|Year : 1969 | Volume
| Issue : 2 | Page : 48-51
E. R. G. in myopia
S.R.K Malik, AK Gupta, PC Gupta, G Singh
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, Singh G. E. R. G. in myopia. Indian J Ophthalmol 1969;17:48-51
Clinically three varieties of myopia are known - developmental, simple and pathological. In the case of developmental myopia, the child is born with an abnormally long eye and the degree of myopia is about 10D. The condition is non-progressive. In case of simple myopia the disease manifests itself in early childhood and gradually progresses till the child stops growing in height. The degree of refractive error is usually limited to about 6 D. (Duke Elder - 1954). The pathological myopia, too, appears in early childhood but progresses more rapidly and is associated with degenerative changes in the vitreous, choroid and retina. However the ophthalmoscopically visible fundus changes may not be necessarily comparable with the degree of myopia, for they may be marked when the myopia is relatively slight and absent when it is gross. It often becomes difficult, therefore, to differentiate between simple and progressive myopia in many cases, without a sufficient follow up. The present study has been undertaken to investigate if E.R.G. can help us in differentiating between simple and pathological myopia in their earlier stages.
| Methods and material|| |
80 eyes of 45 cases of both sexes of myopia of varying degrees were examined electroretinographically. The cases were selected from those attending the eye O.P.D. of Irwin Hospital, New Delhi. The number of eyes in various grades of myopia have been shown in [Table - 1]
Recording Technique and Equipment: The investigation was carried out on the Ahrend Von Gogh-nv 6 Channeled Electroretinograph manufactured upto the recommendations of the I.S.C.E.R.G. (1961). A diffuse xenon surfaced stroboscope of high light intensity was used for the stimulus, which was kept at a distance of 30 cm. from the patients' eyes. [Figure - 1] and [Figure - 2] (p. 42).
The recording conditions and technique have been described fully previously (Malik et al 1968). The same conditions and technique have been employed in examining these patients.
Observations: Can be subdivided into the following groups:
Group 1 Cases with degenerative changes in the fundus.
Sub-Group la - Less than 8 D of Myopia - 4 eyes
Sub-Group 1b - More than 8 D of Myopia - 39 eyes
All the eyes in both these subgroups had subnormal E.R.G. response.
Group II Cases with normal fundus picture.
Sub-group Ila - Less than 8 D of myopia
lla1- Normal E.R.G. response 13 eyes.
IIa2 Subnormal E.R.G. response - 12 eyes.
Sub-group IIb -More than 8 D of myopia
- IIb1 - Normal E.R.G. response - 8 eyes
- IIb2 - Subnormal E.R.G. response - 4 eyes.
The pattern of normal and subnormal E.R.G. responses obtained in these patients is shown in [Figure - 1],[Figure - 2].
The normal values utilized for comparison with the present study are as follows:
| Discussion|| |
From the above observations it is evident that all the eyes with degenerative changes in the fundus irrespective of the degree of myopia showed a sub-normal ERG response. The degree of depression in the ERG response went on increasing with rise in the degree of myopia, as shown in [Table - 5]. In cases with normal fundus, irrespective of the degree of myopia, two types of ERG response were observed-normal or subnormal. The decrease in the potential was observed both in the b-wave as well as a-wave. It was observed that 32.4% of the eyes with subnormal response had myopia of less than 8 D, while 21.6% of the eyes with normal ERG response had myopia of more than 8 D. Karpe (1945) reported subnormal response in three out of four eyes with high myopia. Francois and DeRouck (1954) observed depressed b-wave in 75% of the cases of high myopia, while a-wave showed a variable response. Franceschetti, Dieterle and Schwartz (1960) found reduced b-wave potential in the scotopic ERG. Jayle and Boyer (1960), however, believed that photopic ERG is affected earlier than the scotopic system. Except Francois and DeRouck (1954) who mentioned that E.R.G. changes preceded the ophthalmoscopic changes in degenerative myopia, none of the above mentioned workers concentrated on E.R.G. pattern in early stages of pathological myopia where ophthalmoscopic changes had not yet manifested. It is a common experience, in the absence of degenerative changes it is impossible to draw a distinct line of demarcation between the two types. That is why we wish to lay more emphasis on the E.R.G. pattern in cases of myopia without ophthalmoscopical evidence of degenerative changes in the fundus because in such patients there are no other means, clinically to decide whether the myopia is simple or pathological and therefore electroretinography assumes a very important investigative role. 32.40/6 of the eyes in the present study where the degree of myopia was less than 8 D without any degenerative changes in the fundus would have been classified as cases of simple myopia. However, the subnormal ERG response in these cases shows that they probably belong to the group of degenerative myopia and are likely to progress. Further in 8 eyes where the degree of myopia was high (1OD-18D) and though without degenerative changes in the fundus it would have been difficult for anybody to predict the course of the disease. However, the presence of normal ERG response helps us in deciding that these cases are not likely to progress and deteriorate. These cases are being further followed up to draw definite conclusions.
It can be concluded, therefore, that the present concept of differentiating simple myopia from pathological myopia on the basis of degree of myopia and fundus changes alone needs rationalization on the basis of ERG response.
| Summary|| |
80 myopic eyes of various degrees have been investigated electroretinographically.
The presence of depressed ERG response in cases of myopia of less than 8 D and having normal fundus and normal ERG response in cases of myopia of more than 8 D having normal fundus, have been emphasized.
The importance of ERG investigation in forecasting the course of the disease has been stressed.
| References|| |
Duke Elder S: The Practice of Refraction: Churchill & Company, London P: 78 (1954).
Francois J & DeBouck A: Bull Soc. beige ophtal, 107:303, (1954).
Franceschetti A, Dieterle P and Schwarts A: In Electroretnographia (Symposium, Luhacovice, 1959) P. 247-252. Purkyne Brne. (Acta Fac. med. Univ. Brunesis, 4) (1960).
Jayle G. R. and Boyer R. L.: In Electroretinographia (Symposium, Luhacovice, 1959) P 263-272. Purkyne Brne. (Acta Fac. med. Univ. Brunesis, 4) (1960).
Karpe G: 1945, Acta Ophth. (Kbh.) Suppi. 24 P. 73-75 (1945).
Malik S. R. K., Sood C. C. and Gupta P. C.: 1968, E. R. G. in Primary Retinitis Pigmentosa. Accepted for publication, Oriental Arch (1908).
[Figure - 1], [Figure - 2]
[Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5]