FAQs – Frequently Asked Questions
What is the maximal eccentricity of the HEP?
HEP is designed to test the central visual field up to 30°. Shifting the fixation target to either side allows 60° visual field testing at up to 100 test locations.
Which type of monitor is used to present the stimuli?
The integrated monitor is a CRT, a cathode ray tube. The Cathode Ray Tube (CRT) is a vacuum tube containing an electron gun (a source of electrons) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to create images in the form of light emitted from the fluorescent screen.
The excitation of phosphor molecules on the surface of the monitor creates the HEP stimuli. A CRT is only monochromatic.
Is HEP a projection perimeter?
No, HEP is a monitor-based system.
Is there a certain warm up time when the system is switched on before the first VF examination can be started?
HEP is immediately calibrated and calibrating constantly during the VF examination. Test can be performed immediately. The value of the background luminance is displayed on the operator screen during the whole test procedure: 50 cd/m2 for FDF perimetry and 10 cd/m2 for SAP.
Can the patient use his or her own glasses?
Yes, the patient can use his or her own distance glasses provided the frame fits appropriately and that the distance prescription is not more than 4 D different from the optimal prescription.
A correction for presbyopia is not necessary. HEP is designed for infinity.
If distance glasses or contact lenses are unavailable place trial lenses for the distance prescription in the trial lens holder. The optimum distance between eye and lens holder is approximately 1.3 cm.
The trial lens holder is usually stored in the back drawer of the HEP instrument.
Is it advisable to use the HEP without correcting with lenses?
A correction for presbyopia is not necessary. For myopia we recommend that everyone less than -4 won’t need corrective lenses to use the HEP. Please always correct for astigmatism.
What is the suggested room lighting?
The FDF test is designed to be used with ambient room illumination (be careful to avoid reflectance in the lens). The integrated white eye occluder is designed to maintain light adaptation in the untested eye. Occasionally a patient may, due to issues of ocular dominance, find this method of occlusion inadequate or uncomfortable. Use a standard black eye occluder in such instances. SAP testing should use a darkened room.
Is Standard Automated white-on-white Perimetry (SAP) available on the HEP?
Yes, the Standard Automated Perimetry is the second type of perimetry available on the HEP. HEP uses stimulus sizes Goldmann III and V.
Unique feature of HEP’s SAP is, that because the CRT monitor is limited in luminance distribution, the HEP SAP is limited in its dynamic range. Between 40 and 16 dB a stimulus of Goldmann size III is presented, but below 16 dB HEP does not present the stimulus brighter, but increases stimulus size. The increase in size between 15 and 0 dB is linear and follows a published Goldmann table. This unique feature is an advantage of HEP over conventional perimeters like HFA and published at ARVO 2010 by Goren etal. and 2011 by Ferreras et al.
Is HEP also offering SWAP?
SWAP, Short Wavelength Automated Perimetry, is another name for blue-on-yellow perimetry. This is not possible because of the integrated CRT monitor, which presents black or white stimuli. The same is true for red-on-white perimetry etc.
When do I use Flicker-Defined Form (FDF) Perimetry and when do I use SAP?
We carefully have to distinguish between these two types of perimetry.
FDF is designed and recommended for early glaucoma detection, whereas SAP is recommended for continuous patient care that is visual field progression.
FDF may be applied on glaucoma suspect patients, patients with early to moderate glaucoma. Patients with severe glaucoma will always do the SAP test.
Is there a learning curve with Flicker-Defined Form (FDF) Perimetry known?
Every type of perimetry has a learning curve, even the white-on-white perimetry.
But, FDF perimetry does not have a steeper learning curve than the others, in fact, FDF´´s learning curve is comparable to w/w perimetry (Lamparter et al., Am J Ophthalmol. 2011 Jun;151(6):1057-1064).
Please keep in mind that at least the first VF and then depending on the patient maybe also the second VF examination should be ignored and discarded. Only the third VF examination should be used for diagnosis and be starting point of a trend analysis.
For FDF perimetry, because of its uniqueness and its novelty, an extended first introduction of the stimulus is highly recommended. Please always use the integrated demonstration mode inside the HEP system.
Which threshold strategy is applied on the HEP?´
HEP uses its own and unique threshold strategy, the Adaptive Staircase Thresholding Algorithm – ASTA. ASTA has been developed by Prof. John Flanagan from Universities of Waterloo and Toronto, Canada. ASTA is a bracketing strategy with quick termination.
