Verteporfin photodynamic therapy for neovascular age-related ...

146 Appendix 1Appendix 5:Protocol for logMAR visual acuity assessment andrefractionStandardising visual acuity testing is the key to obtaining repeatable and reliablemeasurements. The procedure described below has been developed and refined from anumber of previously conducted clinical trials including the MPS studies, SFRADS andTAP/VIP.• Acuity testing should preferably be undertaken in dedicated facilities using chartswith standardised and uniform lighting.• The testing distances should be accurately marked out and the procedure followedshould be identical from one patient to the next and when the patient returns forsubsequent visits.• While equipment and light bulbs may be replaced as required every attempt must bemade to keep conditions as unchanged and as standardised as possible.1 ETDRS LogMAR Visual Acuity Charts• There are a number of ETDRS charts. For the purposes of the cohort study onlyCharts 1 and 2 and Chart R are needed.• Chart R is used for refraction, and for recording presenting BDVA (see 7 below).• After refraction is complete Charts 1 and 2 are used for testing the right and left eyerespectively.• Each line has 5 uniformly sized and spaced letters which decrease progressively insize from the top most line.LogMAR charts were developed and popularised by Bailey and Lovie and hence they aresometimes referred to as Bailey Lovie Charts. The visual angle is largest with the largestletters. The advantage of these charts is that there is a geometric progression of the visualangle with a doubling or a halving with every 3 line change. Therefore calculation of thevisual angle is very simple and allowances are made for the testing distance.• The charts may be standardised for testing at any distance, provided the appropriateconversions are clearly understood.• Changing the testing distance simply extends the range of acuity the chart can test.• Thus, for example, when used at a distance of 4M the acuity range is -0.3 logMAR to1.0.• By moving the chart to 2M, the range becomes 0.0 logMAR to 1.3.• When testing is undertaken at 1M, acuities as poor as 1.6 can be assessed.• Although standardised for the 4M distance, the chart can be easily used at 2M or 1M.• In order to obtain an acuity, when the chart has been used at 2M or 1M the examinersimply adds 15 letters or 0 letters (for 2M and 1M respectively) to the number ofletters read at the testing distance. (DPs already familiar with recording logMARacuities in logMAR units may use this format instead of letters, but must inform theData Management Centre that they wish to do so.)• Details of how the results of the tests should be recorded and scored are providedbelow (see 7 and 8). Duplicate forms for recording logMAR acuities will be suppliedto DPs.