Use of an Artificial Intelligence-Generated Vascular Severity Score Improved Plus Disease Diagnosis in Retinopathy of Prematurity.

PURPOSE: To evaluate whether providing clinicians with an artificial intelligence (AI)-based vascular severity score (VSS) improves consistency in the diagnosis of plus disease in retinopathy of prematurity (ROP). DESIGN: Multireader diagnostic accuracy imaging study. PARTICIPANTS: Eleven ROP experts, 9 of whom had been in practice for 10 years or more. METHODS: RetCam (Natus Medical Incorporated) fundus images were obtained from premature infants during routine ROP screening as part of the Imaging and Informatics in ROP study between January 2012 and July 2020. From all available examinations, a subset of 150 eye examinations from 110 infants were selected for grading. An AI-based VSS was assigned to each set of images using the i-ROP DL system (Siloam Vision). The clinicians were asked to diagnose plus disease for each examination and to assign an estimated VSS (range, 1-9) at baseline, and then again 1 month later with AI-based VSS assistance. A reference standard diagnosis (RSD) was assigned to each eye examination from the Imaging and Informatics in ROP study based on 3 masked expert labels and the ophthalmoscopic diagnosis. MAIN OUTCOME MEASURES: Mean linearly weighted κ value for plus disease diagnosis compared with RSD. Area under the receiver operating characteristic curve (AUC) and area under the precision-recall curve (AUPR) for labels 1 through 9 compared with RSD for plus disease. RESULTS: Expert agreement improved significantly, from substantial (κ value, 0.69 [0.59, 0.75]) to near perfect (κ value, 0.81 [0.71, 0.86]), when AI-based VSS was integrated. Additionally, a significant improvement in plus disease discrimination was achieved as measured by mean AUC (from 0.94 [95% confidence interval (CI), 0.92-0.96] to 0.98 [95% CI, 0.96-0.99]; difference, 0.04 [95% CI, 0.01-0.06]) and AUPR (from 0.86 [95% CI, 0.81-0.90] to 0.95 [95% CI, 0.91-0.97]; difference, 0.09 [95% CI, 0.03-0.14]). CONCLUSIONS: Providing ROP clinicians with an AI-based measurement of vascular severity in ROP was associated with both improved plus disease diagnosis and improved continuous severity labeling as compared with an RSD for plus disease. If implemented in practice, AI-based VSS could reduce interobserver variability and could standardize treatment for infants with ROP. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Impact of postnatal steroids on peripheral avascular retina and severity of retinopathy of prematurity.

BACKGROUND: We investigated the role of postnatal steroids on the severity of retinopathy of prematurity (ROP) and its impact on peripheral avascular retina (PAR). METHODS: A retrospective cohort study of infants born at ≤32 weeks gestation and/or birth weight ≤1500 g. Demographics, the dose and duration of steroid treatment, and age when full retinal vascularization occurred were collected. The primary outcomes were the severity of ROP and time to full vascularization of the retina. RESULTS: A total of 1695 patients were enrolled, 67% of whom received steroid therapy. Their birth weight was 1142 ± 396 g and gestational age was 28.6 ± 2.7 weeks. The total hydrocortisone-equivalent dose prescribed was 28.5 ± 74.3 mg/kg. The total days of steroid treatment were 8.9 ± 35.1 days. After correction for major demographic differences, infants who received a higher cumulative dose of steroids for a longer duration had a significantly increased incidence of severe ROP and PAR (P < 0.001). For each day of steroid treatment, there was a 3.2% increase in the hazard of the severe form of ROP (95% CI: 1.022-1.043) along with 5.7% delay in achieving full retinal vascularization (95% CI: 1.04-1.08) (P < 0.001). CONCLUSION: Cumulative dose and duration of postnatal steroid use were independently associated with the severity of ROP and PAR. Thus, postnatal steroids should be used very prudently. IMPACT: We report ROP outcomes in a large cohort of infants from two major healthcare systems where we have studied the impact of postnatal steroids on the severity of ROP, growth, and development of retinal vessels. After correcting our data for three major outcome measures, we show that high-dose postnatal steroids used for a prolonged duration of time are independently associated with severe ROP and delay in retinal vascularization. Postnatal steroids impact the visual outcomes of VLBW infants significantly, so their clinical use needs to be moderated.

