eye-sos.com: Programs of Diagnostic

Programs of Diagnostic

DIAGNOSTICS

In this section we will examine in more detail the functioning only two (active) of 8 parts incorporated into the diagnostic programs system – “THRESHOLD/LABILITY TEST” and "CRITICAL FREQUENCY OF FLICKER FUSION TEST".

The strategy of the performed physical therapy treatment using VCKprof and VCKuser system is based on the analysis of the diagnostic indications of two very important and informative tests which are “THRESHOLD/LABILITY TEST” and "CRITICAL FREQUENCY OF FLICKER FUSION TEST" (hereinafter T-L and CFFF).

Despite the fact, that these diagnostic tests are subjective diagnostic methods, they allow to obtain overall and rather reliable characterization of the condition of entire visual analyzer, from the retina photoreceptors to the cerebral cortex.

The data obtained as in the process of the diagnostics by T-L and CFFF tests allows to evaluate the progress of the effectiveness of the performed therapeutic procedures. This is basic data used for determining physical parameters of the administered treatment.

THRESHOLD/LABILITY Diagnostic Test

Human visual organ is intended for the perception of light; however, visual sensations can be obtained with the stimulation by other physical factors: by mechanical, chemical agents and by the electric current pulses, which is the universal stimulant of living tissue, and its intensity, frequency and pulse duration can be easily regulated.

Under the effect of current pulses by order of several tens of microamperes (uA) on the human eye light sensation in the form of very weak colourless or bluish flashes, called the electrical phosphene, are generated.

The minimum current required for the stimulation of the electrophosphene is defined as the threshold of the electrical sensitivity of retina (TESR).

The results of numerous experimental works and clinical data revealed that TESR characterizes the functional condition of internal retina layers, i.e. the layer of its ganglion cells. It is known that the value of TESR correlates with the total area of pathologic scotomas in the visual field: the greater the area of the visual field loss, the higher the threshold of electrophosphene and the lower the electrical excitability of retina. The threshold current at which barely noticeable light flickers are generated depends on the frequency of the current pulses, for example, at 20 Hz minimum current is required for stimulation of electrophosphene in the eye.

With a smooth increase in the current frequency there comes the moment, when one ceases to sense electrophosphene. This moment is defined as the critical frequency of the disappearance of electrophosphene flickers, and it is the indicator of the functional condition of the axial (central) beam of optic nerve. The critical frequency of the disappearance of electrophosphene (lability) depends on the current and has the hyperbolic nature (see Tab. 1).

At the intensity of pulse current which is 3-4 times higher than threshold intensity (250-300 uA), the critical frequency of the disappearance of electrophosphene reaches maximum values – 50-55 Hz (in rare cases in healthy person this value reaches 60 Hz).

Tab. 1. Dependence of the electric lability level on the current

The numbers on the curve denote the ratio of the current to its threshold value (according to E. N. Semenovskaya, 1963)

In healthy persons, the value of TESR varies in the range of 35-80 uA, while the critical frequency of the disappearance of electrophosphene (lability) is 40-55 Hz. Individual differences are relatively small. The lowest TESR and highest electric lability (EL) are observed at the age of 20-25.

In children aged from 6 to 15, the indices of TESR are higher, while EL is lower, which can be attributed to the yet imperfect development of neurovisual apparatus on the one hand, and to the fact that these tests are subjective and require clear estimation of the subject sensations. During the examination, general somatic-psychological condition of a person is important: his excitability or retardation, tiredness, the level of wakefulness.

Tab. 2 Measurement of the electrical sensitivity of the eye

The measurements of the electrical sensitivity of the eye are taken under the conditions of mesopic illumination (10-15 lx) after the preliminary 10-minute adaptation of the patient. We used a bipolar electrode which looks like a pen with two insulated poles. The patient holds the electrode by the positively charged end, and touches his skin on the upper eyelid (from the side of the temple) with the negatively charged end of the electrode. Both eyes of the patient are closed.

