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  1. Over 50 Years Supporting Paediatric Vision Testing Worldwide Since 1975

Research

Research Compendium

The Frisby Stereotest — academic, clinical & peer-reviewed evidence from 1975

53 studies · 15 countries · five decades of published research • Compiled 2026

This document draws together the academic, scientific and clinical research literature on the Frisby range of stereotests, spanning five decades since the test's introduction in 1975. Each study is summarised with its key finding highlighted. Studies originally published in French, Spanish and Japanese have been translated into English and are marked accordingly.

The Frisby Product Range

This compendium covers all three products in the Frisby Stereotest range:

Frisby Near Stereotest

The original 3-plate test (1975). A free-space, real-depth test read at near distances (30–50cm) without glasses, measuring stereoacuity from 600″ down to 6″.

Frisby Screener Pocket Test (1-plate & 2-plate) (2014)

Portable screening versions of the Near Stereotest in a pocket-sized case, designed for quick screening of infants, pre-verbal children and shy pre-schoolers.

Frisby Davis Distance Stereotest (FD2) (2003)

Developed with Helen Davis OBE, Professor of Orthoptics, extending the same real-depth, glasses-free principle to distance testing (up to 6m).

Why the Frisby: A Summary of the Evidence

Individual study findings are summarised on their own terms throughout this pack. Drawing them together, several themes recur across the literature:

  • No monocular false-positive identifications in the largest independent comparison of seven leading stereotests, in either normal or strabismic subjects (Hahn et al., 2010).
  • Less affected than random-dot tests when monocular acuity was experimentally degraded (Odell et al., 2009).
  • Reported as the most-used stereotest in the British Isles for both younger and older children (Vancleef et al., 2019).
  • Selected as a primary outcome measure in the NIH-funded, multi-centre Infant Aphakia Treatment Study (Lambert et al., 2014).
  • Built on real, natural-depth targets rather than simulated disparity — a design unchanged in principle since 1975 (Frisby, 1975).
  • Meets each of the criteria Gerald Westheimer set out for effective stereoacuity testing, as the evidence throughout this compendium demonstrates (Westheimer, 2013).

