Diagnosing Declines in Visual Acuity

Visual acuity slowly decreases in the later decades of life.  In that advanced optical quality metrics can detect a wide range of minor imperfections in the visual performance of the eye, Darren E. Koenig, from the University of Houston College of Optometry (Texas, USA), and colleagues have identified three advanced optical measures that may help in predicting which older patients will have larger drops in visual acuity over time. The researchers completed a follow-up study in 148 older adults, aged 50 to 80 years. In addition to standard visual acuity testing, the participants underwent wavefront error (WFE) testing—a computerized test that can detect subtle abnormalities in the eye's handling of light. About 40 optical components based on WFE were calculated, including 31 different image quality measures, four measures of light scatter in the eye, and four measures of opacification (clouding) of the lens of the eye. Four years later, visual acuity was measured again. The optical metrics were evaluated for their ability to predict the rate of decline in visual acuity during that time. The goal was to see whether any of the image quality or other metrics could predict which patients would have faster than usual age-related declines in vision. Overall, the average change in visual acuity during follow-up was loss of 1.6 letters on the standard eye chart. That was consistent with the expected age-related decline. However, a subgroup of 50 patients had larger changes in visual acuity during follow-up. In this group the average change was loss of 3.4 letters. With adjustment for other factors, three optical measures predicted a larger change in visual acuity. These included one optical quality measure ("trefoil"), one measure of optical light scatter ("point spread function entropy"), and one measure of lens clouding (posterior subcapsular cataract).  Together, these three measures accounted for 32% of the change in visual acuity in patients with larger-than-expected change in visual acuity. Observing that: “change in optical quality metrics was the most important factor in eyes that lost or gained four or more letters of acuity,” the study authors write that: “4-year acuity change … indicate[s] that these optical quality markers can be used to help identify those on a faster track to an acuity change.”