Optic nerve sheath diameters in nontraumatic brain injury: A scoping review and role in the intensive care unit

Table 4 Differences between A scan and B scan on ultrasonography

A scan	B scan
Amplitude modulation scan	Brightness modulation scan
8 mHertz frequency with small non focused probe	10 mHertz with a larger focused probe
One-dimensional image of spikes of varying amplitudes along a baseline	Two-dimensional image
Provides quantitative information: Ex length of eyeball before surgery.	Provides topographical information
Basis of ocular biometry	Evaluation of ocular pathology
No blooming effect	Blooming effect while measuring ONSD
Not available as bedside equipment	Part of point-of-care ultrasonography, easily available

ONSD: Optic nerve sheath diameter.