Comparing the RETeval® portable ERG device with more traditional tabletop ERG systems in normal subjects and selected retinopathies.

PURPOSE: Our study aimed to determine if ISCEV standard-like ERGs recorded with the LKC RETeval® portable ERG unit compared to those obtained using the more traditional tabletop unit. METHODS: ERGs recorded from normal subjects and patients affected with retinal ON and OFF pathway anomalies were compared. Analysis included peak time and amplitude measurements as well as time-frequency domain analysis with the discrete wavelet transform of waveforms obtained with the two systems. RESULTS: Although both systems were similarly able to record reliable and highly reproducible ERG responses, there were major discrepancies in ERG responses between the portable and tabletop units, pointing toward a weaker stimulation of the retinal OFF pathway with the portable RETeval® unit. CONCLUSION: The portable RETeval® unit appears to be able to record highly reproducible and diagnostically useful clinical ERGs, albeit with some significant differences in waveform composition compared to those obtained with more standard tabletop systems. Given the unknown origin of these waveform discrepancies, if left uncorrected, these differences could potentially lead to erroneous interpretation when used in the clinical context and/or compared to ERGs recorded using more traditional table top units. Clearly, more research is warranted before handheld devices, such as the RETeval®, can be homologated as a diagnostically sound ERG devices.

Organic visual loss measured by kinetic perimetry and retinal electrophysiology in children with functional amblyopia.

PURPOSE: To demonstrate an organic (retinal) amblyogenic defect in functional amblyopes not responding to treatment. METHODS: Twenty-four children (Mean age: 5.9 ± 1.8 years; range: 4-10 years) with functional amblyopia were recruited for this study. All these children underwent complete ophthalmic and orthoptic evaluation. In addition, Kinetic Goldman Visual Fields (KGVF), Spectral Domain Optical Coherence Tomography (SD-OCT), full field flash electroretinograms (ffERG) and multifocal electroretinograms (mfERG) were also performed. Ratios were subsequently derived by comparing the amplitudes obtained from the amblyopic eye (AE) to the good eye (GE) for the a- and b-waves of the ffERG, as well as for the ring analysis of the mfERG. RESULTS: KGVF showed a central scotoma of varying size (3°-7°) and density (absolute to relative), with increasing target size in 14/24 patients whose best post-treatment vision in the AE ranged from 20/100 to 20/40. The scotoma decreased in size and density with improving vision until a plateau of recovery was reached. The remaining 10/24 patients with a vision ≥ 20/30 showed no scotoma. SD-OCT showed no significant difference between the AE and GE. ffERG and mfERG were obtained in 18/24 patients. The ffERG AE/GE ratio was abnormal in 7 patients, 5 of which had large scotomas on KGVF. The mfERG ring 1 AE/GE ratio was significantly (p < .05) attenuated in 9/18 patients out of which 3 were no longer amblyopic. However, there was no significant difference (p > .05) in ring 1 AE/GE amplitude ratio between those who achieved 20/50-20/40 (.81 ± .26) and those with ≥ 20/25(.86 ± .25). CONCLUSIONS: The combined findings of central scotoma on KGVF and mfERG anomalies in patients who did not achieve optimal vision with treatment suggest an underlying organic defect impairing macular function.

Ring analysis of multifocal oscillatory potentials (mfOPs) in cCSNB suggests near-normal ON-OFF pathways at the fovea only.

