in the middle of the optic nerve. This will help identify the axis/direction of the optic nerve. However, care should be taken to limited duration of color doppler use (Figure 10).

Pro Tip: ONSD normative values are not well established in pediatrics. Multiple studies attempted to set normal cutoffs for ONSD in various age groups. While measurement more than 5 mm in adults is considered abnormal, a value of 4 mm for infants and 4.5 mm in older children is used as the cut off [1]. The are different cutoffs that are used in the literature with variable sensitivity and specificity. See literature review section. ONSD is also highly operator dependent. An inappropriate technique in measuring the ONSD can lead to under- or over-estimation of the diameter. 

Ocular POCUS: Abnormal Ultrasound Findings

Optic Disc Elevation (ODE)

When ODE is >1 mm, it suggests papilledema, which is concerning for an increased ICP. The following figures and videos below illustrate abnormal ODE measurements. Note that normal ODE ranges are an active area of study.

Optic Nerve Sheath Diameter (ONSD)

Assessment of the optic nerve can provide information about intracranial pressure. Increased ICP is suggested when you see an enlarged ONSD.

 

Pseudopapilledema is a mimicker

Pro Tip: Pseudopapilledema (anomalous elevation of one or both optic discs without edema of the optic nerve) is a mimicker of papilledema and can be caused by a number of conditions including:

• Optic nerve head drusen: Calcified deposits in the optic disc appear hyperechoic with posterior shadowing, and cause swelling (Video 4, Figure 15)
• Congenital anomalies
• Vitreopapillary traction
• Systemic disease

In these mimic cases, the POCUS ODE is typically <1 mm, whileas true papilledema is ≥1 mm. If the findings are equivocal, providers should perform additional evaluation for papilledema and elevated ICP.

Ocular POCUS: Facts and Literature Review

Ocular POCUS has been used in the Emergency Department for detection of various ocular conditions, including increased ICP. The American Academy of Pediatrics (AAP) supported its use for ocular evaluation in its policy statement [2].

Optic Disc Elevation (ODE)

ODE has been reported as a method for detection of increased ICP with decent accuracy. There has been multiple attempts to assess the quantitative measurement of ODE and its correlation with increased ICP (table 1). This is an area of ongoing research with early studies limited by small sample sizes.

Optic Nerve Sheath Diameter (ONSD)

Normal values for ONSD have been established in adults [5]. It is still a controversial topic in children. The current standard is that an ONSD >4 mm in infants and 4.5 mm in children older than 1 year is considered abnormal, based on pediatric study of 102 healthy children [1]. There have been multiple studies to assess the sensitivity and specificity of this exam (table 2). 

Case Resolution

You perform an ocular POCUS exam with a linear probe. The following image was obtained. What do you see?

ED Course

This patient’s POCUS showed optic disc swelling with optic disc elevation and an enlarged optic nerve sheath diameter suggesting elevated ICP. The brain MRI was normal without signs of hydrocephalus. Ophthalmology evaluation confirmed the presence of papilledema. After consulting with neurology, an ultrasound-assisted lumbar puncture (LP) was performed. The patient’s opening pressure was 35 mm H2O. CSF was removed until a goal pressure of 25 mm H2O was achieved. The patient was diagnosed with idiopathic intracranial hypertension (formerly known as pseudotumor cerebri). The patient symptoms were resolved after the LP. She was admitted for further evaluation and management.

Hospital Course

The patient was evaluated by neurology while on the inpatient unit. She was started on acetazolamide and discharged home. After multiple follow-up visits at the neurology clinic, her symptoms continue to be well-controlled.

Learn More…

• PEM POCUS Series
• Ultrasound for the Win Series

References

1. Ballantyne J, Hollman AS, Hamilton R, et al. Transorbital optic nerve sheath ultrasonography in normal children. Clin Radiol. 1999 Nov;54(11):740-2. PMID: 10580764.
2. Marin JR, Lewiss RE; American Academy of Pediatrics, Committee on Pediatric Emergency Medicine; Society for Academic Emergency Medicine, Academy of Emergency Ultrasound; American College of Emergency Physicians, Pediatric Emergency Medicine Committee; World Interactive Network Focused on Critical Ultrasound. Point-of-care ultrasonography by pediatric emergency medicine physicians. Pediatrics. 2015 Apr;135(4):e1113-22. PMID: 25825532.
3. Teismann N, Lenaghan P, Nolan R, Stein J, Green A. Point-of-care ocular ultrasound to detect optic disc swelling. Acad Emerg Med. 2013 Sep;20(9):920-5. PMID: 24050798.
4. Tessaro MO, Friedman N, Al-Sani F, Gauthey M, Maguire B, Davis A. Pediatric point-of-care ultrasound of optic disc elevation for increased intracranial pressure: A pilot study. Am J Emerg Med. 2021 May 21;49:18-23. PMID: 34051397.
5. Blaivas M, Theodoro D, Sierzenski PR. Elevated intracranial pressure detected by bedside emergency ultrasonography of the optic nerve sheath. Acad Emerg Med. 2003 Apr;10(4):376-81. PMID: 12670853.
6. Le A, Hoehn ME, Smith ME, et al. Bedside sonographic measurement of optic nerve sheath diameter as a predictor of increased intracranial pressure in children. Ann Emerg Med. 2009 Jun;53(6):785-91. PMID: 19167786.
7. Marchese RF, Mistry RD, Binenbaum G, et al. Identification of Optic Nerve Swelling Using Point-of-Care Ocular Ultrasound in Children. Pediatr Emerg Care. 2018 Aug;34(8):531-536. PMID: 28146012.