Felix Schmeidler,1985

Interpretation of solar-limb light-deflection measurements
Schmeidler, F.
Abstract
Optical and radio measurements of the gravitational deflection of light from stars at the solar limb are compiled in tables and compared. It is pointed out that the radio observations are in good general agreement with the deflection (1.75 arcsec) predicted by relativity theory, but that the optical measurements tend to be significantly higher. This difference is attributed to the fact that the strongest optical deflections are measured in stars too close to the limb for radio determinations to be made. A second term decaying as 1/r squared (or as 1 over a higher power of r) is proposed for the deflection equation, and the possibility that this term is due to a solar effect, as suggested by Bouet (1980 and 1982), is considered.
https://ui.adsabs.harvard.edu/abs/1985AN....306...77S/abstract

Zur Interpretation der Messungen der Lichtablenkung am Sonnenrand
Astronomische Nachrichten (ISSN 0004-6337), vol. 306, no. 2, 1985, p. 77-80. In German.
http://articles.adsabs.harvard.edu/pdf/1985AN....306...77S