Diabetic retinopathy (DR) is the most common microvascular complication of diabetes mellitus (DM).1 In its natural history, worsening capillary nonperfusion and retinal ischemia cause progression from the nonproliferative form of the disease (NPDR) to proliferative diabetic retinopathy (PDR),2,3 which is one of the main causes of vision loss in diabetic patients.4 Another important cause of visual impairment in DR is diabetic macular edema (DME),5 which arises from the diabetes-induced breakdown of the blood-retinal barrier (BRB) and consequent vascular leakage.
The effectiveness of laser treatment in the form of panretinal photocoagulation (PRP) as treatment for PDR has been proven by large, randomized clinical trials that took place between 1976 and 1985.6–8 The rationale of the laser is to convert the ischemic retina to an anoxic state, thus reducing the intravitreal vascular endothelial growth factor (VEGF) levels and the stimulus for retinal neovascularization.9 Although PRP lowers the risk of visual loss in patients with PDR, it may be associated with complications such as visual field restriction, visual loss, retinal or choroidal detachment, and changes in the macular anatomy, which are thought to be related to the pro-inflammatory state triggered by laser.10 Most of these changes are ophthalmoscopically undetectable and need more advanced structural and functional diagnostic techniques to be recognized, such as optical coherence tomography (OCT), multifocal electroretinogram (mERG), and microperimetry.11–13
OCT angiography (OCTA) indirectly provides information about the perfusion state of the retina based on red blood cells motion within the blood vessels. This device has been extensively used to depict the macular vascular changes in eyes with DR and DME.14 Since the introduction of OCTA in the clinical practice, an increasing number of studies have investigated the macular perfusion state in patients with different stages of DR with and without DME.15,16 A review of the literature has shown that patients with PDR who underwent PRP before or during follow-up had been excluded in all of these analyses.17
To the best of our knowledge, no study has investigated whether PRP actually modifies the macular perfusion in diabetic eyes. The main aim of the study is to quantify and compare the vessel density (VD) in the superficial capillary plexus (SCP) and the deep capillary plexus (DCP), as well as the size of the foveal avascular zone (FAZ) calculated by means of OCTA in patients with PDR before and after PRP.
Patients and Methods
This clinical, prospective study, enrolling patients who presented from September 2017 to January 2018, was conducted in the Department of Ophthalmology, Miulli Hospital Acquaviva delle Fonti, Italy. The study adhered to the tenets of the Declaration of Helsinki, and patients signed a general written consent to be part of clinical research before being included in the study.
Inclusion criteria were: (1) age older than 18 years; (2) diagnosis of diabetes mellitus, either type 1 or type 2; (3) biomicroscopic and fluorescein angiography (FA) evidence of PDR. Exclusion criteria were: (1) diagnosis of any other retinal condition (eg, retinal vein occlusion, age-related macular degeneration); (2) presence of severe PDR, featuring vitreous hemorrhage or retinal detachment; (3) media opacities; (4) history of ocular surgery (including cataract surgery or anti-VEGF injections) 6 months or less before the inclusion; (5) any previous laser treatment (panretinal or focal laser photocoagulation) in the study eye. Patients who underwent anti-VEGF intravitreal injections or posterior pole laser for DME treatment during the follow-up were excluded from the study, to avoid confounding factors on the macular perfusion evaluation.
Each patient underwent a comprehensive ophthalmologic examination, including measurement of best-corrected visual acuity (BCVA) on standard ETDRS charts, dilated slit-lamp biomicroscopy, FA (Spectralis + HRA; Heidelberg Engineering, Heidelberg, Germany), spectral-domain OCT (SD-OCT), and OCTA (AngioVue XR Avanti; Optovue, Fremont, CA) at baseline. Demographic and clinical history data were also collected.