Coats Plus Syndrome in a Premature Infant, With a Focus on Management.

Purpose: A premature infant was diagnosed with Coats plus syndrome based on a genetic evaluation showing biallelic heterozygous pathogenic CTC1 variants. Methods: A case study was performed, including findings and interventions. Results: A premature infant born 30 weeks gestational age weighing 817 g was evaluated for retinopathy of prematurity at 35 weeks corrected gestational age. An initial dilated fundus examination showed an exudative retinal detachment (RD) in the right eye and avascularity post-equatorially in the left eye with telangiectasias and aneurysmal dilations. Genetic evaluation showed biallelic heterozygous pathogenic CTC1 variants, diagnostic of Coats plus syndrome. Sequential examination under anesthesia with fluorescein showed progressive ischemia despite confluent photocoagulation. Conclusions: CTC1 gene variants manifest as Coats plus syndrome, which has a clinical appearance consistent with retinovascular ischemia, capillary remodeling, aneurysmal dilation, and exudative RD. Systemic and local corticosteroids in conjunction with peripheral laser ablation decreased vascular exudation and avoided intraocular intervention.

Referable Macular Hemorrhage-A Clinically Meaningful Screening Target in Newborn Infants. Position Statement of the Association of Pediatric Retina Surgeons.

Universal newborn eye screening facilitates early diagnosis of ocular abnormalities and mitigates vision loss. "Referral warranted" eye disease is present at birth in about 5.5% of term infants, with "macular hemorrhage impinging on the fovea" representing about 50% of referral warranted disease. The Association of Pediatric Retina Surgeons held a symposium on February 9, 2021 that culminated in a position statement on "referable macular hemorrhage" (RMH) in newborn infants. RMH is meaningful in that in can cause amblyopia through deprivation, can be readily captured with wide-angle photography in a safe and efficient manner, and may lead to early intervention with mitigation of vision loss. [Ophthalmic Surg Lasers Imaging Retina. 2022;53:3-6.].

The U.S. National Trend for Retinopathy of Prematurity.

OBJECTIVE: The use of supplemental oxygen in premature infants is essential for survival. However, its use has been associated with unintended complications. The restricted use of oxygen is associated with increased mortality and necrotizing enterocolitis (NEC), whereas its liberal use is associated with increased risk for retinopathy of prematurity (ROP). Although there is no clear consensus on the acceptable oxygen saturation range, clinicians have recently become more liberal with the use of oxygen. We aim to assess (1) the national trends for ROP in very low birth weight preterm infants, and (2) the associated trends in mortality, NEC, intraventricular hemorrhage (IVH), and length of hospital stay (LOS). STUDY DESIGN: We analyzed deidentified patient data from the National Inpatient Sample (NIS) of the Healthcare Cost and Utilization Project (HCUP) from 2002 to 2017. All infants with gestational age ≤32 weeks and birth weight <1,500 g were included. Trends in ROP, severe ROP, mortality, NEC, IVH, severe IVH, and LOS were analyzed using Jonckheere-Terpstra test. RESULTS: A total of 818,945 neonates were included in the study. The overall mortality was 16.2% and the prevalence of ROP was 17.5%. There was a significant trend for increased ROP over the years (p < 0.001). Severe ROP was also significantly increased (p < 0.001). This was associated with a significant trend for increased median LOS in survived infants (p < 0.001). Mortality was significantly decreased (p < 0.001), whereas NEC and severe NEC did not change over time (p = 0.222 and p = 0.412, respectively). CONCLUSION: There is a national trend for increased ROP and severe ROP over the 16 years of the study period. This trend was associated with a significant increase in the LOS in survived infants without change in NEC. KEY POINTS: · Prevalence of ROP and severe ROP has increased in VLBW infants over the 16-year study period.. · The prevalence of NEC did not change over the same time period.. · Increased ROP and severe ROP were consistent in all three GA and BW subgroups..

Hyperoxia Induced Hypomyelination.