Contents: Index of Studies

Study
Authors
Year
Institution
Part One — Frisby Near Stereotest
A. History & Foundational Design
Use of random-dot stereograms in the clinical assessment of strabismic patients
Frisby, J.P., Mein, J., Saye, A., Stanworth, A.
1975
University of Sheffield, UK
Introduced the first stereotest to use real, natural-depth random element targets requiring no dissociating glasses.
B. Validity & Monocular-Clue Studies
Assessing the Frisby stereo test under monocular viewing conditions
Cooper, J., Feldman, J.
1979
USA
Only 1 of 34 adult subjects could pass the test using monocular clues alone.
The validity of the Frisby stereotest as a measure of precise stereoacuity
Rosner, J., Clift, G.D.
1984
USA
Correlation (r = 0.73, p<.001) between Frisby and TNO results.
A comparison of the Frisby, Random-Dot E, TNO, and Randot circles stereotests in screening and office use
Simons, K.
1981
Wills Eye Hospital, Philadelphia, PA, USA
Frisby reliably graded stereopsis in both preschool screening and clinical office settings; missed some cases that RDE/TNO caught.
Étude comparative des stéréotests chez les enfants: T.N.O., R.D.E., Wirt, Frisby Translated from French
Piro, M., Salmon, D., Ardouin, M.
1982
Rennes, France
“The Frisby test seemed to be the best test for children” when correctly presented.
Testing stereopsis in the pre-school child: is it clinically useful?
Manny, R.E., Martinez, A.T., Fern, K.D.
1991
USA
No child with normal binocular vision could pass the Frisby test monocularly; children with constant strabismus couldn’t detect even large disparities; two anisometropic amblyopes tested within normal limits.
Does binocularly perceived depth correlate with reduced stereoacuity?
Lindstrom, A., Davis, H., Frisby, J.P.
2009
UK
Examines the relationship between measured stereoacuity and perceived binocular depth, co-authored by the test's own developers.
An improved training procedure as a precursor to testing young children with the Frisby Stereotest
Saunders, K.J., Westall, C.A.
1996
UK / Canada
A structured training protocol improved reliable testability in very young children.
The modified Frisby stereotest
Saunders, K.J., Woodhouse, J.M., Westall, C.A.
1996
University of Wales College of Cardiff, UK
Extended reliable Frisby testing down to 7 months of age; over 60% testable by 12 months.
Stereopsis, stereotests, and their relation to vision screening and clinical practice
Fricke, T.R., Siderov, J.
1997
University of Melbourne / Victorian College of Optometry, Australia
Frisby stereoacuity is virtually unaffected by refractive blur, unlike the RDE stereotest — supporting its use where other RDS tests are compromised.
Comparison of the binocular stereoacuity measured by the TNO stereotest vs the Frisby Stereotest Near (FSN) in healthy adult subjects Poster
Fauveau, M., Rousseau, B., Crepy, P., et al.
2012
Hôpital d'Instruction des Armées, Clamart / Institut Mutualiste Montsouris, Paris, France
In 77 Air Crew applicants, Frisby Near averaged 15″ vs TNO's 60″, with no significant agreement between the two tests.
Normative Values for Near and Distance Clinical Tests of Stereoacuity
Piano, M.E.F., Tidbury, L.P., O'Connor, A.R.
2016
Strabismus, 24(4), 169-172
Independent normative stereoacuity values for Frisby Near and FD2, cross-checking earlier normative datasets.
Test-retest variability in stereoacuity measurements
Mehta, J., O'Connor, A.
2023
University of Liverpool, UK
Frisby had the narrowest limits of agreement (best test-retest reliability) of TNO, Frisby, Lang Stereopad and Asteroid.
Monocular Clues in Seven Stereotests
Hahn, E., Comstock, D., Durling, S., MacCarron, J., Mulla, S., James, P., LaRoche, R.
2010
IWK Health Centre / Dalhousie University, Canada
The only stereotest of 7 major tests with zero monocular identification in either normal or strabismic subjects.
Stereoacuity norms for school-age children using the Frisby stereotest
Anketell, P.M., Saunders, K.J., Little, J-A.
2013
Ulster University, UK
Normative dataset for 6-16 year-olds: median 20″ (primary) / 10″ (post-primary).
Clinical evaluation of stereopsis
Westheimer, G.
2013
University of California, Berkeley, USA
The Frisby's design satisfies each of the criteria Westheimer (2013) set out for effective stereoacuity testing, as demonstrated by the evidence throughout this compendium.
C. Screening Performance in Amblyopia & Strabismus
Screening merits of the Lang II, Frisby, Randot, Titmus, and TNO stereo tests
Ohlsson, J., Villarreal, G., Abrahamsson, M., Cavazos, H., Sjöström, A., Sjöstrand, J.
2001
Gothenburg, Sweden / Monterrey, Mexico
Frisby recorded the highest individual sensitivity of the five stereotests tested, though — like all of them — it isn't sufficient alone for amblyopia/strabismus screening.
The Effect of Refractive Amblyopia on the Frisby Stereotest
Nanda, K.D., Nischal, K.K.
2022
UPMC Children's Hospital of Pittsburgh, PA, USA
Frisby stereoacuity correlates with amblyopia severity, supporting its use for monitoring binocular status during treatment.
D. Stereopsis & Ageing
Stereopsis and ageing
Wright, L.A., Wormald, R.P.W.
1992
Moorfields Eye Hospital, London, UK
In 728 patients over 65, only 27% had normal stereopsis on the Frisby test and prevalence of loss rose with age.
Effect of age on adult stereoacuity as measured by different types of stereotest
Garnham, L., Sloper, J.J.
2006
Moorfields Eye Hospital, London, UK
Frisby stereoacuity declined only mildly with age; unlike TNO, it did not show a sharp collapse to screening-level results in older subjects.
Ocular contributions to age-related loss in coarse stereopsis
Schneck, M.E., Haegerstrom-Portnoy, G., Lott, L.A., Brabyn, J.A.
2000
Smith-Kettlewell Eye Research Institute, San Francisco, CA, USA
Age-related stereopsis loss on the Frisby test tracked ocular health, not cortical decline — healthy-eyed older adults showed no significant drop.
Single and Multiple Visual Function Impairments and Associated Vision-Related Quality of Life Impact in Older Adults Aged 60 to 100 Years
Gupta, P., Vu, T.A., Wong, C.M.J., et al.
2025
Singapore Eye Research Institute / Duke-NUS Medical School, Singapore
Frisby used as the depth-perception measure in a 2,380-participant population cohort study of vision and quality of life in older adults.
E. Major Multi-Centre Clinical Trials Using Frisby as an Outcome Measure
Stereopsis Results at 4.5 Years of Age in the Infant Aphakia Treatment Study
Infant Aphakia Treatment Study Group (Lambert, S.R., et al.)
2014/2015
Multi-centre, NIH-funded, USA
Frisby selected as one of three primary stereopsis outcome measures in a major NIH-funded multicentre RCT.
Factors associated with stereopsis and a good visual acuity outcome among children in the Infant Aphakia Treatment Study
Infant Aphakia Treatment Study Group
2016
Multi-centre, NIH-funded, USA
Earlier surgery and better visual acuity were the strongest predictors of achieving measurable stereopsis.
Presenting features and early management of childhood intermittent exotropia in the UK: inception cohort study
Buck, D., et al.
2009
Multi-centre, UK
Stereoacuity did not predict which treatment a child received; control of the deviation did.
F. International Literature
Concordancia de resultados entre las pruebas de estereopsis Frisby, test de Titmus vs Howard Dolman test en pacientes de entre 6 a 12 años con ambliopía y grupo control Translated from Spanish Thesis
Soto Pinzón, J.C., Urdiales Suárez, J.A. (advisor: Jurado Medina, S.P.)
2023
Universidad de La Salle, Bogotá, Colombia
Compared Frisby and Titmus against the Howard-Dolman in amblyopic children (undergraduate thesis).
Fiabilidad de los test de estereopsis de cerca: Titmus, Randot, TNO y Frisby Translated from Spanish
Cirac, A., Jarabo, C., et al.
2016
Universidad de Zaragoza, Spain
Failure rates under 10% for all four tests, incl. Frisby, in 200 healthy young adults.
Detección de estrabismo y ambliopía con el uso de pruebas para estereopsis en población infantil Translated from Spanish
Hernández-Muñoz, M.T., Hernández-Ordóñez, T., De la Fuente-Torres, M.A.
2003
Mexico City / Ciudad Victoria, Mexico
100% specificity for strabismus and amblyopia in 1,048 Mexican children — a reliable rule-out screening tool.
近見立体視検査における3検査法の比較 (Comparison of three near-stereoacuity test methods) Translated from Japanese
Kawachi, E.
1983
Japan
One of the earliest non-English clinical evaluations of the Frisby, published within a decade of its 1975 launch.
Comparison between the Frisby Stereotest and Titmus Stereo Test Translated from Japanese
Abe, H., et al.
2009
Japan
Peer-reviewed Japanese comparison, part of a sustained multi-year Japanese research programme on the Frisby.
Frisby Stereo Test binocular-vision screening in train drivers Translated from Japanese
Igarashi, T., et al.
2011
Japan
Real-world occupational screening of binocular vision in train drivers, a safety-critical profession.
G. Test-Selection & Usage Surveys
Which Stereotest do You Use? A Survey Research Study in the British Isles, the United States and Canada
Vancleef, K., Read, J.C.A., et al.
2019
Newcastle University, UK / international
Frisby is the most-used stereotest in the British Isles for both younger and older children.
H. Screener Pocket Test: Clinical Use & Review
The Frisby stereotest: introduction and review
Optician CPD Series (n.d.)
n.d.
UK Author: Professor J. Frisby
Clinical CPD review of test procedure, scoring and screening use across the full Frisby range.
Personalized surgical informed consent with stereoscopic visualization in neurosurgery — real benefit for the patient or unnecessary gimmick?
Hertzsprung, N., Krantchev, K., Picht, T., Roethe, A.L., Rubarth, K., Fuellhase, J., Vajkoczy, P., Acker, G.
2023
Germany
Frisby Pocket Stereotest used to screen participants' stereopsis before a neurosurgical informed-consent study — an independent, non-ophthalmic clinical use case.
Does stereoscopic imaging improve the memorization of medical imaging by neurosurgeons? Experience of a single institution
Schlinkmann, N., Khakhar, R., Picht, T., Piper, S.K., Fekonja, L.S., Vajkoczy, P., Acker, G.
2022
Germany
Frisby Pocket Stereotest used to confirm normal stereopsis and balance study groups of neurosurgeons before a visualisation-memory task.
Part Two — Frisby Davis Distance Stereotest (FD2)
I. Distance Stereoacuity: Development, Validity & Clinical Application
Does stereoacuity correlate with interpupillary distance for normal observers? Conference paper
Frisby, J.P., Patchick, E., Edgar, R., Davis, H.
2004
University of Sheffield, UK
FD2 stereoacuity did not correlate significantly with interpupillary distance, unlike general laboratory stereo-geometry tasks.
Frisby Davis distance stereoacuity values in visually normal children
Adams, W.E., Hrisos, S., Richardson, S., Davis, H., Frisby, J.P., Clarke, M.P.
2005
Newcastle University, UK
All 59 children (aged 3–6 years) were successfully testable, establishing the first paediatric FD2 norms: mean stereoacuity of 29.6″ arc at 6m (76% of children) and 92.3″ arc at 3m (24%), with only 6.8% showing no measurable response.
Development of distant stereoacuity in visually normal children as measured by the Frisby-Davis distance stereotest
Hong, S.W., Park, S.C.
2008
South Korea
Corroborates the Adams et al. (2005) paediatric FD2 norms in an independent population.
Effects of interpupillary distance on stereoacuity: the Frisby Davis distance stereotest versus a 3-dimensional distance stereotest
Eom, Y., Song, J.S., Ahn, S.E.
2013
South Korea
FD2 stereoacuity improved with increased IPD, matching real-world geometry, unlike a simulated 3D test.
Testing distance stereoacuity with the Frisby-Davis 2 (FD2) test
Holmes, J.M., Fawcett, S.L.
2005
Mayo Clinic, Rochester, MN, USA
Developed a modified staircase presentation protocol that controls for monocular cues at larger disparities.
Improvement in distance stereoacuity following surgery for intermittent exotropia
Adams, W.E., Leske, D.A., Hatt, S.R., Mohney, B.G., Birch, E.E., Weakley, D.R. Jr.
2008
Mayo Clinic, Rochester, MN, USA
FD2 documented measurable improvement in distance stereoacuity after surgery.
Evaluation of factors influencing distance stereoacuity on Frisby-Davis Distance Test (FD2) in intermittent exotropia
Saxena, R., Kakkar, A., Menon, V., Sharma, P., Phuljhele, S.
2011
India
Identifies clinical factors influencing FD2 distance stereoacuity measurement in intermittent exotropia.
Evaluation of FD2 (Frisby Davis distance) stereotest in surgical management of intermittent exotropia
Singh, A., Sharma, P., Singh, D., Saxena, R., Sharma, A., Menon, V.
2013
India
Proposed an FD2 distance-stereoacuity threshold (worse than 20″) to help time surgical intervention.
Stereoacuity with Frisby and Revised FD2 Stereo Tests
Bohr, I., Read, J.C.A., et al.
2013
Open-access, freely available full text
Fair agreement between near-Frisby and FD2 across the lifespan; documents childhood gains and late-adulthood decline.
Contribution of a real depth distance stereoacuity test to clinical management
Young, B.J., Sueke, H., Wylie, J.M., Kaye, S.B.
2009
St Paul's Eye Unit, Liverpool, UK
No subject achieved a passing score monocularly at 6 metres.
Predictive factors of stereopsis outcomes following strabismus surgery
Eshaghi, M., Arabi, A., Banaie, S., Shahraki, T., Eshaghi, S., Esfandiari, H.
2021
Iran / USA
FD2 and near Frisby used as core outcome measures across 182 surgical patients.
J. The Mayo Clinic Stereoacuity Research Programme
Real Depth vs Randot Stereotests
Leske, D.A., Birch, E.E., Holmes, J.M.
2006
Mayo Clinic, Rochester, MN, USA
Patients consistently detected finer disparities on the real-depth Frisby/FD2 tests than on equivalent random-dot tests.
New tests of distance stereoacuity and their role in evaluating intermittent exotropia
Holmes, J.M., Birch, E.E., Leske, D.A., Fu, V.L., Mohney, B.G.
2007
Mayo Clinic, Rochester, MN, USA
Helped establish the FD2's clinical role in evaluating intermittent exotropia, where distance stereopsis is a more sensitive indicator than near stereopsis.
Variability of stereoacuity in intermittent exotropia
Hatt, S.R., Mohney, B.G., Leske, D.A., Holmes, J.M.
2008
Mayo Clinic, Rochester, MN, USA
Stereoacuity in intermittent exotropia can genuinely fluctuate within a single day, regardless of which stereotest is used.
Defining real change in measures of stereoacuity
Adams, W.E., Leske, D.A., Hatt, S.R., Holmes, J.M.
2009
Mayo Clinic, Rochester, MN, USA
Established test-retest reliability thresholds for near-Frisby and FD2, giving clinicians a defensible bar for judging genuine treatment-related change.
The effect of induced monocular blur on measures of stereoacuity
Odell, N.V., Hatt, S.R., Leske, D.A., Adams, W.E., Holmes, J.M.
2009
Mayo Clinic, Rochester, MN, USA
Frisby and FD2 scores were less affected than random-dot tests under simulated monocular visual acuity loss.
K. Independent Expert Review
Stereo vision and strabismus
Read, J.C.A.
2015
Newcastle University, UK
Independent expert review situating Frisby/FD2 within the full clinical stereopsis and strabismus literature, corroborating and contextualising the Adams et al. (2009) reliability data.

