Henson 9000: Technical profile

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Henson 9000: Technical profile

Henson-0005Enhanced visual field screening

Henson 9000 screening test patterns can be extended from 26 to 68 and 136 test points, missed locations can be re-tested and new locations can be manually added in-test. Operators can efficiently rule out those who don’t have any visual field loss, confidently rule in those who do and accurately map the extent of any defect. Further details.

Glaucoma management with ZATA

For the ongoing management of patients with suspected or diagnosed glaucoma, the Henson 9000 offers the ZATA threshold algorithm and progression analysis tools. Using the latest research findings to optimise performance, ZATA is uniquely able to use prior patient data to shorten test times and improve the accuracy of results in patients with established loss. Further details.

Technical specification | Videos | FAQs

Henson screening tests


Both the Henson 7000 and 9000 offer single and multiple stimulus screening tests defined by their sensitivity, specificity and speed. Whilst the 7000 offers 26 and 68 point tests, the 9000 also offers a 136 point test option along with a binocular Esterman visual field test.

Portable, robust and easy-to-use the Henson 7000 is well-suited to central visual field screening, but if you require enhanced screening and threshold testing capabilities then the Henson 9000 is the machine for you.

For more information on how the machines differ see our comparison technical specification for the two machines here.

Glaucoma screening in context

Historically, two important criteria have defined a good glaucoma test:

  • Sensitivity: the percentage of glaucomatous subjects successfully detected
  • Specificity: the percentage of non-glaucomatous subjects that pass the test

100% sensitivity and 100% specificity will never be achieved by an automatic programme – there will always be a few ‘false positives’ (patients without glaucoma who fail the test) and a few ‘false negatives’ who pass it. However, the ability to customise Henson screening tests – adding and re-testing missed points at any stage, as necessary – helps to further reduce false positives and raise specificity.

But what of speed?

Speed is another criterion for successful glaucoma screening whose importance is often overlooked. Speed is of benefit to busy professionals and of comfort to patients, too, so a good screening test should be fast and easy to apply.

Previously sensitivity, specificity and speed have been mutually exclusive – if a faster test was required, sensitivity or specificity were sacrificed.

Good design can make a big difference and that is where the Henson range scores over its competitors – it is built to deliver fast screening without compromising performance.

Sensitivity with the Henson 9000

High sensitivity       

The types of visual field defects peculiar to glaucoma are more likely to occur in certain visual field locations than in others.

This topic has been researched by Professor David Henson who established where the locations for an early visual field defect are most likely to be. Henson’s research demonstrates that you do not need a large number of stimuli to develop a highly sensitive glaucoma screening test. The graph below shows the relationship between sensitivity and the number of test stimuli and illustrates that with just 26 optimally placed stimuli very high sensitivity (almost 100%) to early visual field loss can be achieved.

Figure 1: The sensitivity and specificity of the optimized test patterns with increasing numbers of test locations. The solid line represents a logarithmic relationship between the sensitivity and increased test locations and the dashed line represents a linear relationship between the specificity and increased test locations.

(From Wang Y, Henson DB. ‘Diagnostic Performance of Visual Field Test Using Subsets of the 24-2 Test Pattern for Early Glaucomatous Field Loss‘ in Investigative Ophthalmology & Vision Sciences. 2013;54:756-761.)

Specificity with the Henson 9000

High specificity     

The Henson 9000 glaucoma screening test ensures specificity of over 95% by:

  1. Repeating measures at locations where a stimulus has been missed.
    In the Henson a stimulus has to be missed twice at any given test location before it is recorded as a miss. This alone reduces false positives.
  2. The extension of the test to additional locations.
    Extensions take the number of test stimuli within the central 26 degree field to 68 and then 136 positions. This allows the clinician to differentiate between random misses and glaucomatous ones.
  3. The ability to manually re-test a missed location.
    A unique characteristic of the Henson screening tests. It is not unusual for a patient who has never had a visual field test before to miss some stimuli. To get high specificity the perimetrist must be able to confirm misses are a true defect and not just a false positive. The best way to do this is to allow the re-testing of certain locations as many times as is considered appropriate.
  4. Testing around any missed locations with additional stimuli.
    The stimuli on the Henson perimeters are arranged on a 3 degree square matrix within the central 30 degrees. This allows detailed verification and mapping of any central field defect and further aids differentiation between false positive responses and glaucomatous defects.

