Measuring reading speed
Reading speed is an objective measure of reading performance. Research has shown that patients (with either normal or low vision) often require letters that are two or three times larger than their acuity limits before they can achieve their maximum reading speeds.
The MNREAD ACUITY CHARTS can be used to measure reading speed at different print sizes, and hence, can be used to determine the print size which supports the patient's maximum reading speed.
Measuring reading speed can be combined with the reading-acuity measurement described previously. A blank piece of card should be used to cover the sentences below the one being read (to prevent the patient previewing the subsequent sentences).
Instruct the patient to read each sentence aloud, as quickly and accurately as possible.
Use a stopwatch to record the time taken to read each sentence (to the nearest 0.1 sec.). Make a note of the times on the score sheet and mark any words that are missed or read incorrectly.
Calculation of reading speed
Reading speed is measured in words per minute. With the MNREAD ACUITY CHARTS the reading speed calculation is simplified because each sentence has the same length: 10 standard length words. Reading speed is given by:
reading speed = 600 / (time in seconds)
A more precise reading speed measurement can be achieved by excluding words that were missed or read incorrectly. In this case reading speed is given by:
reading speed = 60 x (10 - errors) / (time in seconds)
If more than 10 errors were made then reading speed can be assumed to be zero.
Determining the critical print size.
The critical print size is the smallest print size at which patient's can read with their maximum reading speed. This is an important measure as it indicates the minimum magnification required for effortless reading. The critical print size is most easily identified from a plot of the patient's reading speed at each print size.
The reverse side of the score sheet carries graph paper for plotting reading-speed data. It is not necessary to calculate reading speed for the sentences if this plotting paper is used. The scale on the vertical axis is reading time. This scale has been transformed so that it corresponds to reading speed (assuming no reading errors were made). Reading speed in words-per-minute is shown on the scale at the right of the plot. The horizontal scale on the plotting paper shows logMAR print size.
Typically, reading time remains fairly constant for large print sizes. But as the acuity limit is approached there comes a print size where reading starts to slow down. This is the critical print size. If a non-standard viewing distance was used, remember to adjust the critical print size to account for the viewing distance.
The reading speed with print larger than the critical print size is the maximum reading speed. This is the reading speed that can be achieved by the patient when print size is not a limiting factor.