Part One — Frisby Near Stereotest

The original 3-plate Frisby Near Stereotest (1975) is the foundation of the whole product range, including the pocket-sized Screener versions, which share the same real-depth optical design. The evidence below spans its design validation, monocular-clue studies, screening performance, stereopsis and ageing, major clinical trials, international literature, usage surveys and the Screener Pocket Test.

A. History & Foundational Design

The Frisby Stereotest was developed by Professor John P. Frisby (University of Sheffield) and introduced in 1975. It presents genuine, real-depth random element targets viewed with completely natural vision — no polarising or red/green glasses are needed — because the test target and background are printed on opposite sides of a clear plastic plate of known thickness.

Use of random-dot stereograms in the clinical assessment of strabismic patients

Frisby, J.P., Mein, J., Saye, A., Stanworth, A. (1975) · British Journal of Ophthalmology, 59(10), 545-552 · University of Sheffield, UK · View paper ↗

Professor John P. Frisby and colleagues introduced a stereotest in which the target and background patterns are printed on opposite faces of a clear plastic plate of defined thickness, so that genuine retinal disparity — real depth — is created optically rather than simulated with polarised or anaglyph glasses. This design principle, building on Bela Julesz's random-dot stereogram work, underpins every product in the Frisby range. This is the original peer-reviewed paper describing the test's clinical use.

Key findingIntroduced the first stereotest to use real, natural-depth random element targets requiring no dissociating glasses.

Also noted in the literature Hinchcliffe, H.A. (1978), Clinical evaluation of stereopsis — an early clinical evaluation including the Frisby. Frisby, J.P. (1980), "The Frisby Stereotest — amended instructions," British Orthoptic Journal, 37, 108-112 — a later refinement of test procedure (no online record found; pre-digital orthoptics journal).

B. Validity & Monocular-Clue Studies

A central question for any stereotest is whether it can be passed by guesswork, using clues other than true binocular depth perception. The studies below address this directly.

Assessing the Frisby stereo test under monocular viewing conditions

Cooper, J., Feldman, J. (1979) · Journal of the American Optometric Association, 50(7), 807-809 · USA · View paper ↗

34 optometry students were tested on the Frisby stereotest under both monocular and binocular viewing conditions. Only one student passed monocularly on first exposure (two more passed after prior binocular exposure to the target). The authors concluded the Frisby performs as well as any commercially available random-dot stereotest in adults, with negligible exploitable monocular cues.

Key findingOnly 1 of 34 adult subjects could pass the test using monocular clues alone.

The validity of the Frisby stereotest as a measure of precise stereoacuity

Rosner, J., Clift, G.D. (1984) · Journal of the American Optometric Association, 55(7), 505-506 · USA · View paper ↗

Twenty binocularly normal adults were tested on both the Frisby and TNO stereotests. A statistically significant intercorrelation (Pearson r = 0.73, p < .001) was found between the two independent test methods, providing early support for the Frisby as a valid clinical measure of stereoacuity.

Key findingCorrelation (r = 0.73, p<.001) between Frisby and TNO results.

A comparison of the Frisby, Random-Dot E, TNO, and Randot circles stereotests in screening and office use

Simons, K. (1981) · Archives of Ophthalmology, 99(3), 446-452 · Wills Eye Hospital, Philadelphia, PA, USA · View paper ↗

Four leading stereotests were compared in preschool vision-screening populations and in patients with strabismus and amblyopia. The Frisby, alongside the other random-dot-principle tests, reliably graded degrees of stereopsis; the study also noted that some cases identified by RDE/TNO were missed by Frisby.

Key findingFrisby reliably graded stereopsis in both preschool screening and clinical office settings; missed some cases that RDE/TNO caught.

Étude comparative des stéréotests chez les enfants: T.N.O., R.D.E., Wirt, Frisby

Piro, M., Salmon, D., Ardouin, M. (1982) · Journal Français d'Orthoptique, 14 (Rennes) · Rennes, France Translated from French · View paper ↗

The authors studied stereoscopic vision in 46 normal children aged 2 to 9 years using four different tests. They concluded the Frisby test was the most valuable of the four for testing children, provided it is correctly presented: the test and the child's head must be still, the plate must be perpendicular to the line of sight, and the testing distance must be accurately measured.

Key finding“The Frisby test seemed to be the best test for children” when correctly presented.

Testing stereopsis in the pre-school child: is it clinically useful?

Manny, R.E., Martinez, A.T., Fern, K.D. (1991) · Journal of Pediatric Ophthalmology & Strabismus, 28, 223-231 · USA · View paper ↗

76 children were tested on the Frisby stereotest under monocular and binocular conditions. No child with normal binocular vision was able to use monocular cues to pass the test. Children with constant strabismus could not detect even large disparities on the Frisby, while some children with anisometropic amblyopia were able to perform within normal limits — an early, independent replication of the monocular-cue resistance later confirmed at scale by Hahn et al. (2010).

