Diabetic Eye Disease

Diabetes mellitus has profound effects on multiple organ systems; however, the loss of vision caused by diabetic retinopathy might be one of the most impactful in a patient's life. The retina is a highly metabolically active tissue that requires a complex interaction of cells, spanning light sensing photoreceptors to neurons that transfer the electrochemical signal to the brain with support by glia and vascular tissue. Neuronal function depends on a complex inter-dependency of retinal cells that includes the formation of a blood-retinal barrier. This dynamic system is negatively affected by diabetes mellitus, which alters normal cell-cell interactions and leads to profound vascular abnormalities, loss of the blood-retinal barrier and impaired neuronal function. Understanding the normal cell signalling interactions and how they are altered by diabetes mellitus has already led to novel therapies that have improved visual outcomes in many patients. Research highlighted in this Review has led to a new understanding of retinal pathophysiology during diabetes mellitus and has uncovered potential new therapeutic avenues to treat this debilitating disease.

CONTEXT: Cognitive dysfunction is a growing and understudied public health issue in the aging type 1 diabetic population and is difficult and time-consuming to diagnose. Studies in long duration type 1 diabetes have reported the presence of proliferative diabetic retinopathy was associated with cognitive dysfunction. OBJECTIVE: This study assessed whether structural and vascular abnormalities of the retina, representing an extension of the central nervous system, are associated with cognitive impairment and other complications of type 1 diabetes. METHODS: An observational cross-sectional study of individuals with 50 or more years of type 1 diabetes (Joslin Medalist Study) was conducted at a university hospital in the United States. The study included 129 participants with complete cognitive testing. Validated cognitive testing measures included psychomotor speed, and immediate, and delayed memory. Optical coherence tomography (OCT) and OCT angiography (OCTA) were performed to obtain neural retinal layer thicknesses and vascular density for superficial (SCP) and deep retinal capillary plexus (DCP). Multivariable modeling was adjusted for potential confounders associated with outcomes in unadjusted analyses. RESULTS: Decreased vessel density of the SCP and DCP was associated with worse delayed memory (DCP: P = .002) and dominant hand psychomotor speed (SCP: P = .01). Thinning of the retinal outer nuclear layer was associated with worse psychomotor speed both in nondominant and dominant hands (P = .01 and P = .05, respectively). Outer plexiform layer thickness was associated with delayed memory (P = .04). CONCLUSION: These findings suggest that noninvasive retinal imaging using OCT and OCTA may assist in estimating the risks for cognitive dysfunction in people with type 1 diabetes.

AIMS/HYPOTHESIS: Proliferative diabetic retinopathy (PDR) with retinal neovascularisation (NV) is a leading cause of vision loss. This study identified a set of metabolites that were altered in the vitreous humour of PDR patients compared with non-diabetic control participants. We corroborated changes in vitreous metabolites identified in prior studies and identified novel dysregulated metabolites that may lead to treatment strategies for PDR. METHODS: We analysed metabolites in vitreous samples from 43 PDR patients and 21 non-diabetic epiretinal membrane control patients from Japan (age 27-80 years) via ultra-high-performance liquid chromatography-mass spectrometry. We then investigated the association of a novel metabolite (creatine) with retinal NV in mouse oxygen-induced retinopathy (OIR). Creatine or vehicle was administered from postnatal day (P)12 to P16 (during induced NV) via oral gavage. P17 retinas were quantified for NV and vaso-obliteration. RESULTS: We identified 158 metabolites in vitreous samples that were altered in PDR patients vs control participants. We corroborated increases in pyruvate, lactate, proline and allantoin in PDR, which were identified in prior studies. We also found changes in metabolites not previously identified, including creatine. In human vitreous humour, creatine levels were decreased in PDR patients compared with epiretinal membrane control participants (false-discovery rate <0.001). We validated that lower creatine levels were associated with vascular proliferation in mouse retina in the OIR model (p = 0.027) using retinal metabolomics. Oral creatine supplementation reduced NV compared with vehicle (P12 to P16) in OIR (p = 0.0024). CONCLUSIONS/INTERPRETATION: These results suggest that metabolites from vitreous humour may reflect changes in metabolism that can be used to find pathways influencing retinopathy. Creatine supplementation could be useful to suppress NV in PDR. Graphical abstract.