Speed with the Henson 9000

High speed  

The 26 point screening program can be conducted in less than 1 minute per eye.

In ~80% of cases a ‘normal’ will see all of the stimuli and the test will end. In ~20% of cases some additional testing will be needed to establish whether missing one or more stimuli was a false positive (a normal but unreliable patient) or a true positive (a case of glaucoma). The time taken for the additional testing will vary. For a false positive it might take another minute for a case of glaucoma it could take longer.

To make things even faster, the Henson perimeters have an option that allows the presentation of multiple stimuli, rather than single stimulus – an option unique to the Henson range.

With multiple stimulus presentations, a pattern of 2, 3 or 4 stimuli is presented at the same time and the patient reports the number that they see. Besides speeding up the test it is also more patient friendly, preventing patients from getting flustered and leading to more accurate results with less false positives.

In summary

Screening features
Multiple and single stimulus presentation options Multiple is faster and more patient friendly, with fewer false positives
Ability to manually re-test any stimulus at any stage of an examination Reduces false positives and increases identification of glaucomatous defects
Manual addition of test locations at any stage of examination Allows further examination of areas around any missed stimuli to confirm defects and establish extent of loss
Extendable screening program (26 > 68 > 136 points) Gives the option of enhanced, in-test specificity and reduces false positives
Optimised Henson test pattern Enables faster test times without loss of sensitivity

ZATA threshold algorithm

Uniquely patient-centred


For the management of patients with suspected or diagnosed glaucoma, the Henson 9000 offers the ZATA threshold algorithm. ZATA uses the latest research findings to optimise performance and keep test times short. Uniquely, ZATA can use prior test result data (where available) to shorten test times and improve the accuracy of results in patients with established loss. ZATA is defined by

Innovation – prior data used to intelligently vary test criteria for more accurate thresholds
Efficiency – ZATA tests can be completed in just 4 minutes per eye (and often faster)
Ease of use – the software is easily operable by all levels of optical staff

ZATA: speed, accuracy and patient comfort

While ZATA is based upon the same principles as SITA it differs in some important ways.

  1. When possible it uses prior data as a starting level. This makes it more efficient and faster especially in eyes where there is some pre-existing visual field defect. It makes better use of prior knowledge.
  2. It does not use a single terminating criteria. It can be thought of as a combination of SITA Standard and SITA Fast. It uses the SITA Standard terminating criteria in locations where there is some visual field loss and in the adjacent test locations but uses a less accurate (faster) terminating criteria in other locations. This reduces test times, especially in patients who have no visual field loss.
  3. It does not attempt to accurately measure thresholds in severely damaged test locations (<10dB). Accurate measures at these locations are impossible to obtain with any algorithm due to changes in the visual system that make it very variable. This again reduces test times in patients with severely damaged test locations and reduces the number of presentations in these areas and the long sequences of ‘not seen’ responses which are non-productive and can be very frustrating to the patient and perimetrist.

The development of threshold testing

Threshold tests are used when there is a need to accurately measure the depth of any visual field loss.

The first threshold algorithm (Full Threshold) was developed in the 1970s. It was reasonably accurate but took in excess of 10 minutes per eye to perform. A later development (FastPac, Fast Threshold) shortened the test time but was less accurate and as such was not widely adopted. In the 1980/90s a series of papers were published by vision scientists on the more efficient Bayesian approach to obtaining thresholds. One of the algorithms promoted by these researchers (King-Smith 1994) was called ZEST (Zippy Estimate by Sequential Testing). In 1997 a Swedish group of ophthalmologists utilised this work to develop a new perimetric algorithm called SITA (Swedish Interactive Threshold Algorithm). The ZEST algorithm has also been used to develop ZATA (Zippy Adaptive Threshold Algorithm) the threshold test used on the Henson 9000.

