Comparison of retinal histomorphology following laser photocoagulation using 577 nm subliminal micropulse laser versus 577 nm laser in pigmented rabbits

Abstract

Background Studies showed that 577 nm subliminal micropulse photocoagulation for retinal diseases is more effective and much safer than 577 nm laser, but its mechanism and sensitive target cells are still unelucidated. Objective This study was to compare the histomorphology changes of rabbit retinas following 577 nm subliminal micropulse excitation and 577 nm laser for retinal photocoagulation and offer a conference for the clinical application of 577 nm subliminal micropulse excitation. Methods Twenty-six Chinese pigment rabbits were randomly divided into normal control group (2 rabbits), 577 nm laser photocoagulation group (6 rabbits) and subliminal micropulse photocoagulation group (18 rabbits), in which the rabbits from subliminal micropulse photocoagulation group were subgrouped into 9%, 12% and 15% subthreshold photocoagulation groups according to the different workload rates, and retinal photocoagulation was performed based on grouping.No treatment was carried out in the normal control group.Fundus camera and OCT were obtained after photocoagulation, and the rabbits were sacrificed to prepare the specimen of eyeball wall.Hematoxylin and eosin staining was employed to examine the histopathological change of choroid and retina under the light microscope. Results The retinal morphology was normal on the fundus color photography and OCT in the normal control group.Obscure of retinal structure and slight edema of retinal neuroepithelial layer with obscure of retinal pigment epithelium (RPE) was found respectively in the 9% and 12% subthreshold photocoagulation group, and serious edema of retinal neuroepithelial layer with local RPE elevation was visible in the 15% subthreshold photocoagulation group.The laser spot was invisible in various subliminal micro pulse groups.However, retinal photocoagulation spots, multifocal elevation of retinal layer and serious detachment of retinal neuroepithelium were found in the 577 nm laser group.Retinal histopathological examination revealed that the photoreceptors, bipolar cells and retinal ganglion cell (RGC) layers were normal, while choroidal vessel deformation and bleeding were visible in the 9% and 12% subthreshold photocoagulation groups, and only photoreceptor membrane swelling was seen in the 15% subthreshold photocoagulation group.However, retinal structure abnormality was displayed in 577 nm laser group, including the structural disorders of inner and outer nuclear layers and RGC layer as well as thinning of RPE layer. Conclusions 577 nm micropulse laser under threshold is sensitive for RPE and choroid rather than retina neurepithelium, which can play a treating role and also does not damage retina seriously.However, 577 nm laser photocoagulation results in retinal structure damage. Key words: Laser coagulation; Pigment epithelium of eye/surgery; Retina/pathology; Subthreshold diode laser micropulse; Rabbits