|Year : 1969 | Volume
| Issue : 2 | Page : 41-47
Electroretinographic studies in normal Indian population
S.R.K Malik, AK Gupta, PC Gupta
Department of Ophthalmology, Maulana Azad Medical College and Associated Irwin and G. B. Pant Hospital New Delhi, India
|Date of Web Publication||8-Jan-2008|
Department of Ophthalmology, Maulana Azad Medical College and Associated Irwin and G. B. Pant Hospital New Delhi
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Malik S, Gupta A K, Gupta P C. Electroretinographic studies in normal Indian population. Indian J Ophthalmol 1969;17:41-7
|How to cite this URL:|
Malik S, Gupta A K, Gupta P C. Electroretinographic studies in normal Indian population. Indian J Ophthalmol [serial online] 1969 [cited 2019 Sep 23];17:41-7. Available from: http://www.ijo.in/text.asp?1969/17/2/41/38420
Karpe introduced electroretinography as a clinical procedure. The increasing use has been helped by the rapid development of electronics in recent years. These have made it possible for the measurement and interpretation of the retinal potentials to be placed on a sound clinical basis. Apart from its use in physiology, electroretinography is proving of value in retinal affections where the diagnosis has not been established or is uncertain.
Dhanda conducted E.R.G. studies in normal Indian population. Subsequently, he published his data Gn the diagnostic and prognostic values of electroretinography in cases of night blindness, vitamin A deficiency, retinitis pigmentosa, cataract, glaucoma, myopic degeneration, hypertensive and vascular retinopathies.,,,,,. He used electrocardiographic equipment with the necessary modification for the purpose of recording ERG. Gokhale and Lamaye reported ERG findings in various diseases without commenting upon its normal value.
In the present study, we undertook the determination of ERG values for normal Indian population which could be utilized as a standard for comparative purpose. At present in the literature no figures of statistical significance are available and whatever work has been reported has been done with less sensitive equipment.
The present study has been conducted on a much sensitive and modern equipment and on a large scale to be of statistical value and with stimuli of different wavelengths.
| Methods and material|| |
400 eyes of 200 normal cases were investigated. These cases were selected from those attending the Eye O.P.D. of Irwin Hospital for various minor ailments such as trachoma, mild conjunctivitis, errors of refraction not exceeding + 2.5D. A detailed fundus examination was carried out under full mydriasis and only those cases having normal fundus picture were taken up for ERG investigation. A clinical examination was carried out to rule out the presence of any systemic disease in the patients.
The cases were selected at random from the various age groups of both sexes as shown below:
| RECORDING EQUIPMENT, TECHNIQUE AND CONDITIONS|| |
The recording equipment, technique and conditions have been discussed fully earlier (Malik, Sood and Gupta).
| Equipment|| |
The equipment consisted of Ahrend Von-Gogh nv 6 channeled electroretinograph [Figure - 1] manufactured upto the recommendations made at the first symposium of the ISCERG Light source used for stimulus consisted of a diffuse surfaced xenon filled stroboscope capable of stimulating both the eyes simultaneously. The electroretinographic set up is shown in [Figure - 2].
| Conditions|| |
By the method of trial and error it was observed that the following recording conditions of the machine :md the patient gave the best results.(Malik et a1)
Time Constant- 0.03 seconds.
Calibration - 200 micro-volts.
Light intensity- 1.8 mega-candles.
Speed of paper - 1.5 cm. per second.
Distance of light from patient's eyes- 30 cm.
Interval between the two successive stimuli- 15 seconds.
Semi-dark adaptation:- 30-45 minutes
Complete dark adaptation:- 10 minutes.
Sedation: - Nil
Pupil:- Dilated with phenylepbrine.
The patient was made to sit in a semi dark room for 45 minutes. Phenylephrine 10% and lignocaine 2% were instilled 4-5 times into each eve during this period to get dilatation of the pupil and topical anesthesia. Patient was explained the procedure going to be performed on him to ,,,et his maximum co-operation during the investigation and to allay his apprehension.
The patient was made to lie on a comfortable mattress table. Two indifferent electrodes were put on the cheeks just below the infra-orbital margin one on each side with the help of bantonite paste. The electrode for earth was placed in the midline on the forehead. The direct electrode was placed on the anesthetized cornea with the help of contact glass [Figure - 2],[Figure - 3]. To make a better contact, the space between the cornea and the contact glass was filled with normal saline through a fine polythene capillary tube. The light source was adjusted at a distance of 30 cms. from the root of the nose, keeping in consideration that both the eyes got equal amount of light stimulus.
The light of the room was switched off. ERG was recorded after 10 minutes of complete dark adaptation with white, red and green light stimuli. The successive stimuli were given at an interval of at least 15 seconds. Critical fusion frequency (CFF) was determined objectively. [Figure - 7],[Figure - 8]. After record of the ERG the contact glasses were removed and an antibiotic ointment was put in the eyes.
| Observations|| |
Observations have been summarized in [Table - 2],[Table - 3],[Table - 4]. The E.R.G. patterns obtained with white, red and green stimuli are shown in [Figure - 4],[Figure - 5],[Figure - 6].