The AngioVue system's speed is 70,000 axial scans per second, using a light source of 840 nm and an axial resolution of 5 μm. Each B-scan in the OCT volume consists of 304 A-scans and is repeated twice at the same retinal location. Automatic segmentation of the retinal layers — SCP, from the inner limiting membrane (ILM) to the inner plexiform layer (IPL); DCP, from the IPL to the outer plexiform layer (OPL), outer retina (OR) from the OPL to Bruch's membrane (BM); and the choriocapillaris (CC) — is provided. Each layer is displayed along with the en face angiogram (C-scan) and co-registered with the cross-sectional OCT B-scan. The depth and width of the inner and outer boundary lines were manually changed in order to better visualize the plane of interest; patients whose OCTA quality was affected by segmentation errors were not considered for the analysis. The automatic quantification of the VD in the SCP and in the DCP was performed using the split-spectrum amplitude decorrelation angiography software.18 VD was defined as the percentage of area occupied by vessels in the foveal area and in a parafoveal ring-shaped region of interest centered on the center of the FAZ, with an inner radius of 1.00 mm and an outer radius of 2.5 mm. The FAZ area, expressed in square millimeters (mm2), and the central macular thickness (CMT) were also automatically calculated.
All patients received the first PRP session within 7 days from the baseline evaluation, using a frequency-doubled Nd:YAG pattern scan laser (Pascal; Topcon Medical Laser Systems, Santa Clara, CA), relying on a 532 nm (green) light. Retinal spot size of 500 μm, laser duration of 0.1 second, and laser intensity ranging from 200 mW to 500 mW titrated up to an evident gray burn spot, were employed. Pattern (5 × 5 or 4 × 4 array) spots were preferred, when applicable. The inferior, nasal, temporal, and superior areas were addressed sequentially; the nasal area was treated starting from greater than 1 disc diameter from the optic disk to the equator; the superior, inferior, and temporal areas from greater than 2 disc diameters from the fovea to the equator. If more than one laser session was needed to complete the PRP, the treatment was repeated two or more times within 10 days from the first treatment.
The patients were followed for a minimum of 6 months. They underwent BCVA measurement, ophthalmic examination, and OCTA at 1 month and at 6 months. FA was repeated at 6 months to assess the need for further laser treatment. During the follow-up, a new or worsened DME was defined as a worsened CMT. Statistical analysis including descriptive statistics for demographics and main clinical records, and comparative analysis were performed through GraphPad Prism 6.0 (GraphPad Software, San Diego, CA). BCVA was expressed as the logarithm of the minimum angle of resolution (logMAR). All data were expressed as mean ± standard deviation and were tested for normality using the D'Agostino-Pearson test. Repeated measure one-way analysis of variance (ANOVA) was used to highlight differences for continuous parametric variables, such as SCP, DCP, and FAZ area. Tukey correction was applied for multiple comparisons. Pearson coefficients were calculated to assess the level of correlation between variables. The chosen level of statistical significance was two-sided P value of less than .05.
A total of 18 eyes of 14 diabetic patients (11 males, 78.6%) were enrolled for the study. Mean age was 64.3 years ± 9.5 years. Patients underwent a mean of four laser treatments, with no major serious adverse events; no further treatment was required after 6 months. VA did not significantly change throughout the follow-up (P = .3), with a BCVA slightly worse at baseline (0.30 ± 0.20) compared to the visual function after 6 months (0.25 ± 0.24). The foveal and the parafoveal CMT featured a little increase after the laser treatment, albeit not statistically significant (P = .6 and P = .8, respectively). No patient was diagnosed with a new or worsened DME during the follow-up, and none received anti-VEGF injections or posterior pole laser treatment for pre-existing DME.
The FAZ area measured 0.33 ± 0.19 mm2 at baseline and 0.33 ± 0.16 mm2 after 6 months (P = .6). The foveal VD did not change either at the SCP (16.4 ± 8.0 at baseline and 16.5 ± 6.5 after 6 months; P = .4), or at the DCP (28.5 ± 8.6 at baseline and 28.2 ± 8.1 after 6 months; P = .8). Similar trends were found in the parafoveal VD at the SCP (38.4 ± 5.7 at baseline and 38.6 ± 4.5 after 6 months; P = .9) and at the DCP (46.1 ± 5.2 at baseline and 43.8 ± 5.1 after 6 months; P = .3) (Table 1). For each patient, each single OCTA parameter showed a high level of correlation across the follow-up (Supplementary Table A, available at www.Healio.com/OSLIRetina). No correlation has been found between visual acuity and VD nor at SCP nor at DCP (P > .5).
