Poster Dongkyu Lee

To investigate the effect of repeated subthreshold micropulse laser photocoagulation (STMLP) on the retina. We performed varying repetitions of 10, 50, 100 and 200 times of STMLP in normal pigmented rabbit eyes using a 577-nm diode laser with spot size of 100 um (not Separated in a 3×3 pattern scan), power of 100 mw, duration of 0.02 ms (duty cycle, 15%). Before STMLP, spectral domain optical coherence tomography (SD-OCT) was performed. At 1, 2, 3 and 4 weeks, fluorescein angiography (FA) and SD-OCT were performed each time. Tissue effects at intervals after treatment were determined in sections of the retina by histologic staining. Immediately after STMLP, there were no obvious laser scars affecting the treated area in any laser sites of the rabbit eyes on colour image or SD-OCT. FA showed hyperfluorescence after more than repeated laser photocoagulation of 50 times, but no obvious change after at 10 times. One week later, no areas of hyperfluorescence were detected in all cases. However, thickening of the photoreceptor layer, especially the outer segment was noticed on histologic sections. This change was maintained until after 4 weeks. Despite the transient hyperfluorescence on FA and no changes on SD-OCT, the repetition of STMLP resulted in irreversible histologic change. We presume that the change was attributed to heat accumulation. Further studies should be proceeded to validate the safety and action mechanism of repeated STMLP.