Anna Brouwer

Is the light adapted ERG sufficient? A disadvantage of the ERG for monitoring is that it takes quite some time to measure both a light adapted (LA) and a dark adapted (DA) ERG. This can put quite some strain on the logistics of an outpatient clinic. Recording only the LA may be sufficient for the monitoring of uveitis, because the most common and characteristic ERG abnormality that we observed in uveitis was the prolonged cone b-IT. When the DA ERG is not measured, the recording time of the ERG will be reduced with approximately half an hour. With time being increasingly important in busy outpatient clinics, this could pave the way for a routine use of the ERG, if a prolonged cone b-wave indeed proves to be the most relevant ERG parameter in the management of uveitis. Also, the burden on patients would be less. To reduce the measurement time even more, it would be interesting if LA could be excluded as well. LA is especially important when a DA ERG is measured prior to the LA ERG. But if the DA ERG is not recorded, and patients are already in a light (waiting) room, the additional value of a full 10 minutes of light adaptation can be questionable. For the multifocal ERG light adaptation is not required, 25 so it could be possible that the additional value of LA is negligible in uveitis, especially because adaptation affects amplitudes more than implicit times. Probably, a reduction of the adaptation time of the LA ERG to 5 minutes may suffice. 26 Another interesting development is a new hand-held ERG device, the RETeval. This device automatically corrects for pupil size, all electrodes are incorporated into one sticker which is placed at the lower lid, and clinics need not acquire a new set of reference values, because the manufacturer has incorporated their own reference values into the device. 27,28 Some issues still need to be addressed, not only correction for pupil size. Pupil size affects the recorded implicit times of the RETeval more than amplitudes. 29 Other factors such as age, axial length, and even gender affect the recorded implicit times of the RETeval. It may also be necessary to correct for the Stiles-Crawford effect with the RETeval. 30 These confounding effects on the recorded implicit times may be important when the RETeval is used in uveitis, because the cone b-IT was often abnormal. Despite these disadvantages, the RETeval shows a great promise, because it is hand-held, doesn’t require mydriasis, and uses a user friendly electrode, it can easily be used in crowded outpatient clinics. Although the RETeval may be more user friendly, it is not superior in its ability to record an ERG to a standard Colordome device that we used in this thesis. 168 Chapter 8