Key findingNo child with normal binocular vision could pass the Frisby test monocularly; children with constant strabismus couldn’t detect even large disparities; two anisometropic amblyopes tested within normal limits.

An improved training procedure as a precursor to testing young children with the Frisby Stereotest

Saunders, K.J., Westall, C.A. (1996) · Eye, 10, 384-388 · UK / Canada · View paper ↗

Established a standardised training/familiarisation phase prior to formal testing, using light-flash rewards to confirm the child's understanding of the pointing task. This training step increased the proportion of young children who could be reliably tested.

Key findingA structured training protocol improved reliable testability in very young children.

The modified Frisby stereotest

Saunders, K.J., Woodhouse, J.M., Westall, C.A. (1996) · Journal of Pediatric Ophthalmology & Strabismus, 33(6), 323-327 · University of Wales College of Cardiff, UK · View paper ↗

165 children aged 0.5 to 47 months were assessed using a modified protocol adding a non-stereo practice plate and an auditory reward for correct responses. These modifications extended the age range over which valid results could be obtained, making infants as young as 7 months testable, with a majority of 12-month-olds successfully completing the test.

Key findingExtended reliable Frisby testing down to 7 months of age; over 60% testable by 12 months.

Stereopsis, stereotests, and their relation to vision screening and clinical practice

Fricke, T.R., Siderov, J. (1997) · Clinical and Experimental Optometry, 80(5), 165-172 · University of Melbourne / Victorian College of Optometry, Australia · View paper ↗

A detailed review of clinical stereotests, including a dedicated technical section on the Frisby's real-depth design. Notably, the authors report that stereoacuity measured with the Frisby is virtually unaffected by significant amounts of refractive blur, in contrast to the RDE stereotest, which is more sensitive to it. (A related but distinct effect: Nanda & Nischal, 2022, below, found Frisby scores do correlate with the severity of diagnosed refractive amblyopia.) The review also cites Manny et al. (1991, above) and positions the Frisby and TNO as the two most appropriate commercially available stereotests for paediatric vision screening, since the Frisby needs no filters — unlike the TNO, which uses red/green glasses — and both are within the cognitive grasp of young children.

Key findingFrisby stereoacuity is virtually unaffected by refractive blur, unlike the RDE stereotest — supporting its use where other RDS tests are compromised.

Comparison of the binocular stereoacuity measured by the TNO stereotest vs the Frisby Stereotest Near (FSN) in healthy adult subjects

Fauveau, M., Rousseau, B., Crepy, P., et al. (2012) · International Orthoptic Congress · Hôpital d'Instruction des Armées, Clamart / Institut Mutualiste Montsouris, Paris, France Poster · View paper ↗

90 adults (aged 20-38) applying for Air Crew vision screening were recruited; 77 were included in the final analysis. Each was tested on the TNO stereotest (with and without strict head positioning control) and the Frisby Stereotest Near. Mean stereoacuity was 15″ on the Frisby vs 60″ on the TNO, and no statistically significant agreement was found between the two tests' results — consistent with the Cirac et al. (2016, below) recommendation to use more than one stereotest per patient. A real-world example of Frisby's use in aviation applicant screening.

Key findingIn 77 Air Crew applicants, Frisby Near averaged 15″ vs TNO's 60″, with no significant agreement between the two tests.

Normative Values for Near and Distance Clinical Tests of Stereoacuity

Piano, M.E.F., Tidbury, L.P., O'Connor, A.R. (2016) · Strabismus, 24(4), 169-172 · View paper ↗

A comparative study reporting normative stereoacuity values across several commonly used near and distance clinical stereotests, including the Frisby Near Stereotest and the FD2 Distance Stereotest — a useful, independent cross-check against the Anketell et al. (2013) and Adams et al. (2005) norms above.

Key findingIndependent normative stereoacuity values for Frisby Near and FD2, cross-checking earlier normative datasets.

Test-retest variability in stereoacuity measurements

Mehta, J., O'Connor, A. (2023) · Strabismus, 31(3), 188-196 (DOI: 10.1080/09273972.2023.2252853) · University of Liverpool, UK · View paper ↗

54 visually normal adults were tested twice on four stereotests: TNO, Frisby, Lang Stereopad and Asteroid (a digital test). Test-retest variability was clinically insignificant for all tests except the Lang Stereopad. The Frisby had the narrowest limits of agreement of the four — the best repeated-measures reliability — though the digital Asteroid test covers a wider measurement range.

Key findingFrisby had the narrowest limits of agreement (best test-retest reliability) of TNO, Frisby, Lang Stereopad and Asteroid.

Monocular Clues in Seven Stereotests

Hahn, E., Comstock, D., Durling, S., MacCarron, J., Mulla, S., James, P., LaRoche, R. (2010) · Dalhousie Medical Journal, 37(1), 4-13 · IWK Health Centre / Dalhousie University, Canada · View paper ↗

133 subjects (100 with normal stereopsis, 33 with manifest strabismus) were tested monocularly and binocularly on seven leading stereotests: Titmus, Randot, Randot Special Edition, Randot Preschool, Lang, Lang II and Frisby. Monocular (false-positive) identification occurred on 6 of the 7 tests in both groups — but there was no monocular identification whatsoever on the Frisby, in either group. The single exception across all 133 subjects was one strabismic patient with alternating exotropia who succeeded binocularly (not monocularly) at the lowest disparity plate.

Key findingThe only stereotest of 7 major tests with zero monocular identification in either normal or strabismic subjects.

Stereoacuity norms for school-age children using the Frisby stereotest

Anketell, P.M., Saunders, K.J., Little, J-A. (2013) · Journal of AAPOS, 17(6), 582-587 · Ulster University, UK · View paper ↗

186 typically-developing school-age children (6-16 years) were tested to establish contemporary normative Frisby stereoacuity values. Median crossed-disparity thresholds were 20 arcsec for primary-school children and 10 arcsec for post-primary children (25″ and 10″ respectively for uncrossed disparity).

Key findingNormative dataset for 6-16 year-olds: median 20″ (primary) / 10″ (post-primary).

Clinical evaluation of stereopsis

Westheimer, G. (2013) · Vision Research, 90, 38-42 (DOI: 10.1016/j.visres.2012.10.005) · University of California, Berkeley, USA · View paper ↗

Vision scientist Gerald Westheimer set out five criteria for effective clinical stereoacuity measurement: targets should be few in number and well articulated; sharply delineated and in good focus binocularly; presented with high contrast and at least medium photopic luminance; minimally reliant on prediction or memory; and as far as possible free of non-stereoscopic depth cues. Westheimer also noted that random-dot stereograms are problematic because not all observers can immediately disentangle the coherent global disparity on first viewing. The Frisby's design and the evidence in this compendium address each of these criteria directly: real, well-articulated targets with no exploitable monocular cues (Cooper & Feldman, 1979; Hahn et al., 2010); a target position that changes with every presentation, limiting reliance on memory or prediction (test design, Frisby, 1975); and viewing conditions that require no dissociating glasses, avoiding the first-viewing disentanglement problem Westheimer describes in random-dot tests.

Key findingThe Frisby's design satisfies each of the criteria Westheimer (2013) set out for effective stereoacuity testing, as demonstrated by the evidence throughout this compendium.

Does binocularly perceived depth correlate with reduced stereoacuity?