HEP uses different strategies for different purposes:
ASTA Standard is the recommended basic test strategy for new patients.
ASTA Follow-Up is developed for progression. ASTA Follow up requires baseline examinations and uses VF results from ASTA Standard as starting values to drive the test. Test time is therefore reduced. ASTA Follow-Up is unique in the perimetry market.
ASTA Fast is a screening strategy, which should be applied for normal patients only. Progression not possible.
What is the test duration of a visual field test on the HEP?
We have to distinguish the different test strategies on the HEP as well as the test patterns (10°, 24°, 30° and 60° VF test).
A 24-2 ASTA Standard test takes approximately 4 to 5 min per eye for a normal patient. Test time is extended due to the patient’s reaction and the disease status.
Test time will be considerably reduced by the ASTA Follow-Up test strategy to approximately 2.5 min per eye.
The supra-threshold screening strategy S-30 needs only 30 sec per eye.
Is it possible to pause the VF test?
The patient may stop the test by keeping the patient response button pressed if a break is needed. Alternatively he or she may ask the operator to pause the test. The instrument continues the test as soon as the patient releases the patient response button or the operator presses resume test.
How does the HEP measure the reliability of the patient?
A small integrated camera recognizes fixation losses as well as patient blinks.
False Positive catch trials are also applied and measured by the patient’s response time. False Negative catch trials are applied several times during the visual field examination by presenting stimuli in already completed locations. All reliability parameters are recorded and the operator can follow the thresholds actually tested as well as the reliability parameters and remaining test time in real time on the operator screen.
Does HEP show the results of the Glaucoma Hemifield Test (GHT) after the VF is completed?
Yes. The Glaucoma Hemifield Test (GHT) is a plain-language classification of threshold test results that analyzes results like an expert system by comparing local defects in zones of the upper field with those found in mirror image zones in the lower hemifield.
What is the size of HEP’s normative database?
More than 436 normal patients and more than 262 glaucoma patients per eye. Covered age range is from 18 to 80 years.
Is the pupil size automatically measured?
Yes, the pupil size is automatically measured and recorded by the device after 45 sec and measurement continues during the whole test procedure. The HEP test can be undertaken with an undilated pupil unless the diameter is smaller than 2.5 mm. In this case, the pupil should be dilated if possible.
Is a trend analysis possible on the HEP?
Following the acquisition of a second visual field, the Progression tab appears within the analysis window. This permits access to methods for the analysis and display of serial visual field data.
HEP offers a trend analysis graph of the Mean Deviation as well as a Pattern Standard Deviation. The MD and PSD values of all available fields of the type selected will be displayed in chronological order. The lower 5th percentile limit (green) and lower 0.05 percentile (red) are indicated. Additionally to the trend analysis HEP offers an event analysis, called Functional Change Analysis (FCA). FCA highlights significant changes in the patient´s sensitivity based on a comparison with an especially collected glaucoma database.
How can HFA data and HEP data be compared?
The default setting for the new Flicker-Defined Form stimulus on the Heidelberg Edge Perimeter has a range from 0 to 28 dB (FDF Units). These units are unique and differ from Standard Automated Perimetry (SAP). In order to offer compatibility of perimetry units and to offer continuous monitoring of patients formerly examined with different perimeters, the Heidelberg Edge Perimeter uses an optional unit conversion from FDF units into so-called legacy scale units.
HEP results can be displayed on the same scale as used on Humphrey perimeters to make the comparison with legacy data easier. For that purpose, please tick “Use legacy scale“ in the viewing window.
HEP SAP tests use the same units as SAP tests on different perimeters that are calibrated for a 10,000 asb maximum luminance stimulus and a 10 cd/m2 background stimulus. As such, the HEP SAP units are directly comparable to other similar perimeter units.
Which configurations of the HEP are available?
1) HEP – stand-alone perimeter
2) HEP S/F – perimeter with structure-function software to establish the joint display of structural HRT data and functional HEP data
Is it possible to transport the HEP?
Yes. The weight of the HEP is approximately 23 Kg. Installation is simple. Generally speaking, a transport would be possible.
Can HEP be connected to Practice-Management Software?
The HEYEX operation system can be connected to patient data management software. This enables quick and convenient import of patient data into the digital patient file.