4. Example data analysis

Example data analysis

This section illustrates the calculation of reading acuity and reading speed using the MNREAD ACUITY CHART. For demonstration purposes a viewing distance of 32cm was used, and the patient started to read from the 1.0 logMAR sentence.

On the score sheet the tester has drawn a line through each word that was missed or read incorrectly, and has noted the reading time (in seconds) beside each sentence. In this case the patient was unable to read any of the last sentence on the chart (-0.5 logMAR).

Reading acuity analysis
Starting from the 1.0 logMAR level, the patient read all or part of 15 sentences. Following the procedure described previously, the three sentences above where the patient started should be counted as readable. Thus, the patient effectively read 18 sentences. From the score sheet it can be seen that the patient made 7 reading errors.

The patient's reading acuity can be calculated from:

        Acuity  =  1.4 - (sentences x 0.1) + (errors x 0.01)

        =  1.4 - (18 x 0.1) + (7 x 0.01) 

        =  1.4 - 1.8 + 0.07  =   -0.33 logMAR.

This value now needs to be corrected for the non-standard viewing distance that was used. The viewing-distance correction table shows that when the chart is viewed from 32 cm, the reading acuity value needs to be adjusted by +0.1 logMAR. Thus, the patient's reading acuity is -0.23 logMAR. This value can be converted to a Snellen fraction using the Snellen conversion table: -0.23 logMAR corresponds to 20/12.

Reading speed analysis
The reading speed data can be plotted on the special plotting paper on the reverse of the score sheet. The data points show the reading time for each sentence. The scale at the right of the graph shows the corresponding reading speed in words per minute.

The graph shows that, for print sizes larger than about 0.0 or 0.1 logMAR, the patient's reading speed was approximately level, constant at 175 words per minute. This is the patient's maximum reading speed.

When the print size is smaller than -0.1 or 0.0 logMAR the patient's reading speed deteriorated. It can be seen that 0.0 logMAR was the smallest print size that could be read close to the maximum reading rate. Thus, 0.0 logMAR is the critical print size. This value needs to be corrected for the non-standard viewing distance that was used.The viewing-distance correction table shows that when the chart is viewed from 32 cm, the reading acuity value needs to be adjusted by +0.1 logMAR. Thus, the patient's critical print size is 0.1 logMAR. Using the Snellen-conversion table, 0.1 logMAR corresponds to Snellen 20/25.