Objective: To investigate the correlation between clinical grading in plus scale and quantified relative afferent pupillary defect (RAPD) using the neutral density filter bar.
Material and Method: This was a prospective analytical cross sectional study. Sixty-nine patients of any ocular disease with relative afferent pupillary defects were prospectively examined. The RAPD was graded twice in each patient by the clinical grading plus scale (grade 1+ to 4+) and then by using a neutral density filter (NDF) bar. Patients with an abnormal pupil or had been dilated with medication were excluded. Both clinical grading of RAPD and quantified RAPD by the NDF bar were performed by the same physician. All patients were tested by the same technique. Statistical analysis was done to compare the results of both methods.
Results: The RAPD grading by the clinical plus scale correlated significantly with the grading by the neutral density filter bar, (p < 0.05). The four clinical grades had corresponding values in the neutral density log unit: grade1+ < 0.6 log unit (94.7%), grade 2+ = 0.6-0.9 log unit (85%), grade 3+ = 1.2-1.5 log unit (88.3%), grade 4+ > 1.8 log unit (84.6%).
Conclusion: The results of the two methods of grading RAPD using the plus scale and the neutral density filter bar are comparable. Each grade had a corresponding value in log units. In a clinical setting where neutral density filter bars are not available, the authors can grade RAPD using the plus scale.

Keywords: Relative pupillary defect, Pupillary light reaction, Neutral density filter, Swinging flashlight test, RAPD grading