Eccentric visual acuity & multiple letter acuity chart (MLAC)

Patients with severe macular diseases need eccentric viewing to see a target because of central scotoma. However, eccentric fixation is often difficult and visual acuity measurements are unstable in these patients. We developed a multiple letter acuity chart (MLAC) in which many Landolt rings ("C") of the same size and direction were printed. This chart projects the "C" outside of the lesion regardless of the status of the patient's fixation, and it allows us to measure eccentric acuity in patients with central scotoma. Macular hole patients revealed better acuity with a MLAC than with a standard acuity chart preoperatively, but the difference between acuities as measured by the 2 charts was minimized postoperatively. This suggests that standard charts underestimate preoperative acuity and then overestimate improvements of acuity after surgery. Similar results were observed in age related maculopathy. Our study suggests that we must be very careful in determining acuity patients with in macular diseases.