Mohammad Reza Jafarinasab - Ophthalmic Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Mohammad Ali Javadi - Ophthalmic Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Sare Safi - Ophthalmic Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Mohammad Hassan Babaei - Ophthalmic Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran

Purpose: To introduce the new topographic criteria for diagnosing and grading the severity of pellucid marginal degeneration (PMD). Methods: In this case-control study, the topography patterns of patients who were referred to Cornea and refractive services of Labbafinejad Medical Center or a private clinic for refractive surgery or management ofcorneal diseases and were diagnosed as early, subclinical or clinical KCN or PMD were reviewed. Results: The topography patterns of 120 subjects were evaluated. The indices and pattern analysis showed that three fundamental parameters can be considered as diagnostic signs characterize all stages including early/subclinical PMD. These parameters included A) an inferior flattening area surrounded by steep areas, inferior to the horizontal axis (IFA), B) an apple shaped pattern, instead of the usual pear shaped pattern that is common in KCN. C) Superior flattest area (SFA), could be helpful for diagnosing of PMD. In addition, we noticed that measuring the extent of IFA could be helpful for staging the PMD. Against the rule astigmatism (flat meridians @45-135 degrees) can be considered as a characteristic for diagnosing the early stage of PMD. Based on these three parameters, 36 cases of PMD were correctly differentiated from KCN and normal corneal topography. Conclusion: Three main signs including inferior flattening, apple pattern and flattest area (quadrant superior) can be consider as the diagnostic signs characterize for PMD.