With the composite term normal variation ( English normal variant ) is in the medicine all referred to what a comparable population does not occur usually, but only in a smaller part. The word is made up of “norm” in the sense of an agreed or specified standard ( norm value ). Everything that is present or found in a high percentage in healthy people is referred to as normal. It also includes the term “variant” in the sense of a “different design”, “variety” or “modification”.
A standard variant is therefore usually a slight, physiological or anatomical deviation from a condition or finding defined as a standard without a pathological background, which is still within a tolerance that can be regarded as “normal”. In this case, the differential diagnosis a process to identify and of normal variants. Also, the boundaries between normal variation and pathological findings are not always clearly defined.
Examples from ophthalmology
In a broader sense, a standard variant can also represent a regular, physiological deviation from an ideal form declared as the standard. An example of this are the refraction ratios of the human eye. Here the state of emmetropia and perfect right-sightedness is considered “normal”, but is only actually achieved by a fraction of people. Marginal deviations with the result of a slight ametropia without a pathological background and negative effects on the individual are the predominant reality here. The same applies to orthophoria and heterophoria in connection with the position of the eyes as well as to a manifest, slightly different pupil width of the right and left eye. In the sense of a statistical distribution, the norm variant becomes the standard.
- Chapter "Norm variants" in Reinhard Rossdeutscher: Thorax - Handbuch diagnostic radiology , 2003, pp. 65-73; SpringerLink .
- Fabian Sommer: Anatomical Variants of the Paranasal Sinuses , Dissertation 2009 .
- Bergener, M. and H. Grobecker: Hypertension in old age: norm variant or illness? 10th Rothenburg Conversation 1984. Schattauer Verlag, Stuttgart. ISBN 3-7945-1017-8 .
- Short stature as a standard variant .
- Standard variants of the EEG in Emedicine (English).