The reciprocal value of the focal length of an optical correction, by which the eye can sharply depict an object at infinite distance without effort (accommodation). This process is also known as an eye test or determination of visual acuity. The determination of visual acuity is part of every preliminary examination. It is used to determine the patient’s condition and to assess the progress of the examination.
The ophthalmologist or optician determines the distance correction and, if necessary, the near addition for reading, also called addition. There are two different practices for this examination.
SUBJECTIVE MEASUREMENT (PHOROPTER)
The subjective measurement is based on the patient’s statement as to when an image is in focus. This can be done with refractive glasses (oculus) or by means of electronic examination (phoropter).
By means of the phoropter we can precisely determine the current visual acuity of the patient.
The objective measurement is carried out with a refractometer or a skiascope, without the patient’s assessment.