PURPOSE: To investigate the center-periphery distribution of ON and OFF retinal responses in complete congenital stationary night blindness (cCSNB). METHODS: Photopic full-field flash ERGs (photopic ffERGs) and OPs (photopic ffOPs) and slow m-sequence (to enhance OP prominence) mfERGs (and filtered mfOPs) evoked by a 37 hexagon stimulus array were recorded from normal subjects and cCSNB patients. Discrete wavelet transform (DWT) analysis of photopic ffERGs and mfERGs was also performed in order to assess the contribution of the ON and OFF retinal pathways (i.e., OFF-to-ON ratio) in both cohorts. RESULTS: As expected, the photopic ffERG (and ffOPs) responses in cCSNB were devoid of the first two of the three OPs (i.e., OP2 and OP3 and OP4) normally seen on the ascending limb of the b-wave. A similar finding was also noted in the mfERGs (and mfOPs) of ring 4. In contrast, the mfERGs (and mfOPs) of ring 1 included all three OPs. DWT analysis revealed that while in normal subjects, the OFF-to-ON ratio of mfERGs slightly increased from rings 1 to 4 (from 0.61 ± 0.03 to 0.78 ± 0.04; p < 0.05; median: from 0.62 to 0.79; p < 0.05), in cCSNB this ratio increased significantly more [from 0.73 ± 0.13 (ring 1) to 1.18 ± 0.17 (ring 4); p < 0.05; median: 0.78 to 1.22; p < 0.05], hence from a normal ON-dominated ratio (central ring) to an OFF-dominated ratio (peripheral ring). CONCLUSIONS: Our results show a clear discrepancy of ON and OFF mfOP components in cCSNB. Responses originating from the most central ring (i.e., ring 1) disclosed a near-normal electrophysiological contribution (as revealed with the presence of OP2, OP3 and OP4 as well as with the DWT OFF-to-ON ratio) of the retinal ON and OFF pathways in mfERG (and mfOPs) responses compared to responses from the more peripheral ring (and ffOP) which are devoid of the ON OPs (i.e., OP2 and OP3).

Revealing a retinal facilitatory effect with the multifocal ERG.

PURPOSE: We have previously shown that the amplitude of the mfERG response obtained to a single (large) hexagon is significantly smaller than that obtained when summating all the mfERG responses evoked to an array of 7-61 hexagons covering the same retinal area. The purpose of this study was to confirm our initial findings in normal subjects of different ages and in selected patients. METHODS: Binocular mfERGs (1, 7, 19, 37 and 61 hexagon arrays; Espion V6.0.54 Diagnosys LLC) were recorded from 40 normal subjects (25 aged 18-25, and 15 aged 3-12). Individual mfERG waveforms evoked in response to the multi-hexagon arrays (7, 19, 37 and 61) were summated, and the amplitude of the resulting composite mfERG waveform was compared to that measured in the response evoked to the single (large) hexagon stimulus to yield the amplitude ratio (i.e., 7:1 X100, 19:1X100, etc.). RESULTS: In normal subjects, the 7:1 ratio was 119.5 ± 9.2%, a value that gradually decreased to reach 109.4 ± 20.6% with the 61:1 ratio and a finding that was similar across all ages. CONCLUSION: The present study indicates a significant enhancement in amplitude of the summed mfERG composite waveform evoked to the 7 hexagon stimulus array (and to a lesser extent to the 19, 37 and 61 stimuli) compared to the 1 hexagon array, possibly mediated through the retinal lateral pathway (horizontal or amacrine cells), a claim that awaits confirmation. Preliminary results obtained from patients treated with Plaquenil suggest that this new method of mfERG analysis might probe a feature of macular function different from that investigated with the more usual method of mfERG ring ratio.

Choroidal Involution Is Associated with a Progressive Degeneration of the Outer Retinal Function in a Model of Retinopathy of Prematurity: Early Role for IL-1ß.