Using electrical stimulator, we applied U-shaped pulse current with fixed frequency of 4 Hz or 10 Hz. The duration of stimulating current pulses is 10 ms. Current intensity grows automatically until the patient notices the appearance of light flickers. The rate of the current augmentation remains constant. The minimum value of current, at which the patient perceived the appearance of phosphene in the eye for the first time, is recorded. The procedure is repeated several times in order to refine the value of TESR. Then the active electrode is located on closed upper eyelid of the patient (from the side of the nose) and the entire measurement procedure is repeated.

Degree of change of a threshold of electric sensitivity and electric lability
Change	TESR, (uA)	EL (Hz)
Norm	35-80	40-50
Insignificant	80-100	39-35
Moderate	110-180	34-30
Significant	181-250	29-25
Rough	>250	<25

The table 3 shows the interpretation of the increase of TESR and corresponding decrease in the level of the functional condition of the cells of retina internal layer, which changes with different ophthalmic pathology.

When developing this diagnostic procedure (1989), we have examined 1556 healthy persons and 587 patients with different ophthalmic pathologies, and revealed that normal difference of TESR in case of nasal and temporal localization of the electrode does not exceed 10-20 uA (13,5±1,5 uA) which is well within the limits of a measurement error. The same result of comparison was obtained in patients with myopia, cataract (without the pathology of eyeground), and involutional macular dystrophy. In patients suffering from glaucoma of different degree, partial atrophy of the optical nerve of vascular genesis, neuritis of optical nerve and macular edemas we observed a firm increase in the difference of TESR measured at two opposite points of the eyeball. The difference could vary from 25 uA to 260 uA.

In patients suffering from descending optical nerve atrophy in case of optico-chiasmatic arachnoiditis, and affection of visual centres due to the craniocerebral injury, the difference of TESR measured at two points of the eyeball did not exceed 15-20 uA. In these cases EL was substantially lower.

The second part of the measurement procedure using electric current includes determination of the critical frequency of flicker fusion of electrophosphene. The value of threshold current is 2-4 times increased (but not higher than 800 uA), and is maintained constant during the testing process. Pulse repetition frequency is gradually increased from 1 to 60 Hz (average pulse duration is 50%) until the patient ceases to sense the flickering of electrophosphene in the eye.

The critical frequency of flicker fusion of electrophosphene is defined as EL. The results of this test are also refined during the second measurement and the final value is recorded. Under any localization of the electrode on the eye, EL changes only within the measuring error range (1-3 Hz) which is the indicator of the functional condition of optical nerve in general, and of its axial beam in particular.

Thus, in cases when the decrease of EL values is observed and no significant difference of TESR is detected on the inner and outer part of the eye, descending optical nerve atrophy can be primarily diagnosed. If the difference of TESR measured under the electrode localization in the opposite angles of the eye exceeds 20 uA, then the hypothesis about the disorder of impulse conduction on the nerve fibres at the retina level is articulated.

The method of characterization of the functional condition of retina and optical nerve using electrophosphene is quick and pathognomonic for the detection of retina and optical nerve disorders. It can be especially useful in the cases of eye optical media opacity. Taking into consideration the information obtained in the process of electrical diagnostics one can immediately determine the direction for the further examination of the patient and conduct preliminary selection for the prescription of the proper treatment.

CRITICAL FREQUENCY OF FLICKER FUSION (CFFF) Diagnostic Test

The minimum frequency of flickers, at which the impression of continuous light emerges, is called the critical frequency of flicker fusion (CFFF). CFFF gives the possibility to generally characterize the condition of the entire visual analyzer from the retina photoreceptors to the cerebral cortex. According to the numerous studies and long-term clinical practice, premature change of CFFF is observed if any part of the visual-nervous system of the eye is affected. Therefore, the importance of the exploration of CFFF in the ophthalmologic practice is highly conceivable.

According to the data of neurophysiologic research, CFFF index is determined by the properties of the superior divisions of the visual analyzer. Recently, great achievement was made in the field of research of the fine mechanisms of information processing in the cerebral cortex at the level of the activity of separate neurons. The receptive fields of the neurons of striatal cortex in the central section of the visual field emit higher spatial frequencies than on the periphery.

