Ophthalmic / Ocular POCUS

POCUS is not a substitute for ophthalmologic examination, tonometry, OCT, fluorescein, gonioscopy, or CT. If open globe is suspected, apply no pressure, place an eye shield, and obtain urgent ophthalmology review.

11.1 ONSD — optic nerve sheath diameter

  • High-frequency linear 12–18 MHz.

  • Coronal section over closed eyelid.

  • 3 mm posterior to optic disc.

  • Perpendicular to nerve axis.

  • 3–5 measurements per eye; use mean.

Adult ONSD

  • Less than 5.0 mm: generally normal.

  • 5.0–6.0 mm: indeterminate or possible elevated ICP.

  • Greater than 6.0 mm: strongly associated with elevated ICP.

ONSD is a surrogate marker, not a direct ICP measurement. It is affected by IOP, age, habitus, head position, and technique. Pediatric and ethnic cutoffs differ. Do not use ONSD alone to manage ICP.

11.2 Posterior segment B-scan

Sequence: globe → lens → vitreous → retina → optic nerve/ONSD → orbit.

Findings

  • Globe rupture: discontinuity of contour, tissue prolapse, lens subluxation. Do not press. Urgent ophthalmology.

  • Retinal detachment: hyperechoic membrane attached to optic nerve and/or periphery, tent or V-shaped, mobile but tethered.

  • Posterior vitreous detachment: thinner membrane, not attached to optic nerve or periphery, free-floating, more independent mobility.

  • Vitreous haemorrhage: diffuse vitreous echoes, obscures retina; can mask RD.

  • Floaters: small, discrete, mobile echoes, not vitreous haemorrhage.

  • IOFB: hyperechoic focus with reverberation or dirty shadowing. CT for definitive localization. MRI contraindicated if metallic IOFB not excluded.

  • Orbital emphysema: hyperechoic linear air with dirty shadowing.

  • Orbital haemorrhage: heterogeneous echoes.

Critical distinction between RD and PVD is attachment to the optic nerve or peripheral retina.

11.3 Anterior segment — limited POCUS role

  • Central anterior chamber depth: approximately 3–4 mm normal; less than 2.5 mm suspicious shallow; less than 2.0 mm high concern for angle closure with clinical context.

  • Lens position, thickness approximately 3–5 mm.

  • Uveal effusion: bowing of iris/ciliary body.

Does not replace slit-lamp examination plus gonioscopy.

11.4 Axial length

Axial length is an A-scan biometry measurement, not routine B-mode POCUS. Adult axial length is approximately 22–24 mm; greater than 25.5–26 mm suggests axial myopia. Formal ophthalmic measurement is required. It is not a bedside POCUS endpoint unless A-scan capability and training are available.

11.5 Ophthalmic-specific pitfalls

  • Applying pressure with suspected open globe: most important safety issue.

  • Misinterpreting vitreous floaters as vitreous haemorrhage.

  • Confusing PVD with RD: key is attachment to optic nerve or periphery.

  • Using ONSD as a standalone ICP diagnosis.

  • Expecting B-mode to diagnose corneal abrasion, epithelial defects, or conjunctival pathology.

  • Normal ultrasound does not exclude occult ocular trauma.

  • Measuring axial length without A-scan capability.

  • Anterior chamber depth on standard posterior B-scan is unreliable for angle closure.