METAMORPHOPSIA AND ITS QUANTIFICATION.
PURPOSE: To discuss and analyze the pathophysiologic mechanisms underlying metamorphopsia, the nature of adaptational mechanisms to this symptom, the development and clinical utility of tests of metamorphopsia, and to discuss the cost-effectiveness of screening populations at risk of exudative age-related macular degeneration using such tests. METHODS: A primary literature search of PubMed and Web of Science was conducted for articles covering the mechanisms and/or tests of metamorphopsia. RESULTS: A number of possible mechanisms of metamorphopsia were identified in addition to lateral photoreceptor displacement. These included disorders of image formation, changes in effective axial length, and pathology of the visual pathways and centers. The simplest tests of metamorphopsia rely on highly subjective assessments of regular patterns, as exemplified by Amsler grids. Such tests seem to offer poor sensitivity when used in real-life home-monitoring situations. Newer tests such as so-called preferential hyperacuity perimetry may offer more robust paradigms to assess the perception of distortion but suffer from an inherent disadvantage of being unable to precisely correlate function to structure. The recently published findings of the AREDS2-HOME trial suggest that formalized monitoring of visual function using a preferential hyperacuity perimetry task results in detection of exudative age-related macular degeneration when vision is better-preserved. A cost-benefit analysis using the data from the AREDS2-HOME trial suggests that the calculated cost of screening per letter gained/saved is $3,351 per year. CONCLUSION: Metamorphopsia is an important symptom in retinal disease and may occur through a variety of mechanisms. Although the human visual system is exquisitely sensitive to metamorphopsia, commonly used tests of this symptom may be unreliable in real-life conditions. Newer tests of metamorphopsia such as preferential hyperacuity perimetry may improve early detection rates of exudative age-related macular degeneration in at-risk populations.