A compact electronic device which enables the user to determine for himself whether his visual acuity reaches a chosen standard has been constructed at a cost of 25 pounds. The instrument provides a test which requires the observer to respond to the orientation of a sequence of red Landolt-Cs and which takes under five minutes to complete. 'Crowding' effects associated with conventional letter charts are avoided and the test does not discriminate against astigmatic observers. One hundred observers were tested on both the new instrument (the Elidice) and a standard Snellen chart under clinical conditions. The overall agreement between the two tests was 87.8%, with the Elidice having an over-referral level of 10-7% and an under-referral level of 1-5% as compared with the letter chart. This makes the Elidice particularly suitable for the regular screening of laser users for reduced visual acuity due to macular damage.