Visual Acuity, Morphological, and Optical Coherence Tomography Angiography Parameters of Patients at Baseline and During Follow-Up
According to the recommendations of the ETDRS group, PRP should be considered in eyes with PDR, and in those with severe NPDR, especially when strict follow-up is not feasible.6 The exact mechanism of action of laser treatment is not clearly understood; several hypotheses have been proposed, including autoregulation of blood flow, improved retinal oxygenation, and metabolic stimulation of the retinal pigment epithelium (RPE).19 Although it is well-proven that PRP prevents severe visual loss in patients with PDR, the treatment is thought to carry a considerable risk of macular disease, as retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC) thinning, photoreceptors damage, or DME worsening. The incidence of new macular edema or worsening of existing macular edema after PRP has been described in 25% to 43% of the eyes,19,20 but the direct link between laser damage and macular thickening is still an object of controversy. Despite the breakdown of the BRB due to thermal injury has been demonstrated in animal models and in human subjects,21 recent pieces of evidence relying on the use of PASCAL laser have denied an increase in CMT in patients without preexisting DME.22,23 In our study, both the foveal and the parafoveal CMT did not show any significant change after PRP, and no patient experienced new or worsened macular edema during the follow-up, confirming the safety of PASCAL laser treatment in eyes with PDR.
The main aim of our research was to assess whether PRP may change the vascular perfusion in the macular region. Although FA still represents the gold standard for the assessment of the retinal vascularization in both healthy and diabetic eyes, OCTA has demonstrated superiority in discriminating the foveal and parafoveal macular microvasculature, especially in cases of FAZ disruption.24,25 PRP is known to cause the upregulation of pro-phlogistic cytokines, such as VEGF, interleukin-6 (IL-6), intercellular adhesion molecule-1 (ICAM-1), and monocyte chemotactic protein-1 (MCP-1), which in turn stimulates vascular permeability and capillary dropout.26,27 It comes natural to hypothesize that these changes negatively sum to the pre-existing amount of DR-related maculopathy, furtherly reducing the perfusion of the posterior pole, increasing the macular ischemia, and enlarging the FAZ area.
Conversely, our study demonstrates that objective perfusion indexes do not significantly change after PRP treatment, as both FAZ and VD at SCP and DCP were comparable in all eyes, irrespectively of being treatment-naïve or laser-treated. To the best of our knowledge, there is no report in the literature investigating these parameters in order to compare and discuss our results. Recently, a Korean group presented a retrospective comparison of the OCTA of patients with PDR before and after PRP, demonstrating a significant increase in SCP and a positive trend in DCP after the treatment [Seo EJ, Kim JG. Perfusion Recovery After Panretinal Photocoagulation Combining Bevacizumab Analyzed with Optical Coherence Tomography Angiography in Diabetic Retinopathy. Presented at EVRS Congress, Florence, 2017]. However, PRP was coupled with intravitreal anti-VEGF injections at baseline, so their results might be considerably influenced by the reperfusion induced by the anti-angiogenic drugs.28,29
A plausible explanation of the relatively small effect of PRP on OCTA evaluation might reside in the use of the PASCAL short-pulse laser (SPL) technology, which delivers multiple laser burns in a 10 ms to 30 ms pulse. Such a short pulse duration clinically results in less destruction within the retina and the choroid, less pain for the patients, and better preservation of retinal sensitivity for the patient than the conventional laser.30 Biochemically, significantly lower levels of VEGF, ICAM-1, IL-6, and MCP-1 have been detected in the vitreous humor of patients who received SPL laser. As these molecules have been linked to the pathogenesis of DME and diabetic maculopathy, we can speculate that SPL is more protective on the macular region with respect to conventional laser treatments.31–33
The main limitations of the study are the small number of patients included and the relatively short follow-up; however, we excluded subjects with DME at baseline or those who received anti-VEGF intravitreal injections during the follow-up - both events extremely likely in the setting of PDR in order to limit bias on OCTA analysis. Moreover, we included exclusively patients with PDR, as any comparison between our results with either diabetic patients with less severe stages of DR or a control healthy group was beyond the scope of our work. Nevertheless, the values in foveal and parafoveal VD are similar to those reported in the literature in patients with PDR, obtained with the same instruments and the same algorithm of quantification.34
In summary, we used objective OCTA parameters to quantify vascular changes after PRP in eyes with PDR. Our study demonstrated that CMT, FAZ, and VD at SCP and DCP are not significantly affected by peripheral laser treatment at both short- (1-month) and medium- / long-term (6-month) follow-up. Further analysis with larger samples and longer duration might be warranted to confirm our results.
