Distinguishing between KCN and PMD is easy in advanced cases, but at early stages, differentiation between the two entities is not so easy.So the purpose of current study was to introduce triads signs for the early diagnosis of pellucid marginal degeneration (PMD).

We reviewed the topography of 120 patients who were referred with a primary diagnosis of KCN or PMD. The cause of referral was obtaining a second opinion for diagnosis and management.

•After analyzing different parameters and indices, we concluded that three findings could be considered fundamental in the diagnosis of PMD. •Based on these parameters, 36 cases of PMD were correctly differentiated from KCN. The most important finding in this group was inferior flattening surrounded by steep areas, inferior to the horizontal axis, which created an apple shaped pattern . The third finding was ATR astigmatism. (Defined as the presence of steep meridians in the horizontal quadrants).

Three cardinal signs of 1)Inferior flattening 2)Apple pattern 3)ATR astigmatism (flat meridians @45-135 degrees) were characterized for diagnosis of the PMD ,even in early stages.