From the McArthur to the Millennium Health Microscope (MHM): Future Developments in Microscope Miniaturisation for International Health
Keith Dunning & Dr. J. Russell Stothard 1
1 Biomedical Parasitology Division, Department of Zoology,
Natural History Museum, London, SW7 5DB, UK
Reproduced with the kind permission of
Following his engineered model a later version, produced in moulded plastic by the Open University (OU), took the design even further forward with the realisation that future low-cost microscopes would inevitably utilise plastic fabrication technology. During his life McArthur received many awards, including the Duke of Edinburgh’s Prize for innovative design in the 1980s for the OU model, but was perhaps never given full recognition for his pioneering work on microscope design, nor for his studies of malaria and mosquitoes in East Asia. Despite good intentions, McArthur’s vision of revolutionising the way microscopy could be used in tropical diseases was sadly never realised. Even with the cheaper OU model, the cost of the instrument was still out of reach of the comparatively meagre financial budgets of Ministries of Health and without an appropriate technology transfer/implementation model between north-south country partnerships, all initiatives ultimately stalled. Although an eminently practical solution in microscope technology, the price of McArthur's impeccably engineered microscope (equivalent to US$2000 at today's prices) was simply unaffordable in its targeted health market and the production of the McArthur microscope sadly ceased following John's death in 1996. The international health scene therefore lost a longstanding advocate and a strong voice for practical field microscopy.
Inspired by McArthur’s work, a small group of Cambridge designers including Keith Dunning and Richard Dickinson (former Head of Design for Sinclair, UK) launched a new folded-optic microscope in 1990, subsequently licensed to Meade Instruments USA and marketed as the Readiview. Like the McArthur the Readiview is extremely compact and measures 105 mm in diameter x 25 mm in height, yet offers full functionality with magnifications of 80x and 160x. Three dimensional optical folding enables the microscope top to form a generously sized stage and the articulated lighting arm provides bright field, dark ground and reflected illumination dependent on position. Unlike the McArthur, the Readiview is capable of viewing opaque specimens in addition to conventional microscope slides and is popular amongst amateur and professional biologists. In 2004, a companion microscope, the Trekker, was launched for those requiring a low power (35x) version for fieldwork in forensics, botany, zoology, entomology and paleontology. Together with its low cost, good ergonomics and supreme ease of use the Trekker has become popular as an introduction to microscopy for young people. More detailed technical descriptions of the Readiview/Trekker concept may be found at www.looksmall.com
With the better affordability of the Readiview at around 70 USD and one tenth the cost of a suitable conventional compound, it was perhaps time to revisit McArthur’s original vision as there remains a pressing need for microscopic diagnosis of tropical diseases. In reality with the continual attrition of facilities within rural health clinics in Africa the demand is ever growing for more sustainable, lower cost equipment. Having visited many rural clinics in Africa, the availability of compound microscopes amongst field-based roving health teams is still a major logistic bottleneck. Whilst improved technology and low-cost instrumentation provide some of the necessary ingredients for a working recipe, other factors need attention, such as the development of a better technology transfer/implementation model which employs ‘on-the-ground’ validation and implementation studies. Undoubtedly, an affordable, durable and effective microscope creates a way forward for infrastructure improvements, but this should be combined with the appropriate technology transfer model to create a sustainable demand for utilisation within the tropical health sector to overcome many of the socio-economic barriers.
Field tests of the efficacy of the Readiview for visualization of helminth eggs have been very good and quite satisfactory for routine diagnosis purposes (see American Journal of Tropical Medicine and Hygiene 73, 949-955). This in itself is very important as control of helminthiasis in school-age children relies upon diagnosis of disease within a sub-set of children from a selection of schools; if the disease is shown to be a problem at each site then all children, and sometimes the surrounding adult community, is offered medications en masse. Although the Readiview is satisfactory for visualisation of blood-borne helminths e.g. microfilariae of lymphatic filariasis, for protists, the optical magnification range of the Readiview needs much further improvement to place it on par with the higher powered McArthur. In so doing this technological improvement would allow visualisation of other blood-borne protists and with this in mind, the Millennium Health Microscope (MHM) was conceived. A significant upgrade to the Readiview the low-cost design of the NHM could nevertheless be fabricated inexpensively in the Far East. The low cost of production and the proven manufacturing techniques already developed for Readiview and Trekker could be the production breakthrough. Hand in hand with this innovation, and with further field validation, real progress towards McArthur's vision could be made.
The ambition to produce a functional miniature microscope suitable for tropical disease diagnostics in developing countries has exercised the ingenuity of many talented designers over the last 75 years. In the early 1930’s the late Dr John McArthur produced the first prototype of his pioneering folded optic design and this portable gem measured a mere 102 x 63 x 51 mm, yet was able to deliver everything which would be expected from a conventional bench microscope of similar optical specification. (see left). To achieve this high degree of miniaturisation McArthur employed folded optical prismatic system: light entered from above the microscope via a mirror and then passed through a small condenser to the specimen, a revolutionary concept at that time. The objectives were arranged below the specimen and the image was reflected by two prisms to the eyepiece. A comprehensive range of interchangeable objectives was offered including 4:1 and a 100:1 oil immersion. McArthur’s vision was predicated on the widespread use of his ultra portable microscopes for the diagnosis of tropical diseases in peripheral health centres.
The prototype McArthur circa1932
READIVIEW
TREKKER
Subject to the availability of seed grant funding to finance R & D, tooling and clinical trials, the MHM could be available within the next 2-3 years at no more than 75USD per unit in its standard form with 10:1 and 40:1 objectives. The MHM will offer a range of interchangeable objectives (10:1, 40:1 and 100:1 oil immersion) integrated lighting, an indexing stage and interchangeable RMS eyepieces. It is hoped that the availability of this instrument will encourage health organisations to purchase and donate the MHM to developing countries in a cost:donation model, alongside major pharmaceutical suppliers, who might be inspired to distribute these inexpensive microscopes as part of a corporate care culture in deserving countries for monitoring and surveillance of tropical diseases. Proposals for funding the MHM are presently being written and we would greatly appreciate any advice from readers of Microscopy Today.
This article was originally featured in the March 2007 edition of 'Microscopy Today' and is reproduced above with the kind permission of the Editor.
READIVIEW
TREKKER
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MILLENNIUM HEALTH UK Charity no. 1119453
Microscope Foundation www.millennium-microscope.org