- Lee R, Wong TY, Sabanayagam C. Epidemiology of diabetic retinopathy, diabetic macular edema and related vision loss. Eye Vis (Lond). 2015;2:17. doi:10.1186/s40662-015-0026-2 [CrossRef]
- Bandello F, Lattanzio R, Zucchiatti I, Del Turco C. Pathophysiology and treatment of diabetic retinopathy. Acta Diabetol. 2013;50(1):1–20. doi:10.1007/s00592-012-0449-3 [CrossRef]
- Caldwell RB, Bartoli M, Behzadian MA, et al. Vascular endothelial growth factor and diabetic retinopathy: Pathophysiological mechanisms and treatment perspectives. Diabetes Metab Res Rev. 2003;19(6):442–455. doi:10.1002/dmrr.415 [CrossRef]
- Klein R, Klein BE, Moss SE. Epidemiology of proliferative diabetic retinopathy. Diabetes Care. 1992;15(12):1875–1891. doi:10.2337/diacare.15.12.1875 [CrossRef]
- Bandello F, Battaglia Parodi M, Lanzetta P, et al. Diabetic macular edema. Dev Ophthalmol. 2017;58:102–138. doi:. Epub 2017 Mar 28. doi:10.1159/000455277 [CrossRef]
- No authors listed. ETDRS report number 9. Early Treatment Diabetic Retinopathy Study Research Group. Ophthalmology. 1991;98(5 Suppl):766–785.
- No authors listed. Treatment techniques and clinical guidelines for photocoagulation of diabetic macular edema. Early Treatment Diabetic Retinopathy Study Report Number 2. Early Treatment Diabetic Retinopathy Study Research Group. Ophthalmology. 1987;94(7):761–774.
- Photocoagulation treatment of proliferative diabetic retinopathy: Relationship of adverse treatment effects to retinopathy severity. Diabetic retinopathy study report no. 5. Dev Ophthalmol. 1981;2:248–261. doi:10.1159/000395330 [CrossRef]
- Evans JR, Michelessi M, Virgili G. Laser photocoagulation for proliferative diabetic retinopathy. Cochrane Database Syst Rev.2014;(11):CD011234.
