An optical biometer measures axial length and other eye dimensions with light and without touching the eye. An A-scan ultrasound measures the same distances with sound through a probe placed on the cornea. Optical biometry is faster and needs no contact, but it needs a clear enough optical path; when a dense cataract or another opacity blocks the light, A-scan ultrasound can still measure. That is why many cataract services keep both. A B-scan is a different ultrasound mode that produces a cross-sectional image of the eye rather than a measurement.
Why axial length matters
Axial length is the distance from the front of the cornea to the retina. Together with keratometry and, for some formulas, anterior chamber depth and lens thickness, it is used to calculate the power of the intraocular lens (IOL) implanted in cataract surgery. Axial length is also tracked over time in myopia-management programmes, because myopia progression is largely an increase in the length of the eye.
How optical biometry works
An optical biometer sends low-coherence light into the eye and detects the reflections from each surface: cornea, lens and retina. From the timing of the reflections it calculates axial length, anterior chamber depth, lens thickness and corneal thickness, and it usually measures keratometry and white-to-white in the same session. Nothing touches the eye, no anesthetic drops are needed, and automatic alignment keeps the result less dependent on the operator.
The ENOCHTEC AL-VIEW Lite uses optical low-coherence reflectometry (OLCR) and reports ten parameters in one measurement: AL, CCT, ACD, LT, VT, K, AST, WTW, PD and CWC.
How A-scan ultrasound works
An A-scan (amplitude mode) sends a single ultrasound beam along the axis of the eye. The echoes from the cornea, lens and retina appear as spikes on a trace, and the distances between them give anterior chamber depth, lens thickness and axial length. In contact A-scan the probe touches the anesthetized cornea, so gentle and consistent probe placement matters: pressing on the cornea can shorten the measured axial length. Sound passes through dense cataracts and other opacities, so A-scan can measure eyes that optical biometry cannot.
Where B-scan ultrasound fits
A B-scan (brightness mode) sweeps the beam across the eye and builds a two-dimensional cross-sectional image. It is used when the back of the eye cannot be seen directly, for example through a dense cataract, a corneal opacity or a vitreous hemorrhage. In short, the A-scan measures and the B-scan visualizes. A combined A/B scanner such as the Enochview-1000 provides both at one workstation.
Optical biometer vs A-scan ultrasound at a glance
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| Optical biometer | A-scan ultrasound (contact) | |
|---|---|---|
| Measuring medium | Light (e.g. OLCR) | Ultrasound |
| Contact with the eye | None | Probe touches the cornea |
| Anesthetic drops | Not needed | Needed for contact A-scan |
| Dense cataract or opacity | May not measure if the light path is blocked | Can still measure |
| Operator dependence | Low; automatic alignment | Higher; probe pressure and alignment affect the result |
| Other parameters in one session | Typically keratometry, ACD, LT, CCT, WTW | ACD and LT; keratometry from another instrument |
| Myopia follow-up | Well suited: non-contact and repeatable | Less common |
Which does a clinic need?
- Cataract surgery service: an optical biometer for most eyes, plus A-scan ultrasound for eyes the optical biometer cannot measure. A combined A/B scanner also covers posterior-segment imaging through opaque media.
- Myopia-management programme: an optical biometer, or an auto refractor with axial-length measurement such as the FRS-810 for refraction, keratometry and axial length in one step.
- General ophthalmology clinic without surgery: a B-scan for posterior-segment assessment when the fundus cannot be seen; biometry depends on whether you refer for cataract surgery.
ENOCHTEC biometry and ultrasound
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| AL-VIEW Lite | Enochview-1000 | FRS-810 | |
|---|---|---|---|
| Type | Optical biometer (OLCR) | A/B ultrasound scanner | Auto refractor keratometer with axial length |
| Contact | Non-contact | Contact A-scan; B-scan via eyecup, gel or aqueous capsule | Non-contact |
| Axial length range | 14–33 mm | 5–40 mm (A-scan) | 11.5–42.0 mm |
| Listed precision | AL repeatability ≤0.025 mm | A-scan measurement error ≤ ±0.05 mm | Confirmed with quotation |
| Other measurements | CCT, ACD, LT, VT, K, AST, WTW, PD, CWC | ACD, LT; B-scan imaging (10 MHz, ≥50 mm depth) | Refraction and keratometry |
| IOL formulas | Confirmed with quotation | SRK-T, SRK II, Holladay, Binkhorst-II, Hoffer-Q, Haigis | — |
| Main use | Biometry and myopia follow-up | Cataract biometry in opaque media; posterior-segment imaging | Myopia-management monitoring with refraction |
Specifications are for reference. The exact configuration, accessories and documentation for your market are confirmed in your quotation.
Compare models in the optical biometry guide and the ophthalmic ultrasound guide, or plan a complete ophthalmology clinic.
Frequently asked questions
Is optical biometry better than A-scan ultrasound?
Optical biometry is non-contact, faster and less dependent on the operator, so it is the usual first choice. It cannot measure when a dense cataract or another opacity blocks the light, and then A-scan ultrasound is used. Many cataract services keep both.
What is the difference between an A-scan and a B-scan?
An A-scan is a one-dimensional trace used to measure distances such as axial length. A B-scan is a two-dimensional cross-sectional image used to examine the vitreous, retina and posterior eye wall, especially when they cannot be seen directly.
Can an optical biometer measure corneal thickness?
Many can. The AL-VIEW Lite reports central corneal thickness from 200 to 1200 μm in the same non-contact measurement as axial length.
Why does probe pressure matter in contact A-scan?
Pressing the probe on the cornea indents it slightly, which can make the measured axial length shorter than it really is. Gentle, consistent probe placement helps avoid this.
Which ENOCHTEC instrument is best for myopia follow-up?
For non-contact axial-length follow-up, the AL-VIEW Lite optical biometer or the FRS-810, which combines refraction, keratometry and axial length, are the usual choices. The clinician decides the follow-up protocol.
Planning biometry for your clinic?
Tell us whether you perform cataract surgery, run a myopia-management programme or both, and how many patients you measure. We will recommend an optical biometer, an A/B scanner or a combination, and send a quotation.
Request a quoteThis guide is general information for equipment buyers. Biometry, IOL calculation and clinical decisions are made by qualified eye-care professionals.
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