Anna Brouwer

It is probable that some of the subgroups of our heterogeneous uveitis population have a better chance of improvement of the ERG, while other subgroups may be more prone to deteriorate. Further research is necessary to investigate if it would be possible to predict which patients are fortunate enough to improve regarding their retinal function. Correlations between the ERG (retinal function) and OCT (retinal structure) In Chapter 4 we investigated possible correlations between a prolonged cone b-IT and the thickness of different retinal layers. We analyzed optical coherence tomography (OCT) scans that were made on the same day as the ERG. Using the software program “Iowa Reference Algorythms”, 5–7 the thickness was calculated of ten retinal layers of the nine regions of the Early Treatment Diabetic Retinopathy Study grid. We hypothesized that differences in thickness between eyes with and without a prolonged cone b-IT were most likely to be present in the layers that contain the bipolar cells or the synapse between the photoreceptor and bipolar cell i.e.: the inner plexiform layer (IPL), the inner nuclear layer (INL) and the outer plexiform layer (OPL). We observed that the IPL was thinner, whereas the INL was thicker in eyes with a prolonged cone b-IT compared to eyes with a normal cone b-IT. We observed no differences in the OPL. However, the correlations between the individual implicit times and thickness of these layers were weak. Also, several clinical parameters (vitritis, FA score, and age) were weakly correlated to retinal layer thickness. Therefore, differences in retinal thickness alone do not fully explain a prolonged cone b-IT. The thickening of the INL may be due to subtle intraretinal edema or inflammatory deposits. This may impair the phototransmission and thereby result 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 to retinal atrophy. We also observed differences in the thickness in other layers, as well between non-uveitis eyes and uveitis eyes with and without a prolonged cone b-IT. These differences in thickness consisted mostly of a thickening of the layers in uveitis eyes with a prolonged cone b-IT, except for the outer segment photoreceptors/retinal pigment epithelium complex layer (OPR), which was thinner. The findings in Chapter 4 illustrate for he first time a correlation, albeit a weak one, between retinal function and retinal structure. Further research is necessary to evaluate if changes occur first on the ERG or on OCT, or if they occur simultaneously, and if changes on these tests can be used for prognosis and treatment decisions. 162 Chapter 8