Can we quantify the quality of vision?

The age of refractive surgery has introduced new aberrations to the human eye that require a shift in how visual performance is evaluated, said Ray Applegate, MD. Mesopic low contrast acuity best quantifies vision quality; it overcomes the weaknesses of other metrics and it can predict visual function among individuals.

Dr Applegate recruited 168 people with 6/6 or better vision across a range of ages and conducted a photopic high-contrast logMAR acuity test. "The test could only account for around 4% of the variation in our sample," he said. "We can't use it to predict the visual function of individuals. However mesopic low-contrast logMAR acuity accounted for a much broader range of the variation."

Dr Applegate said high contrast acuity is a poor metric because it is conducted under high luminance conditions and has excess contrast allowing a loss in contrast and image fidelity without a loss in measured acuity.

Contrast sensitivity, on the other hand, is impractical because it requires measurements along many different orientations. "That is simply not practical in the clinical environment and it is totally insensitive to phase shifts," insisted Applegate.

But mesopic low contrast acuity allows a large physiologic pupil and is sensitive to phase shifts and contrast loss. "It's also a recognition task as opposed to a detection task that's understood by clinicians and patients and it's easy to administer in a clinical setting," he said.

The study will be published shortly in Optometry and Vision Science.

Ophthalmology Times Europe reporting from the XXIV Congress of the ESCRS, London, 9-13 September, 2006.