Moorfields MDT

Moorfields Eye Hospital NHS Foundation Trust

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.

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.

Epidemiology studies show us that the global estimate for Primary Open Angle Glaucoma is in the region of 67 million. 50% of glaucoma sufferers in the industrial world are undiagnosed, with this figure reaching 90% in the developing world.[7-16]

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 standard PC use. The aim is for the test to be affordable (purchase price software only) and accessible, through being distributed to registered clinicians through the internet.

The new 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. Transference of this university led research has strengthened the clinical development of the test.

What is the new Moorfields MDT?

The new Moorfields MDT is a multi-location test which is presented on a standard computer screen. 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 current test uses 32 line stimuli, which are scaled by estimate of retinal ganglion cell density. Each location corresponds to a location on the Humphrey 24-2 program, allowing pointwise comparison between the two instruments. The locations are selected by application of the Garway-Heath map of the anatomic relationship of the optic disc to the visual field.[17] The new 32-location MDT fits on a standard 15-inch laptop screen at a test distance of 30 cm.

The line stimuli are white (124 cd/m2) and presented on a grey background (10 cd/m2), giving a Michelson contrast of 85%. Each stimulus  presentation is three oscillations at 200 msec per cycle.[18, 19] 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 it therefore falls into the category of hyperacuity.[20-22] The MDT 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 MDT stimulus shows a linear relationship with the stimulus energy ([stimulus area] * [stimulus luminance – background luminance]) giving the relationship T = k √E [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).[23]

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

Recent work has included the development of a normative database and pilot comparison with glaucoma. The results of these studies were presented at The Association for Research in Vision and Ophthalmology (ARVO) meeting 2008 (Florida, USA), The International Perimetric Society (IPS) meeting 2008 (Nara, Japan) and the European Glaucoma Society (EGS) meeting 2008 (Berlin, Germany).

City University has developed adaptive algorithms over the last two years which have the benefit of reducing the test duration. The Moorfields MDT now offers two new strategies:

1. ESTA, an enhanced suprathreshold strategy which takes 90 seconds per eye. This is designed for rapid case finding in the community.
2. WEBS, a weighted binary search strategy which takes 4.5 – 5 minutes per eye and is designed for more detailed investigation in the hospital setting.

These two new strategies are currently undergoing validation in a collaborative international study which will compare the Moorfields MDT with Standard Automated Perimetry, the Frequency Doubling Test and the new Heidelberg Edge Perimeter. The study collaborators are:

• Professor John Flanagan PhD MCOptom FAAO, Department of Ophthalmology and Vision Sciences, University of Toronto, Canada.
• Dr Paul Artes PhD, Department of Ophthalmology and Vision Sciences, Dalhousie University, Halifax, Canada.
• Dr Francesco Odone, The Bietti Foundation, Rome.

The Moorfields MDT is also taking part in a community study which is led by Alfonso Antón MD PhD at the Hospital de la Esperanza y el Mar, Instituto municipal de investigaciones Médicas (IMIM, IMAS) and the Universidad Autónoma de Barcelona. The study objective is to assess the cost/effectiveness of screening for glaucoma through telemedicine.

Future studies: The development of a paediatric test is planned in collaboration with Great Ormond Street Hospital for Children NHS Trust and The Institute of Child Health London.

MHRA approval was granted to the Moorfields MDT in 2006 (CE / 2006 / 009073).

What are the Moorfields MDT’s advantages?

