Monocular and binocular reading curves of 20 patients (4 with cataract, 5 with glaucoma, 11 with maculopathy) were recorded by infrared oculography. Reading speed was found to be directly proportional to the visual acuity of the eye tested. However, the same visual acuity in both eyes does not always mean that the subject reads at the same speed with both eyes. For example, paracentral visual field defects impair reading ability and eyes which appear to have good vision may easily become tired. Twelve of 16 examined eyes with maculopathy showed a significant decrease in reading speed during a reading test lasting no more than 2 minutes. In tests of the same duration cataract patients did not tire; their reading speed increased. Binocular vision helps improve reading speed in cases of maculopathy, and even more so in cases of glaucoma with visual field defects. Attention is drawn to Mackensen's suggestion that measurement of reading speed is a valuable function test, and to the fact that in certain cases fatigue of an eye during reading is a new and measurable criterion of the degree of visual impairment.