PURPOSE: To evaluate the association of retinal nonperfusion and diabetic retinopathy (DR) severity with location of vascular caliber measurement using ultrawide field (UWF) imaging. DESIGN: Retrospective image review. PARTICIPANTS: Adults with diabetes mellitus. METHODS: All images from subjects with same-day UWF fluorescein angiography (FA) and color imaging were evaluated. Predominantly peripheral lesions (PPL) and DR severity were graded from UWF color images. Nonperfusion was quantified using UWF-FA in defined retinal regions [posterior pole (PP), mid-periphery (MP), far-periphery (FP)]. Retinal vessel calibers were measured at an optic disc centered inner and outer zone. MAIN OUTCOME MEASURES: Nonperfusion index (NPI) in the PP, MP and FP. Mean arteriole and venule diameter in the inner and outer zones. RESULTS: Two hundred eighty-five eyes of 193 patients (24.9% mild nonproliferative DR [NPDR], 22.8% moderate NPDR, 37.5% severe NPDR and 14.7% proliferative DR [PDR]) were reviewed. No significant associations between inner zone arteriolar diameter and retinal NPI overall or in any retinal region. In the outer zone, eyes with thinnest arteriolar calibers (quartile 1) were associated with a 1.7- to 2.4-fold nonperfusion increase across all retinal regions compared to the remaining eyes (P = 0.002 [PP] to 0.048 [FP]). In the outer zone, the percentage of eyes in the thinnest quartile of retinal arteriolar diameter increased with worsening DR severity (mild NPDR: 10% vs PDR: 31%, P = 0.007). This association was not observed when measured within the inner zone (P = 0.129). All venular caliber associations were not statistically significant when corrected for potentially confounding factors. Thinner outer zone retinal arteriolar caliber (quartile 1) was more common in eyes with PPL compared to eyes without PPL (34.1% vs 20.8%, P = 0.017) as were thicker outer venular calibers (quartile 4) (33% vs 21.3%, P = 0.036). Presence of PPL was associated with thinner outer zone arteriolar caliber (109.7 ± 26.5μm vs 123.0 ± 29.5μm, P = 0.001). CONCLUSIONS: The association of vascular caliber with nonperfusion and DR severity differs based upon the retinal location at which vascular caliber is measured. Peripheral arterial narrowing is associated with increasing nonperfusion, worsening DR severity and presence of PPL. In contrast, inner zone retinal arteriolar caliber is not associated with these findings.