We asked whether hyperoxia might induce hypomyelination of the corpus callosum, clinically described as periventricular leukomalacia (PVL) of the severely preterm infant. Mouse pups and their nursing dams were placed in 80% oxygen from P4-P8, then removed to room air until P11. Corpus callosal sections were probed myelin immunofluorescence, tested for myelin basic protein concentration by Western blot, and both glial fibrillary acidic protein levels and apoptosis quantified. Density of corpus callosal capillaries were measured after lectin staining and hypoxia measured by Hypoxyprobe. Numbers of oligodendrocytes were quantified by immunohistochemistry. We next used hypoxiamimesis as a surrogate to hypoxia by comparing cerebral hypoxia inducible factor (HIF) stabilization to hepatic HIF stabilization. Hyperoxia induced hypomyelination and a reduction of corpus callosal capillaries. Hyperoxia decreased numbers of oligodendrocytes with an increase in corpus callosal fibrosis and apoptosis. Cerebral hypoxiamimesis induced hypomyelination whereas hepatic hypoxiamimesis alone increased myelination, oligodendrocyte numbers, and corpus callosal capillary density. Hepatic HIF-1 dependence on myelination was confirmed using the cre/lox hepatic HIF-1 knockout. These findings suggest that hyperoxia can induce hypomyelination through vasoobliteration and subsequent ischemia, adding a potential oxygen induced mechanism to the diverse causes of periventricular leukomalacia of the severely preterm infant. Targeting hepatic HIF-1 alone led to increased myelination.

Hyperoxia Inhibits Proliferation of Retinal Endothelial Cells in a Myc-Dependent Manner.

Oxygen supplementation is necessary to prevent mortality in severely premature infants. However, the supraphysiological concentration of oxygen utilized in these infants simultaneously creates retinovascular growth attenuation and vasoobliteration that induces the retinopathy of prematurity. Here, we report that hyperoxia regulates the cell cycle and retinal endothelial cell proliferation in a previously unknown Myc-dependent manner, which contributes to oxygen-induced retinopathy.

Assessment of a Hotel-Based COVID-19 Isolation and Quarantine Strategy for Persons Experiencing Homelessness.

Importance: Several jurisdictions in the United States have secured hotels to temporarily house people experiencing homelessness who require isolation or quarantine for confirmed or suspected coronavirus disease 2019 (COVID-19). To our knowledge, little is known about how these programs serve this vulnerable population outside the hospital setting. Objective: To assess the safety of a hotel-based isolation and quarantine (I/Q) care system and its association with inpatient hospital capacity. Design, Setting, and Participants: This retrospective cohort study of a hotel-based I/Q care system for homeless and unstably housed individuals in San Francisco, California, was conducted from March 19 to May 31, 2020. Individuals unable to safely isolate or quarantine at home with mild to moderate COVID-19, persons under investigation, or close contacts were referred from hospitals, outpatient settings, and public health surveillance to 5 I/Q hotels. Of 1009 I/Q hotel guests, 346 were transferred from a large county public hospital serving patients experiencing homelessness. Exposure: A physician-supervised team of nurses and health workers provided around-the-clock support, including symptom monitoring, wellness checks, meals, harm-reduction services, and medications for opioid use disorder. Main Outcomes and Measures: Characteristics of I/Q hotel guests, program retention, county hospital readmissions, and mean length of stay. Results: Overall, the 1009 I/Q hotel guests had a median age of 44 years (interquartile range, 33-55 years), 756 (75%) were men, 454 (45%) were Latinx, and 501 (50%) were persons experiencing sheltered (n = 295) or unsheltered (n = 206) homelessness. Overall, 463 (46%) received a diagnosis of COVID-19; 303 of 907 (33%) had comorbid medical disorders, 225 of 907 (25%) had comorbid mental health disorders, and 236 of 907 (26%) had comorbid substance use disorders. A total of 776 of 955 guests (81%) completed their I/Q hotel stay; factors most strongly associated with premature discontinuation were unsheltered homelessness (adjusted odds ratio, 4.5; 95% CI, 2.3-8.6; P < .001) and quarantine status (adjusted odds ratio, 2.6; 95% CI, 1.5-4.6; P = .001). In total, 346 of 549 patients (63%) were transferred from the county hospital; of 113 ineligible referrals, 48 patients (42%) had behavioral health needs exceeding I/Q hotel capabilities. Thirteen of the 346 patients transferred from the county hospital (4%) were readmitted for worsening COVID-19. Overall, direct transfers to I/Q hotels from emergency and outpatient departments were associated with averting many hospital admissions. There was a nonsignificant decrease in the mean hospital length of stay for inpatients with confirmed or suspected COVID-19 from 5.5 to 2.7 days from March to May 2020 (P = .11). Conclusions and Relevance: To support persons experiencing homelessness during the COVID-19 pandemic, San Francisco rapidly and safely scaled a hotel-based model of I/Q that was associated with reduced strain on inpatient capacity. Strategies to improve guest retention and address behavioral health needs not met in hotel settings are intervention priorities.

