What size of a lesion is classified as geographic atrophy?

Geographic atrophy is identified based on the size of the lesions present in the retinal pigment epithelium (RPE). The threshold for classifying a lesion as geographic atrophy is typically defined as being greater than 175 micrometers (μm) in diameter. This classification is important because it indicates a more advanced form of atrophic changes associated with conditions such as age-related macular degeneration (AMD).

Understanding this threshold clarifies the significance of the chosen answer: 175 μm marks the transition into what is considered geographic atrophy. Lesions smaller than this threshold, like those measured at 100 μm or 150 μm, would not meet the criteria for this classification, as they are indicative of earlier stages of retinal damage and do not reflect the full extent of atrophy that impacts visual function significantly. Thus, recognizing the specific cutoff point is crucial for accurate diagnosis and management of conditions involving geographic atrophy.