PURPOSE: To determine the relationship between refractive error and diabetic retinopathy (DR). DESIGN: Clinical trial. PARTICIPANTS: Type I diabetes individuals with serial refractive error and DR stage measurements over 30 years in the Diabetes Control and Complications Trial (DCCT) and Epidemiology of Diabetes Interventions and Complications (EDIC) follow-up study. METHODS: Stage of DR was measured every 6 months from standard fundus photographs, and refractive error was measured annually during the 6.5 years of DCCT; then, both were staggered every fourth year during EDIC with the full cohort measured at EDIC years 4 and 10. Outcomes of DR were 2- or 3-step progression, presence of proliferative DR (PDR), clinically significant macular edema (CSME), diabetic macular edema (DME), or ocular surgery. Myopia, emmetropia, and hyperopia were defined as a spherical equivalent of ≤-0.5, >-0.5 and <0.5, and ≥0.5, respectively. MAIN OUTCOME MEASURES: For each outcome separately, Cox proportional hazard (PH) models assessed the association between the refractive error status and the subsequent risk of that outcome, both without and with adjustment for potential risk factors. RESULTS: Hyperopia was associated with a higher risk of 2-step progression (hazard ratio [HR], 1.29; 95% confidence interval [CI], 1.05-1.59), 3-step progression (HR, 1.35; 95% CI, 1.05-1.73), and PDR (HR, 1.40; 95% CI, 1.02-1.92) compared with emmetropia in unadjusted models. These associations remained significant after adjustment for DCCT treatment group, cohort, age, sex, smoking, duration of diabetes, systolic and diastolic blood pressures, pulse, low-density lipoprotein, high-density lipoprotein, triglycerides, albumin excretion rate, and DCCT/EDIC mean updated hemoglobin A1c (HbA1c) (2-step progression: HR, 1.28; 95% CI, 1.03-1.58; 3-step progression: HR, 1.30; 95% CI, 1.00-1.68; PDR: HR, 1.38; 95% CI, 1.00-1.90). Myopia was not associated with any of the 5 DR outcomes in the unadjusted models and only marginally associated with 2-step progression (HR, 1.11; 95% CI, 1.00-1.24) in the adjusted models. CONCLUSIONS: Myopia is not associated with DR progression risk. Hyperopia is an independent risk factor for 2-step and 3-step DR progression and PDR.

PURPOSE: To characterize the rates of panretinal photocoagulation (PRP) and anti-vascular endothelial growth factor (VEGF) medications before and after publication of the Diabetic Retinopathy Clinical Research Network protocol S. DESIGN: A retrospective, cross-sectional study from January 2012, through September 2019, using a nationally representative claims-based database, Clinformatics Data Mart Database (OptumInsight, Eden Prairie, MN). PARTICIPANTS: Eyes newly diagnosed with proliferative diabetic retinopathy (PDR), continuous enrollment, and no prior treatment with PRP or anti-VEGF agents. METHODS: Interrupted time series regression analysis was performed to identify the annual change in treatment rates before and after the publication of Protocol S (November 2015). MAIN OUTCOME MEASURES: Annual rates of anti-VEGF or PRP treatments per 1000 treated eyes with PDR. RESULTS: From 2012 through 2019, 10 035 PRP or anti-VEGF treatments were administered to 3685 PDR eyes. Of these, 63.6% (n = 6379) were anti-VEGF agents, and 36.4% (n = 3656) were PRP treatments. Throughout treatment, 88.7% of eyes treated with anti-VEGF received the same agent and 7.7% were treated with both PRP and anti-VEGF agents. Panretinal photocoagulation rates declined from 784/1000 treated eyes in 2012 to 566/1000 in 2019 (pre-Protocol S: β = -32 vs. post-Protocol S: -77; P = 0.005), whereas anti-VEGF rates increased from 876/1000 in 2012 to 1583/1000 in 2019 (β = -48 vs. 161, respectively; P = 0.001). Panretinal photocoagulation rates in diabetic macular edema (DME) eyes did not significantly differ from 474/1000 in 2012 to 363/1000 in 2019 (β = -9 vs. -58 respectively; P = 0.091), and anti-VEGF rates increased from 1533/1000 in 2012 to 2096/1000 in 2019 (β = -57 vs. 187; P = 0.043). In eyes without DME, PRP use declined from 1017/1000 in 2012 to 707/1000 in 2019 (β = -31 vs. -111, respectively; P < 0.001), and anti-VEGF use increased from 383/1000 in 2012 to 1226/1000 in 2019 (β = -48 vs. 140, respectively; P < 0.001). CONCLUSIONS: Following the publication of Protocol S, PRP rates decreased, while anti-VEGF rates increased. Panretinal photocoagulation rates did not significantly change among eyes with DME. Our findings indicate the impact that randomized controlled trials can have on real-world practice patterns.