An important characteristic of these new algorithms is what is known as their terminating criteria. This specifies how accurate the threshold measure should be. As a general rule the more accurate you want a threshold test to be the longer it will take to perform. The Swedish (SITA) group set their terminating criteria to give an accuracy similar to the 1970s Full Threshold technique (termed SITA Standard), later producing a second version that was faster, but less accurate (SITA Fast). Since the development of SITA a lot more has been learnt about how patients with glaucoma respond to stimuli and the importance of keeping test times down to a minimum. These findings have been used to develop ZATA, the fastest, most accurate threshold test available today.

Technical specification

Download in PDF

Test specifications
Maximum temporal range (degrees) 60° (monocular) / 160° (binocular)
Stimulus duration (ms) 200
Stimulus size Goldmann III
Visual field testing distance (cm) 25
Stimulus intensity (maximum) 10,000 ASB
Background illumination 31.5 ASB
Test methods Standard Automated Perimetry (SAP), white-on-white
Screening tests/patterns
Suprathreshold – single stimulus 3 levels (26, 68, 136 points)
Suprathreshold – multiple stimulus 3 levels (26, 68, 136 points)
Esterman (Driving) Groups 1 and 2 (EU standard)
Customised tests Test locations can be manually added to all suprathreshold tests
Threshold tests/patterns
ZATA Standard – threshold central 10-2; 24/30-2 (extendable in-test)
ZATA Fast – threshold central 10-2; 24/30-2 (extendable in-test)
Average testing times
Suprathreshold – single ~90 seconds per eye
Suprathreshold – multiple stimulus <60 seconds per eye
ZATA Standard – threshold central ~4 minutes per eye
Fixation control  
Fixation target Single or 4-point LED diamond pattern
Heiji-Krakau Yes
Video eye monitor Yes
Software features
Patient management database MS Windows compatible; networkable
Practice management integration EMR compatibility (parameter passing and text file)
Hemifield Analysis Yes
Progression Analysis Yes
HFA data import Yes
Languages ENG, CHI, key European languages
DICOM Yes (images)
Ethernet Yes, via connected computer
Database backup Removable, network or cloud storage
Weight (kg) 13.5
Measures (W x D x H / mm) 440 x 400 x 452
Mains operated Yes
Medical device Class 1
Applied part Type B
Control device External PC/laptop running MS WindowsTM Professional, v. 7, 8 & 10
Patient unit inputs/outputs C13 mains input; Patient Response Button; 2 x USB Type B connector
Electrical requirements 85 – 263Vac, 50/60Hz, 60VA
Optional printer Any compatible with controlling computer

Which Henson is right for you?

The Henson 7000 is a dedicated glaucoma screener that supports the quick and reliable identification of those who do/don’t have visual field defects. Its flexible and customisable 26 and 68 point screening tests are perfectly suited to delivering high specificity and ruling out false positives with confidence.

The Henson 9000 performs the same function as the 7000, but extends to a 136 point screening test for enhanced specificity, whilst also offering threshold testing in support of the ongoing monitoring and management of patients with established visual field loss.

Whilst the Henson 7000 might be most suitable in a primary care setting, the Henson 9000 has application across primary, secondary and tertiary care environments.

A technical comparison of the two machines is available in the table below.