Retinopathy of prematurity (ROP), the most common cause of blindness in premature infants, has long been associated with inner retinal alterations. However, recent studies reveal outer retinal dysfunctions in patients formerly afflicted with ROP. We have recently demonstrated that choroidal involution occurs early in retinopathy. Herein, we investigated the mechanisms underlying the choroidal involution and its long-term impact on retinal function. An oxygen-induced retinopathy (OIR) model was used. In vitro and ex vivo assays were applied to evaluate cytotoxic effects of IL-1ß on choroidal endothelium. Electroretinogram was used to evaluate visual function. We found that proinflammatory IL-1ß was markedly increased in retinal pigment epithelium (RPE)/choroid and positively correlated with choroidal degeneration in the early stages of retinopathy. IL-1ß was found to be cytotoxic to choroid in vitro, ex vivo, and in vivo. Long-term effects on choroidal involution included a hypoxic outer neuroretina, associated with a progressive loss of RPE and photoreceptors, and visual deterioration. Early inhibition of IL-1ß receptor preserved choroid, decreased subretinal hypoxia, and prevented RPE/photoreceptor death, resulting in life-long improved visual function in IL-1 receptor antagonist-treated OIR animals. Together, these findings suggest a critical role for IL-1ß-induced choroidal degeneration in outer retinal dysfunction. Neonatal therapy using IL-1 receptor antagonist preserves choroid and prevents protracted outer neuroretinal anomalies in OIR, suggesting IL-1ß as a potential therapeutic target in ROP.

GPR179 is required for depolarizing bipolar cell function and is mutated in autosomal-recessive complete congenital stationary night blindness.

Complete congenital stationary night blindness (cCSNB) is a clinically and genetically heterogeneous group of retinal disorders characterized by nonprogressive impairment of night vision, absence of the electroretinogram (ERG) b-wave, and variable degrees of involvement of other visual functions. We report here that mutations in GPR179, encoding an orphan G protein receptor, underlie a form of autosomal-recessive cCSNB. The Gpr179(nob5/nob5) mouse model was initially discovered by the absence of the ERG b-wave, a component that reflects depolarizing bipolar cell (DBC) function. We performed genetic mapping, followed by next-generation sequencing of the critical region and detected a large transposon-like DNA insertion in Gpr179. The involvement of GPR179 in DBC function was confirmed in zebrafish and humans. Functional knockdown of gpr179 in zebrafish led to a marked reduction in the amplitude of the ERG b-wave. Candidate gene analysis of GPR179 in DNA extracted from patients with cCSNB identified GPR179-inactivating mutations in two patients. We developed an antibody against mouse GPR179, which robustly labeled DBC dendritic terminals in wild-type mice. This labeling colocalized with the expression of GRM6 and was absent in Gpr179(nob5/nob5) mutant mice. Our results demonstrate that GPR179 plays a critical role in DBC signal transduction and expands our understanding of the mechanisms that mediate normal rod vision.

Comprehensive analysis of patients with Stargardt macular dystrophy reveals new genotype-phenotype correlations and unexpected diagnostic revisions.

PURPOSE: Stargardt macular dystrophy (STGD) results in early central vision loss. We sought to explain the genetic cause of STGD in a cohort of 88 patients from three different cultural backgrounds. METHODS: Next-generation sequencing using a novel capture panel was used to search for disease-causing mutations. Patients with undetermined causes were clinically reexamined and tested for copy-number variations as well as intronic mutations. RESULTS: We determined the cause of disease in 67% of our patients. Our analysis identified 35 novel ABCA4 alleles. Eleven patients had mutations in genes not previously reported to cause STGD. Finally, 45% of our patients with unsolved causes had single deleterious mutations in ABCA4, a recessive disease gene. No likely pathogenic copy-number variations were identified. CONCLUSION: This study expands our knowledge of STGD by identifying dozens of novel alleles that cause the disease. The frequency of single mutations in ABCA4 among STGD patients is higher than that among controls, indicating that these mutations contribute to disease. Disease in 11 patients was explained by mutations outside ABCA4, underlining the need to genotype all retinal disease genes to maximize genetic diagnostic rates. Few ABCA4 mutations were observed in our French Canadian patients. This population may contain an unidentified founder mutation. Our results indicate that copy-number variations are unlikely to be a major cause of STGD.

Resting state electroretinography: An innovative approach to intrinsic retinal function monitoring.