Reduction of Glut1 in the Neural Retina But Not the RPE Alleviates Polyol Accumulation and Normalizes Early Characteristics of Diabetic Retinopathy.

Hyperglycemia is a key determinant for development of diabetic retinopathy (DR). Inadequate glycemic control exacerbates retinopathy, while normalization of glucose levels delays its progression. In hyperglycemia, hexokinase is saturated and excess glucose is metabolized to sorbitol by aldose reductase via the polyol pathway. Therapies to reduce retinal polyol accumulation for the prevention of DR have been elusive because of low sorbitol dehydrogenase levels in the retina and inadequate inhibition of aldose reductase. Using systemic and conditional genetic inactivation, we targeted the primary facilitative glucose transporter in the retina, Glut1, as a preventative therapeutic in diabetic male and female mice. Unlike WT diabetics, diabetic Glut1+/- mice did not display elevated Glut1 levels in the retina. Furthermore, diabetic Glut1+/- mice exhibited ameliorated ERG defects, inflammation, and oxidative stress, which was correlated with a significant reduction in retinal sorbitol accumulation. Retinal pigment epithelium-specific reduction of Glut1 did not prevent an increase in retinal sorbitol content or early hallmarks of DR. However, like diabetic Glut1+/- mice, reduction of Glut1 specifically in the retina mitigated polyol accumulation and diminished retinal dysfunction and the elevation of markers for oxidative stress and inflammation associated with diabetes. These results suggest that modulation of retinal polyol accumulation via Glut1 in photoreceptors can circumvent the difficulties in regulating systemic glucose metabolism and be exploited to prevent DR.SIGNIFICANCE STATEMENT Diabetic retinopathy affects one-third of diabetic patients and is the primary cause of vision loss in adults 20-74 years of age. While anti-VEGF and photocoagulation treatments for the late-stage vision threatening complications can prevent vision loss, a significant proportion of patients do not respond to anti-VEGF therapies, and mechanisms to stop progression of early-stage symptoms remain elusive. Glut1 is the primary facilitative glucose transporter for the retina. We determined that a moderate reduction in Glut1 levels, specifically in the retina, but not the retinal pigment epithelium, was sufficient to prevent retinal polyol accumulation and the earliest functional defects to be identified in the diabetic retina. Our study defines modulation of Glut1 in retinal neurons as a targetable molecule for prevention of diabetic retinopathy.

Patient-Reported Complications after Intravitreal Injection and Their Predictive Factors.

PURPOSE: The intravitreal injection (IVI) of pharmacologic agents is the most commonly performed ocular procedure and is associated with a host of complications. Most IVI-related complications data are derived from randomized controlled clinical trials, which report a high adverse event rate. The nature of these protocol-driven trials limit their applicability to the diverse circumstances seen in routine clinical practice. The goal of this study was to determine the prevalence of patient-reported IVI-related complications, their risk factors, and the manner in which patients sought treatment at a tertiary eye care center. DESIGN: Retrospective, institutional review board-approved study. PARTICIPANTS: Forty-four thousand seven hundred thirty-four injections in 5318 unique patients at the Cleveland Clinic Cole Eye Institute from 2012 through 2016. METHODS: Intravitreal injection. MAIN OUTCOME MEASURES: Complication occurrence within 15 days of injection. RESULTS: From 2012 through 2016, a total of 44734 injections were performed in 5318 unique patients. Overall, complication rates were low, representing 1.9% of all injections, with 1031 unique complications in 685 patients (12.9%). The most common minor complications, or those not requiring intervention, were irritation (n = 312) and subconjunctival hemorrhage (n = 284). The most common serious complications, or those requiring intervention, were corneal abrasion (n = 46) and iritis (n = 31). Most complications (66%) were managed adequately by a telephone or Epic (Epic Systems Corp., Verona, WI) electronic message encounter only. Importantly, no injection protocol parameter, such as type of anesthesia, preparation, or post-injection medication, increased the risk of a complication. However, a patient's gender, age, number of previous injections, and provider strongly influenced the risk of patient-reported complications. CONCLUSIONS: Overall, complication rates seen in routine clinical practice were low compared with clinical trial reporting. Providers should feel confident in the safety and administration of IVI during times when follow-up office visits and resources may be limited. When performing an IVI, factors such as a patient's gender, age, number of previous injections, and provider must be taken into account to ensure the best possible outcomes.