AIMS: To compare widefield swept-source optical coherence tomography angiography (WF SS-OCTA) with ultra-widefield colour fundus photography (UWF CFP) and fluorescein angiography (UWF FA) for detecting diabetic retinopathy (DR) lesions. METHODS: This prospective, observational study was conducted at Massachusetts Eye and Ear from December 2018 to October 2019. Proliferative DR, non-proliferative DR and diabetic patients with no DR were included. All patients were imaged with a WF SS-OCTA using a Montage 15×15 mm scan. UWF CFP and UWF FA were taken by a 200°, single capture retinal imaging system. Images were independently evaluated for the presence or absence of DR lesions including microaneurysms (MAs), intraretinal microvascular abnormalities (IRMAs), neovascularisation elsewhere (NVE), neovascularisation of the optic disc (NVD) and non-perfusion areas (NPAs). All statistical analyses were performed using SPSS V.25.0. RESULTS: One hundred and fifty-two eyes of 101 participants were included in the study. When compared with UWF CFP, WF SS-OCTA was found to be superior in detecting IRMAs (p<0.001) and NVE/NVD (p=0.007). The detection rates of MAs, IRMAs, NVE/NVD and NPAs in WF SS-OCTA were comparable with UWF FA images (p>0.05). Furthermore, when we compared WF SS-OCTA plus UWF CFP with UWF FA, the detection rates of MAs, IRMAs, NVE/NVD and NPAs were identical (p>0.005). Agreement (κ=0.916) between OCTA and FA in classifying DR was excellent. CONCLUSION: WF SS-OCTA is useful for identification of DR lesions. WF SS-OCTA plus UWF CFP may offer a less invasive alternative to FA for DR diagnosis.

PURPOSE: To report the outcomes of macular add-on intraocular lens implantation in improving reading vision in patients with bilateral advanced diabetic maculopathy. METHODS: In this retrospective study, a supplementary bifocal sulcus intraocular lens (Scharioth Macular Lens) was implanted in the better-seeing eye of five patients. Baseline-corrected distance vision, corrected near visual acuity, a preoperative simulation test, and multimodal imaging were collected. The primary outcome was the uncorrected near visual acuity at a working distance of 15 cm, at a 12-month follow-up. RESULTS: Study patients included 3 cases of refractory subfoveal exudation and 2 cases of diabetic macular ischemia. A preoperative test to assess the potential gain in near vision showed an improvement of ≥2 paragraphs on the RADNER reading chart in all patients. At 12 months, median reading vision (corrected near visual acuity at 15 cm) significantly improved from 20/125 (range 20/50-20/200) preoperatively to uncorrected near visual acuity (at 15 cm) of 20/50 (range 20/40-20/80) (P = 0.042; Wilcoxon signed-ranks test). Distance vision remained unchanged in four patients. All patients were able to achieve the size of newsprint (20/50 Snellen equivalent), within the first 3 months. CONCLUSION: The macular add-on intraocular lens improves reading vision in visually impaired patients due to end-stage diabetic macular disease.