The objective method of CFFF research is a study of the critical frequency of the reproduction of the light flickers rhythm in the induced visual potentials (see Fig. 4), which reflect the varied activity of the brain, associated with perception and analysis of afferent signals. The reproduction of the light flickers rhythm occurs predominantly in the cortical projection zones, which correspond to the region of the visual field below 15º. Foveal projection zone makes a basic contribution to the reproduction of the rhythm of light flickers.

This agrees well with the morphological data about the structure of the visual analyzer cortex section: the relatively small part of the retina has disproportionately large cortical representation. The magnification factor of the macular zone is 60%. This is determined by the fact that each cone of the central retina zone has its bipolar and ganglion cell. In contrast to this many peripheral photoreceptors converge with the small number of bipolar cells, which in their turn contact with an even smaller quantity of ganglion cells. High resolution ability of the central region of retina, which ensures a good visual acuity and the low resolution ability of its periphery are the direct consequence of such interrelations of nerve cells.

The relatively larger area of the cortical region which is the medium for reproduction of the light flickers rhythm can account for the fact that in patients with the medium damage of the suprachiasmic region of the visual tract no disturbances of the critical frequency of the rhythm reproduction are observed. An insignificant decrease is noted in similar patients only in the case of severe damage which is accompanied, for example, by cortical blindness.

The frequency of the reproduction of the light pulses rhythm is one of the indices of the functional condition of visual analyzer, its formation is usually completed by the age of 15. No substantial changes of CFFF in the older children were detected in comparison with adult patients.

Table of the testing estimation CFFF
Change	GREEN	BLUE	RED
Norm	47 (52-42) Hz	47-44 Hz	42 (46-39) Hz
Insignificant	43 (45-39) Hz	40 Hz	39 (42-37) Hz
Moderate	38 (40-35) Hz	36 Hz	36 (38-35) Hz
Significant	33 (35-30) Hz	32 Hz	32 (34-29) Hz
Rough	< 30 Hz	< 29 Hz	< 28 Hz

Tab. 4 In this table there is the frequency gradation which corresponds to the changes of the condition of the visual analyzer. In brackets the first value refers to young people and the second one - to older people

A number of researchers indicate the expressed effect of illumination, angular dimensions and brightness of the presented object, its location on the retina projection, spectral composition of light, duration and depth of stimuli modulation, and stimuli number in case of repeated presentation on the results of CFFF research. It was established that not all retina sections are equally sensitive to the flickering light. For the central retina zone, CFFF is higher than for the periphery. In the researches different standards for this function are represented. Thus, according to the majority of the authors, CFFF for the foveal region is 40-55 Hz, CFFF for the parafoveal region grows to 55-60 Hz, and on the extreme periphery it decreased to 35-40 Hz.

The estimation of CFFF is a simple, quick and safe testing method; that is why it found extensive application in ophthalmologic practice. The results of a number of researches demonstrate the perspectives of its application for studying color data processing in the visual analyzer in humans.

The CFFF results allows to detect both rough, extensive changes in the photoreceptor complex and fine, early-stage ones which are not yet associated with the structure damage, but only indicate essential dysfunction. The decrease of CFFF below the threshold value indicates the presence of pathology. Out of the total number of patients suffering from dystrophic pathology of eyeground (macular dystrophy, peripheral chorioretinal degeneration, hypertonic retinopathy, partial optical nerves atrophy) CFFF indices were lowered (30,8±0,6 Hz и 31,1±0,7 Hz) compared to the normal indices (43,5±0,6 Hz). CFFF indices are considerably lower in case of retinopathies of different type.

Thus, CFFF values in case of diabetic and hypertonic retinopathies were 28,4±0,5 Hz and 29,2±0,8 Hz, and 22,7±0,3 Hz, 24,3±0,2 Hz, correspondingly. The lowest CFFF indices were observed in case of ischemic retinopathy (22,7±0,3 Hz, 24,3±0,2 Hz). Diabetic retina angiopathy and retinopathy are frequently associated with the onset of pyo-inflammatory processes in soft tissues. CFFF for cases of diabetic retina angiopathy, retinopathy in the presence of pyo-destructive complications of lower extremities was 30,4±0,7 Hz, and for the cases of uncomplicated diabetes mellitus CFFF was 39,5±0,5 Hz.. According to N.N. Pivovarov, lower CFFF indices were observed in cases of proliferating diabetic retinopathy (32±2,6 Hz); compare with cases of diabetic angiopathy (42±1,5 Hz) and diabetic retinopathy (40±2,3 Hz).