Comparison: Henson 7000 vs. 9000

Henson 7000 glacuoma screener

Henson 7000

Henson 9000 glaucoma monitoring

Henson 9000

Test specifications
Visual field test range 60° 60° (monocular)
160° (binocular)
Visual field testing distance 17 cm 25 cm
Stimulus intensity (maximum) 317 ASB 10,000 ASB
Background illumination 10 ASB 31.5 ASB
Stimulus duration 200 ms
Stimulus size Goldmann III
Test methods  Standard Automated Perimetry (SAP), white-on-white
Screening tests/patterns
Suprathreshold – single stimulus 2 levels (26, 68 points) 3 levels (26, 68, 136 points)
Suprathreshold – multiple stimulus 2 levels (26, 68 points) 3 levels (26, 68, 136 points)
Esterman (Driving) No Groups 1 and 2 (EU standard)
Customised tests Test locations can be manually added to all suprathreshold tests
Threshold tests/patterns
Zata Standard threshold central No 10-2; 30/24-2 (extendable in-test)
Zata Fast threshold central No 10-2; 30/24-2 (extendable in-test)
Average testing times
Suprathreshold – single stimulus ~90 seconds per eye
Suprathreshold – multiple stimulus <60 seconds per eye
ZATA N/A ~4 minutes per eye
Fixation control
Fixation target Single or 4-point LED diamond pattern
Heijl-Krakau N/A Yes
Video eye monitor No Yes
Software features
Patient management database MS Windows compatible; networkable
Practice management integration EMR compatibility (parameter passing and text file)
Languages ENG, CHI, key European languages
Hemifield Analysis N/A Yes
Progression Analysis N/A Yes
HFA data import N/A Yes
DICOM Yes (images)
Ethernet Yes, via connected computer
Database backup Removable, network or cloud storage
Weight (kg) 5 13.5
Measures (mm) 270-350 x 230 x 300-350 440 x 400 x 452
Mains operated Yes
Medical device Class 1
Applied part Type B
Control device External PC / laptop / tablet running MS Windows® Professional, v. 7, and above
Patient unit inputs/outputs C13 mains input; Patient Response Button; 1 x USB Type B connector C13 mains input; Patient Response Button; 2 x USB Type B connector
Electrical requirements 85 – 263V AC, 50/60Hz, 60VA
Optional printer Any compatible with controlling computer

© Elektron Technology UK Ltd. All rights reserved.
Microsoft® and Windows® are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries.

Henson 9000 video library

Screening with Henson perimeters

Professor David Henson explains how screening works on Henson perimeters.

Video length: 11:25

Henson screening test patterns

Professor Henson explains the test patterns available on the Henson 7000 and Henson 8000. (The Henson 8000 has now been superseded by the Henson 9000 which has the same three  suprathreshold screening patterns – 26, 68 and 136.)

Video length: 0:54 secs

Multiple stimulus tests and their benefits

Professor David Henson explains the rationale for the faster, more precise and “patient-friendly” multiple stimuli test and how this differs from single stimulus testing.

Video length: 5:40

ZATA vs. other threshold tests

Professor David Henson explains the similarities and differences between his ZATA threshold algorithm and others available.

Video length: 11:33

HFA compatibility

Professor David Henson explains the ways in which the Henson 9000 and its ZATA algorithm are compatible with the Humphrey. (Please note, the 8000 model referred to in the video has now been superseded by the Henson 9000.)

Video length: 1:55

The Hensons and practice management integration

Professor David Henson explains that the Henson software has a patient database that can be easily incorporated in practice management systems.

Video length: 3:33

Frequently asked questions

Which is more important sensitivity or specificity?

  • 100% sensitivity = every screening test would capture those with a visual field defect, i.e. result = fail
  • 100% specificity = every screening test would not fail those with a healthy visual field, i.e. result = pass

Ideally, a screening test would be 100% sensitive and 100% specific, but in reality there will always be anomalies – i.e. ‘false negatives’ (those with the condition who pass the test) and ‘false positives’ (those without the condition who fail the test).

The sensitivity/specificity of a visual field screening test can be altered by changing the fail criteria, e.g. if the fail criteria of a supra-threshold visual field test were to be changed from a single missed point to a cluster of three missed points, then the sensitivity would go down and the specificity would go up.

So, which is the more important? To answer this question you have to answer another. What are the relative costs of a false positive and false negative? When screening for glaucoma in an unselected population, where the prevalence of the disease is low (<2%), it is generally accepted that the specificity should be ≥95%. If it falls much below this figure then we end up failing a relatively large number of people that do not have the disease. If the study population is a high risk one (higher percentage of true cases) then the sensitivity should be increased at the cost of lowered specificity.

How can I screen with the Henson 9000?

There are 2 ways in which you can screen the visual field with the Henson 9000.

You can use the fast and accurate supra-threshold strategies, with a choice of single or multiple stimulus presentations for additional flexibility, or the rigorous and detailed ZATA threshold test.

Screening with the supra-threshold strategies is certainly the fastest option but the testing times of ZATA, compared to other threshold algorithms, make it feasible to offer a threshold strategy by default as a form of enhanced screening test.

How long does a ZATA threshold test take?

The length of a ZATA test will be determined by the extent of a patient’s field loss.

