An evaluation of the accuracy of the Moorfields Motion Displacement Test.

Abstract

Introduction: Recent statistics report a global blind population of 32.4 million and 191 million people with vision impairment, of which more than 90% of the world’s visually impaired live in developing countries. Glaucoma, the third leading cause of blindness in Africa (after cataract), is responsible for approximately 15% of blindness in the continent, requiring early detection, but goes undiagnosed in developing countries because of lack of awareness of the disease and its effects. Screening methods are not always affordable and relatively inaccessible in most developing countries, posing a barrier to identifying people at risk of glaucoma blindness. The Humphrey’s Visual Field Analyser (HVFA), considered as the gold standard in assessing visual fields, is not suited to mass screening due to cost, portability, test time, physical testing requirements among other issues, thereby making it inconvenient for mass screening programmes. These shortcomings motivated the development of the Moorfield’s Motion Displacement Test (MMDT), a new portable visual field instrument, at the Moorfield’s Eye Hospital in London. Aim: To determine the agreement and sensitivity between the Humphrey’s Visual Field Analyser (HVFA) and the Moorfield’s Motion Displacement Test (MMDT). Methods: The study followed a comparative design based on simple random sampling, comprising two hundred and seven subjects. Of the total number of subjects included in the study, the glaucoma group comprised sixty-two subjects, whilst the control group comprised one hundred and forty-five subjects. A total of 293 eyes were included in the study, of which 94 eyes were glaucomatous (case) and 199 eyes were non-glaucomatous (control), of participants who were selected via chart review from two district hospitals in KwaZulu-Natal (KZN), South Africa; McCords Provincial Eye Hospital (case) and Prince Mshiyeni Memorial Hospital (control). Both eyes were tested using the HVFA and the MMDT instruments. All subjects were asked to complete a questionnaire prior to and after testing on both instruments. Results: Non-parametric tests were used because results were not normally distributed. The diagnostic accuracy of the MMDT was high in terms of test sensitivity (100%), but performed less well in terms of specificity (63.3% and 65.3%) for case and control participants respectively. Despite the low specificity, there was a high level of similarity and a faster testing time (for both groups) in detecting glaucomatous visual field defects on the MMDT compared with the HVFA. A significant number of participants (83.5 %) across the different race groups, preferred the MMDT over the HVFA, and found the use of the mouse over a push button to be easier (74.5% across all race groups). Majority of participants (80.5%) reported focusing on a central white dot seemed more comfortable than a central amber light and found anxiety levels reduced whilst using the MMDT. Conclusion: The high sensitivity and design advantages of the MMDT for population screening may help improve glaucoma case finding in the community, and thereby facilitate earlier treatment and better health outcomes for those affected. The specificity issue should be addressed, however, to avoid service delivery problems associated with unnecessary false positive referrals.