Morphologic Changes in the Human Retina After Laser Treatment Using Supra and Sub Threshold Laser Energies Imaged by SD-OCT

Abstract

Purpose: : To evaluate the morphologic changes in retinal structure after laser photocoagulation using supra- and subthreshold energies.

Methods: : Ten patients with proliferative diabetic retinopathy (PDR) or central retinal vein occlusion (CRVO) received scatter laser photocoagulation using a semi-automated patterned scanning laser system (PASCAL, Optimedica). Adjacent to the upper or lower vessel arcades a study area was created. In this area 2x2 pattern laser spots were applied with halving the flux of the laser energies in a stepwise manner starting from an individually selected energy producing the typical grayish lesions. The study areas were than imaged at day one, three and seven, than at month one, two and three using color fundus photography, autofluorescence (AF), infra read (IR) imaging and spectral domain OCT (SD OCT; Spectralis OCT, Heidelberg Engineering).

Results: : The starting suprathreshold energy lesions were well visible in all patients immediately after laser application and throughout the follow up period with both, color fundus photography, IR and AF and showed characteristic changes on OCT. The halved flux laser burns (first step) were funduscopically undetectable during the laser session, but during the follow up were often detectable on IR and AF images and sometimes on fundus photography as well. On OCT they showed similar changes as the supra threshold laser scars, but were much smaller in diameter. The 3rd and 4th steps of the flux halving showed no changes during the laser treatment or at the follow ups on any of the imaging modalities.

Conclusions: : Subthreshold laser burns with halved energy flux produce similar morphologic changes in the retina as suprathreshold energies but with a lesser extent. Energies below this range show no signs of morphologic changes detectable with OCT, autofluorescence, infrared or color fundus photographic imaging.

Clinical Trial: : www.clinicaltrials.gov NCT00682240

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