Case 22

54 yo M w/ no PMH presents w/ sudden onset blurry vision of the L eye. Symptoms have been occurring for 1 hour and have been intermittent. There are no exacerbating or alleviating factors. Prior to onset of symptoms, pt fell asleep in his truck with his neck in flexed postion for 30 min-1 hour. Upon waking pt had blurry vision in L eye. He had questionable flashing lights in visual fields but denies any trauma to the eye or complete vision loss. Eye is not painful and no similar symptoms in past. No other associated symptoms including headache or fever. Pt smokes 1 PPD and used cocaine last night.

ROS:

CONSTITUTIONAL: Negative.
ENT: See HPI.
CV: Negative.
RESPIRATORY: Negative.
GI: Negative.
NEURO: Negative other than noted in ENT exam.

EXAM:

CONSTITUTIONAL: NAD, WDWN.
EYES: PERRL; pupils 2 mm bilaterally; EOMI; no nystagmus; R eye pressure 23; L eye pressure 22
ENT: Normal pharynx.
CV: RRR, Normal S1, S2; no M, R, G.
RESP: CTAB, good respiratory effort; no W, R, R.
NEURO: A&O x 3. CN III-XII intact. Visual acuity: 20/15 in L eye; 20/25 in R eye (w/ corrective lenses). Sensation intact bilaterally.

Questions:

  1. Given the clinical exam, what is your differential diagnosis?
  2. Describe the anatomical structures in the picture below?
  3. What is the depth at which you measure the optic nerve?
  4. Why must you measure at that depth?
  5. What is an ABNORMAL width of the optic nerve?
  6. What transducer do you use for ocular ultrasounds?
  7. What are indications NOT to do ocular ultrasounds?

Answers:

1. Describe the anatomical structures in the picture below?

2. Given the clinical exam, what is your differential diagnosis?

  • Retinal detachment
  • Retinal artery occlusion
  • Retinal vein occlusion
  • Tumor

Here is an example of a retinal detachment circled in the red area below.  Notice the "V"shape and attachment to the area of the optic nerve sheath.

3. What is the depth at which you measure the optic nerve?

  • 3mm posterior to the retina

4. Why must you measure at that depth?

  • To avoid posterior acoustic enhancement, which is a hyperechoic artifact that occurs posterior to cystic structures.  There are also some studies that indicate that the optic nerve immediately posterior to the retina may be more porous and may show signs of increased pressure more readily.  Therefore, measuring 3mm posterior to the retina has become convention.

5. What is an ABNORMAL width of the optic nerve?

  • Greater than 5mm - which may indicate increased ICP in the appropriate clinical scenario.

6. What transducer do you use for ocular ultrasounds?

  • Linear probe

7. What are indications NOT to do ocular ultrasounds?

  • Globe rupture