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 spectacle frames in random order. Monocular visual fields were assessed using an Aimark perimeter in accordance with UK Driver and Vehicle Licensing Authority (DVLA) guidelines. Of the ten frames, seven plastic frames produced an absolute scotoma intruding into a 120 degrees x 40 degrees 'letterbox' area acting as a driving visual field template. Three metal frames gave a relative scotoma; however, our apparatus was too insensitive to plot these scotomata. Relevant frame and patient parameters were measured and entered into a computer program which enabled theoretical visual field defects due to a spectacle frame to be calculated. Good agreement is shown to be possible between actual and computed visual field defects. Spectacle frames can and frequently do cause visual field defects which may affect a driver's fitness to drive. Our data 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 potential defects and suggestions are given to minimise or eliminate them.