Early histological alteration of the retina following photocoagulation treatment in diabetic retinopathy as measured by spectral domain optical coherence tomography.

PURPOSE: To investigate the earliest histological changes of the retina after laser treatment of diabetic retinopathy by using Spectral domain optical coherence tomography (SD-OCT, Heidelberg Engineering, Heidelberg, Germany).
METHODS: This study examined 320 laser burns from 16 eyes of 12 patients with early severe non-proliferative diabetic retinopathy (NPDR) that underwent laser photocoagulation according to the protocol which the Early Treatment Diabetic Retinopathy Study (ETDRS) recommended. SD-OCT scan was performed before the laser treatment, then 1 hour, 24 hours, 48 hours, 72 hours and 1 week after treatment. The main outcome measure was thickness change in outer retina (OR) in the region localized to the laser treatment.
RESULTS: The alterations of retinal thickness at the location of the laser burns mainly occurred within the retinal layers that expand from the outer plexiform layer (OPL) to the outer highly reflective layer (HRL) (IS/OS). From 1 hour to 48 hours after laser treatment, the thickness of retina, from OPL to the HRL, increased with time. At 48 hours post- treatment, the increase of retinal thickness from OPL to the HRL reached a peak. At 72 hours, the thickness of retina from the OPL to the HRL began to decrease as a result of the outward migration of OPL towards the retinal pigment epithelial (RPE). At 1 week post- treatment, hyporeflectivity at the level of IS/OS and RPE atrophy was observed in the areas corresponding with the laser burns; the thickness of retina from the OPL to the HRL was essentially within normal thickness.
CONCLUSIONS: This study demonstrates the subtle in vivo imaging changes of laser lesion and the trend of earliest changes in the thickness of the retina in the level of OPL-HRL, first increasing then subsequently decreasing as shown by SD-OCT in DR post laser treatment.