Lindstrom, A., Davis, H., Frisby, J.P. (2009) · Ophthalmic and Physiological Optics, 29(1), 92-98 · UK · View paper ↗

Co-authored by Helen Davis and John Frisby, this study measured ‘perceived depth’ using the Wirt Fly Stereotest (via pointer-matching, recorded in mm) and correlated it against stereoacuity thresholds from the Frisby Near Stereotest and Randot Circles test — supporting the Frisby Near test as a valid correlate of perceived depth, not just a clinical threshold measure.

Key findingExamines the relationship between measured stereoacuity and perceived binocular depth, co-authored by the test's own developers.

Also noted in the literature Holmes, J.M., Leske, D.A. (1999), “Monocular clues in tests of stereoacuity,” Transactions of the IX International Orthoptic Congress, 103–106 — 100 normal adults were tested with one eye occluded and none could pass the Frisby Near Stereotest; the Frisby was judged the least susceptible to monocular clues of the near stereotests compared. Cited by Hahn et al. (2010, above) (no online record found; congress proceedings).

C. Screening Performance in Amblyopia & Strabismus

A balanced picture: several studies report Frisby's performance directly against other leading tests, including honest caveats about stereotests as standalone screening tools.

Screening merits of the Lang II, Frisby, Randot, Titmus, and TNO stereo tests

Ohlsson, J., Villarreal, G., Abrahamsson, M., Cavazos, H., Sjöström, A., Sjöstrand, J. (2001) · Journal of AAPOS, 5(5), 316-322 · Gothenburg, Sweden / Monterrey, Mexico · View paper ↗

A large field study of 1,035 school children (aged 12-13) in Monterrey, Mexico compared five leading stereotests, including the Frisby, for screening amblyopia and strabismus against a full clinical exam. All five tests had sensitivity below 80% and positive predictive value below 40% as standalone screens; of 60 confirmed cases, only 8 were flagged by every test, and 25 — mostly amblyopic — were missed by all five. Frisby recorded the highest individual sensitivity of the five.

Key findingFrisby recorded the highest individual sensitivity of the five stereotests tested, though — like all of them — it isn't sufficient alone for amblyopia/strabismus screening.

The Effect of Refractive Amblyopia on the Frisby Stereotest

Nanda, K.D., Nischal, K.K. (2022) · Journal of Binocular Vision and Ocular Motility, 73(1), 7-10 · UPMC Children's Hospital of Pittsburgh, PA, USA · View paper ↗

22 children aged 4-12 with unilateral refractive amblyopia were prospectively assessed. A moderate-to-strong correlation was found between visual acuity and Frisby stereoacuity, showing that Frisby scores track the severity of already-diagnosed refractive amblyopia — useful for monitoring binocular status over the course of treatment.

Key findingFrisby stereoacuity correlates with amblyopia severity, supporting its use for monitoring binocular status during treatment.

D. Stereopsis & Ageing

Most Frisby research targets children, but a separate body of work looks the other way along the lifespan — tracking how real-depth stereopsis holds up, or declines, in older adults.

Stereopsis and ageing

Wright, L.A., Wormald, R.P.W. (1992) · Eye, 6(5), 473-476 · Moorfields Eye Hospital, London, UK · View paper ↗

728 individuals over the age of 65 attending a general clinic were tested on the Frisby stereotest, as part of a wider survey of visual function in the elderly. Only 27% achieved normal stereopsis and 29% had no measurable stereopsis at all, with prevalence of defective stereopsis rising with age. This loss occurred in the absence of any other diagnosed ocular morbidity.

Key findingIn 728 patients over 65, only 27% had normal stereopsis on the Frisby test and prevalence of loss rose with age.

Effect of age on adult stereoacuity as measured by different types of stereotest

Garnham, L., Sloper, J.J. (2006) · British Journal of Ophthalmology, 90(1), 91-95 · Moorfields Eye Hospital, London, UK · View paper ↗

60 visually normal subjects aged 17-83 were tested on four stereotests — TNO, Titmus, near-Frisby and FD2 — to compare how each responds to normal ageing. All four tests showed a mild overall decline in stereoacuity with age. A marked drop to screening-level or absent stereopsis was seen in five subjects over 55, but only on the TNO test; the Frisby and Titmus results in the same subjects did not show this collapse.

Key findingFrisby stereoacuity declined only mildly with age; unlike TNO, it did not show a sharp collapse to screening-level results in older subjects.

Ocular contributions to age-related loss in coarse stereopsis

Schneck, M.E., Haegerstrom-Portnoy, G., Lott, L.A., Brabyn, J.A. (2000) · Optometry and Vision Science, 77(10), 531-536 · Smith-Kettlewell Eye Research Institute, San Francisco, CA, USA · View paper ↗

Using the Frisby test in a large, randomly-selected sample of adults over 58, the study asked whether age-related stereopsis loss reflects true cortical decline or degradation of the optical/retinal signal reaching the cortex. Coarse stereopsis declined markedly with age in the sample overall — but among the subset selected for good ocular health, there was no significant age-related decline.

Key findingAge-related stereopsis loss on the Frisby test tracked ocular health, not cortical decline — healthy-eyed older adults showed no significant drop.

Single and Multiple Visual Function Impairments and Associated Vision-Related Quality of Life Impact in Older Adults Aged 60 to 100 Years

Gupta, P., Vu, T.A., Wong, C.M.J., et al. (2025) · Investigative Ophthalmology & Visual Science, 66(2), 18 (DOI: 10.1167/iovs.66.2.18) · Singapore Eye Research Institute / Duke-NUS Medical School, Singapore · View paper ↗

A population-based cohort study of 2,380 multi-ethnic older Asian adults used the Frisby Stereotest as its depth-perception measure, alongside visual acuity, contrast sensitivity and colour vision, to examine the impact of single and multiple visual function impairments on vision-related quality of life. A large-scale, current (2025) demonstration of Frisby's continued use in major epidemiological research on ageing and vision.

Key findingFrisby used as the depth-perception measure in a 2,380-participant population cohort study of vision and quality of life in older adults.

E. Major Multi-Centre Clinical Trials Using Frisby as an Outcome Measure

The Frisby's inclusion as a primary outcome measure in large, government/NIH-funded multi-centre trials reflects its standing as a research instrument.

Stereopsis Results at 4.5 Years of Age in the Infant Aphakia Treatment Study

Infant Aphakia Treatment Study Group (Lambert, S.R., et al.) (2014/2015) · American Journal of Ophthalmology, 159(1), 64-70 · Multi-centre, NIH-funded, USA · View paper ↗

In this randomised controlled trial of 114 infants treated for unilateral congenital cataract (intraocular lens vs contact lens correction), the Frisby stereotest was used alongside Randot Preschool and Titmus Fly as one of three primary stereopsis outcome measures at 4.5 years of age.

Key findingFrisby selected as one of three primary stereopsis outcome measures in a major NIH-funded multicentre RCT.

Factors associated with stereopsis and a good visual acuity outcome among children in the Infant Aphakia Treatment Study

Infant Aphakia Treatment Study Group (2016) · Eye, 30(9), 1221-1228 · Multi-centre, NIH-funded, USA · View paper ↗

Follow-up analysis of the same multicentre trial identifying younger age at cataract surgery and better visual acuity outcome as the strongest predictors of achieving measurable stereopsis, again using the Frisby as a core measurement tool.

Key findingEarlier surgery and better visual acuity were the strongest predictors of achieving measurable stereopsis.

