Purpose. 

To determine predictors of success in reading with low vision aids, in terms of reading acuity, optimum acuity reserve, and maximum reading speed, for observers with vision loss from various causes.

Methods. 

One hundred people with vision loss affecting their daily lives participated. Clinical visual function measurements of distance acuity, contrast sensitivity, binocular threshold visual fields, and near reading performance with a MNRead chart at 40 cm were obtained. Reading performance aided by habitual low vision aids was also assessed with a MNRead chart.

Results. 

Aided reading acuity was best predicted by clinical reading acuity and contrast sensitivity. For most observers, a 2:1 acuity reserve was sufficient to achieve near-maximum reading speed, but one-third of observers with aided reading acuity better than 1.2M required a higher acuity reserve. Aided maximum reading speed was best predicted by clinically assessed reading speed and by clinical reading acuity.

Conclusions. 

People with vision impairment are likely to achieve 1M with a low vision aid if their clinically assessed reading acuity is better than 0.85 logMAR. If acuity is worse than this, but contrast sensitivity is better than 1.05 logCS, 1M is also likely to be achieved. A 2:1 acuity reserve is adequate for 75% of observers, but those with good aided reading acuity may require further magnification to achieve best reading speeds. Fluent reading (>80 words per minute) is likely to be achieved if an observer reads fluently with large print at a fixed working distance and if clinically assessed reading acuity is better than 1.0 logMAR.