VITREOUS SEEDING OF CHOROIDAL MELANOMA.

PURPOSE: To report a case of vitreous seeding in a medium-sized choroidal melanoma and review the literature. METHODS: Observational case report and review of literature for pathogenesis, role of vitreous biopsy, and treatment outcomes. RESULTS: A case of 57-year-old man diagnosed with vitreous seeding in the left eye 1 year after episcleral brachytherapy for medium-sized choroidal melanoma. The patient was initially diagnosed to have subretinal and vitreous hemorrhage due to rupture of a retinal artery macroaneurysm for which focal laser and intravitreal antivascular endothelial growth factor injections were administered. Over the next 9 months, the vitreous hemorrhage cleared and choroidal melanoma with retinal invasion became evident. One year after brachytherapy, the primary tumor regressed with resolution of surrounding subretinal fluid and hemorrhage. However, gradual decline in the visual acuity from 20/50 to 20/500 with increase of pigmented debris over the retinal surface and in the vitreous cavity was noted. A vitreous biopsy confirmed the presence of viable melanoma cells (epithelioid type), and the eye was enucleated. Histopathology showed microscopic persistence of primary tumor with diffuse vitreous seeding. CONCLUSION: Vitreous seeding of choroidal melanoma poses a diagnostic and management challenge.

Rank Order of Small Molecule Induced Hypoxiamimesis to Prevent Retinopathy of Prematurity.

Here we rank order small molecule inhibitors of hypoxia inducible factor (HIF) prolyl hydroxylases (PHDs) using severity of oxygen induced retinopathy (OIR) as an outcome measure. Dose response analyses in cell cultures of hepatoma (Hep3B), retinal Müller cells (MIO-M1) and primary retinal endothelial cells were conducted to evaluate potency by comparing dose to HIF-1,2 protein levels by western blotting. In vivo dose response was determined using the luciferase-transgene HIF reporter (luc-ODD). Each compound was placed in rank order by their ability to reduce neovascularization and capillary drop out in the OIR mouse model. An Epas1 KO confined to retinal Müller cells was used to determine whether successful protection by HIF stabilization requires HIF-2. Two candidate small molecules can prevent OIR by stabilizing HIF-1 to prevent oxygen induced growth attenuation and vascular obliteration. Müller cell HIF-2, the mediator of pathologic retinal angiogenesis, is not required for protection. The lack of dependence on Müller cell HIF-2 predicts that inhibition of HIF PHD will not drive pathological angiogenesis.

Hyperoxia induces glutamine-fuelled anaplerosis in retinal Müller cells.

Although supplemental oxygen is required to promote survival of severely premature infants, hyperoxia is simultaneously harmful to premature developing tissues such as in the retina. Here we report the effect of hyperoxia on central carbon metabolism in primary mouse Müller glial cells and a human Müller glia cell line (M10-M1 cells). We found decreased flux from glycolysis entering the tricarboxylic acid cycle in Müller cells accompanied by increased glutamine consumption in response to hyperoxia. In hyperoxia, anaplerotic catabolism of glutamine by Müller cells increased ammonium release two-fold. Hyperoxia induces glutamine-fueled anaplerosis that reverses basal Müller cell metabolism from production to consumption of glutamine.

Novel mutation in CTNNB1 causes familial exudative vitreoretinopathy (FEVR) and microcephaly: case report and review of the literature.

