Choyce's postulate.
The recently published intraocular lens standards from the American National Standards Institute (ANSI Z80.7) contain a reasonable standard for haptic diameter in section 3.10.1.2. The exception to this is fixed-length anterior chamber tripod lenses, which comprise a distinct category for which no realistic or practical standard is feasible. In accordance with the geometric properties of triangles, such tripod lenses have incorporeal haptic diameters and present special fixation problems that do not exist with either tetrapod or flexible lenses, so their continued use should be minimized.
D006801:Humans; D007910:Lenses, Intraocular / Q000009:adverse effects / Q000592:standards*; D055095:Optics and Photonics