Background: Reading acuity as well as reading speed are good predictors of everyday visual function. As visual acuity tests are poor predictors of the real-world function, performance-based tests, e.g., reading speed measurements, can be used for the determination of visual function. Thus, a German reading chart was developed in order to evaluate reading acuity as well as reading speed.
Methods: Print size is defined as the height of a lower case x and progresses logarithmically from one phrase to another (factor: 1.25). Reading acuity is determined in LogRAD (Reading Acuity Determination). 32 short German phrases were created, comparable concerning grammatical difficulty as well as in number (n = 14), length and position of words. The reading speed parameters measured with a stop-watch in 160 persons (aged: Phi = 21a +/- 3.8a) were calculated in words per minute (w/min). Out of the 32 phrases the 24 most similar ones were selected statistically and used for the reading charts (Radner Reading Charts). With these reading charts a reading acuity score (LogRAD-score) can be calculated considering reading errors in words of different length. Reading speed can be determined at the same time. Reading acuity (LogRAD-Score) was measured in 32 normal eyes of 16 students and compared to the angular visual acuity (LogMAR).
Results: The mean reading speed of the test persons was 211.8 +/- 34.1 w/min. 24 phrases fulfilled the test item criteria for the reading chart: mean +/- 0.25 x SD. The reliability analyses yielded an overall Cronbach's alpha coefficient of 0.98! The mean visual acuity measured in 32 eyes was -0.115 +/- 0.097 LogMAR and the mean reading acuity score was +0.026 +/- 0.091 LogRAD. The mean difference was +0.104 +/- 0.066 and the correlation between LogMAR and LogRAD was good (r = 0.59).
Conclusions: With these reading charts it is for the first time possible to simultaneously determine reading acuity as well as reading speed in German. The high reliability of the 24 phrases and the high correlation between LogMAR and LogRAD leads us to expect a good reproducibility of the reading acuity evaluations. For the "Radner Reading Charts" we have shown that print size is the main reason for changes of reading speed.