Abstract
Purpose: :
To describe changes in the optic disc after panretinal photocoagulation (PRP) using ocular coherence tomography (OCT, Zeiss) and Heidelberg retinal tomography (HRT II, Heidelberg) imaging.
Methods: :
This is a prospective pilot study (IRB #100209, The George Washington University) of six patients (n=10 eyes) that underwent PRP for proliferative diabetic retinopathy in 2003–2005. Optic nerves were examined with HRT II and OCT imaging prior to initiation of PRP, at follow up laser sessions, and at three and six month visits when available as performed by technician. Each eye received PRP laser in the Diabetic Retinopathy Study described technique based on clinical need determined by the clinician. Laser treatment was performed with either an argon green or 532 nm frequency doubled diode laser and slit lamp delivery using 200 micron spot size and Rodenstock lens over three sessions. Analysis of imaging involved comparing all available parameters from optic nerve scans obtained before and after PRP.
Results: :
HRT II scans showed a mean retinal nerve fiber layer thickness (MRNFLT) of 0.203mm (SD 0.088mm) before treatment, and significantly decreased mean MRNFLT of 0.129mm (SD 0.087mm) after initiation of PRP using the minimum thickness measured before and after treatment (difference –0.075mm, p = 0.031, two tailed, paired student T–test). OCT demonstrated a mean cup to disc (C/D) ratio of 0.418 (SD 0.298) before treatment and a significant increase to mean C/D 0.753 (SD 0.323) after treatment (difference +0.335mm, p = 0.050, two tailed, paired, student T–test). These changes are measurable within 6 months of beginning PRP and occur at different times in the course of treatment for different patients. Other optic nerve imaging parameters did not show an apparent significant change with treatment including cup, disk, and rim measures in this sample population. There was significant variability between individuals preventing an apparent positive correlation with the number of laser spots to the amount of retinal thinning seen. It appears that there was no significant difference.
Conclusions: :
This is the first report of OCT and HRT II measured changes in the optic nerve after PRP. Imaging with OCT demonstrated a significant increase in C/D ratio while HRT II showed a significant decrease in retinal nerve fiber layer thickness following PRP for proliferative diabetic retinopathy. Other measurements available from OCT and HRT did not show an apparent trend.
Keywords: optic disc • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • diabetic retinopathy