Differences between recognition and resolution acuity in patients undergoing macular hole surgery.

PURPOSE

The present investigation compared recognition acuities (ETDRS chart) with resolution acuities (Landolt-C chart) in a sample of patients with idiopathic macular holes (MH). Traditionally, visual acuity in a clinical setting is measured with a letter chart. Yet, the ability to recognize a letter differs from a resolution task, such as detecting the direction of a gap in a ring. It was hypothesized that resolution acuity would be more impaired than recognition acuity in patients with MH, because component cues in letter optotypes are not available in Landolt-Cs.

METHOD

Visual acuities of 23 patients with MH (age range, 52-82) were tested, using standard ETDRS and Landolt-C charts. Optical coherence tomography was used to confirm the diagnosis of MH.

RESULTS

Acuities correlated strongly, before and after surgery (r = 0.92 and r = 0.95, respectively). However, paired t-tests determined that resolution acuity was significantly more impaired at both time points than was recognition acuity (P < 0.001). Using Bland-Altman plots, the limits of agreement between the two acuity types indicated that resolution acuity differed from recognition acuity by up to five lines before surgery and up to 3 lines after surgery.

CONCLUSIONS

ETDRS and Landolt-C acuities differ in a clinically significant way in patients before and after MH surgery. Measuring recognition acuity by reading letters may lead to an overestimate of visual ability at the retinal level in patients with MH by including compensatory top-down cognitive processes that are unavailable for resolution tasks.