Anna Brouwer

Prolonged cone b-IT in relation to retinal layer analysis Discussion This study illustrates an association between an abnormal retinal function as measured by ERG, and a difference in retinal thickness on OCT. We observed that eyes with a prolonged cone b-IT, had differences in thickness in the retinal layers which correspond to the bipolar cells, i.e. a thinner IPL and a thicker INL. However, the correlation between the implicit times and thickness was weak and other factors, such as age and uveitis activity, were also correlated to the observed differences in thickness. Therefore, the prolonged cone b-IT is probably multifactorial and a change in thickness can only partly explain the observed differences. This study is to our knowledge the first that investigated the thickness of specific retinal layers in uveitis in relation to retinal function as measured by the ERG. The thickening of the INL in uveitis could be due to subtle intraretinal edema or inflammatory deposits. One can speculate that this impairs phototransmission and therefore results in a prolonged cone b-IT on the ERG. The thinner IPL may indicate a loss of cells, which may lead to permanent damage and possibly even retinal atrophy. Changes in retinal thickness in eyes with a prolonged cone b-IT were also observed in other layers than those which contain the bipolar cells. Except for the OPR, most layers were thickened. This is contrary to many retinal dystrophies where a loss of function is associated with a thinning of retinal layers, indicating a loss of cells. 16 In line with previous reports we observed a weak andmostly negative correlation between age and retinal layer thickness. 17,18 Interestingly, in the INL the correlation coefficient was positive for the inner regions, but negative for the outer regions. This indicates that for the inner regions of the INL, age may be a confounding factor in the current study. Age also affects implicit time, but differences in age cannot fully explain the observed prolonged cone b-IT because uveitis affects the implicit time more than age alone. 5 Future research is necessary to investigate if anatomical or functional changes can be first observed in uveitis. To answer this question, OCT and ERG measurements have to be repeatedly done from the very first start of uveitis symptoms. Preferably, cone ERGs should be recorded with an extended protocol, because the prolonged cone b-IT is often best detected at lower stimulus strengths than at the standard light adapted 3.0 stimulus flash. 5 Several studies compared the thickness of retinal layers during the active phase of uveitis to the thickness in the inactive phase, but these did not investigate the ERG. Because a prolonged cone b-IT is associated with a more active uveitis, 5,6,19 some comparisons with literature can be made. 103 4