Information for Clinicians

Moorfields Motion Displacement Test (MDT)
Background for clinicians

The original Motion Displacement Test (MDT) was first developed in the early 1980s by Professor Fitzke at the Institute of Ophthalmology, London [1, 2]. The original test used a single line stimulus which was presented just above the blind spot (15,9) on a BBC computer (Figure 1).

Figure 1. Diagrammatic representation of original single line MDT
The white circle corresponds to central fixation (0,0) and the open circle the optic nerve head.

Figure 1, Diagrammatic representation of the origional MDT

The single line MDT was found to be a predictor of glaucomatous field loss,[3] with evidence of elevated motion displacement threshold in areas of the visual field estimated to be normal by standard automated perimetry (SAP).[4] The MDT was also found to be robust to the effect of media opacity.[5, 6] It was these properties that provided the rational to take the test onto a multi-location format in 1999.

Epidemiology studies show that the global estimate for open angle and angle closure glaucoma is in the region of 60 million. This figure is expected to approach 80 million by 2020. At least 50% of glaucoma sufferers in the industrial world are undiagnosed, with this figure reaching 90% in the developing world.[7-17]

The vision of the new Moorfields MDT is to address the global challenge of glaucoma detection by providing a modern, windows-based test suitable for PC use. The current test is presented on a 15-inch laptop computer with the aim of offering an affordable and portable method of case-finding in the community.

The Moorfields MDT has been under development since 1999 by the Glaucoma Research Unit at Moorfields in collaboration with the Institute of Ophthalmology, UCL. The partnership expanded to include City University, London in 2006. The test development has been strengthened by this university led research and the Moorfields MDT was awarded overall winner of the Medical Research Council (MRC) translational research innovation awards in the Medical Futures competition of 2008.

What is the Moorfields MDT?

The Moorfields Motion Displacement Test (MMDT) is a windows-based software program which is designed to provide test of the field of vision for the detection and potential monitoring of glaucoma. The test is adaptable for different specifications of monitor which means that it can be presented on a variety of hardware platforms and is adjustable to the modern demands of rapidly changing technology.

The current test format presents 31 line stimuli which are scaled in size by estimate of retinal ganglion cell density[18] Each location corresponds to a location on the Humphrey 24-2 program, allowing spatial comparison between the two instruments. The locations are selected by application of the Garway-Heath map of the anatomic relationship of the optic nerve head to the visual field, with the aim to provide a more even sampling by disc sector.[19] The 31-location format fits a 15-inch laptop screen at a test distance of 30 cm.

The test task has the advantage of being easily understood: the patient is asked to look at a central spot and to press the computer mouse each time a line on the screen is seen to move.

The line stimuli are white and continuously presented on a grey background at a constant Michelson contrast of 85%. Each stimulus presentation is three oscillations at 200 msec per cycle.[20, 21] The threshold is recorded as the minimum detectable displacement, which is measured in minutes of arc. Motion displacement sensitivity is greater than predicted from retinal ganglion cell spacing and therefore falls into the category of hyperacuity.[22-24] The MMDT task is to discriminate the positional change between two lines and may be regarded as a temporal form of vernier acuity.

Study of the summation properties of the MMDT stimulus shows a linear relationship with the stimulus energy ([stimulus area] * [stimulus luminance – background luminance]) giving the relationship T = k vE [T = mdt threshold; K = constant; E = stimulus energy]. This threshold energy displacement law (TED) may be used to predict MDT threshold for different configurations of stimuli. Equivalent thresholds are found for stimuli of equivalent energy, showing that Ricco’s law applies to the MDT stimulus (figure 2).[25]

Figure 2. Plot of log MDT threshold as a function of log stimulus energy

Figure 2 Plot of log MDT threshold as a function of log stimulus energy

A simple staircase MMDT threshold strategy was developed in 2004-5 and a normative database of 120 subjects (20 – 85 years) collected in 2006-8. Pilot comparison with glaucoma showed good topographical correspondence of the Moorfields MDT with standard automated perimetry, with 70% pointwise agreement of the spatially matched locations. The early staircase strategy was found to be too long for screening purposes (5-7 minutes per eye). The team has collaborated with City University since 2006 to develop adaptive algorithms with aim of reducing the test duration.

The Moorfields MDT enhanced suprathreshold algorithm "ESTA" is designed for rapid case finding in the community [26]. It takes in the region of 90 -120 seconds per eye. ESTA applies a spatial filter [27, 28] and multi-sampling techniques [29,30].

