VISUAL-FIELD DEFECTS DUE TO SPECTACLE FRAMES - THEIR PREDICTION AND RELATIONSHIP TO UK DRIVING STANDARDS

One male and one female subject wore a selection of ten current specta cle frames in random order. Monocular visual fields were assessed usin g an Aimark perimeter in accordance with UK Driver and Vehicle Licensi ng Authority (DVLA) guidelines. Of the ten frames, seven plastic frame s produced an absolute scotoma intruding into a 120 degrees x 400 degr ees 'letterbox' area acting as a driving Visual field template. Three metal frames gave a relative scotoma; however, our apparatus was too i nsensitive to plot these scotomata. Relevant frame and patient paramet ers were measured and entered into a computer program which enabled th eoretical visual field defects due to a spectacle frame to be calculat ed. Good agreement is shown to be possible between actual and computed visual field defects. Spectacle frames can and frequently do cause vi sual field defects which may affect a driver's fitness to drive. Our d ata also show that a frame which allows an adequate field of vision at night could cause a marked visual field defect during daylight hours. A model and rule-of-thumb are given to determine the size of these po tential defects and suggestions are given to minimise or eliminate the m.