Presenting features and early management of childhood intermittent exotropia in the UK: inception cohort study

Buck, D., Powell, C., Cumberland, P., Davis, H., Dawson, E., Rahi, J., Sloper, J., Taylor, R., Tiffin, P., Clarke, M.P.; Improving Outcomes in Intermittent Exotropia Study Group (2009) · British Journal of Ophthalmology, 93(12), 1620-1624 · Multi-centre, UK · View paper ↗

This UK inception cohort study recruited 460 children under 12 with previously untreated intermittent exotropia from 26 hospital eye clinics, assessing near stereoacuity with the Frisby Near Stereotest as part of the study group’s baseline battery. Within 12 months, 64.6% received no treatment, 21% were treated for reduced visual acuity, and 19.4% for the strabismus itself (7.6% surgically); poor control of the deviation at recruitment was the strongest predictor of surgery. Stereoacuity and the size of the deviation did not influence which type of management a child received.

Key findingIn this 460-child, 26-centre UK cohort, stereoacuity did not predict which treatment a child with intermittent exotropia received — control of the deviation did.

F. International Literature

Frisby Stereotest research spans continents. This section highlights non-English-language studies, translated and summarised in English below.

Concordancia de resultados entre las pruebas de estereopsis Frisby, test de Titmus vs Howard Dolman test en pacientes de entre 6 a 12 años con ambliopía y grupo control

Soto Pinzón, J.C., Urdiales Suárez, J.A. (advisor: Jurado Medina, S.P.) (2023) · Universidad de La Salle, Bogotá, Colombia Translated from Spanish Thesis · View paper ↗

15 children with amblyopia due to anisometropia and 15 age-matched healthy controls (aged 6-12) were tested with the Frisby and Titmus stereotests, benchmarked against the Howard-Dolman apparatus as the reference ('gold standard') stereopsis measure. The study analysed concordance between each clinical test and the gold standard in both groups. Note: this is an undergraduate thesis rather than a peer-reviewed journal article, included here for completeness of the international literature.

Key findingCompared Frisby and Titmus against the Howard-Dolman in amblyopic children (undergraduate thesis).

Fiabilidad de los test de estereopsis de cerca: Titmus, Randot, TNO y Frisby

Cirac, A., Jarabo, C., et al. (2016) · Óptica Pura y Aplicada, 49(2), 105-113 (DOI: 10.7149/OPA.49.2.48590) · Universidad de Zaragoza, Spain Translated from Spanish · View paper ↗

200 healthy young adult volunteers (mean age 24±8) were tested for near stereoacuity with the Titmus, Randot, TNO and Frisby tests. Failure rates were below 10% for all four tests. The authors found differences in the specific stereoacuity values obtained between tests and recommend using at least two different stereotests per patient for a robust assessment.

Key findingFailure rates under 10% for all four tests, incl. Frisby, in 200 healthy young adults.

Detección de estrabismo y ambliopía con el uso de pruebas para estereopsis en población infantil

Hernández-Muñoz, M.T., Hernández-Ordóñez, T., De la Fuente-Torres, M.A. (2003) · Revista Mexicana de Oftalmología, 77(6), 211-216 · Mexico City / Ciudad Victoria, Tamaulipas, Mexico Translated from Spanish · View paper ↗

A large field study of 1,048 children (760 preschoolers aged 3-5, 288 school-age children aged 6-8) across Mexico City and Ciudad Victoria, Tamaulipas, compared the Lang II, Frisby, Titmus and Random Dot E stereotests against a full eye exam (visual acuity, cover test, cycloplegic refraction and fundus exam) as the reference standard for detecting strabismus and amblyopia. The Frisby test achieved 100% specificity for both conditions in both age groups (100% positive predictive value for strabismus), with sensitivity — as expected for any single screening test used alone — more limited (25% for strabismus and 0% for amblyopia in preschoolers, rising to 66.67% and 14.28% respectively in school-age children). The authors concluded that the Frisby test in preschool and school children reliably rules out strabismus and amblyopia in healthy children.

Key finding100% specificity for strabismus and amblyopia in Mexican preschool and school-age children — a reliable rule-out screening tool, with sensitivity limited as expected when used alone.

近見立体視検査における3検査法の比較 (Comparison of three near-stereoacuity test methods)

Kawachi, E. (1983) · Hiroshima Medicine, 36(3), 305-308 · Japan Translated from Japanese · View paper ↗

One of the earliest published non-English clinical evaluations of the Frisby Stereotest, comparing three near-stereoacuity test methods within a decade of the test’s 1975 launch, in a Japanese regional medical journal.

Key findingOne of the earliest non-English clinical evaluations of the Frisby, published within a decade of its 1975 launch.

Comparison between the Frisby Stereotest and Titmus Stereo Test

Abe, H., Kobayashi, K., Suda, Y., Katsumi, O., Miyanaga, Y., Inouye, J. (2009) · Japanese Journal of Strabismus and Amblyopia, 36, 51-56 · Japan Translated from Japanese · View paper ↗

A peer-reviewed comparison of the Frisby and Titmus stereotests, part of a sustained multi-year Japanese research programme on the Frisby that also produced companion papers (Ganka Rinsho Kiyo, 2(2), 143-148, same year, and a related report by Shimaguchi et al., 2010, in the same journal, 3(2), 166-171).

Key findingPeer-reviewed Japanese comparison, part of a sustained multi-year Japanese research programme on the Frisby.

Frisby Stereo Test binocular-vision screening in train drivers

Igarashi, T., Seiji, K., Kimura, K. (2011) · Traffic Medicine, 65(3-4), 91-97 · Japan Translated from Japanese · View paper ↗

Reports the introduction of Frisby Stereo Test-based binocular-vision function screening for train drivers — an occupational, safety-critical screening use case outside routine ophthalmic practice.

Key findingReal-world occupational screening of binocular vision in train drivers, a safety-critical profession.

G. Test-Selection & Usage Surveys

Beyond individual validity studies, survey research shows which test clinicians actually reach for in daily practice.

Which Stereotest do You Use? A Survey Research Study in the British Isles, the United States and Canada

Vancleef, K., Read, J.C.A., et al. (2019) · British and Irish Orthoptic Journal, 15(1), 15-24 (DOI: 10.22599/bioj.120) · Newcastle University, UK / international · View paper ↗

Two professional surveys of eye care practitioners — one for the British Isles, one for the US and Canada — asked which stereotests are used in daily practice and considered best practice. The Frisby was found to be the most-used stereotest in the British Isles across both younger and older paediatric age groups (Titmus and Randot are more frequently used in the US/Canada).

Key findingFrisby is the most-used stereotest in the British Isles for both younger and older children.

H. Screener Pocket Test: Clinical Use & Review

The pocket-sized 1-plate and 2-plate Screener versions use the same real-depth optical principle as the standard Near Stereotest - two quadrants of the design rather than four - in a portable format built for rapid screening of infants and young children. Dedicated ophthalmic clinical trials isolating the pocket format specifically remain limited, but it has been independently adopted as a quick stereopsis-screening tool well outside ophthalmology, including in two recent neurosurgical studies below.

The Frisby stereotest: introduction and review

Optician CPD Series (n.d.) (n.d.) · Optician, CPD Archive #C40819 · UK Author: Professor J. Frisby · View paper ↗

A continuing-professional-development review article for UK eye care practitioners covering correct test procedure, scoring criteria and screening applications across the Frisby product range, including the pocket screener format used for rapid infant and pre-school screening.

Key findingClinical CPD review of test procedure, scoring and screening use across the full Frisby range.

Personalized surgical informed consent with stereoscopic visualization in neurosurgery — real benefit for the patient or unnecessary gimmick?