According to the results of CFFF estimation, it is possible to provide general characterization of photoreceptor complex for the case of the presence of severe degenerate processes. The estimation of CFFF in patients suffering from macular dystrophy showed its decrease: 31,8±1,6 Hz and 32,6±1,5 Hz As a result of the treatment, an increase in CFFF indices was observed. In patients suffering from central involutional chorioretinal dystrophy CFFF before the treatment was 27,85±6,78 Hz; while after the treatment it increased by 16,2% and reached 32,36±6,8 Hz. CFFF indices in case of idiopathic preretinal fibroplastic syndrome on the average were 40 (32-45) Hz, which by 2,5 units below the norm (N = 45-50 Hz).

According to V. S. Ponomarchuk et al., in the research of the consensual activity of the sensory and oculomotor system of the eyes, in patients with high-degree myopia the indices of CFFF decreased to 35,3±2,5 Hz (CFFF in healthy persons was 41,2±2,0 Hz). In patients suffering from refraction amblyopia a 27% decrease of CFFF was observed. The performed correlation analysis revealed direct correlation between the indices of the pulse mobility frequency and visual acuity, and thresholds of the activity of fovea-afferent tract.

Electrophysiological indices play an important role in the complex diagnostics of the diseases of visual neuron (optical nerve). The results of examination of patients suffering from optical nerve neuritis and atrophies show that CFFF is a fine indicator of nerve fibers conduction abnormalities. As long as conduction of nerve fiber remains adequate, its functions are not impaired, and CFFF remains within the limits of norm. CFFF drops as soon as there is even the smallest deterioration in the nerve fiber conduction.

In case of inflammatory damage of optical-neural tract, the dysfunction of CFFF is manifested earlier than the dysfunction of other visual functions, and its function is restored to the normal condition somewhat later than others. CFFF is considerably decreased to 12-28 Hz, moreover, a decrease of CFFF is observed at the very onset of the disease with the yet normal visual field. The parallelism is observed between the manifestation of changes in the visual acuity and the degree of CFFF decrease, i.e., the higher is optical nerve conduction abnormality and the lower is visual acuity, the lower is CFFF; and between CFFF and color sensation: in the cases of CFFF decrease, the color sensation is for the most part also impaired. With the long-term process dynamics, CFFF steadily grows but restoration to the normal indices is not observed even provided complete restoration of the visual field and visual acuity.

In case of atrophic processes in the optical nerve, the values of CFFF are generally lower than in case of inflammatory processes, even with the same visual acuity, which indicates deeper and more severe damage of the optical nerve fibres, as well as the severity of a disease and its lower reversibility. In patients with the acute postneuritic optical nerve atrophy CFFF in the course of the prescribed treatment grows in accordance with the improvement of visual acuity.

Early diagnostics of the partial optical nerve atrophy when the complete damage of the nerve fibers did not occur has great significance. First of all, in this case the highly differentiated function of the visual analyzer, linked with the functioning of macular region, is impaired. Significant reduction in the foveal photosensitivity is observed and direct dependence between the degree of reduction of the latter and the manifestation of atrophic processes in the optical nerve is revealed.

The data about the change in the thresholds of color sensation with the partial atrophy of optical nerve are a clear sign and have great practical value in complex diagnostics of this pathology. The interrelation between the manifestation of atrophic processes in the optical nerve and the limits of the visual field is revealed. All the efforts of ophthalmologists should be directed towards the prevention of the nerve fibers atrophy.

Thus, in the treatment of the partial optical nerve atrophy of different genesis by the methods of trans-cranial laser-therapy it is possible to highly improve visual functions and their stability with the subsequent improvement within the long-term periods of monitoring. The effectiveness of laser-therapy methods was evaluated according to CFFF results, which increased from 26,9±1,06 Hz to 32,2±1,12 Hz; from 27,8±1,14 Hz to 31,6±1,18 Hz [3].

