Visual acuity
Visual acuity is the ability to resolve detail – for instance to be able to detect a gap between two objects in space. It is a commonly used proxy measure for the degree of visual disability before cataract surgery and the visual improvement resulting from surgery because it is easy to measure and is understood by the lay public. Visual acuity also forms the basis for the legal standard for driving motor vehicles and many other occupational visual standards. However visual acuity should not be used on its own to determine eligibility for cataract surgery because cataract can impair vision by causing glare or reducing contrast sensitivity before visual acuity is significantly reduced. In most patients, there will be a measurable improvement in visual acuity following cataract surgery, though for some patients the visual benefit comes mostly from reduction in glare and improvement in contrast sensitivity (which are not routinely quantified except in research studies).
In audit of cataract surgery, an explanation should be sought for situations where the final best-corrected postoperative visual acuity is worse than the preoperative visual acuity. It might be the result of an operative or postoperative complication of surgery (e.g. postoperative macular oedema), or it might be due to deterioration of a co-existing ocular condition (e.g. age-related maculopathy)