Importance: Vitreous hemorrhage from proliferative diabetic retinopathy can cause loss of vision. The best management approach is unknown. Objective: To compare initial treatment with intravitreous aflibercept vs vitrectomy with panretinal photocoagulation for vitreous hemorrhage from proliferative diabetic retinopathy. Design, Setting, and Participants: Randomized clinical trial at 39 DRCR Retina Network sites in the US and Canada including 205 adults with vison loss due to vitreous hemorrhage from proliferative diabetic retinopathy who were enrolled from November 2016 to December 2017. The final follow-up visit was completed in January 2020. Interventions: Random assignment of eyes (1 per participant) to aflibercept (100 participants) or vitrectomy with panretinal photocoagulation (105 participants). Participants whose eyes were assigned to aflibercept initially received 4 monthly injections. Both groups could receive aflibercept or vitrectomy during follow-up based on protocol criteria. Main Outcomes and Measures: The primary outcome was mean visual acuity letter score (range, 0-100; higher scores indicate better vision) over 24 weeks (area under the curve); the study was powered to detect a difference of 8 letters. Secondary outcomes included mean visual acuity at 4 weeks and 2 years. Results: Among 205 participants (205 eyes) who were randomized (mean [SD] age, 57 [11] years; 115 [56%] men; mean visual acuity letter score, 34.5 [Snellen equivalent, 20/200]), 95% (195 of 205) completed the 24-week visit and 90% (177 of 196, excluding 9 deaths) completed the 2-year visit. The mean visual acuity letter score over 24 weeks was 59.3 (Snellen equivalent, 20/63) (95% CI, 54.9 to 63.7) in the aflibercept group vs 63.0 (Snellen equivalent, 20/63) (95% CI, 58.6 to 67.3) in the vitrectomy group (adjusted difference, -5.0 [95% CI, -10.2 to 0.3], P = .06). Among 23 secondary outcomes, 15 showed no significant difference. The mean visual acuity letter score was 52.6 (Snellen equivalent, 20/100) in the aflibercept group vs 62.3 (Snellen equivalent, 20/63) in the vitrectomy group at 4 weeks (adjusted difference, -11.2 [95% CI, -18.5 to -3.9], P = .003) and 73.7 (Snellen equivalent, 20/40) vs 71.0 (Snellen equivalent, 20/40) at 2 years (adjusted difference, 2.7 [95% CI, -3.1 to 8.4], P = .36). Over 2 years, 33 eyes (33%) assigned to aflibercept received vitrectomy and 34 eyes (32%) assigned to vitrectomy received subsequent aflibercept. Conclusions and Relevance: Among participants whose eyes had vitreous hemorrhage from proliferative diabetic retinopathy, there was no statistically significant difference in the primary outcome of mean visual acuity letter score over 24 weeks following initial treatment with intravitreous aflibercept vs vitrectomy with panretinal photocoagulation. However, the study may have been underpowered, considering the range of the 95% CI, to detect a clinically important benefit in favor of initial vitrectomy with panretinal photocoagulation. Trial Registration: ClinicalTrials.gov Identifier: NCT02858076.

Purpose: To evaluate the performance of a deep learning algorithm in the detection of referral-warranted diabetic retinopathy (RDR) on low-resolution fundus images acquired with a smartphone and indirect ophthalmoscope lens adapter. Methods: An automated deep learning algorithm trained on 92,364 traditional fundus camera images was tested on a dataset of smartphone fundus images from 103 eyes acquired from two previously published studies. Images were extracted from live video screenshots from fundus examinations using a commercially available lens adapter and exported as a screenshot from live video clips filmed at 1080p resolution. Each image was graded twice by a board-certified ophthalmologist and compared to the output of the algorithm, which classified each image as having RDR (moderate nonproliferative DR or worse) or no RDR. Results: In spite of the presence of multiple artifacts (lens glare, lens particulates/smudging, user hands over the objective lens) and low-resolution images achieved by users of various levels of medical training, the algorithm achieved a 0.89 (95% confidence interval [CI] 0.83-0.95) area under the curve with an 89% sensitivity (95% CI 81%-100%) and 83% specificity (95% CI 77%-89%) for detecting RDR on mobile phone acquired fundus photos. Conclusions: The fully data-driven artificial intelligence-based grading algorithm herein can be used to screen fundus photos taken from mobile devices and identify with high reliability which cases should be referred to an ophthalmologist for further evaluation and treatment. Translational Relevance: The implementation of this algorithm on a global basis could drastically reduce the rate of vision loss attributed to DR.