• Easily undestood
• Robust to cataract and refractive blur [5, 6]
• Portable: runs on laptop, therefore may be suitable for case finding in the community
• Inexpensive (purchase price: software)
• Accessible (vision: downloadable to registered practitioners through internet)

Register your interest

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

References

1. Fitzke FW, Poinoosawmy D, Ernst W.Hitchings RA. Peripheral displacement thresholds in normals, ocular hypertensives and glaucoma., in Perimetry Update 1986/1987, E. Greve and A. Heijl, Editors. 1987; Kugler & Ghedini: The Hague, The Netherlands. pp 447-452.
2. Fitzke FW, Poinoosawmy D, Nagasubramanian S.Hitchings RA. Peripheral displacement thresholds in glaucoma and ocular hypertension., in Perimetry Update 1988/1989, A. Heijl, Editor. 1989; Kugler & Ghedini: The Hague, The Netherlands. pp 399-405.
3. Baez KA, McNaught AI, Dowler JG, Poinoosawmy D, Fitzke FW.Hitchings RA. Motion detection threshold and field progression in normal tension glaucoma. Br J Ophthalmol. 1995;79(2):125-8.
4. Westcott MC, Fitzke FW.Hitchings RA. Abnormal motion displacement thresholds are associated with fine scale luminance sensitivity loss in glaucoma. Vision Res. 1998;38(20):3171-80.
5. Membrey L.Fitzke FW. Effect of lens opacity on white-on-white perimetry, frequency doubling perimetry, and motion detection perimetry, in Perimetry Update 2000/2001, M. Wall and J. Wild, Editors. 2000; Kugler Publications: The Hague, The Netherlands. pp 259-266.
6. Membrey L, Kogure S.Fitzke FW. A comparison of the effects of neutral density filters and diffusing filters on motion perimetry, white on white perimetry and frequency doubling perimetry, in Perimetry Update 1998/1999, M. Wall and J. Wild, Editors. 1998; Kugler Publications, The Hague, The Netherlands. pp 75-83.
7. Bourne RR, Sukudom P, Foster PJ, Tantisevi V, Jitapunkul S, Lee PS, Johnson GJ.Rojanapongpun P. Prevalence of glaucoma in Thailand: a population based survey in Rom Klao District, Bangkok. Br J Ophthalmol. 2003;87(9):1069-74.
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14. Topouzis F, Coleman AL, Harris A, Koskosas A, Founti P, Gong G, Yu F, Anastasopoulos E, Pappas T.Wilson MR. Factors associated with undiagnosed open-angle glaucoma: the thessaloniki eye study. Am Ophthalmol. 2008;145(2):327-335.
15. Nizankowska MH.Kaczmarek R. Prevalance of open angle glaucoma and ocular hypertension as a risk factor for primary open angle glaucoma in Wroclaw population. Wroclaw Epidemiology Study. Klin Oczna. 2004;106(1-2 Suppl):147-52.
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17. Garway-Heath DF, Poinoosawmy D, Fitzke FW.Hitchings RA. Mapping the visual field to the optic disc in normal tension glaucoma eyes. Ophthalmology. 2000;107(10):1809-15.
18. Verdon-Roe GM, Westcott MC, Viswanathan AC, Fitzke FW.Hitchings RA. Optimum number of stimulus oscillations for motion displacement detection in glaucoma, in Perimetry Update 2000/2001, M. Wall and J. Wild, Editors. 2000; Kugler Publications: The Hague, The Netherlands. pp 97-102.
19. Westcott MC, Verdon-Roe GM, Viswanathan AC, Fitzke FW.Hitchings RA. Optimum stimulus duration for motion displacement detection in glaucoma, in Perimetry Update 2000/2001, M. Wall and J. Wild, Editors. 2000; Kugler Publications: The Hague, The Netherlands. pp 103-108.
20. Exner S. Uber des Sehen von Bewegung und die Theorie des zusammengesetzten Auges. Sher. Akad. Wiss. Wien. (Math.-nat. Kl., Abt. 3). 1875;72:156-190.
21. Scobey RP.Horowitz JM. Detection of image displacement by phasic cells in peripheral visual fields of the monkey. Vision Res. 1976;16(1):15-24.
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23. Verdon-Roe GM, Westcott MC, Viswanathan AC, Fitzke FW.Garway-Heath DF. Exploration of the psychophysics of a motion displacement hyperacuity stimulus. Invest Ophthalmol Vis Sci. 2006;47(11):4847-55.