In vivo Effects of Macular and Peripheral Laser Treatment on the Retinal Morphology Observed by Polarisation Sensitive Oct (PS-OCT)

Abstract

Purpose: : To image macular and panretinal laser effects on the retinal pigment epithelium (RPE) and their healing response over time in vivo in patients with diabetic macular maculopathy/retinopathy using PS-OCT.

Methods: : Fifteen patients underwent either panretinal (PRP) or grid photocoagulation due to diabetic retinopathy. Photocoagulation was performed using a semi-automated patterned scanning laser system (PASCAL®) providing a raster of effects of homogeneous intensity. At baseline, day 1, week 1 and in monthly intervals until month 3, the characteristic retinal morphologic changes at the level of the RPE following the laser tissue interaction were imaged and the specific intra-retinal healing process followed over time. A PS-OCT prototype was used allowing detection, mapping and measuring the RPE-changes based on their specific polarisation scrambling qualities.

Results: : After one day, the intra-retinal photocoagulation lesions were sharply delineated from the surrounding unaffected retina while RPE changes were rather subtle. In each lesion an intra-retinal traction of the inner retinal layers into the direction of the RPE and a loss of photoreceptor cells (PRL) was seen above all at week 1. At that time, the outer plexiform layer (OPL) was adjacent to the coagulated PRL. Further, there was an augmented area of polarization scrambling layers in each single lesion which could be due to a scarring reaction at the RPE level. During follow up, the intra-retinal traction forces decreased leading to a flattening of the inner retinal layers, whereas the outer layers showed a progression of scar formation in PS OCT.

Conclusions: : PS-OCT is a valuable imaging tool for visualizing RPE changes secondary to retinal laser treatment over time. Due to the RPE's characteristic properties of scrambling polarized light, PS-OCT revealed specific morphologic changes of the outer retinal layers undetectable by spectral domain OCT.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • laser • lesion study