In diabetes there is a long latency between the onset of hyperglycemia and the appearance of structural microangiopathy. Because Ly6C patrolling monocytes (PMo) behave as housekeepers of the vasculature, we tested whether PMo protect microvessels against diabetes. We found that in wild-type mice, diabetes reduced PMo in the general circulation but increased by fourfold the absolute number of PMo adherent to retinal vessels (leukostasis). Conversely, in diabetic NR4A1 mice, a model of absence of PMo, there was no increase in leukostasis, and at 6 months of diabetes, the number of retinal acellular capillaries almost doubled compared with diabetic wild-type mice. Circulating PMo showed gene expression changes indicative of enhanced migratory, vasculoprotective, and housekeeping activities, as well as profound suppression of genes related to inflammation and apoptosis. Promigratory CXCR4 was no longer upregulated at longer duration when retinal acellular capillaries begin to increase. Thus, after a short diabetes duration, PMo are the cells preferentially recruited to the retinal vessels and protect vessels from diabetic damage. These observations support the need for reinterpretation of the functional meaning of leukostasis in diabetes and document within the natural history of diabetic retinopathy processes of protection and repair that can provide novel paradigms for prevention.

BACKGROUND: The American Indian Navajo and Goshute peoples are underserved patient populations residing in the Four Corners area of the United States and Ibupah, Utah, respectively. METHODS: We conducted a cross-sectional study of epidemiological factors and lipid biomarkers that may be associated with type II diabetes, hypertension and retinal manifestations in tribal and non-tribal members in the study areas (n = 146 participants). We performed multivariate analyses to determine which, if any, risk factors were unique at the tribal level. Fundus photos and epidemiological data through standardized questionnaires were collected. Blood samples were collected to analyze lipid biomarkers. Univariate analyses were conducted and statistically significant factors at < 0.10 were entered into a multivariate regression. RESULTS: Of 51 participants for whom phenotyping was available, from the Four Corners region, 31 had type II diabetes (DM), 26 had hypertension and 6 had diabetic retinopathy (DR). Of the 64 participants from Ibupah with phenotyping available, 20 had diabetes, 19 had hypertension and 6 had DR. Navajo participants were less likely to have any type of retinopathy as compared to Goshute participants (odds ratio (OR) = 0.059; 95% confidence interval (CI) = 0.016-0.223; < 0.001). Associations were found between diabetes and hypertension in both populations. Older age was associated with hypertension in the Four Corners, and the Navajo that reside there on the reservation, but not within the Goshute and Ibupah populations. Combining both the Ibupah, Utah and Four Corners study populations, being American Indian ( = 0.022), residing in the Four Corners ( = 0.027) and having hypertension ( < 0.001) increased the risk of DM. DM ( < 0.001) and age ( = 0.002) were significantly associated with hypertension in both populations examined. When retinopathy was evaluated for both populations combined, hypertension ( = 0.037) and living in Ibupah ( < 0.001) were associated with greater risk of retinopathy. When combining both American Indian populations from the Four Corners and Ibupah, those with hypertension were more likely to have DM ( < 0.001). No lipid biomarkers were found to be significantly associated with any disease state. CONCLUSIONS: We found different comorbid factors with retinal disease outcome between the two tribes that reside within the Intermountain West. This is indicated by the association of tribe and with the type of retinopathy outcome when we combined the populations of American Indians. Overall, the Navajo peoples and the Four Corners had a higher prevalence of chronic disease that included diabetes and hypertension than the Goshutes and Ibupah. To the best of our knowledge, this is the first study to conduct an analysis for disease outcomes exclusively including the Navajo and Goshute tribe of the Intermountain West.

