THE GOAL of refractive surgery is to improve unaided vision in ametropic patients without the aid of spectacles and contact lenses. Refraction for the prescription of these appliances has traditionally been based on high-contrast distance visual acuity using Snellen charts. It is under such conditions that residual spherocylindrical refractive error and visual acuity following refractive surgery are usually assessed, and from these measures, the patient's visual function is inferred. It is now generally accepted that high-contrast distance visual acuity and residual refractive error are indeed correlated with overall patient visual function and satisfaction following surgery1;however, there are many refractive surgery patients with minimal residual spherocylindrical error and excellent uncorrected high-contrast distance visual acuity who are dissatisfied with their postoperative quality of vision. Refractive surgeons will be familiar with a variety of problems expressed by such patients, ranging from general, unspecific complaints, to specific phenomena, such as halo formation that arises consistently under mesopic conditions.
McLeod SD. Beyond Snellen AcuityThe Assessment of Visual Function After Refractive Surgery. Arch Ophthalmol. 2001;119(9):1371-1373. doi:10.1001/archopht.119.9.1371