On the cause of disability glare and its dependence on glare angle, age and ocular pigmentation.

BACKGROUND In the 1920s and 1930s, disability glare was a topic of great interest in the Commission Internationale de l'Eclairage (CIE). The Second World War prevented agreement being reached on a standard to quantify disability glare but the Stiles-Holladay formula was widely accepted as such. In 1983, CIE started a new effort to develop a CIE standard making use of research data published in the post-war years. METHODS A committee was formed that agreed that new data and insights justified an extension of the angular domain of a disability glare formula and allowed introduction of an age factor and allowance for ocular pigmentation. RESULTS Three disability glare equations were formulated, each for an appropriately restricted angular domain. The most general, the CIE General Disability Glare equation, covers the full angular range between 0.1 degrees and 100 degrees but for optometrists the CIE Age-adjusted Stiles-Holladay Disability Glare equation, with validity domain between one degree and 30 degrees, will often suffice. CONCLUSIONS Disability glare is due to intraocular scatter and obeys, in the one-degree to 30-degree angular domain, albeit with great individual spread, the Age-adjusted Stiles-Holladay equation: (L(veil) /E(glare))(Age-adjusted Stiles-Holladay) = 10 (1 + [Age/70](4)).1/theta(2). Quantitative examples are given of the manifestation of disability glare, particularly in traffic.