The electroretinogram (ERG) represents the biopotential evoked by the retina in response to a light stimulus. The flash evoked ERG (fERG) is the ERG modality most frequently used clinically to diagnose and monitor retinal disorders. We hereby present a new method to record spontaneous retinal activity, without the use of a flash stimulus, that we named the resting-state ERG (rsERG). The recordings were done in normal subjects under light- and dark-adaptation and with different background light conditions (i.e., variations of wavelength and intensity). Additionally, rsERG recordings were obtained in five patients with retinopathies. The signals were subsequently analyzed in the frequency domain, extracting both periodic (i.e., frequency peaks) and aperiodic (i.e., background trend) components of the signal. The later was further assessed through a multifractal analysis using Wavelet Leaders. Results show that, irrespective of the recording conditions used, the rsERG always includes the same 90 Hz component; a frequency component also present in the fERG response, suggesting a retinally-intrinsic origin. However, in addition, the fERGs also includes a low-frequency component which is absent in the rsERGs, a finding supporting a retinally-induced origin. Comparing rsERGs with fERGs in selected patients with various retinal disorders indicates that the two retinal signals are not always similarly affected (either as a result of underlying retinal pathology or otherwise), suggesting an added value in the assessment of retinal function. Thus, the rsERG could have a similar role in clinical visual electrophysiology as that of the resting-state EEG in neurology namely, to quantify changes in spontaneous activity that result from a given disease processes.

Early manifestations of postnatal hyperoxia on the retinal structure and function of the neonatal rat.

PURPOSE: Postnatal hyperoxia in rats causes an arrest in growth of retinal blood vessels, along with severe changes in retinal ultrastructure and function. Previous studies focused on consequences of postnatal hyperoxia at time points substantially removed from the hyperoxic insult. In this study, the earliest manifestations of this retinopathy were examined. METHODS: Newborn rats were exposed to 80% O(2) from birth to postnatal day 14. The retinas were collected for vascular assessment at postnatal days 6, 9, 12, and 14, and electroretinograms were recorded at postnatal days 15, 16, 17, 19, 24, 30, and 60, after which retinal histology was performed. RESULTS: Hyperoxia significantly attenuated vascular development, especially after 6 and 9 days of exposure which resulted in 64% and 72% of normal coverage, respectively. Vascular growth continued despite hyperoxic exposure, reaching 87% of normal by postnatal day 14. Electroretinograms of hyperoxic rats retained very immature features throughout with nearly abolished b-waves and relatively preserved a-waves. Finally, while retinal structure was virtually complete in the control animals by postnatal day 15, hyperoxic rats always showed a significantly thinner outer plexiform layer (OPL) and lower horizontal cell count (P < 0.05), irrespective of the duration of exposure. CONCLUSION: The findings confirm previous reports of reduced retinal vascular coverage that accompanies the earliest manifestation of postnatal hyperoxia in rats and suggest increased retinal susceptibility to hyperoxia within the first week of life. However, despite the fact that vasculature appears to repair itself, irreversible cytoarchitectural and functional changes occur, the consequences of which are documented immediately after the cessation of hyperoxia.

Recording and Analysis of the Human Clinical Electroretinogram.

The electroretinogram (ERG) represents the biopotential that is produced by the retina in response to a light stimulus. To date, it remains the best diagnostic tool to objectively evaluate the functional integrity of the normal or diseased retina. In the following pages we briefly review the necessary requirements in order to record and analyze the conventional clinical ERG.

Hyperoxic exposure leads to nitrative stress and ensuing microvascular degeneration and diminished brain mass and function in the immature subject.

