Researchers found four fundamental parameters could be considered as diagnostic signs to characterize all stages of PMD, including subclinical disease:

1.  An inferior flattening island, defined as the flattening area surrounded by steep areas inferior to the horizontal axis.
2. An apple-shaped pattern formed by mean power area as a yellow strip.
3. Superior flattest area, defined as the presence of the flattest area at the superior quadrant.
4. Against-the-rule irregular astigmatism (flat meridians at 45-135 degrees).

Additionally, the investigators noticed that measuring the extent of the inferior flattening island could be helpful for staging PMD and could be considered a characteristic sign of early PMD.

Based on these parameters, investigators were able to differentiate 36 cases of PMD from keratoconus.

“Four main topographic signs including inferior flattening island, apple-shaped pattern, superior flattest area and against the rules astigmatisms can be considered as diagnostic signs for PMD,” the researchers wrote in their ARVO abstract.