  • A normal patient with no field loss will complete the test in approximately 3 minutes (with average response times)
  • A patient with significant field loss tested from previously stored data will also complete the test in under 4 minutes due to the ZATA test’s variable termination criteria.
  • A patient with moderate field loss, or one who has no prior data stored, will take approximately 4-5 minutes per eye to complete the test.

How does the ZATA test differ from standard full threshold?

ZATA was developed to counter all of the problems associated with testing patients with field loss on a full threshold type test. It runs the 24/2 test pattern but uses supra- as well as full threshold testing with different terminating criteria. Furthermore, it uses data from surrounding points as well as prior data (if available).

All of these strategies combine to make ZATA an easier test for patients to perform while offering the same level of accuracy as a standard full threshold would in monitoring glaucoma progression.

How does the ZATA algorithm differ from SITA?

The ZATA algorithm is able to make use of prior patient data. If the Henson database contains a record for a previous threshold test then ZATA uploads the previous threshold measures to use as starting values for the new test. This reduces test times and improves accuracy.

Nor does ZATA use a fixed terminating criteria. In areas of severe loss, where thresholds estimates are very variable, and at locations near to normal values, it uses looser terminating criteria, reserving more accurate measures for locations where there is existing mild damage. This again speeds up test times by focusing on locations where change is expected to occur.

In other ways ZATA and SITA are similar. They both use the same test patterns (24/30-2). The threshold values are compatible as are the global indices.

Can the Henson 9000 test a patient's peripheral isopter?

All Hensons are static only perimeters. Isopters require kinetic testing, i.e. a stimulus that moves across the visual field. Kinetic perimetry is only available on selected HFA and Octopus perimeters.

The Henson 9000 performs static determination within the central 30° and qualitative automated threshold perimetry, including the 30-2 and 24-2 patterns of test locations. It is very fast, although exact test times are dependent upon the number of test locations and the type of visual field loss.

In a recent as yet unpublished project with 17 patients, the test time for a 24-2 ZATA Standard test with a superior arcuate defect was 3:01 mins, compared to 7:45 for a Full Threshold test with the same patient sample.

Is the Henson Esterman test DVLA Compliant?

The Henson Esterman test is approved for testing Group 1 and Group 2 drivers.

Why doesn't the Henson 9000 have a trial lens holder?

Because there are certain problems with trial lens holders in perimeters. The lenses that are generally used in perimetry tend to be relatively small in diameter (38mm). This means that very careful alignment between the lens and the patient’s eye is necessary to ensure that no stimuli are occluded during the visual field test. The slightest movement from a patient away from a static, perimeter-mounted lens holder can create artefacts or cause occlusion problems.

The solution is to attach the trial lens to the patient, using a head-mounted trial lens system. The most obvious advantage to this solution is that, should the patient move, the trial lens moves with them, reducing the likelihood of artefacts. A head-mounted system also makes switching lenses easier and avoids the use of unhygienic eye patches by incorporating an occluder within the frame to cover the unused eye.

If you’d like more details about the type of trial lens system used with the Henson 9000, please contact us.

Can the 9000 be operated from any PC?

Yes, it can be operated from any PC running the MS Windows™ Professional operating system (version 7, or above).

The control device must also have two spare USB ports for interfacing with the Henson 9000.

Is the software easy to install?

Yes. The software is supplied on a USB memory stick and is a single file installer. Simply click on it and it will install all parts of the software.

Both Henson machines are supplied with a quick start guide that takes you through the whole process step-by-step.

Why do I get an “internal error has occurred” message when trying to save even though I can see the record has saved in the database?

This relates to a problem with the settings for your backup.

Firstly, check the location of the backup allows files to be created. If it has been set to a read-only drive, or one that is protected by Windows, then the record will save in the database successfully but the backup will fail – hence the error message you are receiving.

Such read-only locations may be: the root of the C drive; a fundus camera (these often show up in Windows as USB flash drives); a Windows system folder or a mapped drive on a computer that is not switched on.

To ensure a successful backup set the location to a mapped network drive on your PC or a removable hard drive/USB flash drive.

Can I use any printer with the Henson software?


The Henson software prints the test result to the default installed printer on the laptop/computer being used as the control device. Printing is done via the default installed PDF viewer (Adobe Reader in the case of Henson 8000). Essentially, as long as the installed printer is Windows-compatible it will work without a problem.