CHAPTER 7: General Discussion

The results that have been presented show that, in electroretinography, the maximal b-potential varies with age, sex and refraction. The variations in the individual case are large, despite a high degree of standardization of the method of examination. In 1947-1967 inclusively, the ERG was recorded at the Eye Clinic, Karolinska Sjukhuset, in about 10,000 patients, using the method described by Karpe (1945). The advantage of this case material is that it is large, and that the b-potential has not been appreciably influenced by the small modifications which the method has undergone during this period (Karpe 1948, 1962). A prerequisite for analysis of such a large material with a reasonable expenditure of work was utilization of the computer technique. The results of these ERG recordings and data from the case records were stored on magnetic tape. By means of a special retrieval programme, eyes with a given diagnosis could be sorted out, and the data presented in the form of a punched card. In order to analyze these data on eyes with pathological changes, a normal material was required. Zeidler (1959) presented, from the material then available at the Eye Clinic, Karolinska Sjukhuset, 411 normal eyes (229 male and 182 female). Altogether 138 had a pathological change in the fellow eye, the reminder being from normal pairs of eyes. No definite difference was found between the b-potential of the right and left eye. In the calculations, both eyes were used as independent cases. Of the 182 female eyes 141 belonged to women with both eyes normal. Of the 229 male eyes, 132 belonged to men with both eyes normal. The present investigation, which was carried out from the spring of 1964 to the spring of 1968, was made with the object of obtaining a larger and more uniform normal material. The criteria which an eye had to fulfil in order to be regarded as normal were stricter than is customary. Only four diagnoses of the fellow eye were admitted; they are listed in Table 2. The first was retrobulbar neuritis in which it was stated in the case record that, at a check-up 1 year later, the disease had not involved the fellow eye as well. For this reason, only 20 of 45 eyes in men could be used, and 14 of 20 in women. For the same reason,