Major difficulties were associated with diagnostics of retrobulbar neuritis, i.e. optical encephalitis of orbital, intracanalicular, chiasmic and tractal localization, since diagnostics for these types of neuritis is determined based on the results obtained using functional research methods: decrement in visual acuity, presence of central scotomas and peripheral defects, significant changes of color thresholds. Predominant increment of thresholds to the short-wave part of the visible spectrum is a special feature to be emphasized.

The impairment of color sensation is directly proportional to the decrement of visual acuity. In patients who had retrobulbar neuritis, pathologic process in the optical nerve has chronic subacute nature. We should emphasize the fact of the generalization of pathologic process to the contralateral clinically safe optical nerve in patients with unilateral retrobulbar neuritis which can be regarded as a sign of the dissemination of the demyelinating process within the vision system. In patients suffering from multiple sclerosis optical tracts are always involved into the pathologic process.

The measurement of CFFF is specifically recommended for early diagnostics of retrobulbar neuritis, since the visual neuron disease is one of the most severe and serious encephalitis, which can lead to irreversible blindness or to the loss of the ability to work. Even insignificant delay in diagnostics can lead to the irreversible dystrophic changes in the visual neurons.

Measurement of CFFF allows to reveal predominantly early abnormalities of the function of papillomacular bundle and corresponding higher divisions of visual analyzer. Special attention should be given to the measurement of CFFF in case of glaucoma. According to N.N. Pivovarov, in case of initial compensated glaucoma, CFFF to the experimental colours did not differ from CFFF in healthy persons. In case of developed glaucoma, CFFF was lower than in healthy persons and reached 28-32 Hz for red and 22-27 Hz for green. Inveterate glaucoma was characterized by the greatest decrease of CFFF which dropped to 16-24 Hz for red and 12-17 Hz for green. In this case specific correlation between the visual field contraction ratio, a manifestation of the optical nerve excavation and a decrease of CFFF was observed, i.e. the more contracted was visual field and the more manifested was excavation phenomena, the lower was CFFF.

Visual acuity in the examined patients varied from 0,1 to 1,0 (in the majority of cases within 0,5-1,0). No direct dependence between the degree of decrement of visual acuity and CFFF was observed. In case of nearly absolute glaucoma, CFFF could not be measured due to low visual acuity. The dependence of macular zone CFFF on the degree of glaucomatous atrophy of the optical nerve is determined.

The impairment of temporary summation in case of glaucoma is, first of all, the indicator of atrophic changes in the neural network of internal retina layer and the axons of ganglion cells. The essential method of functional diagnostics in case of visual-neural system abnormalities is a research of the visual field using CFFF test, especially when other procedures do not allow to perceive such changes in the visual field, which could be reference points for determining topical diagnosis.

The transscleral measurement of photosensitivity thresholds using regulated diascleral radioscopy and modulated CFFF offers new prospects of exploring functional integrity of periphery and centre of the retina with the transparent and opaque optical media. In case of the opaque optical media, CFFF below 14 Hz indicates degradation of the retina functions to the light-sensation and the unfavourable visual result of eye surgery. The transscleral measurement of CFFF on the separate quadrants allows to approximately determine the integrity of the visual field in case of the opaque optical media.

The results of CFFF research demonstrated the involvement of retina and optical nerve in patients suffering from endogenous and postoperative iridocyclite, which allows to regard them not only as the uveal tract pathology, but also as vitreoretinal disorders. In case of myopia, proved dependence between the degree of eyeground changes and CFFF and the absence of direct correlation between the CFFF values and the value of myopia are observed. This data indicates the fact that research of temporary summation provides additional information for the estimation of the functional integrity of papillomacular bundle in case of myopia. According to N.N.

Pivovarov and V.K. Zhdanov, in case of central serous retinitis (with high visual acuity of 0,8-1,0) CFFF is nearly normal (35-38 Hz). Similar data are obtained also for the case of the retinal detachment. The authors observed a decrease of CFFF to 32-34 Hz only in patients with the "cystifrom" retinal detachment and the decrement of visual acuity to 0,04-0,06. The recorded fact of an insignificant decrease in case of central serous chorio-retinitis and retinal detachment indicates stronger dependence of this phenomenon on the conductivity of the second and third neurons of the visual analyzer, than on the damage of the neuroreceptors.

