Protection of the eyes
“That the eyes have to be protected from the strong winds to avoid trachoma is known to all aviators for quite some time, and this protection has been reached with our pilot glasses in a satisfactory way. Less commonly known is the strong influence of radiation to the eye. Within the spectrum of sunlight we’ll find rays that appear to be very bright while others remain unseen and nevertheless can harm the eye. Aviators to whom these blinding rays appeared uncomforting have protected themselves with a variation of colored glasses. Scientific research has proved that even though these were capable to minimize the brightness they let the harmful rays pass through yet.”
Source: Bundesarchiv-Militärarchiv- Freiburg RM 3/8970 Reichsmarineamt, Dienstvorschrift, Einflüsse des Fliegens auf den menschlichen Körper und medizinische Ratschläge für Flieger, Januar 1918