Stereotest Clinical Comparison - Frisby vs Randot, TNO, Titmus & Lang

The Frisby Stereotest has been used in clinics, research and teaching for over 50 years. It is the only widely used near stereotest that measures stereopsis with real physical depth: no glasses and no printed stereograms.

Why clinicians choose the Frisby

• No glasses: glasses-free testing from 6 months.
• True stereopsis only: monocular cues are physically eliminated by design.
• Reliable repeat testing: the target can be moved between presentations, so patients cannot learn the answer. This makes it well suited to monitoring amblyopia treatment over time.
• Engaging for young children: the “find the hidden target” format helps cooperation and gives more reliable results.
• Valid in mild to moderate amblyopia: the larger targets stay resolvable at reduced acuity.
• A research standard: widely used as a reference test in clinical trials, and it meets Westheimer’s criteria for optimal stereoacuity measurement (Vision Research, 2013).

	Frisby Stereotest	Randot (Stereo Optical)	TNO	Titmus / Wirt Fly	Lang I / II ¶
Depth mechanism	Real physical depth	Printed random dot stereogram (RDS), polarised	Printed RDS, anaglyph	Printed contour stereo	Lenticular RDS
Glasses required	None required	Polarised glasses	Red-green anaglyph glasses	Polarised glasses	None required
Monocular cues eliminated	Yes — true disparity only	Partial (if glasses worn correctly)	Yes	No — contour cues present	Lang I: Yes. Lang II: Partial — positional guessing risk in pre-verbal children
Age range	6 months +	2 years + (preschool version available)	3 years +	2 years + (fly / animal); 3 years + (circles)	6 months +
Threshold range (arc seconds)	5 – 600″	20 – 400″ (800″ preschool)	15 – 480″	40 – 3000″	200 – 1200″
Valid in mild to moderate amblyopia †	Yes — larger targets enable treatment monitoring, not just screening	Partial — fine dot patterns may not resolve at low acuity	Partial — fine dot patterns may not resolve at low acuity	Partial — coarser contours help, but monocular cues remain a concern	Partial — fine lenticular pattern may not resolve at low acuity; Lang sensitivity aids detection of amblyopia but does not confirm binocular vision is intact
Repeat testing reliability ‡	Yes — real depth target can be repositioned; patients cannot memorise or predict the correct response on repeat testing	No — fixed printed stimulus; prior exposure risks learned response	No — fixed printed stimulus; prior exposure risks learned response	No — fixed printed stimulus; prior exposure risks learned response	No — fixed lenticular positions; prior exposure risks learned response
Detects binocular vision anomalies	High specificity — reliable confirmatory tool with very few false positives	Moderate specificity	Highest sensitivity among card tests	Low — monocular cues allow guessing	High specificity; good for infant screening
Research & clinical trial use	Widely used as reference standard in clinical trials internationally	Common in US clinical trials	Research use in some settings	Rarely used — monocular cue concern	Screening studies
Equipment dependence	Fully standalone — no lane equipment needed	Commonly bundled with lane systems	Standalone card	Often bundled with lane systems	Standalone card

Green = advantage Red = limitation Amber = partial / context-dependent Highlighted row = key Frisby design feature

The Frisby is UK and Irish clinicians’ first choice for children

In a survey of UK and Irish eye care professionals, the Frisby was the stereotest most often named as best practice for children aged 3–6 and 6–12. Source: Vancleef, K. & Read, J.C.A. (2019) ‘Which Stereotest do You Use? A Survey Research Study in the British Isles, the United States and Canada’, British and Irish Orthoptic Journal, 15(1), 15–24, doi:10.22599/bioj.120.

† The Frisby test uses larger triangular target elements by design, so the stereo stimulus remains resolvable even when acuity is reduced in one eye — enabling valid binocular vision measurement and treatment monitoring in patients with mild to moderate amblyopia. This is distinct from a test’s ability to screen for or detect amblyopia: tests with high sensitivity (such as Lang and TNO) flag cases well but may not yield valid stereo measurements once amblyopia is present.

‡ Because the Frisby target is a real physical object whose position can be varied by the clinician between trials, patients cannot memorise or predict the correct response — making it uniquely suited to longitudinal monitoring and reassessment. Printed and lenticular tests present a fixed stimulus whose location is unchanged between encounters; a patient who has previously seen the answer, or been shown it, may pass on memory rather than stereopsis.

¶ On the Lang II, the position of target objects may be perceived monocularly (though the shape cannot be discerned), creating a risk that pre-verbal children — who are not asked to name the shape — may respond to positional cues rather than true stereopsis. For this reason, some clinicians prefer Lang I in the youngest age groups.

RDS = random dot stereogram. ‘Detects binocular vision anomalies’ reflects specificity and sensitivity characteristics from comparative field studies (Hatt et al.; Greenberg et al.; Simons et al.). High specificity (few false positives) and high sensitivity (proportion of true cases detected) are distinct and both clinically valuable properties. This table covers near-vision card tests only; distance stereotests and digital/tablet-based tests are not included. All clinical decisions should be based on current peer-reviewed evidence.

Request a demonstration unit — we offer complimentary demo units to optometry educators and some clinical research programmes. Contact us at hello@frisbystereotest.com or visit our contact page.