Change In Choroidal Thickness And Prognosis Of Visual Acuity After Panretinal Photocoagulation In Type 2 Diabetic Patients

As one of the most common micro-vascular complications, diabetic retinopathy usually affects people who have diabetes mellitus for over ten years and threatens patients’visual acuity tremendously. As the main stream therapy for DR, panretinal photocoagulation (PRP) is widely practiced by ophthalmologists and gains world-wide recognition for its effect. PRP guarantees enough oxygen supply for macular area by destroying peripheral retina. Traditional ETDRS photocoagulation could cause damage to retina and choroid due to its high energy and long action time, so patients may have a higher incidence of diabetic macular edema after PRP. The advanced Pascal laser system adopts an array spots model and diminishes the action time to 20ms. It not only improve the efficiency of photocoagulation, but also reduced the damage caused by laser.With the rapid development of optical coherence tomography (OCT), the delicate multiple layers of retina are clearly visible. The recently invented enhaced-depth imaging(EDI) mode made the in vivo observation of choroid possible. As the main blood supply for the outer part of retina, will it play a role in retinal vascular disease (e.g. DR)? It has been reported that patients with DR had a thinner choroid than the controls. Will there be a change in choroidal thickness before and after PRP? If so, will the change be related to visual acuity prognosis? This is the core of the present study.As objective tools to evaluate the structure and function of retina, multifocal electroretinography (mfERG) and OCT are widely used in prognosis analysis for a variety of diseases (including DR and diabetic macular edema). But no reports about PRP was found. Will mfERG and OCT be useful in predicting visual prognosis of patients receiving PRP? This is another focus of the present study.Part Ⅰ Choroidal thickness change after panretinal photocoagulation in diabetic patients Purpose:To investigate the changes in choroidal thickness in the macular and photocoagulated areas of patients with diabetic retinopathy after panretinal photocoagulation (PRP) using enhanced-depth imaging optical coherence tomography (EDI-OCT).Methods:Patients with severe non-proliferative diabetic retinopathy (NPDR) or early proliferative diabetic retinopathy (PDR) who needed PRP were included in this study. Choroidal thickness (CT) in the macula and the photocoagulated area was measured with EDI-OCT at baseline, one month, and three months after PRP.Results:The mean subfoveal CT increased significantly at one (318.0±76.4μm, P<0.001) and three months (317.4±75.3μm, P<0.001) post-PRP when compared to baseline (307.2±70.7μm). The mean CT in the photocoagulated area decreased significantly from 227.5±45.0μm to 206.9±41.1μm (P<0.001) at one and 206.0±41.4μm (P<0.001) at three months post-PRP. Unlike the mean change in CT or patients’ systemic conditions, only BCVA and foveal thickness before PRP were statistically significantly correlated with the mean change in BCVA after PRP.Conclusions:In patients with severe NPDR or early PDR, the mean choroidal thickness increased significantly in the macular area and decreased significantly in the photocoagulated area after PRP. The results might reflect a redistribution of choroidal blood flow following PRP, which may be critical for retinal metabolism.Part Ⅱ Prognisis of visual acuity after panretinal photocoagulation in diabetic patientsPurpose:To investigate the prognostic value of multi-focal electroretinography (mfERG) and optical coherence tomography (OCT) in diabetic eyes receiving pan-retinal photocoagulation (PRP).Methods:Patients with severe non-proliferative diabetic retinopathy (NPDR) or early proliferative diabetic retinopathy (PDR) who needed PRP were included in this study. MfERG and OCT data were recorded before PRP, while the final best corrected visual acuity (BCVA) was recorded at 6 months following PRP. The 1-3-6 mm ETDRS macular grid was superimposed over the mfERG hexagonal pattern. For each area of the 9 sectors, the responses from the corresponding hexagons were summed for analysis. The correlation between pre-PRP data and post-PRP BCVA was analyzed using Pearson’s correlation analysis and multivariate linear regression analysis.Results:Among the 42 eyes included,31 eyes (73.8%) had improvement or remained stable in visual acuity while 11 eyes (26.2%) had deterioration in BCVA. The final BCVA was significantly correlated with the amplitude and latency of mfERG in all nine sectors, and the amplitude had a stronger correlation than latency. The foveal photoreceptor inner and outer segment junction (IS/OS) and the external limiting membrane (ELM) status, as well as the retinal thickness in most sectors, were also correlated with the final BCVA. In a multivariate linear regression model, age, pre-PRP BCVA, amplitude of mfERG in the central sector and foveal IS/OS status were significantly correlated with the final BCVA. The retinal thickness was found to be correlated with the amplitude or latency of mfERG in some sectors, and the correlation was tighter in temporal and inferior sectors, especially in the outer ring.Conclusions:A lower amplitude of mfERG and disrupted foveal IS/OS status were significantly correlated with a worse visual prognosis in diabetic eyes after PRP.In summary, the present study found that choroidal thickness in the macular area increased after PRP while choroidal thickness in the photocoagulated area decreased. Though not directed related to change in visual acuity, the shift of blood distribution induced by PRP might be a perquisite for healthy retinal metabolism. The information about retinal structure and function provided by mfERG and OCT played a role in visual prognosis after PRP. Among those various indicators, the amplitude of mfERG and foveal IS/OS status were the most valuable.