B‑scan biometry uses ultrasound to measure the axial length and internal dimensions of the eye, information that is crucial for calculating intraocular lens (IOL) power before cataract or lens surgery.
Technique
Traditional ultrasound biometry can be contact (applanation) or immersion.
- A probe emits sound waves that reflect from ocular structures; travel time is converted into distance.
- Axial length, anterior chamber depth, and lens thickness are recorded.
- Immersion techniques avoid corneal compression and can improve accuracy.
- Modern practices increasingly use optical biometry, but ultrasound remains useful when dense cataract prevents optical measurements.
Clinical Applications
Accurate biometry underpins refractive outcomes in cataract and lens‑based surgery.
- IOL calculation formulas use axial length, keratometry, and other parameters to predict postoperative refraction.
- Ultrasound B‑scan imaging is also employed to visualise the posterior segment when media are opaque, though this is distinct from axial biometry measurements.
- Reproducible measurements are essential, especially in eyes with extreme lengths or previous surgery.
- Quality control and averaging multiple readings help minimise error.