The ERG potentials have been expressed in micro volts and the CFF in rate of stimuli per second.
| Discussion|| |
Since the introduction of electroretinography as a clinical procedure in ophthalmology by Karpe in 1945, the subject has been taken up with great interest and zeal all over the world. The new dimensions and parameters are under study in the laboratories equipped with the most modern machines. However ERG values in normal Indian population with a modern equipment are not yet available.
We have carried out electroretinographic studies on 400 normals of both sexes and of various age groups, as shown in [Table - 1]. ERG was recorded simultaneously in both the eyes. No difference of statistical importance was encountered in the potentials of the various components of the electroretinogram in the two eyes. Therefore the findings on the two eyes have been merged together and the mean values have been described and discussed.
We elicited a deep a-wave to the tune of 63-100.2 micro volts, followed by a large b-wave in the range of 259.8 - 350.4 micro-volts in the electroretinogram obtained with the white light stimulus in the dark adapted eyes. In the scotopic ERG studied by Dhanda, he did not get an a-wave. This could be due to the difference in the intensity of stimulus light used. If the intensity of stimulus light is below the cone threshold, a-wave can be absent. Many other workers Euzeire Passouant and Cazaben Cobb and Morton Burian Mahaneke Rendahl Burian and Spivey Jacobson Hirose and Popkin and Algvere have also elicited a large a-wave in the dark adapted eyes with the use of stroboscope as the light source for stimulation.
The b-wave amplitude of the ERG as obtained by us, falls in the range as reported by other workers. Karpe (1945), Jacobson and O'Brien and Dhanda,, The average values obtained in Indian population does not vary much as compared to other figures.
The amplitude of various waves of the electroretinogram elicited by different types of stimuli, i.e. white, red and green are shown in [Table - 2]. The a-wave potential showed the mean value of 81.6, 11.3 and 50.2 micro volts. The b-wave potential showed a mean value of 130.3, 305.1 and 340.8 micro volts as elicited b v red, green and white stimuli respectively. Holmgren as early as 1865, reported that the potentials vary with the colour of the stimulating light. The wave length of the light which appears most bright to the eye are also most effective in the production of electrical potentials. Adrian, too found decreased b-wave of the scotopic ERG elicited with red stimulus and increased b-wave with blue and green stimuli. The diminution of a and b-wave amplitude in the electroretinogram elicited by red light appears to be on account of decreased light intensity caused by the interposition of red filter.
On analysis of male and female cases separately the b-wave amplitude was found to be higher in females as compared to males which is in agreement with the findings of Vainio Matila and Karpe,,. Vainio Matila explained the increase of ERG values in females on account of the small size of the eyeball which brings the direct electrode closer to the retina giving a better leading off and a better conduction.
Study of ERG recordings in various age groups, showed that the b-wave potential was higher in the age-group of 15-24 years and 25-34 years and lower in the age groups of 35-44 years and 45 years and above. Karpe, Rickenbach and Thomassen found lowered b-wave amplitude in the older age group which he explained on account of lenticular sclerosis. Henkes believed it to be due to vascular sclerosis. Dhanda reported b-wave amplitude as 168, 260, 320 and 290 micro volts in the age groups of: below 7 years, 7-15 years, 10-40 years and above 40 years respectively. He studied cases below the age of 7 years under general anesthesia. We have not taken cases below the age of 15 years into consideration in the present study on account of invariable presence of disturbances due to their non-cooperation in absence of any sedation.
The value of critical fusion frequency in our study ranges between 31.8 to 44.8 stimuli per second. Spilberg (1944) defined the C.F.F. as a phenomenon where in an eye stimulated by intermittent light stimuli, a kind of ripple 'is observed on the electroretinogram which on reaching a certain flicker frequency disappears and a smooth line is recorded on the electroretinogram. Babel and Monnier attached significance to C.F.P. value when they emphasized that it was affected adversely in diseases of the macula. Our C.F.F. values are slightly lower to those reported by Euziere et al who found 48-56 stimuli per second in normal individuals.
| Summary|| |
400 eyes of normal Indian population have been studied on electroretinography with white, red and green stimuli. The critical fusion frequency has been determined objectively.
In electroretinograms elicited with white light, a-wave fell in the range of 63 to 100.2 micro volts and b-wave in the range of 259.8 to 350.4 micro volts.
The mean value of C.F.F. was 38.3 stimuli per second. The ERG potentials have been analysed and discussed in the two sizes and the various age groups.
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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6], [Figure - 7], [Figure - 8]
[Table - 1], [Table - 2], [Table - 3], [Table - 4]