BACKGROUND AND PURPOSE: Neonates that survive very preterm birth have a high prevalence of cognitive impairment in later life. A common factor detected in premature infants is their postnatal exposure to high oxygen tension relative to that in utero. Hyperoxia is known to elicit injury to premature lung and retina. Because data on the exposure of the brain to hyperoxia are limited, we studied the effects of high oxygen on this tissue. METHODS: Rat pups were exposed from birth until day 6 to 21% or 80% O(2). Cerebral vascular density was quantified by lectin immunohistochemistry. Immunoblots for several proteins were performed on brain extracts. We assessed cerebral functional deficits by visual evoked potentials. RESULTS: Exposure of pups to hyperoxia leads to cerebral microvascular degeneration, diminished brain mass, and cerebral functional deficits. These effects are preceded by an upregulation of endothelial nitric oxide synthase (eNOS) in cerebral capillaries and a downregulation of Cu/Zn superoxide dismutase (SOD). The imbalance in nitric oxide (NO) production and antioxidant defenses favors the formation of nitrating agents in the microvessels revealed by increased nitrotyrosine (3-nt) immunoreactivity and decreased expression of NF-kappaB and the dependent vascular endothelial growth factor receptor 2. NOS inhibitors and eNOS deletion as well as an SOD mimetic (CuDIPS) restore vascular endothelial growth factor receptor-2 levels and nearly abolish the vasoobliteration. NOS inhibitors and SOD mimetic also prevent O(2)-induced diminished brain mass and functional deficit. CONCLUSIONS: Data identify NO and nitrating agents as major mediators of cerebral microvascular damage, ensuing impaired brain development and function in immature subjects exposed to hyperoxia.

Structural and functional consequences of trolox C treatment in the rat model of postnatal hyperoxia.

PURPOSE: Previous studies have shown that newborn rats exposed to hyperoxia within the first 2 weeks of life develop vasculopathy in addition to permanent changes in retinal structure and function. It has also been suggested that free radicals may be the source of these pathologic effects. Trolox C, a water-soluble analogue of vitamin E, was previously shown to limit the vascular consequences of exposure to postnatal hyperoxia. The aim of this study was to investigate whether trolox C could also help prevent the functional (electroretinography) and structural (retinal histology) consequences associated with oxygen-induced retinopathy (OIR). METHODS: Newborn albino Sprague-Dawley rats exposed or not exposed to hyperoxia received daily injections of trolox C in doses of 300, 600, and 900 microg/kg (total volume, 50 microL). The effect of treatment was evaluated through electroretinography and retinal histology. RESULTS: Although trolox C tended to have a retinoactive effect on the normal retina, normalization of the hyperoxia-treated group to hyperoxic control and of the normoxia-treated group to normoxic control revealed that the a-wave remained relatively unaffected by hyperoxia exposure and by treatment with trolox C, the efficacy of trolox C at doses of 600 and 900 microg/kg largely outweighed the retinoactive effect, and the oscillatory potentials (OPs) benefited to the greatest extent from trolox C treatment. Furthermore, trolox C was able to limit the reduction in outer plexiform layer thickness but not the concomitant reduction of the horizontal cell count, each of which is associated with OIR. CONCLUSIONS: These results show that, as had been previously demonstrated with retinal vasculature, trolox C limited the retinal functional and structural damages inherent in the rat model of OIR. However, despite treatment, there were still signs (albeit less severe) indicative of OIR. This suggests, as previously advanced, that the pathophysiology of OIR is not solely caused by the action of free radicals or that trolox C is inadequate in treating all aspects of OIR.

Light-induced retinopathy: comparing adult and juvenile rats.

