In their recent article, “The Subject-Fixated Coaxially Sighted Corneal Light Reflex: A Clinical Marker for Centration of Refractive Treatments and Devices,” Chang and Waring review definition, application, and usage of ocular reference axes and angles as well as inconsistencies among them. A literature review is presented comparing reference axes, points, and alternative names in relation to various intraocular and extraocular reference landmarks. The authors describe the variable and, in part, conflicting definitions used in the literature and their lack of clinical applicability. Many of these definitions are adapted from textbook geometrical optics definitions for axis and rotationally symmetrical optical systems. During my career as a vision scientist these inconsistencies have led to misunderstandings and misinterpretations and left me with doubt about the full understanding of the matter on several occasions in discussions with colleagues or while researching the relevant literature. The authors dismantle this complexity and lay bare the shortcomings in an exemplary way.

Newly defined reference markers and axes for centration of refractive treatments and devices are proposed—namely, the subject-fixated coaxially sighted corneal light reflex axis and chord mu. The former provides clinical utility for refractive treatments and consistency for devices as Chang and Waring have outlined. The latter is capable of addressing issues with inconsistencies between various device technologies owing to their measurement capabilities. Inconsistencies would occur if devices capable of generating these angles (including axis location subtended at) relied either on real measurement data or on certain assumptions (ie, topographers vs comprehensive eye scanners vs imaging-based biometers). Image-generating biometers could derive a measured optical axis, whereas topographers or comprehensive eye scanners would have to make assumptions about it or use the pupillary axis.

The work by Chang and Waring has 1 significant drawback that is likely to prevent the community from adapting their new definitions. The naming is certainly correct but is very complex and hard to remember. I therefore propose to change the naming from subject-fixated coaxially sighted corneal light reflex axis to Chang-Waring axis and chord mu to Chang-Waring chord.