Table 1: The 1-2-3-Rule for Corneal Ulcer Severity Classification [16].

Potentially Sight Threatening (PST) – ANY ONE of the following must be present:

  1. Cells ≥ 1+ in the anterior chamber (10 cells or greater in a 1-mm beam)
  2. Dense infiltrate ≥ 2 mm in size in greatest linear dimension (by slit-lamp light measurement)
  3. Edge of infiltrate ≤ 3 mm from the center of cornea (by slit-lamp light measurement)

Rarely Sight Threatening (RST) – ALL of the following must be present:

  1. Cells < 1+ in the anterior chamber (< 10 cells in 1-mm beam)
  2. Dense infiltrate < 2 mm in size in greatest linear dimension (by slit-lamp light measurement)
  3. Edge of infiltrate > 3 mm from the center of cornea (by slit-lamp light measurement)