PURPOSE: To investigate the effect of chronic exposure to a bright, luminous environment, starting at the opening of the eyes, on the retinal structure and function of the suckling rat. METHODS: Juvenile Sprague-Dawley rats were exposed to 10,000 lux, for varying lengths of time between postnatal day (P)14 and P34. Results were compared with those obtained from adult rats exposed to the same light intensity and for the same duration. Electroretinograms (ERGs) were recorded at 1 month and 2 months of age, after which the retinas were harvested for histologic analysis. RESULTS: In juvenile rats, the severity of light-induced retinopathy (LIR) depended not only on the duration of the exposure but, more important, on the age of the rat at the onset of exposure. For example, in adult rats, 6-day exposure reduced the thickness of the outer nuclear layer (ONL) to less than 18% of normal, whereas in juvenile rats, 6-day exposure between P14 and P20 reduced it to 50% compared with 27% after exposure between P28 and P34. An adultlike effect could only be evidenced in rats exposed at the end of the first postnatal month (P28-P34). A similar age-dependent effect was also noted on the electroretinogram. CONCLUSIONS: These results show that, compared with the mature retina, the developing retina appears to be relatively preserved from the devastating consequences of exposure to bright light. This window of resistance to light damage gradually weakens as the juvenile rat approaches its 1-month anniversary.

CRB1 heterozygotes with regional retinal dysfunction: implications for genetic testing of leber congenital amaurosis.

PURPOSE: To test human CRB1 heterozygotes for possible clinical or functional retinal changes and to evaluate whether a patient with Leber congenital amaurosis (LCA) with CRB1 mutations not consistent with previously described CRB1 phenotypes carried a modifier allele in another LCA gene. METHODS: Seven unrelated heterozygous carriers of CRB1 mutations underwent phenotyping by full eye examinations (indirect ophthalmoscopy and slit lamp biomicroscopy) and functional testing (standard full-field electroretinography [ERG] and multifocal ERG). For genotyping of the LCA patients and their parents, denaturing high-performance liquid chromatography (dHPLC) analyses were performed, followed by sequence analysis of CRB1, followed by sequence analysis of the AIPL1 and CRX genes to identify a putative modifier effect in a patient with an atypical CRB1 phenotype. RESULTS: Reduced full-field ERG b-wave amplitudes were observed with scotopic -2 dB flash (140 microV; P < 0.05), normal full-field cone ERGs, and significant regional retinal dysfunction on mfERG in five of seven carriers of CRB1 mutations. A known AIPL1 mutation (p. R302L) was identified as a potential modifier allele in a patient with LCA carrying two CRB1 mutations and with a prominent maculopathy. CONCLUSIONS: In human heterozygotes of CRB1 mutations (parents of offspring with LCA), distinctive regional retinal dysfunctions were found by multifocal ERG measurements that were consistent with the focal histologic abnormalities reported for the two CRB1 knockout mice models. This phenotypic finding may identify CRB1 carriers and point to the causal gene defect in affected LCA offspring, significantly facilitating the molecular diagnostic process. Evidence suggests a modifier allele in AIPL1 in a patient with LCA with prominent atrophic macular lesions and homozygous defects in CRB1.

Assessing the Contribution of the Oscillatory Potentials to the Genesis of the Photopic ERG with the Discrete Wavelet Transform.

The electroretinogram (ERG) is composed of slow (i.e., a-, b-waves) and fast (i.e., oscillatory potentials: OPs) components. OPs have been shown to be preferably affected in some diseases (such as diabetic retinopathy), while the a- and b-waves remain relatively intact. The purpose of this study was to determine the contribution of OPs to the building of the ERG and to examine whether a signal mostly composed of OPs could also exist. DWT analyses were performed on photopic ERGs (flash intensities: -2.23 to 2.64 log cd·s·m-2 in 21 steps) obtained from normal subjects (n = 40) and patients (n = 21) affected with a retinopathy. In controls, the %OP value (i.e., OPs energy/ERG energy) is stimulus- and amplitude-independent (range: 56.6-61.6%; CV = 6.3%). In contrast, the %OPs measured from the ERGs of our patients varied significantly more (range: 35.4%-89.2%; p < 0.05) depending on the pathology, some presenting with ERGs that are almost solely composed of OPs. In conclusion, patients may present with a wide range of %OP values. Findings herein also support the hypothesis that, in certain conditions, the photopic ERG can be mostly composed of high-frequency components.