The ESTA spatial filter [27] applies knowledge of the anatomical relationship of the visual field locations of standard automated perimetry (SAP) to the entry of nerve fibre bundles into the optic nerve head (ONH) [19]. Spatially related locations are clustered in normalised correlated arrays. A new index is calculated for each location which is referred to as the "probability of true damage" (PTD).

A new global index "the global probability of true damage" (GPTD) represents the sum of the PTD for each test location expressed as a quotient of 100. The higher the value of the PTD, the greater the probability of “true damage”.

The first version of ESTA applied large suprathreshold displacements and was reported to outperform the Humphrey 76 point screening test, the Frequency Doubling Matrix screening test and Heidelberg Retinal Tomography in the preliminary findings of the St Kitts Eye Study presented by Associate Professor Paul Artes at ARVO 2008 (The St Kitts Eye Study (SKES): Design and Initial Findings. Artes et al.  IOVS 2008; 49: ARVO E-abstract 4080; ).

The ESTA 99.5 program is the latest version of ESTA and applies displacements at the 99.5th centile of probability according to most recent normative  estimates and is currently undergoing validation.

We are grateful to our many international collaborators who are participating in MMDT related studies, these include:

  • Professor Roger Anderson and James Loughman. The Mozambique Eye Care Project, an Irish Aid/Higher Education Authority (HEA) initiative
  • Alfonso Antón MD PhD and Monica Fallon at the Hospital de la Esperanza y el Mar, Instituto Municipal de Investigaciones Médicas (IMIM, IMAS) and the Universidad Autónoma de Barcelona, Spain.
  • Associate Professor Paul Artes PhD and Glen Sharpe, Department of Ophthalmology and Vision Sciences, Dalhousie University, Halifax, Canada.
  • Associate Professor Tin Aung and Dr Alicia How, The Singapore National Eye Centre (SNEC), Singapore.
  • Dr Phil Clatworthy, Neurologist, North Bristol NHS Trust, Bristol, UK.
  • Kate Coleman FRCOphth
  • Professor John Flanagan PhD MCOptom FAAO and Carmen Balian, Department of Ophthalmology and Vision Sciences, University of Toronto, Canada.
  • Simon Frackiewicz Akamba Aid fund
  • Professor Clare Gilbert, Professor of International Eye Health, The London School of Hygiene and Tropical medicine London UK.
  • Dr Francesco Odone, Dr Lucia Tango and Manuele Michelessi, The Bietti Foundation, Rome.
  • Professor Jugnoo Rahi Great Ormond Street Hospital for Children NHS Trust and The Institute of Child Health London UK.
  • Mrs Florence Rasquin MD, Consultant Ophthalmologist and Mrs Nacima Kisma FEBO MD,  Erasmus Hospital, Brussels.
  • Mr Eamon Sharkawi FRCOphth Consultant Ophthalmologist Dr Corinne Schnyder and Dr Hana Abouzeid Jules-Gonin Eye Hospital, 15 Avenue de France, 1004 Lausanne, Switzerland.
  • Professor Robert Stamper University of California, San Francisco, USA.

Current Development Work at the NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust & UCL Institute of Ophthalmology

One of the challenges of making comparison between the Moorfields MDT and standard automated perimetry is that different measurement scales are applied to the different psychophysical stimuli. The motion displacement threshold is recorded in minutes of arc and differential light sensitivity in decibels. We are currently exploring the relative dynamic range of each stimulus with the aim to provide a reference scale for improved comparison between the instruments.

The pixel size of standard LCD monitors limits the measurement of threshold in areas of high retinal sensitivity. We have recently overcome this by the development of a novel sub-pixel strategy. We are currently working on the development of an improved threshold strategy which we hope will extend the role of the Moorfields MDT to the monitoring of glaucoma progression.

What are the Moorfields MDT’s advantages?

  • easily understood by both patient and operator
  • portability
  • affordability
  • robust to optical blur - designed to test without near optical correction
  • robust to cataract [5, 6, 26]
  • Easy export facility for statistical analysis with anonymising option

Register your interest

Register here for notification when the Moorfields MDT is officially released.

The commercialisation of the Moorfields MDT is being led by UCLB It is anticipated the case finding version ESTA will be available towards the end of 2011 on completion of the validation programs.

MHRA approval was granted to the Moorfields MDT in 2006 for the collection of the normative database (CE Device 1/ 2006 / 009073). The CE mark will be upgraded to from Device 1 to Device 2a before it is commercially released as a case-finding device.


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