Hertzsprung, N., Krantchev, K., Picht, T., Roethe, A.L., Rubarth, K., Fuellhase, J., Vajkoczy, P., Acker, G. (2023) · Acta Neurochirurgica, 165(4), 1087-1098 (DOI: 10.1007/s00701-023-05512-x) · Germany · View paper ↗

All eligible participants in this neurosurgical informed-consent study were first screened for normal stereopsis using the Frisby Pocket Stereotest, before being randomised to a conventional informed-consent discussion or one incorporating stereoscopic MRI visualisation. A genuinely independent example of the Pocket Stereotest being used as a screening tool well outside ophthalmology.

Key findingFrisby Pocket Stereotest used to screen participants' stereopsis before a neurosurgical informed-consent study — an independent, non-ophthalmic clinical use case.

Does stereoscopic imaging improve the memorization of medical imaging by neurosurgeons? Experience of a single institution

Schlinkmann, N., Khakhar, R., Picht, T., Piper, S.K., Fekonja, L.S., Vajkoczy, P., Acker, G. (2022) · Neurosurgical Review, 45(2), 1371-1381 (DOI: 10.1007/s10143-021-01623-0) · Germany · View paper ↗

Neurosurgeons and residents had their stereopsis confirmed with the Frisby Pocket Stereotest to balance two experience-matched groups, before comparing monoscopic vs stereoscopic visualisation for memorising and detecting neurosurgical pathology (aneurysms and tumours). Another independent, non-ophthalmic validation of the Pocket Stereotest as a quick, reliable stereopsis-screening tool.

Key findingFrisby Pocket Stereotest used to confirm normal stereopsis and balance study groups of neurosurgeons before a visualisation-memory task.

Part Two — Frisby Davis Distance Stereotest (FD2)

Developed with Helen Davis OBE, Professor of Orthoptics, to extend the same real-depth, glasses-free principle to distance testing - though using printed contour targets rather than random-dot elements. Most of the published FD2 literature concentrates on strabismus surgical decision-making and intermittent exotropia.

I. Distance Stereoacuity: Development, Validity & Clinical Application

Distance stereoacuity is especially relevant to intermittent exotropia and to occupations requiring depth judgement at range, for example fork-lift truck drivers. The FD2 literature establishes paediatric norms and demonstrates clinical utility in timing strabismus surgery.

Does stereoacuity correlate with interpupillary distance for normal observers?

Frisby, J.P., Patchick, E., Edgar, R., Davis, H. (2004) · Transactions of the 10th International Orthoptic Congress, Sydney/Melbourne · University of Sheffield, UK Conference paper

186 university students had their stereoacuity measured with the Howard-Dolman apparatus at near and distance, and their interpupillary distance (PD) recorded. Relative stereoacuity correlated significantly but weakly with relative PD overall (r = -0.24, p<0.001) — of theoretical interest rather than clinical importance, since PD accounted for only a few seconds of arc of the variation observed. Critically, stereoacuities measured with the FD2 itself did not correlate significantly with PD, indicating the clinical test is robust to this source of individual variation even where general stereo-geometric tasks show a small effect. Co-authored by John Frisby and Helen Davis themselves; presented at the International Orthoptic Congress rather than published as a journal article.

Key findingFD2 stereoacuity did not correlate significantly with interpupillary distance, unlike general laboratory stereo-geometry tasks.

Frisby Davis distance stereoacuity values in visually normal children

Adams, W.E., Hrisos, S., Richardson, S., Davis, H., Frisby, J.P., Clarke, M.P. (2005) · British Journal of Ophthalmology, 89(11), 1438-1441 · Newcastle University, UK · View paper ↗

59 visually normal children aged 36-68 months were examined with the FD2 stereotest. Every child in the study was successfully testable. The results established normative paediatric distance-stereoacuity values and demonstrated a maturational improvement in distance stereopsis with increasing age.

Key findingAll 59 children (aged 3–6 years) were successfully testable, establishing the first paediatric FD2 norms: mean stereoacuity of 29.6″ arc at 6m (76% of children) and 92.3″ arc at 3m (24%), with only 6.8% showing no measurable response.

Development of distant stereoacuity in visually normal children as measured by the Frisby-Davis distance stereotest

Hong, S.W., Park, S.C. (2008) · British Journal of Ophthalmology, 92(9), 1186-1189 · South Korea · View paper ↗

An independent replication of the Adams et al. (2005) paediatric FD2 norms in a Korean population of visually normal children, corroborating the maturational improvement in distance stereopsis with age in a second country and population.

Key findingCorroborates the Adams et al. (2005) paediatric FD2 norms in an independent population.

Effects of interpupillary distance on stereoacuity: the Frisby Davis distance stereotest versus a 3-dimensional distance stereotest

Eom, Y., Song, J.S., Ahn, S.E. (2013) · Japanese Journal of Ophthalmology, 57(5), 486-492 · South Korea · View paper ↗

33 healthy volunteers had their distance stereoacuity measured with the FD2 and with a simulated monitor-based 3D distance stereotest, with interpupillary distance (IPD) artificially increased 2-fold and 3-fold using horizontal periscopes. As IPD increased, FD2-measured stereoacuity improved — matching what happens in real-world depth perception — while the simulated 3D monitor test’s measured stereoacuity worsened.

Key findingFD2 stereoacuity improved with increased interpupillary distance, matching real-world stereo geometry — unlike a simulated 3D monitor-based test, which worsened.

Testing distance stereoacuity with the Frisby-Davis 2 (FD2) test

Holmes, J.M., Fawcett, S.L. (2005) · American Journal of Ophthalmology, 139(1), 193-195 · Mayo Clinic, Rochester, MN, USA · View paper ↗

95 patients with a range of strabismic and non-strabismic conditions were tested with the FD2. The authors developed and validated a modified staircase presentation protocol, confirming the FD2 as a useful measure of distance stereoacuity when the presentation protocol properly accounts for monocular viewing cues.

Key findingDeveloped a modified staircase presentation protocol that controls for monocular cues at larger disparities.

Improvement in distance stereoacuity following surgery for intermittent exotropia

Adams, W.E., Leske, D.A., Hatt, S.R., Mohney, B.G., Birch, E.E., Weakley, D.R. Jr. (2008) · Journal of AAPOS, 12(2), 141-144 · Mayo Clinic, Rochester, MN, USA · View paper ↗

Used the FD2 to track distance stereoacuity before and after strabismus surgery for intermittent exotropia, demonstrating the test's sensitivity to clinical change following treatment.

Key findingFD2 documented measurable improvement in distance stereoacuity after surgery.

Evaluation of factors influencing distance stereoacuity on Frisby-Davis Distance Test (FD2) in intermittent exotropia

Saxena, R., Kakkar, A., Menon, V., Sharma, P., Phuljhele, S. (2011) · British Journal of Ophthalmology, 95(8), 1098-1101 · India · View paper ↗

Examines which clinical factors (e.g. angle of deviation, control of the deviation) influence FD2 distance-stereoacuity measurement in intermittent exotropia, refining how clinicians should interpret FD2 scores in this patient group ahead of the same research group's 2013 surgical-timing study (next).

Key findingIdentifies clinical factors influencing FD2 distance stereoacuity measurement in intermittent exotropia.

Evaluation of FD2 (Frisby Davis distance) stereotest in surgical management of intermittent exotropia

Singh, A., Sharma, P., Singh, D., Saxena, R., Sharma, A., Menon, V. (2013) · British Journal of Ophthalmology, 97(10), 1318-1321 · India · View paper ↗

30 surgical patients and 30 age-matched controls were assessed with the FD2. Preoperative distance stereoacuity improved from a mean of 43.8″ to 27.0″ postoperatively, supporting FD2 stereoacuity as a practical measure for deciding the timing of surgical intervention in intermittent exotropia.

Key findingProposed an FD2 distance-stereoacuity threshold (worse than 20″) to help time surgical intervention.