Immunohistochemical evidence of synaptic retraction, cytoarchitectural remodeling, and cell death in the inner retina of the rat model of oygen-induced retinopathy (OIR).

PURPOSE: Postnatal exposure to hyperoxia destroys the plexiform layers of the neonatal rat retina, resulting in significant electroretinographic anomalies. The purpose of this study was to identify the mechanisms at the origin of this loss. METHODS: Sprague-Dawley (SD) and Long Evans (LE) rats were exposed to hyperoxia from birth to postnatal day (P) 6 or P14 and from P6 to P14, after which rats were euthanatized at P6, P14, or P60. RESULTS: At P60, synaptophysin staining confirmed the lack of functional synaptic terminals in SD (outer plexiform layer [OPL]) and LE (OPL and inner plexiform layer [IPL]) rats. Uneven staining of ON-bipolar cell terminals with mGluR6 suggests that their loss could play a role in OPL thinning. Protein kinase C(PKC)-α and recoverin (rod and cone ON-bipolar cells, respectively) showed a lack of dendritic terminals in the OPL with disorganized axonal projections in the IPL. Although photoreceptor nuclei appeared intact, a decrease in bassoon staining (synaptic ribbon terminals) suggests limited communication to the inner retina. Findings were significantly more pronounced in LE rats. An increase in TUNEL-positive cells was observed in LE (inner nuclear layer [INL] and outer nuclear layer [ONL]) and SD (INL) rats after P0 to P14 exposure (425.3%, 102.2%, and 146.3% greater than control, respectively [P < 0.05]). CONCLUSIONS: Results suggest that cell death and synaptic retraction are at the root of OPL thinning. Increased TUNEL-positive cells in the INL confirm that cells die, at least in part, because of apoptosis. These findings propose a previously undescribed mechanism of cell death and synaptic retraction that are likely at the origin of the functional consequences of hyperoxia.

Choroidal involution is a key component of oxygen-induced retinopathy.

PURPOSE: Retinopathy of prematurity (ROP) is a major cause of visual handicap in the pediatric population. To date, this disorder is thought to stem from deficient retinal vascularization. Intriguingly, functional electrophysiological studies in patients with mild or moderate ROP and in the oxygen-induced retinopathy (OIR) model in rats reveal central photoreceptor disruption that overlies modest retinal vessel loss; a paucity of retinal vasculature occurs predominantly at the periphery. Given that choroidal circulation is the major source of oxygen and nutrients to the photoreceptors, the authors set out to investigate whether the choroidal vasculature system may be affected in OIR. METHODS: Rat models of OIR treating newborn animals with 80% or 50/10% alternated oxygen level for the first two postnatal weeks were used to mimic ROP in humans. Immunohistology staining and vascular corrosion casts were used to investigate the vessel layout of the eye. To investigate the effect of 15-deoxy-Δ12,14-PGJ(2) (15d-PGJ(2); a nonenzymatic product of prostaglandin D(2)) on endothelial cells, in vitro cell culture and ex vivo choroid explants were employed and intravitreal injections were performed in animals. RESULTS: The authors herein demonstrate that deficient vascularity occurs not only in the retinal plexus but also in the choroid. This sustained, marked choroidal degeneration is specifically confined to central regions of the retina that present persistent photoreceptor loss and corresponding functional deficits. Moreover, the authors show that 15d-PGJ(2) is a prominent contributor to this choroidal decay. CONCLUSIONS: The authors demonstrate for the first time pronounced, sustained choroidal vascular involution during the development of ROP. Findings also suggest that effective therapeutic strategies to counter ROP should consider choroidal preservation.

CD36 plays an important role in the clearance of oxLDL and associated age-dependent sub-retinal deposits.

