Second Year 99/00
Clinical Optometry 2
Vision/Visual Acuity testing
Practical
Learning objectives
- To become aware of several vision/visual acuity charts
- To understand the use of these charts
- To obtain vision/visual acuity measures
- To become aware of the advantages and disadvantages of these charts
Introduction
The aim of this practical is to introduce you to several different techniques that can be used to determine distance and near vision/visual acuity. The former is measured without, and the latter with refractive compensation.
Distance vision/visual acuity will be determined using Snellen, Bailey Lovie no. 5 logMAR, Keeler Crowded and Uncrowded Cards, Kay Picture Test and the Cardiff Acuity Cards. Near vision/visual acuity will be determined using the Faculty of Ophthalmologists’ near acuity book, Jaeger near acuity book, the Bailey Lovie near word card and the MacClure reading book.
Practical assessment
Because of time constraints, for all tests obtain binocular results only. In the real world it is important to take monocular and binocular results.
Distance charts
Working in pairs measure your partner’s distance vision, or visual acuity if they need refractive correction, using the following methods:
- With the Snellen chart at 6 m using the plus or minus notation for incomplete lines.
- Use the Bailey Lovie no. 5 chart to determine vision/visual acuity at 6 m, using the logMAR scale on the right side of the chart. Each letter is worth 0.02 log units. Calculate the vision/visual acuity for incomplete lines. Please note the Bailey Lovie no. 5 chart is direct and cannot be used with a mirror. Do not note vision/visual acuity in Snellen equivalents when using this chart.
- Use the Kay Picture Test at 6 m. Open the book with the numbered index on your right and use the right thumb to choose the size and flick the page over so that the chosen picture faces the observer. Begin with a fairly large picture and ask the observer to identify it, then repeat using smaller pictures (not necessarily every size) until you reach the smallest size that the observer can identify, then record the vision/visual acuity.
- For the Keeler Crowded and Uncrowded Cards use the following procedure to measure vision/visual acuity. The test is usually performed at a test distance of 3 min an evenly well-illuminated room. The initial letter acuity level is determined using the screening cards (cards 1 to 3 in each of the cards). The observer should be encouraged to respond to each letter in the series until an error is made. The last successful response is used to determine the starting point for the measurement of line acuity. The appropriate card is then selected and the observer should attempt to identify each of the four letters presented. If the observer is able to identify correctly two or more letters on a line then the next card in the series should be presented. The score for each eye is calculated using a single letter scoring system. Each line on the chart represents a change of 0.1 log unit in the acuity level and each letter having a value of 0.025 log unit.
- For the Cardiff Acuity Test please read and follow the instructions in the enclosed instruction booklet.
Near charts
Using the Faculty of Ophthalmologists’, Jaeger, MacClure Reading chart and the Bailey Lovie word cards note the near vision/visual acuity and the working distance comfortable for the observer. Use an over the shoulder Anglepoise lamp to provide even illumination illumination.