Inner Nuclear Layer Thickness, Metamorphopsia, and Tangential Retinal Displacement
American Journal of Ophthalmology, September 2018
Metamorphopsia is a common early feature of macular diseases such as central serous chorioretinopathy, age-related macular degeneration, and epiretinal membrane (ERM). In a retrospective clinical study, Ichikawa et al. looked at inner nuclear layer (INL) thickness in relation to metamorphopsia and tangential retinal displacement in ERM. They found INL thickness to be a useful biomarker for metamorphopsia, as well as an indicator of tangential retinal displacement in ERM.
The study was a consecutive interventional series of 50 patients (50 eyes) who received surgery for ERM. M-charts were used to measure metamorphopsia. Measurements of INL thickness, outer retinal layer (ORL) thickness, and distances between the intersections of 2 sets of retinal vessels were obtained from Spectralis optical coherence tomography (Heidelberg Engineering) and infrared images.
Outcomes of interest were correlations of INL and ORL thickness with M-chart scores and retinal displacement distances.
The authors noted strong correlations between preoperative INL thickness and the metamorphopsia scores obtained preoperatively and 3 months postoperatively. Moreover, INL thickness at baseline and its change from baseline to 3 months correlated significantly with vertical retinal displacement observed 3 months postoperatively (both p < .001). Neither preoperative nor postoperative ORL thickness was found to correlate with preoperative or postoperative metamorphopsia scores.
Therefore, the authors proposed the utility of INL thickness as a biomarker for the degree of metamorphopsia both before and after ERM surgery. Their findings suggest that changes in the inner retinal layer, which cause distortion of Müller cells, play a large role in the development of metamorphopsia, thus providing further evidence that Müller cells function as optical fibers in the retina. However, the precise mechanisms by which retinal layer shrinkage generates metamorphopsia have not been determined.
Even when ERM surgery is successful, many patients will experience aniseikonia and metamorphopsia afterward. Hence, the authors recommend exploration of more efficient ways to correct irregular positions of retinal Müller cells.
The original article can be found here.