Non-corneal electroretinogram. Parameters in normal children.

In the investigation of suspected visual disorders electroretinography (ERG) is of considerable clinical value. The ERG is usually recorded from a contact-lens type of electrode placed over the cornea. Although this is possible in co-operative adults using only local anaesthesia, the placement of a contact lens electrode in a young or retarded patient is usually not tolerated without a general anaesthetic. Because of the obvious disadvantages of requiring general anaesthesia for such a test procedure, a method was developed in this department at the beginning of I968 to record the ERG from an electrode placed between the eyes on the bridge of the nose. The ERG recorded from such an electrode is of small amplitude but can be easily distinguished from larger amplitude background activity using 'averaging' techniques with the aid of a computer. The combined potential change from the retina of each eye is recorded unless one eye is covered during stimulation. This technique has been used as part ofa combined neurophysiological testing procedure in which the ERG, the cortical visually evoked response (VER), and the electroencephalogram (EEG) are simultaneously recorded (Harden and Pampiglione, I970). This combined approach, which gives information about the level of suspected visual impairment, may be used in babies and young children who are unable to co-operate. No sedation is necessary and where possible the test is carried out in the waking state, with the eyes open. There are few publications on the normal ERG parameters and usually each laboratory determines its own criteria ofnormality with its own techniques (Jacobson, 196 I). However, because ofsome doubts as to the reliability of results using non-corneal electrodes in clinical work, the normal range ofERG parameters recorded with our technique is reported in the present paper.