<p>Usually nodal, principal and focal points are defined independently and thought of as distinct structures with no simple relationship among them. By adopting a holistic approach, in which these threetypes of cardinal points are treated as particular cases of a larger class of special points, this paper develops a method of constructing the locations of the cardinal points of a system graphically directly from the transference. The method provides a useful way of visualising the relationship of the locations of the cardinal points and of how they are affected by changes in the system or when a second optical system is placed in front of the first. Thepaper illustrates the graphical procedure by apply-ing it in several situations of interest in optometryand ophthalmology, including the effect of a contact lens or refractive surgery on a reduced eye and the effect of accommodation, a spectacle lens and an afocal telescope on the Gullstrand-Emsley<br />schematic eye. (S Afr Optom 2011 70(1) 3-13)</p
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