Purpose: Neonatal retinal folds and/or vitreoretinal traction can be signs of isolated ocular or syndromic disorders. Etiologies include retinopathy of prematurity, perinatal infections or inherited vitreoretinal disorders such as familial exudative vitreoretinopathy (FEVR) or Norrie disease. We present the clinical and genetic findings of a two-month-old infant with microcephaly, mild motor developmental delay, and FEVR, who required urgent surgical interventions.Methods: The patient underwent an initial examination under anesthesia (EUA) with fluorescein angiography (FA) and subsequent medical and surgical treatments. Genetic testing was undertaken to identify the etiology.Results: Examination at 2 months of age demonstrated microcephaly with a head circumference smaller than the 1st percentile. Family history was negative for microcephaly or retinal disease. Anterior segment eye exam was normal OU. There were bilateral macular folds involving the fovea and extending from the disc to the temporal periphery. FA demonstrated bilateral incomplete vascularization of the retina most notable nasally. Indirect laser was applied to ischemic retina OU. Scleral buckling procedures were performed OU as well as a vitrectomy in the left eye. Follow-up examinations demonstrated the stable appearance of the folds and attached retinas OU. Genetic testing identified a novel dominant heterozygous c.2046_2047del [p.Phe683Glnfs*9] mutation in CTNNB1, predicted to result in a frameshift causing a truncated protein.Conclusions: CTNNB1 mutations are an uncommon cause of FEVR with microcephaly.

Bilateral Release of Falciform Retrolental Adhesion by Scleral Buckling in Familial Exudative Vitreoretinopathy.

Familial exudative vitreoretinopathy (FEVR) can often present with retinal falciform folds, and rarely with retrolenticular adhesive radial retinal folds. Management of advanced FEVR-associated tractional falciform folds with retrolenticular adhesion to the peripheral retina in the literature has been limited to vitrectomy with or without lensectomy. The authors describe a unique surgical management of a case of bilateral FEVR-associated tractional radial folds with nonaxial retrolenticular adhesion treated with scleral buckling with deferred laser, avoiding the complications associated with vitrectomy and lensectomy on ocular development. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:594-596.].

Stickler syndrome: exploring prophylaxis for retinal detachment.

PURPOSE OF REVIEW: The literature regarding prophylactic treatment of rhegmatogenous retinal detachment in Stickler syndrome remains controversial. We review major published clinical studies and offer a critical analysis of this subject. SUMMARY: Stickler syndrome is a systemic collagenopathy affecting multiple organ systems including the eye, ear, and skeleton. Stickler syndrome is probably the most common cause of genetically determined pediatric rhegmatogenous retinal detachment. Congenital developmental anomalies constitute over half rhegmatogenous detachments (RRD) in patients less than 10 years. The majority are caused by hereditary vitreoretinopathies associated with Stickler syndrome. Sixty percent of patients with Stickler syndrome develop RRD's over their lifetime with possible severe visual loss and subsequent lifelong morbidity. In view of these complications, some have emphasized the importance of prophylactic laser treatment to the retina of patients with Stickler syndrome to reduce the occurrence of and/or prevent future rhegmatogenous retinal detachment, but there appears to be insufficient data to support the absolute benefit of such prophylactic treatment. Guidelines regarding the age at prophylactic treatment as well as type and frequency of intervention are scarce and would benefit from additional clinical investigations.

Serine and 1-carbon metabolism are required for HIF-mediated protection against retinopathy of prematurity.

We determined which metabolic pathways are activated by hypoxia-inducible factor 1-mediated (HIF-1-mediated) protection against oxygen-induced retinopathy (OIR) in newborn mice, the experimental correlate to retinopathy of prematurity, a leading cause of infant blindness. HIF-1 coordinates the change from oxidative to glycolytic metabolism and mediates flux through serine and 1-carbon metabolism (1CM) in hypoxic and cancer cells. We used untargeted metabolite profiling in vivo to demonstrate that hypoxia mimesis activates serine/1CM. Both [13C6] glucose labeling of metabolites in ex vivo retinal explants as well as in vivo [13C3] serine labeling of metabolites followed in liver lysates strongly suggest that retinal serine is primarily derived from hepatic glycolytic carbon and not from retinal glycolytic carbon in newborn pups. In HIF-1α2lox/2lox albumin-Cre-knockout mice, reduced or near-0 levels of serine/glycine further demonstrate the hepatic origin of retinal serine. Furthermore, inhibition of 1CM by methotrexate blocked HIF-mediated protection against OIR. This demonstrated that 1CM participates in protection induced by HIF-1 stabilization. The urea cycle also dominated pathway enrichment analyses of plasma samples. The dependence of retinal serine on hepatic HIF-1 and the upregulation of the urea cycle emphasize the importance of the liver to remote protection of the retina.