Stereoacuity with Frisby and Revised FD2 Stereo Tests

Bohr, I., Read, J.C.A., et al. (2013) · PLOS ONE, 8(12), e82999 · Newcastle University, UK · Open-access, freely available full text · View paper ↗

365 participants across three age bands (5-10, 11-49, and 50-82 years) were tested on both the near-Frisby and revised FD2 tests. The two tests showed fair agreement (Cohen’s kappa) in classifying individuals into three stereovision categories — Class 1 (≤20 arcsec), Class 2 (21–149 arcsec), and Class 3 (≥150 arcsec, equivalent to stereonegative on the FD2). The data revealed stereoacuity improving through childhood and a measurable decline in late adulthood.

Key findingFair agreement between near-Frisby and FD2 across the lifespan; documents childhood gains and late-adulthood decline.

Contribution of a real depth distance stereoacuity test to clinical management

Young, B.J., Sueke, H., Wylie, J.M., Kaye, S.B. (2009) · Journal of Ophthalmology, 2009, Article 343827 · St Paul's Eye Unit, Liverpool, UK · View paper ↗

50 subjects aged 21-62 were tested with the FD2 at 6m, 3m and 1m. No subject achieved the 3-of-4 correct-response passing criterion under monocular viewing at 6 metres — reinforcing that FD2 performance at distance reflects genuine binocular stereopsis rather than monocular guesswork.

Key findingNo subject achieved a passing score monocularly at 6 metres.

Predictive factors of stereopsis outcomes following strabismus surgery

Eshaghi, M., Arabi, A., Banaie, S., Shahraki, T., Eshaghi, S., Esfandiari, H. (2021) · Therapeutic Advances in Ophthalmology, 13 · Iran / USA · View paper ↗

182 patients with a variety of strabismic conditions were assessed using the FD2 (distance), near Frisby, Preschool Randot and Distance Randot tests. The study identified pre-operative deviation, amblyopia, and post-operative residual deviation as key predictors of final stereopsis outcome.

Key findingFD2 and near Frisby used as core outcome measures across 182 surgical patients.

J. The Mayo Clinic Stereoacuity Research Programme

Between 2005 and 2009, a research team at the Mayo Clinic (Rochester, MN), led by Dr Jonathan M. Holmes, ran a sustained programme of studies characterising the Frisby and FD2 tests against their random-dot counterparts — covering comparative sensitivity, clinical application in intermittent exotropia, day-to-day variability, test-retest reliability and resistance to monocular visual acuity loss.

Real Depth vs Randot Stereotests

Leske, D.A., Birch, E.E., Holmes, J.M. (2006) · American Journal of Ophthalmology, 142(4), 699-701 · Mayo Clinic, Rochester, MN, USA · View paper ↗

Stereoacuity was compared using the real-depth near-Frisby and FD2 tests against their random-dot counterparts (Preschool Randot and Distance Randot) in patients with a range of strabismic and non-strabismic conditions. Finer disparities were detected with the real-depth tests than with the corresponding random-dot tests at both near and distance.

Key findingPatients consistently detected finer disparities on the real-depth Frisby/FD2 tests than on equivalent random-dot tests.

New tests of distance stereoacuity and their role in evaluating intermittent exotropia

Holmes, J.M., Birch, E.E., Leske, D.A., Fu, V.L., Mohney, B.G. (2007) · Ophthalmology, 114(6), 1215-1220 · Mayo Clinic, Rochester, MN, USA · View paper ↗

This study helped establish the clinical role of newer distance stereoacuity tests, including the FD2, specifically in evaluating intermittent exotropia — a condition in which distance stereopsis is often more informative of control than near stereopsis.

Key findingHelped establish the FD2's clinical role in evaluating intermittent exotropia, where distance stereopsis is a more sensitive indicator than near stereopsis.

Variability of stereoacuity in intermittent exotropia

Hatt, S.R., Mohney, B.G., Leske, D.A., Holmes, J.M. (2008) · American Journal of Ophthalmology, 145(3), 556-561 · Mayo Clinic, Rochester, MN, USA · View paper ↗

Twelve children with intermittent exotropia were tested three or four times over a single day, at least two hours apart, using the FD2 and Distance Randot at distance, and the near-Frisby and Preschool Randot at near. Four of the twelve patients (33%) showed variable results on the Distance Randot test; three of these also varied on the FD2, and one varied on the FD2 only.

Key findingStereoacuity in intermittent exotropia can genuinely fluctuate within a single day, regardless of which stereotest is used.

Defining real change in measures of stereoacuity

Adams, W.E., Leske, D.A., Hatt, S.R., Holmes, J.M. (2009) · Ophthalmology, 116(2), 281-285 · Mayo Clinic, Rochester, MN, USA · View paper ↗

Patients with stable strabismus were tested twice on the near-Frisby, FD2, Preschool Randot and Distance Randot tests to establish test-retest reliability. The study defined how much change in each test's score represents genuine clinical improvement or deterioration, rather than normal measurement variability.

Key findingEstablished test-retest reliability thresholds for near-Frisby and FD2, giving clinicians a defensible bar for judging genuine treatment-related change.

The effect of induced monocular blur on measures of stereoacuity

Odell, N.V., Hatt, S.R., Leske, D.A., Adams, W.E., Holmes, J.M. (2009) · Journal of AAPOS, 13(2), 136-141 · Mayo Clinic, Rochester, MN, USA · View paper ↗

Monocular visual acuity was artificially degraded using Bangerter filters in 15 visually normal adults, and stereoacuity was then measured on the near-Frisby and FD2 real-depth tests alongside Preschool Randot and Distance Randot. Stereoacuity thresholds were more severely degraded by simulated monocular vision loss on the random-dot tests than on the real-depth Frisby and FD2 tests.

Key findingFrisby and FD2 scores were less affected than random-dot tests under simulated monocular visual acuity loss.

K. Independent Expert Review

A recent expert review situating the Frisby and FD2 within the full clinical picture of stereo vision and strabismus.

Stereo vision and strabismus

Read, J.C.A. (2015) · Eye, 29(2), 214-224 (Cambridge Ophthalmological Symposium) · Newcastle University, UK · View paper ↗

A wide-ranging review of stereo vision and strabismus by Jenny Read (co-author of the Bohr et al. 2013 and Vancleef et al. 2019 papers already in this compendium). The review includes a comparative table of major stereotests' specifications — noting the near-Frisby's 5-600″ range and the FD2's 5-50″ range at 6m — and discusses the reliability factors established by Adams et al. (2009, above): a change of less than a factor of four is not considered clinically meaningful for any of these tests, with the near-Frisby (F=1.7) and FD2 (F=4.8) bracketing the Preschool Randot (F=3.9) and Distance Randot (F=2.9).

Key findingIndependent expert review situating Frisby/FD2 within the full clinical stereopsis and strabismus literature, corroborating and contextualising the Adams et al. (2009) reliability data.

About This Compendium

This pack was compiled via a structured literature sweep of PubMed, publisher databases, institutional repositories and non-English-language sources subsequently translated into English. It is a comprehensive first-pass review, not an exhaustive systematic review — further studies may exist beyond what is catalogued here.

For distributors and academic partners: please contact us if you would like source PDFs of any individual study, or if you are aware of further Frisby Stereotest research — particularly non-English-language studies — that should be added to future editions of this compendium.

Clinical Disclaimer

The studies summarised above are provided for informational purposes only and reflect published research that includes or discusses the Frisby Stereotests and related stereoacuity measurements. They do not constitute clinical guidelines or medical advice. Clinical use should follow local protocols and professional judgement.

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