In the early stages of papillary stasis, CFFF reveals absolute parallelism with other visual functions; in the later stages, when the visual-nerve fibers conduction abnormalities occur, CFFF allows to detect more extensive changes in the visual field, than it is possible using multiple pattern perimetry. Significant fluctuations of visual acuity in the forth stage of edema can be attributed to the fact that in the period of inflammatory process recession in a number of patients some nerve fibers are restored, which were previously depressed, but not affected by atrophic changes.

However, subsequently, as a result of the growth of gliose tissue the nourishment of the visual fibers deteriorates again, which leads to the progressive worsening or degradation of visual functions. Color sensation is most vulnerable in the 4-th stage of inflammatory optical nerve disk edema.

Electrophysiological parameters of the optical nerve and retina function in many respects depend on the severity of the case with postcontusional damages of the visual organ. The research of CFFF in persons with injury revealed firm reduction of CFFF index for the damaged eye (22,2±11,1 Hz) in comparison with that of the healthy eye (33,4±1,4 Hz). In patients with different postcontusional retina changes aged from 9 to 75, the results of CFFF measurements allowed to detect such changes, especially initial ones, which could not be detected by conventional diagnostic methods, and to differentiate retina abnormalities and optical nerve changes.

CFFF was considerably lowered, especially in case of central retinal holes, despite high visual acuity. In case of Berlin’s disease, postcontusional retina swelling and partially in case of retinal hemorrhages, CFFF changed insignificantly and was practically restored to the norm ((40-43 ± 0,5) Hz) when the patient was discharged from the hospital, whereas in case of maculal holes, choroids, and preretinal hemorrhages it remained in effect lowered to the level, which was observed at the patient’s admission ((29-35 ± 0,15) Hz). This, in the opinion of the authors, can be attributed to the fact that in case of the latter forms of postcontusional changes both inner and outer retina layers are affected. This damage has irreversible character.

The measurement of CFFF is a functional research method. In persons with the chronic vibration injury of the optical nerve (under the influence of more than 15 year vibration), the PMFairment of color sensation, equally frequent for all colours is observed (green, red, dark blue). This pathology is distinguished by the slow development of pathologic process and stage of the optic nerve disk atrophy in particular, which can protract for several years even after the vibration stimulation is done. With the extended duration of the vibration stimulation in parallel with the contraction of the visual field limits CFFF also decreases, especially CFFF to red light. The visual field becomes concentric and, as a rule, has persistent character.

The research of CFFF can be used for refined estimation of changes in the visual analyzer, which are stipulated by the effect of various loads. CFFF is a value which characterizes the condition of the visual-neural system of the specific individual under certain conditions. It is used in a number of physiological and hygienic researches aimed at the determination of the degree of the visual fatigue in persons engaged both in physical and mental activities. Thus, for instance, CFFF is the informative criterion for performance and fatigue evaluation in seamen, pilots, human controllers of nuclear and radar stations, astronauts, and transport drivers, and it can be used for determination of the degree of labour intensity for the work-rest scheduling.

Thus, being a fine and sensitive method of research of the functional condition of the visual-neural system CFFF reflects even insignificant deterioration in the papillomacular bundle conduction, and allows to detect, in essence, early abnormalities of corresponding highest divisions of the visual analyzer.

The procedure of CFFF determination is convenient and illustrative as the means of the control of treatment effectiveness. CFFF-based clinical studies of the retina and pathways pathology are promising in view of the selective detection of the neuron structures damage, responsible for the appearance of CFFF. Further studies in the course of the solution of the problems of ophthalomology will be substantially associated with the electrophysiological methods of research which allow more refined approach to the study of the pathophysiological mechanisms underlying both functional retinal abnormalities and organic retinal pathology.

[Fyodorov S.N., Brutskaja L.A., Pivovarov N.N., Kuman I.G., Okovitov V.V., Krutov S.V.]