Age-related macular degeneration (AMD) represents the major cause of vision loss in industrialized nations. Laminar deposits in Bruch's membrane (BM) are among the first prominent histopathologic features, along with drusen formation, and have been found to contain oxidized lipids. Increases in concentrations of oxidized LDL (oxLDL) in plasma are observed with age and high fat high (HFHC) cholesterol diet. CD36 is the principal receptor implicated in uptake of oxLDL, and is expressed in the retinal pigment epithelium (RPE). We determined if CD36 participates in oxLDL uptake in RPE and correspondingly in clearance of sub-retinal deposits. Uptake of oxLDL by RPEin vitro and in vivo was CD36-dependent. CD36 deficiency in mice resulted in age-associated accumulation of oxLDL and sub-retinal BM thickening, despite fed a regular diet. Conversely, treatment of HFHC-fed ApoE null mice with a CD36 agonist, EP80317 (300 µg/kg/day), markedly diminished thickening of BM, and partially preserved (in part) photoreceptor function. In conclusion, our data uncover a new role for CD36 in the clearance of oxidized lipids from BM and in the prevention of age-dependent sub-retinal laminar deposits.

Functional and structural changes resulting from strain differences in the rat model of oxygen-induced retinopathy.

PURPOSE: Results of studies that compared the racial incidence of retinopathy of prematurity (ROP) suggested that ocular pigmentation might offer protection against the development of severe ROP. The structural and functional consequences of postnatal hyperoxia (oxygen-induced retinopathy; OIR) were compared in albino Sprague-Dawley (SD) and pigmented Long-Evans (LE) rats to verify this finding. METHODS: Newborn rats were exposed to 80% O(2) during selected postnatal day intervals. The severity of the OIR was determined by examining retinal flatmounts (retinal vasculature assessment), protein level quantification and cellular localization of fibroblast growth factor (FGF)-2 and ciliary neurotrophic factor (CNTF; Western blot analysis and immunohistochemistry, respectively), retinal histology, and photopic and scotopic electroretinograms (ERGs). RESULTS: Irrespective of the parameter considered, structural and functional deficits resulting from postnatal hyperoxia were significantly more pronounced in LE rats. Although FGF-2 levels in LE rats had a tendency to increase after hyperoxia compared with normoxic littermates, it did not reach statistical significance. A similar finding was observed in SD rats. Of interest, however, baseline levels of FGF-2 were approximately four to five times higher in SD rats than in LE rats. There was a similar, hyperoxia-induced increase in CNTF levels between SD and LE rats. CONCLUSIONS: The findings suggest an increased susceptibility of newborn LE rats to postnatal hyperoxia in comparison with SD rats. Whether a pro-oxidant rather than antioxidant role of melanin or other genetic factors can explain these differences in oxygen susceptibility of the animal model of this retinopathy, remains to be determined.

Structural and functional consequences of bright light exposure on the retina of neonatal rats.

In a previous study we showed that juvenile rats exposed, for various durations of time, to a bright luminous environment between P14 (eye opening) and P34 developed a light-induced retinopathy (LIR), the severity of which depending on the duration of exposure as well as the age of the rat at the onset of exposure. Our study also revealed that the severity of the LIR increased as the time elapsed between the cessation of exposure and the structural/functional evaluation increased, suggesting that the LIR degenerative process proceeded in two distinct steps namely, an initial (rapid) acute phase that was followed by a (slower) chronic phase. In view of the above, the purpose of the present study was to reinvestigate previous claims suggesting that exposure to bright light prior to eyelid opening had no measurable consequences on the retinal structure and function; the claim being that despite a non-detectable acute phase, bright light exposure prior to eyelid opening could nonetheless yield a significant retinopathy during the chronic phase of development of LIR. In order to test our hypothesis, neonatal rats were raised in a bright luminous environment from birth to P14. At P30, analysis of the results obtained from rats exposed between P0-P14 did not reveal, as previously acknowledged by others, significant LIR damages. However, results obtained at P60 disclosed significant functional anomalies with relative sparing of the retinal ultrastructure. Our results confirm that, in spite of closed eyelids, postnatal exposure to bright environment did trigger a slow degenerative process.