Methods for measuring the critical frequency of light flashes

Physiological rationale. Critical fusion frequency is the maximum frequency of flashes of light, which is perceived by the subject as separate flickering. Going beyond this boundary leads to a feeling of solid light.
Equipment required for research. There are numerous ways to measure CFFF. I will focus on the method of using the neurochrometer, mentioned earlier.
The study procedure. CFFF can be measured by increasing the frequency of flashes (from small to large) and reducing the frequency of flashes (from large to small). The second method gives a slightly smaller scatter of the received data. In the study on the neurochronometer, the subject is presented with light flashes of a rectangular shape with a frequency of 7 to 60 Hz. At the time of flicker fusion, the subject responds with the word "together." In the reverse order of presentation of flashes of light, the moment of the appearance of individual flickers of the subject signals the word "separately."
The first attempts to determine the lability are considered trial ones. 10 subsequent attempts have a diagnostic value (separately for merging and splitting). The measure of lability is considered the arithmetic average between the frequency of fusion and the frequency of appearance of individual flickers.

Critical flicker fusion frequency (CFFF) - represents the minimum frequency of flashes of light, which is accompanied by a feeling of continuous uniform glow. If the flickering occurs at a low frequency, the person sees separate flashes of light. As the frequency of flickers increases, a flickering sensation is created. By increasing the frequency of flashes in this way, a picture can be obtained when individual flashes of light are perceived by the eye as continuous light. The determination of the critical frequency of flicker fusion is performed to assess the state of the visual pathways and the functional lability of the retina. Research fields: ophthalmology, neurology, psychiatry. Indications for the study Diagnosis of diseases of the retina and optic nerve - atrophy of the optic nerve, diabetic retinopathy. Diagnosis of amblyopia, glaucoma, myopia and hyperopia of a high degree. The method for performing the Patient is asked to look at the flickering light source and tell the doctor when the light will become permanent for him, not jerky, flickering. The frequency with which flashes are delivered at the time indicated by the patient is estimated as the critical flicker fusion frequency. Modern equipment allows you to explore CFFF not only for white, but also for blue, red and green. To obtain accurate test results, repeat the test three times for each eye. Normal indicators CFFF Norm CFFF for a healthy person - 40-46 Hz. A decrease in CFFF occurs as the body ages, the elderly rarely exceed 38–40 Hz. The magnitude of CFFF in two healthy eyes is usually the same, the maximum difference is 5-8 Hz. Within the same field of view, the CFFF indices are not the same: on the periphery in the nasal and temporal regions they are 10–15 Hz higher than in the region of the macula. State, accompanied by a change CFFF critical flicker fusion frequency is reduced in the pathology papillomacular beam (it processes of nerve cells that are in the optic nerve from yellow retinal spot to the brain): ischemia of the optic nerve, optic neuritis, optic nerve atrophy, multiple sclerosis, glaucoma . In order to carry out a detailed diagnosis, the results of the determination of CFFF are supplemented with data of kinetic or static perimetry (determination of the boundaries of the visual field). The CFFF index below 30 Hz is a sign of defects in the visual field. If the visual pathway of one eye is damaged to the level of chiasm (intersection of the visual pathways at the base of the brain at the level of the Turkish saddle), then the CFFF of only one eye is disturbed. If the visual pathway is damaged at the level of the chiasm or the higher parts of the brain, then the deviations of the CFFF from the norm are fixed in both eyes.
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