- Reddy SV, Husain D. Panretinal photocoagulation: A review of complications. Semin Ophthalmol. 2018;33(1):83–88. doi:10.1080/08820538.2017.1353820 [CrossRef]
- Liang JC, Huamonte FU. Reduction of immediate complications after panretinal photocoagulation. Retina. 1984;4(3):166–170. doi:10.1097/00006982-198400430-00007 [CrossRef]
- Kim J, Woo SJ, Ahn J, Park KH, Chung H, Park KH. Long-term temporal changes of peripapillary retinal nerve fiber layer thickness before and after panretinal photocoagulation in severe diabetic retinopathy. Retina. 2012;32(10):2052–2060. doi:10.1097/IAE.0b013e3182562000 [CrossRef]
- Shimura M, Yasuda K, Nakazawa T, et al. Panretinal photocoagulation induces pro-inflammatory cytokines and macular thickening in high-risk proliferative diabetic retinopathy. Graefes Arch Clin Exp Ophthalmol. 2009;247(12):1617–1624. doi:10.1007/s00417-009-1147-x [CrossRef]
- Vangipuram G, Rezaei KA. Optical coherence tomography angiography as an imaging modality for evaluation of diabetic macular edema. J Ophthalmic Vis Res. 2017;12(4):359–360. doi:10.4103/jovr.jovr_175_17 [CrossRef]
- Toto L, D'Aloisio R, Di Nicola M, et al. Qualitative and quantitative assessment of vascular changes in diabetic macular edema after dexamethasone implant using optical coherence tomography angiography. Int J Mol Sci.2017;18(6). pii: E1181. doi:. doi:10.3390/ijms18061181 [CrossRef]
- Hasegawa N, Nozaki M, Takase N, Yoshida M, Ogura Y. New insights into microaneurysms in the deep capillary plexus detected by optical coherence tomography angiography in diabetic macular edema. Invest Ophthalmol Vis Sci. 2016;57(9):OCT348–355. doi:10.1167/iovs.15-18782 [CrossRef]
- Tang FY, Ng DS, Lam A, et al. Determinants of quantitative optical coherence tomography angiography metrics in patients with diabetes. Sci Rep. 2017;7(1):2575. doi:10.1038/s41598-017-02767-0 [CrossRef]
- Jia Y, Tan O, Tokayer J, et al. Split-spectrum amplitude-decorrelation angiography with optical coherence tomography. Opt Express. 2012;20(4):4710–4725. doi:10.1364/OE.20.004710 [CrossRef]
- Diabetic Retinopathy Study Research Group. Preliminary report on effects of photocoagulation Therapy. Am J Ophthalmol. 2018;185:14–24. doi:10.1016/j.ajo.2017.11.010 [CrossRef]
- Soman M, Ganekal S, Nair U, Nair K. Effect of panretinal photocoagulation on macular morphology and thickness in eyes with proliferative diabetic retinopathy without clinically significant macular edema. Clin Ophthalmol. 2012;6:2013–2017.
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Visual Acuity, Morphological, and Optical Coherence Tomography Angiography Parameters of Patients at Baseline and During Follow-Up
|Baseline||1 Month||6 Months||P Value|
|BCVA||0.30 ± 0.20||0.25 ± 0.25||0.25 ± 0.24||.3|
|FAZ Area (mm2)||0.33 ± 0.19||0.35 ± 0.22||0.33 ± 0.16||.6|
|CRT Foveal (μm)||311.2 ± 47.7||314.9 ± 43.3||327.1 ± 60.3||.6|
|CRT Parafoveal (μm)||355.9 ± 41.8||357.5 ± 32.5||361.4 ± 29.8||.8|
|SCP Foveal||16.4 ± 8.0||17.2 ± 7.1||16.5 ± 6.5||.4|
|SCP Parafoveal||38.4 ± 5.7||38.4 ± 4.8||38.6 ± 4.5||.9|
|DCP Foveal||28.5 ± 8.6||28.8 ± 8.9||28.2 ± 8.1||.8|
|DCP Parafoveal||46.1 ± 5.2||44.7 ± 6.4||43.8 ± 5.1||.3|
Correlation Between Consecutive Optical Coherence Tomography Angiography Parameters
|1 Month||6 Months|
|FAZ Area||Baseline||R = 0.749, P = .001*||R = 0.797, P < .0001*|
|1 month||R = 0.833, P < .0001*|
|SCP Foveal||Baseline||R = 0.941, P < .0001*||R = 0.949, P < .0001*|
|1 month||R = 0.947, P < .0001*|
|SCP Parafoveal||Baseline||R = 0.815, P = .002*||R = 0.725, P = .002*|
|1 month||R = 0.705, P = .04|
|DCP Foveal||Baseline||R = 0.705, P = .003*||R = 0.710, P < .0001*|
|1 month||R = 0.509, P < .0001*|
|DCP Parafoveal||Baseline||R = 0.700, P = .01*||R = 0.932, P = .01*|
|1 month||R = 0.764, P = .02*|