OCT vs ophthalmic ultrasound: which and when

Optical coherence tomography (OCT) and ophthalmic ultrasound are often compared when a clinic plans its diagnostic lane. They are complementary, not competing. The right question is which conditions each modality answers.

What OCT does best

OCT uses light to produce micrometre-resolution cross-sections of the retina, optic nerve head and anterior segment. It is the standard of care for:

• macular disease, including diabetic macular oedema and age-related macular degeneration;
• glaucoma monitoring through retinal nerve fibre layer and ganglion cell analysis;
• anterior segment assessment of the cornea and angle.

Acquisition takes seconds, the examination is non-contact, and automated reports compare each visit to baseline. The limitation is simple: light must reach the retina. Dense cataract, vitreous haemorrhage or corneal opacity block the signal.

What ultrasound does best

Ophthalmic ultrasound uses sound, so it images through opaque media. In a combined platform it offers:

• B-scan for the posterior segment when the view is blocked, such as retinal detachment behind a dense cataract or vitreous haemorrhage;
• A-scan biometry for axial length when optical biometry fails, which is common in mature cataracts;
• pachymetry for corneal thickness, relevant to glaucoma and refractive assessment.

Ultrasound requires contact or immersion, and the operator’s technique affects image quality, so training matters.

Planning the lane

Clinical question	First choice	Backup
Macular oedema, AMD follow-up	OCT	—
Glaucoma progression	OCT	—
Posterior segment behind opaque media	B-scan ultrasound	—
Axial length for IOL calculation	Optical biometer	A-scan ultrasound
Corneal thickness	Pachymetry (ultrasound) or anterior OCT	—

Most eye hospitals need both. A high-volume cataract service in particular should keep A-scan ultrasound available for the eyes an optical biometer cannot measure.

PrecisionMed supplies the MicroClear SKY OCT and the VisionStar RetiWave 1200 A/B/P ultrasound platform, and can configure both into a single diagnostic lane.

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