Practical significance of critical fusion frequency (CFF)

The value of measuring the critical fusion frequency (CFF) as part of ophthalmological diagnostics is examined. The relevant literature on changes of the CFF concomitant with refraction errors, media opacity, age-related macular degeneration, glaucoma and various other opticopathies is discussed regarding the relevance of CFF for the differential diagnosis. Various methods and instruments for measuring the CFF are presented. The CFF is a complex function of the visual system and changes in CFF cannot be ascribed to a specific level of signal transduction. However, measurement of the CFF is a valuable test in the clinical routine to estimate potential visual acuity in the presence of media opacity and to screen for lesions of the optic nerve. Reduction of CFF in an eye that otherwise appears normal may prompt the ophthalmologist to initiate further examination facilitating diagnosis of specific conditions, such as optic neuritis, before visual acuity is reduced. Measuring the CFF is technically simple, inexpensive and fast and can be delegated to medical personnel. Measurement of the CFF should be an integral component of routine ophthalmological examinations.