Importance: Studies have not yet determined whether the distribution of lesions in the retinal periphery alters the association between the severity of diabetic retinopathy (DR) and macular vessel density. Objective: To evaluate the association of DR lesion distribution with optical coherence tomography angiography (OCTA) metrics and DR severity. Design, Setting, and Participants: This cross-sectional observational study was conducted at a tertiary care center for diabetic eye disease among 225 patients with type 1 or 2 diabetes who had undergone imaging between February 15, 2016, and December 31, 2019. Exposures: Optical coherence tomography angiography 3 × 3-mm macular scans and ultra-widefield color imaging. Main Outcomes and Measures: Optical coherence tomography angiography vessel density in the superficial capillary plexus, intermediate capillary plexus, and deep capillary plexus and choriocapillaris flow density. The severity of DR and the predominantly peripheral lesions (PPL) were evaluated from ultra-widefield color imaging. Results: The study evaluated 352 eyes (225 patients; 125 men [55.6%]; mean [SD] age, 52.1 [15.1] years), of which 183 eyes (52.0%) had mild nonproliferative diabetic retinopathy (NPDR), 71 eyes (20.2%) had moderate NPDR, and 98 eyes (27.8%) had severe NPDR or proliferative diabetic retinopathy (PDR). In eyes with no PPL (209 [59.4%]), the mean (SD) vessel density in the superficial capillary plexus (mild NPDR, 38.1% [4.7%]; moderate NPDR, 36.4% [4.6%]; severe NPDR or PDR, 34.1% [4.1%]; P < .001) and the deep capillary plexus (mild NPDR, 45.8% [3.0%]; moderate NPDR, 45.8% [2.2%]; severe NPDR or PDR, 44.5% [1.9%]; P = .002), as well as the mean (SD) choriocapillaris flow density (mild NPDR, 69.7% [6.2%]; moderate NPDR, 67.6% [5.6%]; severe NPDR or PDR, 67.1% [5.6%]; P = .01), decreased with increasing DR severity. These associations remained statistically significant even after correcting for age, signal strength index, spherical equivalent, duration of diabetes, type of diabetes, and correlation between eyes of the same patient. In eyes with PPL (143 [40.6%]), mean (SD) vessel density in the superficial capillary plexus (mild NPDR, 34.1% [4.1%]; moderate NPDR, 35.2% [4.1%]; severe NPDR or PDR, 36.0% [4.3%]; P = .42) and the deep capillary plexus (mild NPDR, 44.5% [1.7%]; moderate NPDR, 45.4% [1.4%]; severe NPDR or PDR, 44.9% [1.5%]; P = .81), as well as the mean (SD) choriocapillaris flow density (mild NPDR, 67.1% [5.6%]; moderate NPDR, 69.3% [4.6%]; severe NPDR or PDR, 68.3% [5.6%]; P = .49), did not appear to change with increasing DR severity. Conclusions and Relevance: These results suggest that central retinal vessel density is associated with DR severity in eyes without, but not with, PPL. These findings suggest a potential need to stratify future optical coherence tomography angiography studies of eyes with DR by the presence or absence of PPL. If DR onset and worsening are associated with the location of retinal nonperfusion, assessment of global retinal nonperfusion using widefield angiography may improve the ability to evaluate DR severity and risk of DR worsening over time.

Diabetic retinopathy (DR) is an eye condition that develops after chronically poorly-managed diabetes, and is presently the main cause for blindness on a global scale. Current treatments for DR such as laser photocoagulation, topical injection of corticosteroids, intravitreal injection of anti-vascular endothelial growth factor (VEGF) agents and vitreoretinal surgery are only applicable at the late stages of DR and there are possibilities of significant adverse effects. Moreover, the forms of treatment available for DR are highly invasive to the eyes. Safer and more effective pharmacological treatments are required for DR treatment, in particular at an early stage. In this review, we cover recently investigated promising oral pharmacotherapies, the methods of which are safer, easier to use, patient-friendly and pain-free, in clinical studies. We especially focus on peroxisome proliferator-activator receptor alpha (PPARα) agonists in which experimental evidence suggests PPARα activation may be closely related to the attenuation of vascular damages, including lipid-induced toxicity, inflammation, an excess of free radical generation, endothelial dysfunction and angiogenesis. Furthermore, oral administration of selective peroxisome proliferator-activated receptor alpha modulator (SPPARMα) agonists may induce hepatic fibroblast growth factor 21 expression, indirectly resulting in retinal protection in animal studies. Our review will enable more comprehensive approaches for understanding protective roles of PPARα for the prevention of DR development.